Aluminum composite materials for multichip modules

Abstract

In the intensive materials development activities for electronic paclazging and thermal management applications, the subclass of materials in which SiC particles reinforce aluminum alloy matrices has emerged as one with an especially attractive combination of physical properties, manufacturing flexibility, and cost. One benefit of these materials is the ability to tailor the physical properties through the selection of both reinforcement and alloy variables to match the thermal expansion coefficient of other electronic materials. In addition, the manufacturing flexibility of the various processes allows for shape complexity as well as selective reinforcement placement in the component to optimize system producibility. Finally, because raw materials are inherently inexpensive and low-cost production routes have been identified, aluminum composites may offer a range of cost-effective solutions to emerging problems in electronic paclazging and thermal-management applications.

Copper alloy-impregnated carbon-carbon hybrid composites for electronic packaging applications

“…The straight line represents the linear regression through the data. As has been reported for the Al-SiC composites, [3] here also, the volume-averaged values for the two constituents (metals and carbon) represent the CTE of these composites. Table IV gives the thermal diffusivity values along the X, Y, and Z directions for the composites, based on the preform C1-1 and two matrix alloys: Cu-6Si-0.3Cr and Cu-0.3Si-0.3Cr.…”

“…They require packaging materials with a high thermal conductivity (k ) and a coefficient of thermal expansion (CTE) which matches the low CTE values (4 to 6 ppm/K) of the substrates (e.g., alumina) and devices (e.g., silicon and GaAs). [1,2] Beryllium oxide or beryllium-beryllia composites are very attractive because of their very low density, outstanding thermal conductivity, and reasonably matching CTE, [3,4] but their toxicity constitutes a serious problem, especially where machining is involved. [2] Copper and aluminum have a very high thermal conductivity (398 and 247 W/m K, respectively) but their CTE is much too large.…”

“…However, their CTE can be brought down to 4 to 6 ppm/K by making composites containing appropriate volume fractions of low-CTE materials such as silicon carbide, aluminum nitride, or carbon. Aluminum and copper alloy composites containing carbon fibers, [2] silicon carbide particles, [3] diamond, [2] and other reinforcements are being investigated for this application.…”

“…[2,3,4] With 70 vol pct silicon carbide, this composite has a CTE of 6 ppm/K and a thermal conductivity of 110 W/m K [2] (a value of 170 W/m K has been reported in the literature, [5] but its original source is inaccessible).…”

“…Bulk densities and the fraction porosities (based on the total mercury intrusion volume) were used, to obtain the skeletal densities. Table I shows that C1-1 and SPC3P have similar median pore diameters (24.0 and 27.5 m respectively) but SPC3P, with a larger fraction of submicron pores, has a 33-pct smaller average pore diameter (i.e., 0.06 carbon fibers, with a density of 1.8 g/cm 3 , and the rest being graphite, with a density of 2.2 g/cm 3 ). However, the skeletal density was actually observed to decrease with a decreasing pore fraction (rectangular symbols in Figure 2(c)).…”