STUDY OF EPOXY FLUX TO IMPROVE RELIABILITY OF IC PACKAGES FOR AUTOMOTIVE APPLICATIONS

摘要

Over recent years, the volume of electronic components in cars has increased at an incredible rate. With the trend toward increased functionality, greater speed and higher integration, the components used in electric vehicles and autonomous driving are simultaneously increasing in size and decreasing in pitch. As a result of these design trends, there is an increasing amount of heat generated within the semiconductor packages and this is contributing to the challenge of ever-increasing reliability specifications. Compared to mobile devices, tablets, laptops and many other applications, automotive components and assemblies have severe temperature cycling requirements. For example, the AEC-Q10 Grade 1 temperature cycling test range is -40°C to 125°C. It is generally known that the upper/package side of the solder joint is susceptible to cracking and failure during this regimen. One approach to addressing this challenge is by increasing the bulk strength of the solder by using high-reliability solder alloy to improve joint strength. Another is to mechanically reinforce the solder joint with polymer-based compounds such as underfill (UF), sidefill (SF) and cornerbond (CB) materials. However, these methods increase the burden on the assembler by adding additional equipment, processes and materials. As an alternative method for improving temperature cycling reliability, the researchers developed a material capable of perform solder ball reinforcement and ball attachment simultaneously in one reflow using epoxy flux for solder ball mounting on a semiconductor package. This evaluation was performed on a 0.3 mm pitch wafer level package (WLP) with SAC305 solder balls. First, solder ball mounting performance was evaluated comparing two epoxy flux formulations to a conventional equipment manufacturer's recommend flux. The second epoxy flux (EF2) performed as well as the standard flux. A simulation analysis was performed modeling the effects of four reinforcement structures. Parts were assembled and subjected to -40°C to 125°C temperature cycling regimen. The results confirmed the simulation analysis that reinforcement of the upper/package-side solder joint increased the reliability performance by approximately three-fold.