Package design and materials selection optimization for overmolded flip chip packaging

In overmolded flip chip (OM-FC) packaging, interface delamination-particularly at the die/underfill interface-is often expected to be a main type of failure mode. In this paper, a systematic stress analysis is performed by means of numerical simulations for the optimal design of package geometries and materials combinations. The behavior of the interfacial stresses at the die/underfill and die/mold-compound (MC) during the molding process is investigated, followed by a parametric study to examine the effects of the package geometries and materials parameters including the underfill fillet size, die thickness, die size, die standoff height, solder mask design pattern, MC used as underfill material, MC properties, etc., on the interfacial stresses. The results demonstrate that a proper selection of these parameters can mitigate the interfacial stresses, and thus is important for the reliability of the low-cost OM-FC packages.