Application of an epoxy cap in a flip-chip package design.

In order to combine the merits of epoxies, which provide good environmental and mechanical protection, and the merits of silicone gels, resulting in low stresses, one can use an encapsulation version, where a low modulus gel is currently under consideration, parallel with a metal cap version, for the 32100 Micropac package design. We recommend that the coefficient of thermal expansion for the epoxy be somewhat smaller than the coefficient of thermal expansion for the supporting firm. In this case the thermally induced displacements would result in a desirable tightness in the cap/frame interface. This memorandum is aimed at the assessment of stresses, which would arise in the supporting frame and in the epoxy cap at low temperatures. Also, the elastic stability of the cap, subjected to compression, is evaluated.