Low-temperature Soldering for Low-temperature PET Substrates for Flexible and Formable 3D Electronics
‘Flexible Hybrid Assemblies’ offer substantial advantages compared to conventional rigid FR-4 based assemblies. Specifically, Flexible Hybrid Assemblies enable weight reduction, facilitate thinner devices/smaller stand-offs and offer remarkable design flexibility. Current generation flexible hybrid assemblies typically use polyimide-based substrates and SAC-based solder pastes with a melting point around 217°C. Polyimide-based substrates are expensive, lack water clear transparency and typically cannot be thermoformed into 3D structures. Furthermore, SAC-based solder pastes, with a peak reflow temperature of around 240°C-250°C, often induce warpage, misalignment and can cause other assembly defects. To address these shortcomings, we present the use of novel low temperatures, high-reliability solders that can be used in concert with flexible and/or formable substrates. This paper will present results and performance data for the entire Flexible Hybrid Ecosystem: - Low Temperature, PET Substrates: Data for various heat stabilized PET (Cu-Flex) substrates will be presented. - Low-Temperature Alloy and Paste Development: Results of HVM compatible, SMT processing to build state-of-the-art assemblies will be presented. - Reliability Assessment: Thermal, Electrical, and Mechanical Performance Testing. In summary, our paper will demonstrate the use of novel low-temperature substrates, assembly materials and SMT-based processes that enable high volume manufacturing (HVM), of next-generation Flexible Hybrid Electronics.