High density, heat-dissipating circuit assembly with accessible components

A circuit assembly includes a platen for pressing carrier plates, bearing heat-dissipating components, against a heat sink. Circuits on one carrier plate are electrically connected with circuits on the other carrier plate by corresponding contacts on each carrier plate which the platen presses into mutual contact as it presses the carrier plates against the heat sink. The surfaces to which the carrier plates are pressed is stepped, which serves to align the carrier plates with respect to each other. One or more substrates, bearing other circuit elements, are attached to the platen and electrically connected to circuits on the carrier plate by resilient contact elements attached to the platen. The resilient contact elements press against contact surfaces of the carrier plates and substrates to make connections. Recesses in the platen also facilitate alignment of the carrier plates and components thereon. The interconnection of components by the resilient contact elements, and the locating effect of recesses in the heat sink and platen makes it possible to assemble and disassemble the circuit assembly rapidly and conveniently.

BACKGROUND OF THE INVENTION 
This invention relates to high-density circuit assemblies that use heat 
sinks to facilitate component cooling and specifically to such circuit 
assemblies where component-bearing carrier plates are pressed against heat 
sinks by platens. 
A known assembly, from the present applicant's Offenlegungsschrift (German 
laid open application) DE-A 4 111 247, includes a circuit assembly 
incorporating a heat sink. A carrier plate has components to be cooled by 
heat transfer to the heat sink. The carrier plate is pressed against the 
heat sink by a platen. The platen has a resilient cushion element which 
faces, and is pressed against, the carrier plate to insure good thermal 
contact between the carrier plate and the heat sink. 
In the applicant's supplementary patent application P 41 22 428, another 
known circuit assembly includes a platen with a rigid mounting element and 
a rigid bridge element, with an resilient cushion element between them. 
In both, of the above-mentioned prior art assemblies (DE-A 4 111 247 and P 
41 22 428), and other circuit assemblies shown in Offenlegungsschrift DE-A 
35 09 456 and DE-A 35 21 572, the carrier plates and their components are 
virtually inaccessible. A first side of the carrier plate is adjacent to 
the heat sink. Because it is desirable to maintain good thermal contact 
between components on the carrier plate and heat sink, the heat sink must 
essentially cover a first side of the carrier plate and any heat 
dissipating components on that side. The carrier plate is pressed from the 
second side of the carrier plate to the heat sink to insure good thermal 
contact between tile carrier plate and the heat sink. The device used to 
press the carrier plate generally covers the second side. Thus, both sides 
of the portion of the carrier plate containing the power-dissipating 
components are essentially covered leaving the components thereon 
virtually inaccessible. Therefore, modification of the overall circuit 
assembly can be very difficult. The same problem exists with, for example, 
the circuit arrangement known from Offenlegungsschrift DE-A 35 09 456 or 
DE-A 35 21 572. 
Still another known circuit assembly from Patentschrift (German Patent) 
DE-C 36 28 556, includes at least one semiconductor wafer with 
semiconductor circuit elements on it. The semiconductor wafer rests on a 
base plate. Conductor elements around the periphery of the wafer are wired 
to the semiconductor circuit elements. The semiconductor circuit elements 
are fully encapsulated in insulation material, and the conductor elements, 
partly so. Contacts of time conductor elements protrude through the 
insulation material on a side facing away from the base plate. Surfaces of 
the protruding contacts lie in a single plane. The protruding contacts are 
thereby available to make electrical contact by pressing against a contact 
plate on another part such as a circuit board. Because the circuit 
elements are encapsulated in the insulation material, they are not 
susceptible to modification. Therefore, this semiconductor assembly 
permits no convenient modification of semiconductor components. 
A semiconductor assembly of hybrid structure is described in 
Offenlegungsschrift DE-A 3 643 288. This semiconductor component assembly 
permits a high degree of integration. The structure also permits 
electrical pretesting of all components prior to final assembly. 
Additionally, the structure permits the simple fastening of components to 
the carrier plate and electrically coupling the components to external 
circuits. 
OBJECTS AND SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a circuit assembly that 
permits a high degree of integration. 
It is another object of the present invention to provide a circuit assembly 
that allows components to be easily and quickly assembled. 
It is still another object of tile present invention to provide a circuit 
assembly that permits heat-dissipating components to be densely packaged. 
It is still another object of the present invention to provide a circuit 
assembly that permits at least some circuit components to be modified 
and/or tested after the circuit has been finally assembled without 
disassembling tile entire circuit assembly. 
It is still another object of the present invention to provide a circuit 
which allows all components to be pretested prior to final assembly. 
It is still another object of the present invention to provide a circuit 
assembly that permits convenient access to high heat-dissipating 
components by means of simple partial disassembly. 
It is still another object of the present invention to provide a circuit 
assembly which achieves a high degree of integration. 
Briefly stated, there is disclosed, a circuit assembly including a platen 
for pressing carrier plates bearing heat-dissipating components, against a 
heat sink. Circuits on one carrier plate are electrically connected with 
circuits on the other carrier plate by corresponding contacts on each 
carrier plate which the platen presses into mutual contact as it presses 
the carrier plates against the heat sink. The surfaces to which tile 
carrier plates are pressed is stepped, which serves to align the carrier 
plates with respect to each other. One or more substrates, bearing other 
circuit elements, are attached to the platen and electrically connected to 
circuits on the carrier plate by resilient contact elements attached to 
the platen. The resilient contact elements press against contact surfaces 
of the carrier plates and substrates to make connections. Recesses in tile 
platen also facilitate alignment of the carrier plates and components 
thereon. The interconnection of components by tile resilient contact 
elements, and tile locating effect of recesses in the heat sink and platen 
makes it possible to assemble and disassemble tile circuit assembly 
rapidly and conveniently. 
According to an embodiment of the present invention, there is disclosed, a 
high density circuit assembly, comprising: a heat sink, a carrier plate 
having at least one component to be cooled, a platen having a substrate 
attached thereto, means for pressing the carrier plate against the heat 
sink, whereby tile carrier plate and tile at least one are cooled, tile 
substrate being substantially electrically insulating, the substrate 
having a first circuit, tile substrate being substantially parallel to the 
carrier plate and the platen having means for electrically compacting tile 
first circuit to the second circuit. 
According to another embodiment of the present invention, there is 
disclosed, a high density circuit assembly, comprising: a heat sink, 
carrier plates, at least one of the carrier plates having at least one 
component to be cooled, each carrier plate having a circuit, two of the 
carrier plates being substantially parallel and lying in different planes, 
a platen for pressing the carrier plates against the heat sink, a 
substrate on the platen, the substrate being substantially electrically 
insulating, the substrate having a circuit, the substrate being 
substantially parallel to the carrier plates and the platen having means 
for electrically connecting at least one of the conductors to at least one 
of the carrier plates. 
According to still another embodiment of the present invention, there is 
disclosed, A high density circuit assembly, comprising: a heat sink, two 
carrier plates, a first of the two having a first circuit, a second of the 
two having a second circuit, at least one of the two having at least one 
component to be cooled, a platen for pressing the carrier plates against 
the heat sink, the platen having a rigid bridge element with a pressing 
surface for pressing against at least one of the two, the platen having a 
rigid mounting element, a resilient cushion element between the rigid 
mounting element and the rigid .bridge element, at least one substrate 
between at least one of tile resilient cushion element and the rigid 
bridge element and the resilient cushion element and the rigid mounting 
element, tile at least one substrate being substantially parallel to the 
carrier plates, the at least one substrate having a third circuit and the 
platen having means for electrically connecting the third circuit to at 
least one of tile first circuit and tile second circuit. 
According to still another embodiment of the present invention, there is 
disclosed, a high density circuit assembly, comprising: a heat sink, 
carrier plates, the heat sink having at least one recess for receiving at 
least one of the carrier plates, each carrier plate having a circuit, a 
platen for pressing the carrier plates, the at least one of the carrier 
plates being positioned in a plane different from at least another of the 
carrier plates, the position being such that a first portion of the at 
least one of the carrier plates overlaps a second portion of the at least 
another of tile carrier plates, first contacts on tile first portion, 
second contacts on the second portion, the first contacts being positioned 
to make electrical contact with the second contacts when the platen is 
pressed against the carrier plates. The above, and other objects, features 
and advantages of the present invention will become apparent from the 
following description read in conjunction with the accompanying drawings, 
in which like reference numerals designate the same elements.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1, a circuit assembly 10a, according to an embodiment of 
the present invention, is shown. Circuit assembly 10a includes a heat sink 
12 with a stepped receiving surface 14. Heat sink 12 also includes a 
receptacle 16 to accommodate a discrete component 18 connected to a 
carrier plate 22. Circuit assembly 10a may include many such elements as 
receptacle 16 and discrete component 18. Only one such pair is shown for 
clarity. Stepped receiving surface 14 receives carrier plate 22 and 
another carrier plate 20 will separate portions of stepped receiving 
surface 14. Carrier plate 22 includes conductive strips 24 and 26 to which 
component 18 is electrically connected. Stepped receiving surface 14 of 
heat sink 12 is shaped so that carrier plates 20 and 22, resting on 
respective steps of stepped receiving surface 14, are positioned in 
different parallel planes. The distance between the planes of the steps of 
stepped receiving surface 14 is such that contacts 30 on carrier plate 20 
can make pressure contact with contacts 28 on carrier plate 22 when a 
platen 38 presses carrier plates 20, 22 to heat sink 12. Carrier plates 20 
and 22 are staggered in a horizontal plane. Carrier plate 20 has 
conductive strips 32 on or near its surface. Carrier plate 20 also has 
contact surfaces 34 for connecting with similar surfaces on a substrate 
50. Carrier plate 20 also includes heat-dissipating components 36 to be 
cooled. Components 36 may be, for example, uncovered semiconductor circuit 
("chip") elements. 
Circuit assembly 10a includes platen 38 for pressing carrier plates 20, 22 
to heat sink 12 to facilitate heat transfer from carrier plates 20, 22 to 
heat sink 12. Platen 38 also aligns carrier plates 20 and 22 with respect 
to each other and with respect to heat sink 12. Another simultaneous 
function of platen 38 is to make connections between carrier plate 20 and 
substrate 50 through resilient contact elements 58 as described below. 
Still another function of platen 38 is to effect contact between 
respective contacts 28 and 30. 
Platen 38 includes a rigid mounting element 40 and a rigid bridge element 
42. Sandwiched between rigid mounting element 40 and a rigid bridge 
element 42 is a resilient cushion element 44. Rigid mounting element 40 
and rigid bridge element 42 are made of suitable rigid materials, 
preferably non-conductive, such as plastic. Resilient cushion element 44 
is made of a suitable resilient material, such as rubber. Platen 38 is 
fastened to heat sink 12 by suitable fastening means and its position 
precisely adjusted so that the pressure applied to carrier plates 20, 22 
is optimal. The fastening means could a be a set of longitudinal 
connectors (not shown), such as bolts with nuts. Only center lines 46, 
which would correspond to such connectors, are shown. 
Rigid bridge element 42 is designed with a stepped pressing base surface 
48. When a stepped pressing base surface 48 is pressed against carrier 
plates 20, 22, it fixes positions of carrier plates 20, 22 in relation to 
each other, heat sink 12 and platen 38. Stepped pressing base surface 48 
may have recesses to accommodate components 36. In addition, such recesses 
can serve to align components 36. Another use of the alignment capability 
of stepped pressing base surface 48 would be to align and press components 
36 against component contacts (not shown) on carrier plates 20 and/or 22, 
thereby connecting the to circuits on carrier plates 20 and/or 22. 
Platen 38 includes electrically insulating substrate 50, which is held at a 
specified distance front platen 38 by spacer elements 52. Components 56 
are interconnected by a circuit network 54 on substrate 50. In circuit 
assembly 10a, substrate 50 is attached to a side of platen 38 that faces 
away from heat sink 12. Thus, substrate 50 is accessible for testing and 
replacement of components 56. Circuit network 54 on substrate 50 is 
electrically connected with associated contact surfaces 34 on carrier 
plates 20, 22 by resilient contact elements 58. 
Resilient contact elements 58 are flexible to permit the position of platen 
38, and connected substrate 50, to be adjusted. In addition, the 
flexibility of resilient contact elements 58 causes ends of resilient 
contact elements 58 to be forcibly pressed against contact surfaces 34 to 
insure positive electrical contact. Resilient contact elements 58 may be 
pins with elastic loops, angled pins, pins with a threaded section, or any 
other suitable device. Resilient contact elements 58 extend through 
passages in platen 38 which are located to position resilient contact 
elements 58 precisely. Resilient contact elements 58 may also be embedded 
in platen 38 or any of its components: rigid bridge element 42, resilient 
cushion element 44 and rigid mounting element 40. Ends of resilient 
contact elements 58 may electrically connect with corresponding contact 
surfaces 34 by being brought into pressure contact after assembly and 
adjustment of platen 38, substrate 50 and carrier plate 20, 22. 
Referring to FIG. 2, a sectional view of a circuit assembly 10b, according 
to another embodiment of the present invention, is shown. Circuit assembly 
10b differs frown circuit assembly 10a of FIG. 1 in that there are two 
substrates, a first substrate 50a and a second substrate 50b, instead of 
one. In addition, locations of substrates 50a and 50b are different in 
relation to rigid bridge element 42 and rigid mounting element 40. First 
substrate 50a is sandwiched between rigid mounting element 40 and 
resilient cushion clement 44. Second substrate 50b is sandwiched between 
resilient cushion element 44 and rigid bridge element 42. As in circuit 
assembly 10a, resilient contact elements 58 electrically connect 
substrates 50 with carrier plates 20, 22. Additional resilient contact 
elements 58 electrically connect the first substrate 50 with the second 
substrate 50. 
In circuit assembly 10b, rigid bridge element 42 is attached to a side of 
substrate 50b that faces heat sink 12. Rigid bridge element 42 of circuit 
assembly 10b has stepped pressing base surface 48 on the side facing heat 
sink 12. Rigid bridge element 42 of circuit assembly 10b also has a 
stepped pressing base surface 60 on the side facing away from heat sink 
12. Recesses in stepped pressing base surfaces 48 and 60 accomodate 
components 36 and 56 respectively. 
Referring to FIG. 3, a circuit assembly identical to the embodiment of FIG. 
1, except for the inclusion of contact surfaces 85, is shown. Contact 
surfaces 85 are electrically connected components 56 and/or circuit 
network 54 on substrate 50. Contact surfaces 85 are electrically connected 
to resilient contact elements 58 when resilient contact elements 58 are 
pressed against contact surfaces 85. Thus, when platen 38 is assembled to 
carrier plates 20, 22, the connections between substrate 50 and resilient 
contact elements 58 and those between resilient contact elements 58 and 
carrier plates 20, 22 may be effected simultaneously. 
Details of structure in FIGS. 2 and 3 that arc similar to those of FIG. 1 
are given the same reference numbers as in FIG. 1, and are not described 
again. 
In FIG. 1, no interconnections are shown between components 56 or circuit 
network 54 on opposite sides of substrate 50. However, note that it is 
possible for components 56 and/or circuit network 54 to be connected by 
conductors (not shown) passing through substrate 50 or around substrate 
50. The same is true with respect to components 56 and circuit networks 54 
on substrates 50a and 50b of FIG. 2. 
The objects of the present invention are achieved by a circuit assembly 
that includes at least one electrically insulating substrate 50, 50a 
and/or 50b attached to a platen 38 and located a distance from carrier 
plates 20, 22 which contain high heat-dissipating components 36. At least 
one of substrates 50, 50a and 50b is positioned parallel to carrier plates 
20, 22, permitting electrical connection between the substrate and carrier 
plate 20, 22 to be conveniently achieved by means of resilient contact 
elements 58 in platen 38. Platen 38 is thus used for pressing carrier 
plates 20, 22 to heat sink 12 to facilitate cooling and also for effecting 
electrical contact between circuits on one or both of carrier plates 20, 
22 and substrate 50, 50a, and/or 50b by means of resilient contact 
elements 58. The pressing of platen 38 effects electrical contact between 
carrier plate 20 and carrier plate 22 through contacts 28 on carrier 
plates 20 and 22. In addition, the pressing of platen 38 fixes positions 
of carrier plates 20, 22 with respect to each other and with respect to 
heat sink 12. 
At least one electrically insulating substrate 50, 50a and/or 50b is 
mounted in a plane that differs from that of at least one of carrier 
plates 20, 22. Resilient contact elements 58 provide a means for 
connecting circuit network 54 and components 56 to components 36 on 
carrier plate 20. Resilient contact elements 58 are precisely and 
accurately positioned by platen 38. Thus, platen 38 serves not only press 
each carrier plates 20, 22 against heat sink 12 to facilitate heat 
removal, but also to position resilient contact elements 58, thereby 
establishing desired connections between substrates 50, 50a and/or 50b and 
carrier plates 20, 22. The assembly of carrier plates 20, 22, platen 38 
and respective substrates 50, 50a and/or 50b also establishes and fixes 
the mutual physical positions of these elements relative to each other for 
packaging purposes. 
The accuracy of the positioning of resilient contact elements 58 may be 
sufficient to permit chips on any of substrates 50, 50a and/or 50b to be 
connected directly by means of resilient contact elements 58. A chip may 
be connected to circuit assembly 10a or 10b by pressing resilient contact 
elements 58 in platen 38 directly to contact points on the chip itself. A 
circuit assembly designed in that way has the advantage of permitting a 
high degree of integration. In addition, because of the accessibility of 
components 56 and circuit network 54 on substrates 50, 50a and/or 50b, and 
carrier plates 20, 22, electrical pretesting of all components is possible 
prior to the final assembly of circuit assembly 10a, 10b. 
Note, also, that multiple fastening of components 36 in relation to each 
other is possible with the present invention. That is, platen 38 with 
integral recesses in stepped pressing base surface 48 serves to position 
components precisely. In addition, with such fastening, simple, reliable 
and mechanically accurate contacting of the appropriate components with 
each other or with associated circuit structures is also feasible. 
Moreover, the occasional need to disassemble and replace defective 
components with unused new components is facilitated because circuit 
assemblies 10a and 10b may be taken apart and reassembled without 
destroying any circuit elements. 
Circuit assembly 10b has at least one substrate 50b located between 
electrically insulating rigid bridge clement 42 and electrically 
insulating resilient cushion element 44 of platen 38. The appropriate 
positioning of resilient contact elements 58 between substrate 50b and 
carrier plate 20 is accomplished in this case by rigid bridge element 42. 
Resilient contact elements 58 in rigid bridge element 42 are located to 
make appropriate connections between substrate 50b and carrier plate 20. 
Additionally, with this configuration, at least one substrate 50b is thus 
positioned, by rigid bridge element 42 and resilient cushion element 44, 
to fit exactly. 
Another possibility is to locate substrate 50a between electrically 
insulating resilient cushion element 44 and electrically insulating rigid 
mounting element 40 of platen 38. Resilient contact elements 58 are 
positioned, by electrically insulating rigid bridge element 42 and 
resilient cushion element 44, to fit exactly and to make contact between 
carrier plate 20 and substrate 50a. Resilient contact elements 58 are 
positioned, by electrically insulating resilient cushion element 44, to 
fit exactly to make contacts between substrate 50a and substrate 50b when 
second substrate 50b is also present, as in circuit assembly 10b. 
Circuit components 56 and portions of circuit network 54 within platen 38 
may be inaccessible in, for example, circuit assembly 10b, because 
portions of substrates 50a and/or 50b may be sandwiched within platen 38. 
However, it is problem can be avoided, where necessary, by locating 
components 56, for which accessibility is desired, on portions of 
substrate 50a or 50b that are outside of platen 38. In other words, 
components 56, for which accessibility is desired, can be located on 
portions of substrates 50a and/or 50b that are not sandwiched between one 
of rigid bridge element 42, resilient cushion element 44 and rigid 
mounting 40 and another of rigid bridge element 42, resilient cushion 
element 44 and rigid mounting 40. Another way to avoid making components 
inaccessible is to mount substrate 50a or 50b on a side of rigid bridge 
element 42 facing away from heat sink 12 so that its entire surface is 
accessible. 
In circuit assembly 10a it is advantageous for substrate 50 to be removed 
frown rigid mounting element 40 by spacer elements 52. Spacer elements 52 
can be separate elements or integral with rigid mounting element 40. 
In circuit assemblies 10a and lob, it is advantageous to stagger carrier 
plates 20 and 22 if more than one is used. Staggering facilitates pressing 
electrical contacts 28 when carrier plates 20, 22 are pressed to heat sink 
12. Stepped receiving surface 14 of heat sink 12 serves to position 
carrier plates 20, 22 with respect to each other to insure proper 
alignment of contacts 28. Circuit assemblies 10a and 10b are simply 
designed and can be easily and rapidly assembled because of the automatic 
locating function of stepped receiving surface 14 of heat sink 12. This 
ease of assembly also facilitates repair. 
In circuit assemblies 10a and 10b, it is also advantageous for heat sink 12 
to have a receptacle 16 for each discrete component 18 on carrier plate 
22. Discrete component 18 could be a power capacitor, electrical reel or 
current sensor. Receptacle 16 and heat sink 12 advantageously promotes 
dissipation of heat from discrete component 18. The promotion of heat 
dissipation permits compact configurations which may increase circuit 
speeds by reducing circuit paths. Compactness may also be desirable as an 
end in itself. An example of a type of circuit that takes advantage of the 
characteristics of the present invention is rectifier circuit assembly. 
Power components of the rectifier circuit assembly would be located on 
carrier plates 20, 22. One or more substrates 50, 50a and/or 50b would 
have the non-power components of the circuit. In this configuration, the 
non-power components remain accessible for modification and testing. 
Note that the above advantages apply to circuits employing multiple 
discrete components, of which discrete component 18 shown in FIGS. 1 and 3 
is merely representative. Many such discrete components could be mounted 
on the same carrier plate 20 and/or 22. 
Having described preferred embodiments of the invention with reference to 
the accompanying drawings, it is to be understood that the invention is 
not limited to those precise embodiments, and that various changes and 
modifications may be effected therein by one skilled in the art without 
departing from the scope or spirit of the invention as defined in the 
appended claims.