Thermo-Mechanical Test of SnBi and SnCu Solder Joints on Different Surface Finishes

The article deals with the heating factor influence on the solder joint reliability. A specific goal was to reveal the influence of the heating factor on the thickness of the Intermetallic Layer (IML)for Copper, Electroless Nickel Immersion Gold (ENIG)and Hot Air Solder Levelling (HASL)surface finishes and two lead free solders Sn42Bi58 and Sn99.3CuO. 7. Three different heating factors were used for hot air reflow of the Bismuth solder paste and another three for reflow of the SnCu solder paste. Micro-sections were prepared and the IMC (Inter-Metallic Compound)layer thickness was measured. The manufactured samples were subjected to destructive shear strength testing at laboratory temperature (20 °C)and at 65 °C. The results show an influence of intermetallic layer thickness on the shear strength and a minor decrease of the shear strength at elevated testing temperature for a low temperature Bismut based solder paste. When SnCu solder was used, the IMC layer was thicker and also the shear strength was lower, in an average (on all surface finishes)by 19%.