|Ask the Experts|
September 1, 2017
Clean before wave soldering
Is it necessary to clean (using isopropyl alcohol) PCBs before wave soldering? If it is necessary, then why? If not, then why? Is there alternative practice for this process?
|Expert Panel Responses|
The first objective especially if the PCB assembly is being manufactured using No clean technology is to avoid handling and contamination where ever possible. Handling contamination will have the potential for two effects
In my 20 years of experience in PCB assembly, the only time I have seen companies clean before soldering was in very high-end aerospace and military requirements. And there is some logic to this…. The most corrosive or damaging residues on a PCB are the salts (also called "halites" or "activators") that are in the fluxes. They make the flux "wetter" and help the soldering materials flow into each other, creating stronger solder joints. But heat increases the rate of corrosion development, and a warm circuit board in a working electronic device can develop dendrites and other corrosive conditions in just weeks or months. So cleaning AFTER soldering should, in theory, remove these residues and provide PCBs with longer operational lives. But over the years a few companies cleaned before soldering. Their logic was that cleaning was a cheap way to ensure that (a) no contamination was trapped in the solder joints, which would create a weak joint, and (b) no contamination blocked the flow of solder and produced incomplete wetting. After all, there are many other contaminates on circuit boards besides just fluxes: fingerprints contain salts and oils; but also dust, marking inks, Kapton tape residues, and even humidity all are found on the boards and can cause problems. By removing all those residues they increase the chances for perfect soldering and decrease the opportunities for problems. There's no doubt that pre-cleaning adds expense to the manufacturing process. So unless you're building a space probe that's engineered for cruising through the solar system, in most cases it is an expense that's hard to justify. My suggestion would be to do a systematic test of 200 boards; clean 100 and don't clean the others, and see if your QC people can detect any differences.
This would only be required if there were heavy deposits of grease or other contaminates on the PCB. Otherwise the normal cleaning action of the flux will provide the cleaning necessary for the soldering operation.
Regional Sales Manager
OK International Inc.
Cleaning PCB's before wave soldering is certainly not a normal procedure. The only reason I can think of that would require cleaning is if the boards had been contaminated with some material that required IPA to remove. Boards should not be handled with bare hands as the oils in the skin can contaminate the solder pads and interfere with the solder process.
Senior Applications Engineer
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