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topic 2412

Immersion gold plating Q&A's, Problems & Solutions


An ongoing discussion from 1998 through today . . .

(1998)

Q. Hi everybody. Can anyone explain why a pair of pliers would become Au plated by dipping in a Au bath although they were not connected to a rectifier. This occurred while removing damaged material on a reel to reel plating line while the line was running.

George Livingston


(1998)

A. This is an immersion plate that will form on an unplated ferrous substrate, a non-adherent film which will cause the steel to turn gold. This will also happen with cyanide silver bath. Hope that helps you.

Jeff Mills
metal finishing shop - Gorham, Maine


simultaneous (1998)

A. An immersion plate is a possibility. Some immersions plates have a good adherence and some have a lousy one.

My guess is that you formed a good enough ground to the pliers that it allowed it to plate.

It is possible that the hub of the pliers was a significantly different metal and in solution, it formed a very tiny battery that was good enough to allow a very thin plate.

You now own one of the most rust resistant pliers on earth :-)

James Watts
- Navarre, Florida


(1998)

A. The term is IMMERSION plate or galvanic plating.

The difference in potential between the ferrous metal and the gold bath causes iron to go into solution. The counter reaction is the reduction of gold ions to metal on the surface of the tool.

bill vins
Bill Vins
microwave & cable assemblies
Mesa (what a place-a), Arizona 


(1998)

A. This phenomenon is known as immersion plating. The pliers you are using may be plated with another metal such as chrome or may be a bare ferrous substrate. Because gold is a very noble metal (meaning it is very inactive) it prefers to be in the solid metal state rather than in the ionic form which would be found in the gold bath. Iron or chrome are active metals when compared to gold so these metals will dissolve (become ionized) into the bath to replace the gold ions which will become solid (gold plate). The following chemical equation show how the basic process works in a potassium gold cyanide bath:

3KAu(CN)2 + Fe(solid) = 3Au(solid)+ K3Fe(CN)6

This can also be looked at as an electrical process (as all chemical reactions are) as electrons are passed from the iron to the gold. Gold atoms in the ionic form have electrons missing from their outer electron orbits (these missing electrons are hanging around the cyanide-CN ion) giving the gold ions a positive electrical charge. Electrons in orbit around iron atoms prefer to be in orbit around the positively charged gold atoms. This means that the gold electron orbit provides a lower energy state for the electrons than does the iron orbit and according to the laws of thermodynamics --- processes always move towards the lowest energy state. So without ever applying an external electrical power source - an electrical circuit is created in the gold bath.

If properly set up you could create a gold battery - similar to a lead acid battery but with different chemistry and much more expensive.

Greg Haataja
helicopters - Fort Worth, Texas



(1999)

Q. I am looking for a commercial or military specification for immersion gold plating.

Mike Steele
- Cincinnati, Ohio


(1999)

A. Immersion deposits are useful for some things, but in the wet process world, the deposits are so thin and transient that I have trouble imagining anything more than a visual inspection for a gold color, and some mild abrasion test to see if the gold will rub off onto a linen napkin.

tom pullizzi monitor
Tom Pullizzi
Falls Township,
   Pennsylvania 




Need equipment for electrogravimetric measurement to analyze immersion gold solution

(2002)

Q. Hello, friends,

I will do immersion gold plating by end of this year. So, I need equipment to analyze the gold content (1.5 to 3.5 g/L). Someone recommend me to use the electrogravimetric method to analyze this gold content. Anybody know that where we can get equipment to do this electrogravimetric analysis in Malaysia. Any instrument/equipment supplier have supply this equipment (in Malaysia)?

Thank you very much for your helpfulness!

Regards,

Wymen Lee
- Penang, Malaysia
outdated

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Immersion Gold - not wetting Lead-Free Solder

(2006)

Q. We are inserting a Gold Pin Thru Hole Connector into a Immersion Gold finished PCB.
The connector is being hand soldered using Lead-Free water soluble solder wire.
Our problem is on about 20% of the leads won't wet all the way thru to the top of the PCB.
It doesn't matter how long you hold the soldering tip to the lead or how much flux you use.
We are using a big enough tip for heating purposes I think. It is the largest that will work in the confines of the soldering area. The solder on the leads melt instantly upon contact with the tip so I think the heat is sufficient.
Any ideas what might be causing this?

Thanks,

Brandon Goodwin
- Austin, Texas


(2006)

A. Brandon,
How much Tin is in your solder?

Mike Carter
- West Palm Beach, Florida, USA



Immersion gold peeling from electroless nickel

(2007)

Q. Who can suggest me the reason why gold peeling form nickel, always found gold peeling on bottom of pad close to solder mask ?

What are the possible root cause of gold peeling from nickel ?

Satit
PCB - Bangkok, Thailand


simultaneous (2007)

A. The main cause is that the nickel surface becomes passive, and you are losing adhesion values. There should not be any delay between EN and Au. If the boards are baked after solder mask, it tends to lift the Au from the underplate. This is why you need good adhesion of the gold on nickel. Good Luck!

Mark Baker
Process Engineer - Syracuse, New York USA


(2007)

A. Firstly your question is not supported by a description of your process. How was it determined that the gold is peeling from the EN layer? Was it by means of a tape test?

Generally if the peeling is at the edge of pad nearest to the solder mask, it is likely that there are there may be impurities trapped at the recesses of the solder mask. Make sure that your post rinsing after the EN plating is with DI water. This is important if your process is a continuous one where immediately after the EN process the board goes into the immersion gold tank.

I am not sure if your are familiar with "Black pad". If this occurs there is a chance that the peeling between the Immersion gold layer and EN occurs.

Alan Logan
- Singapore



To minimize searching and offer multiple viewpoints, we've combined multiple threads into the dialog you're viewing. Please forgive any resultant repetition or failures of chronological order.



November 25, 2009

Q. Hello, I have a problem about Au/Ni peel off. My process is immersion gold used for PCB industrial. Once a day, in process occurs problem of Au/Ni peel off. First, I was check initial this defect show as 1) After tape test found Ni peel off from Cu plate
2) I found this problem just 5 cycle continuously for mass production, next cycle not found this defect.
What is cause occurence of defect ? Thank you for any answer or recommendation

Vasin Keawmalee
Process Engineer - Thailand


November 25, 2009

A. I have had the best success with a 10% sulphuric dip for 1 minute before nickel. Don't let the work sit in the rinsewater too long prior to nickel. Depending on the quality of the water, copper will oxidize rather quickly and cause adhesion problems with Nickel on Copper. If you are using electrolytic nickel, make sure you go in live. Hope this helps.

Mark Baker
Fellow Plater - Syracuse, New York, USA


December 8, 2009

A. Au/Ni peel off sounds like you are not getting proper activation of your nickel deposit.

Activation of nickel can sometimes require more than just an acid dip, due to its catalytic properties. A nickel rejuvenation process usually helps with this.

Robert H Kinner
- Toledo, Ohio


December 9, 2009

A. Robert,
The main problem here was Ni peeling from Cu, not Au peeling from Ni. Vasin stated that by giving the results of his tape test. Obviously the Au will peel because it's on top of the Ni. Sometimes I have to read the questions twice, just to be sure.

Mark Baker
Fellow Plater - Syracuse, New York USA


December 26, 2009

A. Hello please check oil condition of diffusion pump & rotary pump also time to reach the required vacuum level also cooling water temperature or maybe some where water leak in your machine.

Mukunda Charan
- Kenjhar, Orissa, India



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