Electrochemical migration of Sn and Sn solder alloys: a review

Abstract

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.

Effect of Recrystallization on β to α-Sn Allotropic Transition in 99.3Sn–0.7Cu wt. % Solder Alloy Inoculated with InSb

“…The 99.3Sn-0.7Cu wt. % alloy (and its micro-alloyed variation) is widely used in the electronics industry [2]. Bulk samples were prepared by casting, according to the tin pest induction method developed by Skwarek et al [28].…”

“…Tin (Sn) is one of the most frequently used materials in the electronics industry. Sn is the base metal of solder alloys, surface finishes of solder pads, and component leads [1,2]. Furthermore, it is used as an optical layer [3] and as an anode in batteries [4].…”

Evidence for Ag participating the electrochemical migration of 96.5Sn-3Ag-0.5Cu alloy

“…As soon as the Ag dissolves from Ag3Sn, the Ag + ions will be formed as described by reaction (6). At the same time, the OHwill be produced at cathode because of the O2 reduction and H2O reduction, as expressed in reactions (1) and (2). Then, the Ag + will migrate toward that cathode and OHwill migrate toward anode.…”

“…This process occurs when two oppositely biased and closely spaced electrodes are connected by a continuous electrolyte layer. Metal ions are produced at the anode and then migrate toward the cathode, where they can be reduced to metallic dendrite and grows toward the anode [1,2]. As soon as the dendrite reaches the anode, the short circuit occurs and then causes the failure of electronics.…”

“…According to the definition of ECM, ECM can be considered as a consecutive three-step process: (i) dissolution of metal, (ii) ion migration and (iii) deposition of metal ions [2]. During the ECM of Sn-Ag or Sn-Ag-Cu alloys, as soon as the dissolution of Ag3Sn occurs and Ag + is produced, then it migrates in the electrolyte layer, finally deposited at cathode.…”