Or, if you have to clean, water-soluble! It has been shown time and time
again that vapour phase cleaning is not always a good solution. HFC
cleaners are very poor and it is just the additives that do the work.
Alcohols are not very good solvents, as they tend to saturate easily.
Furthermore, if the stuff in the boiling sump is contaminated with flux,
as must be the case after a few hours of use, by definition, each bubble
of vapour bursting throws up a few droplets of dirty solvent into the
vapour phase. The solvent part of these droplets is in an exchange
liquid/vapour phase condition and the solids form an aerosol in the
vapour. Many times I've demonstrated this by taking a measurably
ionically clean board, putting it in the vapour phase and measuring the
ionic contamination, often to levels increased by an order of magnitude
(e.g. starting at 0.2 µg/cm2 eq. NaCl, to end at about 2 µg/cm2 eq.
NaCl).
Anyway, what does your paste vendor recommend for cleaning?
Brian
> Bev Christian wrote:
>
> Ramsey,
> Just to play devil's advocate here, can you consider changing over to
> no-clean?
>
> regards,
> Bev Christian
> Nortel Networks
>
> -----Original Message-----
> From: Ramsey's [SMTP:[log in to unmask]]
> Sent: Friday, November 05, 1999 7:35 PM
> To: [log in to unmask]
> Subject: [TN] White residue on SMT after vapor cleaning
>
> A few weeks ago I wrote asking for help on with a white residue
> problem.
> Some technetters ask for a follow-up. Here it is.
> Case: White residue appears on ref lowed SMT land patterns after
> exposure to vapor cleaning. No white residue appears on wave
> soldered
> land patterns. Even on mixed technology boards.
> RMA type paste for SMT. Synthetic Activated flux applied as foam
> at
> solder wave.
> Vapor cleaner loaded with Vertrel XMS Plus (HFC, Trans Diclor,
> and
> alcohol). Ultra sonic scrub rinse.
> Prior to exposure to vapor process the flux residue is very thin
> clear
> and almost invisible. After cleaning the residue appears as a
> white
> powder where ever there was flux.
> We tried a co-solvent Axerel 32 in the boil sump, with board
> immersion
> instead of vapor cleaning. Rinse in Vertrel distillate with
> Ultrasonic
> scrub. Slight improvement.
>
> Result: We discovered that the residue was flux activators, not
> rosin.
> We experimented with a few flux formulation until we found an old
> Alpha
> Metals paste formulation that cleaned beautifully in the
> co-solvent
> process. 40% Axerel 32 by volume in the boil sump. We have not
> found an
> RMA paste that will clean completely in the traditional vapor
> process
> with Vertrel XMS.
>
> Did anyone ever hear of an SA solder paste formulation?
>
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