Latest Technologies of Epoxy Molding Compound (EMC) for FO-WLP

FO-WLP is used for RF etc. for mobile as a package excellent in low profile, low warpage, cost reduction, electric performance etc. and this market is expanding since it began to be used in Application processer (AP) in 2016. It is expected that adoption to AP for mobile will continue to grow and further expansion to other products is also expected. Meanwhile, Epoxy molding compound (EMC) for FO-WLP is required to have functions not found in EMC for low-end packages. For example, since the molding area is large and the molding thickness is thin, if a conventional EMC is used, the warpage becomes large after curing and it cannot proceed to the subsequent process. In order to control warpage after curing, it is important to reduce cure shrinkage of EMC. In addition, in order to fill completely the gap between flip chip bumps of large size chip, control of filler size, melt viscosity etc. is more severely required.

Enhanced thermal conductivity of epoxy/alumina composite through multiscale-disperse packing

Inspired by the size of the voids in closest packing structures, we propose to use the combination of spherical particles with different size scales to increase the loading fraction of the fillers in epoxy-based composites. In this study, high loading up to 79 vol% has been achieved with multiscale particle sizes of spherical Al2O3 particles. The highest thermal conductivity of Al2O3-filled liquid epoxy measured by steady-state method is 6.7 W m−1 K−1 at 25°C, which is approximately 23 times higher than the neat epoxy (0.28 W m−1 K−1). Three models based on Maxwell mean-field scheme (MMF), differential effective medium (DEM) and percolation theory model (PTM) were utilized to assess our measured thermal conductivity data. We found that both DEM and PTM models could give good results at high volume fraction regime. We have also observed a considerable reduction (10–15%) of thermal conductivity in our Al2O3-filled cured epoxy samples. We attribute this reduction to the increasing of thermal interfacial resistance between Al2O3 particles and cured epoxy matrix, induced by cure shrinkage during the reaction. Our experiments have demonstrated that systems with multiscale particle sizes exhibit lower viscosity and can be filled with much higher fraction of fillers. We thus expect that higher thermal conductivity (probably >12 W m−1 K−1 based on DEM) can be achieved in future via filling higher thermal conductivity spherical fillers (e.g., AlN, SiC), increasing loading fraction by multiscale-disperse packing and reducing the effect from cure shrinkage.