Study on the thermal load of the laser impulse metal bonding process to the metallized thermal sensitive substrate

The laser impulse metal bonding (LIMBO) process opens a new possibility to join a thick interconnector on a thin metal layer which lays on a sensitive substrate such as epoxy resin (FR4) material. Since the FR4 tolerates only limited amount of the thermal load during the joining process, the LIMBO process applies a novel approach to separate the melting and joining phase. Hence, the thermal load on the underlying substrate during the joining phase is minimized and therefore allows a welding approach even for electric as well as electronic components. However, the substrate is thermally affected due to the heat conduction which is induced during the joining phase. In this paper, the thermal cycle induced to the sensitive substrate during the LIMBO process and the overlap welding process for enlarging the weld joint area will be investigated. To evaluate the maximal amount of thermal load on the sensitive substrate below a thin copper layer by given setting, the thermal destruction threshold of substrate is exceeded on purpose. For the understanding of the heat distribution during the joining stage, the experimental results are validated with simulation results.