Simulation and experimental analysis of large area substrate overmolding with epoxy molding compounds

This paper presents new experimental and numerical methods to characterize the transfer overmolding of substrates with epoxy polymer. We investigated Multi Chip Modules on ceramic panels as well as on printed circuit boards encapsulated as a Mold Array Package (MAP). Experiments show that the polymer flow during the overmolding process depends significantly on the mold height: While standard MAP-type mold cavities are filled homogeneously and symmetrically in most cases, low cavity heights (<500 m) can cause the flow front to concentrate on a few flow paths (flow front fingering). We developed a numerical method to describe this inhomogeneous polymer flow. The reason for flow front fingering seems to be local variations of polymer viscosity which enforces a necking on distinct flow paths. Fingering can cause the formation of air traps and excessive wire sweep. We also developed new experimental methods to measure the pressure distribution within cavities: our sensor is based on commercially available, passive pressure sensitive films from FUJUFILM and is operational at temperatures up to 180°.