So what's the truth about lead-free solder ?

[N Cook]

But those are RoHS compliant.

More to the point, for removing laquer , not hard tin , from round surface.
I just tried a Skarstan blade , singly, in its normal wooden handle and it
scrapped the hard tin off some of the flat leads of the latest batch of
TIP35C/36C power trannies that I bought. Down to the copper with no
difficulty, I think I can ignore the tin-pest developinmg on the narrow
edges as long as the main surface contact areas are functionally solderable.

 

[PeteS]

It's not a troll.

New data ought be available as to the effects on actual in-service reliability of
lead-free by now. It seems as I expected, anecdotally, that musical equipment
products that tend to see high levels of vibration are suffering.

Graham

This subject came back to bite me yet again today. There's a great part
I wanted to use, but we'll have to refinish the pins first if I do, so
I'll see if there's a different part I can use in this application. For
the record, it's a high speed (not full speed) USB peripheral controller
and the lead finish is 98/2 SnCu.
I consulted with a few of the manufacturing people and one of the
biggest problems with RoHS profiles is the solders aren't eutectic, so
getting a proper bond is more difficult quite apart from the problem
with tin whiskers.

Cheers

PeteS

 

[Chris Jones]

But those are RoHS compliant.

More to the point, for removing laquer , not hard tin , from round
surface.

Ok, it was just a thought. I was imagining the round pin of a T03 when I
thought of that.

I just tried a Skarstan blade , singly, in its normal wooden
handle and it scrapped the hard tin off some of the flat leads of the
latest batch of TIP35C/36C power trannies that I bought. Down to the
copper with no difficulty, I think I can ignore the tin-pest developinmg
on the narrow edges as long as the main surface contact areas are
functionally solderable.

Do you mean tin pest or whiskers? I would have thought that the edges would
be the worst place for whiskers to sprout from.

As for solderability, I would have thought that if the pins are exposed to a
sufficient quantity of sufficiently hot SnPb solder for a sufficient time,
then the tin would dissolve into the solder, like fine copper wire has an
annoying tendency to do. If overheating of the semiconductor device is a
risk, then perhaps it could be done in a couple of goes, allowing to cool
in between. The resulting tin-rich solder could either be removed and
replaced with fresh solder, or just diluted with more fresh solder.

I'm sure there would be plenty of people interested if you find a good
technique for small-scale use.

Chris

 

[ChairmanOfTheBored]

What's the application that requires this refinishing ?

High temp mag wire... not the shitty for high temp uses "Nyleeze" does
NOT burn off with the application of heat, and requires scraping to
remove the insulation. Before Nyleeze, the requirement was the standard
for decades.

 

[N Cook]

N Cook wrote:

Do you mean tin pest or whiskers? I would have thought that the edges would
be the worst place for whiskers to sprout from.

As for solderability, I would have thought that if the pins are exposed to a
sufficient quantity of sufficiently hot SnPb solder for a sufficient time,
then the tin would dissolve into the solder, like fine copper wire has an
annoying tendency to do. If overheating of the semiconductor device is a
risk, then perhaps it could be done in a couple of goes, allowing to cool
in between. The resulting tin-rich solder could either be removed and
replaced with fresh solder, or just diluted with more fresh solder.

I'm sure there would be plenty of people interested if you find a good
technique for small-scale use.

Chris

With the sort of stuff I deal with, geometry-wise, tin whiskers have no
relevance I would have thought.
It is that film of tin , all lovely mirror shiney when new turning to grotty
dusty grey (tin pest) , expanding in the process , and physically pushing
the solder away from any conduction maybe only 2 years down the road.
I am not sure just heating legs with solder would affect the integrity of
that initial tin film without some sort of mechanical intrusion while hot
and mixing.