Types of lead-free solder

If you mean wire solder, we use pure tin. If you mean paste, it is SAC? and I don't recall the number.

Paul

Wire. But pure tin, not even 0.3% copper? I thought that was only for wire bonds or something.

Pick a solder formulation:

For general repair, when I must use RoHS solder, I have several rolls of 0.031" 96.5% tin, 3.0% silver and 0.5% copper alloy with no clean flux:

I have no clue if this solder is better or worse than any other type. I bought a case fairly cheap, and plan to use it until it runs out. There are cheaper formulations without the silver which might be useful.

I also use 63% tin, 37% lead solder for older devices. It works MUCH better than the RoHS stuff. I'll sometimes use it on boards that use RoHS solder, but only if I suck off the RoHS solder first. Mixing the two solder types results in a dull dross-like mixture.

I've wondered about this too. Are you saying that every time I do a component level repair on a board that was built according to RoHS specs I need to remove all the RoHS solder associated with that/those components first? That would just about involve everything new that comes from Europe or Asia wouldn't it? Lenny

"klem kedidelhopper" wrote in message news: snipped-for-privacy@v8g2000yqk.googlegroups.com...

When the directive first came in, I did a lot of research on this for a couple of trade magazine articles that I wrote. I had some very detailed discussions with a very highly qualified metallurgist (PhD level) who was part of a government-sponsored agency to advise industry on the implications of the legislation. He was quite adamant that leaded and lead-free solder should not be mixed in the same joint, as this would lead to the joint integrity being compromised. As he was far more 'expert' at this than I was, I took it to be the case, and have always advised anyone who has asked me, that mixing was a bad idea. I certainly don't do it myself, but it is actually quite rare to find non-RoHS equipment that was constructed using lead-free, ahead of the requirement in June 2006. Sony was one such company. However, in variance with what my metallurgist doctor said, Sony insisted that all of their service agents changed over to using lead-free solder for repair of *all* of their products, irrespective of the solder type that they had originally been constructed with. Rather than being a reasoned response to the impending legislation, I believe that it actually came about as a mis-understanding of what was required. It was amazing how many companies and individuals within the industry, mistakenly believed that the use of lead-free solder had been either totally banned ahead of the legislation date, or was going to be immediately after. One of the major soldering equipment manufacturers - I think it was Cooper (Weller) but might have been Pace - even published their own document, incorrectly advising of this total ban that never was. Again, I think it was an honest wrong interpretation as a result of a knee-jerk reaction to the legislation, but since most people believed that they were going to have to buy all new soldering equipment to cope with the higher temperatures that lead-free required, the more cynical amongst us, might believe that it was a deliberate ploy to increase sales of replacement stations ...

I continued to advise against using lead-free to carry out repairs on items originally constructed with leaded solder. As the regulations stand, there is no requirement to use lead-free to repair any item 'brought to market' prior to June 2006, irrespective of whether or not it was constructed using lead-free. After that date, all items brought to market have to be RoHS compliant, and it is a legal requirement that the compliance is not compromised in any way by the process of repair, which means that as service engineers, we are legally obliged to use lead-free solder, and RoHS certified components to carry out any repair on such equipment. Of course, I don't think that there is any such requirement to maintain the original certification on your side of the pond. So I would say, go right ahead, and use 'proper' solder to carry out your repairs, but suck or wick as much of the lead-free solder off the joint as you can, before remaking the joint.

Arfa

Will there not always be a residual film of the original solder, and would that not cause a crack along the entire interface?

It is the absence of lead rather than presence of tin that is causing the problems, you have tin in both leaded and lead-free solder. It is the lead that gives the forgiveness, perhaps someone knows the technical rather than folksy term for this

Sorry, I misread your previous post. I was thinking of the opposite. If the joint used SnPb originally you would never be able to remove all the lead, so could you use Pb-free after cleaning?

Yep. That's about it. If you want to use tin-lead solder, you have clean off the tin-silver-copper RoHS solder first. Try mixing the solder for yourself. The resultant dross-like joint should be obvious.

After some experimentation, I've found that it's not really necessary to totally remove the RoHS solder. Just clean it up to the point where it looks like solder plating on the pads.

Yes, agreed

Arfa