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Top-Gate Molding Process Development of Cavity Down TBGA for High Density Wire Bonding and Low K Dielectric Wafer Technology Application

Top-gate molding systems have been commercially available for mass production for more than 5 years. Key attractions to this relatively new molding concept are its improvement in wire sweep performance for ultra fine pitch wire bonding and ability to capitalize desirable mold compound mechanical properties over liquid encapsulation material for low k dielectric wafer technology application. This paper covers the development effort of top-gate molding in Freescale Semiconductor to replace liquid encapsulation process for cavity down TBGA package. Besides the ultra fine pitch and multi-tiers wire bonding, the key challenges of the development include substrate level delamination at various layers. Molding process conditions, substrate design, and mismatch between substrate and molding compound properties were identified as the causes of delamination. Design of experiments and finite element analysis (FEA) simulation methodologies were applied to determine the optimum molding process conditions and the suitable substrate base material properties for overall process robustness improvement. With the robust design in place, package performance and reliability at MSL3@260C and 1000 cycles temperature cycling has been successfully achieved.