Mechanical assembly for regulating the temperature of an electronic device, having a spring with one slideable end

A mechanical assembly, for regulating the temperature of an electronic device, includes a gimbal and a heat-exchanger which is attached to the gimbal. The gimbal includes a base member, a carrier member, and a spring which has—1) a first end with a rigid coupling to one of the base and carrier members, and 2) a second end with a slideable coupling to the remaining member. The slideable coupling prevents any gap from occurring between the heat-exchanger and the electronic device when they are pressed together.

BACKGROUND OF THE INVENTION

This invention relates to a mechanical assembly that regulates the temperature of an integrated circuit chip (IC-chip) by pressing a temperature controlled heat-exchanger against a planar surface of the IC-chip.

One particular use for the above mechanical assembly is in a chip testing system. There, test signals are sent to the IC-chip while the mechanical assembly maintains the temperature of the IC-chip at a set point.

In the prior art, one mechanical assembly which regulates the temperature of an IC-chip is shown in FIGS. 1 and 2 of U.S. Pat. No. 4,791,983. The mechanical assembly in patent '983 includes a coil spring 20 which presses a planar surface of a liquid cooling jacket 15 against a planar surface of the IC-chip 11. Squeezing those two planar surfaces together enables heat to flow by thermal conduction from the IC-chip 11 to the liquid cooling jacket 15.

But due to various manufacturing tolerances, the planar surface of the IC-chip in a chip testing system can be oriented at different angles relative to a nominal position. To accommodate these different angles, the mechanical assembly in patent '983 includes a guidepost 18 which has one end that is rigidly attached to the cooling jacket 15, and has an opposite end that pivots on a frame 14. The coil spring 20 is coiled around the guidepost 18. Thus the guidepost 18, together with the coil spring 20 and the cooling jacket 15, can tilt at different angles.

After initial contact occurs in patent '983 between the planar surface of the cooling jacket 15 and one edge of the IC-chip 11, the guidepost 18 must pivot on the frame 14 to make the cooling jacket 15 lie flat against the IC-chip 11. However, the present inventors have determined that as the guidepost 18 pivots on the frame 14, the spring 20 can exert a lateral force on the cooling jacket 15 which may cause a gap to occur between the IC-chip 10 and the planar surface of the cooling jacket. When this gap occurs, the IC-chip 10 will not be adequately cooled. This lateral force problem is analyzed herein in detail in conjunction with the Detailed Description of FIGS. 4 and 7.

Also in the prior art, another mechanical assembly which regulates the temperature of an IC-chip is shown in FIGS. 10 and 11 of U.S. Pat. No. 6,116,331. This mechanical assembly includes a single leaf spring 80 which presses a planar surface 91 of a heat-exchanger 90 against a planar surface of an IC-chip.

However, the leaf spring 80 in patent '331 lies parallel to the planar surface 91 of the heat-exchanger 90, and that leaf spring must have a certain length in order to have the proper flexibility. If the leaf spring 80 is too short, it will be so stiff that the heat-exchanger 91 will press against the IC-chip with too much force and thereby damage the IC-chip.

But as the length of the leaf spring 80 is increased, the density with which multiple copies of the mechanical assembly can be arranged side-by-side in a chip testing system is decreased. Thus, the total number of IC-chips which can be tested concurrently per unit area in a chip testing system is decreased.

According, a primary object of the present invention is to provide an improved mechanical assembly for regulating the temperature of an IC-chip in which all of the above drawbacks with the prior art are overcome.

BRIEF SUMMARY OF THE INVENTION

The present invention is a mechanical assembly for regulating the temperature of an electronic device. This mechanical assembly includes a gimbal which has a base member and a carrier member that is loosely held by the base member such that the carrier member can tilt and move relative to the base member by predetermined distances. This mechanical assembly also includes a heat-exchanger that is attached to the carrier member and which has a face for pressing against the electronic devices. The mechanical assembly further includes a spring, between the base and carrier members, which is in compression and urges the carrier member away from the base member.

The above spring has a first end with a rigid coupling to only one of the base and carrier members, and has a second end with a slideable coupling to the remaining member. In one preferred embodiment, the slideable coupling includes a plate that has—a) one face which is attached to the second end of the spring, and b) an opposite face with indentations which hold three ball bearings. These ball bearings roll on a surface of the remaining member of the gimbal.

Since the ball bearings roll on the surface of the remaining member of the gimbal, any force which the ball bearings exert on that member will be essentially perpendicular to its surface. This is important because any non-perpendicular force will tend to prevent the heat-exchanger from lying flatly against the electronic device. A mathematical analysis of why this is so is described herein in conjunction withFIGS. 3 and 4.

DETAILED DESCRIPTION

With reference now toFIGS. 1-6, one particular mechanical assembly10will be described which constitutes one preferred embodiment of the present invention. This mechanical assembly10consists of a heat-exchanger20and a gimbal30which are permanently attached to each other, as shown inFIG. 1.

Inspection ofFIG. 1shows that the heat-exchanger20includes a thin flat electric heater21and a conduit22which is permanently attached to the heater21. The heater21has a pair of terminals21afor passing electrical current through the heater. The conduit22has an input port22aand an output port22bfor passing a liquid coolant through the conduit.

FIG. 1also shows that the gimbal30includes a base31, a carrier32, and a coiled spring33. The carrier32is loosely held by the base31such that the carrier can tilt and move away from the base31within a predetermined range of distances. In theFIG. 1implementation, the carrier31is provided with three legs32a, only two of which are shown. Each leg32aextends loosely through a respective hole31ain the base31. Also, each leg32ahas an end32bwhich is too wide to pass through its respective hole31a.

FIG. 1also shows that the coiled spring33is interposed between the base31and the carrier32. This coil spring33is in compression such that it urges the carrier32away from the base31. In its quiescent state, the spring33presses the wide end of each leg32aagainst the base31. This centers the heat-exchanger20over the base31such that the heater21is at a predetermined position.

FIG. 1further shows that the coiled spring33has a first end with a fixed coupling34to the base31, and a second end with a slideable coupling35to the carrier32. In theFIG. 1embodiment, the slideable coupling35includes a plate35aand three ball bearings35b.

One surface of the plate35ais rigidly attached to the spring33. The opposite surface of the plate35aholds each of the ball bearings35bin a respective indentation. All of the ball bearings35bare pressed by the plate35aagainst the carrier32. Also, all of the ball bearings35broll on the carrier32and slip in their respective indentation in the plate35a.

One particular use for the above described mechanical assembly10is to regulate the temperature of an integrated circuit chip (IC-chip) while the IC-chip is being tested in a chip testing system. An IC-chip which is being tested in a chip testing system is commonly called a “DUT”, which means “device under test”. One DUT is shown inFIG. 1as item41. This DUT41has input/output terminals41athat are held by a socket42in the chip testing system.

The DUT41can be an IC-chip by itself, and in that case the terminals41aextend directly from the IC-chip. Alternatively, the DUT41can be the combination of an IC-chip plus a substrate which is attached to the IC-chip. In that case, the terminals41aextend from the substrate. When the DUT includes a substrate, the DUT41can also include a cover which encloses the IC-chip and is attached to the substrate.

Initially in a chip testing system, the mechanical assembly10is positioned spaced-apart from the DUT41, as shown inFIG. 1. In that spaced-apart position, the DUT41and the heater21will ideally lie in parallel planes. However, due to various tolerances in multiple components within the chip testing system, the DUT41and the heater21will almost always lie at an unpredictable angle with respect to each other. For example,FIG. 1shows that the DUT41may be tilted in the socket42. As another example,FIG. 1also shows that the DUT41may have a non-uniform thickness.

From the spaced-apart position that is shown inFIG. 1, the mechanical assembly10is moved up, or the DUT41is moved down, by a predetermined distance in the vertical direction. This vertical movement can be performed by any prior art positioning mechanism (not shown) such as a robotic arm. As this vertical movement occurs, the heater21initially contacts one edge of the DUT41. Then as the vertical movement continues, the gimbal30and the attached heat-exchanger20tilt such that the heater21can lie flat against the DUT41.

FIG. 2shows the position of the heat-exchanger20, the gimbal30, and DUT41after the above vertical movement is complete. InFIG. 2, the spring33is compressed by a force which the positioning mechanism exerts against the base31in an upward direction, or against the DUT41in the downward direction. Consequently, the wide end32bof each carrier leg32ahas moved away from the base31, and that allows the carrier32plus the heat-exchanger20to tilt.

However, in order for the carrier32plus the heat-exchanger20to tilt so much that the heater21lies flat against the DUT41, the slideable coupling35on the coil spring33must slide relative to the carrier32from the initial position shown inFIG. 1to another position shown inFIG. 2. InFIG. 1, the initial position of the ball bearings35bis labeled A, B, C, and inFIG. 2the new position of ball bearings35bis labeled A′, B′, C′. As this sliding occurs, the spring33stays essentially vertical and the slideable coupling35stays essentially centered with the vertical axis of the spring33.

To closely analyze the forces and moments which cause the slideable coupling35to move, reference should now be made toFIGS. 3 and 4. InFIG. 3, two forces F1and F2are exerted as shown on the heat-exchanger20and the gimbal30, respectively. This occurs at the time instant when one edge of the DUT41initially contacts the heater21. The force F2generates a clockwise moment M1about point P.

By comparison inFIG. 4, four forces F1′, F2′, F3and F4, are exerted as shown on the heat-exchanger20and the gimbal30. This occurs at the time instant when the vertical movement of the DUT41toward the mechanical assembly10has been completed by the handler mechanism. The force F2′ generates a clockwise moment M1′ about point P, whereas the forces F3and F4generate a counter-clockwise moment M2about point P.

InFIG. 3, the force F1is exerted by the one edge of the DUT41that initially contacts the heater21. This force is shown as occurring in the −Y direction at a point P.

Also inFIG. 3, the force F2is exerted by the spring33. This force is shown as occurring in the +Y direction in alignment with the central axis33aof the spring33. The forces F1and F2are separated in the X direction by a distance d2. Consequently, the force F2produces the moment M1in the clockwise direction around the point P.

A mathematical expression50for the moment M1is derived by equation 1 inFIG. 3. In the expression50, kyis the spring constant in the Y direction for the spring33. Also in the expression50, ΔY is the amount by which the spring33is compressed in the Y direction from its undeformed length. Further in the expression50, the product (ky) (ΔY) is the force F2which is exerted by the spring33. When the assembly10is in the state shown inFIG. 1, a small ΔY produces a preload force F2that keeps the wide ends32bof the carrier legs32apressed against the base31.

Due to the moment M1, the gimbal30and the attached heat-exchanger20start to rotate in a clockwise direction. This rotation occurs about point P because at that point the heater21is held by friction against the edge of the DUT41. As this rotation occurs, another moment M2is generated, as shown inFIG. 4, which opposes the rotation.

As the gimbal30and the attached heat-exchanger20rotate clockwise, the ball bearings35bmove relative to the carrier32from the positions A, B, C to the positions A′, B′, and C′. This is shown inFIG. 4.

InFIG. 4, two forces F1′ and F3are exerted on the heater21by the DUT41. The force F1′ occurs at the initial point of contact P. The force F3occurs at the opposite edge of the DUT41, which is at a distance d3in the −X direction from point P.

Note that in actuality, the DUT41will exert a distributed force against the heater21at all points where the DUT41contacts the heater21. However, to simplify the present analysis, this distributed force is replaced inFIG. 4with the two equivalent point forces F1′ and F3.

Also inFIG. 4, two forces F2′ and F4are exerted on the slideable coupling35by the spring33. The force F2′ is due to the spring33being compressed to a new amount ΔY′ in the Y direction. The force F4is due to the spring33being deflected by an amount ΔX in the X direction at the point where spring33connects to the slideable coupling35. The deflection ΔX occurs as the carrier32and the attached heat-exchanger20rotate clockwise about point P.

InFIG. 4, the force F2′ produces the clockwise moment M1′ around the point P. A mathematical expression51for the moment M1′ is derived by equation 2 inFIG. 4.

Also inFIG. 4, the forces F3and F4produce the counter-clockwise moment M2around the point P. A mathematical expression52for the moment M2is derived by equation 3 inFIG. 4. In the expression52, kxis the spring constant for the spring33in the X direction.

When the mechanical assembly10is in a state of equilibrium inFIG. 4, the moments M1′ and M2are equal in magnitude. This is stated by equation 4 inFIG. 4. When that occurs, the expression51equals the expression52.

Also when expression51equals expression52, the force F3must be greater than zero. Otherwise, the DUT41will not be pressing flatly against the heater21. Therefore, setting expression51equal to expression52, and setting force F3to be greater than zero, yields equation 5. This equation must be satisfied in order for the DUT41to lie flat against the heat-exchanger20.

In equation 5, the term (kx)(ΔX) is the horizontal force F4which the spring33exerts on the plate35a. Also in equation 5, the term (ky)(ΔY′) is the vertical force F2′ which the spring33exerts on the plate35a. These forces F4and F2′ are shown inFIG. 4.

However, the same two forces F4and F2′ are also exerted by the ball bearings35bon the underside of the carrier32when any friction against the ball bearings is negligible. And, since the ball bearings35bcan roll on the carrier32, the vector sum of the two forces F4and F2′ must be perpendicular to the surface of the carrier32at the points A′, B′, C′. Otherwise, the ball bearings35bwill roll from those points.

Thus it follows that the horizontal force F4will always be small whenever the carrier32rotates by only a small angle in order for the DUT41to lie flat against the heater21. This means that the term (kx) (ΔX) in equation 5 will always be small. Consequently the condition which must be satisfied in order for the DUT41to lie flat against the heater21(as expressed by equation 5) is easily met.

It is important to realize that equation 5 cannot be met by simply making various terms in that equation larger or smaller, as desired. For example, the force (ky)(ΔY′) cannot be made so large that damage will occur to the DUT41. Also, the distance d2′ cannot be made larger than one-half the width of the DUT41. Further, the distance d4cannot be made so small that there is no room for the heater41, the conduit22, and the carrier32. In addition, as the overall length of the spring33is decreased in order to reduce the total height of the assembly10, the spring33becomes stiffer, which increases kx. But, with the present invention, all of these practical limitations are overcome by the slideable coupling35which causes ΔX to be small in equation 5.

Next, with reference toFIGS. 5 and 6, additional details regarding the slideable coupling35will be described. These figures show that the plate35ahas three indentations35c. In the illustrated preferred embodiment, each indentation35chas a semi-spherical shape with a radius that is larger than the radius of the ball bearings35b. One respective ball bearing35blies in each indentation35c.

Preferably, the plate35aand the ball bearings35bare made of materials that easily slip on each other. In one particular embodiment, the plate35ais made of a plastic such as Teflon, and the ball bearings35bare made of a metal such as steel.

Also in the illustrated preferred embodiment, the indentations35care spaced at equal distances from each other. These indentations35chave a geometric center35don the plate35a. The geometric center35don the plate35awill be close to, but slightly offset from, the central axis33aof the spring33, as shown inFIG. 5. This offset is caused by various tolerances with which the entire mechanical assembly10can be manufactured.

Suppose now, for comparison purposes, that the slideable coupling35inFIGS. 1 and 2is replaced with a rigid coupling34′ between the spring33and the carrier32. This change is shown inFIG. 7. All other components in the assembly10ofFIG. 7are the same as the components which have corresponding reference numerals inFIGS. 1 and 2.

InFIG. 7, the DUT41is being pressed against the heater21; however, the DUT41is not lying flat against the heater21. Instead inFIG. 7, only one edge of the DUT41presses against the heater21at the initial point of contact.

When the DUT41inFIG. 7contacts the heater21, the gimbal30starts to rotate in the clockwise direction due to the moment M1′ that was previously described in conjunction withFIG. 4. But that clockwise rotation is opposed by the counter clockwise moment M2that also was previously described in conjunction withFIG. 4.

One of the terms in the moment M2was shown by equation 3 ofFIG. 4to be (F4)(d4), where F4is the horizontal force that is exerted by the spring33. That horizontal force F4is limited in the embodiment ofFIGS. 1-2by the presence of the ball bearings35b. However, with the change that is made inFIG. 7, the ball bearings35bare eliminated; and consequently, the horizontal force F4which the spring33can exert on carrier32is not limited.

Thus inFIG. 7, the counter clockwise moment M2balances the clockwise moment M1′ before the DUT41lies flat against the heater21. In other words, the moments M2and M1′ balance while the force Fjis zero. This results in a gap between the DUT41and the heater21. Due to this gap, the temperature of the DUT41cannot be regulated accurately by the heat-exchanger20.

Next for comparison purposes, suppose that the plate35aofFIGS. 5 and 6is replaced in the assembly10with a different plate35a′ which has only a single indentation35c′ at its geometric center that holds a single ball bearing35b′. This change is shown inFIG. 8. All of the other components in the assembly10ofFIG. 8are the same as the components which have corresponding reference numerals inFIG. 1.

InFIG. 8, the spring33is in compression, and the DUT41is not exerting any force on heater21. Thus inFIG. 8, the wide end32bof each leg32ain the carrier32presses against the base31, and the single ball bearing35b′ presses against the carrier32.

However, when the single ball bearing35b′ inFIG. 8presses against the carrier32at a slight offset from the central axis of the spring33, the position of the ball bearing35b′ is unstable. That is because the ball bearing35b′ will roll on the base32unless the ball bearing35b′ is in perfect alignment with the central axis33aof the spring33. But from the prior description ofFIGS. 5-6it is evident that the single ball bearing35b′ will virtually never be perfectly aligned with the axis33aof the spring33.

Once the single ball bearing35b′ starts to roll on the carrier32, that movement will continue until one edge of the plate35a′ hits the carrier32. Then movement of the ball bearing35b′ will stop due to friction between the plate35a′ and carrier32. This position for the ball bearing35b′ and the plate35a′ is shown inFIG. 8.

But if the ball bearing35b′ cannot move on the carrier32, the connection between the spring33and the carrier32is in effect fixed just like it is inFIG. 7. Thus, a gap will occur between the DUT41and the heater21when the DUT41is pressed against the heater21.

Next, with reference toFIG. 9, one modification to the mechanical assembly10ofFIGS. 1-4will be described. In thisFIG. 9modification, the spring33together with the rigid coupling34and the slideable coupling35are rotated 180°. Thus inFIG. 9, the spring33has a fixed coupling34to the carrier32(instead of the base31), and the spring33has a slideable coupling35to the base31(instead of the carrier32).

All of the remaining components in theFIG. 9modification are the same as they are in the mechanical assembly10ofFIGS. 1-4. Those remaining components in theFIG. 9modification are identified with the same reference numerals that they have inFIGS. 1-4.

When the modified embodiment ofFIG. 9is in a quiescent state, the DUT41is spaced apart from the electric heater21. Thus, the wide ends32bof the legs32aare pressed against the base31due to the force exerted on the carrier32by the spring33. Also in that quiescent state, the ball bearings35bare at the positions A, B, C on the base31, as labeled inFIG. 9.

Thereafter, the DUT41and the mechanical assembly10are moved towards each other by a predetermined distance in the vertical direction.FIG. 9shows the position of the heat-exchanger20, the gimbal30, and the DUT41after this vertical movement is complete.

InFIG. 9, the heater21lies flat against the DUT41, and the ball bearings35bhave moved from the positions A, B, C to the positions A′, B′, C′. This movement of the ball bearings35bis caused by forces and moments which are similar to those that where previously analyzed in conjunction withFIGS. 3-4.

Next, with reference toFIGS. 10 and 11, a second modification to the mechanical assembly10ofFIGS. 1-4will be described. In this modification, the slideable coupling35ofFIGS. 1-4is replaced with a solid plate35′. The plate35′ has one face that is rigidly attached to the spring33and an opposite face that has a small coefficient of friction such that it easily slides on the carrier32.

All of the remaining components in the modification ofFIGS. 10-11are the same as they are in the mechanical assembly10ofFIGS. 1-4. These remaining components in the modification ofFIGS. 10-11are identified with the same reference numerals that they have inFIGS. 1-4.

When the modified embodiment ofFIGS. 10-11is in a quiescent state, the DUT41is spaced apart from the electric heater21. Thus, the wide ends32bof the legs31aare pressed against the base31due to the force exerted on the carrier32by the spring33. Also in that quiescent state, the edges of the solid plate35′ are at the positions A and C on the base31, as shown inFIG. 10.

Thereafter, the DUT41and/or the mechanical assembly10are moved towards each other by a predetermined distance in the vertical direction.FIG. 11shows the position of the heat-exchanger20, the gimbal30, and the DUT41after this vertical movement is complete.

InFIG. 11, the heater21lies flat against the DUT41, and the edges of the plate35bhave moved from the positions A, C to the positions A′, C′. This movement of the plate35b′ is caused by forces and moments which are similar to those that where previously analyzed in conjunction withFIGS. 3-4.

One preferred embodiment of the present invention, and two preferred modifications, have now been shown in the figures and described in detail. In addition, however, other modifications can also be made which will now be described with reference to those same figures.

For example, inFIGS. 10 and 11, the spring33together with the slideable plate35b′ and the rigid coupling34can be rotated 180°. With this modification, the plate35b′ slides on the base31, whereas the rigid coupling34is between the spring33and the carrier32.

As another example, inFIGS. 5 and 6, the indentations35cand respective ball bearings35bcan be increased to any desired number greater than three. This modification can be incorporated into the assembly10ofFIGS. 1-2and/or the assembly10ofFIG. 9.

As still another example, the rigid coupling34between the spring33and the plate35inFIGS. 1,2, and9, can be implemented as desired. In one particular implementation, the spring33is welded or brazed to the plate35. In another implementation, the spring33is held to the plate35with screws or other similar fasteners. In still another implementation, the spring33is held to the plate35by protrusions from the plate35around the spring, or an indentation in the plate35, or simply by friction.

As yet another example, the heat-exchanger20that is shown in the embodiments ofFIGS. 1,2,9,10and11can be replaced with any other type of heat-exchanger. As one such modification, the electric heater21can be deleted. In that case, the conduit22gets pressed against the DUT41, instead of the heater21getting pressed against the DUT41. Also, the conduit22can be one which passes coolant that stays in a liquid state between the input port22aand the output port22b, or the conduit22can be one which changes the coolant from a liquid state to a gas state between the input port22aand the output port22b.

As still another example, the spring33inFIGS. 1,2,9,10and11can be a cylindrical coil spring, instead of the conical coil spring that is shown. Also, the spring33inFIGS. 1,2,9,10and11can be one which lies only in the plane of those figures. Such a spring inFIG. 1could extend upward from the base31, then loop in the plane ofFIG. 1, and then continue upward to the plate35a. Alternatively, this loop in the plane ofFIG. 1could be replaced with a “C” shaped bend.

As another example, a lubricant can be coated on the ball bearings35binFIGS. 5 and 6in order to reduce any friction which is exerted on those ball bearings. Similarly, a lubricant can be coated on the surface of the plate35′ inFIGS. 10 and 11in order to reduce any friction which is exerted on that plate by the carrier32.

Accordingly, it is to be understood that the present invention is not limited to just all the details of one particular embodiment, but is defined by the appended claims.