Soldering to gold and silver metallizations

[Chris Carlen]

Hi:

As I understand, Ag and Au may be leached from surfaces when using
standard Sn63Pb37 and Sn60Pb40 type electronic solders.

Why is this to be avoided? Does it result in "intermetallic compounds"
near the interface that compromise mechanical properties?

Is this enough of a concern that typical gold plated component leads and
silver plated hook-up wire in general shouldn't be soldered with
tin-lead, but rather some non-leaching solders such as indium lead
alloys for gold, or SnPbAg alloys for silver platings?

Or is it only relevant to specialized applications that place
substantial mechanical stress or thermal fatigue cycles on soldered joints?

What is the difference between the issues involved in soldering Ag and
Au platings, versus thick or solid Ag or Au surfaces?


Thanks for input.

Good day!





--
_______________________________________________________________________
Christopher R. Carlen
Principal Laser/Optical Technologist
Sandia National Laboratories CA USA
[email protected]
NOTE, delete texts: "RemoveThis" and "BOGUS" from email address to reply.

 

[Chris Carlen]

Hi:

As I understand, Ag and Au may be leached from surfaces when using
standard Sn63Pb37 and Sn60Pb40 type electronic solders.

Why is this to be avoided? Does it result in "intermetallic compounds"
near the interface that compromise mechanical properties?

Is this enough of a concern that typical gold plated component leads and
silver plated hook-up wire in general shouldn't be soldered with
tin-lead, but rather some non-leaching solders such as indium lead
alloys for gold, or SnPbAg alloys for silver platings?

Or is it only relevant to specialized applications that place
substantial mechanical stress or thermal fatigue cycles on soldered joints?

What is the difference between the issues involved in soldering Ag and
Au platings, versus thick or solid Ag or Au surfaces?


Thanks for input.

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
[email protected]
NOTE, delete texts: "RemoveThis" and "BOGUS" from email address to reply.

 

[Ted Edwards]

As I understand, Ag and Au may be leached from surfaces when using
standard Sn63Pb37 and Sn60Pb40 type electronic solders.

Why is this to be avoided? Does it result in "intermetallic compounds"
near the interface that compromise mechanical properties?

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

 

[CF]

As I understand, Ag and Au may be leached from surfaces when using

standard Sn63Pb37 and Sn60Pb40 type electronic solders.

Why is this to be avoided? Does it result in "intermetallic compounds"
near the interface that compromise mechanical properties?

Is this enough of a concern that typical gold plated component leads and
silver plated hook-up wire in general shouldn't be soldered with
tin-lead, but rather some non-leaching solders such as indium lead
alloys for gold, or SnPbAg alloys for silver platings?

Or is it only relevant to specialized applications that place
substantial mechanical stress or thermal fatigue cycles on soldered
joints?

What is the difference between the issues involved in soldering Ag and
Au platings, versus thick or solid Ag or Au surfaces?

Eric: Rates of dissolution affect whether issue or not, and vary with

t>emp. 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.

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

 

[Chris Carlen]

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.

Very clever!


--
_______________________________________________________________________
Christopher R. Carlen
Principal Laser/Optical Technologist
Sandia National Laboratories CA USA
[email protected]
NOTE, delete texts: "RemoveThis" and "BOGUS" from email address to reply.

 

[Jim Yanik]

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

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.)

 

[Pooh Bear]

Hi:

As I understand, Ag and Au may be leached from surfaces when using
standard Sn63Pb37 and Sn60Pb40 type electronic solders.

Why is this to be avoided? Does it result in "intermetallic compounds"
near the interface that compromise mechanical properties?

Is this enough of a concern that typical gold plated component leads and
silver plated hook-up wire in general shouldn't be soldered with
tin-lead, but rather some non-leaching solders such as indium lead
alloys for gold, or SnPbAg alloys for silver platings?

Or is it only relevant to specialized applications that place
substantial mechanical stress or thermal fatigue cycles on soldered joints?

What is the difference between the issues involved in soldering Ag and
Au platings, versus thick or solid Ag or Au surfaces?

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