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Best way to solder gold-plated components?

bst

Member
2005-10-01 5:43 pm
I'm running across more and more components (e.g. tube sockets, coupling-cap leads) which have gold flashing or plating. A quick web search opened my eyes to the problems associated with gold-contaminated solder joints. I'm trying to find the best way to remove this layer so that I can assemble circuits which won't deteriorate after just a few months.

Some technical papers recommend repeatedly tinning and wick-wiping the surfaces, others recommend multiple passes through a solder pot to prepare the components for final assembly. I have been mechanically removing the gold flashing with a Scotchbrite pad or wire-brushing with a Dremel tool, but this is tedious at best.

Anyone know of a quick chemical means of stripping gold without damaging the substrate? I'm increasingly frustrated with the time wasted removing gold flashing, which seems to serve no purpose other than marketing hype.
 

poynton

Member
2005-03-10 11:57 pm
UK
Don't forget that all good joints should be mechanical first, solder second!
This is especially true where heat is involved eg tube sockets.

Personnally, I have never had any problem soldering to gold-plated contacts or components. As AndrewT says, they are easy to solder to.


Andy


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gold removal

There are methods to chemically strip gold from base metalls, but they use pretty toxic and caustic ingredients... not recommended for the non-chemist

If I metioned reverse current in concentrated sulfuric acid is the least hazardous method, that'd give you an idea of the problem amateurs using these techniques would have...:eek:

John L.
 
Hi bst,
Please could you cite your sources.

There are many pcb's out there that I have built using components that had gold plated pins. Should I worry?.

I've always believed that solder joints between gold plated components were just as good as solder joints between tinned copper components

The only tip I can give is that if your that worried then use a flux pen.

Brgds Bill
 
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The only real issue I am aware of is a mechanical one. The solder bonds to the gold plating, however if the gold plating delaminates from the core material you will loose that connection. I don't generally worry about tube sockets, though. They are made in China and probably have no more than a few atoms worth of gold on them. I doubt it survives soldering, but that's just a guess.
 

bst

Member
2005-10-01 5:43 pm
This inquiry started when I overheard a conversation between two test engineers grumbling about how long it had taken them to isolate the fault in a complicated lab measurement set-up. I later saw a reference to the necessity of gold removal in one of John Broskie's blogs.

Here's a reference to a paper where SMDs were literally falling off PCBs due to gold embrittlement:

http://www.semlab.com/goldembrittlementofsolderjoints.pdf

And a reference to the removal of gold by tinning and wicking:

Circuit Design - Gold Embrittlement in solder joints

It may be that I'm looking for a problem where none actually exists; most likely, the flashing is so thin on most audio components that the solder joint alloy wouldn't reach the concentration required to cause trouble. I'm just trying to prevent signal degradation and eventual failures down the road.
 
I generally tend to avoid the gold plated parts whenever I can. On the few occasions where I get stuck with a gold plated RCA jack or a gold plated tube socket, I use the Dremel tool on low speed with a sanding drum. It takes off the gold plate quickly. Sure, it's a bit of a nuisance, but I imagine it would be a lot more trouble if I had to strip the amp down to the sockets for a rebuild.
 

poynton

Member
2005-03-10 11:57 pm
UK
Tin-lead solder normally used in electronics is not compatible with gold plating. Gold readily alloys with tin-lead, but when the gold concentration exceeds a few percent
the alloy becomes weak during thermal cycling. This phenomenon is called gold embrittlement. As long as the gold plating thickness is small (20-30 µin) this is not considered a problem. For thickness above 100 µin, indium based alloys rather than tin-lead solder are recommended
to ensure the integrity of solder joints.

It would seem the problem is more for surface mount components or wave soldered stuff rather than through-hole or point-point.

As I said above, a mechanical joint is better.


Andy


.
 
Hi bst,

Many thanks for posting your sources.

The pdf was an interesting read and will take some time to digest. It's hard to disagree with the existence of gold embrittlement. It's even harder to assess it's relevance for the DIYer who solders by hand with all the other problems that entails.

Poynton - when you say "a mechanical joint is better" do you mean "crimping"

Brgds Bill
 
He means to make sure the connection is mechanically held together before soldering. Looping leads through socket eyelets and squeezing them down. Making hooks out of wire and looping them togther when making butt-joints, etc. You don't want the solder to provide the mechanical strength of a joint. That will cause sheering that could contribute to gold delaminating from contact surfaces. Even without the gold, a solder joint won't provide the mechanical strength over time.
 
That's the way it looks to me, but since I've recently become aware of this problem, I use 600 or 1000 grit sandpaper to remove most of the gold from resistor leads, socket tags, wherever it occurs. Only takes a swipe or three to do it, and this surely will dilute the gold content in the joint to safe levels. You might even be able to carefully do this to PCB pads, though I don't care, as I eschews PCBs.

Aloha,

Poinz
AudioTropic
 
There are methods to chemically strip gold from base metalls, but they use pretty toxic and caustic ingredients... not recommended for the non-chemist

If I metioned reverse current in concentrated sulfuric acid is the least hazardous method, that'd give you an idea of the problem amateurs using these techniques would have...:eek:

John L.


John is correct. The "classic" way to dissolve Gold is by using aqua regia. Aqua regia is a mixture of concentrated nitric and hydrochloric acids. That mix attacks Gold, Silver, Copper, steel, Platinum ... It's obviously unsuited for the job at hand, for several reasons.

Another mixture that attacks Gold is cyanide and hydrogen peroxide. Aside from EXTREME toxicity, the mix attacks Silver and Copper too. It could be good on Gold plated steel, but do you want to run the risk of a hideous death? Can you safely dispose of the HAZARDOUS waste?

John, acid Gold plating solutions are citrate based. Would it be in the realm of possibility for anodic electrolysis in a solution of Sodium citrate and citric acid to work in removing unwanted Gold flashing?
 

poynton

Member
2005-03-10 11:57 pm
UK
.....

Poynton - when you say "a mechanical joint is better" do you mean "crimping"

Brgds Bill

He means to make sure the connection is mechanically held together before soldering. Looping leads through socket eyelets and squeezing them down. Making hooks out of wire and looping them togther when making butt-joints, etc. You don't want the solder to provide the mechanical strength of a joint. That will cause sheering that could contribute to gold delaminating from contact surfaces. Even without the gold, a solder joint won't provide the mechanical strength over time.

Many thanks for that rknize - that's the lessons I find when I strip down old gear.


Brgds Bill

Hi.
Sorry for the delay. I'm on a survey ship off the Philippines doing shifts so on a different time zone!

That's exactly my point. When I was taught to solder, it was hammered into me to make the joint mechanically strong. Don't rely on the solder as a glue.
Stripping 1940's radio gear is fun !! Every joint is mechanical then soldered.

Half the problems with today's gear could be down to joint failure either cold joints or something like this gold embrittlement/delamination.

Look at the fiasco over the Sony PS3 and the yellow light syndrome - joint failure.

Surface mount may be good for mass production but I've never liked it.

maybe I'm just old-school.


Andy


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