Effect of Flux Activator in Reflow Process Related Flux Residue on the Climatic Reliability of Surface-Mount Electronic Devices

This paper investigated the effect of flux activator used in reflow flux formulation on the electrochemical reliability of electronic devices. The focuses were placed on the perspective of surface insulation resistance (SIR), cleanliness, and its morphology transformation and redistribution behavior of flux residue under climatic exposure. Standardized accelerated climatic test on SIR comb-structure pattern was performed to benchmark the humidity interaction of the tested flux formulations used in solder paste. The influence of stand-off height for the surface-mount component on the humidity robustness was analyzed using an in-house designed dummy test rig and electrochemical impedance spectroscopy. Scanning electron microscopy and conductivity measurement was used to understand the hydrolytic degradation of the flux residue and the release of the conductive ionic residues during climatic exposure. Results indicate the spreading area and the hydrolytic degradation behavior of the flux residue were influenced by the type of flux activators used in flux formulation. The climatic reliability was influenced by the combined effect of the aggressiveness of flux activator and the spreading of the flux residue. However, result also shows that the climatic reliability of the surface-mount device can be improved by increasing the stand-off height of the components together with selected flux formulation.