CONTRACT MANUFACTURING
conductors along with the increased use of leadless and bottom termination components increase the probability that contamination like flux residue gets trapped on the PCB. If the contamination isn’t cleaned, especially hard-to-clean white residue left behind from no-clean fluxes, the risk of the board malfunction is high. If a conformal coating is 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 causing corrosion, signal transmission problems, or even complete component failure. Therefore, it is important for the PCB designer to choose an appropriate flux remover to clean any residue from the boards.
Select an effective cleaning process
Choosing the right cleaning fluid and method is important as it ultimately contributes to the functionality and reliability of the board. PCB components can be loosened, connections can be broken and substrates can be damaged if the wrong cleaning fluid or inappropriate cleaning method is used. For example, a cleaning fluid with a very high cleaning strength may potentially attack plastics or other soft materials on the PCB. Or a high-pressure spray used to clean under tight-fitting components could possibly knock delicate components out of alignment. To avoid PCB damage, the cleaning fluid should be compatible with all materials on the board. The cleaner should be strong enough to effectively remove the flux residue, yet not cause damage to plastics or coatings. Designers should also match the cleaning fluid to the contaminant to be removed, whether it is flux residue, marking inks, dust or fingerprint oils.
Test your cleaning
Choosing a flux and solder paste early in the design process only to discover later that they can’t be cleaned is a problem. Therefore, early pre-testing is recommended. Test cleaning gives a designer insight as to how their choices of pastes, fluxes and cleaners impact the performance of the board.
Some designers recognise the benefit of test-cleaning in small batches prior to full- scale manufacturing. They find it beneficial to produce and clean a limited run of PCBs first, ensuring cleanliness before going into full production mode. Once the cleaning fluid and process are proven to work on a smaller scale, then they ramp up to the higher volumes they need. Through small-batch preemptive testing, they are minimising surprises and ensuring better board reliability
Figure 3:
PCB batch cleaning: Test cleaning small batches gives designers insight as to how their choices of pastes, fluxes and cleaners impact PCB performance
before it becomes a major headache. Some design engineers can do their own cleanliness testing in-house. For those who do not have testing capabilities, they can out-source their cleanliness testing. There are a number of reputable companies that conduct comprehensive cleaning trials using designer-supplied, real-world PCBs and contaminants, not just test coupons. The cleaning evaluations are conducted to the cleanliness standards specified by the PCB designer whether it be simple visual testing or strict IPC-610 requirements. The methodic testing results produced in a lab are verified and documented to validate the cleaning process. Pre-testing also helps with production planning by predicting and verifying expected outcomes.
Figure 2:
Miniature PCBA: Today’s smaller PCBs filled with tightly packed components are more difficult to clean
When designing a PCB, cleanliness is a factor that designers must consider to ensure long-term PCB performance, functionality and reliability. It is recommended that they select cleaning fluids and methods early in the design process since it is easier to resolve cleaning problems before manufacturing begins. This helps reduce unforeseen problems including rework and scrapped boards.
Designers should partner with a cleaning expert to select the best cleaning methods and fluids. It will help prevent production delays, improve product quality and positively improve the bottom line.
MicroCare, LLC
www.microcare.com
MAY 2021 | ELECTRONICS TODAY 47
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