Center Gate Molding challenges and improvements for cavity down TBGA packages

Center Gate Molding or also known as Pin Gate Molding is a molding method that is gaining a lot of interest in the market in recent times. This is due to its improvement in wire sweep performance for ultra fine pitch wire bonding and ability to capitalize desirable mold compound mechanical properties. The main reason for this is the mold flow of the compound is radial with the wire which will minimize flow stress on bonded wire rather than opposing the wire in the typical side gate molding. This paper discusses the key challenges and the improvements that have been implemented for the center gate molding for the cavity down TBGA (Tape Ball Grid Array) package in the High Volume Manufacturing (HVM). Substrate type which includes the different stack up of the polyimide tape was one of the major concerns for implementing molding on the cavity down TBGA package. The various substrate stack up of the polyimide tape were evaluated and Design of Experiments (DOE) were applied to determine the optimum molding process conditions in order to achieve a material set for overall process robustness.