2^nd Level Reliability Improvement on WLCSP

Recently the package market is demanding the smaller package size and the lower impedance electrical path with a short interconnection. The wafer level chip scale package is one of them, which has the solution of the market needs above. However, WLCSP technology is still not fully accepted on the large device size that is larger than 5mm × 5mm. It needs to overcome 2^nd level reliability issue on both solder joint and drop reliability test. To improve 2^nd level reliability, we need to apply the longer stand–off design such as Cu –post and double solder ball instead of single solder ball, and low modulus material on polymer layer under the solder pad for releasing thermal stress which result in the solder joints crack due to CTEs (Coefficient of Thermal Expansion) mismatch between organic PCB and WLCSP. In this paper, the double ball structure is introduced as one of them can provide the longer stand off. In addition of improving 2^nd level reliability and drop test it may need to apply different solder ball component properties to increase Thermal cycling and drop test. The WLCSP structured a double solder ball showed a better 2^nd level reliability result. This paper describes the molding process for double ball process and 2nd level reliability by solder property variation.