Hi Julie-

Sorry for the late response.  I have a lot of experience with this or similar material.  Yes, burnishing helps.  I also deliberately use an iron tip that doesn't wet well.  Paste with SMT works too, and is more controllable.  We typically used the SnPbAg alloy with about 2%Ag, but I don't know if that helped.  Our rule of thumb was you got three shots to solder to it, IF you used pre-heat and were very careful.  BUT, this product is cake to solder to compared with AgPd, which most of the thick film commercial products used.  That stuff would only survive a very carefully controlled single reflow.

One thing we learned is that the leach rate SKYROCKETS if the designer put the PtPdAu directly on top of thick film Au where the solder was going to be.  That recipe leaches just as bad as plain gold.  The overlap MUST be behind a solder dam.  (The thick film vendors only tell you this AFTER you figure it out on your own!)  By the way, plain gold solders just fine on ceramic using SnAu eutectic solder.  It is very expensive and is quite hot (270C or so).  The joints are very pretty shiny silver and very strong.  You can also weld copper wires to thick film gold or silver.  MiniCircuits sells piles of RF parts containing tiny transformers attached this way, and this technique is also used on RF inductors which are wound on an alumina mandrel.

We ended up having a low temperature copper put on top of the gold whenever we could.  It is much more robust--still wets horribly though!

Wayne Thayer

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steven Creswick
Sent: Wednesday, November 28, 2012 8:59 AM
To: [log in to unmask]
Subject: Re: [TN] Termination finishes, Cu thickness under Ag, Au-Pt-Pd

Julie,

Yes, the addition of a small amount of Pt does slow up the rate of the conductors leaching into the solder.  From practical experience, the more Pt is added, the better the leach resistance.  However, the more Pt is added, the greater are wetting problems.

Thick film ink suppliers [used to] offer inks with different amounts of Pt so you could slightly 'chose your poison.'

Also can depend on whether it is a fritted, or a frit-less, system.

Like Mike says - BURNISH before solder IS the general rule!

Never was something you really 'wanted' to solder to, unless you had no other choice.


Steve Creswick
Sr Associate - Balanced Enterprise Solutions http://www.linkedin.com/in/stevencreswick
                         616 834 1883



-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Julie Silk
Sent: Tuesday, November 27, 2012 8:02 PM
To: [log in to unmask]
Subject: Re: [TN] Termination finishes, Cu thickness under Ag, Au-Pt-Pd

The claim of the supplier is that the Pt prevents the Au from dissolving into the solder.  Hmmm.  Can anyone back that up?
The recent info on this is that it's looking like a wettability problem more than a dissolving-into-the-joint problem, although neither is confirmed.

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