Mechanistic Insight into water film formation and subsequent corrosion-linked dendritic growth on PCBs

Temperature and humidity fluctuations can cause condensation on a PCB surface which creates a continuous electrolyte pathway between two biased connector pads, leading to current leakage and subsequent dendrite growth. The effect of concentric droplet growth and inter-droplet layer on corrosion failure was investigated using a custom-designed test Printed Circuit Board (PCB) under simulated condensing conditions using DC chronoamperometry, in-situ imaging of the growth and coalescence of water droplets and subsequent dendrite growth, along with the COMSOL secondary current model analyzing leak currents for different droplet coalescence morphologies. While the secondary current model has limitations of not incorporating mass transport phenomena, it can still be used to get some insights into factors such as the effect of droplet coalescence on the occurrence of leakage currents, which indicate dendrite growth. Results indicate that for the investigated PCB layout, droplet coalescence is necessary to cause leakage currents and dendrites. • Droplet and current path development analyzed by in-situ DC measurement and imaging. • Complete droplet coalescence needed for dendrite growth; partial is insufficient. • Dendrites can connect points along longer paths, due to coalesced droplets. • Thin inter-droplet film of ∼100 µm gap and ≤ 20 µm height can prevent dendrite growth. • COMSOL modeling done of current changes with different water droplet shapes.