Interpretation of corrosion observed after IPC humidity test on PCB's with various flux types and electrical loads

摘要

No-clean fluxes are widely used in the electronics manufacturing industry. This requires special attention to electronic corrosion of products used in humid environments as no-clean fluxes leave a small amount of residues on or around the solder joints, which under certain conditions can lead to reliability problems. Particular types of no-clean fluxes are hygroscopic and can accordingly attract moisture which may lead to electrochemical migration significantly below a relative humidity of 100% i.e. also in a non-condensing environment. Different types of weak organic acids (WOA's) are used as active components to facilitate the soldering process and a bench mark conducted by CELCORR (Centre for Electronic Corrosion) of no-clean flux systems for corrosion reliability has revealed that the WOA's show different behavior as regards to the water load and thus the PCB's susceptibility to electrochemical migration (ECM) after soldering. At Grundfos a/s, we produce pumps with integrated electronics and humidity testing is part of our process control in order to maintain product quality and reliability during service life. Based on the results from tests according to the test conditions specified in IPC TM 650 No 2.6.3.7 the susceptibility to ECM of two different flux types used for selective soldering will be presented. Special attention will be paid to high voltage areas under both AC and DC loads.