Development of moisture-proof thin and large QFP with copper lead frame

摘要

A novel thin and large Quad Flat Package (QFP) with copper lead frame was developed having a dimension of 28 mm-squared body size and 1.4 mm package thickness. The package accommodated as large as a 12 mm-squared die and, without dry pack, could accomplish the JEDEC LEVEL 1 condition in terms of volume production assurance. Along with the package development, a new simulation methodology was established which could predict the occurrence of delamination and cracking and be applied to similar package designs. In the course of the current study, we initially investigated the dependence of adhesion strength of Epoxy Molding Compound (EMC) on the copper film oxide thickness and, applying this result, obtained the upper limit of the oxide thickness below which sufficient adhesion strength was ensured. Upon this underlying relationship, for the sake of the oxide growth suppression under the threshold, we developed a new packaging process controlling such parameters as heating temperature, heating time and oxygen concentration of an ambient. Since the contact area between EMC and die pad has the smallest adhesion strength among all interfaces inside the package, we adopted split or window die pad designs aiming to hold the area as small as possible. The removal of organic contaminants from the rear side of die by virtue of Ultra-Violet (UV) irradiation enhanced the adhesion strength between EMC and the surface. Also the selections of appropriate EMC and die attach material were conducted from several candidate ones.