Gold-PLated PCBs?

[Robert Latest]

When I'm doing small runs or singles of PCBs I use a manufacturer who pools
many small batches into one large one to save costs. Consequently, some
minor aspects (like the color of the solder mask and silk screen) cannot be
specified because you'll get whatever the main batch gets you're hitching
your ride on.

Another unspecified aspect is the finish: They'll either do tin-plated or
gold-plated. Usually it's tin-plated, but today I got a gold-plated board.

Wowwwy. Talk about spiffy.

But aren't there issues with the gold dissolving in solder or some such
thing? I seem to recall that tin and gold form some unfavourable alloy.
Personally I don't care because I dont have millions of units in the field
to watch out for, but if these issues are extant, why gold-plate a PCB in
the first place?

robert

 

[Phil Allison]

"Robert Latest"

When I'm doing small runs or singles of PCBs I use a manufacturer who
pools
many small batches into one large one to save costs. Consequently, some
minor aspects (like the color of the solder mask and silk screen) cannot
be
specified because you'll get whatever the main batch gets you're hitching
your ride on.

Another unspecified aspect is the finish: They'll either do tin-plated or
gold-plated. Usually it's tin-plated, but today I got a gold-plated board.

Wowwwy. Talk about spiffy.

But aren't there issues with the gold dissolving in solder or some such
thing? I seem to recall that tin and gold form some unfavourable alloy.
Personally I don't care because I dont have millions of units in the field
to watch out for, but if these issues are extant, why gold-plate a PCB in
the first place?

** Gold plated connectors that require normal, 60/40 SnPb, solder to use
have been around for many DECADES.

No problems in sight as of 2007.

Gold plate is just soooo easy to solder.




........ Phil

 

[krw]

When I'm doing small runs or singles of PCBs I use a manufacturer who pools
many small batches into one large one to save costs. Consequently, some
minor aspects (like the color of the solder mask and silk screen) cannot be
specified because you'll get whatever the main batch gets you're hitching
your ride on.

Another unspecified aspect is the finish: They'll either do tin-plated or
gold-plated. Usually it's tin-plated, but today I got a gold-plated board.

Wowwwy. Talk about spiffy.

But aren't there issues with the gold dissolving in solder or some such
thing? I seem to recall that tin and gold form some unfavourable alloy.
Personally I don't care because I dont have millions of units in the field
to watch out for, but if these issues are extant, why gold-plate a PCB in
the first place?

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).

 

[James Beck]

"Robert Latest"


** Gold plated connectors that require normal, 60/40 SnPb, solder to use
have been around for many DECADES.

No problems in sight as of 2007.

Gold plate is just soooo easy to solder.




....... Phil

Must have hitched a ride with a RoHS product.
My PCB fab uses ENIG for their RoHS PCBs.
http://www.trianglecircuits.com/ENIG.html

Jim

 

[John Larkin]

When I'm doing small runs or singles of PCBs I use a manufacturer who pools
many small batches into one large one to save costs. Consequently, some
minor aspects (like the color of the solder mask and silk screen) cannot be
specified because you'll get whatever the main batch gets you're hitching
your ride on.

Another unspecified aspect is the finish: They'll either do tin-plated or
gold-plated. Usually it's tin-plated, but today I got a gold-plated board.

Wowwwy. Talk about spiffy.

But aren't there issues with the gold dissolving in solder or some such
thing? I seem to recall that tin and gold form some unfavourable alloy.
Personally I don't care because I dont have millions of units in the field
to watch out for, but if these issues are extant, why gold-plate a PCB in
the first place?

robert

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

 

[Eeyore]

But we dumped the lead-free thing.

Why was that John ?

Graham

 

[John Larkin]

Why was that John ?

Graham

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

 

[Eeyore]

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.

I agree with you 100%.

I was just intertested to see what your decision was based on.

Graham

 

[Robert Baer]

When I'm doing small runs or singles of PCBs I use a manufacturer who pools
many small batches into one large one to save costs. Consequently, some
minor aspects (like the color of the solder mask and silk screen) cannot be
specified because you'll get whatever the main batch gets you're hitching
your ride on.

Another unspecified aspect is the finish: They'll either do tin-plated or
gold-plated. Usually it's tin-plated, but today I got a gold-plated board.

Wowwwy. Talk about spiffy.

But aren't there issues with the gold dissolving in solder or some such
thing? I seem to recall that tin and gold form some unfavourable alloy.
Personally I don't care because I dont have millions of units in the field
to watch out for, but if these issues are extant, why gold-plate a PCB in
the first place?

robert

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.

 

[Robert Baer]

"Robert Latest"




** Gold plated connectors that require normal, 60/40 SnPb, solder to use
have been around for many DECADES.

No problems in sight as of 2007.

Gold plate is just soooo easy to solder.




....... Phil

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

 

[Robert Baer]

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).

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.

 

[Robert Baer]

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

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

 

[[email protected]]

Gold looks sexy, but can cause rather expensive problems.

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?

 

[Rene Tschaggelar]

When I'm doing small runs or singles of PCBs I use a manufacturer who pools
many small batches into one large one to save costs. Consequently, some
minor aspects (like the color of the solder mask and silk screen) cannot be
specified because you'll get whatever the main batch gets you're hitching
your ride on.

Another unspecified aspect is the finish: They'll either do tin-plated or
gold-plated. Usually it's tin-plated, but today I got a gold-plated board.

Wowwwy. Talk about spiffy.

But aren't there issues with the gold dissolving in solder or some such
thing? I seem to recall that tin and gold form some unfavourable alloy.
Personally I don't care because I dont have millions of units in the field
to watch out for, but if these issues are extant, why gold-plate a PCB in
the first place?

robert

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

 

[DaveM]

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.


--
Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate characters in the
address)

Some days you're the dog, some days the hydrant.

 

[Rich Grise]

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

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

 

[Rich Grise]

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?

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

 

[John Larkin]

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.

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

 

[Spehro Pefhany]

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

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


Best regards,
Spehro Pefhany

 

[Robert Baer]

Robert Baer wrote:




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?

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