Gold-PLated PCBs?

"Robert Latest"

No problems in sight as of 2007.

Gold plate is just soooo easy to solder.

....... Phil

It's likely you have only a gold flash on the boards. IIRC, gold will pollute the solder bath but should be no problem to your boards. If it is only a gold flash there shouldn't be any problem.

Gold is generally only used for contacts (and more than a flash).

Must have hitched a ride with a RoHS product. My PCB fab uses ENIG for their RoHS PCBs.

Jim

Gold and copper diffuse into each other, messing up the gold layer. The only way to prevent this is to use very thick gold (too expensive, usually) or to first plate a diffusion barrier layer, usually nickel. So the "gold" plated boards you buy are probably electroless nickel on the copper followed by a tiny layer of immersion gold. What the gold is doing is making the nickel solderable!

There's only microinches of gold on a pcb, 10 maybe, so when it dissolves into the solder, it pretty much vanishes.

We did some gold plated boards when we were experimenting with lead-free assembly. They look beautiful and solder great. But we dumped the lead-free thing.

Gold-copper and gold-aluminum intermetallic compounds (like Purple Plague) are often brittle, but there's too little gold on most gold plated boards and connectors to make trouble.

John

Some of our aerospace customers are explicit in *not* wanting lead-free. And the process temps are a lot higher, with possible reliability issues. And the solder joints look like hell, making them harder to inspect.

We now know that we can do it if we have to, but so far nothing is forcing us to do so. The whole thing is silly; the solder on pcb's is not soluble, is easily identified and kept out of landfills anyhow, and constitutes only a couple of per cent of lead usage.

John

From what little i have seen, the problem appears at/near the solder connection of the wire from the case (negative electrode) of an aluminum capacitor; classic "purple plague". The solder "pool" around the lead lifts off with no gold apparent anywhere on the PCB or the solder, and ther is a lot of whitish "dust" / crystals in the region, and the cap end is discolored. In certain circumstances, it can be worse that tin whiskers. Almost any metal other than tin or lead will dissolve in eutectic tin/lead solder; hence the advent of Savbit (2% copper added if i remember right so the copper bits would not be leached away) as well as the special roll of silver-bearing solder found in all old Tektronix scopes (to protect the silver plating on the ceramic standoffs). Gold looks sexy, but can cause rather expensive problems.

You must not have been in the industry much; i have seen too many corroded connections over the years.

Gold for contacts is OK, as long as it is kept away from solder connections...and most especially solder connections to aluminum capacitor (negative) leads.

Gee, go down to Radio Shack and get some Silver Bearing Solder and use that; it looks spiffier than old tin/lead!

Robert, Silver has a limited lifetime. Is becomes black from fingerprints (sulfur) and it is said to become harder to solder when oxidized.

HAL is said to becoem hader to solder after a certain time too.

Gold aparently is keeping fresh and solderable for an unlimited time.

I never had any issues, also not with any I came across. It might be the warnings come from manufacturers.

I'm fine with silver. Gold costs 10% more. Leadfree is no problem at all. I had to replace my old Weller with a new one though. The old one went through tips at an unbelievable rate.

Rene

Assuming no cost constraints (customer paying thousands of dollars for the design, deliverables are ten small PWBs), no Rohs requirement, and a normal office environment, which would you choose? Gold over nickel over copper? Some sort of exotic alloy for the solder? Or good old copper traces and 63/47 solder?

In my experiences of long ago while working as a cal-lab tech and as a tech in the Navy, I have noticed a significant number of equipment failures related to gold-over-nickel plated terminals, soldering posts, component leads, etc. The reason was that the gold would delaminate from the nickel and create an open circuit, or even worse, an intermittent connection that was a nightmare to find. After recognizing this problem, when I had to replace a component or terminal that was gold-over-nickel, I would always heavily tin the gold area, then wick away all the solder, taking the gold with it, before making the final solder joint. And, if I noticed any joints that looked suspicious, I would always try to leach all the gold away from the joint and resolder. Never had a repeat failure by doing that.

They tell me that that black stuff (whether it's oxide or sulfate or whatever) conducts almost as well as just plain silver.

But a little liquid silver polish will clean that right up. I don't know if "Brasso" is abrasive, but if not, it would probably make the silver look like new.

Cheers! Rich

The only gold plating I've ever seen on a PCB has been edge connectors. Of course, they plug into sockets with gold-plated contacts. They're usually gold over nickel over copper, but the rest of the board is usually tinned and has solder mask.

Cheers! Rich

It was common for old Tek and HP gear, roughly 1970 vintage, to have pcb's with heavy gold plating everywhere, ususlly with no solder mask. Nowadays, you see gold flash over nickel on high-density BGA boards, or on boards that will be used with lead-free solder. We fabbed a few boards like this recently... they looked like jewelry.

John

There's not much, if any, price difference between elect. gold and HAL these days.

Best regards, Spehro Pefhany

For the main PCB, standard copper with tin/lead solder. For contact fingers *only* then gold may be considered (gold over nickel over copper).

Silver plate does not have a "lifetime" problem, it is a corrosion problem (oxides and sulfides). And there are inexpensive solutions: SilverSaver paper against board in a sealed package; el-cheapo is mothballs with board in sealed package.

HAL does pick up oxides, so a simple sealing would suffice; additoin of mothballs would extend safety.

These solutions appear to be viable for a year or so.

find.

try

Thanks for the sharing of your experience!