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

Modern electronic assemblies are becoming increasingly compact and sensitive to contamination. Learn why cleaning PCBs and electronic assemblies is essential for preventing electrochemical corrosion, improving conformal coating adhesion, and ensuring long-term reliability in demanding applications.

Increasing Complexity in Modern Electronic Assemblies

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.

Are there any limitations of No-Clean Soldering Processes

During the 1990s, the electronics industry increasingly adopted so-called “no-clean” soldering processes to reduce manufacturing costs and eliminate cleaning steps. Before this transition, nearly all electronic assemblies were cleaned after soldering.

However, the limitations of no-clean technology soon became evident, especially for high-density and high-reliability applications. One major challenge is the narrow thermal process window during soldering. Insufficient thermal exposure can prevent complete decomposition of flux activators, leaving residues that are susceptible to electrochemical corrosion.

Additionally, resin residues are intended to encapsulate ionic contaminants and activator remnants after soldering. Under elevated humidity or temperature fluctuations, these resin layers can lose density and allow moisture penetration. Once moisture reaches ionic residues, corrosion processes can begin.

Why Flux Residues Become a Serious Reliability Risk

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.

Electrochemical Corrosion: A Hidden Threat in Electronics Manufacturing

Electrochemical corrosion represents one of the greatest long-term reliability risks in electronic assemblies. The effects may include:

  • Unpredictable leakage currents
  • Dendritic growth between conductors
  • Electrical short circuits
  • Functional instability
  • Premature system failures
  • In extreme cases, fire hazards

Electrochemical corrosion occurs only when three conditions are simultaneously present:

  • Moisture
  • Electrical bias
  • Ionic contamination

Removing at least one of these factors can significantly reduce the risk. Since moisture and electrical bias are often unavoidable during operation, minimizing ionic contamination through proper cleaning becomes one of the most effective preventive measures.

The Role of Cleaning Before Conformal Coating

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!

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Cleaning as a Critical Process Step in Modern Electronics Manufacturing

Today’s electronic assemblies are exposed to increasingly demanding operating environments, including:

  • Rapid temperature cycling
  • High humidity
  • Condensation
  • Chemical vapors
  • Automotive environments
  • Aerospace applications
  • Naval electronic applications
  • Medical electronics
  • Industrial automation systems

In these applications, assembly cleanliness is no longer optional. Cleaning has become a critical quality assurance step that directly influences reliability, durability, and operational safety.

Modern cleaning processes remove not only soldering flux residues, but also process-related contamination generated during manufacturing. That significantly improves insulation resistance and reduces the likelihood of electrochemical failures throughout the product lifecycle.

Validate your Cleaning Process with Cleaning Diagnostics

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.

Cleaning Diagnostics 24

Cleaning Diagnostics

Learn how we support cleanliness evaluation and process optimization with cleaning diagnostics.

Read more
Cleaning Diagnostics 24

FAQs: Cleaning Electronic Assemblies

Cleaning removes flux residues, ionic contamination, oils, particles, and other process impurities that can lead to electrochemical corrosion, leakage currents, and electrical failures. It significantly improves the long-term reliability of electronic devices.

Uncleaned assemblies can suffer from corrosion, dendritic growth, insulation failures, short circuits, and reduced operational lifetime. In harsh environments, contamination can even lead to catastrophic failures.

Electrochemical corrosion is a complex of chemical reactions caused by the combination of moisture, electrical bias, and ionic contamination. These conditions create movement of ions which can build conductive paths between conductors and permanently damage assemblies.

No-clean processes can be used under controlled conditions and for less demanding applications. However, for electronics with high component density, high reliability requirements, or in harsh environments, cleaning is often still necessary to ensure long-term performance.

Modern SMT assemblies feature extremely small conductor distances and higher component densities. Even microscopic contamination can therefore cause electrical leakage or corrosion between conductors.

BTCs are electronic components where solder connections are located underneath the component body. These designs can trap flux residues during soldering, making cleaning and contamination control more challenging.

Cleaning ensures proper coating adhesion and prevents contaminants from being trapped underneath the protective layer. That improves moisture resistance and long-term reliability.

Industries with strict reliability requirements, including:

  • Automotive electronics
  • Aerospace and defense
  • Medical electronics
  • Industrial automation
  • Telecommunications
  • Power electronics

Cleaning processes typically remove:

  • Flux residues
  • Ionic contamination
  • Oils and greases
  • Dust and particles
  • Fingerprints
  • Process chemicals

Yes. Proper cleaning significantly reduces corrosion risks and electrical failures, helping electronic assemblies maintain stable performance over many years of operation.

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