Patent Application
20080073765
These and other features of this invention will be more readily understood from the following detailed description of the various aspects of the invention taken in conjunction with the accompanying drawings that depict various embodiments of the invention, in which:
It is noted that the drawings of the invention are not to scale. The drawings are intended to depict only typical aspects of the invention, and therefore should not be considered as limiting the scope of the invention. In the drawings, like numbering represents like elements between the drawings.
Turning to the drawings,
Metal stiffener 122 includes a fluid-based pressure compensator 140 contacting an underside 142 of PCB 116, which provides automated tolerance compensation and enables relaxation of flatness and thickness variation tolerances. Fluid-based pressure compensator 140 may be positioned in a recess 154 of metal stiffener 122. In one embodiment, fluid-based pressure compensator 140 includes a fluid filled sealed packet 150 within recess 154 of metal stiffener 122. Sealed packet 150 may be made of any durable and fluid-impervious material such as plastic, a metal foil or other materials known in the art. In one embodiment, fluid 160 may include a gel such as a silicone based material. In this case, shifting of chip package 100 during shipping or use or aging may be compensated by fluid based pressure compensator 140. In another embodiment, fluid 160 may include a curable material and may reduce the life requirements of the seal of fluid sealed packet 150. In another embodiment, the curable fluid remains flexible after curing. In one embodiment, fluid filled sealed packet 150 may include two different polymer materials such as a resin and a catalyst, in advance, with a separating membrane that can easily be ruptured just prior to assembly. Fluid 160 may cure at room temperature or near usage temperature. Another embodiment may include a fluid 160 in the form of a very viscous material that fills recess 154, which never cures, yet does not require a tight seal, e.g., like a putty. Fluid 160, however, may take a variety of other forms. For example, fluid 160 may include, but is not limited to, incompressible liquids such as: water, oil, etc.
Although one particular embodiment of a fluid based pressure compensator 140 has been disclosed herein, it is understood that a variety of different mechanisms may be employed within the scope of the invention. For example,
In operation, IC chip(s) 112 may be packaged by providing chip module 120 and PCB 116 coupled to chip module 120 by LGA connector 118. Chip module 120 holds at least one IC chip 112. Next, chip module 120 is coupled to metal stiffener 122 with PCB 116 and LGA connector 118 therebetween. As noted above, metal stiffener 122 includes at least one fluid-based pressure compensator 140 contacting underside 142 of PCB 116. At least one fluid-based pressure compensator 140 is used to automatically compensate for a non-uniform spring force applied to at least one of PCB 116, LGA connector 118 and chip module 120. One embodiment may include simply providing fluid-based pressure compensator 140. Where fluid 160 includes a curable material, the method may further include curing fluid 160. As noted above, in one embodiment the curable material should remain flexible after curing.
As a result of fluid based pressure compensator 140, couplers 132 with springs (not shown) may need less force, thus significantly reducing component size and cost, and component flexure. Accordingly, geometric variations such as chip module 120 out of flatness, PCB 116 out of flatness and PCB 116 thickness variations can be accommodated. Fluid based pressure compensator 140 provides a nearly uniform pressure under LGA connector 118. Moreover, by applying a particular pressure for each chip package 100, the pressure will be automatically individualized to the dimensional idiosyncrasies of that particular set of parts. The correct pressure may be determined by prior experimentation. This enables relaxation of flatness and thickness variation tolerances.
The above-described embodiments may also be applied to non-LGA connector 118 applications that demand a high degree of stability over time. For example, bare die assemblies using column grid array (CGA) or ball grid array (CBGA) modules that do not require high compression loads mandated by LGA connector 118. Some methods of bare die interface of large mass heat sinks essentially anchor the heatsink to the surrounding structure, while applying a moderate load (typically around 40 lb) to maintain a compressive load between the module and anchored heatsink. This level of compression load does not always fully remove the initial warp in PCB 116, and subsequent creep of PCB 116 as it flattens over time to conform to a backside stiffener can create relative motion between the module and the heatsink. For bare die interfaces which are typically very thin bond lines (30-40 μm typically), even small relative motion can disturb the thermal interface and significantly degrade its performance. A fluid based pressure compensator 140 may contribute to stabilizing the motion between PCB 116 and metal stiffener 122, and hence mitigate thermal performance degradation due to PCB 116 creep. Further, a fluid 160 in the form of a cured gel between PCB 116 and metal stiffener 122 could be used.
The foregoing description of various aspects of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and obviously, many modifications and variations are possible. Such modifications and variations that may be apparent to a person skilled in the art are intended to be included within the scope of the invention as defined by the accompanying claims.
