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Study of Factors Which Influenced to Bump Shape and Voids in Bumps during Bump Formation with Solder Paste
Keywords: solder paste, bump, reliability
Regarding to inner bump formation using solder paste for FC-BGA and FC-CSP, the voids and abnormal bump shape generation are undesirable problems to achieve high quality assembly. The solder pastes which contain small solder particle and flux are applied to wafer bumping and substrate bumping method. However, as the bump pitch becomes tighter, the influence of those problems gets more serious especially for yield issue. In this study, we tried to solve the following issues 1)voids generation using 99.3mass%Sn-0.7mass% Cu solder paste and other alloys, 2)the dint bumps generation on the top of bumps using 95mass%Pb-5mass%Sn paste and 3)the needle and plate like intermetallic compound generation on the top and side of bumps using 96.5mass%Sn-3mass%Ag-0.5mass%Cu paste and 95.5mass%Sn-4mass%Ag-0.5mass%Cu paste. In terms of 1), it was available to understand when and where voids were generated by in-situ soft x-ray observation, and we could construct our original consideration why voids were generated during bumping process. In terms of 2) and 3), it was found that some kind of impurities affected on the dint, needle and plate like IMC generation. Furthermore, we tried to understand from the influence of reflow profile. By understanding these defects, we believe we can bring benefits to operating solder paste for printing method.
Masayuki Ishikawa, Assistant to Manager, R&D Department
Mitsubishi Materials Corporation
Sanda-shi, Hyogo

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