Study of molding compound for BGA [package]

The current plastic Ball Grid Array (BGA) package has some disadvantages such as low level of solder crack resistance, large package warpage, and low cost performance at molding. In this paper, the author examined the improvement of the solder crack resistance, warpage and cost performance for a BGA. Firstly, solder crack resistance: as the author examined various combinations of materials used for the BGA package (molding compounds, die attach paste, and substates), it became clear that the molding compound is the most important factor for improvement of solder crack resistance. Also the molding compound factors which are necessary to withstand JEDEC level 2 treatment can be conjectured as the result of analysis of water absorption of the BGA package. Secondly, warpage: the author estimated warpage of a BGA when low Tg (below 175°C) molding compound is used. In case of high Tg (about 180 to 200°C) molding compound warpage can be calculated by an ideal elastic model. However, in case of low Tg it was clear that the visco-elasticity model of a polymer network is important for calculation. Thirdly, the cost performance of molding: a molding compound that can satisfy all of a plasma processing-less, short-cycle time (cure time 60 seconds), and post-cure-less for the improvement of cost performance, was examined. However, it seems difficult to satisfy all of the above items with a compound due to the problem of decrease of adhesion strength between the molding compound and the solder resist, at present