A novel solvent swell system with enhanced performance on versatile laminate materials

The implementation of the RoHS Directive in 2006 has led to a requirement that solders used in the fabrication of PCBs should be lead-free. Higher melting point lead-free solder alloys require increases in reflow temperatures, compared to eutectic tin-lead alloy solders. This has led to a substantial increase in the number of lead-free capable laminate materials over the last few years. Multi-functional epoxy resins using phenolic curing systems and halogen-free materials now represent the main stream materials used for PCB fabrication, Such materials provide higher thermal stability and lower coefficients of thermal expansion, but also have higher chemical resistance than normal performance materials. In order to properly desmear materials with increased chemical resistance, optimized solvent swell systems are required. This article presents experimental data to illustrate the limitations of typical solvent swell system performance on those newly developed materials in terms of desmear rate, surface topography, and reliability performance. The performance of a new solvent swell process capable of overcoming the drawbacks of current solvent swell systems will be described. This new process is compatible with the full range of high performance laminate materials available in the market.