Sn and Sn solder alloys in microelectronics are the most susceptible to suffer from electrochemical migration (ECM) which significantly compromises the reliability of electronics. This topic has attracted more and more attention from researchers since the miniaturization of electronics and the explosive increase in their usage have largely increased the risk of ECM. This article first presents an introductory overview of the ECM basic processes including electrolyte layer formation, dissolution of metal, ion transport and deposition of metal ions. Then, the article provides the major development in the field of ECM of Sn and Sn solder alloys in recent decades, including the recent advances and discoveries, current debates and significant gaps. The reactions at the anode and cathode, the mechanisms of precipitates formation and dendrites growth are summarized. The influencing factors including alloy elements (Pb, Ag, Cu, Zn, etc.), contaminants (chlorides, sulfates, flux residues, etc.) and electric field (bias voltage and spacing) on the ECM of Sn and Sn alloys are highlighted. In addition, the possible strategies such as alloy elements, inhibitor and pulsed or AC voltage for the inhibition of the ECM of Sn and Sn solder alloys have also been reviewed.

No abstract

No abstract

No abstract

No abstract

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-

No abstract

The effect of copper substrate roughness and tin layer thickness were investigated on whisker development in the case of Sn thin-films. Sn was vacuum-evaporated onto both unpolished and mechanically polished Cu substrates with 1 µm and 2 μm average layer thicknesses. The samples were stored in room conditions for 60 days. The considerable stress—developed by the rapid intermetallic layer formation—resulted in intensive whisker formation, even in some days after the layer deposition. The developed whiskers and the layer structure underneath them were investigated with both scanning electron microscopy and ion microscopy. The Sn thin-film deposited onto unpolished Cu substrate produced less but longer whiskers than that deposited onto polished Cu substrate. This phenomenon might be explained by the dependence of IML formation on the surface roughness of substrates. The formation of IML wedges is more likely on rougher Cu substrates than on polished ones. Furthermore, it was found that with the decrease of layer thickness, the development of nodule type whiskers increases due to the easier diffusion of other atoms into the whisker bodies.