Issue link: https://iconnect007.uberflip.com/i/1532052
58 SMT007 MAGAZINE I FEBRUARY 2025 Electronics deployed in harsh environments oen face: • Electrochemical migration (ECM): A failure mechanism wherein conductive paths, typically dendrites, form between conductors due to the presence of ionic contaminants and moisture (Figure 1). • Corrosion: e chemical or electrochemi- cal degradation of metals, resulting in open circuits or reduced conductivity. • ermal stress: Repeated expansion and contraction of materials due to tempera- ture fluctuations, leading to mechanical fatigue and failure. • Contamination sensitivity: Residues le from fluxes, cleaning processes, or envi- ronmental exposure can exacerbate ECM and corrosion risks. The Role of Residue Tolerance in Assembly Design Residue tolerance refers to the ability of an electronic assembly to function reliably despite the presence of ionic or non-ionic contami- nants. is tolerance varies depending on the assembly's design, manufacturing processes, and intended application environment. rough-hole technology (THT) assemblies generally exhibit a higher tolerance for residues compared to SMT assemblies. e increased spacing between conductors in THT reduces the likelihood of electrochemical interactions, even in the presence of contaminants. Conversely, SMT assemblies feature finer pitch components and smaller standoff heights, making them more susceptible to ECM and corrosion. is sensi- tivity is particularly critical as miniaturization trends in electronics continue to shrink com- ponent sizes and interconnect distances. For example, a THT assembly designed for industrial use may tolerate residues le by no-clean fluxes, fabrication, and assembly processes without immediate reli- ability concerns. In contrast, an SMT assem- bly for aerospace applications, exposed to high humidity, may fail if even trace ionic residues are present. us, residue tolerance must be carefully evaluated based on the assembly's operating environment and design constraints. Electrochemical Migration: A Silent Threat ECM is among the most insidious threats to electronics reliability in harsh environ- ments. is phenomenon occurs when ionic residues, oen originating from solder fluxes, board and component fabrication, humans, or environmental contamination, combine with moisture to create an electrolytic solu- tion. Under the influence of an electric field, Figure 1: Required Elements for ECM. Dendritic growth. Source: Process Sciences