Feature: Medical electronics
pure, clear and dense vapour blanket. PCBs are lowered into the boiling cleaning fluid, which heats, loosens and removes most of the contamination. Ten they are moved to the rinse area where any final vestige of contamination rinses away. Finally, the PCBs are raised so they sit inside the vapour blanket, where they quickly dry and cool, as the vapour passes under the low-mounted components. PCBs exit the vapour degreaser just 8-15 minutes aſter the start of the cleaning cycle.
Manual drying on the benchtop, with wipes Wipes are some of the most common drying method used during manual PCB cleaning at the benchtop; see Figure 2. Whether capturing the excess spray of flux remover or gently pushing the wipes under surface-mounted components to absorb cleaning fluids and contaminants, wipes are quick and effective, without leaving lint or fuzz behind. However, not all wipes are equal and they should be chosen carefully. Tree things to consider are absorbency, material and packaging. • Absorbency: It is important to check the wipe will absorb the specific moisture encountered. For example, some wipes are made to absorb cleaning fluids, but will not absorb water, whilst others are good at absorbing oils. So, it is essential to match the type of absorbency to the contamination to be removed.
• Material: Lint-free, non-woven wipes are one of the best choices for drying PCBs because they are made without glues or binders that could leave residue or foreign object debris behind.
• Packaging: When choosing drying wipes, packaging is important. For example, wipes sealed in electrostatic-discharge- safe wrappers will limit dust attraction and reduce static discharge damage to the PCBs. In some cases, fabricators may need clean-room wipes, which are typically cut and packaged in a clean- room environment to ensure their purity.
Dust removers for drying Some fabricators choose to use dust removers, also known as dusters, to dry PCBs at the benchtop; see Figure 3.
Whether it is heat, air, vapour, wipes
or compressed gas, there is a method to help ensure PCBs are dry and ready to provide optimum performance and reliability
A quick blast from a duster blows trapped moisture from underneath components that a wipe alone might not reach. Te dust remover can also target the hard-to- reach nooks and crannies. Using a duster in combination with a wipe doubles the drying power and prevents the cleaning fluid from being pushed back onto the board and spreading around any residual contaminant. However, dusters must be chosen
and used with caution – safety is key. Inexpensive canned air is readily available from retail outlets; however, some of these formulations may pose a hazard due to their high flammability. A safer alternative is to use a dust remover made with non-flammable gas. Using the duster may also take a bit of practice, but once the operator understands the velocity of the high-purity gas, the moisture is blown away quickly and efficiently without damaging the PCB or leaving residue.
Avoid negative impact Moisture leſt on modern PCBs may negatively impact their function, reliability and longevity. Water or cleaning fluid leſt behind aſter rinsing may cause defects that could render the PCBs unusable. To prevent these problems it is imperative that PCBs are completely dry aſter cleaning. It is recommended to work with a
partner with specialised experience and expertise in PCB cleaning and drying to choose the best drying method.
Figure 1: Circuit boards in a vapour degreaser – PCBs come out of the vapour degreaser clean, dry, spot-free and cool
Figure 2: Circuit board with wipes – it is essential to match the type of wipe absorbency to the contamination to be removed
Figure 3: Dust remover – a quick blast from a duster blows trapped moisture from beneath larger components
www.electronicsworld.co.uk July/August 2022 39
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