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Gold-PLated PCBs?

Discussion in 'Electronic Design' started by Robert Latest, Feb 22, 2007.

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  1. 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
     
  2. Phil Allison

    Phil Allison Guest

    "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
     
  3. krw

    krw Guest

    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).
     
  4. James Beck

    James Beck Guest

    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
     
  5. John  Larkin

    John Larkin Guest


    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
     
  6. Eeyore

    Eeyore Guest

    Why was that John ?

    Graham
     
  7. John Larkin

    John Larkin Guest

    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
     
  8. Eeyore

    Eeyore Guest

    I agree with you 100%.

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

    Graham
     
  9. Robert Baer

    Robert Baer Guest

    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.
     
  10. Robert Baer

    Robert Baer Guest

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

    Robert Baer Guest

    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.
     
  12. Robert Baer

    Robert Baer Guest

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

    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?
     
  14. 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
     
  15. DaveM

    DaveM Guest

    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.
     
  16. Rich Grise

    Rich Grise Guest

    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
     
  17. Rich Grise

    Rich Grise Guest

    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
     
  18. John  Larkin

    John Larkin Guest

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


    Best regards,
    Spehro Pefhany
     
  20. Robert Baer

    Robert Baer Guest

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