(Dr. Daniel Baldwin, advisor)
"Flip Chip Processing of Lead-Free Solders and Halogen-Free High Density Microvia Substrates"
While flip chip technology is heavily focused on developing and refining the next generation of flip chip assembly processes and reliability, consumer demand and legislation restricting the use of lead and other hazardous materials are driving forces in a lead-free movement in microelectronics. The trend is not only towards smaller products, with higher capability, but also towards greener, more environmentally friendly products. The focus of this research is to characterize and implement environmentally conscious low cost flip chip material systems and processing, using a lead-free-solder interconnect system and microvia halogen-free substrates, thus minimizing the environmental impact. The objective is to ensure that environmentally friendly materials are selected, along with acceptable process technology for all materials as well as for the flip chip assembly.
An assembly process for environmentally conscious low cost flip chip assembly to microvia laminate substrates will be presented, based on a fully integrated high speed flip chip assembly line. Flux and underfill material compatibility will be discussed, and data will be presented analyzing the quality of the solder joint formation and underfill adhesion to halogen-free solder masks. Reliability results from air-to-air thermal shock testing and SIR Bias 85/85 testing are presented. Process and failure mode analysis are presented, based on x-ray inspection, C-SAM analysis, and assembly cross sections.