COMPARISON OF IONIC CONTAMINATION TEST METHODS TO DETERMINE THEIR ABILITY TO RELIABLY PREDICT PERFORMANCE RISKS

摘要

In the Electronic Manufacturing Services Industry, one of the known failure mechanisms is caused by the presence of ionic contamination. Ionic contamination leads to electrochemical migration and dendritic growth. Through the years, there have been various methods employed to verify the ionic cleanliness of electronic components, printed circuit boards and their assemblies. The accepted industry standard test is Surface Insulation Resistance, SIR, testing. Although this is recognized as the test of merit, it can take weeks to prepare the test vehicles, run the test and analyze the results. By the time this is complete, the product has shipped. If failures are found in test, it is too late to be of practical use. The industry is looking for a test which can be run quickly and is representative of the product currently in production so that decisions, and potential corrective actions can be implemented prior to shipping product to customers. One alternative method is Resistivity of Solvent Extract, ROSE, testing. This method is primarily aimed at product which has gone through a cleaning process just prior to the test. However, in printed circuit board assemblies, PCBAs, there has been a shift from water wash fluxes followed by cleaning, to a process that utilizes no-clean flux with no cleaning. If ROSE testing is used in conjunction with no-clean flux, it often will lead to false fails, because no-clean fluxes are known to contain ionic residues. Another more recent test is the Critical Cleanliness Control, C3, test, which is designed to test specific regions on a PCBA that may be prone to ionic contamination related failures. In this paper, a direct comparison will be made between ROSE testing, SIR testing and C3 testing. The test results will be augmented by a detailed visual inspection, Ion Chromatography, IC, testing, and other tests, as required.