Daan
If you haven't already got a copy, go to the nearest university library
or suchlike and borrow a copy of my book. On pp 157-161, there is a
discussion on white residues. In fact, although they are not all
discussed here, I have identified 22 causes of them to date. In my
experience, the most common causes are improper curing of the solder
mask. During cleaning, this may locally remove the surface, causing a
change in appearance, often mistaken as a deposit or residue.
Alternatively, it may also allow hydrogen-bonding to occur to flux
molecules or activator molecules. Dibasic acid activators can be a devil
for this, even worse than rosin. Fig 15.1 in ibid.cit. shows an
excellent example where everything conspired to produce an 'orrible
result.
Best regards
Brian
"d. terstegge" wrote:
>
> Hello Technet,
>
> We've got some expensive boards here with white residues after cleaning. Most of it is invisible for the naked eye (conforming IPC class 3 standards), but each board has a few small spots that are visible (if you look really good).
> Now the customer wants proof of what this residue is. Not because they can see the residue, but because they know it's there.
> These are double reflow boards, soldered with RMA solderpaste. After each soldering step the boards are cleaned with Axarel 32 and rinsed with deionised water.
> Our ionograph shows that there is hardly any ionic contamination on these products.
>
> Some questions:
> 1) When there's so little residue present, will it be possible to do an analyses ? To collect a few grams I'd have to scrape the residues of hundreds of boards !
> 2) What kind of analyses should be done ?
> 3) Any recommendations on where to have the analyses done ? Locations in Western Europe are prefered.
>
> All answers are more than welcome.
>
> Kind regards,
>
> Daan Terstegge
> Thales Communications
> Unclassified mail
> Personal Website: http://www.smtinfo.net
>
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