Patent Application
20080024991
So that the manner in which the above recited features, advantages and objects of the present invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings.
It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
The present invention generally relates to heat dissipation in a computing device, and more specifically, to a method and apparatus for applying a specified compressive force by a heat dissipation device for an integrated circuit. In one embodiment, a method for applying a specific compressive force from a heat dissipation device onto one or more integrated circuit devices includes placing the integrated circuit device onto a printed circuit board (PCB) and then placing the heat dissipation device onto the integrated circuit device. The method further includes tightening an actuation screw threaded through a spring plate against a portion of the heat dissipation device. The actuation screw may be prevented from being tightened beyond a mechanical constraint corresponding to a pre-set calibration for the specific compressive force.
In the following, reference is made to embodiments of the invention. However, it should be understood that the invention is not limited to specific described embodiments. Instead, any combination of the following features and elements, whether related to different embodiments or not, is contemplated to implement and practice the invention. Furthermore, in various embodiments the invention provides numerous advantages over the prior art. However, although embodiments of the invention may achieve advantages over other possible solutions and/or over the prior art, whether or not a particular advantage is achieved by a given embodiment is not limiting of the invention. Thus, the following aspects, features, embodiments and advantages are merely illustrative and are not considered elements or limitations of the appended claims except where explicitly recited in a claim(s). Likewise, reference to “the invention” shall not be construed as a generalization of any inventive subject matter disclosed herein and shall not be considered to be an element or limitation of the appended claims except where explicitly recited in a claim(s).
In one embodiment, the heatsink 102 may be secured to a front-side stiffener 108. The heatsink 102 may apply pressure to the IC package 104, which may cause the PCB 110 to flex. In order to reduce this flex, the PCB 110 may be held between the front-side stiffener 108 and a back-side stiffener 112. Alternatively, the no front-side and/or back-side stiffener 108, 112 may be present and the heatsink 102 may be secured directly to the PCB 110.
In one embodiment, the heatsink 102 may contain a channel 116 called a U-channel 116 embedded in the top of the heatsink 102. The U-channel 116 may contain a horizontal member called a U-channel support beam 118, onto which a spring plate 124 may be set. An actuation screw 120 may be threaded through the spring plate, and may rest on the U-channel support beam 118, as described below.
In one embodiment, a back-side stiffener 112 and a front-side stiffener 108 may be mounted to the PCB 110 at step 204. For example, the front-side stiffener 108 may surround the sides of the IC package 104 (and the IC socket if applicable), and the back-side stiffener 112 may cover the PCB 110 on the side opposite the IC package 104. Alternatively, the IC socket may be built into the front-side stiffener 112. Optionally, there may be an insulator between the back-side stiffener 112 and the PCB 110.
In one embodiment, the front-side stiffener 108 may include one or more load arms attached to one or more spring rods. The spring rods may be pliable metal or non-metal rods fixed at their ends to the front-side stiffener 108. The gauge of the spring rods and their material may vary, depending on the specified compressive force which may need to be applied to the IC device 104 by the heatsink 102. For example, embodiments of the present invention may be used to apply a compressive force of between 70 and 700 lbs to an IC package 104, which may correspond to a spring rod gauge of between 3 and 5 mm. The specified force range of between 70 and 700 lbs is exemplary and, in some cases, other desired ranges may be utilized with embodiments of this invention.
In one embodiment, the load arm may be an arm which is attached to the spring rod and may be able to pivot around the spring rod. The load arm may be made out of a material with little to no creep and may be metallic. Creep may refer to a material's slow permanent deformation when under high temperature and/or pressure. One or more hooks may be located at the end of the load arm opposite the spring rod. The load arm may be made up of two branches joined at the hooked end of the load arm so that air may flow between the individual branches of the load arm.
In one embodiment, once the IC package 104 is mounted to the PCB 108, a thermally conductive material 106 may be placed on top of the IC package 104 at step 206. This thermally conductive material 106 may eventually form a seal between the IC package 104 and a heatsink 102, and may further serve to facilitate the dissipation of heat 114 from the IC package 104. Alternatively, in some cases, thermally conductive material 106 may not be used.
In one embodiment, the heatsink 102 may be placed on top of the IC package 104 and front-side stiffener 108 at step 208. The heatsink 102 may have a U-channel 116 in it that may line up with the load arms attached to the front-side stiffener 108. Spring plate retention pin guide slots may be located at the ends of the U-channel 116.
In one embodiment, a spring plate 124 with an actuation screw 120 may be placed in the U-channel 116 at step 210. The spring plate 124 may be a pliable metal or non-metal plate. The thickness and material of the plate may vary, depending on the specified force applied to the integrated circuit 104 by the heatsink 102, as discussed above with respect to the spring rods. To cover the range of forces discussed above, between 70 and 700 lbs, the spring plate 124 may range from a single 1.5 mm thick plate to several 3 mm plates contributing to create a laminated spring plate.
In one embodiment, the actuation screw 120 may be a screw threaded through the spring plate 124. The actuation screw 120 may have a mechanical constraint so that when the actuation screw 120 reaches a designated depth through the spring plate 124, the actuation screw 120 may not be threaded any deeper. Such a mechanical constraint may include anything that prevents the actuation screw 120 from being threaded any further into the spring plate 124, including a screw head 122, a washer, a spacer, a nut, a non-threaded portion of the actuation screw 120, a pin through the actuation screw 120, and a discontinuity in the thread pattern of the actuation screw 120 (e.g., a smooth, unthreaded portion of a shaft of the screw). When the actuation screw is tightened to a limit corresponding to the mechanical constraint, the deflection in the spring plate 124 may cause the heatsink 102 to exhibit the specified compressive force onto the integrated circuit device 104.
In one embodiment, the actuation screw 120 may be a typical screw where the diameter of a threaded portion is such that the screw may be threaded into a similarly sized hold in the spring plate 124. The diameter of a head 122 of the screw, however, may be too large to fit through the hole. In this case, the head 122 of the screw may be the mechanical constraint, and a length of the screw may correspond to the specified compressive force. In another embodiment, at least one spacer, such as a washer, may be used in addition to the typical screw. The spacer may have a hole with a diameter larger the threaded potion of the screw, but smaller than the head 122 of the screw. Therefore, the spacer, and not the head 122 of the screw, may be the mechanical constraint since it may contact the top of the spring plate. In this embodiment, one of a plurality of spacers, each corresponding to a different specified compressive force, may be used so that a single actuation screw 120 may be used to obtain one of a plurality of corresponding specified compressive forces.
In one embodiment, spring plate retention pins may be inserted through the spring plate retention pin guide slots at the ends of the U-channel 116 at step 212. The spring plate retention pins may be any type of pin capable of being secured in the spring plate retention pin guide slots and able to withstand the stresses placed upon them by the spring plate 124, as is described below. For example, each spring plate retention pin may be a nut and a bolt combination, a screw and retainer-clip combination, a rivet, or a metal bar.
In one embodiment, the load arms may be pivoted about the spring rods so that the load arms are positioned over the spring plate retention pins at step 214. The arrangement of the spring plate retention pin guide slots may be such that the spring plate retention pins may be vertically limited by the load arms before the pin would be able to reach the top of the spring plate retention pin guide slot.
In one embodiment, at step 216, the actuation 120 screw may be threaded until the mechanical constraint, such as the head 122 of the actuation screw, is reached and the actuation screw 120 is prevented from being threaded any deeper into the spring plate 124. As the actuation screw 120 is threaded into the spring plate 124, the bottom of the actuation screw 120 may contact a U-channel support beam 118, which may be a flat plate into which the actuation screw 120 cannot be threaded. In response, the spring plate 124 may rise as the actuation screw 120 is threaded. As the spring plate 124 rises, its sides may contact the spring plate retention pins, causing them to rise (confined in the spring plate retention pin guide slots) with the spring plate 124. When the spring plate retention pins contact the hooked portions of the load arms, the spring plate retention pins, and thus the sides of the spring plate 124, may be vertically constrained.
As the actuation screw 120 is further threaded, causing the bottom of the actuation screw 120 to press with more force against the top of the U-channel support beam 118, the spring plate 124 may begin to deflect, rising in its middle but remaining stationary at its vertically constrained sides. This spring plate deflection may cause a force to be exhibited downward from the actuation screw 120 onto the heatsink 102, which may exhibit a compressive force on the IC package 104. The compressive force may increase as the actuation screw 120 is threaded deeper into the spring plate 124. An upward force equal to the downward force from the bottom of the actuation screw may be distributed to the load arms through the interface of the spring plate 124 and the spring plate retention pins. Once the mechanical constraint of the actuation screw 120 is reached, the compressive force on the IC package 104 from the heatsink 102 may be at a pre-calibrated specified compressive force, as described above.
In the above configuration, the actuation screw 120 may be in compression, exerting force downward on U-channel support beam 116 of the heatsink 102 as a result of the upward force exerted on the spring plate 124 by the actuation screw 120, according to one embodiment. The spring plate 124 may deflect as a result of the upward force and distribute the upward force into the load arms through the spring plate retention pins. The load arms, in tension, may deflect the middle of spring rods upwards so that the spring rods and the spring plate 124 contribute in series to a total deflection distance, which is proportional to the downward force onto the IC package 104. Thus, after determining a desired specified compressive force on the IC package 104, the spring rod spring constant, and the spring plate 124 spring constant, a desired deflection distance for the spring plate 124 and the spring rods may be calculated. The desired deflection distance may then be used to select an appropriate mechanical constraint for the actuation screw 120 as described above, thereby ensuring that when the actuation screw 120 is fully tightened, the correct specified compressive force is applied to the heatsink 102.
In one embodiment, at step 218, once the heatsink 102 is attached to the IC package 104, the thermally conductive material 106 may be cured. Any acceptable thermally conductive material 106 may be used. Furthermore, any acceptable method of curing may be used, including using infrared light, heat, or self-curing paste. Alternatively, the thermally conductive material 106 may not be cured.
In one embodiment, one or more non-influencing fasters may be engaged to further secure the heatsink 102 to the IC package 104 at step 220. Non-influencing fasteners are fasteners on the front-side stiffener 108 that when engaged, may expand outwards and grip the heatsink 102. Alternatively, other fasteners may be used, or no fasteners may be used.
In one embodiment, utilizing the process 200 may result in a compressive force on the IC package 104. The compressive force may be greater than or equal to a minimum compressive force, while remaining less than or equal to a specified maximum compressive force. The specified maximum compressive force may correspond to the greatest force able to be applied to the IC package 104 before it is damaged, which may be specified by the manufacturer of the IC package 104. The minimum compressive force may correspond to a minimum thermal interface pressure for obtaining a necessary amount of heat flow 114 into the heatsink 102. Alternatively, the minimum compressive force may correspond to a minimum contact pressure allowable at an interface between the IC package 104 and the PCB 110 or a socket.
In one embodiment, the compressive force may be within ±5% of the required compliance load for the IC package 104. Optionally, another desired tolerance may be utilized. The tolerance may be maintained across the entire IC package 104. This may be beneficial because, as described above, if the compressive force on the IC package 104 is well below the required compliance load, the electrical stability at the contact interface of the IC package 104 and PCB 108 may be compromised and IC performance may suffer. If the IC package 104 is held in place with a compressive force greater than what is necessary, there may be a risk of mechanical damage to the IC and/or a possibility of electrical shorting.
The process 200 describes a process for installing a heatsink apparatus for applying a specified compressive force to an integrated circuit device, according to one embodiment of the invention. Illustratively,
In one embodiment, as described in step 202 of the process 200, an IC package 104 is contained within an IC socket 302 mounted onto a PCB 110, as depicted in
In one embodiment, as described in step 204 of the process 200, a front-side stiffener 108 and a back-side stiffener 112 may be added to the existing PCB 110 and IC package 104 combination, as is illustrated in
In one embodiment, as described in step 206 of the process 200, a thermally conductive material 106 may be added to the top of the IC package 104, as depicted in
In one embodiment, as described in step 210 of the process 200, a spring plate 124 with an actuation screw 120 may be placed in the U-channel 116, as depicted in
In one embodiment, as described in step 212 of the process 200, spring plate retention pins 802 may be added to the assembly. As depicted in
In one embodiment, as described in step 216 of the process 200, the actuation screw 120 may be threaded into the spring plate 124 until the mechanical constraint (e.g., screw head 122) of the actuation screw 120 is snug against the spring plate 124. As described above, threading the actuation screw 120 may raise the spring plate 124 until its sides press against the spring plate retention pins 802. As the actuation screw 120 continues to be threaded, the sides of the spring plate 124 may be obstructed by the spring plate retention pins 802 restricted by the hooks in the load arms 406. As the actuation screw 120 is threaded further, the spring plate 124 may deflect, generating a tension in the load arms 406 and a downward force on the heatsink, as is depicted in
In one embodiment, the thermally conductive material 106 may need to be cured, as in step 218. After curing, non-influencing fasteners 1102 may be engaged, as described in step 220 of the process 200, so that the heatsink 102 is tightly held onto the front-side stiffener 108 without affecting the force exerted on the IC package 104 by the heatsink 102. A possible location of the non-influencing fasteners 1102 may be seen in
In one embodiment, the process 200 can be utilized to install a heatsink 102 for applying a calibrated pressure to the IC device 104, as described above. Calibration may be possible because the pressure exerted on the IC device 104 may be a function of the deflection in the spring rods 404 and spring plate 124 as well as the length of the actuation screw 120. If the actuation screw 120 is longer, and/or the spring rods 404 and/or spring plate 124 are stiffer, the pressure exerted on the IC device 104 by the heatsink 102 may be greater.
In one embodiment, a combined deflection of the spring rods 404 and the spring plate 124 may produce the compressive force applied to the heatsink 102 and to the IC device 104. Thus the pressure exerted on the IC device 104 may be due to deflection of both the spring rods 404 and the spring plate 124. Optionally, in one embodiment, the spring rods 404 may not deflect, and all of the applied compressive force may be generated by the deflection of the spring plate 124 (e.g., the collective deflection may be equal to the deflection of the spring plate 124). Similarly, in one embodiment, the spring plate 124 may not deflect, and all of the applied compressive force may be generated by the deflection of the spring rods 404 (e.g., the collective deflection may be equal to the deflection of the spring rods 404).
One skilled in the art will recognize that there are many variations possible to the present invention that do not change the scope of the invention. For example, the spring plate retention pin guide slots 604 may be omitted and/or the spring plate retention pins 802 may be affixed to the spring plate 124.
While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
This application is related to U.S. patent application Ser. No. 11/201,972, Attorney Docket No. ROC920050088US1, entitled METHOD AND APPARATUS FOR MOUNTING A HEAT SINK IN THERMAL CONTACT WITH AN ELECTRONIC COMPONENT, filed Aug. 11, 2005, by John Lee Colbert et al. This related patent application is herein incorporated by reference in its entirety.
