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NOVEMBER 2024 I SMT007 MAGAZINE 57 mal cycling common in many harsh environments, such as elec- tronics used in aerospace applica- tions where electronic devices are repeatedly exposed to alternating high and low temperatures, places additional stress on the integrity of circuit assemblies. ese condi- tions can cause residues to migrate and redistribute across the surface of the assembly, increasing the like- lihood of ECM over time. Additionally, the combination of high temperature and humidity— oen referred to as "tropical" environments— poses an especially severe risk. Under these conditions, the synergy between moisture and heat accelerates the growth of dendrites, reducing the time to failure. Corrosive Gases and Pollutants In industrial, automotive, and urban envi- ronments, electronic devices may be exposed to corrosive gases such as sulfur dioxide (SO₂), nitrogen dioxide (NO₂), and hydrogen sulfide (H₂S), as well as airborne contaminants like dust and particulate matter. ese substances can interact with residues on circuit assem- blies, increasing their ionic conductivity and promoting the formation of dendrites. In par- ticular, sulfur-based compounds are notori- ous for their corrosive effects on metals com- monly used in PCB manufacturing, like silver, copper, and lead. e corrosive action of these gases can introduce new ionic species or exac- erbate the degradation of existing residues, further heightening the risk of electrochemical migration. Corrosive pollutants can also damage the protective coatings (conformal coatings) that are oen applied to circuit assemblies to shield them from environmental exposure. Once these barriers are compromised, residues and contaminants become more vulnerable to environmental stressors, leading to increased ECM susceptibility. Case Studies in Harsh Environment Failures Documented failures of electronic systems in harsh environments illustrate the critical importance of residue management in mitigat- ing ECM. One high-profile case occurred in the automotive industry, where electronic control units (ECUs) were exposed to high humidity and sulfur-containing gases during operation. e combination of these environmental fac- tors, coupled with insufficient cleaning of the circuit assemblies, resulted in electrochemi- cal migration, leading to intermittent failures in the vehicle's electronic systems. e cost of these failures was significant, both in terms of warranty repairs and reputational damage to the manufacturer. In another example, a telecommunications infrastructure in a coastal environment suf- fered from corrosion-related ECM failures. Salt in the air combined with the high humid- ity and high temperatures of the coastal region to create ideal conditions for dendrite growth. Over time, failures in the equipment caused significant service disruptions, prompting a costly retrofit of the affected systems with bet- ter cleaning processes and protective coatings. Even in environments where the humidity levels are moderate, ECM can occur. A major video game manufacturer experienced this firsthand. e game console's motherboard design featured densely packed components,