Chemical bonding of copper and epoxy through a thiol-based layer for post 5G/6G semiconductors

With the development of post 5G/6G high-speed communication, the current frequency in the substrate is increasing. A flat copper substrate surface is wanted to reduce the signal loss caused by the skin effect. However, a flat surface harms the bonding strength between copper and epoxy, resulting in poor reliability for printed circuit boards (PCBs). This work tried to improve the bonding strength between a flat copper surface and an epoxy by bonding copper and epoxy chemically via 4-aminothiophenol (4-ATP). We investigated the influence of the treatment time of copper in a 2 mM 4-ATP ethanol solution. The treated surfaces were characterized by SEM, IRRAS, Raman, AFM, and XPS. In addition, we compared the experimental XPS results with the simulated XPS spectrum obtained via Simulation of Electron Spectra for Surface Analysis (SESSA) software, enabling us to understand the treated surface quantitatively. The interaction between treated cooper surface and epoxy was analyzed via Density Function Theory (DFT). The best treatment time is 1 h. Under this condition, the shear strength between copper and epoxy improved from 8.2 MPa to 24.1 MPa. The processing and bonding mechanisms were discussed. The results are expected to contribute significantly to fabricating of high-speed communication PCBs.