Effect of hygroscopic atmospheric particles deposition on the corrosion reliability of electronics

Atmospheric corrosion of printed circuit board assembly (PCBA) surface is synergistically affected by many factors, such as temperature (T), relative humidity (RH), chemical composition of atmospheric contaminants and electric field. In this work, a prototype rotating impactor was developed to deposit sub-micrometer atmospheric particles contaminants on surface insulation resistance (SIR) patterns for a minimum of 24 hours. The test boards were exposed to varying RH conditions (309930% RH) with different RH ramping rates and T. Water film formation was monitored by impedance response at 1kHz, whereas the corrosive behavior was investigated under 5V DC bias. Particles chemical composition of the watersoluble (WS) inorganic fraction and monoand di-carboxylic acids were characterized by means of ion chromatography from PM2.5 samples. Thin electrolytic-layer formation due to deliquescence of WS compounds (about 40% in mass) abruptly decreased the impedance measured during increasing RH ramp, whereas it showed a hysteresis comparing with the response at decreasing RH ramp. The RH value at which sharp change in impedance observed was affected by T of the surrounding air and RH ramping rate. The formation of conductive layers leads to tin corrosion far below the condensing conditions. High leakage current values were observed even below 70% RH due to particles hygroscopicity and SEM-EDS analyses highlighted tin migration.