Modern PCB Cleaning Methods Improve Avionics Reliability

Author: Elizabeth Norwood, MicroCare Sr. Chemist

Today’s aircraft use sophisticated avionics to control a variety of on-board critical functions. These electronics systems include communications, engine controls, flight controls, navigation, flight recorders, lighting systems, security systems, fuel control, weather radar and hundreds of other flight management operations. As a general rule, the more complex the aircraft is, the more complex the avionic system is that controls it.

However, as these systems become more sophisticated and provide increased functionality, they also bring a set of new problems.  Engineers demand more fault-less functionality from their avionic designs, but must do it using less room inside the craft, and without adding more weight. This requires smaller, denser, more compact electronic components and the printed circuit boards (PCBs) contained within.

But, smaller, denser PCBs are typically more challenging to clean. PCBs are exposed to all types of contamination during fabrication. This includes flux residue, fingerprint oils, dust and other production debris. PCBs used in avionics are often multilayered and tightly-packed with bottom-terminated or low-standoff components such as BGAs, CSPs, MLFs, QFNs, and D-Paks. The smallest contaminant can cause electrochemical migration, board delamination, parasitic leakage, dendrite growth and shorting.

If the contamination isn’t cleaned, the PCBs run the risk of intermittent or complete field failure. This is simply not an option within the aerospace industry where a failure can be catastrophic. PCBs must operate reliably each and every time, without exception. Therefore, it is essential to get PCBs perfectly clean to ensure trouble-free PCB performance.

Improve Reliability with Effective PCB Cleaning

There are few different methods to reliably clean PCBs. They include manual benchtop cleaning or automated cleaning using either aqueous or vapor degreasing equipment.

Benchtop cleaning is ideal for lower production runs or if the PCB needs special handling. For instance, a PCB may have very delicate or moisture-sensitive, hand-soldered components that require extra care when cleaning.  Benchtop cleaning requires a four-step method for success. The four steps are wet, scrub, rinse and dry.  First wet the PCB with a non-aqueous, solvent-based flux remover, then gently scrub the contaminant off the board with a good quality scrubbing brush. Next, rinse away the dissolved contaminant with additional cleaning fluid. Finally, dry the PCB using a lint-free wipe, a high-quality air duster, or a combination of both to ensure no residue or particulate is left behind.

Sealed fluid dispensing systems, like the TriggerGrip™ PCB Cleaning Tool are replacing the pump bottles and brushes often used for benchtop cleaning. Using a controlled dispensing system keeps the flux remover clean for each use.  A quality dispensing system also delivers the right amount of fluid to wet the PCB completely, but without overspray or waste; using up to 30% less fluid to help cut cleaning costs.

Aqueous cleaning is used when batch cleaning larger quantities of PCBs. It typically uses heated deionized water and a detergent in a series of washing and rinsing cycles which takes place in large machines. A second step, using heat or air, dries the PCBs. Aqueous systems are considered by many to be environmentally friendly. However, they consume relatively large amounts of electricity, require continuous water monitoring and stringent wastewater management. The cost of these additional steps should be considered when deciding on which PCB cleaning method to use.

Vapor degreasing is also used for batch cleaning PCBs. It offers excellent performance when cleaning miniature components and uses an environmentally sustainable cleaning fluid, instead of water. PCBs come out of the vapor degreaser clean, dry, spot-free and cool enough to handle for immediate coating or packaging.

The cleaning fluids used inside the vapor degreaser have a very low surface tension and low viscosity, typically much lower than water. This enables the cleaning fluid to flow under tight components, dissolve the contaminants, and then flow back out without trapping any contaminants on the PCB. 

Also, vapor degreasers recycle and reuse the cleaning fluid for hundreds of hours before the fluid needs to be refreshed, making it a cost-effective and environmentally sound cleaning method.

A Cleaning Processes That’s Right for You

The increasing focus on PCB miniaturization is set to continue. Avionics designers are pushing the boundaries by incorporating the latest technology into smaller packages. But the move to smaller PCBs brings reliability issues. PCB cleaning is a mission-critical process, if it is not completed effectively, the avionics system simply will not function reliably for its required life.

Successful PCB cleaning involves selecting the best combination of cleaning fluid and cleaning method to effectively remove contamination. Balancing these factors helps control PCB reliability. To implement the right cleaning procedures, it is recommended that PCB fabricators and avionic device manufacturers work with MicroCare. We specialize in cleaning fluids for aerospace applications.  Our experts can help choose the best cleaning process and fluids to deliver quality cleaning results and high reliability components.