Improvement of wettability and drop impact reliability by Al addition in SnAgCu solder

SnAgCu solder is most popular solder composition system in the package industry. Therefore, SnAgCu solder has been studied by many researchers to improve its properties. In this study, we ran tests to verify the effect of Al additive metal in SnAgCu solder in term of wettability and drop impact reliability. The test solder compositions were Sn1.0Ag0.5Cu solder (Ref. solder) and Sn1.0Ag0.5Cu-xwt%Al solder and Al contents were 0.005,0.01,0.02,0.1, and 0.12wt%. Generally, a higher wettability solder has high wetting force and short wetting time. In addition higher wettability solder shows enhancement of the bonding property on metal pads due to an increase in bonding area. In the results of the wettability test, Al doped solders showed higher wetting force and shorter wetting time than the Ref. solder. Meanwhile, wetting property was enhanced by increasing the additive content of Al metal. However, too much Al addition over 0.1 wt% resulted in a poor wetting property due to an increase in oxides In this study, the optimal content of the Al additive was selected to be 0.01~0.02wt%Al. In addition Sn1.0Ag0.5Cu0.02Al (under Al doped solder) and the Ref. solder were tested for their bonding property and drop property. Generally, IMC thickness, IMC shape, and the ductility of the solder bulk are the most influential factors in drop impact tests. Therefore, before the drop impact test, these factors were tested as multi-reflows. At first, in the ball shear test, the bonding property was stable as multi-reflows in all samples. In addition, there were no differences in IMC shape and IMC growth observed after 5 reflows between the Ref. solder and the Al doped solder. Meanwhile, in the hardness test, the Al doped solder showed lower hardness values compared with the Ref. solder. Thus, we judged that the Al doped solder after reflow has higher ductility and estimated that the Al doped solder would show enhanced drop properties in the drop impact test. Actually, in the results of t- - he drop impact test on Cu-OSP PCB, Al doped solder showed an over 30% better drop impact reliability compared to the Ref. solder. Through this study, we could found that wettability and drop property of Sn-Ag-Cu solder system can be improved through the Al additive. However, Al doped solders actually have to be tested more for the application of PKG.