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Reliability Study on Copper Pillar Bumping with Lead Free Solder

With the increasing connection density of ICs, the bump pitch is growing smaller and smaller. The limitations of the conventional solder bumps are becoming more and more obvious due to the spherical geometry of the solder bumps. A novel interconnect structure - copper pillar bump with the structure of a non-reflowable copper pillar and a reflowable solder cap is one of the solutions to the problem. The scope of this paper covers flip chip assembly of the copper pillar bump soldered to lead free flip chip solder on the SAC substrate with bump pitch of 150mum. Reliability study result including high temperature storage (HTS) and temperature cycling (TC) would be detailed discussed in this paper.