Vapor degreasing ensures electronics reliability

Features - Cleaning

As automakers increase electronic content in vehicles with advanced safety systems, autonomous driving modes, and electrified powertrains, critical systems require advanced cleaning technologies.

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December 14, 2020

Vapor degreasers use two sumps, a boil sump, and a rinse sump to clean parts with high-purity cleaning fluids.
All photos courtesy of MicroCare

Applications for automotive printed circuit board assemblies (PCBA) are growing as more vehicles are designed with control and information systems, satellite navigation systems, near field monitors, and multimedia devices. Autonomous vehicles (AVs) and electric vehicles (EVs) will only increase the industry’s need, so electronic assemblies must be highly reliable and operate without fault as the potential consequences to human life are too high without this assurance.

Automotive electronic devices must have long-term functionality and withstand rigorous regulations. Procedures established during design and manufacturing should guarantee component reliability. An important step to ensure electronic device reliability is using consistent, high-quality cleaning.

Reliability at risk

Failing PCBAs could become more common as use increases. The global automotive printed circuit board (PCB) market is expected to reach more than $14 billion by 2024. Rising applicability of rigid-flex PCBAs, penetration of in-vehicle infotainment systems, arrival of new energy vehicles, and use of PCBs in advanced driver assistance systems (ADAS) are all driving growth, according to China-based PCB manufacturer and distributor Pcbcart.

Miniaturized PCBAs that facilitate these applications have extremely complex assemblies, incorporating delicate components on compact, densely packed boards. If cleaning isn’t planned and executed properly, devices can become a reliability risk.

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

Typically, it’s much easier to pinpoint cleaning problems and resolve them prior to prototyping and production, so designers and manufacturers are taking steps to research cleaning to ensure they are proactive in their approach before mass production, specifying cleaning details in the early stages of PCBA design for clean, reliable boards.

Contaminated PCBAs

One of the main causes of electronic device failure is PCBA contamination. Even the smallest amount of contaminant can form a barrier between electrical contacts. If not cleaned sufficiently, PCBAs are susceptible to a host of problems – electrochemical migration and delamination, parasitic leakage, dendrite growth, and shorting. The cleaning process should be performed to guarantee longevity of the electronic assembly and must meet exacting standards, such as those stipulated by the Automotive Electronics Council.

All automotive PCBAs require cleaning during production to remove contaminants such as flux, dust, marking inks, oils, or inorganic contamination resulting from the manufacturing process. However, this is becoming more difficult due to reduced PCBA size and complexity. For example, Pcbcart notes that the volume of an electronic control unit (ECU) used in vehicles was approximately 1,200cm3 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 isn’t cleaned, particularly with hard-to-remove white residue left behind from no-clean fluxes, the risk of board malfunction grows.

Conformal coating applications create another reason to effectively clean PCBAs. Delicate electronic assemblies used within vehicles must withstand harsh environments, so automakers and suppliers typically add a conformal coating protective layer that also electrically insulates the PCBA. If cleaning isn’t successfully completed before conformal coating, any contaminant left on the board can inhibit sufficient bonding of the coating to PCBA substrates. For example, flux residue or process oils left on boards can cause defects in the conformal coating such as delamination, de-wetting, uneven coverage, pinholes, and air bubbles that result in craters and small circular flaws called fish eyes.

After cleaning, PCBAs should be dry and free of residue.

Attaining critically clean

Finding a cleaning process that ensures critical cleaning can be a challenge and requires consideration of many factors. The process must easily and reliably clean miniaturized electronic assemblies and meet specific cleaning standards. It must also be a sustainable and cost-effective method.The answer lies with vapor degreasing.

Extremely effective at cleaning PCBAs, vapor degreasing uses a closed-loop system with a boil sump and a rinse sump. Cleaning fluid is heated within the boil sump and the PCBAs are immersed and cleaned in the fluid. Once cleaned, the boards automatically transfer to the rinse sump for final cleaning in clean, uncontaminated fluid. Finally, the PCBAs are lifted and held inside the vapor blanket, allowing the parts to dry and cool.

Low viscosity and surface tension ratings of modern vapor degreaser cleaning fluids, 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 slower-drying fluids, such as water, cannot clean or may become trapped. PCBAs exit the process dry and without any residue or spots left on the component.

Small printed circuit board assemblies (PCBAs) have dense spacing and hard-to-reach areas that make cleaning a challenge.

Reliable electronics

Vehicles are becoming more dependent on technology and the electronics for easier driving, and their importance is growing as new advances and innovations are applied. Producing anything less than 100% reliable PCBAs is not an option. They must perform as they were intended as any malfunction could be catastrophic.

Effective critical cleaning can help achieve this. Cleaning experts recommend a method that is flexible enough to adapt to any future changes, such as regulatory and environmental changes, or changes to specific cleaning requirements.

Vapor degreasing is established, sustainable, and 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, complex assemblies and contaminants.

MicroCare LLC https://www.microcare.com

About the author: Emily Peck is a senior chemist at MicroCare LLC. She has been in the industry more than 6 years and holds a MS in Chemistry from Tufts University. She can be reached at 800.827.0626.