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2nd Level Reliability Improvement on WLCSP
Keywords: WLCSP, Dobule Ball , Solder joint
Recently the package market is demanding the smaller package size and the low impedance electrical path with a short interconnection. The wafer level chip size 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 49mm2. It needs to overcome 2nd level reliability issue on both solder joint and drop reliability test still. To improve 2nd 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 a one of them can provide the longer stand off. In addition of improving 2nd level reliability and drop test it may need to apply different solder ball mechanical properties to increase the life time 2nd level reliability and drop test. The WLCSP structured a double solder ball showed a better 2nd level reliability result. This paper describes the IMC growth between solder ball and UBM (under bumped metal) pad that affect to the life time of 2nd level reliability on this study.
Seungwook Park, Senior Engineer
Samsung Electro-Mechanics Co. LTD.
Suwon, Gyunggi-Do, 443-743,
Korea


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