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  1. #1
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    Soldering Gold Plated PWBs

    Have any of you actually done any soldering on gold plated PWBs?

    I noticed that the Nocticon PWBs that they were selling at Mountain Electronics had gold platted pads. I cringed when I saw that knowing the difficulty you have making a reliable solder joint on a gold plated part. This seems a bit insane, as the average hobbyist is usually not an expert when it comes to soldering.

    Gold plating requires a nickel underplating to prevent the copper from migrating into the gold. When you solder, most of the gold leeches into the solder joint. You are basically soldering to nickel plating, which can be tricky.

    Soldering to bare copper is simple. Clean and deoxidize the copper pads on the PWB before soldering and then solder using a mild flux.

    With tin plated PWB pads it is the same. Clean and deoxidize the tin and then solder.

    Here are a few references on the subject.

    Soldering to Gold:
    Soldering to Gold | Indium Corporation® | Indium Corporation Blogs | Flux | Gold Solder | Indium | Indium Alloy | Indium Corporation | ITO | Lead Free Solder | No Clean Flux | No Clean Solder | Pb-Free | Pb-Free Solder | SMT Solder | Solder | Solder

    Soldering to Gold Over Nickel Surfaces
    https://www.kester.com/Portals/0/Doc...ver_Nickel.pdf

    The Need For Gold Removal On Solderable Surfaces:
    https://www.eptac.com/wp-content/upl...c_10_17_12.pdf

    J-STD-001 Revision Changes Regarding The Requirements for Gold Plating Removal:
    https://www.eptac.com/j-std-001-revi...ating-removal/

    Manufacturing concerns when soldering with gold plated component leads or circuit board pads:
    Manufacturing concerns when soldering with gold plated component leads or circuit board pads - IEEE Journals & Magazine

    Soft Soldering Gold Coated Surfaces:
    https://link.springer.com/content/pd...BF03215142.pdf


    Scott Novak

  2. #2
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    When I was working, one new project we had involved soldering a lead to a gold plated beryllium copper grounding clip. I argued the soldering to gold issue with the customer's engineer without success. It was not until they started having some field failures with solder joints failing that they issued an ECO to not plate the area to that the lead was soldered to. These parts were not nickel plated prior to gold plating. IME, nickel under gold is not universal.

    Embrittlement of solder joints on gold plated components is real but in most cases only when the plating thickness is over a few microns in thickness or the ratio of gold to solder exceeds some percentage.

    The gold on the Noctigon MCPCB is very thin. I do not have a spec, but visually it appears to be just flash plated over copper. The ratio of solder to the amount of gold that dissolves into the solder in the typical large power lead joint on a high current LED should keep the joint well below the ratio where gold embrittlement occurs. I've soldered several with no problems.
    GoPro adapters for bike lights http://www.pacifier.com/~kevinb/index.html

  3. #3
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    Whenever I solder gold plated material I use a lot of solder so that it dissolves all of the gold, remove the solder and then solder it again with fresh solder.

    At one company we were having problems with a switch with gold plated leads that was tack soldered to a PWB. What actually stopped the joint failures was using SN 62, a tin, lead, sliver solder. It's not actually supposed to help, but it did. It's possible that it just had a more active flux.

    I'm a bit leery about who might be soldering LEDS to those Noticgon PWBs. I know what kind of problems can happen within an ISO-9000 certified company. I'd hate to think about what happens with a small non-certified manufacturer.

    Scott Novak

  4. #4
    RAKC Industries
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    No expert, but I use noctigons for EVERYTHING I can put custom MCPCBs in. My flashlights are the main one. And they have been abused for years not a single problem with them.

    I know there are 100s is not 1000s of others that have done the same with 0 issues I am aware of.

    Not saying there isnt issues regarding gold plating but noctigon got it right.

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  5. #5
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    There isn't any question that a PWB with clean unoxidized copper pads will produce the most reliable solder joint.

    Any appreciable amount of gold can cause premature solder joint failures with SN63 (63% Tin - 37% Lead eutectic alloy). While a solder joint may look good initially, in time the intermetallic region can grow large enough for the solder joint to become physically weak.

    The lead free SAC alloy(Tin Silver Copper alloy) apparently tolerates the gold a bit better than Tin Lead alloys.

    From what I've been reading about gold plating, there are about three different methods of gold plating. Two with a nickel underlayment and one flash gold directly over copper (DIG Direct Immersion Gold).

    But apparently the flash gold over copper has a gold layer thin enough that it doesn't impact the reliability too much. PROVIDED that the PWB is soldered within FOUR MONTHS! Otherwise too much of the copper will migrate through the gold layer and oxidize. Oxides adversely affect solder joint reliability. A hobbyist has to seriously question the age of a gold plated PWB. It could easily have been sitting on the supplier's shelf for over a year.

    To be on the safe side, if a PWB has any gold on the pads, I'd still recommend soldering the pad, removing the solder from the pad, and only then soldering the wire lead to the pad. Especially so if this a tack solder joint, rather than a through hole solder joint. Not only are you removing the gold, but you are also removing copper oxide from the pad.

    NASA has had a requirement that gold must be removed by tinning or other similar method before the final soldering.

    What is driving a lot of the alternative PWB pad finishes is very fine pitch SMDs which is NOT a concern with large LED PWB pads. The other factor is the near hysteria about lead alloyed solder joints.

    Of all the potential sources of lead contamination, electronic solder would be at the bottom of the list. Lead free electronic solders have not shown ANY environmental improvement over lead based electronic solders.

    Also note, that the E.U. has an exemption that allows high reliability electronics to use tin lead solder, which is more reliable than most, or perhaps all, of the lead free alternatives for PWBs.

    Scott Novak

  6. #6
    RAKC Industries
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    As I said I know LITTLE about those specific details. Nice to have another person around here that is knowledgeable in those fine, yet can be critical details.

    I never bothered to check or care about the solder pads beyond cheap stuff sucks (looses bond from board way too easily) and ones like noctigons (DTP) are good for squeaking out every lumen possible especially when maxing out or over driving an LED.

    There are also sink pads which seem to be straight copper but similar design.

    We are getting a rather well rounded group around here now. Vanc on machining, your an Electrical engineer of sorts I gather, outbound is an optical engineer. Then the rest of us that dont have titles but live and breathe everything LED lighting.

    Sent from my SM-G950U using Tapatalk
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  7. #7
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    I'm not a degreed engineer, but I have learned enough over the years to do some basic design work. I've spent most of my career debugging new electronic designs.

    At my first job out of electronic school in the early 80's, double side circuit boards with plated through holes were the latest and greatest. But we were having problems with shorts between circuit paths caused by inadequate etching. We had to measure each and every PWB to make sure that there were no shorts.

    You would think after all of these years, considering everything that the industry has learned about process control and designing for reliability, that we wouldn't have to worry about circuit foils delaminating from the PWBs. But there always seems to be somebody willing cut corners to make more money.

    I tend to be a compulsive perfectionist. My first choice would also be a copper DTP MCPCB. But I'd be inclined to use it for improved reliability. The slightly higher light output would just be a side benefit. But if the light case was designed well with an adequate amount of aluminum directly behind the LED, an aluminum DTP MCPCB would likely work well enough.

    Scott Novak

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