Determination of Average Failure Time and Microstructural Analysis of Sn-Ag-Bi-In Solder Under Electromigration

• Published in: Journal of electronic materials 2009-12, Vol.38 (12), p.2780-2785
• Main Authors: Wu, Albert T., Sun, K.H.
• Format: Article
• Language: English
• Subjects: Applied sciences; Brazing. Soldering; Characterization and Evaluation of Materials; Chemistry and Materials Science; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Diffusion in solids; Electromigration; Electronics and Microelectronics; Exact sciences and technology; Failure analysis; Growth from melts; zone melting and refining; Instrumentation; Intermetallic compounds; Joining, thermal cutting: metallurgical aspects; Lead free solders; Materials Science; Metals. Metallurgy; Methods of crystal growth; physics of crystal growth; Microstructure; Optical and Electronic Materials; Physics; Solid State Physics; Transport properties of condensed matter (nonelectronic)
• ISSN: 0361-5235; 1543-186X
• DOI: 10.1007/s11664-009-0931-z

Despite the extensive use of Sn-Ag-Cu as a Pb-free solder alloy, its melting point is significantly higher than that of eutectic Sn-Pb solder. Sn-Ag-Bi-In solder is an alternative Pb-free solder, with a melting temperature close to that of eutectic Sn-Pb. This study elucidates the electromigration behavior of Sn-Ag-Bi-In solder and then compares the results with those of the Sn-Ag-Bi system. The behavior of Pb-free Sn-Ag-Bi-In solder strips under electromigration is examined by preparing them in Si (001) U-grooves. The samples are then tested under various temperatures and current densities. Although the compounds thicken near both electrodes with current stressing, the thickness at the anode exceeds that at the cathode. Experimental results of the average failure time indicate that Sn-Ag-Bi-In solder has a longer lifetime than does Sn-Ag-Bi, which is attributed to the ζ phase. Additionally, the ζ phase dissolved by the current in the early stage replenishes the outgoing atomic flux. These atomic fluxes also enhance the growth of abnormally large particles in the middle of the strips. Field-emission electron probe microanalysis (FE-EPMA) results indicate that the amount of indium is reduced after the ζ phase near the cathode is exhausted for extended current stressing time.