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Why did the electronics industry move to SAC,when the MP is greater than simple tin/silver?

Seems some like nickel, some LOVE gold so combine them for "better" (ENIG). Would you believe that gold can accelerate corrosion, especially over time?

In our application, temperatures can get to 204C/400F which "helps" the corrosion mechanisms. More specifically, the dis-similar metal interface between the pad surface and the regrettable use of SAC.

We started with the use of Kester Sn06.3/Ag3.7 solder; we understand that Kester now says that they never made it (have physical proof they did). Its melting point is a bit lower than SAC, the electronics industry raised a big fuss when RoHS was instituted due to the higher processing temperature for soldering. We fail to understand why they chose the higher temp SAC which is less compatible with the chemistry of immersion silver. The copper adds no benefit.

Reply to
Robert Baer
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I'm guessing that the solubility of copper is lessened; that's important with the early generations of plated-through holes (and maybe still is). Silver has a similar effect, but is rather more expensive.

Reply to
whit3rd

I do not accept that as a "reason" because boards go thru a plating-like process called Immersion Silver; and SAC _has_ almost the same percentage of silver....

Reply to
Robert Baer

Never made it usually means that it wasn't a catalog item. It wouldn't stop them from making a test batch, or as a custom alloy for a barge customer.

Reply to
Michael Terrell

Who uses immersion silver?

I've moved several designs /off/ it, as a matter of fact. ENIG is much more popular, for a variety of reasons.

Tim

--
Seven Transistor Labs, LLC 
Electrical Engineering Consultation and Design 
Website: https://www.seventransistorlabs.com/
Reply to
Tim Williams

But it WAS a catalog item; i ordered it online from Mouser or Digikey.

Reply to
Robert Baer

Then tell me those "reasons". Re ENIG: Would you believe that gold can accelerate corrosion, especially over time?

Reply to
Robert Baer

Then send them a copy of the purchase order.

Reply to
Michael Terrell

That would not get them to make/offer the SN96.3AG3.7 alloy in either wire or paste form.

Reply to
Robert Baer

So, go with Indalloy 241; it's 95.5 Sn, 3.8 Ag, 0.7 Cu or thereabouts. Indalloy 267 is close, too.

But, you might have to accept a bag of shot, or an ingot, instead of flux-core wire.

Reply to
whit3rd

241 is SAC, and not Tin/Silver, 267 is tin/lead. Want tin/silver.

Grainger carries it in crappy form: FAT wire, no flux specified. Some other vendors lie and offer a solder with Antimony or Bismouth or no Silver or... Google search comes up with the worst crap.

Reply to
Robert Baer

It would prove that they did make it, in spite of their claims to the contrary.

Reply to
Michael Terrell

Recheck: Indalloy 267 is Sn 97, Ag 3; there's no lead

There's some copper in 241, but the usual SAC formula is 0.5% Ag, 1% Cu, and 241 is rather closer to the 3.7% silver content.

Reply to
whit3rd

  • Took a little snooping, but YES, that is correct. Unknown flux if any.
Reply to
Robert Baer

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