Soldering to Gold Fingers - Page 1
Forum section: electronics / beginners

author: ahjustflipit
author_rank: Newbie
timestamp: February 14, 2017, 10:09:50 pm
content: Hi,I need to solder wires to 15 closely placed small gold plates with not much surface area as seen here:I was hoping for some thorough advice as I've already seemingly made some bad soldering joints. The most difficult part is the fact that the plates are so small and seem to melt when in contact with heat.I'm currently using 30 AWG silver plated wire with 60/40 solder.Advice on technique would be particularly useful.

author: RobertHolcombe
author_rank: Frequent Contributor
timestamp: February 14, 2017, 10:20:55 pm
content: If you're intending to still use it as an interface apply kapton tape to the row of gold fingers to avoid solder wicking over the fingers, if using 30 AWG you can make very small joints and then use adhesive to create strain relief by sticking the wire to the board.Use liquid/gel flux, tin the exposed area of finger, hold the wire over the joint and tap your iron on it, if you're still "melting" or lifting fingers then use a lower temperature setting or consider that your dwell time when tinning or creating the joint may be too longEDIT: Jeri's video sprung to mind after I posted this - not completely related but useful techniques none the less

author: jdraughn
author_rank: Regular Contributor
timestamp: February 14, 2017, 10:43:21 pm
content: I am still working on my own technique, but how I generally try to solder something like that is to pre tin the wire - if the heat melted the insulation on the wire down, I make sure to trim off the excess wire. I also use some flux and pre tin the gold finger. Then I will make sure the wire is in the correct position, using helping hands or a vise to hold the board and the hand which is not holding my soldering iron to hold the wire, and then melt a small dab of solder to my soldering iron and dab that to the wire and gold finger.

author: ahjustflipit
author_rank: Newbie
timestamp: February 14, 2017, 11:43:09 pm
content: I appreciate the responses. To clarify, I am trying to repair my calculator.My understanding isn't as good as it should be. Would you mind helping clear up my understanding?QuoteWhat kind of adhesion would you recommend? Could the solder flow over the tape and essentially hover over the next gold finger?QuoteEssentially a small amount of solder to the wire and let it cool?QuoteThis I didn't understand at all. What kind of adhesive?QuoteHow should flux be applied? As a thin layer? To do what? Can I use a q-tip to spread flux?Thanks again for your response. It's been of great help.

author: RobertHolcombe
author_rank: Frequent Contributor
timestamp: February 15, 2017, 02:28:28 am
content: QuoteKapton tape is adhesive backed, just apply it where you don't want solder to go and unless you apply excessive heat or solder, it will do the job of masking the fingers. I suggested using it specifically so you could mask say 75% of the finger to avoid coating all of the gold plating with solder, retaining use of the gold fingers for whatever their intended purpose was.QuoteAs above, by masking most of the finger and using such small wire you can create very small joints relative to the overall size of the finger.QuoteIf creating very small joints with delicate wire they will be fragile and will not require much force to rip off, which could potentially take the finger with it. Apply hot glue, expoxy, super glue, etc to the wire and affix it somewhere on the board so that the adhesive will stop the solder joint(s) being subjected to any force when the wires are handled.QuoteMask the fingersApply flux to the exposed areas of the fingersTin the fingersApply flux to the tinned fingersStrip, tin and trim the wire as requiredHold the prepared wire over a tinned fingerApply soldering iron to the joint for a second to attach the wireRepeat as necessaryApply adhesive for strain reliefRemove the kapton tape from the fingersClean the board (optional)

author: DavidDLC
author_rank: Frequent Contributor
timestamp: February 15, 2017, 02:47:34 am
content: I highly recommend to use magnetic wire #34 for example.Just tin the tip of the wire with the solder iron and solder, and then you are ready to solder into the Gold FingersPM your address and I can send you for free some wire.I have no pictures right now, but can send you some tomorrow when I'm at the officeDavid.

author: MarkF
author_rank: Super Contributor
timestamp: February 15, 2017, 07:48:37 am
content: The next time you're buying solder, I find 63/37 works better for me. It changes from a liquid to a solid faster.The last I bought was Kester - 44 RA Solder Wire, .031" dia., Sn63Pb37

author: ConKbot
author_rank: Super Contributor
timestamp: February 15, 2017, 12:56:41 pm
content: Gold fingers are hard gold plated and not cosidered solderable by IPC standards. Excess gold makes joints very brittle.Tinning the pad three times will get the gold content low enough. Do your masking, tin the pad generously, use solder wick to remove the solder, clip the used wick off so you don't recontaminate, and re-tin the pad, wick clean, tin a third time and solder your wire on.The first time will dissolve the gold into the solder. After wicking, the solder left still has a "lot" of gold. The second tin and wick dilutes it down further and removes most the gold, leaving it ready for soldering on the third tinning.Do you have to? No. But if you skip it and get broken joints, you know how to fix it.