Study on Mechanical Behavior and Long-term Storage Reliability of Micro Flip Chip Mixed Solder Joints

In this paper, a mixed solder joint with higher height compared with single component joint was formed by welding high melting point bumps (90Pb10Sn, 80Pb20Sn, Sn1.8Ag) of 100µm in diameter with low melting point solder (63Sn37Pb) under 63Sn37Pb reflow process, mechanical properties, grain distribution, IMC deformation behavior and crack propagation behavior during shear test were studied and analyzed as well. The results of this work were listed: (1) Sn1.8Ag bumps showed a better fusion effect with 63Sn37Pb solder. Uniformly dispersed Sn phase, Pb-rich phase and Ag3Sn phase alloys could be observed in Sn1.8Ag/63Sn37Pb solder joints, and Sn phase was significantly enriched at the edges of the 90Pb10Sn/63Sn37Pb and 80Pb20Sn/63Sn37Pb solder joints.(2)Plastic deformations were observed mainly in two forms: sliding (or double-sliding) and deformation zone in shearing test. Dynamic recovery occurred during plastic deformation process, forming recovered sub-crystal, and the crack propagation generally proceeds in form of trans-crystal. (3)The shape of IMC was the fundamental factor affecting the mechanical properties of the micro solder joints, 80Pb20Sn/63Sn37Pb mixed solder joints turned out to have better mechanical properties.