Lead-Free Assembly and Reliability of Chip Scale Packages and 01005 Components
Type of DegreeDissertation
Electrical and Computer Engineering
MetadataShow full item record
Chip Scale Packages (CSPs) are widely used in portable and hand-held electronic devices due to their small size and availability. Consumers expect portable products to survive being dropped repeatedly, and drop testing is now common in the reliability evaluation of portable product designs. Lead-free assembly is another trend in electronics industries because of legislation and market factors. Underfill materials are often used to improve the reliability of a variety of electronic components. In this research, the assembly processes for three underfill options (capillary underfill, fluxing underfill and corner bond underfill) compatible with lead-free assembly have been developed and evaluated. CSPs with eutectic SnPb and without underfill were compared with lead-free and underfilled CSPs. Drop tests were carried out to evaluate the drop reliability of the CSPs as a function of assembly materials. Failure analysis was performed to reveal the typical failure modes for different underfills. The mechanical shock reliability over the life of the product is very important to the customer. The effects of different surface finishes (Immersion Sn and Immersion Ag), reflow profiles (two cooling rates) and thermal aging on the drop reliability of lead-free CSPs were investigated. Drop test results for assemblies as-built and as a function of aging at 125°C were correlated with cross sectional analyses of the solder joints. Microstructural and failure analyses were also conducted to study IMC evolution and the formation of Kirkendall void and the effect of these changes on drop reliability. Reducing the size of the passive components and the spacing between them increases the package density and is an efficient way to miniaturize many electronic products. To satisfy this demand, 01005 chip components are now commercially available. However the implementation of such tiny components in new products presents some novel design and assembly process issues. A 01005 test vehicle was designed to investigate the effect of PCB pad design on assembly yield. Process capability of 01005 test board manufacturing was evaluated. A Design of Experiment (DOE) was used to optimize the solder paste printing based on 3D solder paste inspection. Lead-free solder was used for all assembly trials. Several tests were performed to explore the influence of process parameters on placement accuracy and reflow defects. As a results of this analyses of experimental results and a post-reflow inspection for assembly defects, recommendations for PCB design and assembly processes are made.