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Cleanliness: A Dilemma in Printed Circuit Board Assembly

11th May 2015

The printed circuit board assembly industry has developed ever-smaller component packages whose dimensions are mere fractions of a millimetre and are almost invisible. These components are fixed close together on a circuit board and become almost invisible. So how do you know they are clean?

Printed Circuit Board Asssembly

Over the last decade, the solution has been to use a "no clean" technology. "No clean" is effectively a solder paste. The use of this has speeded up manufacturing processing time. It has reduced the costs of material handling and has, supposedly, eliminated the need to clean the circuit board after assembly.

Further advantages have accrued from cutting the costs of extra factory floor space, chemicals, equipment, water and electrical power, all of which are used in the post-assembly cleaning process. Between 70 and 90 per cent of electronics manufacturing companies use this process, but they remain the most avid cleaners.

This is because the manufacturers have discovered three major myths of the electronics assembly industry. These assumptions were that all of the bare boards coming from suppliers were super-clean. Not true. They assumed that that all delivered components were uncontaminated. Also wrong. Finally, they assumed that flux will never present any problems. Wrong.

All printed circuit board assembly processes leave behind a flux residue. These residues not only have a detrimental aesthetic effect on consumer electronics such as sound and video boards, but they also damage conformal coatings and make the whole circuit fail. This second point is a serious issue if the device is located outdoors in a harsh environment.

These flux residues add noise to any system, they cannot be tolerated in a high-voltage set-up and they cause numerous difficulties during repairs.

When these problems were recognised, manufacturers began to clean "no clean" fluxes from their circuit boards. The entire cleaning process cannot be achieved just with water but needs an additional saponifier or special solvent.

Newer "no clean" solders are easier to clean than older ones that build up alongside board components. But this also depends on following the instructions provided by the cleaning-product manufacturers, especially regarding the temperature. If the cleaning process is too hot, the flux will be difficult to remove. If the temperature is too low, the whole board can look as though it is covered in flux.

So when choosing a "no clean" solder, make sure it's one that is easy to clean. If you have any questions on cleaning, or would like to know more about printed circuit board assembly, feel free to contact us.