Abstract We made head-shaped Cu-Sn solder joints with diameters about 10 μm, 20 μm, and 50 μm and reflowed the samples at 240 oC, 260 oC, and 280 oC for… Click to show full abstract
Abstract We made head-shaped Cu-Sn solder joints with diameters about 10 μm, 20 μm, and 50 μm and reflowed the samples at 240 oC, 260 oC, and 280 oC for 60 s to 600 s. In the 10 μm bumps, there is only one Cu6Sn5 grain after reflow, thus the classic model of scallop-type grain growth of Cu6Sn5 does not apply. Also, the grain growth in the small size bumps has the faster growth rate. We proposed a surface diffusion-controlled model to explain the new kinetics. According to our model, the diffusion activation energy is calculated to be QS = 0.18 ± 0.02 eV/atom and diffusion frequency factor to be DS0 = 5.65 ×10-3 cm2/s.
               
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