Cleaning can quite often be an afterthought once the initial design of the PCB has been planned. Or it may come into question as the planning process nears completion after important decisions about coatings, solder pastes and other materials have already been finalised. This results in a PCB that looks the part but performs poorly and is vulnerable to failure resulting in product recalls and costly returns. It can also have a substantial effect on manufacturing schedules, as designers seek answers to malfunctioning boards and post-production cleaning solutions to rectify the problem.
Cleaning early in process
Early planning is key for PCB manufacturing success and is becoming more significant with the continuing miniaturisation of components. The push to downsize has been driven by several industries particularly for medical applications and within the automotive sector with autonomous and intelligent transport systems advancing at speed. Because of the increasing need for sophisticated electronics, PCB designers are recognising the benefit of specifying their cleaning choices earlier in the design process, as they understand that one of the main causes of electronic device failure is contamination on the PCB.
It is very often simpler to detect and rectify any cleaning problems before the prototyping and production stages. This is particularly true when manufacturing high-reliability PCBs such as those used within the military industry, or in medical devices like pacemakers where cleanliness is not just critical, it is a matter of life or death. Designers are starting to change their mindset by taking a proactive approach to PCB cleaning. They recognize the importance of successful cleaning and are stipulating cleaning details in the early stages of PCB design.
Early identification of contamination
The use of smaller PCBs filled with densely placed components makes managing faults problematic and cleaning a challenge. It is important to first identify the contaminant. There are two forms of contamination found on a PCB, ionic and non-ionic. Ionic contamination is most typically flux residue left behind during the manufacture of the board, or after the soldering process – and is usually inorganic salts or acids. This ionic residue contains molecules that are conductive when in a solution. If it is exposed to levels of moisture, the ionic residue can split into negatively or positively charged ions increasing the overall conductivity of the solution. If left untreated, it will degrade and may lead to corrosion and dendrite growth causing leakage and short-circuits, ultimately resulting in the failure of a device.
The risk of malfunction increases further if a conformal coating is being used. Trapped moisture absorbed by the flux residue may be released during curing operations, causing the conformal coating to separate from the board. This can allow corrosive materials, dust, or water to penetrate the PCB leading to an array of potential problems. It is therefore important for the PCB designer to choose an appropriate flux remover to clean any residue from the boards.
Selecting a PCB cleaning process that works
Once the contaminant has been determined during the planning stage, the next question to ask is what PCB cleaning fluid and method should be used?
Effective cleaning ultimately contributes to the functionality and reliability of the board but it has to be performed using a process that will not damage the PCB. Components can be loosened, connections broken and substrates impacted if the wrong cleaning fluid or inappropriate cleaning method is used. For example, a strong cleaning fluid can dissolve plastics or other soft materials on the PCB. If a high-pressure spray is used to clean under low-standoff components, it could displace delicate components.
The fluid used to clean a PCB has to be compatible with a variety of substrates, without damaging any coatings, yet strong enough to successfully remove the flux residue. The cleaning fluid needs to be matched to the contaminant to effectively clean without compromising the board.
Pre-testing – the answer to successful PCB production
Fundamental to PCB design is pre-testing. Understanding how to clean all the elements of the PCB early in the design process must be investigated. By instigating test cleaning at the initial concept stage, designers have an understanding of how their choices of pastes, fluxes and cleaners impact the performance of the board.
Test-cleaning in small batches prior to full-scale manufacturing can be beneficial to achieving a successfully functioning part. Once the cleaning fluid and process have been demonstrated to work on a smaller scale, production can be increased to the higher volumes required. Through small-batch preemptive testing, any elements of surprise are eliminated to ensure better board reliability.
Pre-testing can take place in-house if a facility has the correct capabilities, however, out-sourcing is a popular choice for the assurance of PCB cleanliness. Specialist companies can undertake comprehensive testing and cleaning trials, which adhere to the standards specified by the PCB designer. This can be anything from simple visual testing to strict IPC-610 requirement testing.
Visual inspection looks for any apparent flux material or white residue left behind after production. With no quantitative results, it is an important method to use alongside other processes, particularly in high-reliability electronics manufacturing. If precision is critical, for example in the medical industry, stringent testing must be completed. This can include methods like Surface Insulation Resistance testing (SIR) which focuses on determining the reliability of an electrical component based on the strength and quality of the signal that comes through the component after cleaning. Another technique is Ion Chromatography (IC) testing. This is the only test that detects and quantifies weak organic acids and individual ions. It is an excellent process to quickly troubleshoot the source of contamination and predict the effect of each ionic type.
Critical cleaning testing like SIR and IC are usually undertaken in critical cleaning labs. Sample parts are methodically tested to ensure cleaning success. Results are verified and documented to validate the cleaning process. Recommendations are then made confirming the cleaning fluid and process that will work effectively when full-scale production commences.
Call in the cleaning experts
To ensure cleanliness designers should consult with a critical PCB cleaning partner that specialises in collaboration and cooperative problem-solving. Carrying out cleaning trials on PCBs that use the industry’s leading flux and solder pastes takes place daily within these dedicated critical cleaning labs. This means specific cleaning fluids and processes can be easily identified to successfully clean the PCB and ensure its reliability. A service like this will have substantial benefits to the bottom-line if applied during the planning process.
Before out-sourcing any cleaning tests, there are a few fundamentals to look for when choosing a critical cleaning partner.
- Do they have the technical expertise? Can they offer specific advice on cleaning a diverse range of PCB substrates through the use of different cleaning methods? There is no one size fits all when it comes to cleaning PCBs, so cleaning tests are essential. These can be performed through on-site cleaning audits or in a critical cleaning lab. Both methods will determine the contamination and what cleaning fluid and process will work effectively.
- Pre-testing may have been undertaken in the early design stages, which has led to the correct cleaning process, however, testing should be ongoing. Choose a vendor that supports PCB designers throughout each phase of the process from research and design to testing and manufacturing and can respond quickly to change. This will help to identify any issues before they become critical.
- Seriously consider testing in a critical cleaning lab. It is here where cleaning tests are conducted to match the cleaning fluid to the flux and paste contaminants. This ensures the PCBs are clean and will function properly.
Plan, plan, plan
Early planning is key to the successful production of electronic products, particularly when it comes to PCB cleaning. Designers must put cleanliness at the top of the agenda when designing a PCB, this will help to ensure long-term PCB performance, functionality and reliability.
Initiating pre-testing and through the selection of cleaning fluids and methods in the initial design stage will help to resolve cleaning problems before manufacturing begins reducing rework and discarded boards.
Partner with a cleaning expert to quickly and effectively identify the best cleaning methods and fluids for the job. The long-term benefits will be substantial when it comes to time, finances and the successful production of a fail-safe product.
Emily Peck, Senior Chemist, MicroCare Corporation
Die Leiterplatte (PCB) ist eines der wichtigsten Elemente beim Design eines elektronischen Produkts. Ein wesentlicher Aspekt, der jedoch während der Entwurfsphase des Designs häufig übersehen wird, ist der kritische Prozess der Reinigung der Leiterplatte, um deren Zuverlässigkeit zu gewährleisten.
Le circuit imprimé (PCB) est l’un des éléments les plus importants de la conception d’un composant électronique. Bien qu’il soit souvent négligé pendant la phase initiale de la conception, le processus de nettoyage du circuit imprimé est critique et essentiel pour garantir la fiabilité du circuit.
Печатная плата (PCB) является одним из важнейших элементов при проектировании электронного устройства. Однако ключевым аспектом, который часто упускается из вида на этапе проектирования, является процесс очистки печатной платы, критически важный для обеспечения ее надежности.
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