How to make an electrical connection to thin gold plating?

Question

Hello fellow engineers.

I am trying to make an electrical connection with some gold plating. The gold plating is shaped like a rectangle, with dimensions of 3mm x 1.5mm x 0.1μm thick. Here is what the part looks like, it's quite small.

My procedure is:

Tin some 24 gauge stranded copper wire
Apply flux to the gold pad
Attempt to solder the wire to the pad

Every time I try to solder (using standard solder: 63% tin, 37% lead solder wire, flux core, 0.6mm diameter. the solder I used), I end up with a failed connection within one second of solder flow. What I mean by this is, all the gold seems to disappear, and I am left with an extra-tinned wire. I think what happens is the gold is absorbed into the solder, as Wikipedia states here.

I am wondering, how do you suggest I make a reliable electrical connection to this part?

Edit 1

Per comments: - Tip: Metcal STTC-144, with a MX-PS5200 PSU. I am not sure what temperature the tip is at during soldering. - Substrate: from the product description that the substrate is Si, with 0.3μm of SiO2, then 0.01μm of Cr, then 0.1μm of Au.

You're burning it away? What is the substrate? And what tip, iron, and temperature? are you using? Photos of the damage too. — DKNguyen, Jul 09 '19 at 01:20
It says "bonding and soldering are easy" :P. If we can't help you get it soldered, you could always try conductive epoxy. — TimWescott, Jul 09 '19 at 01:25
That tip isn't doing you any favours. It's both small and round for poor contact rather than large and flat. But 0.01um of Cr is real thin. I thought there would be something more under the Au but I guess not. — DKNguyen, Jul 09 '19 at 02:28

score 3 · Accepted Answer · answered Jul 09 '19 at 01:28

3

Gold dissolves in tin. There is an indium solder called "TIX". It requires a strong flux, "TIX flux". You can get it on Amazon.

answered Jul 09 '19 at 01:28

Robert Endl

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Thank you @Robert Endl, I just bought a TIX kit, ASIN [B017L4EHCY](https://www.amazon.com/gp/product/B017L4EHCY/ref=ox_sc_act_title_1?smid=A1DPYO2JO3I12K&psc=1). Will circle back on how it performs! – Intrastellar Explorer Jul 09 '19 at 01:41
This worked!! I think their antiflux is quite useful :) My method consisted of 1. thin wire (tinned with TIX solder), ~26 AWG stranded. 2. I placed the chip with the 0.1μm thick pads on the table. 3. I placed a thin strip of metal over the interdigitated electrodes, to protect them from solder spatter (I found antiflux too hard to work with in this case, lol). 4. I placed the tinned wire on the pad. 5. I applied flux to both the tinned wire and the pad. 6. I put a bit more solder on my iron (flat tip), and pressed it down, completing the solder! – Intrastellar Explorer Jul 12 '19 at 02:22
Thank you again @RobertEndl! – Intrastellar Explorer Jul 12 '19 at 02:23
Be sure to clean the flux off. I think the stuff is corrosive. – Robert Endl Jul 12 '19 at 06:34

How to make an electrical connection to thin gold plating?

1 Answers1