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Soft gold plating Q&A's





Q. I would like to know about how to spec soft gold plating and EN plating such that post-machining can be achieved successfully without peeling!

Thank you

Ang Kah Kiong, Alfred
national laboratories - Singapore
2000


A. What is peeling? Gold off Electroless Nickel? It is difficult to get soft (pure) gold to adhere to EN adequately. You should first strike with an acid (Cobalt preferably) Gold, about 0.5 Microns.

If EN is peeling off the substrate then your problem is more about fundamental pre-treatment, depending upon what the substrate is.

Peter Vivian
- U.K.
2000



A. Hi Mr Ang,

Are you sure your problem is one of adhesion and not one of trying to machine off too much on one pass? Most electrodeposits respond better to grinding than machining and this is highlighted when you have a soft deposit on top of a substantially harder one. Try grinding, and do it slowly and it should work fine .

Regards,

John Tenison-Woods
John Tenison - Woods
- Victoria Australia
2000

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Ed. note: Readers may also be interested in letter 44804, "Red Discoloration/spots in soft gold plating", and letter 37430, "Analysis of soft gold plating bath, removing nickel contaminants".




Soft gold on PCB

Q. Direct gold plating of 3 µm on copper PCB track is reliable? What is soft gold? Does it also need a barrier layer on copper?

K Soni
- HYDERABAD,TELANGANA, India
March 13, 2015



March 14, 2015

A. Hi Soni,

Soft gold is pure gold without nickel or cobalt co-deposit. Usually a nickel layer is plated on top of copper follow by gold plating as a barrier of copper migration into gold. 3 micron gold is abnormal high. Do you mean 3 microinch instead?

Regards,
David

David Shiu
David Shiu
- Singapore



March 16, 2015

Q. Hi David,

Thanks for reply.

Yes, it is 3 microns gold directly on copper without nickel barrier. I can't use nickel because of its losses.

Earlier we did 0.5 microns gold and my PCB tracks got damaged because of copper migration. Going to more thick gold to avoid that problem.

Is it reliable? How long will my PCB track be safe from copper migration?

Does operating environment have an effect on this migration?

soni

K. Soni [returning]
- HYDERABAD,TELANGANA, India



March 17, 2015

Hi Soni,

3 micron thick gold is suitable for wire bonding but may not good for soldering. Copper migration depends on storage condition like temperature, humidity as well as copper deposit grain morphology (e.g. columnar structure might favor copper migration), etc.

Regards,
David

David Shiu
David Shiu
- Singapore




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