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Contamination/process issues of SMT and wave soldered pcb's


Loz

#25052

Contamination/process issues of SMT and wave soldered pcb's | 3 July, 2003

I have been advised recently about pcb manufacturers, that somehow or other supply pcb's with contamination. Visually they are fine, but problems arise during SMT manufacture, ie solder balling, non-wetting on pads, and also during wave solder process, solder balling etc. I hear a lot about under cured resist, which is causing process problems. Has anybody else come across this, and if so how can you get round the above issues. We are a sub-contractor so mostly recieve free-issue pcbs, so we are at the mercy of our customers, who when contacted do not really understand the impact on the long term quality of their products. Any ideas will be appreciated.

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#25054

Contamination/process issues of SMT and wave soldered pcb's | 3 July, 2003

That has to be the worst of all worlds. Someone goes out and buys the cheapest parts they can find, gives them to you [Loz], and wants you to assemble a perfect product. Well, it would be nice if you could console yourself by making Derick Jetter money, wouldn't it?

What you say could be true, but we are tactical group here, not to say that we don't wax philosophic periodically. We will help you sort through the specific issues of your problem, but we don't do well with broad or generalized problems.

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Loz

#25055

Contamination/process issues of SMT and wave soldered pcb's | 3 July, 2003

OK. Point taken, lets keep this simple then, how about just the issue of under cured solder resist? Any body else encountered such issues. Just feedback, 'cause its something that just seems to have been highlighted to me. Thanks.

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Kris

#25056

Contamination/process issues of SMT and wave soldered pcb's | 3 July, 2003

Hi,

undercured solder resists may be a defect people have seen so far. Some of the probles arising is blistering as well as reaction with wave solder flux that may lead to some kind bad gel like formations.

Gels the idea would be to reflow the bare boards once and that hopefully should cure the resist. If you have the leverage toss the boards back to the vendor saying that you wont be able to work with it

Thanks

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#25057

Contamination/process issues of SMT and wave soldered pcb's | 3 July, 2003

It might be easier to answer what we haven�t seen. In today�s economy everyone is looking for a deal. Just remember "there is no sex in the Champaign Room"

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Kris

#25063

Contamination/process issues of SMT and wave soldered pcb's | 3 July, 2003

What have you not seen ?

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RDR

#25064

Contamination/process issues of SMT and wave soldered pcb's | 3 July, 2003

Kris, I don't know what I HAVEN'T SEEN yet cuz I haven't seen it. (HAHAHA) It is kind of like when you are looking for something and you always say after you found it that it was the last place you looked (Why would anyone keep looking for something after it was found?) Just a stupid little joke for the holiday.

P.S. I haven't seen anything that goes exactly perfect as planned yet, Perfect HASL finish, water going uphill, helium sinking in our atmosphere, turning lead into gold, and probably a few other things.

Happy fourth

Russ

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#25068

Contamination/process issues of SMT and wave soldered pcb's | 4 July, 2003

With poorly cured mask: * Wave soldering: Expect to see thin wavy band of dross imbedded in the mask in the wave solder side. * Reflow soldering: Expect to see a pinto board where the two tones of mask are [1] normal color and [2] a lighter color, almost milky. There have been threads here on SMTnet describing solderballs imbedded in the solder mask.

We wash. So, solder balls are not one of our problems.

Your board fabricator is going to stare at you in disbelief when you complain about poorly cured mask. Fabs believe that the causticness [nontechnical use here, maybe nastiness is better] of post mask processing will highlight any cure issues during preship inspection. Maybe.

We have not seen cure issues in a couple of years, knock on wood, but that doesn't mean that they are not occurring.

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Randy Womack

#25123

Contamination/process issues of SMT and wave soldered pcb's | 9 July, 2003

LOZ. Under-cured or out-of-spec(sloppily) applied resist is realistic. What other physics: Shiny resist surface is more prone to balls then matte finish. How about an operator eating fish & chips before handling the boards. Don't laugh... ... saw that.

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