Electrochemical Migration on Lead-Free Soldering of Pcbs

Abstract

It is well known that in printed circuits boards assembled by SMT technology may occur electrochemical migration (ECM). The electrochemical migration may become a potential reliability problem in electronic soldering when lead free technology is used in soldering electronic devices. Electrochemical migration is an electrochemical process where metal on an insulating material, in a humid environment and under an applied electric field, leaves its initial location in ionic form and redeposits. In a PCB two adjacents terminal may behave as electrodes so the dendrites grow from cathode to anode. A structure with a comb shape printed on FR4 substrate was used in the experiments. The distance between the fingers was 105 or 254 micron, in order to simulate a real distance between dispositive terminals. The parameters considered during the experiments were surface finishing, solder paste composition, distance between terminals and applied voltage. Al the experiments were performed two times. Tin was the main metal that migrates.