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OCTOBER 2026 I SMT007 MAGAZINE 23 industrial products have successfully used no-clean processes for decades. No-clean can provide several advantages, including lower manufacturing cost, reduced process complexity, and lower resource consump- tion (e.g., water and electricity). If the assembly design, flux chemistry, and operating environment are compatible, a properly controlled no-clean process can deliver excellent reliability. The important phrase here is properly controlled. Qualification data, SIR testing, and process valida- tion still matter. Assemblies should not be consid- ered reliable simply because the flux label says "no-clean." Industry guidance now emphasizes that no-clean residues must be validated for their intended environment rather than assumed to be acceptable by default. When Cleaning Still Makes Sense There are also many situations where cleaning remains the better engineering choice, even when no-clean materials are used. One obvious example is high reliability electronics. Medical devices, aerospace systems, defense products, automotive electronics, and mission- critical controls often operate in environments where failure carries significant consequences. In these applications, engineers frequently choose to remove residues to reduce uncertainty and maxi- mize reliability margins. During manufacture, residues may become trapped beneath components or concentrate in areas where environmental exposure is difficult to predict. Research has shown that flux residues can absorb moisture and contribute to leakage currents, reduced insulation resistance, electro- chemical migration, and corrosion-related failures under humid conditions. Another common reason for cleaning is the application of conformal coatings, where cleaning may improve both coating adhesion and long-term reliability. Reliability: The Real Decision Driver Perhaps the most important lesson is never to ask, "Is this a no-clean flux?" Instead, ask, "What level of cleanliness does this product need to achieve its reliability requirements?" Those are fundamentally different questions. A no-clean residue may be entirely acceptable for a consumer electronic device stored indoors for five years. The same residue may be unac- ceptable for an autonomous vehicle controller, a satellite communication system, or an implantable medical device. Reliability depends on the interaction between an ensemble of parameters, including but not limited to, the chemistry of the materials involved, design choices, environmental exposure, and electrical loading. No single flux designation can account for all these variables. The industry has accumulated ample evidence that residues can contribute to electrochemical migration, dendritic growth, corrosion, leakage currents, and reduced surface insulation resis- tance when sufficient moisture and electrical bias are present. At the same time, countless successful products demonstrate that qualified no-clean processes can provide years of reliable service when used appropriately. Both statements are true. The Clean Truth The biggest myth surrounding no-clean flux is that the name itself answers the cleaning question. It does not. "No-clean" is a material or process clas- sification, not a reliability strategy. The term originated because certain residues could remain on assemblies without requiring mandatory post-solder cleaning under appropriate conditions. It was never intended to mean that cleaning is unnecessary, undesirable, or irrelevant. Every assembly still requires an engineering deci- sion based on risk, environment, design complexity, and reliability expectations. The clean truth is that no-clean means cleaning is optional only when the evidence says it is. When reliability demands it, no-clean can quickly become must-clean. SMT007 Dr. Adam Klett is director of science at KYZEN. T H E C L E A N T R U T H