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White residue on PCB's

Ian Harrison

#2778

White residue on PCB's | 11 October, 2000

Some boards that are populated by one of our subcontractors are getting a white powdery residue forming on them. I think it is the non clean flux and process which they are using that is causing the problem. Their process is as follows. Flux is put into wave solderer at beginning of week. As the flux is used up, they top up. The flux is left in the machine all week and drained at the end of the week. All flux drained out is thrown away. The flux they use is Alpha E191/1 Can anyone comment on the process above or give any ideas as to where the residue is coming from. All help appreciated. Thanks

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Verm

#2779

Re: White residue on PCB's | 11 October, 2000

Try the following steps : FIRST CHECK THE ARCHIVE for further information, it WILL help you.

Step One : What�s the chemical analysis of this white res? Obtain a sample. It could be tin, rosin, or something else???

Step Two : The fastest way I know to get "white" res' is to get water on a no-clean flux. This is usually done by 'water' washing boards with no-clean flux residues on them.

Step Three : In some geographic areas, people complain about this all the time. Moisture in the air can cause white residues on a no-clean flux.

Step Four : about the wave solder set-up: � Suggested preheat is approx. 225�F (107�C). � Check the flux solids content. � Check the conveyor speed, ~ 3.5 - 5.5 ft/min.

White residues tend to be cosmetic only and can generally be dry brushed off!

Regards

George

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DennisF

#2780

Re: White residue on PCB's | 12 October, 2000

The white residue can be caused by putting Alcohol on the no clean product. Some people will attempt to clean an area they have reworked.

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Robert Steltman

#2781

Re: White residue on PCB's | 13 October, 2000

Looking at the original post, it seems that the white residue is formed on the board after wave soldering and becomes evident when it has been left standing for a while. From what I understand, it seems that the solids content of the "no clean" flux used in the wave soldering process is out of spec, due to the fact that the flux is left in the foam fluxer all week and is just topped up - I assume that it is a foam fluxer.

The solvents in the flux evaporate, leaving the solids behind. The fluxer is then topped up again, but now the solids to solvent ratio is out of spec. In the beginning of the week the flux in the machine will be low in solids, but as the week progresses, the solids content will increase, leaving behind more and more flux residue. This will most likely be evident on the underside of the PCB as well as around components where the flux is drawn to the top of the board due to the capillary action of through-holes and vias. As the board stands, the residue, which initially is not very visible, turns gradually to a white powder.

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#2782

Re: White residue on PCB's | 13 October, 2000

George and the others make good points. Check Les Hymes response to a similar question in 7/00 "Circuits Assembly"

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