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ABSTRACT This paper investigates the impact of reflow cycle parameters on via reliability in printed circuit boards (PCBs). The primary objective was to determine how variations in ramp rate, peak temperature, dwell time, and soak time influence the integrity and reliability of plated through hole (PTH) vias. Using a 20-layer commonly used high Tg FR4 test board with 10 mil through holes, a series of typical assembly reflow profiles based on SAC 305 solder were tested using Interconnect Stress Testing (IST)[8]. Key findings indicate that peak temperature and time near peak temperature are the most significant factors affecting via reliability. The paper also highlights the importance of interactions between variables, particularly the three-way interaction of peak temperature, time near peak, and soak time. The results demonstrate that while ramp rate alone is not statistically significant, its interactions with other variables are crucial. All work was conducted through the HDP User Group International Consortium under the project titled Reflow Cycle Via Reliability Impact, facilitated by Jack Tan. All raw data and full versions of the project documents are available to member companies ( www.hdpusergroup.org ).