Soldering to gold and silver metallizations

I got some info from Indium Corp about this:

Eric: Rates of dissolution affect whether issue or not, and vary with temp. At 200C, electronics SnPb alloys will dissolve 35u-in/s/unit area of gold. For Ag, about 21u-in/s. Au reacts with Sn to form a brittle intermetallic. Flash Au plate isn't thick enough to make enough SnAu intermetallic to be a problem.

But for Ag platings, the Ag3Sn intermetallic is actually stronger but also less ductile. So it depends. Since the SnPbAg solders contain silver, duh, they simply reduce the rate of leaching of Ag from the plated surface.

It would seem that the AuSn intermetallic is generally to be avoided, and InPb alloys should be used on gold.

_______________________________________________________________________ Christopher R. Carlen Principal Laser/Optical Technologist Sandia National Laboratories CA USA snipped-for-privacy@BOGUSsandia.gov NOTE, delete texts: "RemoveThis" and "BOGUS" from email address to reply.

Very clever!

t>emp. At 200C, electronics SnPb alloys will dissolve 35u-in/s/unit area

Yes, gold embrittlement IS a problem.

We just "wick" the gold off by tinning and solder-wicking the lead and then solder it. This removes the gold.

Carey

Back when Tektronix scopes were built with components soldered into ceramic tie strips with silver plated U's for the leads, a small roll of silver bearing Sn-Pb solder was mounted inside the scope for use in replacing any failed components. Apparently the molten Sn-Pb solder would disolve the Ag but a relatively small Ag addition would prevent this. Sorry, I don't recall the % added.

Ted

Ted Edwards wrote in news:vnDte.84421$tt5.17111@edtnps90:

In addition,465 and later TEK scopes used gold-plated attenuator PCBs that were soldered with ordinary electronic solders. (not the 3% Ag stuff,either.That was only used for the ceramic strip scopes.)

This is totally unrelated to your question ( other than being about using silver plating ).

After the TWA 800 crash, the fuel tank systems of Boeing 747s were closely investigated. Early models used silver plated wire for the fuel quantity indication system with silver plated crimp lugs mounted to silver plated terminal blocks in the fuel tanks.

It was discovered by examining a few old 747s that had experienced fqis problems that sulphur in the fuel combined with the silver plating to form semi-conducting silver sulphide that then washed over the terminal block coating it with a thin layer.

One example when tested with a 9V battery actually 'flashed' between terminals. I assume the active sensing voltage and energy is lower than this though.

Nickel plated wire is used now.

Graham