Join Cu to Au/Pt... - Page 1
Forum section: electronics / projects

author: wiss
author_rank: Frequent Contributor
timestamp: August 31, 2015, 11:58:32 am
content: For a project I will need to join small pieces (1 mm diameter, 5 mm long) of gold and platinum pins to a wire (Copper would be handy).What method would be best?Any kind of soft solder (Sn-free)?Welding?Conductive glue?

author: helius
author_rank: Super Contributor
timestamp: August 31, 2015, 12:12:16 pm
content: search for "gold embrittlement", it's a definite problem when soldering to gold parts. Most device leads that use gold only have a very thin layer, a few microns at most, and less for "flash" gold which is the thinnest visible layer. Normally there is not enough gold in this layer to cause severe embrittlement. But when more gold is present then soldered joints will be very brittle. I don't know about platinum but expect it acts similarly to gold.I do not have direct experience in this area, but it seems like the preferred solders for use with gold are indium-lead alloys such as In70Pb30.

author: wiss
author_rank: Frequent Contributor
timestamp: August 31, 2015, 12:24:19 pm
content: The pins are not coated but pure solid Au or Pt, any Sn-solder is out of the picture.

author: Stray Electron
author_rank: Super Contributor
timestamp: August 31, 2015, 02:02:12 pm
content: Tektronix used to recommend silver loaded solder to avoid embrittlement when soldering to gold. In fact, back in the 1960s they used to give a small amount of silver loaded solder away with their scopes so that user's WOULD use it. IIRC it contained about 2 or 4% silver andIIRCthe remainder was 67/33 lead-tin alloy.You should go look on Kester's (or other solder manufacturer's) website and see what they recommend. If you can't find it (which would surprise me!) then contact them and ask.FWIW I bought up a bunch of Kester 2% silver solder years ago and I use it on everything. I LOVE that stuff!

author: LaserSteve
author_rank: Super Contributor
timestamp: August 31, 2015, 03:16:55 pm
content: Talk to Indium Corp, they are more likely to have something then Kester.In 60/40 Tin/Lead solder, fine gold fires dissolve amazingly fast, faster then you can see without a high speed camera. Twenty years ago, I had 40 modules with broken bond wires to repair, I ended up with ~25 working. The customer was thrilled even with that 50% rate of recovery, because this is a difficult task without the exact correct alloy.I ended up with a home made tin/silver alloy that was less then optimal and turned grey when it cooled.If I had to do it again, I'd certainly buy the correct materials.1 mm wire has better far stability then the bonding wire, but I would still find the correct alloy.Steve

author: wiss
author_rank: Frequent Contributor
timestamp: August 31, 2015, 04:02:04 pm
content: So silver saturates tin? That was useful information!Sn95.5/Ag3.8/Cu0.7 is available from my regular supplier, this would do?

author: robrenz
author_rank: Super Contributor
timestamp: August 31, 2015, 05:03:57 pm
content: Radio Shack sold 62/36/2 silver bearing rosin core solder.Edit: I guess that wont do you any good in Sweden

author: tautech
author_rank: Super Contributor
timestamp: August 31, 2015, 05:18:42 pm
content: RS has plenty of solders with various silver contents:http://nz.rs-online.com/web/c/tools/soldering-desoldering-tools/solders/?searchTerm=solder

author: wiss
author_rank: Frequent Contributor
timestamp: August 31, 2015, 05:59:41 pm
content: Quote from: robrenz on August 31, 2015, 05:03:57 pmUnder state purchase requirements as well in this caseAbsence of lead would be a plus, and since our contracted supplier carry the Sn/Ag/Cu-solder I will try that!

author: LukeW
author_rank: Frequent Contributor
timestamp: August 31, 2015, 07:33:35 pm
content: This sounds like a job for the Big Wikipedia Table of Exotic Solders.https://en.wikipedia.org/wiki/SolderAu80/Sn20 is recommended for gold, as is In100 (pure indium).They're also the only alloys of choice if you must have Pb-free.In70/Pb30 and In75/Pb25 sound OK for gold.In80/Pb15/Ag5 is also gold-compatible.

author: LaserSteve
author_rank: Super Contributor
timestamp: August 31, 2015, 07:55:12 pm
content: Under state purchase requirements as well in this caseIf it makes you feel better, so am I... Dreaded rules that industry no longer follows..Steve

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: September 01, 2015, 02:30:19 am
content: Quote from: Stray Electron on August 31, 2015, 02:02:12 pmNo, Tektronix specified it to solder to the silver-plated ceramic strips they used back then. If you used too much regular solder, the strip would lose its plating and you'd have to replace it.http://www.vintagetek.org/ceramic-strip-soldering-techniques-1964/http://www.reprise.com/ash/clients2/parts_shop/ceramic_strips.htmlThe only gold back then was on the leads of the tunnel diodes, and on the early PCBs. SnPb was good enough for that.

author: wiss
author_rank: Frequent Contributor
timestamp: September 01, 2015, 08:43:16 am
content: Found this:http://buy.solder.com/Indium-Wire-99-99-Indium-3-ft/P159_61/.The sizes:"2.815 kgs/Anode" @ 95$, is this a block of 2815 grams?"3 ft spool" @ 95$, 3 feet of 0.03" wire for the same cost as 2815 grams? What are those units???

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 01, 2015, 03:04:31 pm
content: http://buy.solder.com/99-99-Indium-Anode/P98_57/this sounds more like it...No idea what they mean by that. If it's $95 worth of anode, it ain't much, that's for sure.Tim

author: wiss
author_rank: Frequent Contributor
timestamp: September 01, 2015, 03:07:40 pm
content: Yea, that prise makes more sense!