Surface Metallization of PTFE and PTFE Composites by Ion Implantation for Low-Background Electronic Substrates in Rare-Event Detection Experiments

Polytetrafluoroethylene (PTFE) is a low-background polymer that is applied to several applications in rare-event detection and underground low-background experiments. PTFE-based electronic substrates are important for reducing the detection limit of high-purity germanium detectors and scintillator calorimeters, which are widely applied in dark matter and 0υββ detection experiments. The traditional adhesive bonding method between PTFE and copper is not conducive to working in liquid nitrogen and extremely low-temperature environments. To avoid adhesive bonding, PTFE must be processed for surface metallization owing to the mismatch between the PTFE and copper conductive layer. Low-background PTFE matrix composites (m-PTFE) were selected to improve the electrical and mechanical properties of PTFE by introducing SiO2/TiO2 particles. The microstructures, surface elements, and electrical properties of PTFE and m-PTFE were characterized and analyzed following ion implantation. PTFE and m-PTFE surfaces were found to be broken, degraded, and cross-linked by ion implantation, resulting in C=C conjugated double bonds, increased surface energy, and increased surface roughness. Comparably, the surface roughness, bond strength, and conjugated double bonds of m-PTFE were significantly more intense than those of PTFE. Moreover, the interface bonding theory between PTFE and the metal copper foil was analyzed using the direct metallization principle. Therefore, the peel strength of the optimized electronic substrates was higher than that of the industrial standard at extremely low temperatures, while maintaining excellent electrical properties.