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Old 25th September 2002, 03:17 PM   #1
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Default Gold or silver plating soldered boards?

Is it possible to (ideally) chemically gold plate boards after they have been soldered? Another cool option would be to Copper or silver plate the same way, but gold is more robust.

From my high school chemistry I seem to recall that gold is fairly low on the electrochemical table and thus chemical gold plating should be possible, at least on the copper. What then about the soldered pad?

Any ideas?

Petter
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Old 25th September 2002, 03:36 PM   #2
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If the board has been soldered, then the plating chemicals will either plate or corrode the leads of the parts you've soldered down. It might make a real mess of switches and connectors, if there are any soldered to the board. I'd worry about plating chemicals trapped under components not getting thoroughly washed out. That isn't going to improve reliability a bit...

Many plating processes involve applying voltages to the surfaces to be plated. This could cause some real trouble for electronic components.

Most PCB houses can apply gold plating to boards they manufacture. It costs a little more, but if you really want it, just specify it when you order your boards.

Most of the time there isn't much point because solder mask will cover the copper and protect it. If you get gold plating, most of it will be covered by solder mask unless you open up the solder mask layer (or delete it) in your layout files. Would having exposed conductors that are shiny gold be better than having insulated, nonshiny conductors?

MR
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Old 25th September 2002, 03:53 PM   #3
tiroth is offline tiroth  United States
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I've been told silver plating is a reasonably inexpensive alternative to hot air solder leveling (HASL). All the prices for gold I've seen were astronomical for small orders.
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Old 25th September 2002, 05:24 PM   #4
dice45 is offline dice45  Germany
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Petter,

the German company Kepets (website under construction, has a link with an email adress) sells a wide variety of PCB manufacturing reagents. Among those is a bath for tin-plating and silver plating. Both bathes work without applying voltage and by chemically depositing only. I have tried them out, both work fine. I would not recommend to use them after components have been soldered; they are meant to plate the PCB before soldering and to enease soldering.

However i would be reluctant to sliver-plate amp PCBs. My experinece with cables shows that pure copper has better sonics than tin- or silver-plated one.
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Bernhard
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Old 25th September 2002, 05:36 PM   #5
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HP (now Agilent) gold plates their boards, fwiw. Silver is a great conductor, but oxidizes very quickly. If you want to protect the board from oxidation, there are any number of coatings some of which are easy to apply and don't require a laminar flow hood.
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Old 25th September 2002, 05:46 PM   #6
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Default I'd Like To Try It Too....

In past discussions with a jeweller friend, I am told that it is not possible to easily electroplate onto Lead (Pb) - solder.
A jewellry making process is to make a lead die, and then electroform a thick deposit of copper, which can then be peeled off - no adhesion.
The other obstacle is any remnants of the electroplating salt soloutions used, as already said.

Eric.
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Old 25th September 2002, 11:50 PM   #7
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Default PLATING

Guys,

As Dice45 pointed, out plating after soldering is not a task you want to get in to.
As far as cunductivity goes:silver is a better conductor then gold and even when oxidized conducts very well.
Gold,on the other is a worse conductor then copper and when oxidized does not condict too well.
If oxidation is your main concern you can tropicalize your circuit whith some special spray-on product.
How all that is going to sound is another story...


Greets,
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Old 26th September 2002, 01:59 AM   #8
haldor is offline haldor  United States
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Default Re: PLATING

Quote:
Originally posted by fdegrove
Gold,on the other is a worse conductor then copper and when oxidized does not condict too well.
I am not a proponent of gold plating PCB's except for card edge finger contacts, but I have never even heard that gold can oxidize. What is your source of information about gold oxidizing?

Phil
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Old 26th September 2002, 02:12 AM   #9
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Default Re: Re: PLATING

Quote:
Originally posted by haldor
I am not a proponent of gold plating PCB's except for card edge finger contacts, but I have never even heard that gold can oxidize. What is your source of information about gold oxidizing?
It doesn't oxidize under normal conditions. You can get it to oxidize under high heat and pressure, but the oxide is unstable and quickly reverts back to metallic gold.

Suffice to say that it won't oxidize under any conditions existing in audio systems.

Now, gold can interdiffuse with other metals. So for example a thin gold plating over a copper substrate can result in the gold interdiffusing with the copper which effectively brings the copper to the surface and the copper can oxidize. That's why much of the gold plating in the electronics industry is done with a nickel barrier between the gold and the copper.

se
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Old 26th September 2002, 02:38 AM   #10
haldor is offline haldor  United States
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Default Re: Re: Re: PLATING

Quote:
Originally posted by Steve Eddy
Now, gold can interdiffuse with other metals. So for example a thin gold plating over a copper substrate can result in the gold interdiffusing with the copper which effectively brings the copper to the surface and the copper can oxidize. That's why much of the gold plating in the electronics industry is done with a nickel barrier between the gold and the copper.se
Hi Steve,

That explains why cheap gold contacts corrode so easily. We used to make a retail (food market) product that used telephone modular jacks for connection to a RS485 mutli-drop network. Those gold plated copper wires in the modular jacks would corrode at the first hint of moisture. Use to have major problems keeping those jacks working in fish departments.

Phil
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