Investigation of the influence of electrochemical migration (ECM) on the reliability of electronic assemblies after rework using lead-free solders and No-Clean flux mixtures

摘要

In the IGF-research project 17960N "Investigation of the influence of electrochemical migration (ECM) on the reliability of electronic assemblies after rework using lead-free solders and No-clean flux mixtures" the reliability of flux mixtures using different materials in inline assemblying and rework has been systematically studied. A zero defect production is still not fully realized in manufacturing of electronic assemblies, despite all efforts. Necessary rework and repair are often performed with other fluxes than used in inline reflow or wave soldering processes. They can be mixed and react with each other. Especially, if the used flux doesn't reach soldering peak temperature or if excess flux amount remains on the assembly after soldering, a great danger of ECM is given in particular under the influence of moisture. Using different No-clean flux materials and No-clean solder pastes for lead free application a variation of processing parameters (e.g. time, temperature) was performed. The combination of inline reflow soldering with wave soldering, selective wave soldering, manual iron soldering and rework soldering was studied with Surface Insolation Resistance (SIR) Test. Electrochemical impedance spectroscopy and electrochemical noise measurements has been performed accompanying. Results show that if the flux doesn't reach the soldering temperature especially in combination with flux type L1 or M1 the danger of ECM rises. These results will help assembly manufacturers to assess their production process regarding possible danger of ECM. A recommendation for a preparation procedure of SIR Test patterns to be implemented in DIN EN standards should be worked out.