|Title of Invention
ELECTRICAL CONNECTOR AND METHOD FOR MAKING
|An electrical connector includes an electrical contact array (17) having a plurality of contact elements (15) where each contact element has at least one conductive, resilient spring portion.
THE PATENTS ACT, 1970
(39 of 1970)
THE PATENTS RULES, 2003
(See section 10, rule 13)
"ELECTRICAL CONNECTOR AND METHOD FOR MAKING
NEOCONIX, INC. of 754 N. Pastoria Avenue, Sunnyvale, CA 94085, United States of America.
The following specification particularly describes the invention and the manner in which it is to be performed.
 ELECTRICAL CONNECTOR AND METHOD FOR MAKING
 FIELD OF INVENTION
 The present invention relates to electrical connectors, and in
particular, to a reconnectable and remountable electrical connector and a method for making same.
 Electrical interconnects or connectors are used to connect two or
more electronic components together or to connect an electronic component to a
piece of electrical equipment, such as a computer, router, or tester. The term
"electronic component" includes, but is not limited to, printed circuit boards, and
the connector can be a board-to-board connector. For instance, an electrical
interconnect is used to connect an electronic component, such as an integrated
circuit (an IC or a chip), to a printed circuit board. An electrical interconnect is
also used during integrated circuit manufacturing for connecting an IC device
under test to a test system. In some applications, the electrical interconnect or
connector provides a separable or remountable connection so that the electronic
component attached thereto can be removed and reattached. For example, it may
be desirable to mount a packaged microprocessor chip to a personal computer
motherboard using a separable interconnect device so that malfunctioning chips
can be readily removed, or upgraded chips can be readily installed.
 There are also applications where an electrical connector is used to
make direct electrical connection to metal pads formed on a silicon wafer. Such an electrical connector is often referred to as a "probe" or "probe card" and is typically used during the testing of the wafer during the manufacturing process. The probe card, typically mounted on a tester, provides electrical connection from the tester to the silicon wafer so that individual integrated circuits formed on the wafer can be tested for functionality and compliance with specific parametric limits.
 Conventional electrical connectors are usually made of stamped
metal springs, which are formed and then individually inserted into an insulating carrier to form an array of electrical connection elements. Other approaches to making electrical connectors include using isotropically conductive adhesives, injection molded conductive adhesives, bundled wire conductive elements, springs formed by wirebonding techniques, and small solid pieces of metal.
 Land grid array (LGA) refers to an array of metal pads (also called
lands) that are used as the electrical contact points for an integrated circuit
package, a printed circuit board, or other electronic component. The metal pads
are usually formed using thin film deposition techniques and are coated with gold
to provide a non-oxidizing surface. Ball grid array (BGA) refers to an array of
solder balls or solder bumps that are used as the electrical contact points for an
integrated circuit package. Both LGA and BGA packages are widely used in the
semiconductor industry and each has its associated advantages or disadvantages.
An LGA connector is usually used to provide removable and remountable
socketing capability for LGA packages connected to PC boards or to chip modules.
 Advances in electronic device packaging technology have led to
shrinking package geometries and increasing lead count. That is, the spacing (or the pitch) between each component electrical connection (also referred to as a "lead") on an electronic device is decreasing, while the total number of connections is increasing. For example, existing IC packages may be built with a pitch of one mm or less with 600 or more connections. Furthermore, IC devices are designed to be operated at increasingly higher frequencies. For example, IC devices for use in telecommunication and networking applications can include input and output signals at frequencies over 1 GHz. The operating frequencies of the electronic devices, the package size, and lead count of the device packages place stringent requirements on the interconnect systems used to test or connect these electronic devices.
 Advances in semiconductor technologies have also led to shrinking
dimensions within semiconductor integrated circuits, and particularly to
decreasing pitch for the contact points on a silicon die or a semiconductor package. For example, contact pads on a semiconductor wafer can have a pitch of 250 microns or less. At the 250 micron pitch level, it is prohibitively difficult and expensive to use conventional techniques to make separable electrical connections to these semiconductor devices. The problem is becoming even more critical as the pitch of contact pads on a semiconductor device decreases below 50 microns and simultaneous connection to multiple contact pads in an array is required. In particular, the mechanical, electrical, and reliability performance criteria of an interconnect system are becoming increasingly demanding. Conventional interconnect technologies have not been able to meet all of the mechanical, electrical, and reliability requirements for use with high speed, small dimension, and large pin count IC devices.
 A particular problem encountered by today's interconnect systems is
the variation in coplanarity (vertical offset) and positional misalignment of the leads in the electronic components to be connected. Coplanarity variations result in some contact elements being compressed more than others. This difference results primarily from the sum of the following three factors: (1) variations in the planarity of the package, (2) variations in the planarity of the board, and (3) any tilting of the package with respect to the board.
 In a conventional LGA package, the pads (the leads) of the package
can become non-planar due to substrate warping. When the amount of the resulting vertical offset exceeds the tolerance of a LGA connector, some of the pads may not be able to make electrical contact with the connector at all. Planarity variations of the pads of an LGA component make it difficult to make high quality and reliable electrical connections to all the leads of the electronic component.
 Moreover, the location of the leads may also deviate from their
predefined ideal position due to manufacturing limitations, resulting in positional misalignment. An effective interconnect must accommodate the horizontal positional variations of the leads of the electronic components to be connected. To make matters worse, the positional deviation of a lead relative to
the lead size itself, due to either coplanarity variations, positional misalignments, or both, on an electronic device from its ideal location increases as the size of the package decreases.
 Planarity problems are not limited to IC packages but may also
exist on the printed circuit board (PCB) to which these IC packages are attached. Planarity problems may exist for LGA pads formed as an area array on a PCB due to warping of the PCB substrate. Typically, deviation from flatness in a conventional PCB is on the order of 75 to 125 microns or more per inch. The LGA connector must be able to accommodate the overall deviations in coplanarity between the components being connected, a package and a PCB for example. This means that the contact elements must function in both the least compressed state, where the curvature and tilt of the package and PCB are such that they are farthest apart from each other, and the most compressed state, where the curvature and tilt of the package and PCB are such that they are closest together. Hence, it is desirable to have a scalable electrical contact element that can behave elastically so that normal variations in coplanarity and positional misalignment of the contact points can be tolerated.
 While LGA connectors can be effectively used to electrically connect
an LGA package to printed circuit boards or modules, the connector interface between the connector and the component to be connected are subject to potential reliability degradation. For instance, corrosive materials or particulate debris can enter the interface area, preventing a proper electrical connection from being made. Also, the repeated mating and separation of an LGA package may degrade the LGA connector, causing intermittent connection conditions and inhibit reliable electrical connection.
 When making electrical connections to contact pads, such as metal
pads on a silicon wafer or on a LGA package, it is important to have a wiping action or a piercing action when the contact elements engage the pads in order to break through any oxide, organic material, or other films that may be present on the surface of the 'inetal'pads'randthat mightotherwise inhibit the electrical connection. Figure 1 illustrates an existing contact element engaging a metal pad
on a substrate. Referring to Figure 1, a connector 100 includes a contact element 102 for making an electrical connection to a metal pad 104 on a substrate 106. The connector 100 can be a wafer probe card and the contact element 102 is then a probe tip for engaging the pad 104. Under normal processing and storage conditions, a film 108, which can be an oxide film or an organic film, forms on the surface of the pad 104. When the contact element 102 engages the pad 104, the contact element 102 must pierce through the film 108 in order to make a reliable electrical connection to the pad 104. The piercing of the film 108 can be performed by a wiping action or a piercing action of contact element 102 when the contact element 102 engages the pad 104.
 While it is necessary to provide a wiping or piercing action, it is
important to have a well-controlled wiping or piercing action that is strong
enough to penetrate the surface film 108 but soft enough to avoid damaging the
metal pad 104 when electrical contact is made. Furthermore, it is important that
any wiping action provides a sufficient wiping distance so that enough of the
metal surface is exposed for a satisfactory electrical connection.
 Similarly, when making contacts to solder balls, it is important to
provide a wiping or piercing action to break through the native oxide layer on the solder balls to create a good electrical contact to the solder balls. However, when conventional approaches are used to make electrical contact to solder balls, the solder balls may be damaged or dislodged from the package. Figure 2a illustrates the existing contact element 100 being applied to contact a solder ball 200 formed on a substrate 202. When the contact element 102 contacts the solder ball 200, such as for testing, the contact element 102 applies a piercing action which often results in the formation of a crater 204 on the top surface (also called the base surface) of the solder ball 200.
 When the substrate 202 is subsequently attached to another
semiconductor device, the crater 204 in the solder ball 200 can lead to void formation at the solder ball interface. Figures 2b and 2c illustrate the result of attaching the solder ball 200 to a metal pad 210 of a substrate 212. After solder reflow (Figure 2c), the solder ball 200 is attached to the metal pad 210. However,
a void 214 is formed at the solder ball interface due to the presence of the crater 204 on the top surface of the solder ball 200. The presence of the void 214 can affect the electrical characteristics of the connection and more importantly, degrades the reliability of the connection.
 Conventional interconnect devices, such as stamped metal springs,
bundled wire, and injection molded conductive adhesives, become stiff and difficult to manufacture as the dimensions are scaled down, rendering them unsuitable even for accommodating electronic components with normal positional variations. This is particularly true when the spacing between the contacts scales below one millimeter, where the electrical path length requirement also scales to below one millimeter to minimize inductance and meet high frequency performance requirements. In this size regime, existing interconnect technologies become even more stiff and less elastic and cannot accommodate normal variations in system coplanarity and positional misalignments with a reasonable insertion force of about 30 to 40 grams per contact.
 Therefore, it is desirable to provide an electrical contact element
that can provide a controlled wiping action on a metal pad, particularly for pads with a pitch of less than 50 microns. It is also desirable that the wiping action provides a wiping distance of up to 50% of the contact pad. Furthermore, when electrical contact to solder balls are made, it is desirable to have an electrical contact element that can provide a controlled wiping action on the solder ball without damaging the contact surface of the solder ball.
 It is desirable to provide an electrical interconnect system which can
accommodate normal positional tolerances, such as coplanarity variations and positional misalignments, in electronic components to be connected. Furthermore, it is desirable to provide anelectrical interconnect system adapted for use with small geometry, high lead density electronic devices operating at high frequencies.
 SUMMARY .
 The present invention discloses an electrical connector, and in
another aspect, discloses methods for making an electrical connector.
 BRIEF DESCRIPTION OF THE DRAWINGS
 A more detailed understanding of the invention may be had from the
following description of a preferred embodiment, given byway of example, and to
be understood in conjunction with the accompanying drawings wherein:
 Figure 1 is an existing contact element engaging a metal pad on a
 Figure 2a is an existing contact element to contacting a solder ball;
 Figures 2b and 2c are the result of attaching a damaged solder ball
to a metal pad of a substrate;
 Figures 3a and 3b are enlarged, perspective sectional views of a
beam ball grid array (BBGA) system of the present invention and its attachment
to a printed circuit board (PCB);
 Figures 3c and 3d are sectional views of two respective contact
schemes used to electrically connect the contact system of Figure 3a to a PCB;
 Figure 3e is a schematic of the structure for cradling a solder ball, in
accordance with the embodiment shown in Figures 3a and 3b;
 Figure 3f is a plan view of the contact arm array shown in Figure
 Figure 3g is a plan view of several different contact arm designs;
 Figure 4a is a cross-sectional view of a surface mount version of a
beam land grid array (BLGA) system and its attachment to a PCB;
 Figure 4b is a cross-sectional view of a separable version of a BLGA
system and its attachment to a PCB;
 Figure 5 is an enlarged sectional view of the contact arms for a
BLGA contact array;
 Figure 6 is an enlarged perspective view of different contact arm
WO 2004/093252 PCT/US2004/011074
 Figure 7 is a perspective view of a connector according to one
embodiment of the present invention;
 Figure 8 is a connector including contact elements formed using
multiple layers of metals according to another embodiment of the present
 Figures 9a and 9b are cross-sectional views of a connector according
to one embodiment of the present invention;
 Figures 10a and 10b are cross-sectional views of a connector
according to an alternate embodiment of the present invention;
 Figure 11 is a cross-sectional view of a connector according to an
alternate embodiment of the present invention;
 Figure 12 is a perspective view of a connector according to an
alternate embodiment of the present invention;
 Figures 13a to 13c are cross-sectional views of one embodiment of a
connector being applied in a hot-swapping operation;
 Figures 14a and 14b show two embodiments of a circuitized
connector in accordance with the present invention;
 Figure 15a is a cross-sectional view of a connector including a
coaxial contact element according to an alternate embodiment of the present
 Figure 15b is a top view of the coaxial contact element of Figure 15a;
 Figure 16 shows the mating of an LGA package to a PC board
through the connector of Figure 15a;
 Figures 17a to 17h show cross-sectional views of the processing
steps for forming the connector of Figure 9a according to one embodiment of the
 Figures 18a and 18b show cross-sectional views of the processing
steps for forming a connector according to an alternate embodiment of the
 Figures 19a-19d are flowcharts showing the steps of a method for
making a connector in accordance with an alternate embodiment of the present
 Figure 20 is a cross-sectional view of the resist film applied to a
sheet of spring material in accordance with the method shown in Figures 19a-
 Figure 21 is a cross-sectional view of UV light being applied to the
resist film, in accordance with the method shown in Figures 19a-19d;
 Figure 22 is a plan view of a sheet of contact elements formed in
accordance with the method shown in Figures 19a-19d;
 Figure 23a is a view of each layer of a stack up used in one of the
steps of the method shown in Figures 19a-19d; and
 Figure 23b is a side view of the assembled stack up shown in Figure
 DETAILED DESCRIPTION OF THE PREFERRED
 Figures 3a and 3b are cross-sectional views of a beam ball grid array
(BBGA) system constructed in accordance with the present invention. In the first construction 300 illustrated in Figure 3a, solder balls 302 provide a method of establishing an electrical contact between the device, packages, or module 304, and a carrier 306. The solder balls 302 are shown disposed within plated through holes or vias 308 that have been fabricated into the carrier 306 by printed circuit techniques. The solder balls 302 are given elasticity by virtue of their suspension upon flexible contact arms 310 formed as part of a layer 312. The contact arms 310 cradle the solder ball 302, as shown in Figure 3e, and provide a spring-like support as shown in Figures 3c and 3d.
 An array of contact arms 310 is fabricated in layer 312, as better
observed with reference to Figure 3f. Different design patterns for the contact arms 310 are respectively illustrated by elements 310a, 310b, 310c, and 310d in Figure 3g.
 In Figure 3b, the fabrication continues with the attachment of the
structure 300 to a pad 314 of a PCB 316 by means of electrical contact elements
318, which may include beam land grid array (BLGA) contact elements, a LGA, a
pin grid array (PGA), or other types of contact elements as described below.
 In Figure 3c, the carrier 306 makes electrical contact with the PCB
316 by means of a solder ball 320 that touches the pad 314. In Figure 3d, the carrier 306 makes contact with the pad 314 by means of contact arms 318. The contact arms 310 can be stamped or etched with the desired geometry. As will be described in greater detail hereinafter, they are then assembled in a PCB-like fabrication process.
 Figure 4a is a cross-sectional view of a surface mount version of a
BLGA electrical contact element 400 constructed in accordance with the present invention. The BLGA system includes a carrier layer 402 having an array of arms 404 that form elastic elements out of the plane of the carrier 402. The angle, thickness, and number of the arms 404 can be readily changed to provide specific design features such as contact force, current carrying capacity, and contact resistance. The carrier 402 is shown making electrical contact with a PCB 406, by means of a solder ball 408 that touches a pad 410. The arms 404 can have shapes similar to arms 310a-d in fig 3a.
 Figure 4b is a cross-sectional view of a separable version of a BLGA
contact element 400a constructed in accordance with the present invention, including the carrier 402 making contact with the pad 410 by means of BLGA contact wipers 412, which are similar to the contact arms 404 at the top of the carrier 402.
 Figure 5 shows a cross-sectional view of a connector 500 in
accordance with the present invention, including showing some exemplary dimensions for the size of the portions of the contact element 502. The spacing between the distal ends of the facing spring portions 504 is 5 mils. The height of the contact element 502 from the surface of the substrate to the top of the spring portion is 10 mils. The width of a via through the substrate can be on the order of 10 mils. The width of the contact element 502 from the outer edge of one base
portion to the outer edge of the other base portion is 16 mils. Contacts of this size can be formed in accordance with the method of the invention as described below, allowing connectors with a pitch well below 50 mils and on the order of 20 mils or less. It is noted that these dimensions are merely exemplary of what can be achieved with the present invention and one skilled in the art will understand from the present disclosure that a contact element with larger or smaller dimensions could be formed.
 According to one embodiment of the present invention, the following
mechanical properties can be specifically engineered for a contact element or a
set of contact elements, to achieve certain desired operational characteristics.
First, the contact force for each contact element can be selected to ensure either a
low resistance connection for some contact elements or a low overall contact force
for the connector. Second, the elastic working range of each contact element can
be varied. Third, the vertical height of each contact element can be varied.
Fourth, the pitch or horizontal dimensions of the contact element can be varied.
 Referring to Figure 6, a plurality of contact arm designs are shown
for either a BBGA or a BLGA system. As aforementioned, these contacts can be either stamped or etched into a spring-like structure, and can be heat treated before or after forming.
 Figure 7 is an exploded perspective view showing the assembly of a
connector 700 according to one embodiment of the present invention. The connector 700 includes a first set of contact elements 702 that are located on a first major surface of a dielectric substrate 704 and a second set of contact elements 706 that are located on a second major surface of the substrate 704. Each pair of contact elements 702 and 706 is preferably aligned with a hole 708 formed in the substrate 704. Metal traces are formed through the hole 708 to connect a contact element from the first major surface to a contact element from the second major surface.
 Figure 7 shows the connector 700 during an intermediate step in the
manufacturing'process for forming the connector. Therefore, the array of contact elements is shown as being connected together on a sheet of metal or metallic
material from which they are formed. In the subsequent manufacturing steps, the metal sheet between the contact elements is patterned to remove unwanted portions of the metal sheet, so that the contact elements are isolated (i.e., singulated) as needed. For example, the metal sheet can be masked and etched to singulate some or all of the contact elements.
 In one embodiment, the connector of the present invention is formed
as follows. First, the dielectric substrate 704 including conductive paths between the top surface and the bottom surface is provided. The conductive paths can be in the form of vias or an aperture 708. In one embodiment, the dielectric substrate 704 is a piece of any suitable dielectric material with plated through holes. A conductive metal sheet or a multilayer metal sheet is then patterned to form an array of contact elements including a base portion and one or more elastic portions. The contact elements, including the spring portions, can be formed by etching, stamping, or other means. The metal sheet is attached to the first major surface of the dielectric substrate 704. When a second set of contact elements is to be included, a second conductive metal sheet or multilayer metal sheet is similarly patterned and attached to the second major surface of the dielectric substrate 704. The metal sheets can then be patterned to remove unwanted metal from the sheets, so that the contact elements are isolated from each other (i.e., singulated) as needed. The metal sheets can be patterned by etching, scribing, stamping, or other means.
 In an alternate embodiment, the protrusion of the elastic portions
can be formed after the metal sheet, including patterned contact elements, has
been attached to the dielectric substrate. In another alternate embodiment, the
unwanted portions of the metal sheets can be removed before the contact
elements are formed. Also, the unwanted portions of the metal sheets can be
removed before the metal sheets are attached to the dielectric substrate.
 Furthermore, in the embodiment shown in Figure 7, conductive
traces are formed in the plated through holes 708 and also on the surface of the dielectric substrate 704 in a ring-shaped pattern 710 encircling each plated through hole. While the conductive ring 710 can be provided to enhance the
electrical connection between the contact elements on the metal sheet and the
conductive traces formed in the dielectric layer 704, the conductive ring 710 is
not a required component of the connector 700. In one embodiment, the connector
700 can be formed by using a dielectric substrate including through holes that
are not plated. A metal sheet including an array of contact elements can be
attached to the dielectric substrate. After the metal sheet is patterned to form
individual contact elements, the entire structure can then be plated to form
conductive traces in the through holes, connecting the contact elements through
the holes to the respective terminals on the other side of the dielectric substrate.
 Figure 8 illustrates a connector 800 including contact elements
formed using multiple layers of metals according to another embodiment of the present invention. Referring to Figure 8, the connector 800 includes a multilayer structure for forming a first group of contact elements 802 and a second group of contact elements 804. In this embodiment, the first group of contact elements 802 is formed using a first metal layer 806 and the second group of contact elements 804 is formed using a second metal layer 808. The first metal layer 806 and the second metal layer 808 are isolated by a dielectric layer 810. Each metal layer is patterned so that a group of contact elements is formed at desired locations on the specific metal layer. For instance, the contact elements 802 are formed in the metal layer 806 at predefined locations, while the contact elements 804 are formed in the metal layer 808 at locations not occupied by the contact elements 802. The different metal layers may include metal layers with different thicknesses or different metallurgies, so that the operating properties of the contact elements can be specifically tailored. Thus, by forming a selected contact element or a selected group of contact elements in a different metal layer, the contact elements of the connector 800 can be made to exhibit different electrical and mechanical properties.
 In one embodiment, the connector 800 can be formed using the
following process sequence. The first metal layer 806 is processed to form the first groupi of contact elements; 802. Themetal layer 806 can then be attached to a dielectric substrate 812. Subsequently, an insulating layer, such as the dielectric
layer 810, is located over the first metal layer 806. The second metal layer 808 can be processed to form the contact elements and attached to the dielectric layer 810. Via holes and conductive traces are formed in the dielectric substrate 812 and in the dielectric layer 810 as needed to provide a conductive path between each contact element to a respective terminal 814 on the opposing side of the substrate 812.
 Figures 9a and 9b are cross-sectional views of a connector according
to one embodiment of the present invention. Figures 9a and 9b illustrate a connector 900 connected to a semiconductor device 910 including metal pads 912 formed on a substrate 914 as contact points. The semiconductor device 910 can be a silicon wafer where the metal pads 912 are the metal bonding pads formed on the wafer. The semiconductor device 910 can also be a LGA package where the metal pads 912 represent the "lands" or metal connection pads formed on the LGA package. The coupling of the connector 900 to semiconductor device 910 in Figures 9a and 9b is illustrative only and is not intended to limit the application of the connector 900 to connecting with wafers or LGA packages only. Figures 9a and 9b illustrate the connector 900 turned upside down to engage the semiconductor device 910. The use of directional terms such as "above" and "top surface" in the present description is intended to describe the relative positional relationship of the elements of the connector as if the connector is positioned with the contact elements facing upward.
 Referring to Figure 9a, the connector 900 includes an array of
contact elements 902 located on a substrate 904. Because the connector 900 can be built be for connecting to semiconductor devices at semiconductor scales, the connector 900 is usually formed using materials that are commonly used in semiconductor fabrication processes. In one embodiment, the substrate 904 is made of quartz, silicon, or a ceramic wafer and the contact elements 902 are located on a dielectric layer which could be a spin on silica (SOS), spin on glass (SOG), boron phosphorus tetraethoxysilane (BPTEOS), or tetraethoxysilane (TEOS)Tayer formed oh the top surface of the substrate 904. The array of contact elements 902 is typically formed as a two-dimensional array arranged to mate
with corresponding contact points on the semiconductor device 910 to be contacted. In one embodiment, the connector 900 is formed to contact metal pads having a pitch of 50 microns or less. Each contact element 902 includes a base portion 906 attached to the top surface of the substrate 904 and a curved or linear spring portion 908 extending from the base portion 906. The spring portion 908 has a proximal end contiguous with the base portion 906 and a distal end projecting above the substrate 904.
 The spring portion 908 is formed to curve away or angle away from
a plane of contact, which is the surface of the contact point to which the contact element 902 is to be contacted, the surface of the metal pad 912. The spring portion 908 is formed to have a concave curvature with respect to the surface of the substrate 904, or is formed to be angled away from the surface of the substrate 904. Thus, the spring portion 908 curves or angles away from the surface of the metal pad 912, which provides a controlled wiping action when engaging the metal pad 912.
 In operation, an external biasing force, denoted F in Figure 9a, is
applied to the connector 900 to compress the connector 900 against the metal
pads 912. The spring portion 908 of the contact element 902 engages the
respective metal pad 912 in a controlled wiping action, so that each contact
element 902 makes an effective electrical connection to the respective pad 912.
The curvature or angle of the contact elements 902 ensures that the optimal
contact force is achieved concurrently with the optimal wiping distance. The
wiping distance is the amount of travel the distal end of the spring portion 908
makes on the surface of the metal pad 912 when contacting the metal pad 912. In
general, the contact force is on the order of five to 100 grams depending on the
application, and the wiping distance is on the order of five to 400 microns.
 Another feature of the contact element 902 is that the spring portion
908 enables a large elastic working range. Specifically, because the spring portion 908 can move in both the vertical and the horizontal directions, an elastic working range on the order of the electrical path length of the contact element 902 can be achieved. The "electrical path length" of the contact element 902 is
defined as the distance the electrical current has to travel from the distal end of the spring portion 908 to the base portion 906 of the contact element 902. The contact elements 902 have an elastic working range that spans the entire length of the contact elements, which enables the connector to accommodate normal coplanarity variations and positional misaUgnments in the semiconductor or electronic devices to be connected.
 The contact elements 902 are formed using a conductive metal that
can also provide the desired elasticity. In one embodiment, the contact elements 902 are formed using titanium (Ti) as a support structure that can later be plated to obtain a desired electrical and/or elastic behavior. In other embodiments, the contact elements 902 are formed using a copper alloy (Cu-alloy) or a multilayer metal sheet such as stainless steel coated with a copper-nickel-gold (Cu/Ni/Au) multilayer metal sheet. In a preferred embodiment, the contact elements 902 are formed using a small-grained copper beryllium (CuBe) alloy and then plated with electroless nickel-gold (Ni/Au) to provide a non-oxidizing surface. In an alternate embodiment, the contact elements 902 are formed using different metals for the base portions and the spring portions.
 In the embodiment shown in Figure 9a, the contact element 902 is
shown as having a rectangular shaped base portion 906 with one spring portion
908. The contact element of the present invention can be formed in a variety of
configurations and each contact element only needs to have a base portion
sufficient for attaching the spring portion to the substrate. The base portion can
assume any shape and can be formed as a circle or other useful shape for
attaching the contact element to the substrate. A contact element can include
multiple spring portions extending from the base portion.
 Figures 10a and 10b illustrate a connector 1000 according to an
alternate embodiment of the present invention. The connector 1000 includes an array of contact elements 1002 formed on a substrate 1004. Each contact element 1002 includes a base portion 1006 and two curved spring portions 1008 and 1010 extending from the base portion 1006. The spring portions 1008 and 1010 have distal ends projecting above the substrate 1004 and facing towards each other.
Other characteristics of the spring portions 1008 and 1010 are the same as spring
portion 908. That is, the spring portions 1008 and 1010 curve away from a plane
of contact and each has a curvature disposed to provide a controlled wiping action
when engaging a contact point of a semiconductor device to be contacted.
 The connector 1000 can be used to contact a semiconductor device
1020, such as a BGA package, including an array of solder balls 1022 mounted on a substrate 1024 as contact points. Figure 10b illustrates the connector 1000 being fully engaged with the semiconductor device 1020. The connector 1000 can also be used to contact metal pads, such as pads on a land grid array package. However, using the connector 1000 to contact solder balls provides particular advantages.
 First, the contact elements 1002 contact the respective solder balls
1022 along the side of the solder balls. No contact to the base surface of the solder ball 1022 is made. Thus, the contact elements 1002 do not damage the base surface of the solder balls 1022 during contact, and effectively eliminate the possibility of void formation when the solder balls 1022 are subsequently reflowed for permanent attachment.
 Second, because the spring portions 1008 and 1010 of the contact
elements 1002 are formed to curve away from the plane of contact, which in the
present case is a plane tangent to the side surface of the solder ball 1022 being
contacted, the contact elements 1002 provide a controlled wiping action when
contacting the respective solder balls 1022. In this manner, an effective electrical
connection can be made without damaging the surface of the solder balls 1022.
 Third, the connector 1000 is scalable and can be used to contact
solder balls having a pitch of 250 microns or less.
 Lastly, because each contact element 1002 has a large elastic
working range on the order of the electrical path length, the contact elements 1002 can accommodate a large range of compression. Therefore, the connector of the present invention can be used effectively to contact conventional devices having normal coplanarity variations or positional misahgnments.
 Figures 11 and 12 illustrate connectors according to alternate
embodiments of the present invention. Referring to Figure 11, a connector 1100 includes a contact element 1102 formed on a substrate 1104. Contact element 1102 includes a base portion 1106, a first curved spring portion 1108, and a second curved spring portion 1110. The first spring portion 1108 and the second spring portion 1110 have distal ends that point away from each other. The contact element 1102 can be used to engage a contact point including a metal pad or a solder ball. When used to engage a solder ball, contact element 1102 cradles the solder ball between the first and second spring portions 1108 and 1110, similar to what is shown in Figure 3e. Thus, the first and second spring portions 1108 and 1110 contact the side surface of the solder ball in a controlled wiping motion in a direction that curves away from the plane of contact of the solder ball.
 Figure 12 illustrates a contact element 1200 located on a substrate
1202. The contact element 1200 includes a base portion 1204, a first curved
spring portion 1206 extending from the base portion 1204, and a second curved
spring portion 1208 extending from the base portion 1204. The first spring
portion 1206 and the second spring portion 1208 project above the substrate 1202
in a spiral configuration. The contact element 1200 can be used to contact a metal
pad or a solder ball. In both cases, the first and second spring portions 1206 and
1208 curve away from the plane of contact and provide a controlled wiping action.
 Figures 13a to 13c are cross-sectional views of a connector 1300
which can, for example, be applied in a hot-swapping operation. Referring to Figure 13a, the connector 1300 is shown in an unloaded condition. The connector 1300 is to be connected to a land grid array (LGA) package 1320 and a printed circuit board (PC board) 1330. A pad 1322 on the LGA package 1320 represents a power connection (that is, either the positive power supply voltage or the ground voltage) of the integrated circuit in the LGA package 1320 which is to be connected to a pad 1332 on the PC board 1330. The pad 1332 is electrically active or "powered-up". A pad 1324 on the LGA package 1320 represents a signal pin of the integrated circuit which is to be connected to a pad 1334 on the PC board
1330. To enable a hot-swapping operation, the power pad 1322 should be
connected to pad 1332 prior to the signal pad 1324 being connected to pad 1334.
The connector 1300 includes contact elements 1304 and 1306 in a substrate 1802
which have an extended height and a larger elastic working range than contact
elements 1308 and 1310, such that a hot-swapping operation between the LGA
package 1320 and the PC board 1330 is realized using the connector 1300. The
height of the contact elements 1304 and 1306 is selected to obtain the desired
contact force and desired spacing to achieve a reliable hot-swapping operation.
 Figure 13b illustrates an intermediate step during the mounting
process of the LGA package 1320 to the PC board 1330 using the connector 1300. When the LGA package 1320 and the PC board 1330 are compressed together against the connector 1300, pad 1322 and pad 1332 will make electrical connections to respective contact elements 1304 and 1306 prior to the pads 1324 and 1334 making connection to contact elements 1308 and 1310. In this manner, the power connection between the LGA package 1320 and the PC board 1330 is established before the signal pads are connected.
 Figure 13c illustrates the mounting of the LGA package 1320 to the
PC board 133 0 in a fully loaded condition. By applying further compression force, the LGA package 1320 is compressed against the connector 1300 so that contact element 1308 engages the signal pad 1324. Similarly, the PC board 1330 is compressed against the connector 1300 so that contact element 1310 engages the pad 1334. The LGA package 1320 is thus mounted onto the PC board 1330. In the connector 1300, as the taller contact elements 1304, 1306 are compressed more to allow the shorter contact elements 1308, 1310 to engage, the contact force required for the connector will increase. In order to minimize the overall contact force required for the connector, the taller contact elements 1304,1306 can be designed with a lower spring constant than the shorter contact elements 1308,1310 such that all contact elements are at the optimal contact force in the fully loaded condition.
" Figure 14a-illustrates one embodiment of a circuitized connector
1400 in accordance with the present invention. The connector 1400 includes a
contact element 1404 on the top surface of a dielectric substrate 1402 connected to a contact element 1406 on the bottom surface of dielectric substrate 1402. The contact element 1404 is connected to a surface mounted electrical component 1410 and an embedded electrical component 1412. The electrical components 1410 and 1412 may be decoupling capacitors, for example, which are positioned on the connector 1400 so that the capacitors can be placed as close to the electronic component as possible. In conventional integrated circuit assembly, such decoupling capacitors are usually placed on the printed circuit board distant from the electronic component. Thus, a large distance exists between the electronic component to be compensated and the actual decoupling capacitor, thereby diminishing the effect of the decoupling capacitor. By using the circuitized connector 1400, the decoupling capacitors can be placed as close to the electronic component as possible to enhance the effectiveness of the decoupling capacitors. Other electrical components that may be used to circuitize the connector include a resistor, an inductor, and other passive or active electrical components.
 Figure 14b illustrates another embodiment of a circuitized connector
according to the present invention. Connector 1420 includes a contact element
1424 on a dielectric substrate 1422 coupled to a solder ball terminal 1426
through a via 1428. The contact element 1424 is connected to a surface mounted
electrical component 1430 and to an embedded electrical component 1432. The
connector 1420 further illustrates that the placement of the terminal 1426 does
not have to be aligned with the contact element 1424 as long as the contact
element is electrically coupled to the terminal, such as through the via 1428. It is
noted that a connector in accordance with the present invention can be
constructed without a relief hole in the substrate. The electrical contact or via
can be defined in an offset hole or in any suitable manner to provide electrical
connections internally or to opposite sides of the substrate.
 According to another aspect of the present invention, a connector
can include one or more coaxial contact elements. Figures 15a and 15b show a connector 1500 including a coaxial contact element according to one embodiment
of the present invention. Referring to Figure 15a, the connector 1500 includes a
first contact element 1504 and a second contact element 1506 formed on the top
surface of a dielectric substrate 1502. The contact elements 1504 and 1506 are
formed in proximity to, but electrically isolated from, each other. The contact
element 1504 includes a base portion formed as an outer ring of an aperture 1508
while the contact element 1506 includes a base portion formed as an inner ring of
the aperture 1508. Each of the contact elements 1504,1506 includes three elastic
portions (Figure 15b). The elastic portions of the contact element 1504 do not
overlap with the elastic portions of the contact element 1506. The contact
element 1504 is connected to a contact element 1510 on the bottom surface of the
dielectric substrate 1502 through at least one via 1512. The contact elements
1504 and 1510 form a first current path, referred to as the outer current path of
the connector 1500. The contact element 1506 is connected to a contact element
1514 on the bottom surface of the dielectric substrate 1502 through a metal trace
1516 formed in the aperture 1508. The contact elements 1506 and 1514 form a
second current path, referred to as the inner current path of the connector 1500.
 As thus constructed, the connector 1500 can be used to interconnect
a coaxial connection on a LGA package 1520 to a coaxial connection on a PC
board 1530. Figure 16 illustrates the mating of the LGA package 1520 to the PC
board 1530 through the connector 1500. When the LGA package 1520 is mounted
to the connector 1500, the contact element 1504 engages a pad 1522 on the LGA
package 1520. Similarly, when the PC board 1530 is mounted to the connector
1500, the contact element 1510 engages a pad 1532 on the PC board 1530. As a
result, the outer current path between pad 1522 and pad 1532 is formed.
Typically, the outer current path constitutes a ground potential connection. The
contact element 1506 engages a pad 1524 on the LGA package 1520 while the
contact element 1514 engages a pad 1534 on the PC board 1530. As a result, the
inner current path between pad 1524 and pad 1534 is formed. Typically, the
inner current path constitutes a high frequency signal.
 A particular advantage of the connector 1500 is that the coaxial
contact elements can be scaled to dimensions of one millimeter or less. Thus, the
connector 1500 can be used to provide a coaxial connection even for small geometry electronic components.
 Method for making an electrical connector
 Figures 17a to 17h illustrate the processing steps for forming the
connector 900 of Figure 9a, according to one embodiment of the present invention. Referring to Figure 17a, a substrate 1700 on which the contact elements are to be located is provided. The substrate 1700 can be a silicon wafer or ceramic wafer! for example, and may include a dielectric layer formed thereon (not shown in Figure 17a). The dielectric layer, of SOS, SOG, BPTEOS, or TEOS for example, can be formed on the substrate 1700 for isolating the contact elements from the substrate 1700. Then, a support layer 1702 is formed on the substrate 1700. The support layer 1702 can be a deposited dielectric layer, such as an oxide or nitride layer, a spin-on dielectric, a polymer, or any other suitable etchable material. The support layer 1702 can be deposited by a number of different processes, including chemical vapor deposition (CVD), plasma vapor deposition (FVD), a spin-on process, or when the substrate 1700 is not covered by a dielectric layer or a conductive adhesive layer, the support layer 1702 can be grown using an oxidation process commonly used in semiconductor manufacturing.
 After the support layer 1702 is deposited, a mask layer 1704 is
formed on the top surface of the support layer 1702. The mask layer 1704 is used in conjunction with a conventional lithography process to define a pattern on the support layer 1702 using the mask layer 1704. After the mask layer is printed and developed (Figure 17b), a mask pattern, including regions 1704a to 1704c, is formed on the surface of the support layer 1702 defining areas of the support layer 1702 to be protected from subsequent etching.
 Referring to Figure 17c, an anisotropic etching process is performed
using regions 1704a to 1704c as a mask. As a result of the anisotropic etching process, the portions of the support layer 1702 hot covered by a patterned mask layer is removed. Accordingly, support regions 1702a to 1702c are formed. The
mask pattern including regions 1704a to 1704c is subsequently removed to expose the support regions (Figure 17d).
 The support regions 1702a to 1702c are then subjected to an
isotropic etching process. An isotropic etching process removes material under
etch in the vertical and horizontal directions at substantially the same etch rate.
Thus, as a result of the isotropic etching, the top corners of the support regions
1702a to 1702c are rounded off as shown in Figure 17e. In one embodiment, the
isotropic etching process is a plasma etching process using SFe> CHF3, CF4, or
other well known chemistries commonly used for etching dielectric materials. In
an alternate embodiment, the isotropic etching process is a wet etch process, such
as a wet etch process using a buffered oxide etch (BOE).
 Then, referring to Figure 17f, a metal layer 1706 is formed on the
surface of the substrate 1700 and the surface of support regions 1702a to 1702c. The metal layer 1706 can be a copper layer, a copper alloy (Gu-alloy) layer, or a multilayer metal deposition such as tungsten coated with copper-nickel-gold (Cu/Ni/Au). In a preferred embodiment, the contact elements are formed using a small-grained copper beryllium (CuBe) alloy, and are then plated with electroless nickel-gold (Ni/Au) to provide a non-oxidizing surface. The metal layer 1706 can be deposited by a CVD process, electro plating, sputtering, PVD, or other conventional metal film deposition techniques. A mask layer is deposited and patterned into mask regions 1708a to 1708c using a conventional lithography process. The mask regions 1708a to 1708c define areas of the metal layer 1706 to be protected from subsequent etching.
 The structure in Figure 17f is then subjected to an etching process
for removing the portions of the metal layer not covered by mask regions 1708a to 1708c. As a result, metal portions 1706a to 1706c are formed as shown in Figure 17g. Each of the metal portions 1706a to 1706c includes a base portion formed on the substrate 1700 and a curved spring portion formed on a respective support region (1702a to 1702c). Accordingly, the curved spring portion of each metal portion assumes the shape of the underlying support region, projecting above the surface of the substrate 1700.
 To complete the connector, the support regions 1702a to 1702c are
removed (Figure 17h), such as by using a wet etch, an anisotropic plasma etch, or
other etch process. If the support layer is formed using an oxide layer, a buffered
oxide etchant can be used to remove the support regions. As a result, free
standing contact elements 1710a to 1710c are formed on the substrate 1700.
 Variations in the above processing steps are possible to fabricate the
connector of the present invention. For example, the chemistry and etch condition of the isotropic etching process can be tailored to provide a desired shape in the support regions, so that the contact elements have a desired curvature. Through the use of semiconductor processing techniques, a connector can be fabricated with contact elements having a variety of properties. For example, a first group of contact elements can be formed with a first pitch, while a second group of contact elements can be formed with a second pitch that is greater or smaller than the first pitch. Other variations in the electrical and mechanical properties of the contact element are possible.
 Figures 18a and 18b illustrate the first and last processing steps for
forming a circuitized connector similar to the connector 1400 of Figure 14a, according to an alternate embodiment of the pi'esent invention. Referring to Figure 18a, a substrate 1800 including predefined tircuitry 1802 is provided. The predefined circuitry 1802 can include interconnected metal layers or other electrical devices, such as capacitors or inductors, which are typically formed in the substrate 1800. A top metal portion 1804 is formed on the top surface of the substrate 1800 to be connected to the contact element to be formed. A support layer 1806 and a mask layer 1808 are formed on the top surface of the substrate 1800.
 A process similar to that described above in connection with Figures
17b to 17g is used to form a contact element 1810 (Figure 18b). As thus formed, the contact element 1810 is electrically connected to the circuit 1802. In this manner, additional functionality can be provided by the connector of the present invention. For example, the circuit 1802 can be formed to electrically connect certain contact elements together. The circuit 1802 can also be used to connect
certain contact elements to electrical devices such as a capacitor or an inductor formed in or on the substrate 1800.
 Fabricating the contact element 1810 as part of an integrated circuit
manufacturing process provides further advantages. Specifically, a continuous electrical path is formed between the contact element 1810 and the underlying circuit 1802. There is no metal discontinuity or impedance mismatch between the contact element and the associated circuit. In some prior art connectors, a gold bond wire is used to form the contact element. However, such a structure results in gross material and cross-sectional discontinuities and impedance mismatch at the interface between the contact element and the underlying metal connections, resulting in undesirable electrical characteristics and poor high frequency operations.
 According to another aspect of the present invention, a connector is
provided with contact elements having different operating properties. That is, the connector can include heterogeneous contact elements where the operating properties of the contact elements can be selected to meet requirements in the desired application. The operating properties of a contact element refer to the electrical, mechanical, and reliability properties of the contact element. By incorporating contact elements with different electrical and/or mechanical properties, a connector can be made to meet all of the stringent electrical, mechanical, and reliability requirements for high-performance interconnect applications.
 According to alternate embodiments of the present invention, the
electrical properties can be specifically engineered for a contact element or a set of contact elements to achieve certain desired operational characteristics. For instance, the DC resistance, the impedance, the inductance, and the current carrying capacity of each contact element can be varied. Thus, a group of contact elements can be engineered to have lower resistance or to have low inductance. The contact elements can also be engineered to display no or minimal performance degradation "after environmental stresses such as thermal cycling, thermal shock and vibration, corrosion testing, and humidity testing. The contact
elements can also be engineered to meet other reliability requirements defined by industry standards, such as those defined by the Electronics Industry Alliance (EIA).
 The mechanical and electrical properties of the contact elements can
be modified by changing the following design parameters. First, the thickness of the spring portion of the contact element can be selected to give a desired contact force. For example, a thickness of about 30 microns typically gives a low contact force on the order of 10 grams or less, while a flange thickness of 40 microns gives a higher contact force of 20 grams for the same displacement. The width, length, and shape of the spring portion can also be selected to give the desired contact force.
 Second, the number of spring portions included in a contact element
can be selected to achieve the desired contact force, the desired current carrying
capacity, and the desired contact resistance. For example, doubling the number of
spring portions roughly doubles the contact force and current carrying capacity,
while roughly decreasing the contact resistance by a factor of two.
 Third, specific metal composition and treatment can be selected to
obtain the desired elasticity and conductivity characteristics. For example, copper alloys, such as beryllium copper, can be used to provide a good tradeoff between mechanical elasticity and electrical conductivity. Alternately, metal multilayers can be used to provide both excellent mechanical and electrical properties. In one embodiment, a contact element is formed using titanium (Ti) coated with copper (Cu), then with nickel (Ni), and finally with gold (Au) to form a Ti/Cu/Ni/Au multilayer. The Ti provides elasticity and high mechanical durability, the Cu provides conductivity, and the Ni and Au layers provide corrosion resistance. Finally, different metal deposition techniques, such as plating or sputtering, and different metal treatment techniques, such as alloying, annealing, and other metallurgical techniques can be used to engineer specific desired properties for the contact elements.
 Fourth, the shape of the spring portion can be designed to give
certain electrical and mechanical propei'ties. The height of the spring portion, or
the amount of projection from the base portion, can also be varied to give the desired electrical and mechanical properties.
 Figures 19a-19d are flowcharts of a method 1900 for forming contact
elements in accordance with an alternate embodiment of the present invention.
Figures 20-23b will be discussed in the context of the discussion of the method
1900. The method 1900 also relates to batch fabrication of the contact elements
using masking, etching, forming, and lamination techniques. The method 1900
produces a plurality of highly engineered electrical contacts, capable of use in a
separable connector such as in an interposer, or the contacts can be directly
integrated into a substrate as a continuous trace that then functions as a
permanent onboard connector. However, rather than using additional masking
and etching steps to form the three dimensional spring portions, they are created
in flat arrays and are then formed into three dimensional shapes.
 First, a base spring material for the sheet of contacts is selected,
such as beryllium copper (Be-Cu), spring steel, phosphorous bronze, or any other material with suitable mechanical properties (step 1902). The proper selection of material enables the contact elements to be engineered to have the desired mechanical and electrical properties. One factor in the selection of the base material is the working range of the material. Working range is the range of displacement over which the contact element meets both contact force (load) and contact resistance specifications. For example, assume that the desired contact resistance is less than 20 milliohms and the maximum allowed contact load is 40 grams. If the contact element reaches a resistance range of less than 20 milliohms at 10 grams of load and then is carried over to the maximum load of 40 grams for the beam member, while mamtaining a resistance of less than 20 milliohms, then the distance over which the contact element has traveled between 10 grams and 40 grams of load would be the working range of the contact.
 The sheet can be heat treated prior to subsequent processing (step
1904). Whether the sheet is heated at this point in the process is detenninedby the type of material selected for the sheet. The heating is performed to move the
material from a half-hard state into a hard state or highly-tensile state that
provides desired mechanical properties for forming the contacts.
 A contact element is designed and is copied into an array form, for
use in batch processing (step 1906). The number of contacts in an array is a
design choice, and can vary depending on the requirements for the connector. The
arrays are repeated into a panel format, analogous to chips or die in a
semiconductor wafer, resulting in a scalable design that lends itself to batch
processing. After the contact design has been completed (usually in a CAD
drawing environment), the design is ported to a Gerber format, which is a
translator that enables the design to be ported to a fabrication facility to produce
the master slides or film to be used in the subsequent steps.
 The panel format can have anywhere between one and a large
number of contacts, because the use of lithography permits placing a high density
of contacts onto a panel. This high density of contacts provides an advantage over
existing methods in that a batch process can be used to singulate the contacts, as
opposed to stamping and forming individual contacts. The method 1900 permits a
large number of contacts to be patterned, developed, and etched at once.
 A lithographically sensitive resist film is then applied to both sides
of the sheet (step 1908 and Figure 20). A dry film can be used for larger feature sizes ranging from one to 20 mils, and a liquid resist can be used for feature sizes less than one mil.
 Using the artwork defined in step 1906, both the top and bottom of
the sheet are exposed to ultraviolet (UV) light and then developed to define
contact features in the resist (step 1910 and Figure 21). Portions that are
intended to be etched are left unprotected by the mask. Using a lithographic
process to define the contact elements enables the printing of lines with a fine
resolution, similar to that found in semiconductor manufacturing.
 The sheet is then etched in a solution specifically selected for the
material being used (step 1912). Each particular material that can be selected for the sheet typically has a specific etch chemistry associated with it to provide the best etch characteristics, such as etch rate (i.e., how well and how fast the
solution performs the etch). This is an important consideration in the context of throughputs. The etchant selected also effects other characteristics like the sidewall profile, or the straightness of a feature as seen in cross section. In the method 1900, chemicals common in the industry are used, such as cupric chloride, ferric chloride, and sulfuric hydroxide. Once etched, the protective layer of resist is removed in a stripping process, leaving the etched features in the sheet (step 1914 and Figure 22).
 A batch forming tool is designed, based upon the artwork defined in
step 1906 (step 1916). In one embodiment, the batch forming tool includes of a plurality of ball bearings arranged into an array format, preferably by being set into an array of openings in a support surface. The ball bearings can be of different sizes, to apply different forces to the contacts, thereby imparting different mechanical characteristics to contacts on the same panel. The curvature of the ball bearings is used to push the flanges away from the plane of the sheet. The flanges of the contacts are then formed in all three axes by applying the forming tool to the sheet, to produce the desired contact elements in a batch process (step 1918).
 The sheet can be heat treated to correct grain dislocations caused by
the forming process (step 1920). As with step 1904, the heating step 1920 is optional, and is dependent upon the material selected for the sheet. Based upon the material and the size of the contacts to be defined on the sheet, heating may be performed to obtain the physical properties desired for optimal forming conditions.
 The sheet is then surface treated to enhance adhesion properties for
a subsequent lamination process (step 1922). If there is inadequate adhesion, there is a propensity for the sheet to separate from a substrate or delaminate. Several methods for performing the surface treating can be used, including micro etching and a black oxide process. The micro etching is used to pit the surface of the sheet, effectively creating a greater surface area (by making the surface rough and cratered) to promote better adhesion. However, if the micro etching is not properly controlled, it can lead to damage on the sheet.
 The black oxide process is a replacement process involving a self-
limiting reaction in which an oxide is grown on the surface of the sheet. In this reaction, the oxygen diffuses only through a set thickness, thereby limiting the amount of oxide grown. The oxide has a rough surface in the form of bumps, which helps to promote adhesion. Either the micro etching or the black oxide processes can be used for the surface treatment step, and a preference for one process over the other is a design choice.
 Prior to pressing, a low flow adhesion material and dielectric core
are processed with relief depressions or holes located beneath flange elements (step 1924). This is intended to prevent excess flow of material up on the flange during the lamination process. Should this flow happen, the contact properties would be altered, causing the contact element to be unsuitable for electrical and mechanical use.
 The following list is a typical stack up generated for lamination
pressing (step 1926). This arrangement could be altered to have the contact elements inserted as internal layers. Figure 23a shows each layer of the stack
 a. Layer 1 is a top press plate material
 b. Layer 2 is a spacer material with a relief hole over the spring
 c. Layer 3 is a release material with a relief hole over the spring
 d. Layer 4 is a top sheet of formed contact sheets
 e. Layer 5 is an adhesion material with a relief hole beneath the
 £ Layer 6 is a core dielectric with relief holes under and above
the spring contact
 g. Layer 7 is an adhesion material with a relief hole above the
 h. Layer 8 is a bottom sheet of formed contact elements
 i. Layer 9 is a release material with a relief hole below the
 j. Layer 10 is a spacer material with a relief hole below the
spring contact element
 k. Layer 11 is a bottom press plate material
 The stack up is pressed under temperature conditions optimized for
desired adhesions and flow conditions for the adhesion material (step 1928 and
Figure 23b). During this operation, the top and bottom contact sheets are bonded
to a core dielectric material. After a cool down period, the stack up is removed
from the press plates, leaving a panel comprised of Layers 4-8 (step 1930).
 The panel surfaces and openings are then plated to electrically
connect the top and bottom flanges (step 1932). This step takes the top flange and
electrically connects it to the bottom flange by a plating process known as an
electroless process. The process effectively deposits a conductive material on the
top surface, into the through hole to connect both sheets of contact elements, and
then onto the sheet on the other side of the substrate. The plating process creates
a route for an electrical current to travel from one side of the board to the other.
 Nest, a photosensitive resist film is applied to both sides of the
panel (step 1934). A pattern is exposed and developed to define the individual contact elements (step 1936). A determination is then made as to the contact finish type, either hard gold or soft gold (step 1938). Hard gold is used in specific applications where the numbers of insertions required are high, such as a test socket. Hard gold itself has impurities that cause the gold to be more durable. Soft gold is a pure gold, so it effectively has no impurities, and is typically used in the PCB or networking space, where the number of insertions is fairly low. For example, a package to board socket used in a PC (soft gold) will typically see on the order of one to 20 insertions, whereas other technology using hard gold will see a number of insertions between 10 and 1,000,000.
 If the contact finish type is a hard gold, then a partial etching is
performed to almost singulate the contact elements (step 1940). The resist film is removed via a stripping process (step 1942). A new layer of resist is applied,
covering both sides of the panel (step 1944). The previously etched areas are exposed and developed (step 1946). The panel is then submitted for electrolytic Cu/Ni/Au plating via a hard gold process (step 1948).
 The resist is removed to expose previous partially etched scribe lines
(step 1950). The entire panel is etched using electrolytic Ni/Au as a hard mask to complete singulation of the contact array (step 1952). Final interposer outlines are routed out of the panel to separate the panel into individual connector arrays (step 1954), and the method terminates (step 1956).
 If a soft gold finish is used (step 1938), then etching is used to
completely singulate the contact elements (step 1960). The resist film is removed
via a stripping process (step 1962). Electroless Ni/Au, also known as a soft gold,
is plated onto the panel to complete the contact elements (step 1964). Final
interposer outlines are routed out of the panel to separate the panel into
individual connector arrays (step 1954), and the method terminates (step 1956).
 The soft gold finishing process singulates the contacts prior to
plating. Ni/Au will plate only on metal surfaces, and provides a sealing mechanism for the contact element. This helps to prevent potential corrosive activity that could occur over the system life of the contact, since gold is virtually inert. Singulation prior to plating is a means to isolate or encapsulate the copper contact with another metal, resulting in cleaner imaging and a cleaner contact, which has a low propensity for shorting.
 Those skilled in the art will recognize that a connector according to
the present invention could be used as an interposer, a PCB connector, or could be formed as a PCB. The scalability of the present invention is not limited, and can be easily customized for production due to the lithographic techniques used and the simple tooling die used for forming the connector elements in three dimensions.
 While specific embodiments of the present invention have been
shown and described, many modifications and variations could be made by one skilled in the art without departing from the scope of the invention. The above description serves to illustrate and not limit the particular invention in any way.
WO 2004/093252 PCT/US2004/011074
[received by the International Bureau on 25 April 2005 (25.04.2005); original claims 1-21 replaced by amended claims 1-19]
1. An electrical connector, comprising;
a dielectric substrate having surfaces with vias connecting the surfaces;
an electrical contact array including a plurality of comact elements, each contact element having at least one conductive spring portion biased outwardly from the array and a base portion,
said contact array bonded to a first surface of said substrate to align at least one of said contact element base portions with one of the vias in said substrate, respective ones of said contact elements and vias plated with conductive material to form a unitary structure; and
said contact elements electrically isolated from each other.
2. The connector according to claim I, the dielectric substrate comprising a plurality of relief openings.
3. The connector according to claim 2, in which the contact elements of the contact array are arranged in a predetermined pattern and at least some of the plurality of relief openings are arranged in a pattern that corresponds to the predetermined pattern.
4. The connector according to claim I, in which the at least one spring portion is formed by a photolithographic masking and a chemical etching of me conducnve sheet.
5. The connector according to claim 1, further comprising;
a second electrical contact array including a plurality of contact elements, each contact element having at least one conductive spring ponion biased outwardly from the array and a base ponion,
said second contact array bonded to a second surface of said substrate to align at least one of said contact element base portions with one of the vias m said substrate,
AMENDED SHEET (ARTICLE 19) 34
WO 2004/093252 PCT/US2004/011074
respective ones of said contact elements and vias plated with conductive material to form a unitary structure; and
said contacts electrically isolated from each other.
6. The connector according to claim 5, in which the connector forms an interposer located between an electrical device and a socket
7. The connector according to claim 1, in which the dielectric substrate is a printed circtri board.
8. The connector according to claim 1, in which the at least one conductive spring ponion includes a non-linear flat pattern to provide an extended length resilient contact.
9. The connector according to claim 1, in which the at least one conductive spring ponion of at least some of the contact elements has at least one of a different shape, elastic spring rate, coniact force, or effective working range wan other spring portions of other ones of the contact elements.
10. The connector according to claim 1, farther comprising a coating of a second conductive material on at least the at least one conductive spring portion.
11. The connector according to claim 1, in which a spring force of the at least one conductive spring portion is between 10 and 40 grams.
12. A method of producing an electrical connector, comprising the steps of:
forming an array of electrical contact elements in a conductive, resilient sheet, the
electrical contact array being arranged in a first predetermined pattern, each contact element including at least one spring portion and a base portion;
biasing the at least one spnng portion outwardly away from the conductive sheet;
AMENDED SHEET (ARTICLE 19) 35
bonding the conductive sheet to a first surface of a dielectric substrate having through holes, the at least one spring portion extending outwardly away from the first surface of the dielectric substrate;
plating the through holes and the contact elements to electrically connect, with a unitary structure, respective'ones of the contact elements to respective ones of the through holes in the dielectric substrate;
masking the conductive sheet according to a predetermined arrangement of the contact elements; and
chemically etching the conductive sheet to singulate at least some of the contact elements from one another.
13. The method according to claim 12, further comprising the step of:
biasing the at least one spring portion outward such that the at least one spring
portion is three-dimensionally formed to a portion of a generally spherical surface.
14. The method according to claim 12, further comprising the step of:
providing a biasing die formed from an array of ball bearings of at least one
selected size located in an array of openings corresponding to the array of contact elements.
15. The method according to claim 12, further comprising the step of:
pre-treating a bonding surface of the conductive sheet by micro-etching to
16. The method according to claim 12, further comprising the step of:
pre-treating a bonding surface of the conductive sheet by an oxide treatment to
17. The method according to claim 12, further comprising the step of:
plating a second conductive material on at least the at least one spring portion.
18. The method according to claim 12, further comprising the steps of:
forming a second array of contact elements in a second conductive, resilient
sheet, in a second predetermined pattern, at least a portion of which corresponds to the first predetermined pattern, each contact element in the second array including at least one spring portion and a base portion;
biasing the at least one spring portion outwardly away from the second sheet;
bonding the second conductive sheet to a second surface of the dielectric substrate, the-at least one spring portion of the second array of contact elements extending outwardly and away from the second surface of the dielectric substrate;
plating the contact elements to electrically connect, with a unitary structure, respective ones of the contact elements to respective ones of the through holes in the dielectric substrate; and
chemically etching the second conductive sheet to singulate at least some of the second plurality of contact elements from one another.
19. A method for batch fabrication of an array of electrical contacts, comprising
the steps of:
creating a photolithographic image of die array of contacts;
applying a lithographically sensitive film to a first conductive sheet and a second conductive sheet;
creating the array of contacts on the first sheet and the second sheet via a lithographic process using the image of the array of contacts;
etching the array of contacts on the first sheet and the second sheet;
using a forming tool to form the array of contacts in three dimensions on the first sheet and the second sheet;
laminating first sheet and the second sheet to opposite sides of a substrate to a panel;
applying a photoresist film to both sides of the panel;
exposing a pattern to define individual contact elements on both sides of the panel; and
singulating the contact elements on both sides of the panel by etching.
20. An electrical connector substantially as herein described with reference to
21. A method of producing an electrical connector substantially as herein described with reference to accompanying drawings.
22. A method for batch fabrication of an array of electrical contacts substantially as herein described with reference to accompanying drawings
Dated this 5th day of October, 2005.
OF K & S PARTNERS
AGENT FOR THE APPLICANT(S)
An electrical connector includes an electrical contact array (17) having a plurality of contact elements (15) where each contact element has at least one conductive, resilient spring p
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