Title of Invention

AN ARRANGEMENT,IN PARTICULAR, FOR AN ELECTRONIC CONTROL UNIT AND A METHOD THEREOF.

Abstract In order, in the case of an arrangement comprising a carrier substrate and a heat sink, the carrier substrate being provided with at least one power component, which is arranged on a first large-area conductor track, on a first side and with a second large-area conductor track on a second side opposite to the power component, which second large-area conductor track is thermally conductively connected to the first conductor track via plated-through holes, the carrier substrate being applied by the second side to the heat sink in a thermally conductive manner, to realize good thermal coupling of the carrier substrate to the heat sink and, at the same time, to avoid undesirable electrical contact between potential-carrying conductor tracks and the heat sink, it is proposed to place the carrier substrate with spacer elements, which are arranged on the second side, onto the heat sink and keep it at a defined spacing from the heat sink, the gap, formed by the spacing, between the carrier substrate and the heat sink being filled with a thermally conductive filler.
Full Text

Arrangement comprising a carrier substrate for power components and a heat sink, and method for the production of the same
Prior Art
The invention relates to an arrangement having a carrier substrate for power components and a heat sink with the features specified in the preamble of Claim 1, and also to a method for the production thereof.
An arrangement of this type is already disclosed in the document DE 195 28 632 Al. The carrier substrate shown in this document is a printed circuit board which is provided on its top side with an electronic circuit comprising at least one power component which generates a heat loss. Underneath the power component, the printed circuit board is provided with plated-through holes which dissipate the heat generated by the power component to the underside of the printed circuit board. A thermally conductive filler is arranged between the underside of the printed circuit board and a control unit housing serving as heat sink. During operation, the heat generated by the power component is conducted via the plated-through holes to the underside of the printed circuit board, from where it is dissipated via the thermally conductive filler to the housing serving as heat sink. A disadvantage here is that potential-carrying conductor tracks on the underside of the printed circuit board can come into contact with the heat sink when the printed circuit board is mounted in the control unit. A short circuit caused as a result of this can damage or destroy the sensitive electronic components on the printed circuit board.

Furthermore, an arrangement having a carrier substrate and a heat sink is shown in German Patent Application DE 1 97 23 409. On the top side of the printed circuit board, a power component is applied to a large-area conductor track which is connected via piated-through holes to a large-area conductor track on the underside of the printed circuit board. On the underside of the printed circuit board, a metal layer is applied underneath the large-area conductor track arranged there, via an insulation layer, which metal layer is in turn placed via a soldering resist mask onto a housing part of a control unit, which housing part is provided as heat sink. In the case of such an arrangement, although electrical contact between the conductor tracks and the heat sink is prevented by the insulation layer, it must be regarded as disadvantageous that the insulation layer and the further metal layer make it more difficult for heat to be transferred directly to the heat sink, increase the space requirement of the arrangement and, in addition, raise production costs,
Advantages of the invention
The arrangement according to the invention, having the characterizing features of Claim 1, avoids the disadvantages which occur in the prior art. Spacer elements applied to that side of the carrier substrate which is opposite the power components, and a thermally conductive filler introduced between the carrier substrate and the heat sink, afford the advantages that, on the one hand, good thermal coupling of the carrier substrate to the heat sink is achieved and, on the other hand, undesirable electrical contact between the heat sink and the potential-carrying conductor tracks located on this side of the carrier substrate is reliably avoided. Moreover, a particularly space-saving arrangement can be realized with the solution proposed. Additional layers which make production more expensive, such as e.g. an additional insulation layer or a

further metal layer applied to the insulation layer, are unnecessary, so that the costs for them can be saved.
It is particularly advantageous, moreover, if the spacer elements comprise conductor area portions on the underside of the carrier substrate which are coated with a defined amount of solder, since this does not require an additional production step, particularly in the case of carrier substrates which are populated on both sides. The conductor area portions can be produced together with the terminal pads of electronic components provided on the underside and be coated with solder.
A soldering resist which is applied to that side of the carrier substrate which is opposite to the power components prevents solder from inadvertently reaching points which are not intended for it in the course of solder application.
If the power component and the heat sink are at the same electrical potential, it is advantageous to produce the conductor area portions such that they are integrated directly in the second large-area conductor track, since this improves the heat transfer.
It is advantageous, moreover, if the thermally conductive filler provided between the carrier substrate and the heat sink is a thermally conductive adhesive or a thermally conductive adhesive film, by means of which the carrier substrate can also be fastened mechanically on the heat sink.
The spacer elements resting on the heat sink can also be used, advantageously, as an earth connection of the carrier substrate to the heat sink and to improve the EMC behaviour (electromagnetic compatibility).
Furthermore, the invention relates to a method for the production of an arrangement comprising a carrier substrate and a heat sink. No additional production steps are required to carry out the method, particularly in the case of carrier substrates which

are populated on both sides. The conductor area portions can be produced together with conductor tracks provided on the second side. The deposition of solder necessary for producing the spacer elements can be carried out on the conductor area portions together with the application of solder to terminal pads for components, as a result of which the method becomes particularly economical since the production of the spacer elements gives rise to virtually no additional costs.
It is advantageous to print the solder onto the conductor area portions in a soldering paste printing station, since this technique is particularly well suited to the deposition of a defined amount of solder and can be well controlled. The solder is melted in a subsequent reflow soldering step, spacer elements having a height defined by the applied amount of solder being formed in the process. In an advantageous manner, the reflow soldering step can be performed together with the reflow soldering of SMD components provided on the carrier substrate.
It is particularly easy initially to apply a thermally conductive adhesive or a thermally conductive adhesive film to the heat sink and then to place the carrier substrate onto the heat sink coated with the adhesive or the adhesive film, in such a way that the spacer elements are pressed into the adhesive, in which case they can make contact with the heat sink by means of the layer of solder.
Drawing
An exemplary embodiment of the invention is illustrated in the drawing and is explained in more detail in the description below. In the figures
Figure 1 shows a simplified cross-section through an arrangement disclosed in the prior art, having an insulation layer and an additional copper plate,

■ Figure 2 shows a simplified cross-section through an arrangement according to the invention and
Figure 3 shows a simplified cross-section through the arrangement according to the invention, for a second exemplary embodiment.
Description of the exemplary embodiments
Figure 1 shows an arrangement, disclosed in the prior art, for dissipating the heat loss generated by a power component in a control unit. A printed circuit board 2 is provided with a first large-area " conductor-track 10 on the first side 8, facing upwards, and with a second large-area conductor track 11 on the second side 11, facing downwards. The first large-area conductor track 10 and the second large-area conductor track 11 are connected to one another in a readily thermally conductive manner via numerous piated-through holes 4, which extend through the printed circuit board. A power component 3, for example an SMD component, is applied to the first large-area conductor track 10 and is conductively connected via terminals 14 to further conductor tracks 12, which are insulated from the large-area conductor track 10, on the top side 8 of the printed circuit board 2. For the sake of simplicity, only one conductor track 12 is illustrated. Still further potential-carrying conductor tracks 13, which are arranged such that they are insulated from the second large-area conductor track 11, are situated on the underside 9. In addition, still further SMD components (not illustrated) are provided on the underside 9, these components being soldered to terminal pads (not shown) on the underside. Furthermore, a copper plate 6, serving as heat sink, is applied via an electrically insulating, thermally conductive insulation layer 5 to the second large-area conductor track 11 and the conductor tracks 13, A soldering resist 15 is in turn applied to the copper plate 6 and prevents the deposition of solder on the copper when solder is applied to the terminal pads for

the SMD components. Provided underneath the soldering resist 15 is a thermally conductive adhesive 7, which is applied to a bottom part 1 of a control unit housing, which bottom part is provided as heat sink. It is also known to press the copper plate directly onto the heat sink by means of screwable fastening means. The heat generated by the power component 3 is always dissipated via the plated-through holes to the large-area conductor track 11 and via the insulation layer 5 to the copper plate 6. From there, the heat is dissipated through the soldering resist 15 either directly or via the thermally conductive adhesive 7 to the heat sink 1. If the printed circuit board 2 were applied to the heat sink without the insulation layer 5 and the copper sink 6, then a short circuit between the potential-carrying conductor tracks 13 might lead to damage to the components. What is disadvantageous about the arrangement shown in Figure 1, however, is the fact that two further, separate production steps are necessary to apply the insulation layer 5 and the additional copper plate 6.
Figure 2 shows an arrangement according to the invention for dissipating the heat loss of a power component, which is preferably inserted into an electronic control unit of a motor vehicle. At least one power component, for example a power semiconductor, is applied to a large-area conductor track 10 on the top side 8 of a carrier substrate 2, which may be a printed circuit board, a hybrid or another substrate provided with an electronic circuit. In the exemplary embodiment shown here, the substrate 2 is a printed circuit board populated on both sides. As may further be discerned in Figure 2, a terminal 14 of the power component 3 is electrically connected to a terminal conductor track 12, which is insulated from the conductor track 10, on the top side 8 of the printed circuit board 2. A second large-area conductor track 11 is applied on the underside 9 of the printed circuit board 2 and is thermally conductively connected to the

first conductor track 10 on the top side 8 via plated-through holes 4 . In addition, even further conductor tracks (not illustrated) belonging to the circuit and also a number of terminal pads for SMD components are provided on the underside 9. As is illustrated in Figure 2, moreover, conductor area portions 17 are provided on the underside 9 of the printed circuit board 2, which conductor area portions may be produced together with the remaining conductor tracks and terminal pads and from the same material on the underside of the printed circuit board. This can be done by the customary, known techniques. In the exemplary embodiment shown in Figure 2, a voltage is transferred from the power component 3 via the piated-through holes 4 to the second large-area conductor track 11. The conductor area portions 17 are therefore arranged on the carrier substrate such that they are insulated from the conductor track 11. Furthermore, a soldering resist 9 is applied to the underside 9 in a known manner, cutouts in the soldering resist being provided at the locations of the conductor area portions 17 and of the terminal pads (not illustrated) for SMD components. In the course of the production of the arrangement shown in Figure 2, soldering paste is printed onto the printed circuit board 2 with the underside 9 turned upwards, in a soldering paste printing station. In this case, solder is applied to the conductor area portions 17 and to the terminal pads for SMD components. The soldering resist 15 prevents solder from reaching other parts of the circuit, in the process. After the solder has been printed on, the printed circuit board 2 is fed to a component mounting machine which presses the SMD components into the solder paste applied to the terminal pads on the underside 9, turned upwards, of the printed circuit board. The printed circuit board then passes through a reflow soldering station in which the solder is melted. In this case, in an advantageous manner, the SMD components are soldered to the terminal

pads and the spacer elements 17, 18 are formed at the same time. The way in which this happens is that the solder 18 printed onto the conductor area portions 17 is liquefied in the reflow furnace and soldering bumps or soldering caps of defined size, whose shape depends only on the size of the conductor area portions 17 and the amount of solder printed on, form due to the surface tension of the solder on the area portions 17 . In particular, the method described enables all the spacer elements to be formed with a precisely defined, uniform height. It is particularly advantageous here that the solder paste printing step and the reflow soldering step have to be carried out in any case for printed circuit boards which are populated on two sides, with the result that there is no need for an additional manufacturing step in order to produce the spacer elements. Instead of the production method described above, it is also possible to wet the conductor area portions with liquefied solder in a wave soldering bath, for example. It is crucial that the spacer elements are produced with a defined height. After the production of the spacer elements 17, 18, a thermally conductive adhesive 7 is applied to a heat sink 1 by a dispensing apparatus. Another exemplary embodiment provides for the adhesive to be replaced by the use of a thermally conductive film which is adhesive on both sides. A housing part of the control unit, for example the bottom of the housing, serves as heat sink. The printed circuit board 2 is then placed onto the adhesive with the underside 9 facing the heat sink 1 and is pressed on in the direction of the heat sink in such a way that the spacer elements 17, 18 penetrate the adhesive 7. In doing so, they can touch the heat sink 1 and thus ensure a minimum separation. A depression (not illustrated in Figure 2) in the form of a well in the bottom of the housing of the control unit then accommodates the components arranged on the underside of the printed circuit board. The spacer elements 17, 18 form a defined gap between the

underside of the printed circuit board and the heat sink, which gap, as shown in Figure 2, is completely filled by the adhesive 7. Since the spacer elements can be produced with a defined, small height, the gap can be chosen to be very small without the heat sink touching the underside of the printed circuit board, thereby improving the heat dissipation to the heat sink.
In a different manner from that described here, the arrangement shown in Figure 2 can alternatively be produced in the following way: for example, the printed circuit board 2 is firstly placed with the spacer elements 17, 18 onto the heat sink and only then is a capillary-flowable adhesive introduced into the gap between the underside of the printed circuit board and the heat sink.
In an advantageous manner, the spacer elements 17, 18 can also serve for EMC protection (electromagnetic compatibility) of the arrangement. Since the spacer elements are composed of an electrically conductive material, they establish electrical contact with the heat sink, that is to say spacer elements and heat sink are at the same potential. If at least some of the conductor area portions 17 are connected to conductor tracks belonging to the circuit, a short and thus low-radiation earth connection can be realized via the spacer elements.
A further exemplary embodiment is shown in Figure 3. Identical numerals denote identical parts. The arrangement shown in Figure 3 differs from the arrangement shown in Figure 2 by the fact that the power component 3 and the heat sink are at the same potential. For this reason, in the example shown in Figure 3, the conductor area portions 17 can advantageously be integrated directly in the second large-area conductor track 11 of the carrier substrate 2. The soldering resist mask 15 applied on the second side 9 of the carrier substrate 2 has cutouts which define the conductor area portions 17. The soldering

caps 18 are formed on these conductor area portions in the manner described above. The carrier substrate is subsequently placed onto the heat sink 1 via the adhesive 7. Since the power component 3, the conductor track 11 and the heat sink 1 are at the same potential, no short circuit is produced by the spacer elements 18. The heat transfer by the arrangement of soldering caps 18 on the second large-area conductor track 11 can be improved in comparison with Figure 2.




Robert Bosch GmbH, 70442 Stuttgart
Claim
1 . Arrangement, in particular for use in an electronic control unit, comprising a carrier substrate (2) and a heat sink (1), the carrier substrate (2) being provided with at least one power component (3), which is arranged on a first large-area conductor track (10), on a first side (8) and with a second large-area conductor track (11) on a second side (9) opposite to the power component (3), the first large-area conductor track (10) and the second large-area conductor track (11) being connected to one another in a thermally conductive manner via at least one plated-through hole (4), and the carrier substrate (2) being applied by the second side (9) to the heat sink (1) in a thermally conductive manner, characterized in that the carrier substrate (2) is placed with spacer elements (17, 18) , which are arranged on the second side (9) of the carrier substrate (2), onto the heat sink (1) and is kept at a defined spacing from the heat sink (1), the gap, formed by the spacing, between carrier substrate (2) and heat sink (1) being filled with a thermally conductive filler (7).
2. Arrangement according to Claim 1, characterized
in that the spacer elements provided are conductor area
portions (17), which are arranged on the second side
(9) of the carrier substrate (2) and are coated with a defined amount of solder (18) .
3. Arrangement according to Claim 2, characterized in that the second side (9) of the carrier substrate (2) is coated with a soldering resist (15) having cutouts at least for the conductor area portions (17) .
4. Arrangement according to Claim 3, characterized in that the power component (3) and the heat sink (1) are at the same electrical potential, and in that the

conductor area portions (17) are integrated in the second large-area conductor track (11). (Fig. 3)
5. Arrangement according to Claim 1, characterized in that the thermally conductive filler (7) is a curable thermally conductive adhesive or a thermally conductive film which is adhesive on both sides.
6. Arrangement according to Claim 2, characterized in that the contact between the conductor area portions (17), which are coated with solder (18), and the heat sink (1) simultaneously serves as an earth connection of the carrier substrate (2) to the heat sink.
7. Method for the production of an arrangement comprising a carrier substrate (2) and a heat sink (1), the carrier substrate (2) being provided with at least one power component (3), which is arranged on a first large-area conductor track (10), on a first side (8) and with a second large-area conductor track (11) on a second side (9) opposite to the power component (3), and the first large-area conductor track and the second large-area conductor track being connected to one another in a thermally conductive manner via at least one plated-through hole (4), and the second side (9) of the carrier substrate (2) being thermally conductively connected to the heat sink (1)/ characterized by the following method steps:
- provision of conductor area portions (17) on
the second side (9) of the carrier substrate,
application of a soldering resist (15), having cutouts at least for the conductor area portions (17) , to the second side (9) of the carrier substrate (2),
- coating of the conductor area portions (17) with a defined amount of solder (18), and production of spacer elements (17, 18) having a height which is defined by the applied amount of solder,
- emplacement of the carrier substrate (2) with the spacer elements (17, 18) on the heat sink (1), a thermally conductive filler (7) being introduced

between the second side (9) of the carrier substrate (2) and the heat sink (1).
8. Method according to Claim 7, characterized in
that the solder (18) is printed onto the conductor area
portions (17) in a soldering paste printing station and
the spacer elements (17, 18) are produced by subsequent
reflow soldering of the carrier substrate (2) in a
reflow soldering station.
9. Method according to Claim 7, characterized in
that firstly a thermally conductive, curable adhesive
or a thermally conductive film which is adhesive on
both sides is applied, as thermally conductive filler
(7), to the heat sink (1) and then the carrier substrate (2) is placed onto the heat sink coated with the adhesive (7) in such a way that the spacer elements
(17, 18) are pressed into the adhesive (7) , in which case they can touch the heat sink (1) with the layer
(18) of solder.
10. Arrangement, in particular for use in an electronic control unit, substantially as herein described, with reference to the accompanying drawings.
11• Method for the product ion of an arrangement, substantially as herein described, with reference to the accompanying drawings.


Documents:

1568-mas-1998-abstract.pdf

1568-mas-1998-claims duplicate.pdf

1568-mas-1998-claims original.pdf

1568-mas-1998-correspondance others.pdf

1568-mas-1998-correspondance po.pdf

1568-mas-1998-description complete duplicate.pdf

1568-mas-1998-description complete original.pdf

1568-mas-1998-drawings.pdf

1568-mas-1998-form 1.pdf

1568-mas-1998-form 26.pdf

1568-mas-1998-form 3.pdf

1568-mas-1998-other documents.pdf


Patent Number 205219
Indian Patent Application Number 1568/MAS/1998
PG Journal Number 26/2007
Publication Date 29-Jun-2007
Grant Date 22-Mar-2007
Date of Filing 14-Jul-1998
Name of Patentee ROBERT BOSCH GMBH,
Applicant Address P.O.BOX 30 02 20,,70442, STUTTGART
Inventors:
# Inventor's Name Inventor's Address
1 BERND WEBER SCHOZACHSTRASSE,8/1,74232 ABSTATT
2 DIETMAR HOFSAESS SCHWENNINGER STRASSE,12,71522 BACKNANG
3 WERNER BURSCHKAU, WESTENDSTRASSE,35,74321 BIETIGHEIM-BISSINGEN
4 THOMAS DITTRICH, NEUHAUSENER STRASSE 7/2,75242 NEUHAUSEN
5 PETER SCHIEFER, EULENWEG 8,74199 UNTERGRUPPENBACH
PCT International Classification Number H05K7/20
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 197 36 962.6 1997-08-25 Germany