The Role of Polymer Shrinkage and Oxidation in Thermal Aging Induced Crack Formation in Glass Fiber Reinforced Printed Circuit Boards

This research presents a comprehensive analysis of crack formation induced by thermal aging within printed circuit boards (PCBs). It highlights novel findings related to polymer shrinkage and debonding phenomena at the interface between epoxy matrix and glass fibers, which elucidate the underlying mechanisms and root causes of this critical reliability issue in miniaturized electronic components. The cracking induced by thermal aging of fiber-reinforced polymer composites in PCBs represents a significant reliability risk, particularly as temperature requirements continue to rise. The study encompasses an evaluation of three commercial PCB materials, focusing on the role of thermal oxidation in the polymer matrix and the associated chemical changes, as evidenced by Fouriertransform infrared spectroscopy (FTIR). The FTIR analysis reveals notable differences among the studied PCB materials, demonstrating that polymer oxidation leads to shrinkage phenomena. Optical inspections utilizing laser scanning microscopy (LSM) provide visual evidence of surface changes before and after thermal aging, while roughness measurements from LSM illustrate the trend of polymer shrinkage over time. Furthermore, the research identifies polymer shrinkage as a critical factor in crack initiation, with scanning electron microscopy (SEM) revealing debonding between the polymer and the reinforcing fibers. Finally, the study establishes a correlation between the increasing trend of polymer shrinkage and the propagation of crack length, indicating that the material exhibiting the highest shrinkage also experiences the most significant crack lengths. This research marks a significant advancement in understanding the damage mechanisms associated with crack formation within glass bundles in PCBs, emphasizing that crack formation is primarily driven by thermooxidative induced shrinkage phenomena.