Mechanical Reliability of Epoxy Sn–58wt.%Bi Composite Solder Under Temperature-Humidity Treatment with Organic Solderability Preservatives (OSP) Surface Finish

Abstract

The microstructures and mechanical reliability of Sn–58Bi solder and epoxy Sn–58Bi composite solder joint were investigated with organic solderability preservative surface finishes. The mechanical reliabilities of Sn58Bi and epoxy Sn58Bi solder were evaluated by the board-level drop test and the 3-point bend test after temperature-humidity storage testing. The microstructure and chemical composition of the solder joints were characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy, respectively. The addition of epoxy in solder paste did not affect the morphology of the intermetallic compound. The thickness of the scalloped-shaped Cu6Sn5 intermetallic compound of solder/OSP joint increased with aging time. The drop number until fail for the epoxy Sn58Bi/OSP joint was higher than that for the Sn–58Bi/OSP joint; the average numbers of drops withstood by the Sn–58Bi/OSP joint and epoxy Sn–58Bi/OSP joint following the reflow process were fewer than 10 drops and 180 drops, respectively. The drop number of solder/OSP joints decreased with increasing aging time. The result of the 3-point bend tests shows that the number of bend cycles for the epoxy Sn–58Bi/OSP joint was 30 times higher than that for the Sn–58Bi/OSP joint. The number of bend cycles for solder/OSP joints was decreased with increasing aging time.