The formation and conversion of intermetallic compounds in the Cu pillar Sn–Ag micro-bump with ENEPIG Cu substrate under current stressing

The intermetallic compound growth behavior of Cu pillar micro-bump solder joint, with electroless Ni/electroless Pd/immersion Au (ENEPIG) metallization on substrate, was investigated with and without current stressing. The high volume of PdSn4 was formed in the as produced micro-bump joint. Electric current stressing caused the growth of and the conversion between PdSn4 and Ni3Sn4. The conversion of PdSn4 to Ni3Sn4 was accompanied by voids formation between the neighboring intermetallic compounds. The void formation was attributed to the volume difference between the two compounds.