Cleaning: the driving force behind reliable electronics

Author : Elizabeth Norwood | Senior Chemist | MicroCare

01 November 2022

Small PCBAs with dense spacing & hard-to-reach areas make PCBA cleaning extra challenging
Small PCBAs with dense spacing & hard-to-reach areas make PCBA cleaning extra challenging

Applications for PCBAs (printed circuit board assemblies) used within the automotive sector are growing. They have always been instrumental; however, their importance is increasing as more & more vehicles are designed with control & information systems, satellite navigation systems, near field monitors & multimedia devices...

This article was originally featured in the November 2022 issue of EPDT magazine [read the digital issue]. And sign up to receive your own copy each month.

The future of PCBAs in the automotive industry is now looking towards autonomous and electric vehicles (EVs). It is therefore now essential, as Elizabeth Norwood, Senior Chemist at electronics cleaning experts, MicroCare explains here, that the electronic assemblies used within them are highly reliable and operate without fault – the potential consequences to human life are simply too high without this assurance…

Electronic devices used within the automotive industry must have long-term functionality and stand up to rigorous regulations put in place by governing bodies. It is therefore vital that procedures are established during the design and manufacturing stages to guarantee the electronic components’ reliability. An important production step to ensure an electronic device performs consistently during its lifetime is consistent and high-quality cleaning.

Reliability is at risk

The risk of failing PCBAs has the potential to become more prevalent as their use increases. The global automotive PCB (printed circuit board) market is expected to reach more than $14 billion during 2018-2024, according to a report from Research and Markets. The rising applicability of rigid-flex PCBs, the penetration of in-vehicle infotainment systems, the arrival of new energy vehicles, and the utilisation of printed circuit boards in advanced driver assistance systems (ADAS) is expected to witness significant traction in the coming years.

The rising demand for miniaturised PCBAs to facilitate these applications, alongside the extremely complex nature of these assemblies, which incorporate delicate components on compact densely-packed boards, can prove to be a reliability risk if cleaning is not properly planned and executed.

Furthermore, in use, the boards have to withstand many different environmental conditions, from extreme temperature and humidity, to rain and snow. Add to this the exposure to vibration and the potential for failure rises further. These threats are why designing for reliability is key to a PCBA’s functionality. An essential element of this is critical cleaning prior to conformal coating.

Vapour degreasing is extremely effective at cleaning PCBAs
Vapour degreasing is extremely effective at cleaning PCBAs

When designing a PCBA, cleanliness is a factor that designers must consider to ensure long-term performance and consistency. In general, it is much easier to pinpoint any cleaning problems and resolve them prior to prototyping and production. This is particularly important when manufacturing high-reliability PCBAs found in vehicles. Therefore, some designers and manufacturers are taking the steps to research cleaning, and ensure they are proactive in their approach before mass production. They are specifying cleaning details in the early stages of PCBA design in order to produce clean, reliable boards.

Contaminated PCBAs could prove your failing

One of the main causes of electronic device failure is contamination on the PCBA. Even the smallest amount of contaminant can form a barrier between electrical contacts. If PCBAs are not cleaned sufficiently, they are susceptible to a whole host of problems. This can include electrochemical migration and delamination, to parasitic leakage, dendrite growth and shorting. This is why cleaning is crucial to ensuring the reliability of a PCBA. The cleaning process should, however, be executed correctly and effectively to guarantee the longevity of the electronic assembly. It must also meet with exacting standards, for example those stipulated by the Automotive Electronics Council, which focuses on component functionality and reliability.

All PCBAs in the automotive sector require cleaning during production to remove contaminants like flux, dust, marking inks, oils or inorganic contamination resulting from the manufacturing process. This, however, is becoming more and more difficult, due to reduced printed circuit board assembly size and increased complexity. For example, the volume of an ECU (electronic control unit) used in vehicles was approximately 1200cm3 at the beginning of 2000. Today it is less than 300cm3.

Condensed assemblies housing small PCBs with denser spacing and hard-to-reach areas makes PCBA cleaning extra challenging. If the contaminant is not cleaned, particularly hard to remove white residue left behind from no-clean fluxes, the risk of board malfunction is high.

Applying a conformal coating is yet another important reason to effectively clean a PCBA. The delicate electronic assemblies used within vehicles have to withstand harsh environments, so it is therefore important to add a conformal coating protective layer, that also serves to insulate the PCB. If cleaning is not successfully completed before a conformal coating is used, any contaminant left on the board can inhibit the sufficient bonding of the conformal coating to the PCB substrates. For example, if flux residue or process oils are left on the boards, they can cause defects in the conformal coating. These include delamination, de-wetting, uneven coverage, pinholes and air bubbles resulting in craters and small circular flaws, called fish eyes.

How to attain critically clean PCBs

Finding a cleaning process that ensures critical cleaning is completed successfully can be a challenge. There are many factors that have to be considered. It needs to be a process that can easily and reliably clean miniaturised electronic assemblies and meet specific cleaning standards. It must also be a method that is sustainable and cost-effective. The answer lies with vapour degreasing.

PCBAs exit the vapour degreaser dry & without any unacceptable residue or spots
PCBAs exit the vapour degreaser dry & without any unacceptable residue or spots

Vapour degreasing is extremely effective at cleaning PCBAs. It is a process that uses a closed-loop system, which contains a boil sump and a rinse sump. The cleaning fluid is heated within the boil sump and the PCBAs are then immersed and cleaned in the fluid. Once cleaned, the boards are automatically transferred to the rinse sump for final cleaning in clean, uncontaminated fluid. Finally, the PCBAs are lifted and held inside the vapour blanket, allowing the parts to dry and cool.

The low viscosity and surface tension ratings of modern cleaning fluids used within a vapour degreaser, combined with their volatility, allow them to easily remove all inhibiting particles and contaminants, even from tightly-packed, small assemblies.

The fluids are easily removed from small, closely packed PCBAs, whereas more slow-drying fluids, such as water, cannot clean or may become trapped. PCBAs exit the process dry and without any unacceptable residue or spots left on the component, making it the ideal cleaning method for critical applications used within the motor industry.

Electronics reliability is essential for new capabilities

The future of vehicles is becoming more dependent on advanced technology and the electronics that drive it. Their importance is growing as new advances and innovations are applied. Producing anything less than 100% reliable PCBAs is not an option. PCBAs must perform as they were intended; any malfunction could be catastrophic.

Manufacturers in the automotive sector need to proactively seek solutions to ensure reliability. Effective critical cleaning is one area that will help to achieve this. Cleaning experts recommend a method that has the flexibility to adapt to any future changes, such as regulatory and environmental changes, or changes to specific cleaning requirements.

Vapour degreasing is an established and sustainable cleaning process that efficiently and effectively cleans PCBAs, quickly and economically. When used with progressive next-generation cleaning fluids, it provides excellent cleaning performance, even on the most difficult and complex assemblies and contaminants, ensuring PCBA reliability. The future of automobiles relies heavily on PCBA technology, and maintaining PCBA cleanliness and reliability will continue to be a requirement as this field advances.

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