Corrosion study on Cu/Sn-Ag solid-liquid interdiffusion microbumps by salt spray testing with 5 wt.% NaCl solution

The progressive miniaturization and the increasing efficiency of microelectronic components generates a demand for decreasing joint sizes and solder volumes. Consequently, the generation of heat and thermal load of the interconnects increases which require an effective thermal management by an air or liquid cooling system. An aqueous cooling media sets special demands on the interconnect composition. Corrosion can have a serious impact on microscopic interconnects due to the small joint size. In this study, the influence of salt spray testing, up to 94 h with a 5 wt.% NaCl solution, on Cu/Sn-3.5Ag microbumps with intermetallic compounds is investigated. The results show that the corrosive NaCl solution affects unconsumed solder and exposed Cu areas, and can seriously damage the interconnect. The intermetallic compound Cu3Sn shows no significant degradation, and can therefore be used as passivation layer for Cu. Corrosion products are examined by EDX and reactions causing corrosion are discussed in this study.