Mounting system for high-mass heatsinks

A system for mounting heatsinks, in particular, high-mass heatsinks, on printed circuit boards, such as motherboards. The mounting system includes a backplate, disposed beneath the motherboard, with pins protruding up through the motherboard, and a linkage assembly, which is fixably attached to a base portion of a heatsink assembly. The linkage assembly includes scoops, for grasping the pins during engagement, and a ratcheting system, for compressing the heatsink and thermal interface material onto the package. The mounting system is designed to effectively distribute the heatsink weight, as well as the forces caused by chronic and dynamic stresses, through, rather than upon the motherboard, such as to a chassis. The mounting system thus alleviates stress cracks, component pullout, solderball stress, and other damaging conditions to the motherboard. The mounting system may be engaged and disengaged without the use of tools.

FIELD OF INVENTION

This invention relates to heatsinks, and, more particularly, mounting systems for heatsinks.

BACKGROUND OF THE INVENTION

Semiconductors, including microprocessors and other integrated circuits (ICs), generate heat during use. Current microprocessors, for example, can emit 50 watts of power or more. The temperature of the microprocessor or IC has a direct impact upon its performance. Empirical studies have shown that the failure rate doubles for every 10° C. increase in the junction temperature (i.e., the temperature of a transistor within the IC).

Unless microprocessors and other ICs are thermally managed during use, they will not operate reliably. Failures include phenomena such as junction fatigue, electromigration diffusion, thermal runway, and electrical parameter shifts. For most uses of a semiconductor device, a proper mechanism for heat dissipation is needed.

Heat may be transferred from the semiconductor by convection, radiation, or conduction. Convection is the transfer of heat by moving air. Radiation is the transfer of heat from one surface to another via electromagnetic waves. Conduction is the transfer of heat between two solids, from a higher temperature object to a lower temperature one. Each of these principles may have a part in the operation of heatsinks.

Heatsinks are devices that attach directly to a microprocessor or other hot surface to enhance heat dissipation from the surface. Heat flows from the surface to cooler air through the heatsink. A heatsink is generally designed with a first surface, for engaging directly with the microprocessor, and a second surface, for contact with the cooler air. The second surface, often formed of a plurality of projections or fins, is designed for maximum surface area, and thus maximum contact with the air, to allow heat to dissipate more quickly. The second surface may also include channels, cooling towers, tubes, cold plates, fans, refrigeration systems, or other embedded features.

Typically, a thermal interface material (TIM) is disposed between the heatsink and one or more microprocessors, known as a processor package, or package. The TIM is a synthetic pad composed of materials such as silicon or zinc oxide, which conducts heat away from the microprocessor and toward the heatsink. The TIM achieves this, in part, by evenly distributing the physical contact between the heatsink and the microprocessor.

During operation of a computer or other processor-based system, the package heats up the TIM, which conducts the heat to the surrounding heatsink. The metal in the heatsink conducts the heat to the fins, channels, tubes, or other embedded cooling elements. Where present, the heatsink fan blows air past the cooling elements to dissipate the heat to the ambient air.

One consideration when designing a heatsink is weight. Although copper-based heatsinks may be preferred over aluminum due to better heat transfer results, copper is a heavier material. A typical copper-based heatsink with a fan, for example, is over 500 grams in weight.

A motherboard or other printed circuit board (PCB) within the computer or other processor-based system typically supports the weight of the heatsink. A larger heatsink thus imposes greater stress on the motherboard than a comparable heatsink of smaller mass. A 450-gram heatsink has been shown to deflect a PCB, which can cause component damage as well as damage to the PCB traces and solder pads. Such chronic stresses can cause cracks or component pullout holes, which may damage the electrical circuitry or signal traces, possibly rendering the computer system defective or inoperable.

Dynamic stresses, such as those caused by shipment and other handling, impose particular constraints on computer systems having high-mass heatsinks. Computer systems are expected to arrive at the customer intact, despite rough handling, for example. The forces resulting from dynamic stresses may damage the motherboards that are supporting the larger heatsinks. Stress cracks, component pullout, solderball stress, or other damage to the electrical circuitry may result from such dynamic loading.

Thus, there is a continuing need for a heatsink mounting system that structurally supports large heatsinks while avoiding damage to the system motherboard during both normal operation and dynamic loading conditions.

DETAILED DESCRIPTION

In accordance with the embodiments described herein, a mounting system is disclosed that firmly mounts a heatsink to a processor on a motherboard, such as for a computer or other processor-based system. The mounting system is designed to alleviate chronic and dynamic stresses that may be imposed on the motherboard, stresses which are particularly associated with high-mass heatsinks. As used herein, high-mass heatsinks are defined to be heatsinks that weigh 400 grams or more, and, more particularly, those that weigh at least 700 grams.

Chronic stresses are defined herein to be those stresses that result from the continuous weight of the heatsink itself during normal use of the computer or other processor-based system, as well as stresses caused by the vibration of the heatsink, such as may be caused by an oscillating fan. Dynamic stresses, by contrast, are defined to be those stresses generally associated with the transportation and handling of a computer or other processor-based system, such as when the computer system is moved during shipment, and may result from such events as dropping or bumping the system.

In the following detailed description, reference is made to the accompanying drawings, which show by way of illustration specific embodiments in which the invention may be practiced. However, it is to be understood that other embodiments will become apparent to those of ordinary skill in the art upon reading this disclosure. The following detailed description is, therefore, not to be construed in a limiting sense, as the scope of the present invention is defined by the claims.

FIG. 1is an exploded perspective view of a mounting system100, according to some embodiments. The mounting system100includes a linkage assembly140and a backplate10, for securing a heatsink assembly130upon a motherboard110. A package120is disposed upon the motherboard110, and may include one or more, processors and a thermal interface material (TIM). The package120is the source of heat on the motherboard110and the heatsink assembly130is designed to conduct heat away from the package.

As will be shown, the mounting system100securely and evenly couples the heatsink assembly130to the package120, for efficient transfer of heat from the package. The mounting system100further distributes the weight of the heatsink assembly through, rather than upon, the motherboard, to the backplate10, thus reducing the adverse effects of both chronic and dynamic stresses.

The backplate10is a rigid structure that includes a plurality of transversely disposed mounting pins15. The backplate10may be composed of metal, such as aluminum, and may be a solid plate, a rectangular structure, such as inFIG. 1, a cross-bar structure, a circular structure, or may conform to a variety of other shapes. The backplate10may be an autonomous structure or it can be mounted to a chassis or other structure.

The backplate10is disposed beneath the motherboard, with the mounting pins15facing the motherboard. The motherboard110includes a plurality of holes112, through which the mounting pins15are inserted. The heatsink assembly130includes a body195and a base portion190, the width of the body being smaller than the width of the base portion. Like the motherboard110, the base portion190features a plurality of holes215for receiving the mounting pins15. The holes215in the heatsink base195and the holes112in the motherboard110have substantially the same spatial configuration and are aligned with one other, as well as with the mounting pins.

Although the body195of the heatsink assembly130is depicted as a simple, featureless structure, the heatsink body195may also include fins, channels, tubes, embedded fans, top-mounted fans, and other cooling elements not shown inFIG. 1. The base portion195of the heatsink assembly130may include a cavity (not shown), which is approximately the size of the package120mounted on the motherboard110. The base portion195of the heatsink assembly130is not thicker than the package120. These dimensions ensure that the heatsink body190makes direct contact with the package120when the mounting system100is fully engaged. An evenly distributed contact between the heatsink body190and the package120ensures efficient conduction of heat away from the package.

The mounting pins15attached to the backplate10are inserted through the loose-fitting holes112in the motherboard, then through the holes215in the heatsink assembly130, so as to protrude above the base portion195of the heatsink assembly.

When the mounting system100is engaged, the linkage assembly140, which is fixably attached to the base portion195of the heatsink assembly, latches through the mounting pins15, to securely unite the heatsink assembly130to the package120on the motherboard110. In this manner, the heatsink assembly130is tightly and evenly coupled to the package120. A fully engaged mounting system100is depicted inFIG. 2.

The linkage assembly140is a mechanical assembly that, when engaged, compresses the heatsink assembly130onto the package120. The linkage assembly140includes a structural assembly and a ratchet assembly. The structural assembly includes scoops20A,20B,20C, and20D (collectively, scoops20), rotational rods60A and60B (collectively, rotational rods60), partially thread bolts55, and pressure blocks65A,65B,65C, and65D (collectively, pressure blocks65). The ratchet assembly includes a ratchet handle35, ratchet gears30, ratchet springs40, a ratchet bar45, a secondary ratchet handle50, rotational pins70, and a latch75.

The pressure blocks65are fixably attached to the base portion195of the heatsink assembly130, allowing the other features of the structural assembly to essentially surround the heatsink body190, during both engagement and disengagement. The pressure blocks65may be attached to the base portion195using a high-temperature adhesive, weld, screws, or other material for securely and permanently affixing them. InFIG. 1, the pressure blocks65are disposed proximal and adjacent to the holes215, as indicated by the dotted lines. However, other configurations of the pressure blocks are possible, so long as the linkage assembly140is fixably mounted to the base and surrounds the body of the heatsink assembly.

The rotational rods60are each threaded through two of the pressure blocks65. The rotational rod60A is threaded through the pressure blocks65A and65B while the rotational rod60B is threaded through the pressure blocks65C and65D, such that the rotational rods are transverse to the pressure blocks. The rotational rods60are preferably made from a sturdy, yet lightweight, material, such as aluminum or titanium, or a composite material designed for strength and low weight.

The ratchet handle35is coupled to the rotational rod60A by way of a cylindrical end member185, while the secondary ratchet handle50is similarly coupled to the rotational rod60B. A ratchet bar45connected between the ratchet handle35and the secondary ratchet handle50ensures that when the ratchet handle35is moved, the secondary ratchet handle50moves in a substantially similar fashion. A pin70is disposed transversely through a lower portion of the ratchet handle35, for pivotable connection to one end of the ratchet bar45. A second pin70is disposed transversely through a lower portion of the secondary ratchet handle50, for pivotable connection to the other end of the ratchet bar45. The ratchet assembly may be formed using lightweight, sturdy materials.

When the ratchet assembly is engaged, the ratchet bar45effectively transfers any rotational motion of the ratchet handle35to the secondary ratchet handle50. The ratchet bar45maintains a substantially parallel orientation between the ratchet handle35and the secondary ratchet handle50, during any movement of the assembly. The ratchet handle35and the secondary ratchet handle50(as well as their respective rotational rods60A and60B) rotate simultaneously and in the same orientation.

The rotational rods60, which may be somewhat close-fitting through the pressure blocks65, are nevertheless capable of rotating in both clockwise and counter-clockwise directions. When the ratchet handle35is moved, such as during engagement of the ratchet assembly, both rotational rods60move in the same direction and to the same degree. For example, when the ratchet handle35moves from the unengaged position (FIG. 1) to the engaged position (FIG. 2), both rotational rods60move in a counter-clockwise direction. When the ratchet handle returns to the unengaged position, both rotational rods move in a clockwise direction, back to their original positions.

Scoops20are attached at the ends of each rotational rod60and are disposed transverse to the rods. Each scoop20is approximately adjacent to one corner of the heatsink body190. Rotational rod60A is threaded through scoop20A and20B while rotational rod60B is threaded through scoop20C and20D. The scoops20mate with the mounting pins15when the mounting system100is engaged, providing a secure, yet even coupling between the heatsink body190and the package120. The configuration and operation of the scoops20are more particularly described inFIGS. 5 and 6, below.

InFIG. 2, the mounting system100is shown in its fully engaged position. The ratchet handle35has been moved to the left, as compared toFIG. 1, such that each of the scoops20grapple, grasp, or otherwise engage with their respective mounting pins15, for a secure connection between the linkage assembly140and the backplate10(not shown). The mounting pins15are visible above the base portion195of the heatsink assembly130. The secure engagement of the mounting system100ensures that the heatsink body190is pressed against the package120on the motherboard110.

Also part of the ratchet assembly, a latch75is disposed between the ratchet bar45and the ratchet handle35. When the latch is set, the ratchet handle35is unable to move. This inhibits the unintentional disengagement of the mounting system100. Designers of ordinary skill in the art can appreciate many other ways to fasten the ratchet handle35such that unintended movement is avoided.

FIG. 3is a perspective view of the backplate10, which is to be positioned beneath the motherboard (not shown). The backplate10includes holes12, for receiving each of the mounting pins15. The mounting pins15each include a head17at one end of the shank, whose diameter is large enough to keep the end of each mounting pin beneath the backplate, while the shank of each mounting pin is threaded through the motherboard110, then through the base195of the heatsink assembly130.

At the other end of the shank, the mounting pins each include a channel19and a tip18. The diameter of each channel is slightly smaller than the diameter of the tip. The channels19of the mounting pins facilitate engagement by the scoops20. In the figures, the diameter of the tip18is substantially the same as the diameter of the shank of the mounting pin. However, the diameter of the shank of the mounting pin may instead be substantially the same as the diameter of the channel. The engagement mechanism, which is described in more detail, below, is effective when the diameter of the tip18is greater than the diameter of the channel19.

By coupling the heatsink assembly130to the backplate10via the mounting pins15, where the backplate is attached to a chassis, chronic or dynamic stresses that may be imposed on the motherboard110due to the weight of the heatsink assembly130are substantially avoided. Instead, the backplate10and the mounting pins15of the mounting system100help to distribute the weight of the heatsink transverse to or through, rather than upon, the motherboard110. By contrast, a motherboard upon which a high-mass heatsink is mounted directly is likely to be damaged or rendered inoperable. Thus, the mounting system100provides a mechanism by which high-mass heatsinks can be used on a computer or other processor-based system, without imposing limitations on the system's use, so as to avoid dynamic and/or chronic stresses.

InFIG. 4, a perspective view of the linkage assembly140is shown, without the heatsink assembly130. A pair of optional support bars80is depicted, using dashed lines. These support bars may be disposed between the pressure blocks for connection thereto. Thus, a first support bar80connects the pressure block65A and the pressure block65D together while a second support bar80connects the pressure block65B and65C together. The support bars80and the rotational rods60thus form a rectangular structure that surrounds the heatsink body (not shown), and helps to maintain the shape of the linkage assembly140.

FIG. 5is a close-up perspective view of the scoop20A and associated hardware used in the mounting system100, according to some embodiments.FIG. 6is a side view of the scoop as it relates to the mounting pins15of the backplate10. The scoops20of the linkage assembly140are described in more detail withFIGS. 5 and 6in mind.

Each scoop20includes a hole26, through which the rotational rods60are threaded, as illustrated inFIG. 6. The scoops20A and20B are threaded through the rotational rod60A while the scoops20C and20D are threaded through the rotational rod60B. The hole26in each scoop is small enough that the rotational rod is tightly coupled to each scoop. Thus, when the ratchet handle35moves the rotational rods, the scoops move with the rotational rods.

The scoop20A inFIG. 5includes two side-by-side claws27, disposed transverse to the rotational rod60. The claws27are roughly crescent-shaped. The claws27are to be positioned on either side of their respective mounting pins15during engagement of the mounting system100. Recall that each mounting pin15of the backplate10includes a channel19and a tip18, in which the diameter of the channel is smaller than the diameter of the tip. The distance between the claws27of the scoop20A is slightly longer than the diameter of the channel19of the mounting pin15, but shorter than the diameter of the tip18. This ensures that a portion of the claws27is disposed beneath the tip of the mounting pin, substantially inhibiting movement of the mounting pin or the linkage assembly, once engagement of the mounting system100occurs.

When the ratchet handle35is moved to actuate or engage the linkage assembly140, the claws27rotate, along with the rotational rods60. The inner surface of each claw is ramped slightly upward so that, when the mounting system100is engaged, the claws27actually pull their respective mounting pins upward slightly, for a tight coupling between the linkage assembly and the backplate10. Because of the ramp on each scoop20, a specified force will be applied to the package120that may be quite low. However, the ability of the scoop to resist pullout loads during dynamic events is very high, in some embodiments.

In other embodiments, the tips18of the mounting pins15are replaced with an eye or loop, while the scoops20include a single claw rather than two claws, for engagement through the loop. In other embodiments, the mounting pins15have a cross-bar member instead of a tip and a channel, such that the claws27of the scoops20can effectively grasp the mounting pins. Mechanical designers of ordinary skill in the art recognize a variety of possible implementations for effectively grasping the mounting pins by the scoops.

The scoop20A includes a reverse stop25. The reverse stop25is transverse to the claws27and parallel to the rotational rod60A. The width of the reverse stop25slightly exceeds the width of the claws27, one of which is proximal to the pressure block65A.

When the mounting system100is fully engaged, the reverse stop25makes contact with a lower portion of the pressure block, inhibiting further movement of the scoop. At this point, the claws27are fully engaged with the tip18of the mounting pin15, and a tight engagement between the linkage assembly140and the backplate10is achieved. When the mounting system is fully disengaged, the reverse stop makes contact with an upper portion of the pressure block, also inhibiting further movement of the scoop. At this point, the claws are fully disengaged from the tip18, and the heatsink assembly130, including the linkage assembly140, may be removed from the motherboard110.

The scoop20A may include a ratchet gear30, such as is depicted inFIG. 5. The ratchet gear30is cylindrical, so as to completely surround the rotational rod60, with gear teeth32extending along one side of the cylinder. In some embodiments, the scoop20A includes a ratchet gear30while the scoops20B,20C, and20D include no ratchet gear. In other embodiments, scoops20A and20C (i.e., scoops on one side of the linkage assembly) include ratchet gears. Like the scoop, the ratchet gear30does not freely rotate on the rotational rod60A, but moves with the rotational rod during engagement and disengagement. Thus, while the end portion185of the ratchet handle35rotates, the ratchet gear30is fixed to the rotational rod60.

In addition to the scoop20A, the close-up view ofFIG. 5also depicts the ratchet handle35in more detail. The ratchet handle35includes an end portion185, which extend from the base of and is disposed transverse to the ratchet handle. The end portion185of the ratchet handle35includes gear teeth34, which are disposed facing the gear teeth32of the ratchet gear30. The ratchet handle35and end portion185may be molded as a single piece of material. Like the ratchet gear30, the end portion185is cylindrical, for mating with the ratchet gear30.

The gear teeth34of the end portion185mesh with the gear teeth32of the ratchet gear30. Accordingly, when the ratchet handle35rotates, the rotational rod60A rotates and the scoops20A and20B (as well as the rotational rod60B and the scoops20C and20D) move simultaneously. Once the enmeshed gear teeth begin making a clicking noise, the desired torque of the rotational rods60is achieved. The secondary ratchet handle50may also have gear teeth for coupling to a second ratchet gear (not shown).

The gear teeth32of the ratchet gear30and the gear teeth34of the end portion185are characterized by two slopes, a small slope and a steep slope, according to some embodiments. When the mounting system100is engaged, the relatively smaller slope of the gear teeth ensure that, if the ratchet handle35is rotated excessively, the gear teeth32of the ratchet gear30and the gear teeth34of the end member185slip past one another under the force of the ratchet springs40, rather than further compressing. The shallow slope along with the spring force of the ratchet springs40controls how much install force occurs for the package120and the heatsink assembly130. The steep slope ensures that the scoops20can be disengaged at all times, since the steep slope will provide higher forces than the shallow slope. As the reverse stop25makes contact with the pressure blocks65A during disengagement, the ratchets are reset to ensure adequate throw for a subsequent engagement of the linkage assembly140. As the desired torque is achieved, the backplate10is pulled up against the motherboard110at the same time the heatsink body190is pulled against the package120. The opposing force of the backplate against the weight of the heatsink substantially inhibits deflection of the motherboard, according to some embodiments.

Also shown inFIG. 5, the rotational rod60A may be threaded on one or both ends to accept partially threaded bolts55. The bolts55hold the various threaded components in place. A ratchet spring40, disposed between the bolt55and the end portion185of the ratchet handle35, provides a force in the direction of, or parallel to, the rotational rod60, for holding the opposing teeth34and34together. (Rotational rod60B may likewise include bolts as well as a ratchet spring.) Mechanical designers of ordinary skill will recognize that other springs and configurations may be employed to provide a force for holding the opposing gear teeth together.

The ratchet spring40produces a force against the ratchet gear30and the end portion185. Additionally, when the mounting system100is engaged, the scoops20produce a rotational force. Each scoop20engages with the tip18of its respective mounting pin15, causing a force to push on the base195of the heatsink assembly130. These forces thus provide compression between the heatsink assembly130and the package120. The strength of the ratchet spring40can be selected to achieve the desired compression between the heatsink assembly130and the package120. The distribution of the scoops20and the mounting pins15along the outer region of the heatsink body190ensures that the compression is evenly distributed, thus facilitating the even conduction of heat away from the package to the heatsink.

The mounting system100thus provides a mechanism for distributing the weight of the heatsink transverse to the motherboard110, thus minimizing the possibility of board and/or component damage thereon. The placement of the linkage assembly140, the backplate10, and the mounting pins15so as to surround the heatsink body190facilitates the even distribution of the heatsink weight, promoting an even distribution of contact between the heatsink body190and the package120. The number of scoops, pressure blocks and mounting pins used by the mounting system100may vary.

The mounting system100may be assembled, according to some embodiments, as follows. The linkage assembly140is permanently affixed to the base195of the heatsink assembly130. At this point, the heatsink assembly need not be coupled to the motherboard110. The backplate10is attached to the underside of the motherboard110, aligned with the package120, and the mounting pins15are threaded through the holes112in the motherboard. The operations for installing the linkage assembly140and the backplate10may be performed in reverse order.

Once the mounting pins15are protruding from the motherboard110, the heatsink assembly130may be lowered onto the package120. The mounting pins are threaded through the holes215in the heatsink base195. The mounting system100is thus assembled for use. Accordingly, the ratchet handle35of the linkage assembly140is actuated or engaged, causing the scoops20to grasp their respective mounting pins15. Once the gear teeth32of the ratchet gear30and the gear teeth34of the end member185begin clicking, the mounting system100is fully engaged and actuation of the ratchet handle35may cease. The latch75located between the ratchet handle35and the ratchet bar45may be engaged, as a safety mechanism, to ensure that the fully engaged position of the linkage assembly140is maintained. The engagement of the mounting system100is thus complete.

To disengage the mounting system100, the following operations are performed. The latch75is unfastened, freeing the linkage assembly140. The ratchet handle35is then moved back to its original, unengaged position (a shift to the right, in the figures). The gear teeth32of the ratchet gear30and the gear teeth34of the end member185remain engaged, causing the scoops20to retract, freeing the respective mounting pins15from their grasp. Next, the reverse stop25hits the pressure block65A and the force of the ratchet spring40is overcome. The ratchet gear30and the end portion185move relative to one another, causing the entire linkage system to be reset for a subsequent installation of a heatsink assembly. Once the ratchet handle35is returned to its original position, the linkage assembly140, the heatsink assembly130, to which the linkage assembly is now permanently attached, and the backplate10can be removed from the motherboard110.

The mounting system100advantageously achieves the desired compression between the heatsink body190and the package120, facilitating the efficient transfer of heat away from the package. For some heatsink assemblies, the package pushes against the motherboard, resulting in an unnecessarily high displacement gradient (solderball stress), particularly for installations involving two or more processors, and an associated risk of solderball cracks in durability testing.

The mounting system100provides a particular package load for a wide tolerance range and controls deflection of the motherboard110due to chronic stresses. The structure of the mounting system100, which causes the weight of the heatsink to be distributed through rather than upon the motherboard, or passed directly to the chassis via a direct attachment of the backplate10to the chassis, also provides a very stiff resistance to dynamic loads, such as may occur when the computer or other processor-based system is dropped or bumped. The mounting system100thus provides a systematic approach to achieving a specified, relatively low force on the package, satisfying TIM limitations, while providing a high load resistance for dynamic loads that substantially reduces the possibility of package pullout and TIM separation.

The mounting system100further provides a tool-less approach to processor/heatsink installations. Some heatsink installations involve multiple threaded screws and standoffs, which must be individually removed and re-inserted when the processor is added, replaced, or otherwise serviced. By contrast, the mounting system100makes processor and heatsink installations tool-less.