Title of Invention

A MULTI-PIN VACUUM FEEDTHROUGH

Abstract This invention relates to a multi-pin vacuum feedthrough for bringing out electrical connections from the inside of a vacuum encapsulation comprising a disk shaped shell (1) having inner and outer circle with equally spaced plurality of holes provided therein, the said plurality of equally spaced multiple holes enclosing multiple pins (2) of equal size for providing electrical compactions, characterized in that the said multiple pins (2) glass to metal sealed inside the said plurality of holes of the said disk shaped shell (1) using plurality of glass capillaries (3).
Full Text FIELD OF INVENTION:
This invention relates to a multi-pin vacuum feedthrough made by using glass capillaries
PRIOR ART:
A vacuum feedthrough is a connector, which helps bringing out electrical connections from the inside of a vacuum encapsulation to the outside world, without disturbing the vacuum conditions inside. For an IR detector dewar, a multi-pin vacuum feedthrough is a very important component as all the device connections can be accessed only through its pins. At the same time, the feedthrough has to preserve the vacuum integrity of the IR detector dewar and also be able to stand the required baking temperature, before the final sealing of the dewar. Further, as the heat load of a dewar is very critical, from the point of view of its cooling, the feedthrough has to be such that it offers minimum heat load to the dewar.
Vacuum feedthroughs are well known in the art and various vacuum feedthroughs have already been made in different designs in different ways for many practical applications.
One of these types of feedtroughs, known in the art, are metal to ceramic sealing type feedthroughs, which are used for transmitting tubes, synchrotron, etc. This type of feedthrough comprises of a metal cylinder and a disc shaped ceramic pin holder having multi-pins as described in US Patent No.4176901. However, these ceramic type of feedthroughs suffer from the disadvantages.
Primary disadvantage of these feedthroughs is that these are fairly big in size and as these feedthroughs can not be utilised in an IR detector dewar which are essentially miniature type.
Another disadvantage of these feedthroughs, known in the art, is that these feedthroughs can cause tremendous additional heat load to the dewar which could be prohibitive in case of miniature tactical dewars .
Another type of feedthroughs, known in the art, are shield type coaxial vacuum feedthroughs which are essentially used for connecting an external wire to an electronic equipment inside a vacuum vessel. These feedthroughs, as described US Patent No 4231003, are also ceramic to metal sealed feedthroughs comprising of a metal pin in the shape of a metal round bar, a ceramic cylinder enclosing the metal pin and a metal cylinder enclosing the ceramic cylinder. This feedthroughs are more suited for high voltage / high frequency operations and are meant for delivering high frequency signals, such as microwaves to an accelerator.
However, these feedthroughs are also suffer from the disadvantage that these are bulky and are not suitable for any miniature tactical IR detector dewars.

Yet another type of feedthroughs, known in the art, are lead-frame type of feedthroughs, which are made with the help of a metallic lead frame which is glass to metal sealed to a metal casing. The metallic lead frame, made of Kovar, is formed either by fine machining or chemical etching operation, performed on a very thin metallic sheet of about 4 to 5 mils. This lead frame with parallel leads, which are initially connected at the ends, pass through the open ends of a Kovar casing and the in-between space is filled by a suitable sealing glass. This glass to metal sealing results in the final feedthrough, with leads projecting through glass at the open ends of the metal casing. These types of feedthroughs are described in US Patent No 4874910. However, these feedthroughs also suffer from several disadvantages.
Primary disadvantage of these feedthroughs, known in the art, is that these feedthroughs, due to its thin leads and very thin sheet, suffer from poor rigidity.
Another disadvantage of these feedthroughs, known in the art, is that the geometry of such feedthroughs is not very suitable from the view point of integration with an IR detector dewar.
Yet another disadvantage of these feedthroughs, known in the art, is that the thick glass layers of these feedthroughs develop micro-cracks while welding them to the main dewar by micro-TIG or laser welding.
As described in US Patent No. 4565925, embedded wires are also used as a feedthrough for taking out electrical connections from an IR detector dewar through wires, embedded in the glass tube of the inner dewar and running parallel to the tube axis. On the closed end of the tube, where the IR detector sits, the device connections are made by ultrasonic wire bonding between the device pads and the wire ends, whereas on the other side, the wires come out of the vacuum encapsulation along with the glass tube. The extending wires coming out of glass thickness can be terminated on a small PCB. However, these feedthroughs, known in the prior art, also suffer from several disadvantages.
Primary disadvantage of these feedthroughs, known in the art, is that these feedthroughs involve taking out electrical connections by embedded wires through the inner dewar glass tube which make these feedthroughs fairly cumbersome.
Another disadvantage of these feedthroughs, known in the prior art, is that these feedthroughs render the dewar tube more intricate and vulnerable to leaks.
Yet another disadvantage of these feedthroughs, known in the prior art, is that numer of leads in these feedthroughs are .limited by the inner diameter of the dewar.

OBJECTS OF INVENTION:
Primary object of the invention is to provide a multi-pin vacuum feedthrough which can be used for the integration of a miniature tactical IR detector dewar.
Another object of the invention is to provide a multi-pin vacuum feedthrough which is made by glass to metal sealing of fine Kovar pins, using glass capillaries, to the main Kovar shell
Yet another object of the invention is to provide a multi-pin vacuum feedthrough which can easily take out all electrical connections from an IR detector, sitting inside the dewar, thereby adding minimum heat load through its leads.
Yet further object of the invention is to provide a multi-pin vacuum feedthrough of an excellent vacuum integrity having its theoretically Helium leak rate at about 4.11E-14 std.cc/s.
Still further object of the invention is to provide a multi-pin vacuum feedthrough having a substantial shelf-life.
Yet further object of the invention is to provide a multi-pin vacuum feedthrough with "sealing material such as Kovar alloy and Kovar matching glass thereby enhancing its vacuum integrity.
Still further object of the invention is to provide a multi-pin vacuum feedthrough, which is strong and rugged and which can be used under rough environmental conditions as normally encountered in warfare situations.
Yet further object of the invention is to provide a multi-pin feedthrough in which the basic shell of the feedthrough has been made by deep drawing method thereby increasing its strength by cold working of the Kovar material used.
Yet further object of the invention is to provide a multi-pin vacuum feedthrough, which is very versatile in which the number of pins can easily be added or reduced as per the specific requirement.
Still further object of the invention is to provide a multi-pin vacuum feedthrough which is" very compact thereby making it highly suitable for integration with miniature tactical dewar.
Yet further object of the invention is to provide a multi-pin vacuum feedthrough which has a simpler design with higher manufacturing repeatability.
Still further object of the invention is to provide a multi-pin vacuum feedthrough which is cheaper to manufacture SUMMERY OF INVENTION
According to this invention there is provided a multi-pin vacuum feedthrough for bringing out electrical connections from the inside of a vacuum encapsulation comprising a disk shaped shell having inner and outer circle with equally spaced plurality of holes provided therein, the said plurality of equally spaced multiple holes enclosing multiple pins of equal size for providing electrical compactions, characterized in that the said multiple pins glass to metal sealed inside the said plurality of holes of the said disk shaped shell using plurality of glass capillaries.
In accordance with the present invention, there is provided a multi-pin vacuum feedthrough for bringing out electrical connections from the inside of a vacuum encapsulation to the outside which is made by glass to metal sealing of fine Kovar pins, using glass capillaries, to the main Kovar shell. The feedthrough of the present invention comprises a deep drawn Kovar Shell with plurality of holes provided in two circles. The Kovar shell is glass to metal sealed with plurality of Kovar pins using plurality of glass capillaries. The glass capillary is drawn by a hot extrusion process from a bigger size tube of Kovar matching hard borosilicate glass. The whole feedthrough is integrated with the dewar with the help of welding lips, provided in the body of the Kovar shell, either by micro-TIG welding or by laser welding due to their localized heating effect. The feedthrough has been designed in such a way that the welding process induces minimum thermal stresses in the glass to metal sealings.
The design of the feedthrough is simpler, easier and it is cheaper to manufacture. Further, the feedthrough is strong, rugged with a high vacuum integrity and higher shelf life of about 10 years the design of the feedthrough is highly versatile and the number of connecting pins can be increased suiting the specific requirement.
DESCRIPTION OF THE DRAWINGS:
Any further characteristics, advantages and applications of the invention will become evident from the detailed description of the preferred embodiment which has been described and illustrated with the help of the accompanying wherein.
Figure-1: shows an isometric view of a multi-pin Feedthrough
Figure-2: shows top view of the multi-pin feedthrough
Figure-3: shows sectional front view of the multi-pin feedthrough
Figure-4: shows a two-piece graphite jig used for assembling the multi-pin feedthrough
DESCRIPTION OF THE INVENTION WITH RESPECT TO DRAWINGS
The multi-pin vacuum feedthrough of the present embodiment is made by glass to metal
sealing of fine Kovar pins, using glass capillaries, to the main Kovar shell. The
feedthrough shell is deep drawn in a single piece from a Kovar sheet. The glass capillary
is drawn by a hot extrusion process from a bigger size tube of Kovar matching, hard
borosilicate glass. The feedthrough shell, the multiple Kovar pins and the glass
capillaries, are assembled in a graphite jig and heated in a furnace to get the desired glass
to metal sealing. Initially, the Kovar pins of the feedthrough are kept straight during
sealing but later on, the alternate

pins are bent at right angles at different pitch circle diameters, so that they can be terminated on a specially designed PCB for further connections. The connections from the IR detector are made on the top of the feedthrough pins, either by soldering or ultra-sonic bonding. The whole feedthrough is integrated with the dewar with the help of welding lips, provided in the body of the Kovar shell, either by micro-TIG welding or by laser welding due to their localized heating effect.
Referring to Fig (1) and Fig (2), the feedthrough comprises a deep drawn disk shaped shell (1) preferably made from Kovar with multiple holes (76 holes in the present embodiment) provided in two circles. The shell has multiple pins (76 pins in this embodiment) preferably made from Kovar which are is glass to metal sealed using multiple glass capillaries (3) ( 76 glass capillaries in this embodiment). The disk shaped shell (1) is made by deep-drawing process out of a Kovar sheet of 1.3mm thickness, by using various combinations of dies and punches in about 5 to 6 steps. The plurality of holes are then drilled in the shell, of the size corresponding to the outer diameter of glass capillary to be used. These plurality of holes are drilled in two circular rows with half of these holes provided in each of these circles. The Kovar pins (2) of about 0.45mm diameter are cut to size and then both the ends are lapped to make them flat. The straightness of the pins is also checked so that they can be assembled easily in the graphite jig. The precision bore glass capillaries (3) of about 0.5mm bore, are drawn by a controlled hot extrusion process from a bigger size tube of Kovar matching, hard borosilicate glass. Initially they are drawn in about 300 mm lengths, and then cut to an optimum length by a precision glass slicing machines. The size of the capillary is determined as per the quantity of glass required for the sealing work, in such a way that no surplus glass overflows on the metallic shell surface. A graphite jig is made for assembling the feedthrough components together and to maintain them in the same position even at an elevated temperature, when the glass becomes molten, during the fusing operation of the feedthrough.
Referring to Fig (3), welding lips (4) & (5) are provided in the body of the Kovar shell (1). These welding lips are provided for integration of feedthrough with any vacuum encapsulation or devar..
Referring to Fig (4), the graphite jig comprises of two parts. The first part consists of a central pillar (6) ending in a circular plate, whereas the second part (7) acts as a base plate for the first part. At the circular plate of the first part, multiple through holes (76 in this embodiment) are drilled of the Kovar pin size, matching in pattern with the multiple holes in the Kovar shell, so that the pins erected in this graphite plate, can be accurately aligned with the Kovar shell holes. The drilled plate is kept centrally over the base plate, the main purpose of which is to prevent the pins from falling down. The feedthrough shell is assembled upside down on the graphite jig. It is inserted through the central pillar and then its holes are matched with that of the graphite plate. The Kovar pins are inserted in the graphite holes through the shell holes. The glass capillary tubes are placed between the pin and the shell hole. The accurate matching of the graphite jig holes with that of the feedthrough shell holes is very important for easy insertion of the fine glass capillaries , without applying undue pressure on

them. The feedthrough assembly is then placed in a muffle furnace and heated to a higher temperature during which the glass melts and dissolves in the metallic surface yielding a strong glass to metal sealing point.
The present embodiment of the invention, which has been set forth above, was for the purpose of illustration and is not intended to limit the scope of the invention. It is to be understood that various changes, adaptations and modifications can be made in the invention described above by those skilled in the art without departing from the scope of the invention, which has been defined by following claims.









WE CLAIM;
1. A multi-pin vacuum feedthrough for bringing out electrical
connections from the inside of a vacuum encapsulation
comprising a disk shaped shell (1) having inner and outer circle
with equally spaced plurality of holes provided therein, the said
plurality of equally spaced multiple holes enclosing multiple pins
(2) of equal size for providing electrical compactions, characterized
in that the said multiple pins (2) glass to metal sealed inside the
said plurality of holes of the said disk shaped shell (1) using
plurality of glass capillaries (3).
2. A multi-pin vacuum feedthrough as claimed in claim 1 wherein
said disk shaped shell (1) comprises welding lips (4) & (5) for
integration of the said multi-pin vacuum feedthrough with any
vacuum encapsulation or dewar.
3. A multi-pin vacuum feedthrough as claimed in claim 1, wherein said disk shaped shell (1) and said multiple pins (2) for providing electrical connection are made for Kovar.
4. A multi-pin vacuum feedthrough as claimed in claim 1, wherein said multiple pins (2) for providing electrical connections are glass to metal sealed with said disk shaped shell (1).
5. A multi-pin vacuum feedthrough as claimed in claim 1, wherein said disk shaped shell (1) is a deep drawn Kovar shell.
6. A multi-pin vacuum feedthrough as claimed in claim 1, wherein said multiple pins (2) providing electrical connections in the said disk shaped shell (1) can be more than 76 in numbers.
7. A multi-pin vacuum feedthrough substantially described and claimed herein.


Documents:

1138-DEL-2003-Abstract-(15-12-2009).pdf

1138-del-2003-abstract.pdf

1138-DEL-2003-Claims-(15-12-2009).pdf

1138-del-2003-claims.pdf

1138-DEL-2003-Correspondence-Others-(15-12-2009).pdf

1138-del-2003-correspondence-others.pdf

1138-del-2003-correspondence-po.pdf

1138-DEL-2003-Description (Complete)-(15-12-2009).pdf

1138-del-2003-description (complete).pdf

1138-del-2003-drawings.pdf

1138-del-2003-form-1.pdf

1138-del-2003-form-18.pdf

1138-del-2003-form-2.pdf

1138-DEL-2003-Form-3-(15-12-2009).pdf

1138-DEL-2003-GPA-(15-12-2009).pdf

1138-del-2003-gpa.pdf


Patent Number 240634
Indian Patent Application Number 1138/DEL/2003
PG Journal Number 22/2010
Publication Date 28-May-2010
Grant Date 20-May-2010
Date of Filing 11-Sep-2003
Name of Patentee DIRECTOR GENERAL, Defence Research and Development Organisation, Ministry of Defence, Govt. of India, B-341, Sena Bhawan, DHQ P.O., New Delhi- 110011.
Applicant Address DEFENCE RESEARCH AND DEVELOPMENT ORGANISATION MINISTRY OF DEFENCE, GOVT. OF INDIA, B-341, SENA BHAWAN, DHQ P.O. NEW DELHI-110011.
Inventors:
# Inventor's Name Inventor's Address
1 SUSHIL KUMAR, an Indian national of Solid State Physics Laboratory, Timarpur, Delhi-54. SOLID STATE PHYSICS LABORATORY, TIMARPUR, DELHI-54.
2 RAJENDRA KUMAR MADARIA, an Indian national of Solid State Physics Labratory, Timarpur, Delhi-54. SOLID STATE PHYSICS LABORATORY, TIMARPUR, DELHI-54.
3 GOVIND PRASAD KOTHIYAL, an Indian national of TP & PED, Bhabha Atomic Research Centre, Trombay, Mumbai-400 085. TP&PED, BHABHA ATOMIC RESEARCH CENTRE,TROMBAY, MUMBAI-400 085.
4 PRADI ANANDRAO WAGH, an Indian national of TP & PED, Bhabha Atomic Research Centre, Trombay, Mumbai-400 085. TP&PED, BHABHA ATOMIC RESEARCH CENTRE,TROMBAY, MUMBAI-400 085.
PCT International Classification Number H01B 3/08
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA