Investigation Of The Effects Of Plating Process And Dielectric Properties Of Dust On Electrochemical Migration

With large scale integrated circuits developing, the electronic components become smaller and have an increasingly higher density. The pitch between PCB conductors, solders and PCB connectors are increasingly smaller, which makes the electrochemical migration (ECM) phenomena occur easily. This problem causes increasing concerns. In the internal electronic components, PCB board and its mating connector has different plating processes, thus the mechanism and the time to failure (TTF) of ECM are different. In addition, in the actual work environment, dust changed the main factors leading to ECM, and can also cause changes in the mechanism and TTF of ECM.This study focused on the effects of plating process and dust dielectric properties on ECM. On the one hand, by using water drop (WD) test, composition analysis of ECM dendrites and polarization test, the effects of electroless plating Ag and electroplating Ag material, intermediate layer of nickel and the thickness of the plating on ion migration characters were studied, and the different ECM mechanisms were analyzed. On the other hand, by Ansys simulation, the impact of dielectric constant and electric charge of dust on the parallel electric field was studied, and further its effects on ECM were determined.Silver electroplating has more pores, but electroless silver plating has defects on the side of copper traces, so the underlying metal material were exposed easily. When ECM occurs, galvanic corrosion will occur firstly, the underlying metals were ionized to become the main material transported to the cathode. And the more coating defects had, the less silver migration was, the longer TTF was. When the thickness of silver coating increased, the migration content of silver increased, so that TTF decreased. When there was an intermediate layer of nickel, galvanic corrosion occurred, so that migration material became nickel and copper at the defects of plating, also delayed the failure of ECM.Through electrostatic field finite element analysis, it showed that dielectric properties and charges of dust had impact on the parallel electric field. The electric field at the top and bottom of the dust became stronger, and a minimum electric field appeared inside the dust particles. The impact of charges can be ignored comparing with the impact of the permittivity of dust. Finally, by the accelerating experiments of ECM, it was proved that under the dust contamination, dendrites always grew along the direction of maximum potential gradient, so that the path of ECM was bended and extended, which caused the TTF was increased.