Are you basing your alloy choice on a supplier's list of possible alloys, or has it been
specified to you  by someone perhaps making this decision using such a list? I feel you
may have difficulty sourcing 90Sn/10Au.

Can I respectfully ask:
Why this alloy?
Have you found a supplier? Well done if you have one and very well done if you have more
than one.
Suggest you check those that offer it. Specifically: what presentations are offered by
them as repeatable standard items previously made from a documented process....

With regard to your questions, a general/theoretical answer would be along the lines:

Subject to actual tests on your proposed assembly, the use of high gold containing
solder/brazing alloys is perfectly feasible and well suited to joining to gold substrates.
Under these circumstances Au embrittlement of more conventional Sn/Pb based alloys is not
a factor as this is not what is being considered.

So far as piggy back soldering is concerned an alloy of melting point 217 is not very
different from 221C which is the MP of Sn/3.5 Ag. This latter alloy is commonly used  in
assembling components which are themselves subsequently soldered using Sn63, so subject to
.. (you can write in your own standard qualification of this statement...)

So far as cost is concerned an alloy consisting of 10% Au will be expensive compared to
other more conventional alloys. Typically gold costs around $300 per troy ounce. This
makes metal costs a total of around $1000 per kilogram (say $500/pound) alone. To this
your supplier would have to add alloying costs, processing charges, fabrication
costs/losses, overheads such as financing, quality control, packaging, shipping, etc to
arrive at an actual purchase price.

Happy hunting and good luck.

Mike Fenner
Bonding Services & Products
T: +44 1295 722992
F: +44 1295 720937

----- Original Message -----
From: Gabriela Bogdan <[log in to unmask]>
To: <[log in to unmask]>
Sent: 17 October 1999 21:00
Subject: [TN] TIN/GOLD alloy


> Dear TechNetters!
> Please could you comment on the use of Tin/Gold 90/10 solder ?
> The application is for microwave applications when soldering to gold.
> Its melting temp. is 217C .
> I have the following questions:
> How does this composition correlate with the maximum gold content in a
> solder joint?
> Would it be possible to pass such a subassembly through a secondary
> reflow with 63/37 Tin/Lead?
> Is it recommended ONLY for soldering to gold?
> It must be very expensive too??!!
> Paul, Werner, my apologies.
> Thank you
> Gaby

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