WO2009117900A1

WO2009117900A1 - A clamp for the heat sink of the chip

Info

Publication number: WO2009117900A1
Application number: PCT/CN2009/000318
Authority: WO
Inventors: 吴力航; 彭勃
Original assignee: Wu Lihang; Peng Bo
Priority date: 2008-03-26
Filing date: 2009-03-26
Publication date: 2009-10-01
Also published as: CN201171048Y

Abstract

A double clamp for the heat sink of the chip, include: a substrate (2) with a chip (7) and a heat sink (1), characterized in that: there are the upper spring (3) and the lower spring (4) on the upper and the lower surface of the substrate (2); the upper spring (3) and lower spring (4) connect with the substrate (2) and make the resultant bending moment of the upper spring (3) and lower spring (4) relative to the substrate (2) and the heat sink (1) zero.

Description

Chip heat sink clamping structure

The present invention relates to a clamping structure, and more particularly to a double spring type clamping structure for a chip heat sink.

Background technique

The BGA package chip directly mounted on the main board is very sensitive to the deformation of the substrate, and it is easy to destroy the plane coplanarity between the chip pad and the substrate due to the deformation of the substrate, so that the tantalum between the chip and the substrate Cracks or even shearing occur due to the tensile stress and shear stress occurring in the deformation of the substrate, which deteriorates the electrical continuity of the solder joint and causes electrical failure. Therefore, it is very important to prevent the warpage of the substrate during use in the electrical board produced by BGA plus SMT technology.

Since the chip emits a large amount of heat during operation, a local high temperature region having a temperature much higher than other portions appears on the chip portion on the substrate. The substrate material in this local high temperature zone is inevitably thermally expanded, but the substrate material to be expanded is limited by the substrate material in the lower temperature region. It is free to freely extend along the plane of the substrate, which will cause this. The substrate of the high temperature portion has only two upward and the lower free surface directions (because there is no deformation constraint in the normal direction of the substrate), and the warp deformation of the protrusion or the depression forms a partial protrusion or depression. At the same time, as the temperature rises, the deformation resistance of the substrate material also decreases. Therefore, this high temperature zone is again a partial "softening zone" on the substrate. When the protrusion of the chip is deformed, the defect near the middle of the chip is pulled by the pulling force; when the deformation of the recess occurs, the solder joint near the outer edge of the chip is pulled off by the pulling force. In general, since the die pad material and the substrate material have different coefficients of thermal expansion, the defect is subjected to tensile stress in the deformation of the substrate and is also subjected to shear stress. This comprehensive state of stress is one of the most dangerous stress states that are most prone to dislocation. Some high-power chips in electronic devices require special heat sinks for them. The clamping structure for fixing the heat sink on the chip directly applies a continuous force to the substrate, and the fixing manner of the clamping structure determines the force state on the substrate. It is conceivable that in the absence of the force of the heat sink clamping structure, whether the deformation of the substrate caused solely by thermal expansion is upward or downward is a random result. However, under the force exerted by the heat sink clamping structure, the tendency of the substrate to thermally expand and deform will be induced by the force exerted by the clamping structure and have a certain deformation direction. The mechanical structure of the conventional heat sink clamping structure not only does not inhibit this thermal deformation warping, but is often the promoter of such deformation. At the same temperature, the greater the force applied by the clamping structure, the greater the degree of deformation of the substrate, the faster the process of deformation, and the shorter the time required for the final failure of the defect.

The various chip heatsink clamping structures currently used in practice, although in many different forms, are mechanically superior in terms of "pull prestressing type" and "zero prestressing type" - type. The pull pre-stressed clamping structure is fixed on the substrate by direct or indirect connection, so that a pulling force on one side of the substrate is always applied to the substrate, and the pulling force is to promote the substrate at the chip. The inducing force of warping deformation in this direction. The effect of the effect and the effect of the depression caused by the heat generated by the chip are superimposed, which aggravates the severity of the warpage deformation of the substrate. The zero pre-stressing type clamping structure is a single spring type structure which does not apply a force to the substrate, but forms a clamping force between the heat sink body inside the holding structure itself and the support point under the substrate. Although it does not pre-stress the substrate, it acts on the heat sink body with a bending moment that causes the heat sink body to bend. At the same time, it does not provide any correction for substrate deformation (free thermal expansion deformation) caused purely by local high temperature. Therefore, the main board of the heat sink is fixed by the clamping structure, and the substrate, especially the heat sink body, can still be thermally deformed (the deformation of the heat sink body is also an important cause of deformation of the substrate).

The force characteristics of the two types of clamping structures mentioned above refer to their opposite substrate and heat sink body. The continuous force of action causes deformation to cause the weld to fail. In fact, there is another important mechanical factor that causes the chip solder joint to fail. This is the fatigue damage of the solder joint caused by the reciprocating stress. As the chip works or stops working, the temperature of the chip part changes, and the thermal expansion protrusions and depressions change accordingly, thus forming an alternating stress that varies with the temperature of the chip. This alternating stress causes fatigue damage of the chip solder joint. And make it invalid. It is not difficult to imagine that since the above two types of existing clamping structures do not have the correcting function for the deformation of the substrate protrusions (or depressions), they cannot eliminate even the fatigue load which is relieved.

It can be said that the force application state of the chip heat sink clamping structure is one of the two decisive factors that cause the substrate deformation factor, and the only one that can be modified by human active design. By properly designing the state of application of the clamping structure to the substrate, it is possible to minimize the damage of the substrate by thermal deformation. It can even be turned out to be a favorable factor, which in turn can turn the chip into a large amount of heat and the substrate is easily deformed, which can be more effectively prevented from deforming the substrate. SUMMARY OF THE INVENTION The present invention is directed to a design concept of a chip heatsink holding structure having such a technical feature and a specific embodiment thereof. Summary of the invention

The invention aims to reasonably design the state of the force applied by the clamping structure to the substrate, and proposes a double spring type clamping structure for the chip heatsink which can automatically provide the thermal deformation correcting force of the substrate, so as to instantaneously and automatically deform the substrate. Corrects and reduces the fatigue load on the solder joints, effectively preventing the BGA chip solder joints from being dislocated.

The double-spring type clamping structure for the chip heat sink of the present invention comprises a substrate on which a chip and a heat sink are mounted, wherein an upper spring and a lower spring are respectively arranged on the upper and lower surfaces of the substrate, and the upper spring and the upper spring a lower spring is coupled to the substrate and the upper spring and the lower spring are combined with the base plate and the heat sink The moment is zero.

Further, the dual-spring type clamping structure for the chip heat sink includes upper and lower springs respectively located on the lower and lower sides of the substrate, and the upper and lower springs are connected by two holes located on the substrate. a pair of two links, and a fixed structure for fixing the link to the hole.

As the springs on the upper and lower surfaces of the substrate which provide the clamping structure clamping force and the substrate deformation correcting force main body, the mechanical state of the mounting method relative to the substrate is an important key to the function of the clamping structure. The principle is that the mounting of the upper spring and the lower spring on the substrate must ensure that they maintain a state in which the bending moment is zero, whether it is relative to the substrate or to the heat sink fixed thereto. The fixed points of the upper spring and the lower spring on the substrate are outside the high temperature region away from the chip position, and the plane position determined by these mounting points is the position where the bending moment of the double spring system is zero. As for the specific technical method of fixing the upper and lower springs to the substrate, it can be in various forms. For example, the spring is directly fixed to the substrate: !:, the upper and lower springs are connected by a connecting member and then the connecting member is fixed to the substrate.

Further considering that the appliance is in use, even if the fixing of the D hole position in which the bending moment is zero is correctly determined at the initial installation, the fixing is still likely to occur over time due to the fastener itself. And the change caused by the creep of the substrate. Therefore, the upper elastomer or (and lower elastic) support points of the present invention are made adjustable. Can be adjusted according to the offset of the actual balance position

(or below) the relative position of the support point to the position of the D hole. This further calibrates the offset of the D-hole plane position that occurs gradually during use of the appliance. This adjustable fulcrum structure is shown in Figure ³ .

To sum up, this double spring clamping structure has three structural features that are not available in all current clamping structures and therefore have a unique function. The three structural features are as follows -

1. Double Spring - The double spring provides a function of fixing the heat sink on the surface of the chip while also providing an elastic force capable of correcting the deformation of the substrate. The double spring can take any shape, Any material made of elastomer. The upper and lower elastic bodies are not limited to the same amount of elastic force, and the elastic material is not limited to be the same material. It is only necessary to ensure that the second point structure is implemented when the two springs are in elastic balance. After the D point in the feature is fixed, the function of correcting the deformation of the substrate of the clamping structure can be realized.

2. Fixed at point D (ie, hole 5 in Figure 1)—The fixation of point D provides the reference plane position for correcting the deformation of the substrate in the dual spring system. The D point may be a hole in the substrate or other reliable non-deformable fixing point which is outside the substrate but which is always constant with respect to the horizontal position of the substrate.

3. Adjustable head on the spring body - The adjustable head can further adjust and correct possible changes in the position of the D point that occurs during long-term use of the motor. The adjustable apex can be located only on the upper or lower elastic body, or on the upper and lower elastic bodies at the same time.

The upper and lower springs are springs having the same, similar elastic modulus, which maintains the clamping structure in a "zero pre-stressed" state at all times.

The upper and lower springs include a steel spring, a copper spring, a rubber spring, and a spring

Dragon springs. The spring should use a material with a high modulus of elasticity as much as possible. Under the same degree of substrate deformation, the clamping structure can provide the largest possible correction force.

The fixing structure comprises a back cap type fixing structure, a bonding fixing structure, and a hole locking knot

Structure.

The connection of the upper and lower springs to the substrate can also be connected by a "linkless" connection, such as bonding, snapping, and the like.

The hole is disposed away from the chip mounting position and is a low temperature region on the substrate, that is, a high deformation resistance region on the substrate. ' The hole includes a circular hole, an elliptical hole or a rectangular hole.

The connecting rod includes a screw for a back cap type fixing structure, and a light for bonding the fixing structure

Spring-loaded connecting rod for rod and hole locking structure.

The connecting rod includes a metal connecting rod and a rigid plastic connecting rod, which cannot be deformed by itself.

The function is to connect the upper and lower springs through the holes or to connect the upper and lower springs to form the clamping elastic force; the other is to fix the upper and lower springs on the substrate in the elastic balance state.

The plug on the adjustable spring includes a hard plastic tip having a threaded adjustment structure, the head being positionable on both the upper and lower springs, or an adjustable head on only one spring.

The beneficial effects of the present invention compared to the prior art are:

The structure is simple and the manufacturing cost is low. Since the correcting force against the thermal expansion deformation of the substrate is provided, it is equivalent to reducing the thermal expansion coefficient of the substrate material. Since the position of the D hole is fixed by the clamping structure, it also provides the expansion deformation constraint in the plane direction of the substrate, thereby reducing the difference in thermal expansion coefficient between the substrate material and the die pad material, thereby also reducing the chip defect. The degree of damage between the disk and the substrate due to the difference in thermal expansion coefficient. Especially for substrates which have never been used, i.e., have not undergone any deformation, it is best to prevent deformation in the future from being used. At the same time, it makes it possible to use an inexpensive PCB substrate with low deformation resistance and softening in actual production, which can reduce the manufacturing cost of the product.

In addition to being used as a clamping structure for fixing the chip heatsink, the clamping structure can also be single

The sole use is to correct the clamping structure for the purpose of correcting the deformation of the substrate. It can instantly and automatically correct the deformation of the substrate, effectively preventing the BGA chip solder joints from being desoldered. Its innovation

The main points are not only the double spring type improvement of the upper and lower springs, but also the substrate.

In addition, a fixed point to the clamping structure itself and an adjustable spring head are added. Fixed point protection on the substrate The upper and lower springs are always in the state of elastic balance, so that an elastic system that is automatically balanced is established inside the clamping structure itself and relative to the substrate. When the plate is not deformed, the elastic system is in equilibrium, and will not be right. The substrate applies a sustained force in any warping direction. When the substrate is deformed by protrusions or depressions in either direction, the balance of the elastic system is broken, and the elastic system instantly provides an additional correction force opposite to the deformation direction to automatically correct the deformation. . The greater the degree of deformation of the substrate, the faster the corrective force is automatically increased simultaneously. It can be seen that the clamping structure capable of automatically providing the correcting force can effectively prevent the warpage deformation of the substrate caused by heat or only the receiving side, thereby always ensuring the BGA chip and the substrate. The plane coplanarity. The adjustable head can further eliminate the deviation of the "zero pre-stress" condition caused by the inevitable stress relaxation of the clamping structure, so that the clamping structure can always be in an ideal working state.

The double spring type clamping structure of the invention is essentially a "zero pre-stressing" clamping structure, and does not generate any inducing force for creeping the substrate, even if the substrate at the chip is deviated from the planar state, It is also possible to correct the deformation instantly and automatically. For the alternating fatigue load due to temperature change, it is also due to the function of instantly correcting the deformation of the substrate, and it can also greatly reduce the stress amplitude of the alternating stress, thereby effectively reducing the risk of fatigue damage of the chip solder joint. By adopting the clamping structure with such a function, the electric device can maintain good planar coplanarity between the chip and the substrate in the long-term use, and effectively eliminate the chip solder joints caused by the deformation and stress fatigue of the substrate. Awkward phenomenon.

All of the foregoing is a general introduction to the clamping structure of a dual spring type chip heatsink. Specifically, in terms of the repair of the "three red lights" failure of Microsoft's X box360 game console, there are two other points that need special explanation.

1. The actual deformation of the GPU chip in a machine with three red faults

When the heat sink is thick enough to ignore the deformation of the heat sink itself, it can be considered as just The substrate undergoes thermal expansion deformation and the chip itself does not deform. In the actual situation, especially in the case of a compact space, due to the weakness of the heat sink body size, creep deformation is highly prone to occur, so that it is impossible for the chip body itself to be completely deformed, but only to a degree comparable to the substrate. Be slightly more. Now I am at

The GPU heatsink clamping structure used in the Xbox360 is a single spring clamping structure. Although the principle is a "zero pre-stressed" clamping structure, this "zero pre-stressing" actually refers to the force applied to the substrate. In the case of "zero pre-stressing", the force state on the fin body is not "zero pre-stressing" in the interior of the clamping structure, but is always subjected to the bending moment of the four corners and the top of the center. of. That is, the elastic force of the single spring clamping structure always exerts a bending moment on the heat sink body. Since the thickness of the heat sink body is small (after the height of the heat sink comb is removed, the thickness of the heat sink body root is only about 4 mm), and the material used for the heat sink is an extruded aluminum alloy material having a low creep strength. It is prone to creep deformation. Therefore, under the combined action of the spring force of the spring and the long-term high temperature of the chip, permanent bending deformation of the heat sink itself is inevitable. In fact, almost all of the alloy fins removed from many three red machines have found that they have indeed undergone significant bending deformation. From the case of the GPU chip itself of the three red machine, the deformation of the aluminum heat sink on the top of the chip itself has also caused the chip itself to be deformed. From the measurement of the GPU chip on some three red machines, it is found that the outer surfaces of the main and secondary cores on the chip are no longer on the same plane, and the surface of the large main core in the center is already significantly higher than the side. The surface of the small core has a height misalignment of 0.21-0.12 mm. That is to say, a three-red GPU chip has undergone a warping deformation of the protrusion itself. It reflects the fact that the chip and its motherboard have been warped.

It can be seen that the Xbox360 mainframe is in actual use. Due to the unreasonable design of the existing heat sink and its clamping structure, the heat sink, the GPU chip and the substrate are inevitably deformed. The biggest deformation may lead to the dislocation of the solder joint between the chip and the motherboard. Secondly, the circuit inside the chip may also change. Destroyed in shape. It is not difficult to imagine that even if the heat sink and the chip itself are deformed, the deformation on the substrate is more complicated and serious.

2. The mechanical structure of the GPU heat sink clamping structure is unreasonable

As mentioned above, the "four-cornered intermediate top" is the mechanical structure of the current heat sink clamping structure, which causes the bending deformation of the heat sink body and the deformation of the chip. Although the double spring clamping structure is equivalent to a single spring zero prestressing type clamping structure when the point D on the substrate is not fixed, there is a significant difference between them. Double spring type clamping structure, it is easy to see that since the upper and lower springs are oppositely applied with the clamping force according to the center line, the force is collinear. Unlike the current single spring clamping structure, the forces on the upper and lower faces are misaligned and not collinear. In addition, the four connecting springs on the double spring type clamping structure are not fixed on the heat sink like the existing clamping structure, and they are freely passed through the holes in the heat sink. Therefore, this double spring clamping structure does not exert a bending force on the heat sink body itself. Even if the automatic deformation of the substrate deformation function brought about by the fixing of the D point is not considered, the rationality of the force condition is only mentioned. The double spring type clamping structure is also much better than the current one. Single spring clamping structure.

This "center-to-top" urging structure of the double spring type clamping structure is of great importance and irreplaceable for the thin electronic device. Because of the limited space in thin electrical appliances, the chip fins can only be made into a thin plate shape, so the ability of the fin itself to resist creep deformation is inherently insufficient due to its dimensional characteristics. Only the center-to-top force application method can completely eliminate the deformation of the heat sink itself, thereby preventing the chip and the motherboard from being deformed.

In summary, in the current clamping structure of the Xbox360, the GPU heatsink clamping structure not only does not automatically correct the deformation of the motherboard, but will cause deformation of the motherboard or even the chip and the heat sink itself due to the weakness of the heat sink (although The same clamping method is used at the CPU, and there is no correction work. Yes, but due to the thickness of the heat sink, the deformation of the motherboard is much more). So say, for

For the Xbox360's GPU chip heatsink and other chip heatsinks in thin and light electronic devices such as laptops, this dual-spring chip heatsink clamping structure will highlight the significant advantages it can't be replaced.

Finally, I talked about the repair of the Xbox360 with three reds using the double spring type clamping structure. Through practice, it has been proved that this clamping structure is really effective for eliminating the "three red light death" fault caused by the GPU's desoldering. For example, an Xbox 360 game console purchased on July 14, 2006, for the first time in 11 months, experienced three red light failures. Although various methods of eliminating the deformation of the main plate at the GPU are employed, the three red light failures can be temporarily eliminated, but it is not long before the failure still recurs. After correcting the deformation of the main board and restoring the electrical contact of the solder joint to eliminate the three red light phenomenon, the double spring type clamping structure is installed, and the machine does not add any additional cooling measures to maintain the original machine. Cooling settings. After the clamping structure was installed, the machine has been used for more than 9 months, and no three red light failures have occurred. During the period, various tests were considered to be the most prone to three red light failures. Such as,

Rapid cooling test: After the machine has been running for a period of time, the internal temperature is still high. Immediately power off and put the machine into a refrigerator of about 5°. After it has cooled down, immediately restart the machine. As a result, three red lights did not appear in the same three tests, and the machine could be started and run normally every time.

Long-running game test: Running the game for 17 hours in an environment with a temperature of 40° and no air conditioning. Although there have been two crashes during the period, it can run normally immediately after the shutdown is restarted. No three red light failures occurred.

Long time to stand still does not boot test: According to quite a lot of game console users, Xbox360 game master After the machine has been used, if it is not turned on for a long time (several days), it will have three red light failures when it is turned on again (most of the "three red machines" appear in this case). For this point, the repaired machine was carried out several times, each time for a 10-day rest test. One is in the summer of high temperatures; the other is in the winter when the temperature is close to zero. There were no three red lights.

DRAWINGS

1 is a schematic structural view of a specific embodiment of the present invention;

Figure 2 is a top plan view of Figure 1;

Fig. 3 is a schematic view showing the structure of another embodiment in which an adjustable plug is attached. '

detailed description

The high-power BGA chip heatsink 1 shown in FIG. 1, FIG. 2, and FIG. 3 uses a double-spring type clamping structure, and includes an upper spring 3 and a lower spring 4 respectively on the upper and lower sides of the substrate 2, and the upper spring 3 The lower spring 4 passes through the connecting rod 6 which is connected to the hole 5 on the substrate 2, and the back cap type fixing structure which fixes the connecting rod 6 to the hole 5.

The upper spring 3 and the lower spring 4 are steel springs having the same, similar elastic modulus, which can maintain the "zero pre-stress" state of the clamping structure and provide the largest possible correction force.

The hole 5 is disposed away from the mounting position of the BGA chip 7, and is a low temperature region on the substrate 2.

That is, the high deformation resistance zone of the substrate 2.

The connecting rod 6 is a metal screw for a back cap type fixing structure, and the connecting rod 6 is fitted by the back cap 8

Fixed to the substrate 2.

The adjustable head 9 is a threaded adjustable hard plastic head on the spring that can be adjusted to adjust the relative horizontal position of the head relative to the spring fixed point D by rotating the threaded body.

The above is a further detailed description of the present invention in conjunction with a specific preferred embodiment, It is to be understood that the specific embodiments of the invention are limited only by the description. For those skilled in the art to which the present invention pertains, a number of simple derivations or substitutions may be made without departing from the inventive concept, and should be considered as belonging to the invention as defined by the appended claims. protected range.

Claims

Rights request

A double-spring type clamping structure for a chip heat sink, comprising a substrate on which a chip and a heat sink are mounted, wherein an upper spring and a lower spring are respectively disposed on the upper and lower surfaces of the substrate, and the upper spring and The lower spring is coupled to the substrate and the bending moment of the upper spring and the lower spring relative to the substrate and the heat sink is ordered.

2. The dual spring type clamping structure for a chip heat sink according to claim 1, comprising: an upper spring and a lower spring respectively located on the lower and lower sides of the substrate, wherein the upper and lower springs are located at the Two pairs of holes connected to the holes on the substrate, a pair of two links, and a fixing structure for fixing the links to the holes.

3. The double spring type clamping structure for a chip heat sink according to claim 2, wherein: the upper and lower springs are located, or only one of the springs is provided with a hard plastic thread adjustable top, which can be changed by adjusting the thread. Its apex is relative to the position of the spring fixed point.

The double spring type clamp structure for a chip heat sink according to claim 2, wherein the upper spring and the lower spring are springs having the same and similar elastic modulus.

The double spring type clamp structure for a chip heat sink according to claim 2 or 3, wherein the upper spring and the lower spring comprise a steel spring, a copper spring, a rubber spring, and a nylon spring.

The double spring type clamping structure for a chip heat sink according to claim 5, wherein the fixing structure comprises a back cap type fixing structure, a bonding fixing structure, and a hole locking structure.

7. The dual spring type clamping structure for a chip heat sink according to claim 5, wherein the hole is disposed away from the chip mounting position. '

8. The dual spring type clamping structure for a chip heat sink according to claim 6, wherein the hole comprises a circular hole, an elliptical hole, and a rectangular hole.

The double spring type clamping structure for a chip heat sink according to claim 7, wherein the connecting rod comprises a screw for a back cap type fixing structure, a polished rod for bonding a fixing structure, and a hole locking structure. A connecting rod with a spring piece.

10. The dual spring type clamp structure for a chip heat sink according to claim 8, wherein the link comprises a metal link and a rigid plastic link.