Improvements of the Epoxy-Copper Adhesion for Microelectronic Applications

Upcoming electronic devices are required to be further miniaturized. The microelectronics industry and packaging technology focus efforts on optimizing adhesion between plated copper and printed circuit board (PCB) substrate (here epoxy/glass buildup composite), while keeping smooth surfaces for high-frequency application. We propose herein to review and deepen the basic understanding of the sequential buildup process employed worldwide for the past several decades for multilayered PCB manufacturing. This multiscale and interdisciplinary study aims to establish the relationships between degrees of precuring (alpha), oxidative etching (permanganate desmear wet treatment), and copper adhesion. The epoxy curing states on industrial coupons were evaluated by diffuse-reflectance infrared Fourier transform spectroscopy. Then, atomic force microscopy (AFM) described the desmear performances through topography evolution with alpha between the different sequence steps. Finally, polymer-copper adhesions were investigated by using peel strength tests, AFM, and X-ray photoemission spectroscopy. We remark that high adhesion strengths were obtained for very smooth surfaces. This study outlines the contribution of the polymer network viscoelasticity (relaxation dynamic) on the polymer-copper adhesion. We observed that faster polymer relaxation rates tended to increase polymer-copper adhesions.