John
If someone asked you if it would be dangerous to put your head in a
bucket of water and keep it there for ten minutes, what would you reply?
One cannot write specifications or standards governing every stupidity
that people can think up. As it is, we have, BY FAR, too many already.
There is such a thing as commonsense and what you are asking falls into
this category. Dammit, when Moses came down from his mountain, he
carried only ten commandments (OK, I know it was cut down from 14, but
he wasn't allowed to scrap the one on adultery!). I think if there were
one, 'thou shalt not mix fluxes', it would be classed as #23,326,738.
Brian
Vivari, John wrote:
> Dear TechNetters,
>
> A customer of ours came to us with a request for a reference to an IPC
> document or other industry standard that explicitly states the hazards of
> mixing flux types on an assembly. He asked for this because his contract
> manufacturer built a set of boards using a No-clean solder paste and
> reworked some BGAs with a water soluble solder paste. The contract
> manufacture states that he cannot find a standard "anywhere" that says the
> flux types should not be mixed or that there will be any long term
> reliability issues. I know this seems naive but that is their position.
>
> We have searched our library of specifications, books, and industry
> periodicals and have come up empty except for vague statements about having
> to clean between soldering operations for certain classes of product without
> explaining why and a reference in Ning-Cheng Lee's new book cautioning
> against combining incompatible fluxes between reflow and wave soldering. We
> are well versed in the hazards of mixing our own fluxes (never mind others)
> but have never been asked to provide "industry standard documentation"
> before (as opposed to a letter of explanation).
>
> Can anyone point to a reference that we have missed?
>
> Hopefully yours,
>
> John Vivari
> Technical Service Engineer
> EFD Inc.
> [log in to unmask]
> www.efdsolder.com
> Ph: 401-333-3800
> Fx: 401-333-4954
>
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