Effects of Temperature–Humidity Treatment on Bending Reliability of Epoxy Sn–58Bi Solder with Electroless Nickel Immersion Gold (ENIG) and Electroless Nickel Electroless Palladium Immersion Gold (ENEPIG) Surface Finishes

An epoxy Sn–58wt.%Bi solder joint was evaluated by a three-point bending test with electroless nickel immersion gold (ENIG) and electroless nickel electroless palladium immersion gold (ENEPIG) surface finishes aged at 85 °C and 85% relative humidity. Scanning electron microscopy and electron probe microanalysis were carried out to study intermetallic compound variation. The morphology, total thickness, and chemical composition of intermetallic compound in epoxy Sn58Bi solder joints were the same as those of Sn–58wt.%Bi solder joints with each surface finish. The average number of bending-to-failure cycles for the epoxy Sn–58wt.%Bi solder/ENIG joints and epoxy Sn–58wt.%Bi solder/ENEPIG was more than 4000 and 5000, respectively. The average number of bending-to-failure cycles of the epoxy Sn–58wt.%Bi solder joint decreased with increasing age. Three-point bending reliability of epoxy Sn–58wt.%Bi solder joints was higher than that of Sn–58wt.%Bi solder with both surface finishes. Cracking of all solder joints subjected to as-reflowed was propagated through the solder matrix. However, after aging for 1000 h, cracking occurred primarily between intermetallic compound layers.