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Soldering to hard gold

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Soldering to hard gold | 2 May, 2013

Looking for advice on soldering lead free paste to a board with very heavy gold plating. I have learned from the Customer that this is HARD GOLD and that it is 10-20 Micro Inches Hard Gold over 100 Micro inches of Nickel. When we reflowed the solder it looked like is stuck but we found out that is was not. The solder came off of the gold pads very easily. Is there something we can change in the reflow profile?

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Soldering to hard gold | 3 May, 2013

To be short, no change in profile is going to get you through this.

As I recall the point of hard gold is to retard the wetting process, so no surprise here. For example a connector might have hard gold plating at the mating surface, but not at the solderable leads. At the leads the gold is thin enough to be dissolved into the solder joint, and still be below the ratio of total gold allowed in the joint.

Too much Gold leads to brittle solder joints, as you are experiencing.

You might find a way be removing the gold by a pre-tinning procedure, that could leave you with an actual solderable surface. But without any additional detail, not much more can be said other than to get id of the excessive gold somehow. 'hege

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Soldering to hard gold | 6 May, 2013

Gold in solder alloys can be brittle. We always used to talk about keeping gold LT 3% in order to avoid embrittlement. Some military contracts require removal of gold from soldered contacts.

Adding gold to a solder alloy that you're familiar with will: * Make the surface of the solder connection look less shiny * Require that you add more energy to obtain a smooth solder flow

Here's a paper that explains what's going on

I receive no benefit from providing this link.

BR davef

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Soldering to hard gold | 20 May, 2013

Hi I meet problem by PCB with diameter 300cm and thick 6mm i used tin-lead with profile normal, soak time 60-90 sec, Temp peak is 220 degree C, But solder see not good, not shiny. Any body recomend help me to fix this problem for Hard gold playing..some time i meet this problem but cann't fix it please he;p

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Soldering to hard gold | 24 May, 2013

you need to reduce your time above liquidus to as low as you can...maybe 10~30 secs to allow the solder to wet to the gold but minimise the amount of gold that is dissolved into the solder joint...try also reducing the peak temp to 200~210 deg C. This should give you a joint with the minimum amount of gold dissolution. Of course it is not ideal to be soldering to thick gold layers and it'll be for you or your customer to decide if joint brittleness is an issue...

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