The reliability investigation of lead-free solders is still a current issue. In this paper, Electrochemical Migration (ECM) behaviour of novel lead-free micro-alloyed low Ag content solders was investigated by water drop test in
IntroductionIn microelectronics industry, the applied solder materials are one of the most important factors related to the reliability of the products. According to the Restrictions of Hazardous Substances (RoHS) directive of European Union, lead bearing solders had to be replaced with lead-free ones [1]. In this context, alternative binary alloys had been examined as replacements for SnPb solders, such as near-eutectic SnAg, SnCu and SnZn alloys. However, ternaries (SnAgCu, SnZnAg, SnZnIn, etc.) and even quaternary alloys (SnZnAgAl, SnAgBiCu, SnInAgSb) had also been studied as candidates for lead-free solders [2][3][4][5][6][7].The reliability investigation of lead-free solders is still a current issue. One of the important reliability topics is the electrochemical migration (ECM) failure phenomenon. The common characteristics of the ECM phenomenon include the presence of moisture on conductor-dielectric-conductor systems under bias voltage, the electrochemical process and the metallic dendrite growth. This process is driven by the applied electric field from the anode to the cathode. Dendrite growth occurs as a result of metal ions being dissolved into a solution from the anode and deposited at the cathode, thereby growing in needle or tree-like formations. This effect causes short-circuits in electronic circuits, which may lead to a catastrophic failure.Many papers can be found about ECM investigations carried out on different lead-free solder alloys. Takemoto et al. have found that some tin based lead-free solder alloys are more resistant to ECM than Sn-Pb40 alloy and pure Indium. In-48Sn and In-50Pb alloys were found to be immune to ECM in high purity water [8]. Yu et al. have described that in Sn-37Pb and Sn-36Pb2Ag systems the main migration element is Pb, while in Sn-Ag and Sn-Ag-Cu solder alloys Sn leads the migration in high purity water [9,10].Other publication reported that SAC305 lead-free solder alloy has longer ECM lifetime in 0.001% NaCl solution than in 0.001% Na2SO4, since the passivity layer formed of SnO2 is thicker in the case of NaCl solution and Sn is the only element that contributes to ECM at room temperature [11]. The migration behaviour and the deposition process of Sn, Cu and Ag in case of SAC305 solder alloy were also observed in a thermal-