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chemistry question

#5793

chemistry question | 29 March, 2001

All arguments about using OA pastes on high frequency boards to eliminate alledged RF interference aside, is it acceptable to touch up SMT components on these boards with a no clean flux cored wire after wave solder? All of our wave machines are using nc flux, so it's already on the board. I wouldn't be doing the fine pitch stuff, which is what engineering says drives the use of OA fluxes.

My first concern is allowing OA flux trapped in voids on SMT components on to the board surface and not removing it. Maybe the volume is less than would necessitate cleaning? I suppose I'd like to know whether or not the two compounds combined make anything more or less corrosive or conductive also. Should I just clean it up with alcohol and call it good?

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#5807

chemistry question | 29 March, 2001

I'm confused. [Swatts nu, eh?]

Are you trying to avoid cleaning yer OA? [if so, don't do it. (but you know that)]

I assume use OA with yer SMT then wash and then NC with yer PTH and third processes. Reet?

Are you concerned about post-wash OA res comingling widyer NC res and causing a flux Cernoble? Er wattt?

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#5815

chemistry question | 30 March, 2001

Surprise, surprise. ;)

Wouldn't think of it....

Yep.

I'm not as concerned about two flux chemistries mixing and causing a substrate China syndrome as I am about the OA flux retained in voids and subsequently released in a touchup operation. If we touchup with nc, is the OA released in this process of significant volume that it would need to be cleaned? We have been supposedly touching up with nc all along, but became concerned about this only recently due to some other investigations.

What I'd like to do is tell the post-wave folks that there is to be no OA flux anywhere in the area, and don't clean anything.

I have to admit, though, that I am a little curious about the chance that two fluxes might combine to make something at least as bad as the OA by itself. Seems remote, but I really have no idea and can't find anything on the subject.

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#5824

chemistry question | 31 March, 2001

Consider having one of those left coast test labs do a bit of ion chromatagraphy testing to help clairify.

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