Any experience soldering platinum to stainless steel? [SOLVED]

Thread Starter

blah2222

Joined May 3, 2010
582
Hello,

Currently, I am using a cold-bonding conductive epoxy to bond stainless steel stranded wire to 1mm x 2 mm platinum contacts.
This approach works, but the epoxy doesn't hold up as well as I would have hoped.

Wondering if I could just solder the two together for a more durable connection.

From what I have read, the stainless would require a very clean surface (via flux with a strong acid) but it can be tinned with a soldering iron and regular 60/40 solder.

As for the platinum, it seems that I might need a much higher temperature (via torch) to get rid of surface oxides prior to tinning, but it is still do-able.


Any suggestions?
Thanks!
 

GopherT

Joined Nov 23, 2012
8,012
Hello,

Currently, I am using a cold-bonding conductive epoxy to bond stainless steel stranded wire to 1mm x 2 mm platinum contacts.
This approach works, but the epoxy doesn't hold up as well as I would have hoped.

Wondering if I could just solder the two together for a more durable connection.

From what I have read, the stainless would require a very clean surface (via flux with a strong acid) but it can be tinned with a soldering iron and regular 60/40 solder.

As for the platinum, it seems that I might need a much higher temperature (via torch) to get rid of surface oxides prior to tinning, but it is still do-able.


Any suggestions?
Thanks!

Call Indium Corporation. They likely have an indium/gallium/tin/lead/antimony alloy of some sort that will work for you. They are amazing.
 

kubeek

Joined Sep 20, 2005
5,770
As for the platinum, it seems that I might need a much higher temperature (via torch) to get rid of surface oxides prior to tinning, but it is still do-able.
I don´t think that platinum should have any oxides on its surface (unless you really tried hard to make it oxidize - 400°C in acidic atmosphere and high oxygen pressure).
 

recklessrog

Joined May 23, 2013
985
I remember a similar problem when I was working on transducers for analogue engine control computers for a fighter jet engine back in the 60's.
The only long term solution that was used then was wire crimping because the effects of adding any sort of soldering, brazing, caused unpredictable performance overtime due to the hot environment they were exposed to.
Having said that, I repaired an automotive exhaust gas analyser that used a thin platinum wire which appeared to have been spot welded to the contacts, maybe that may be the answer to your problem.
 

Kermit2

Joined Feb 5, 2010
4,162
Interface corrosion. It starts at the edges of the braze and proceeds into the interfaced alloy just a few microns beneath the brazed area until the brazed joint lifts free like an old scab coming off a healed wound.

All brazed stainless steel is susceptible to it, except the high nickel content austenitic stainless steels.

A pladium silver copper brazing alloy (54Ag-25Pd-21Cu) called pallabraze 950 works well and will not corrode. Gold bearing brazing alloys are also good.
 

Thread Starter

blah2222

Joined May 3, 2010
582
Thank you all very much.

From the replies, it seems as though high temperature brazing is what will be required for this, with the use of a less common solder.
My Hakko FX-888D goes up to 480C (896F), do you think that will be suitable or is a torch a better idea?

When I have some time, I plan to test this out with my current setup before buying new materials.
 

Thread Starter

blah2222

Joined May 3, 2010
582
Thanks joeyd999, but the two things I am soldering are fairly small and delicate (thin SS stranded wire and small platinum contact).
 

Thread Starter

blah2222

Joined May 3, 2010
582
Hi all,

I was able to find a product that worked for my purpose.

Superior #71 Stainless Steel Flux worked great and can be purchased from SRA Soldering Products:
http://www.sra-solder.com/flux-71-flux-high-activity-for-stainless-steel-4-oz

Superior RubyFluid Stainless Steel Flux also seemed to work:
http://www.sra-solder.com/rubyfluid-stainless-steel

I transferred each flux solution into their own flux bottle applicators with needle tip. It only required a few drops on the stranded wire to take effect. I was then able to tin the bare wire with either leaded or lead-free solder with no issue and a bit of a nice hissing sound. As per the product recommendations, I agitated the freshly tinned stainless steel wires in hot tap water for 3-5 minutes to remove any residues. Soldering to other metals was then a breeze. I would recommend using gloves with this flux.

I preferred the #71 as it was a more aggressive flux and I had better results when tinning.

Hope this helps someone down the line.
 
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