LAUSR

Micron level Cu-pillar microbumps, which appear as the size of three-dimensional packaging shrinks down, have to introduce many unexpected reliability problems. The fast growth of intermetallic compounds (IMC) and voids tend to be a serious one. In this paper, the growth behaviors of IMC and voids were investigated in Sn–3.5Ag/Ni/Cu bumps, which were in the diameter ranging from 6 to 11 μm and fabricated under same reflow process. The consequence manifested that the growth rate of interfacial IMC increased from 0.448 to 0.578 μm/min as the bump diameter decreased from 11 to 6 μm and the acquired IMC could be divided into two layers: the (Cu, Ni)6Sn5 layer and Ni3Sn4 layer. As a result of the migration of Ni atoms, many voids were left in the interface between (Cu, Ni)6Sn5 and Ni3Sn4. In the edge of Cu pillar, side wall wetting reaction was detected, which was confirmed by the formation of voids and (Cu, Ni)6Sn5 phase. Further, as the bump diameter decreased, the side wall wetting reaction aggravated, which partly contributed to the acceleration of IMC growth.