Development of molding compounds for BGA

Recently, semiconductor packages have become thinner and smaller like TSOP and TQFP in accordance with the trend from insert type to surface mount devices. On the other hand, pin counts have become more and more due to higher integration and functions of semiconductor devices, and in this background, BGA is now newly being put to practical use instead of QFP as it can be mounted on PWBs easily. The difference of BGA from conventional package designs like QFP is one-side molding, and specific properties are required for molding compounds for BGA in comparison to requirements for conventional packages. Therefore, we started development of molding compounds for BGA for satisfying specific requirements. At first we analyzed stress by FEM and investigated the relation to package warpage. The warpage occurred in the stress concentration area and CTE and Tg were found to influence the warpage especially. We made molding compound samples of various CTE, Tg, and so on for this study and could confirm correlations with the analysis result. This result gave us a direction of molding compound development for warpage prevention. Next, as a substrate is used for BGA instead of a metal leadframe for conventional packages, we checked adhesion to the substrate and found additives for better adhesion. From the above results, we have developed new molding compounds for BGA, which have small warpage and good adhesion to the substrate.