Comparison of Gold-Plated PCB Finishes after Thermal Stress

The article deals with thermal cycling influence on the electrical and mechanical properties of the soldered joint on various gold-plated surfaces. The purpose was to determine the effect of thermal aging on the properties of the soldered joint of Galvanic Gold and Electroless Nickel Immersion Gold (ENIG) surface finishes and two lead-free solder alloys SAC305 NC257-2 and SAC305 M8. Two different heating factors of limit values - minimum value of 218 s°C at which the solder is still possible to reflow and a maximum value of 2295 s°C which still fits to the manufacturer's specifications - were used for reflow process of used solders. Prepared samples were thermally cycled in a shock test chamber (-40°C, +125°C) or aged at 85°C and 85% RH (HH, Heat-Humidity chamber). The results show the influence of shock temperatures on the shear strength and resistance of soldered joints. The shear strength decreased after 1000 thermal cycles by 40% and soldered joints reflowed with a higher heating factor were stronger than the soldered joints reflowed with a lower heating factor. In contrast to shock temperatures, HH test did not have a significant effect on shear strength.