Abstract

This study investigates the backward compatibility solder joint formed at high peak reflow temperature in aerospace industries. The backward compatibility solder joint is made up of lead-free ball grid array mounted on printed circuit board using tin–lead solders at a maximum reflow temperature ranging from 241.9 to 242.45 °C. The reflow process was conducted under a nitrogen atmosphere in a full convection reflow oven for 80.12–81.27 s. The scanning electron microscopy cross section of the solder ball depicts fairly uniform composition and phase distribution of the Pb-free plastic ball grid array and the tin–lead solder paste across all joints. Nanoindentation tests showed better mechanical properties with higher elastic modulus at 68.64 GPa and acceptable hardness value at 0.26 GPa as compared to those of Sn–Pb and Pb-free solder balls. Intermetallic compound formation at both joints seen in the scanning electron microscopy shows a scallop shape and randomly directed growth because of the uniformly distributed Pb-rich phase on the solder ball. The average intermetallic compound thickness measured by scanning electron microscopy equipped with energy-dispersive X-ray analysis was 3.633 μm, which was less than the specified thickness of 12 μm from the laboratory request.

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