Growth mechanisms of intermetallic compounds and Bi-rich layer in ball grid array structure Cu/Sn-58Bi/Cu solder joints during solid–solid and liquid–solid electromigration

• Published in: Journal of materials science. Materials in electronics 2022-05, Vol.33 (13), p.10297-10313
• Main Authors: Huang, Jiaqiang, Wang, Xudong, Chen, Junyu, Wei, Weichun, Liu, Fengmei, Qin, Binhao, Wang, Haiyan, Zhang, Yupeng
• Format: Article
• Language: English
• Subjects: Anodes; Arrays; Ball grid packaging; Bismuth; Cathodes; Characterization and Evaluation of Materials; Chemical potential; Chemistry and Materials Science; Copper; Diffusion; Electromigration; Intermetallic compounds; Materials Science; Melt temperature; Ohmic dissipation; Optical and Electronic Materials; Potential gradient; Resistance heating; Solders; Stressing; Tin; Wind effects; Wind forces
• ISSN: 0957-4522; 1573-482X
• DOI: 10.1007/s10854-022-08018-x

Sn-58Bi solder has attracted much attention due to its low melting temperature and low cost in recent years. However, Sn-58Bi solder might occur locally melting due to the high local temperature by Joule heating and consequently raises serious reliability problems. In this study, the growth mechanisms of interfacial intermetallic compounds (IMCs) and Bi-rich layer of the ball grid array structure Cu/Sn-58Bi/Cu joints during both solid–solid (S–S) electromigration in solid solder and liquid–solid (L–S) electromigration in molten solder were investigated comprehensively. Results show that during S–S electromigration at 70 ο C, current stressing induces a reverse polarity effect on the growth of interfacial IMCs, i.e., the interfacial IMCs on the cathode side is thicker than that on the anode side. Besides, Bi atoms accumulate to form a Bi-rich layer on the anode side. During S–S electromigration at 135 ο C, current stressing causes a reverse polarity effect on the growth of interfacial IMCs, and Bi atoms on the anode side reversely diffuse into the solder, resulting in the disappearance of Bi-rich layer. During L–S electromigration at both 150 ο C and 170 ο C, current stressing induces a polarity effect on the growth of interfacial IMCs, i.e., the interfacial IMCs on the anode side is thicker than that on the cathode side. Furthermore, there is no Bi-rich layer on the anode side. The transition in growth mechanism of interfacial IMCs from the reverse polarity effect to the polarity effect is determined by the combined effect of the electronic wind force flux ( J em ) and the chemical potential gradient flux ( J chem ).