Friction riveting of printed circuit boards (P.C.B.) and aluminum hybrid joints: joint formation analysis and characterization

Abstract

This work addressed the feasibility study of the Friction Riveting joining process on glass-fiber-reinforced epoxy resin laminate sheet (FR4-PCB) and 2024-T351 aluminum alloy rivets by investigating the rivet scale effects, the amount of copper layer on the surfaces of the plates, and their influence on heat development, and material behavior as well as subsequent joint formation and properties, including microstructure and mechanical performance of the joints. The research work was carried out at the Institute of Materials Mechanics Solid State Joining Processes Helmholtz-Zentrum Hereon in Germany in collaboration with the Material Engineering Department of the Federal University of São Carlos. The one-factor-at-a-time (OFAT) approach was used to investigate the influence of process parameters on the process temperature, macro and microstructural deformation, and mechanical properties. The macro and microstructural characterization were carried out by light optical microscopy (L.O.M.) and the mechanical properties of the joints were determined by T-pull tensile testing. The results demonstrated the viability of the process for the case of FR4 material with AA2024; joints with good mechanical performance (828 N ± 65 N) were achieved using FR4 composites plates with reduced thickness (1.5 – 3.0 mm), the thinnest plates successfully joined via Friction Riveting so far. The downscaling was accomplished regarding the size of the rivet and the joints made with a smaller diameter (4mm) rivet demonstrated similar results to the joints with a 5mm diameter rivet. To improve and analyze the main process parameters, the Design of Experiments (D.O.E.) was used. Considering the effect on the temperature generated during the process, the rotational speed shows a high impact, followed by the material combination (one or double copper layer), once the higher rotational speed generates greater friction between the metal and the composite and the high conductivity of the copper contributes to the heating spread.