Molding technology development of large QFN packages

Encapsulation of large QFN packages (>; 5 × 5 mm) are quite challenging as compared to normal small QFN packages as the big die pad in leadframe and multiple narrow gaps between leads may caused mold void rejects at the half etch areas. High density of fragile wires is prone to have wire sweep too as the EMC flow impact on longer wire length is significant which can caused wires sweep during mold filling. Air vent in mold design becomes very important for large QFN packages. In this paper, a new design of air vent has been introduced in order to eliminate mold void. This report also included the correlation study between pot & plunger friction and mold void rejects whereby the excessive friction in pot and plunger caused the significant transfer pressure lost while packing and subsequently intrdouced mold void rejects. In this paper, analysis showed that wire sweep rejects were caused by the unbalance flow of mold compound. Modification on the flood gate depth has been done in order to reduce the jetting effect of mold compound. This paper also discusses the effect of vacuum mold on large QFN packages.