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ENIG vs Flash Gold

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Hoss

#40627

ENIG vs Flash Gold | 24 March, 2006

I have no experience with soldering to a flash gold finish. We have specified ENIG for a prototype PCB order and the supplier is asking us if they can use flash gold. They are telling us that the two are interchangable which I don't believe.

These are prototypes that will never see the field. What potential issues or process modifications do I need to consider?

Thanks.

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Chris

#40629

ENIG vs Flash Gold | 24 March, 2006

Flash gold is just thin gold plating over electroless nickel or electrolytic nickel. Flash gold is electrolytic gold where the panel is connected to a plating rectifier and current causes the plating process to occur. Gold thickness is controlled by time in the bath and current density. Flash gold will become thick gold if time in the bath goes too long.

Immersion gold is gold plating over electroless nickel. Immersion gold is an ion exchange process and it is autocatalytic or it needs no current to cause plating. Plating is a chemical reaction and not an electrical one. The gold plating process stops when all the ions are exchanged. You can not overplate or increase immersion gold thickness more that about 6 micro inches.

Which one is better? I worked in PCB fab for 4 years and we always struggled with immersion gold. I converted many PCBs from immersion to electrolytic flash gold. The flash gold process is just an easier chemistry to maintain. You should have better adhesion of the gold to the nickel with electrolytic flash gold. Your only worry would be overplating the flash gold.

My guess is that your PCB supplier will plate the flash gold on the entire panel, etch the copper using the plated gold as the resist, and then apply solder mask. ENIG would most likely be performed after the soldermask is applied. So if you scrape off the solder mask the traces will be gold under the soldermask if using flash gold. The traces will be copper under the ENIG plated panel.

My PCB supplier likes to use flash gold. We have used both ENIG and Flash Gold. We see no difference if ENIG is done correctly. We have seen issues with ENIG if the nickel passivates prior to immersion gold plating. This passivation of the nickel is not as much of an issue in electrolyic flash gold plating because electrical current diminishes the passivated nickel.

That is my opinion. Others may disagree.

Chris

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#40632

ENIG vs Flash Gold | 25 March, 2006

We agree with Chris. If your gold is applied properly and is the correct thickness, you will see no difference.

One nit on Chris' comments: immersion gold will plate-out [self-limit] around 8 thou, although we've heard 12 thou.

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RDR

#40655

ENIG vs Flash Gold | 27 March, 2006

Flash gold is usually to thick and will cause embrittlement of your solder joints if concentration exceeds I beleive 6% in the joint

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Huub

#41079

ENIG vs Flash Gold | 20 April, 2006

Do you have experience with wear resistance of spring contacts on ENIG vs Flash Au?

regards, Huub.

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#41091

ENIG vs Flash Gold | 20 April, 2006

I've seen embrittlement %s down to 3%, but a standard 5 mil solder pad would require well over 100uIn of plated gold to cause embrittlement.

-Other Russ

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