Why Cleaning Electronic Assemblies Is Essential for Reliability and Long-Term Performance

Modern electronic assemblies such as populated printed circuit boards (PCBs), ceramic substrates and other miniaturized devices have become significantly more complex over the last few decades. As electronic components continue to shrink, conductor spacing and terminal pitches have decreased dramatically. While older electronic assemblies featured relatively large conductor distances, modern SMT technologies brought IO pitches to 1,27mm, but they soon shrank to 1mm and 0,5mm. At the same time, the insulation distances between matrix-array terminals decreased to about 100 micrometers. Additionally, new assemblies, such as interposers for active components and wafer-level packages, represent new categories that came into consideration only several years ago.

This extreme miniaturization creates new challenges regarding electrical insulation resistance, contamination sensitivity, and long-term reliability. Even small amounts of ionic residues or moisture can negatively affect performance and increase the risk of failures.

Modern electronic packages, especially bottom-terminated components (BTCs), create additional cleaning and reliability challenges. During soldering, trapped flux residues underneath these components cannot fully outgas. As a result, critical areas between contacts remain contaminated with residues containing ionic substances and vehicle materials.

Many flux activators are hygroscopic or deliquescent, meaning they absorb moisture from the environment and can even become liquid and ion-conductive at relatively low humidity levels. In some cases, relative humidity values around 60% are already sufficient to activate electrochemical corrosion processes.

That creates an ideal environment for electrochemical migration and corrosion, particularly in densely packed assemblies with small conductor distances.

Protective conformal coatings are commonly used to increase dielectric robustness and to shield electronic assemblies from humidity, condensation, chemicals, and other harsh environmental conditions. However, coatings alone cannot guarantee reliability if contaminants remain on the surface.

For proper coating adhesion and long-term hermetic protection, assemblies must first be thoroughly cleaned and surface-activated. Any remaining flux residues, oils, particles, or ionic contamination can reduce coating adhesion and create hidden corrosion sites beneath the protective layer.

Therefore, one of the most effective strategies for high-reliability electronics manufacturing is:

Clean First – Then Coat

This process ensures maximum surface cleanliness, optimal coating performance, and significantly improved product lifetime. Read more about cleaning before conformal coating!

Long-term reliability through cleaning requires optimal settings of all relevant parameters and the creation of objective evidence that the cleaning results meet the requirements. There results must be periodically validated. Cleaning diagnostics help to keep the quality ans stability of the cleaning, identify contamination risks, evaluate cleaning performance, and support the optimization of cleaning parameters for demanding electronic assemblies.