PCBs
Add cleaning processes to your design to achieve reliable PCBs
By Emily Peck, senior chemist, MicroCare E
ffective printed circuit board (PCB) design practices are critical in order to deliver a board that performs as intended. When designing a PCB, there are
many factors an engineer must consider. Everything from properly orienting the components on the board to carefully routing the signal traces to determining the best flux/paste mixture. All must be planned before any prototyping or production starts. However, cleaning is a critical aspect of PCB design that is often overlooked during initial planning. Previously, some PCB designers didn’t think about PCB cleaning until the very end of their project. Or, at least well into the process after important decisions about coatings, solder pastes and other materials had already been finalised. This left designers with an elegantly designed PCB, but also possibly one with flux residues which could not be removed. That resulted in a poor performing PCB that was susceptible to catastrophic field failures, disruptive product recalls and costly returns. It also impacted production timelines and budgets as designers searched for a post-manufacturing cleaning fix that might work.
Recently though, more PCB designers are recognising the benefit of specifying
their cleaning choices earlier in the design process and taking a proactive approach. It is typically much easier to identify and resolve any cleaning problems prior to prototyping and production. This is especially true when manufacturing high-reliability PCBs such as in military or medical products where cleanliness is critical or validation is required.
Specify a PCB cleaning fluid As the electronics industry continues to use smaller PCBs filled with tightly packed components, they become more difficult to clean. Reductions in pitch between 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
36 November 2021 Components in Electronics
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
Ensure long-term functionality 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.
www.microcare.com
www.cieonline.co.uk
need. Through small-batch preemptive testing, they are minimising surprises and ensuring better board reliability 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.
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58
