Laser welding of thin NiTi shape memory alloy wires on printed circuit boards for actuator applications
Marvin Schuleit, Cemal Esen, Jan Frenzel, Nicole Stötzel, Aleksander Kostka, Burkhard Maaß, Gunther Eggeler, Andreas Ostendorf
Abstract
The present study demonstrates the potential of laser welding nickel–titanium (Ni-Ti) shape memory alloy wires to copper-tin (Cu-Sn) coated printed circuit boards (PCBs), achieving mechanical strengths of up to 705 MPa ± 23 MPa. Nanosecond laser pulses enabled the formation of robust joints without visible thermal damage to the thermally sensitive PCB. Scanning and transmission electron microscopy revealed a complex microstructure in the fusion zone, including sharp gradients in grain size, and intermetallic phases such as NiTi (B2), NiTiSn, Cu 6 Sn 5 , Sn, and Cu. Despite the presence of these microstructural constituents, mechanical testing confirmed a good structural integrity of the joints. Under the specific actuation fatigue testing conditions considered in this study, fatigue failure primarily occurred in the unprocessed base NiTi material, suggesting that the welded regions did not significantly affect fatigue lives. Thermal imaging revealed that the SMA wires in joint regions did not undergo complete phase transformations as the adjacent Cu-Sn-layers of the PCB act as a heat sink. This contributes to the good fatigue performance. The findings of the present study highlight the potential of this joining method for straightforward and reliable integration of NiTi wires into actuator systems.