Board-level drop reliability and fracture behavior of low-temperature soldering Sn-Ag-Cu/Sn-Bi-X hybrid BGA solder joints for consumer electronics

Low-temperature soldering technology (185-195 degrees C) is applied for assembling consumer electronics with various Bi contents, and board-level drop reliability of hybrid Sn-Ag-Cu/Sn-Bi-X ball grid array (BGA) solder joints interconnected chip components and PCB boards was evaluated. A hybrid solder joint structure of a partial melting Sn-Ag-Cu BGA solder ball wrapped by a continuous Bicontaining region was fabricated, and the effects of low Bi content and minor additives of Sn-Bi-X solders on microstructure and board-level drop reliabilities were revealed. The thicker interfacial Cu6Sn5/(Cu,Ni)(6)Sn-5 intermetallic compounds (IMCs) accompanied with larger Bi-rich phases formed at the solder/Cu interface with decreasing Bi content of Sn-Bi-X solder. Drop impact-induced cracks initiated and propagated within the larger Bi-rich phases in a wear-out failure mode, compared with cracks initiated and propagated along the solder/IMC interface in an early failure mode if fine Bi-rich phases segregated at the solder /IMC interface. The Sn-49Bi-1Ag solder was the optimum low-temperature solder for assembling Sn-Ag-Cu/Sn-Bi-X hybrid solder joints, which failed in a wear-out failure mode with the highest drop characteristic lifetime of 420 drops, significantly higher than those failed in an early failure mode.

Automated summary

Low-temperature soldering technology is used in assembling consumer electronics with various Bi contents. The study evaluated the board-level drop reliability of hybrid Sn-Ag-Cu/Sn-Bi-X solder joints and found that Sn-49Bi-1Ag solder was the optimal choice, providing significantly higher drop characteristic lifetime.