US20040150954A1 - Power module for multi-chip printed circuit boards - Google Patents

Abstract

A power module assembly for multi-chip printed circuit boards: A heat distribution plate has first and second fields of receptacles integrally formed therein. The receptacles are populated with first and second fields of thermally-conductive pins. A power module printed circuit board is mounted to the heat distribution plate and has first and second clearance holes formed therein. The first and second fields of pins protrude through the first and second clearance holes. A multi-chip printed circuit board may be mounted underneath the power module such that the thermally-conductive pins contact a surface of first and second supplied chips. The supplied chips are physically close to the power module, and thermal management for the supplied chips is provided by virtue of contact between the supplied chips and the thermally-conductive pins. Space on the multi-chip printed circuit board is conserved.

Description

FIELD OF THE INVENTION
• This invention relates generally to power modules for multi-chip printed circuit boards.[0001]
BACKGROUND
• Many modern integrated circuit chips, such as microprocessors for example, require relatively high supply current delivered at a very tightly controlled voltage. It is common, therefore, to employ a special-purpose module including voltage converters, voltage regulators and the like to supply power to such a chip. And it is known that disposing the power module physically close to the supplied chip helps to reduce negative effects associated with the delivery of power via cables.[0002]
• Recently it has become popular to deploy two or more high-power chips on a single multi-chip printed circuit board. Among the problems presented by this approach is how to dispose the power module sufficiently close to the supplied chips while at the same time providing adequate thermal management for the supplied chips and conserving space on the printed circuit board.[0003]
• It is an object of the present invention to provide a power module for a multi-chip printed circuit board such that: (1) the power module is disposed physically close to the chips on the printed circuit board, (2) thermal management is provided for the supplied chips, and (3) space is conserved on the printed circuit board.[0004]
SUMMARY OF THE INVENTION
• In a power module assembly according to a preferred embodiment of the invention, a heat distribution plate is provided having first and second fields of receptacles integrally formed therein. The receptacles are populated with first and second fields of thermally-conductive pins capable of moving independently in a direction orthogonal to the plate. A power module printed circuit board is mounted to the heat distribution plate and has first and second clearance holes formed therein. The first and second fields of pins protrude through the first and second clearance holes. A multi-chip printed circuit board may be mounted underneath the power module such that the thermally-conductive pins contact a surface of first and second supplied chips. In this manner, the supplied chips are physically close to the power module, and thermal management for the supplied chips is provided by virtue of contact between the supplied chips and the thermally-conductive pins. Z-axis compliance provided by the pin/receptacle assemblies enhances thermal conductivity even when the supplied chips have differing heights relative to the top of the multi-chip printed circuit board. Space on the multi-chip printed circuit board is conserved because the power module is not part of the multi-chip printed circuit board, but rather is mounted on a separate printed circuit board disposed over the top of the multi-chip printed circuit board.[0005]
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is an exploded bottom oblique view of a printed circuit board stack that includes a power module assembly according to a preferred embodiment of the invention.[0006]
• FIG. 2 is an exploded top oblique view of the printed circuit board stack of FIG. 1.[0007]
• FIG. 3 is a sectional view of the printed circuit board stack of FIG. 1.[0008]
• FIGS. 4 and 5 are assembled bottom and top oblique views, respectively, of the printed circuit board stack of FIG. 1.[0009]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
• FIGS.[0010]1-5 illustrate a printedcircuit board stack100 that includes a power module according to a preferred embodiment of the invention. Stack100 also includes cooling apparatus that is claimed in U.S. patent application Ser. No. ______, filed Jan. ______,2003, titled “Cooling Apparatus for Stacked Components” (HP Attorney Docket Number 200209132-1).
• Power Module.[0011]Power module assembly102 includes aheat distribution plate104 and a power module printedcircuit board106.Heat distribution plate104 includesfields108 ofreceptacles300 populated with thermally-conductive pins302. Thepins302 are capable of independent movement in thedirection110 orthogonal toplate104. Power module printedcircuit board106 includesclearance holes112 adapted toclear pin fields108.Board106 is preferably mounted to the underside ofheat distribution plate104 by means of fasteners such as screws. When this is done,pin fields108 protrude throughclearance holes112 on the underside of power module printedcircuit board106 so that the pins may make contact with the top surfaces of heat-generating integratedcircuit chips200 mounted on a multi-chip printedcircuit board116. This contact provides thermal management forchips200 by conducting heat from the chips intoheat distribution plate104. An active or a passiveheat sink device114 may optionally be mounted overplate104 to enhance the removal of heat therefrom.
• One or more of[0012]pin fields108 may be disposed on raisedbosses118 integrally formed onplate104. In such an embodiment, the bosses themselves may protrude throughclearance holes112 to shorten the lengths ofpins302 necessary for adequate contact withchips200. Because of the forces applied againstchips200 bypins302, bowing of multi-chip printedcircuit board116 may occur. If so, it may be desirable to mount abolster plate122 to the underside ofboard116 to prevent or reduce the bowing. Such abolster plate122 may optionally include raisedbosses124 to provide direct support againstboard116 under one of more of thechips200. Optionally, an insulator may be interposed betweenbosses124 andcircuit board116.Bolster plate122 may be fastened to any suitably rigid member, such asheat distribution plate104 or anintermediate frame126.
• A[0013]power connector component120 may be mounted to the underside of power module printedcircuit board106. And a correspondingpower connector component202 may be mounted to the top side of multi-chip printedcircuit board106. When printedcircuit board stack100 is assembled,power connector components120,202 mate by virtue of their proximity and alignment. Such connectors may be used to efficiently transfer power between power module printedcircuit board106 and multi-chip printedcircuit board116. In one embodiment, blade-style power connector components were used for this purpose (as illustrated). In other embodiments, alternative power connectors may be used. Whenpower connector components120,202 are oriented orthogonal to their respective host circuit boards as shown, and the circuit boards oriented parallel to the heat distribution plate, alignment and automatic mating of the connector components are easily achieved.
• Although any suitably rigid heat conducting material may be used to make[0014]heat distribution plate104 andintermediate frame126, in one embodiment aluminum was used for this purposed because of the combination of its strength, ease of machining, and thermal conductivity.Bolster plate122 may also be made using any suitably rigid material. In an embodiment,bolster plate122 was made of steel for strength.Pin fields108 may be constructed according to any suitable technique, including for example those disclosed in U.S. patent application Ser. No. 10/074,642, filed Feb. 12, 2002, titled “Thermal Transfer Interface System and Methods,” which by this reference is hereby incorporated entirely as if fully set forth in this application.
• Cooling Apparatus. Printed[0015]circuit board116 may include heat-generating components mounted on its top side as well as its bottom side. For example, heat-generating components128 may be mounted on one side ofboard116, andheat generating components204 may be mounted on the other side ofboard116 as shown in FIGS.1-3. Across-member206 may be integrally formed onframe126 and disposed overcomponents204. A thermally-conductive strap130 is provided having first andsecond legs132,134. In an embodiment,strap130 was made of copper because of the desirable thermal conductivity of that material. In other embodiments, other thermally-conductive materials may be used.
• When[0016]circuit boards106 and116 are assembled,cross-member206 is thermally coupled tocomponents204, andleg132 ofstrap130 is thermally coupled tocomponents128. The thermal couplings may be achieved by direct contact between the cross-member or strap and the corresponding components, or optionally a compliant thermally-conductive material may be interposed between the strap or cross-member and the corresponding components. For example, in one embodiment, die-cut wafers136 of thermally-conductive material were interposed as shown in FIGS.1-3. One example of a material suitable to use for this purpose would be “TPUTTY-502,” manufactured and sold by THERMAGON. Another example would be thermal grease.Leg134 ofstrap130 is thermally coupled to one end offrame126 and to one end ofheat distribution plate104. The latter thermal coupling may also be accomplished by direct contact betweenstrap130 and the frame and plate, or optionally a compliant thermally-conductive material such as those just mentioned may be interposed between the strap and the frame or plate.
• An active or passive[0017]heat sink assembly114 may optionally be thermally-coupled to heatdistribution plate104 to enhance removal of heat fromcomponents128,204. Note that the cooling apparatus just described may be beneficially employed regardless of whether or not heatdistribution plate104 includes pin-fields108, and pinfields108 may be beneficially employed regardless of whether the just-described cooling apparatus is included in the assembly. Similarly,circuit board106 need not be a power module such as the one described herein above in order for the just-described cooling apparatus to be effectively applied.
• Preferably, the portion of[0018]leg132adjacent components128 is a substantially planar surface extending over the top surface ofcomponents128 as shown.Leg132 may also include one ormore walls138 extending between the planar surface of the leg and an electrically conductive trace oncircuit board116. If so, then strap130 functions not only as a heat removal device, but also helps to contain electromagnetic energy radiating fromcomponents128. (For such an application,strap130 should not only be thermally conductive but electrically conductive as well. Copper, of course, exhibits both behaviors.)Walls138 may be sectioned or may be formed as one continuous wall. In the arrangement shown,wall sections138 form three sides of a rectangle aroundcomponents128, and the transverse dimension ofleg134 forms a fourth side of the rectangle, thus completing at least a partial electromagnetic enclosure aroundcomponents128. To further enhance electrical contact betweenwalls138 andcircuit board116, a compliant electricallyconductive material142 may optionally be interposed between the edge ofwall138 andcircuit board116. One example of a material suitable for this purpose would be a liquid-dispensed material having part number5537 manufactured and sold by CHOMERICS.
• In any printed circuit board stack such as[0019]stack100, mechanical tolerances are additive. To accommodate such a tolerance build-up,legs132,134 ofstrap130 may be joined at anelastic elbow140. If so, thenlegs132,134 may be moved slightly relative to one another during assembly ofstack100. Anelastic elbow140 may be created, for example, by manufacturingstrap130 from one unitary piece of metal and causing the juncture betweenlegs132,134 to be thinner than either of the two legs. Alternatively, braided metal may be used to provide an elastic elbow junction betweenlegs132,134. Also, it is beneficial to provide over-sized screw holes onlegs132,134 for attachment ofstrap130 to frame126 andplate104. The over-sized holes help to accommodate varying tolerances instack100.
• While the invention has been described in detail in relation to a preferred embodiment thereof, the described embodiment has been presented by way of example and not by way of limitation. It will be understood by those skilled in the art that various changes may be made in the form and details of the described embodiment without deviating from the spirit and scope of the invention as defined by the appended claims.[0020]

Claims (7)

What is claimed is:

1. A power module assembly, comprising:

a heat distribution plate having at least first and second fields of receptacles integrally formed therein and populated with first and second fields of thermally-conductive pins, respectively, the pins capable of moving independently in a direction orthogonal to the plate responsive to forces applied to them; and

a power module printed circuit board mounted to the heat distribution plate and having first and second clearance holes formed therein;

wherein the first and second fields of pins protrude through the first and second clearance holes.

2. The power module assembly ofclaim 1, further comprising:

a multi-chip printed circuit board mounted adjacent to the power module printed circuit board and having first and second heat generating chips mounted thereon;

wherein a surface of the first heat generating chip contacts the first field of pins, and a surface of the second heat generating chip contacts the second field of pins.

3. The power module assembly ofclaim 1, wherein:

the first and second fields of receptacles are disposed on first and second bosses, respectively, the bosses integrally formed on the heat distribution plate.

4. The power module assembly ofclaim 3, wherein:

the first and second bosses protrude through the first and second clearance holes.

5. The power module assembly ofclaim 2, further comprising:

a first power connector component mounted to the power module printed circuit board; and

a second power connector component mounted to the multi-chip printed circuit board;

wherein the first and second power connector components mate.

6. The power module assembly ofclaim 5, wherein:

the first and second power connector components comprise a blade-style connector assembly.

7. The power module assembly ofclaim 5, wherein:

the first and second power connector components are oriented orthogonal to the heat distribution plate; and

the planes of the power module circuit board and the multi-chip circuit board are oriented parallel to the heat distribution plate.

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