The Effect of SnxAgCu and SnAgCuX on the Mechanical Drop Performance in Lead Free CSP Package

In the study, one 14x14 lead free CSP BGA with 0.3 mm/0.5 mm ball diameter/pitch was adopted as test vehicle. The intermetallic compounds morphology evolution which can be generated when using SnxAgCu and SnAgCuX solder ball in combination with electrolytic NiAu-plated substrates was investigated during 150degC thermal aging, such as single layer SnNi IMC and complex layer SnNi/SnNiCu IMC in the interface through top and X-section view, respectively. In addition, the intensity of plate-like Ag3Sn IMC formation in the SnxAgCu solder bulkfrom 1 to 4%Ag was observed by SEM as well. The CSP BGA package with above combination was assembled to PC boards with OSP finish using Sn3Ag0.5Cu solder paste under 245degC peak temperature reflow. The test vehicle assembled was subject to mechanical drop test following JESD22-B111 to evaluate the solder joint integrity after zero and 150degC/250 hrs thermal aging. The effect of interfacial IMC morphology evolution and Ag3Sn intensity in solder bulk by x (Ag percentage) and X (forth element addition) on the mechanical drop performance will be concluded. Furthermore, one approaching in IMC microstructure control to overcome SnAgCu drop concern will be presented.