Planning ahead to prevent PCB manufacturing headaches

14th October 2020
Joe Bush

Some PCB (printed circuit board) designers wait until the very end of the design phase to select the cleaning methods and cleaning fluids to use on their completed boards. Typically, they don’t make cleaning decisions during initial planning, but wait until later in the process - after important decisions about solder pastes, conformal coatings and other materials are already finalised. Microcare explain.

However, this can be a mistake. Designers who don’t plan their cleaning processes early enough often end up with beautifully designed boards, but ones with flux residue, and other manufacturing contaminants that can’t be removed. Contaminants can create a whole host of performance and reliability problems for the boards. These include dendrite growth, electrochemical migration, noise to the board or even a catastrophic field failure.

This leaves PCB designers rushing to find a post-reflow cleaning fix that might work. In the meantime, production delays and budget overages mount. So, it is important for PCB designers to plan ahead and choose an appropriate flux remover proven to work on their chosen solder paste, flux and PCB substrate early in the planning phase. That way they can avoid cleaning headaches during production and be assured their PCBs will perform as intended.

The challenge to be clean

Electronics manufacturers are producing micro-sized PCBs filled with tightly packed components to fit into today’s smaller electronic devices. They are crowded with leadless and bottom termination components with ultra-tight pitches between them. But as PCBs get smaller and denser, they are also more difficult to clean. Low-clearance surface mount PCBs can trap contamination, like flux residue, under or between the components. This makes it a real challenge to remove. But, if the contamination isn’t cleaned, especially hard-to-clean white residue left behind from no-clean fluxes, the risk of board malfunction is high.

Choose cleaning fluid wisely

There are a number of brands and formulations of PCB cleaners or flux removers on the market to choose from. These fluids get under tight-fitting components and remove contaminants before they cause problems. They target fingerprint oils, uncured solder paste, conformal coatings, marking inks and other contaminants.

In-lab cleaning trials help ensure PCBs are clean and will function properly

Above: In-lab cleaning trials help ensure PCBs are clean and will function properly

The first step in getting good, consistent circuit board cleaning is choosing the right cleaning fluid for the job. There’s an old saying in the industry, ‘like cleans like’. Or in other words, match the cleaner to the contaminant. Designers should identify the contaminant on their PCBs and then match the cleaning fluid to it. For example, inorganic, polar contaminants such as no-clean flux residue should be removed with a polar cleaning fluid. It has a more aggressive solvency to dissolve the stubborn white residue left behind by no-clean fluxes. On the other hand, organic, non-polar contamination, such as rosin-based flux residue, does not require as strong a cleaner. They are cleaned with milder non-polar cleaning fluids that are safer for the PCB materials.

Materials compatibility is important

When choosing a cleaning fluid, materials compatibility is important to consider. To avoid PCB damage, the cleaning fluid must be compatible with all materials on the board. It should be strong enough to effectively remove the contaminant, yet not cause damage to plastics or coatings. Typically, the stronger the cleaning fluid, the higher the risk that it damages the board you are cleaning, especially plastics. Test clean the cleaning fluid on your components first to determine if it is safe for use on your materials. When in doubt, opt for a milder cleaning fluid to start and then gradually increase the strength or Kb value of the cleaner until you get optimal cleaning results without damage.

Pre-test your cleaning fluids

In addition to materials compatibility testing, some designers also run pre-production cleaning trials. They test-clean their PCBs in a limited run first. They find it helpful to produce and clean a small batch of PCBs first, ensuring the process works before moving into full-scale production. Once the cleaning fluid and process are proven to work on the smaller batch, then they scale up to the higher volumes needed. Through small-batch preemptive testing, they minimise cleaning surprises, avoid major production headaches and ultimately help ensure better board quality.

Let the experts do the work

Some PCB designers do their own cleanliness testing in-house. But for those unsure about which cleaning fluid or method to use for their particular project, they should partner with an expert cleaning fluid vendor. Some vendors do the legwork for them. They proactively test their cleaning fluids on the industry’s leading fluxes and pastes to identify which cleaning fluids work best on each type. They perform cleaning studies using both benchtop cleaning methods and vapour degreasing to ensure their cleaners meet the IPC-A-610 standards. So, regardless of what flux and paste designers use, they can depend on their cleaning vendor partner to recommend the best cleaning fluid to help validate their cleaning process and keep their PCBs reliable and trouble-free.

As PCBs get smaller and denser, they are also more difficult to clean

Above: PCBs get smaller and denser, they are also more difficult to clean

Start early

Designers should consult with a critical cleaning vendor partner as early in the PCB design process as possible. By consulting with their chemists and cleaning experts during the planning stages, designers reap many benefits. These include avoiding unexpected cleaning failures, reducing costs, ensuring PCB reliability and delivering their finished PCBs faster. Here is what to look for in a vendor partner.

  • Cleaning Lab: Some companies conduct in-lab cleaning studies to match the cleaning fluid to the flux and paste contaminants. This ensures the PCBs are clean and function properly.
  • On-site technical expertise: Look for a supplier with technical expertise in cleaning a variety of PCB substrates using different cleaning methods. This includes both benchtop and vapour degreasing cleaning. The experts can perform on-site cleaning audits to identify materials used and the contamination to be removed. They can suggest which cleaning tools, methods and fluids will work best without harming the substrates.
  • Ongoing field support: Choose a vendor that supports PCB designers throughout each phase of the process from research and design to testing and manufacturing. They can identify and solve potential cleaning problems well before the PCBs go into production.

Smart PCB designing for the future

There are many factors to consider when designing PCBs to ensure long-term performance, functionality and reliability. Designers plan every aspect of the PCB design. From board materials and trace layouts to component placement and the best solder paste to use. Yet, how to clean flux residue and other contaminants from the PCBs isn’t typically considered until well into the design process. Or even after production starts. This can be problematic since the designer may end up with a PCB that is more difficult and time-consuming to clean than expected. This translates into possible scrapped boards, rework and production delays.

No-clean flux residue should be removed with a polar cleaning fluid

Above: No-clean flux residue should be removed with a polar cleaning fluid

So, smart PCB designers should take a more proactive approach to PCB cleaning by selecting their cleaning needs earlier in the process. This allows them to pre-empt any potential cleaning challenges before manufacturing begins. By specifying the cleaning details in the early stages of their PCB design, they can produce clean, reliable boards using a trouble-free manufacturing process. When planning their PCB cleaning, designers should partner with a cleaning expert. They can suggest the cleaning tools, methods and fluids that work best to produce top quality and reliable boards.

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