For much of the electronics manufacturing industry’s history, cleaning printed circuit assemblies after soldering was not optional. Prior to the early 1990s, virtually all assemblies were cleaned as a standard process step to remove flux residues and other manufacturing contaminants. This practice changed dramatically following the implementation of the Montreal Protocol, which eliminated the use of widely adopted chlorofluorocarbon-based cleaning solvents due to their impact on ozone depletion. The sudden loss of these effective solvents created an urgent need for alternative approaches, leading to the development and adoption of no-clean flux chemistries.

This webinar provides a fundamentals-based introduction to circuit assembly cleaning, with a specific focus on why no-clean flux residues are still frequently removed today. Intended for engineers with limited background in cleaning processes, the presentation explains what flux residues are, how they interact with other forms of contamination, and why the absence of cleaning does not only leave flux behind, but also leaves all other residues present on the assembly. These include ionic contamination, solder paste additives, handling residues, and environmental debris introduced throughout the manufacturing process.

The presentation further discusses how advances in miniaturization, reduced conductor spacing, and low standoff components have significantly lowered the tolerance for residues on modern assemblies. In addition, harsh operating environments such as high humidity, temperature cycling, condensation, and chemical exposure can activate residues that may appear benign under standard conditions. In these environments, even small amounts of contamination can contribute to electrical leakage, corrosion, and electrochemical migration over time.

By combining historical context with practical fundamentals, this presentation aims to clarify how no-clean flux came to be, why it was never synonymous with no residue, and why cleaning remains an essential reliability tool in many applications today. The goal is not to advocate cleaning in all cases, but to equip engineers with a foundational understanding of when, why, and how cleaning supports long-term circuit reliability.