Substrate Design & Process Optimization of LGA (BT-based) Package

With the trends moving towards smaller packaging technologies, land grid array (LGA) is rapidly becoming the package of choice. BT (bismaleimide triazine) substrate is being used due to its excellent electrical insulation, low CTE and high Tg. Optimized substrate design is essential in ensuring reliable package performance at field. Finite element analysis was performed on two different substrate designs in selecting the most optimized design with the lowest stress level and best performance in assembly process. Process optimization is another important aspect in attaining a robust package. Characterization of two-step wafer sawing has shown to be helpful in minimizing back side chipping for a 6 mils die laminated with non-conductive die attach film. With the use of DAF, die attach is necessary to be done at elevated temperature. Optimized setting of bond force, temperature and cure profile has shown to be crucial in achieving desirable BLT, minimum bleed, void and out-gassing from the adhesive. Wire bond temperature has been demonstrated to be critical to bonding quality with the tradeoff of DAF out-gassing at high temperature. Heater block design coupled with the right setting of pre-heat delay and temperature are necessary in achieving sufficient ball shear strength for BSOB. Plasma cleaning is another area of focus where magazine design, plasma loading capacity and the parameters were shown to be the important factors in ensuring effective cleaning.