Geometrical outline evolution and size-inhibiting interaction of interfacial solder bubbles and IMCs during multiple reflows

By utilizing synchrotron radiation X-ray imaging technique for in situ observation, the geometrical outline evolution and size-inhibiting interaction of solder bubbles and IMCs during multiple reflows were investigated in this work. It was found that the interfacial bubbles can inhibit the growth of IMC grains caused by the hindering effect of bubbles on contact and reaction between solder and substrate; meanwhile, following the growth of IMC grains, the bubble size in return got smaller and its aspect ratio became larger with reflow cycle, which is the result of inhibiting effect of solid IMC grains on solder voids; Because of boundary segregation and thermomigration, Cu atoms tend to gather on the bubble boundary and form a Cu-rich phase, consequently resulting in the formation of IMCs at the gas/solder interface area.