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FEBRUARY 2025 I SMT007 MAGAZINE 59 metal ions migrate between conductors, form- ing dendritic structures (Figure 2). ese den- drites can eventually bridge the gap between conductors, leading to short circuits or inter- mittent electrical faults. Key factors influencing ECM include: • Ionic contamination: Residues containing chlorides, bromides, or other ionic species promote ECM. ese residues can origi- nate from solder pastes, cleaning agents, or environmental exposure. • Humidity and moisture: Moisture is a criti- cal enabler of ECM, as it dissolves ionic res- idues to form conductive solutions. • Voltage bias: While ECM can occur even in relatively low voltage conditions, higher voltage differentials between conductors accelerate the migration process. • Component spacing: Smaller distances between conductors, common in SMT designs, increase susceptibility to ECM. To mitigate ECM, manufacturers must employ rigorous process controls, including effective cleaning to remove residues, con- formal coatings to protect against moisture ingress, and design strategies to optimize con- ductor spacing. Corrosion: The Enemy of Longevity Corrosion poses another significant chal- lenge to electronics in harsh environments. is degradation process occurs when metals react with environmental agents such as oxygen, sul- fur, or chlorides. Common forms of corrosion in electronics include: • Galvanic corrosion: Arising from electro- chemical interactions between dissimilar metals. • Pitting corrosion: Characterized by localized attacks that create small pits in metal surfaces. • Crevice corrosion: Occurring in confined spaces where moisture and contaminants accumulate. • Creep corrosion: A type of corrosion that occurs in electronic assemblies, par- ticularly on PCBs, where corrosion prod- ucts migrate or "creep" across the surface of the board or components. It is typi- cally caused by the reaction of sulfur-con- taining gases with exposed metal surfaces, such as copper or silver, under certain environmental conditions. Case Study #1: LED Lighting Modules Sulfur contamination in the air has been par- ticularly problematic in certain industrial and urban environments. Early LED lighting mod- ules suffered significantly from sulfur-induced degradation, which led to creep corrosion, and ultimate failure. ese microscopic, filament- like structures grew on the surfaces of sol- dered connections, creating electrical shorts and diminishing the reliability of the mod- ules. is failure mode highlighted the need for sulfur-resistant materials and coatings in LED designs, particularly for outdoor or industrial applications 1 . Many forms of corrosion can compromise electrical connectivity, increase contact resis- tance, and lead to mechanical failure. For example, connectors exposed to salt fog in marine environments oen exhibit rapid cor- rosion, leading to intermittent or failed con- nections. Similarly, circuit traces subjected to sulfur-rich industrial atmospheres may expe- rience accelerated degradation, resulting in open circuits. Strategies to combat corrosion include: • Material selection: Using corrosion-resis- tant materials, such as gold-plated connec- tors or conformal-coated PCBs. • Environmental sealing: Enclosures with appropriate ingress protection (IP) ratings shield assemblies from contaminants. • Protective coatings: Conformal coat- ings and potting materials provide barriers against moisture and corrosive agents.