Abstract:
A mechanical assembly for regulating the temperature of an integrated circuit chip is comprised of a frame which has at least two spaced-apart spring supports. Respective leaf springs extend from each of the spring supports towards each other. And, a heat exchanger lies in the space between the spring supports, attaches to all of the leaf springs, and has a face for mating with the chip. With this assembly, the heat exchanger exerts a very small force at its initial point of contact on the chip; the length of the leaf springs do not add to the profile of the assembly; no slippage occurs between the heat exchanger and the chip; and, the leaf springs prevent the heat exchanger from twisting and becoming offset relative to the chip.

Description:
RELATED CASES 
     The above-identified invention is related to two other inventions which are described herein with one common Detailed Description. These two other related inventions are: 
     “MECHANICAL ASSEMBLY FOR REGULATING THE TEMPERATURE OF AN ELECTRONIC DEVICE WHICH INCORPORATES A HEAT EXCHANGER THAT CONTACTS AN ENTIRE PLANAR FACE ON THE DEVICE EXCEPT FOR ITS CORNERS,” filed Dec. 10, 1998 having U.S. Ser. No. 09/210,259; and, 
     “MECHNICAL ASSEMBLY FOR REGULATING THE TEMPERATURE OF AN ELECTRONIC DEVICE WHICH INCORPORATES A SINGLE LEAF SPRING FOR SELF-ALIGNMENT PLUS A LOW INITIAL CONTACT FORCE AND A LOW PROFILE”, filed Dec. 10, 1998 having U.S. Ser. No. 09/210,266. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to mechanical assemblies that regulate the temperature of an electronic device, such as an integrated circuit chip, by pressing a temperature controlled heat exchanger against the chip. 
     In the prior art, one assembly of the above type is described in U.S. Pat. No. 4,791,983 which is assigned to the assignee of the present invention. The assembly in patent &#39;983 uses a coil spring 20 to press a planar surface of a liquid cooling jacket against a planar surface of an integrated circuit chip. More specifically, the coil spring 20 is compressed in a direction perpendicular to the planar surfaces of the liquid cooling jacket and the integrated circuit chip to squeeze those surfaces together and thereby lower the thermal resistance between them. 
     Due to various manufacturing tolerances, the planar surface of the integrated circuit chip (to which the cooling jacket mates) can be oriented at different angles and different heights relative to a nominal position. To accommodate these variances, the assembly in patent &#39;983 includes a guidepost 18 which is attached to the cooling jacket, extends perpendicular to the mating faces of the cooling jacket and the integrated circuit chip, and is loosely held by a beam 14. This guidepost, together with the coil spring and the cooling jacket, can tilt at different angles and move to different heights to thereby accommodate the variations in the orientation of the integrated circuit chip. 
     With the assembly of patent &#39;983, it is desirable for the coil spring to have a small spring constant. That is because when the planar surface on the cooling jacket initially contacts the planar surface on the integrated circuit chip, those two surfaces will be at different angles, so contact will initially occur at a single point on the corner of the chip. If the coil spring has a small spring constant, then the force that is exerted at the initial point of contact will be small and the chances of cracking the corner of the chip will be reduced. 
     On the other hand, to insure that the thermal resistance between the mating surfaces of the cooling jacket and the chip is sufficiently small, the final force with which those two surfaces are pressed together must be large. Thus to achieve this large final force with a small spring constant, the coil spring 20 must have a long length. However, increasing the length of the spring 20 inherently increases the minimal distance with which several of the assemblies can be placed side-by-side in a rack within an end-product. 
     Also, after initial contact occurs between the planar surface of the cooling jacket in patent &#39;983 and one corner of the chip, the cooling jacket must pivot on the guidepost to make the cooling jacket lie flat against the chip. However, in order for the cooling jacket to pivot on the guidepost, its planar surface must slip on the chip at the initial point of contact. And, such slippage between the cooling jacket and the chip can damage the chip. 
     Further with the assembly of patent &#39;983, the planar surface of the cooling jacket can become twisted and/or offset relative to the planar surface of the chip. To accommodate the above problem, the planar surface of the cooling jacket can be made substantially larger than the planar surface of the integrated circuit chip. But, such an increase in the size of the cooling jacket will be prohibited if the chip is held by a socket which the enlarged cooling jacket can hit, or another component lies next to the chip which the enlarged cooling jacket can hit. 
     Accordingly, a primary object of the present invention is to provide an improved mechanical assembly for regulating the temperature of an integrated circuit chip in which all of the above drawbacks with the prior art are overcome. 
     BRIEF SUMMARY OF THE INVENTION 
     In accordance with the present invention, a mechanical assembly for regulating the temperature of an integrated circuit chip is comprised of a frame which has at least two spaced-apart spring supports. Respective leaf springs extend from each of the spring supports towards each other. And, a heat exchanger lies in the space between the spring supports, attaches to all of the leaf springs, and has a face for mating with the chip. 
     With this assembly, the leaf springs deflect while the frame is moved such that the face of the heat exchanger presses against the chip. When the face of the heat exchanger initially contacts the chip, the leaf springs have a minimal deflection. Thus, the heat exchanger exerts a very small force at its initial point of contact with the chip. 
     Subsequently, when the face of the heat exchanger is pressed with a large final force against the chip, the leaf springs have a maximum deflection. But only the length of that deflection, and not the length of the leaf springs, adds to the profile of the assembly. Consequently, the minimal distance with which several of the assemblies can be placed side-by-side is small. 
     As the face of the heat exchanger moves from its initial point of contact with the chip to its final position where the large force is exerted on the chip, the leaf springs slip on the spring supports or the heat exchanger. No slippage occurs between the face of the heat exchanger and the chip. 
     Also, the leaf springs only deflect in one direction. Thus, the leaf springs prevent the face of the heat exchanger from twisting relative to the mating surface of the chip; and, the leaf springs also prevent the face of the heat exchanger from becoming offset relative to the mating surface of the chip. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a mechanical assembly, for regulating the temperature of an electronic device, which constitutes one preferred embodiment of the present invention. 
     FIG. 2 shows an enlarged top view of a heat exchanger which is held to a frame by four leaf springs in the FIG. 1 embodiment. 
     FIG. 3 shows a sectional view taken along lines  3 — 3  in FIG.  2 . 
     FIG. 4 shows an example of how the FIG. 1 embodiment is used to regulate the temperature of an electronic device. 
     FIGS. 5A-5D show a sequence of steps during which the leaf springs in the FIG. 1 embodiment deflect and thereby accommodate misalignments between the heat exchanger and the electronic device. 
     FIG. 6 shows a modification to the FIG. 1 embodiment. 
     FIG. 7 shows another modification to the FIG. 1 embodiment. 
     FIG. 8 shows still another modification to the FIG. 1 embodiment. 
     FIG. 9 shows yet another modification to the FIG. 1 embodiment. 
     FIG. 10 shows a mechanical assembly, for regulating the temperature of an electronic device, which constitutes a second preferred embodiment of the present invention. 
     FIG. 11 shows an underside view of the second embodiment of FIG.  10 . 
     FIG. 12A shows the top view of a bearing that is used in a modification to the second embodiment of FIG.  10 . 
     FIG. 12B shows the side view of the bearing in FIG.  12 A. 
     FIG. 12C shows the top view of a bushing that holds the bearing of FIG.  12 A. 
     FIG. 12D shows the side view of the bushing in FIG.  12 C. 
     FIG. 13 shows another modification to the second embodiment of FIG.  10 . 
     FIG. 14 shows a heat exchanger which constitutes a third embodiment of the present invention and which can be incorporated into the assembly of FIG.  1  and/or the assembly of FIG.  10 . 
     FIG. 15 shows a face on the heat exchanger in FIG. 14 as viewed perpendicular to the face. 
     FIG. 15A shows how the heat exchanger of FIG. 14 avoids cracking the tip of the electronic device by not exerting any force on that tip. 
     FIG. 16 shows a modification to the heat exchanger in FIG.  14 . 
     FIG. 17 shows another modification to the heat exchanger of FIG.  14 . 
     FIG. 18 shows another modification to the heat exchanger of FIG.  14 . 
    
    
     DETAILED DESCRIPTION 
     With reference now to FIG. 1, the details of a preferred embodiment of the present invention will be described. This FIG. 1 embodiment includes a flat, rigid, frame  10  which lies in a single X-Y plane, and which has nine openings that are indicated by reference numeral  11 . Within each of the openings  11  is a heat exchanger  20  that has a face  21  for mating with an electronic device (not shown) whose temperature is to be regulated. Each heat exchanger  20  is held spaced-apart from the frame  10  by a respective set of four leaf springs  30   a - 30   d  which extend from the frame  10  to the heat exchanger. 
     Also attached to the frame  10 , in the FIG. 1 embodiment, is an input manifold  40  and an output manifold  41  for a liquid coolant. This liquid passes from the input manifold  40  through each of the heat exchangers  20  and then to the output manifold  41 . Flexible tubes, which lie on the back of the frame  10 , carry the liquid between the heat exchangers  20  and the manifolds  40  and  41 ; and those tubes are hidden from view in FIG.  1 . 
     An enlarged top view of one of the heat exchangers  20  with its four leaf springs  30   a - 30   d  is shown in FIG. 2; and a corresponding cross-section taken through that heat exchanger is shown in FIG.  3 . These FIGS. 2 and 3 illustrate that one end of each leaf spring  30   a - 30   d  is held in a slot  12  in the frame  10 , while the opposite end of each leaf spring is held in a slot  22  in the heat exchanger  20 . Leaf springs  30   a  and  30   c  are able to slide in the Y direction in their slots, while leaf springs  30   b  and  30   d  are able to slide in the X direction in their slots. 
     With the above embodiment, the leaf springs  30   a - 30   d  hold face  21  of the heat exchanger  20  at an initial position in the X-Y plane; and the leaf springs  30   a - 30   d  prevent face  21  of the heat exchanger  20  from twisting from that initial position in the X-Y plane. These features are desirable because they ensure that face  21  will not be offset in the X or Y direction with the corresponding face on the electronic device to which the face  21  mates. 
     Also with the above embodiment, face  21  on the heat exchanger  20  is free to move in the Z direction, which is perpendicular to the X-Y plane. In addition, face  21  on the heat exchanger  20  is free to tip with respect to the X-Y plane. These features are desirable because they enable the heat exchanger  20  to accommodate misalignments between the X-Y plane and the face on the electronic device (not shown) to which the face  21  mates. 
     Turning now to FIG. 4, it shows an example of how the embodiment of FIGS. 1,  2  and  3  is used to regulate the temperature of an electronic device  50 . In FIG. 4, the electronic device  50  is an integrated circuit chip, and it has a face  51  that is to mate with face  21  of the heat exchanger  20 . In FIG. 4, the electronic device  50  has input/output terminals  52  which are soldered to a substrate  53 ; and the substrate  53  is held in a socket  60  which is mounted on a printed circuit board  61 . 
     Integrated into the substrate  53  and the printed circuit board  61  are hundreds of microscopic electrical conductors which carry power and signals between the electronic device  50  and the printed circuit board. One conductor in the substrate  53  is indicated by reference numeral  53   a;  a corresponding conductor in the printed circuit board  61  is indicated by reference numeral  61   a;  and they are interconnected by a fuzz-button  60   a  in the socket  60 . As the signals on those conductors change from one state to another, the amount of power which is dissipated within the electronic device  50  changes; and that in turn causes the temperature of the electronic device  50  to change. 
     To regulate the temperature of the electronic device  50 , face  21  of the heat exchanger  20  is placed flush against face  51  of the electronic device while a constant temperature liquid is passed through a conduit  23  on the back of the heat exchanger. Contact is made between face  51  of the electronic device  50  and face  21  of the heat exchanger  20  by moving the frame  10  in the Z direction via any suitable positioning mechanism. Such a mechanism is attached to the frame  10  by several bolts that pass through the holes  13  that are shown in the frame  10  in FIG.  1 . 
     Due to various manufacturing tolerances, face  51  of the electronic device  50  in FIG. 4 will always be tilted with respect to the X-Y plane. These manufacturing tolerances include, for example, variations in the respective distances D and D′ at which two moveable arms  60   b  in the socket  60  hold the substrate  53  from the printed circuit board  61 , and variations in the distance by which the solder connections  52  hold the electronic device  50  above the substrate  53 . However, the tilting of face  51  with respect to the X-Y plane is accommodated by the operation of the four leaf springs  30   a - 30   d;  and this operation is illustrated in FIGS. 5A-5D. 
     In FIG. 5A, face  21  of the heat exchanger  20  lies parallel to the X-Y plane; whereas face  51  of the electronic device  50  is tilted at an angle of about five degrees with respect to the X-Y plane. Consequently, when the frame  10  is moved in the Z direction, face  21  of the heat exchanger  20  will initially touch face  51  of the electronic device  50  at only one point  51   a.  When that occurs, the point on face  51  which is spaced furthest from face  21  is indicated by reference numeral  51   b,  and its spacing is indicated as distance D 1 . 
     Then, after the frame  10  is moved in the Z direction by the distance D 1 / 2 , the entire face  51  on the electronic device  50  will be in contact with face  21  on the heat exchanger  20 . This is shown in FIG.  5 C. During the transition from FIG. 5B to FIG. SC, the leaf springs  30   a - 30   d  deflect, and that enables face  21  on the heat exchanger to become aligned with face  51  on the electronic device  50 . 
     Thereafter, the frame  10  is moved an additional distance D 2  in the Z direction as shown in FIG.  5 D. During the transition from FIG. 5C to FIG. 5D, each of the leaf springs  30   a - 30   d  slip in their respective slots  12  and  22  while the amount of deflection in each of the leaf springs increases. This increases the force with which the two mating faces  21  and  51  are pressed together; and consequently, the thermal resistance between those mating faces decreases. 
     While the heat exchanger  20  is pressed against the electronic device  50  as shown in FIG. 5D, the electronic device  50  can be operated and/or tested by passing electrical signals between it and the printed circuit board  61 . During that exercise, the temperature of the electronic device  50  is regulated by the heat exchanger  20 . Subsequently, when the operating/testing of the electronic device  50  is completed, the heat exchanger  20  is separated from the electronic device  50  by moving the frame  10  from its position in FIG. 5D to its position in FIGS. 5C,  5 B and  5 A. Then, the electronic device  50  is removed from the socket  60  and replaced with another electronic device which is to be operated/tested. 
     One feature of the above-described embodiment is that during the transition from FIG. 5B to FIG. 5C, the maximum force which is exerted by the leaf springs  30   a - 30   d  on face  51  of the electronic device  50  is very small. That force is proportional to the distance D 1 / 2  times the effective spring constant for the four leaf springs  30   a - 30   d.  But, D 1 / 2  is very small; and the effective spring constant is also made small simply by decreasing the thickness of the leaf springs  30   a - 30   d  and/or increasing the distance which the leaf springs traverse between the heat exchanger  20  and the frame  10 . Having the leaf springs exert a small force during the transition from FIG. 5B to FIG. 5C is important because exerting a large force at the single point  51   a  on the electronic device can crack or otherwise damage the electronic device. 
     Another feature of the above-described embodiment is that it has an overall height, in the Z direction, to which all of the leaf springs  30   a - 30   d  contribute insignificantly. This height in the Z direction is seen, for example, in FIG. 1 where the only contribution which is made by the leaf springs  30   a - 30   d  is their thickness. Having a small height in the Z direction is important because it enables the FIG. 1 embodiment to be incorporated into a larger high-density structure where several of the frames  10  are stacked in parallel X-Y planes that are separated in the Z direction by a minimal distance. 
     A preferred embodiment of the present invention has now been described in detail. However, as one modification to the above-described embodiment, the leaf springs  30   a - 30   d  can be increased or decreased in number. Preferably, the total number of leaf springs which interconnect each heat exchanger  20  to the frame  10  is between two and ten. Such a modification is shown in FIG. 6 wherein only two leaf springs  30   b  and  30   d  couple the heat exchanger  20  to the frame  10 . 
     As another modification, the slots  12  and  22  which support the leaf springs  30   a - 30   d  can be changed to a different type of support. For example, each of the leaf springs  30   a - 30   d  can be tightly connected to the frame  10  and can slip only in the slots  22  in the heat exchanger  20 . Conversely, each of the leaf springs  30   a - 30   d  can be tightly connected to the heat exchanger  20  and can slip only in the slots  12  in the frame  10 . Such a modification is shown in FIG. 7 wherein the leaf springs  30   b  and  30   d  are braised to the heat exchanger  20 . 
     As still another modification, each of the leaf springs  30   a - 30   d  can be connected to the heat exchanger  20  such that they pivot, rather than bend, at their connection with the heat exchanger. An example of this modification is shown in FIG.  8 . There, the heat exchanger  20  is provided with triangular-shaped slots  22 ′ which pinch the leaf springs  30   a - 30   d  as they enter the slots. With this modification, each leaf spring will pivot at its pinched connection without bending because the end of the leaf spring is free to move inside the triangular slot. Consequently, no bending moment occurs in the leaf springs at their connection with the heat exchanger. 
     With the modification of FIG. 8, the bending moment in each leaf spring  30   a - 30   d  increases linearly as the distance along the leaf spring from the pivot point increases. Thus, to achieve a nearly constant bending stress in the leaf springs, they each have a tapered width which increases in proportion to bending moment. This taper is shown in FIG. 2; and it makes bending stress constant because bending stress is proportional to the bending moment divided by the width of the leaf spring. 
     Having a nearly constant bending stress in each leaf spring  30   a - 30   d  enables the thickness of each leaf spring to be reduced without overstressing the leaf spring at any one point; and, having a thin leaf spring enables the slots  12  in the frame  10  to be moved closer together without making the leaf spring too stiff. Consequently, the density with which the heat exchangers  20  can be arranged in FIG. 1 is increased. 
     As yet another modification, the frame  10  of FIG. 1 can be increased or decreased in size in the X-Y plane to thereby hold any number of the heat exchangers. Also, as another modification, all of the openings  11  in the FIG. 1 frame  10  can be eliminated, and the leaf springs  30   a - 30   d  can be attached to spring supports which extend from a base plate. This modification is shown in FIG. 9 wherein the base plate with none of the openings  11  is indicated by reference number  10 ′, and two spring supports which extend from the base plate and hold the leaf springs is indicated by reference number  10 ″. 
     Referring now to FIG. 10, the details of a second preferred embodiment of the present invention will be described. This FIG. 10 embodiment includes a frame  70  which has a central opening  71 , and it includes a pair of spring supports  72  that are spaced-apart by the opening  71 . Extending from one spring support to the other is a single leaf spring  80 , and a heat exchanger  90  contacts the leaf spring  80  at its center. 
     This heat exchanger  90  has a face  91  for mating with an electronic device, such as the previously described electronic device  50  in FIG.  4 . Also, the heat exchanger  90  pushes the leaf spring  80  against the spring supports  72 , and it pivots on the center of the leaf spring  80 . 
     To ensure that all of the components  70 ,  80 , and  90  stay held together, the FIG. 10 embodiment also includes a pair of stops  100 . Each stop has one end that is connected by a screw  100   a  to a respective arm  92  on the heat exchanger, and it has another end  100   b  which passes through a hole  73  in the frame  70 . End  100   b  tapers outward, and it has a flange which engages the frame  70  whenever the deflection of the center of the leaf spring  80  is at a predetermined minimum distance. 
     With the FIG. 10 embodiment, the temperature of an electronic device is regulated by pressing face  91  of the heat exchanger  90  against a corresponding face of the electronic device while a constant temperature liquid passes through a conduit  93  in the heat exchanger. This is achieved by moving the FIG. 10 embodiment in the Z direction in a manner similar to that which was described previously in conjunction with FIGS. 5A-5D. 
     Initially, before the heat exchanger  90  contacts the electronic device, face  91  of the heat exchanger is aligned in the X-Y plane. This alignment occurs automatically due to the operation of the stops  100 . In particular, the flange on end  100   b  of each stop  100  engages the frame  70  to thereby hold face  91  of the heat exchanger in the X-Y plane; and the taper on end  100   b  moves face  91  sideways and rotationally in the X-Y plane to a particular position in that plane. 
     Thereafter, the frame  70  is moved in the Z direction until face  91  of the heat exchanger contacts the electronic device at a single point, such as point  51 a in FIG.  5 B. Then, as the frame  70  is moved an additional distance D 1 / 2  in the Z direction, face  91  of the heat exchanger  90  will tilt out of the X-Y plane and lie flush against the corresponding face  51  of the electronic device. Lastly, the frame  70  is moved an additional distance D 2  in the Z direction to increase the force with which the two mating faces  91  and  51  are pressed together; and that decreases the thermal resistance between those mating faces. 
     An underside view of the FIG. 10 embodiment is shown in FIG.  11 . There, the spring  80  is shown in a deflected position which occurs after the frame  70  has been moved in the Z direction by the distances D 1 / 2  and D 2 . FIG. 11 also shows two structural details which enable face  91  of the heat exchanger  90  to align itself with the corresponding face of the electronic device. One of those details is that the bottom of the heat exchanger  90  includes a dimple  94  which contacts the center of the leaf spring  80 ; and the other detail is that the stops  100  have shafts which fit loosely in the frame holes  73 . Due to that loose fit, face  91  of the heat exchanger  90  is free to pivot and slide on the dimple  94  as soon as a flanged end  100   b  of a stop  100  disengages the frame  70 . 
     One additional feature of the embodiment in FIGS. 10 and 11 is that the ends of the leaf spring  80  are free to pivot, without bending, on the spring supports  72 . Consequently, no bending moment occurs in the ends of the leaf spring  80 . 
     In the leaf spring  80 , the bending moment is the largest at the center of the leaf spring, and it decreases linearly with distance from the center of the leaf spring. To achieve a nearly constant bending stress throughout the leaf spring  80 , the leaf spring has a tapered width which is proportional to the bending moment. This taper is shown in FIG. 10, and it causes bending stress to be nearly constant because bending stress is proportional to the bending moment divided by the spring width. 
     Having a nearly constant bending stress in the leaf spring  80  allows the thickness of the leaf spring to be reduced without overstressing the leaf spring at any one point; and, having a thin leaf spring enables the spring supports  72  to be moved close together without making the leaf spring too stiff. Consequently, several of the assemblies in FIGS. 10-11 can be packaged in an array (such as the array of FIG.  1 ), with a high density. 
     Still another feature of the embodiment in FIGS. 10 and 11 is that the length of each stop  100  can be selected such that the flange on end  100   a  engages the frame  70  when the leaf spring  80  exerts a force on the heat exchanger  90  which only slightly exceeds the weight of the heat exchanger. In that case, the weight of the heat exchanger  90  in the Z direction will be cancelled out by the force which the leaf spring  80  exerts in the −Z direction. Consequently, face  91  of heat exchanger will exert essentially no force on the corresponding face of the electronic device when initial contact with that device is made; and thus, the risk of cracking the electronic device is minimal. 
     A second preferred embodiment of the present invention has now been described in detail in conjunction with FIGS. 10 and 11. However, as one modification to that second embodiment, the dimple  94  on the bottom of the heat exchanger  90  can be replaced with an alternative structure which allows the heat exchanger to pivot on the center of the leaf spring  80 . For example, the entire bottom surface of the heat exchanger  90  can have a convex shape. Alternatively, the bottom surface of the heat exchanger  90  can be flat; and a dimple, such as the dimple  94 , can be incorporated into the leaf spring  80 . 
     Also, a gimbal can be incorporated into the leaf spring  80  which allows face  91  of the heat exchanger to pivot out of the X-Y plane, but limits twisting in the X-Y plane. An example of such a gimbal is shown in FIGS. 12A-12B; and it consists of a bearing  101  and a bushing  102 . The bushing  102  has a bottom portion  102   a  which is press-fit into a hole (not shown) in the center of the leaf spring. Also, the bushing  102  has a key  102   b  which prevents the bushing from turning in the hole in the leaf spring. 
     The bearing  101  has a spherical-shaped bottom surface  101   c  with a fin  101   d.  Surface  101   c  of the bearing rests on a flat surface  102   c  in the bushing; and the fin  101   d  of the bearing fits loosely in a slot  102   d  in the bushing. Thus, surface  101   c  is free to pivot on surface  102   c,  but the fin  101   d  in slot  102   d  limits the twisting of surface  101   c  about the Z axis. 
     Similarly, the bearing  101  has a spherical-shaped tope surface  101   e  with a fin  101   f.  Surface  101   e  of the bearing rests on a flat surface on the bottom of the heat exchanger; and the fin  101   f  of the bearing fits loosely in a slot (not shown) in that heat exchanger. Thus, the heat exchanger is free to pivot on surface  101   e,  but the fin  101   f  limits the twisting of the heat exchanger about the Z axis. 
     As another modification, the stops  100  in FIG. 10 can be replaced with a different structure which performs in a similar fashion. For example, each stop  100  in the FIG. 10 embodiment can be rotated 180° in the X-Z plane. With that modification, the holes  73  are deleted from the frame  70  and incorporated into the arms  92  of the heat exchanger; and the screws  100   a  are deleted from the arms  92  and added to the frame  70 . Such a modification is shown in FIG.  13 . 
     Turning now to FIG. 14, the details of a third embodiment of the present invention will be described. The FIG. 14 embodiment is the same as the first embodiment of FIGS. 1-9, or the same as the second embodiment of FIGS. 10-13, with the exception that it includes a different heat exchanger  110 . This heat exchanger  110  has a face  111  which is shaped to make contact with the entire planar surface  51  of the electronic device  50  except for each of the corners  51   a - 51   d  on that surface. 
     To ensure that the corners  51   a - 51   d  of the electronic device  50  are not contacted by face  111  of the heat exchanger  110 , the heat exchanger has four grooves  112   a - 112   d  which extend from face  111  and which respectively align with the corners  51   a - 51   d.  Consequently, when face  111  lies flush against the planar surface  51 , the corners  51   a - 51   d  are exposed by the grooves  112   a - 112   d.    
     The perimeter of the face of the heat exchanger  110 , as viewed in the −Z direction, is shown by the solid lines  111  in FIG.  15 . Also, superimposed on that face  111  in FIG. 15 are dashed lines  51  which show the perimeter of the planar surface on the electronic device  50  when that planar surface lies flush against face  111  of the heat exchanger. From these two superimposed perimeters it is clear that the corners  51   a - 51   d  on the electronic device are not contacted by face  110  on the heat exchanger because the corners are in the grooves  112   a - 112   d.    
     One particular feature of the above-described FIG. 14 embodiment, is that when face  111  on the heat exchanger initially contacts the planar surface  51  on the electronic device, no force is exerted by the heat exchanger on the tip of any of the corners  51   a - 51   d.  Instead, the initial contact between face  111  on the heat exchanger and the planar surface  51  on the electronic device occurs on an edge which is spaced-apart from the tip of a corner. 
     The above feature is illustrated in FIG. 15 a  which is a blow-up of corner  51   d  in FIG.  14 . In FIG. 15 a,  the initial contact between face  111  on the heat exchanger and surface  51  on the electronic device causes a force F to be exerted at a point P. Point P is spaced from the tip T of corner  51   d  because the tip is in the groove  112   d.  By comparison, if the groove  112   d  was eliminated, a force F′ would be exerted on the tip T of the electronic device. 
     Preferably, the grooves  112   a - 112   d  have a rounded connection with face  111  of the heat exchanger. This insures that the initial contact at point P, between the heat exchanger and the electronic device, always involves at least one dull edge, which helps prevent the electronic device from cracking. 
     Also preferably, the grooves  112   a - 112   d  are made sufficiently wide such that face  111  of the heat exchanger contacts the planar surface  51  of the electronic device no closer than 8.0 mils or 0.2 millimeters from the tip of any corner. This also helps reduce the chances of cracking the electronic device  50 . At the same time, the grooves  112   a - 112   d  preferably are kept sufficiently small such that at least 75% of the entire planar surface  51  of the electronic device is contacted by face  111  of the heat exchanger. This limitation ensures that grooves  112   a - 112   d  have no significant effect on the heat transfer between the electronic device and the heat exchanger. 
     As a modification to the FIG. 14 embodiment, the heat exchanger  110  can be enlarged in the X-Y directions, in which case the grooves  112   a - 112   d  need not extend to the sides of the heat exchanger. That is, the grooves  112   a - 112   d  can lie entirely within face  111  of the heat exchanger. 
     As another modification to the FIG. 14 embodiment, the heat exchanger  110  can be changed such that it has a face  121  as shown in FIG.  16 . From that face, four sides  122   a - 122   d  extend at beveled angles and expose the corners  51   a - 51   d  of the electronic device  50 . These beveled sides  122   a - 122   d  replace the grooves  112   a - 112   d  in the FIG. 14 embodiment. Alternatively, the beveled sides can be rounded rather than flat; and/or they can extend from face  121  of the heat exchanger with a rounded edge. 
     As another modification, the heat exchanger  110  can be changed such that it has a face  131  as shown in FIG.  17 . From that face, four sides  131   a - 132   d  extend at right angles and expose the corners  51   a - 51   d  of the electronic device  50  by crossing those corners at a diagonal. These four sides  132   a - 132   d  replace the grooves  112   a - 112   d  in the FIG. 14 embodiment. 
     As still another modification, the heat exchanger  110  in FIG. 14 can be changed such that it has a face  141  as shown in FIG.  18 . From that face, several sides  142   a - 142   d  extend at right angles and expose the corners  51   a - 51   d  of the electronic device by crossing the corners in a non-straight path. 
     Three preferred embodiments of the present invention, as well as several modifications to each of those embodiments, has now been described in detail. In addition however, further changes can be made to the illustrated preferred embodiment and the illustrated modifications without departing from the nature and spirit of the invention. 
     For example, with each of the three embodiments, the heat exchanger that regulates the temperature of the electronic device is not limited to a heat exchanger which only cools the device. In particular, the heat exchanger can be one which maintains the electronic device at a constant temperature by heating or cooling the electronic device in response to control signals. Once such heat exchanger as shown in FIG. 1 of U.S. Pat. No. 5,821,505 which is assigned to the assignee of the present invention and is herein incorporated by reference. In that patent, the heat exchanger is comprised of a thin, flat electric heater  13  and a liquid cooled heat sink  14  which are laminated together. Such a heat exchanger can be held by multiple leaf springs in the assembly of FIGS. 1-9, or by a single leaf spring in the assembly of FIGS. 10-13; and, such a heat exchanger can have any of the faces of FIGS. 14-18. 
     Accordingly, it is to be understood that the invention is not limited to just the details of the illustrated preferred embodiment and modifications, but is defined by the appended claims.