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What happens to overheated solder?

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#46302

What happens to overheated solder? | 20 December, 2006

I am looking for white papers or information on what happens to 63/37 solder paste alloys when overheated. I have had some solder joint analysis done regarding missing finish on some of the joints. The analysis came back showing a low lead content on most of the subject joints. The subject joints originally had insufficient solder out of surface mount, during inspection these joints were hit with a solder iron. I believe because of the component size 0402 and the manual touchup this was causing the metalization of the joint to change and possibly burn up the lead thus causing the low lead content in the joints. I am looking for information on what happens to overheated solder joints or other people that have had similar occurences.

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#46310

What happens to overheated solder? | 20 December, 2006

I'm no metallurgist but I don't think you're going to burn up lead with a soldering iron.

That said, I would surmise that you could pull a lot of the metallization from the component terminations (very likely lead free) and the pads on the board (is it possibly lead free as well?) via dissolution and change the composition of the overall joint.

Exactly how low in lead were these test samples? Do you have lead free wire anywhere in your plant? If that's a positive then you probably need to confirm that someone didn't grab the wrong spool before you pursue anything else.

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CK the Flip

#46311

What happens to overheated solder? | 20 December, 2006

I've seen smaller components have a "charred" appearance and a lack of wetting up the component termination. Also, extended heat exposure may introduce excessive IMC (intermetallic) formation - the bad kind, that is. That's where your IMC layer will pick up extra atoms of copper or tin, it'll be "too thick" and not as reliable of a joint.

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#46313

What happens to overheated solder? | 20 December, 2006

I worked for a company that had a nurse come in to talk to us about lead exposure. She assured us we had nothing in facility that would come close to vapourizing lead.

Are you sure they didn't touch up using leadfree solder?

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#46317

What happens to overheated solder? | 20 December, 2006

We're not real clear on the issue. [Got ourselves wrapped around lead (Pb) versus lead (termination), we think.] That aside, comments are: * Boiling point of lead [Pb] is [/K]: 2022 [or 1749 �C (3180 �F)] * It's possible that the material that comprised the end termination of your component dissolved into the solder. * It's possible that the end termination of your component was not well plated and appears to be missing. * Epoxy holding the pad on the board will give way from the heat of soldering before the composition of the solder will be affected. * Metallurgists use a phase diagram to determine how materials react at various temperatures and materials combinations. Look here: http://www.chemguide.co.uk/physical/phaseeqia/snpb.html

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