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RoHS parts - leaded solder

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RoHS parts - leaded solder | 25 October, 2005

Sorry this is such a long thread but I would like as much input as possible to everything I ramble on about... :)


We are now seeing more and more RoHS parts showing up in our SMT inventory and a question has been popping up more and more....

"Can you safely use RoHS parts in a fully leaded production line?"

We use a highly active water-wash flux in our reflow process which sees a maximum reflow temperature of 215C +/- 5C. (we wash all our boards) One of the engineers I work with was reading the manufacturer's specs on one of the parts which said that you should reflow the part to a maximum peak of 260C. He now thinks we should simply crank up our oven to 260C and be done with it. I know this can't be done as it affects just about ever aspect of the proccess. (boards, flux, parts, etc) Then, yesterday, our purchasing manager came to me and said that a couple of our suppliers have been getting complaints from other customers. They say that they are having problems soldering with leaded solder to RoHS parts. My only thought on this is maybe the majority of companies still using leaded solder are using no-clean paste which wouldn't solder as well to begin with?

What I'd really like is confimation, via IPC standard, formal test results or SOMETHING that shows that it is indeed possible, agreeing with every lead-free conference I've been to over the years.... it's perfectly OK to use lead-free components in a leaded proccess.

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RoHS parts - leaded solder | 25 October, 2005

It is not OK to use leadfree BGA's with a lead process. Other parts "should" be reverse compatable. But I first saw problems over 5 years ago with Paladium leads and a lead process. Don't confuse saying "it's ok to use lead free parts in a leaded process" with "it's ok to use lead free parts in a leaded process". Seriously when someone says it's ok, do they mean for some parts, or all parts. I"m betting they mean that you can't say "you can't use lead-free parts in a leaded process." But that does not mean all parts can be used. If my memory was better I could name the logical falicy involved.

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RoHS parts - leaded solder | 26 October, 2005


We've been soldering tin plated components and Ni/Sn (100% Tin) boards with leaded solder in the 80's in hirel and military applications. We never experienced reliability issues with the mechanical or electrical properties of the solder joint (we did not change temp's in soldering).

That said we had some serious issues with whisker growth, it was so bad the whiskers grew between the FR4 laminate. We also found that the absence of lead on pads not fully wetted with leaded solder created a greater potential for dendrite formation in humid conditions.

If your products are not exposed to high temperature variations, humidity, vibration or other stresses you probably won't have any problems. Just consider yourself fortunate you can still use leaded solder���

The peak temp of 260C is just to make sure that that temp is not exceeded in lead-free soldering and has nothing to do with the profile you use in your current process.

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