A STUDY OF THE FAILURE MECHANISMS IN LEAD-FREE AND EUTECTIC TIN-LEAD SOLDER BUMPS FOR FLIP CHIP ASSEMBLYAuthors: Julia Y. Zhao, David Mackessy, and John Jackson
Company: Analog Devices Incorporated
Date Published: 9/25/2005 Conference: SMTA International
Daisy chain resistance changes monitored during High Temperature Storage (HTS) were compared to shear strength changes. The effect of thermal aging on bump fatigue performance was evaluated; shear strength did not directly reflect fatigue resistance. Bump degradation monitored as an increase in the daisy-chain resistance was correlated to Intermetallic Compound (IMC) morphology changes and crack growth during temperature cycling testing (TCT). For material selection studies, HTS is recommended as a precursor to TCT.
For Pb-free bumps the dominant failure mechanism was found to be brittle fracture between the solder and IMC near the under bump metallurgy (UBM). Crack segments developed at the edge of the UBM as well as in the middle between IMC and solder. Underfill materials need to be carefully selected to optimize TCT performance.
Key Words: SAC, SnPb, Flip Chip, Pb-free, Brittle Fracture, Intermetallic Compound, Reliability
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