Thermal Degradation and Decomposition of FR4 Laminate PCB Substrates Joined by Friction Riveting

Abstract

This study investigates the thermal degradation and chemical transformations of friction-riveted glass fiber-reinforced epoxy laminate (FR4) printed circuit boards (PCBs) with different copper configurations. The primary objective is to identify the critical degradation temperatures and the impact of copper layers on joint integrity and thermal stability. Cross-sectional analyses revealed that joints produced at 250 °C exhibited minimal rivet deformation, while those at 360 °C showed significant deformation and increased epoxy degradation. Thermal analyses, including Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA), identified critical degradation temperatures at 327 °C for FR4-I Cu with a single copper layer and 329 °C for FR4-II Cu with double copper layers. The presence of the additional copper layer in FR4-II Cu significantly improved thermal stability, with total mass loss reduced from 29.8% (FR4-I Cu) to 23.5% (FR4-II Cu) at a heating rate of 20 °C/min. The loss of flame-retardant components at elevated temperatures raises concerns for the fire safety of PCBs in electronic devices. These findings highlight the importance of selecting appropriate FR4 configurations for applications exposed to high temperatures, enhancing reliability and safety in the electronics industry.