Study of IMC vs Drop Test effect on Leadfree SAC and Polymer Solder Ball

Abstract

Leaded solder ball was replaced by leadfree solder ball which is now widely used in semiconductor industries, due to the hazardous effects of lead to human’s health and toxicity for environment. Due to this, poor solder joint strength for Ball Grid Array (BGA) packages on leadfree devices is a reliability concern when subjected to reliability stress test. With a polymer core in the solder ball may be a good strategy to dissipate stress better from environment stresses compared to the conventional solder ball. However, polymer core solder ball tends to form a thicker Intermetallic Compound (IMC) layer when subjected to environmental stress. This could affect the drop test performance and caused ball drop. Thicker IMC for polymer core solder ball is due to the diffusion rate of Cu that is faster than Tin (Sn). To reduce IMC layer, the polymer core solder ball can be coated with 1 µm thickness of Nickel (Ni) on the Copper (Cu), thus offer better drop test performance by limit the Cu diffusion. IMC measurement and tray drop test were conducted in this research study under Moisture Stress Level (MSL) 2 and 3 stress to verify the reliability of the solder balls. From this study, it can be conclude that the MSL level 3 perform better performance in drop test and thinner IMC layer than MSL level 2.