Issue link: https://iconnect007.uberflip.com/i/1545206
JUNE 2026 I SMT007 MAGAZINE 13 Thermal and Power Density Effects Modern assemblies frequently operate at higher power densities, generating more heat during operation. Elevated temperatures accelerate chemical reactions and enhance moisture diffu- sion, increasing the reactivity of otherwise benign residues. Under these conditions, contaminants that might remain stable in low-power applications can become active contributors to corrosion, leak- age, and electrochemical migration. The Reality of No-clean Flux No-clean fluxes are widely used in high-density assemblies to streamline processing and mini- mize cleaning requirements. However, the term "no-clean" can be misleading. While these materi- als are formulated to leave minimal and gener- ally benign residues, their performance depends on environmental conditions and electrical bias. Under high humidity and voltage, even low levels of ionic content can promote leakage and failure between closely spaced conductors. Several different failure mechanisms are driven by residues, including electrochemical migration (ECM), dendritic growth, leakage currents, and cor- rosion. We'll look at each of these three causes. Electrochemical Migration (ECM) ECM, a critical failure mechanisms in dense assem- blies, occurs when ionic residues and moisture combine under electrical bias to form conduc- tive filaments between conductors. Key accel- erators for ECM include high humidity, DC bias, tight conductor spacing, and residues contain- ing halides or weak organic acids. Notably, ECM failures are often latent, emerging only after prolonged environmental exposure rather than during initial testing. Dendritic Growth Closely related to ECM, dendritic growth involves the dissolution and redeposition of metal ions, forming tree-like conductive structures between conductors. This phenomenon is particularly prevalent beneath bottom-terminated components where residues are difficult to remove. Leakage Currents and Signal Integrity Issues Even in the absence of catastrophic failure, contamination can degrade electrical perfor- mance. Common effects include increased leak- age currents, impedance instability, timing errors in high-speed circuits, and noise coupling between adjacent conductors. For advanced electronics, these subtle degradations can be just as problem- atic as outright failures. Figure 3: Corrosion potential as a function of voltage. Figure 4: Flux contamination under environmental stress. Figure 5: Leakage currents from partially cleaned flux residues. Figure 6: Dendritic growth from flux residue under a dual row QFN.