Effects of Ag content on the reliability of LED package component with Sn–Bi–Ag solder

Abstract

The effects of Ag content on the mechanical and electrical properties of the Sn–58Bi solder joints in light emitting diode (LED) package were studied. The Sn–58Bi, Sn–57.6Bi–0.4Ag and Sn–57Bi–1Ag solder were used as solder joints. The LED package was bonded on the printed circuit board (PCB) with the organic solderability preservative (OSP) surface finish, and then it was aged at 85 °C for 100, 300, 500 and 1000 h, respectively. In order to evaluate the mechanical and electrical properties, the shear test was conducted and the change of current versus voltage was measured. The shear strength and electrical conductivity of solder joints decreased with an increasing aging time. With an addition of 1.0 wt% Ag, the shear strength was improved and higher than those of other solder joints. The microstructure and composition of the solder joints were investigated with a scanning electron microscope, an energy dispersive spectrometer and an electron probe micro analyzer. The Cu6Sn5 intermetallic compounds (IMCs) formed between solder and OSP surface finished Cu pad of PCB. The thickness of the IMCs increased with an increasing aging time. By an addition of 0.4 wt% Ag, fine Ag3Sn particles were dispersed inside the solder matrix and large-sized primary Ag3Sn IMCs were formed with 1.0 wt% Ag addition.