Application of SnAg5 Solder in Resistance Element Soldering Technology

This study evaluates the applicability of lead-free SnAg5 solder in Resistance Element Soldering (RES) technology for joining an AISI 304 stainless steel sheet and a PMMA (polymethyl methacrylate) thermoplastic. The microstructure and properties of the resulting soldered joints were assessed. By utilizing Chemet CHM-A-014 flux, excellent wettability of the SnAg5 solder on the AISI 304 steel sheet surface was observed at 275 °C, achieving a contact angle of 3.5°. During resistance heating with the selected parameters, only a specific volume of solder in the core of the Cu/SnAg5 bimetallic elements was consistently remelted. Mechanical testing of the RES joints revealed that shear strength ranged from 26.66 to 39.32 MPa, which corresponds to 62–92% of the solder’s bulk shear strength. Joint failure occurred predominantly within the solder and partially at the steel/solder interface, with the fracture surfaces exhibiting a ductile character. Finally, XRD analysis confirmed that the dominant fracture path propagated through the solder, identifying the presence of FeSn2 and Fe2Sn intermetallic phases on the fracture surfaces.