Building Reliability into the PWB: Optimization of the Desmear and Metalization Processes for Use on High Frequency and Lead Free Laminate Materials

摘要

High Frequency and Lead-Free laminate materials are finding increased use in the PWB fabrication industry driven by end user requirements for high-speed signal transmission and lead-free soldering temperatures. Along with these newer materials has been the need for improved reliability. End users are continually pushing for thermal performance to exceed five solder floats and exceed 300 cycles to failure on IST testing. The PWB industry, faced with ever increasing reliability requirements compounded by the fact that these new resin materials are more difficult to desmear and metalize, have become more concerned with plating adhesion to the copper interconnect and resin material. Concerns over interconnect defects and resin adhesion of the copper are causing fabricators to reinvestigate their metallization technologies. The purpose of this paper is to provide information on how to improve the adhesion of the copper deposit through a closer study of the critical success factors influencing the metal adhesion to both the interconnect and hole wall. The research showed that the electroless copper grain structure, plating rates and desmear parameters have a significant influence on PTH reliability. Specially designed high layer count test vehicles were employed to quantify the adhesion and overall PTH reliability. The results were verified with micro section evaluation after multiple solder float excursions and Interconnection Stress Testing (IST). This work validates the necessity of the metallization process to improve the robustness of the PTH under high temperature conditions.