Effects of Zn and Ga Additions to Suppress PdSn4 Growth at a Solder/Pd Interface Under Current Stressing

• Published in: Journal of electronic materials 2018, Vol.47 (1), p.1-8
• Main Authors: Wang, Chao-hong, Li, Kuan-ting, Chen, Ke-hsing
• Format: Article
• Language: English
• Subjects: Characterization and Evaluation of Materials; Chemistry and Materials Science; Electromigration; Electronics and Microelectronics; Instrumentation; Lead free; Materials research; Materials Science; Optical and Electronic Materials; Palladium; Solders; Solid State Physics; Stressing; Thickness
• ISSN: 0361-5235; 1543-186X
• DOI: 10.1007/s11664-017-5676-5

PdSn 4 is the major phase formed in the interfacial systems of Pd with lead-free solders. In this study, we examined the interfacial behaviors of the Sn/Pd/Sn system under current stressing of 5000 A/cm 2 at 180°C. The results revealed that the electromigration effect on the PdSn 4 was insignificant. However, the PdSn 4 growth was very fast, similar to that without current stressing. The thickness of the PdSn 4 layer was ∼44  μ m after only 6 h of current stressing, and further increased to be ∼83  μ m after a 24-h test. The PdSn 4 phase had a superior electromigration-resistance, but the fast growth was a major concern for the interfacial reliability of the solder joints. To suppress the PdSn 4 growth, minor amounts of Zn or Ga were added into the Sn-based solder to investigate the solder/Pd couples under current stressing. Remarkably, only minor 0.5 wt.%Zn addition effectively inhibited the PdSn 4 growth under current stressing. After 6 h of current stressing, the thickness of the PdSn 4 layer was reduced to ∼17  μ m. In addition, minor Ga addition had a similar inhibiting effect. In the Sn-0.5 wt.%Ga/Pd couple, the PdSn 4 layer was only ∼12  μ m thick even after current stressing of 24 h. The inhibiting effects of Zn and Ga on the PdSn 4 growth under current stressing and the related possible reasons are further discussed.