Sound technical content, curated with aloha by
Ted Mooney, P.E. RET
Pine Beach, NJ
The authoritative public forum
for Metal Finishing since 1989
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Immersion gold plating Q&A's, Problems & Solutions
Q. Electrolytic gold plating is immersion depositing on non-electrified housing.
I have parts that have hermetically glass sealed pins assembled into them. The pins are wired to gold plate. I run parts through Wood's nickel at 30 ASF, nickel sulfamate at 5 ASF and then a potassium cyanide at 5 ASF. After the gold plating the housings made of 304 SS are discolored from an immersion gold. This immersion gold causes problems down stream when we go to weld the assemblies into a flange.
Reading through this thread I noticed the mention of a galvanic reaction in the plating bath. Could this be the cause of the immersion gold? Would it attribute to nickel contamination in the plating bath?
I can perform a light gold back strip and remove the immersion gold but it's a lot of added time and it's tough to ensure all of the gold is gone from the housing. Is there a method for prevention of immersion gold all together?
- Laurens, South Carolina, USA
January 8, 2020
January 2020
A. Hi Benjamin. This thread is wandering between the subject of the immersion gold plating process and the subject of inadvertent gold deposits, so I was slow to understand your situation ... which apparently is that you are doing electrolytic gold plating on the pins but the gold solution is inadvertently immersion depositing on the stainless steel housing.
Galvanic current cannot flow between things that are electrically insulated from each other, and I assume the stainless housing would be isolated from the pins. So I don't think that's it. Rather, it's a displacement reaction whereby some metal in the housing is going into solution as the gold comes out of solution. Are the pins stainless steel or kovar? Is that why you are doing the Wood's Nickel? Just from book knowledge rather than experience I would expect the stainless steel housing to remain passive and not amenable to immersion deposits if no electricity was applied to it during the nickel strike process; but maybe your pretreatment cycle is somewhat activating it.
Hopefully someone with experience in glass-to-metal seals will jump into the conversation and help us out :-)
Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Ted, the pins are RA330 SS. I think you were right about the pretreatment process. I was using a sodium fluoride activator and I ran a trial going back to the HCl activation bath instead and the parts did not receive any immersion gold.
Although the sodium fluoride is a really good activator I think I will stay away from it for assemblies.
- Laurens, South Carolina USA
January 16, 2020
Q. I am diving into this project more again and facing the same issues. The problem is definitely associated to the activation and the housing staying active through the process. With previous processes I was using a week HCl mix of roughly 17% free acidity (around 5% concentration). This low concentration HCl solution was a process hand down from the previous plating engineer. The problem with the low concentration is that it is not strong enough to activate the parts to to allow for proper adhesion. Therefore parts would fail a bend test. Through all of this I have started to move towards more industry standard with a 50/50 HCl solution (50 % v/v DI water and 50% v/v 37% concentration HCl). This works great to improve my adhesion potential, but puts me back into a position where I am dealing with the immersion gold on the housing again. Now I have a customer that requires no mechanical abrasion (bead blasting) before or after plating and has suggested a reverse trickle current on the housing during gold plating, but they have been deliberately vague on how to do this. Apparently this is a common practice in the gold plating industry but there is not a whole lot of detail on how to do it. Can I use the same anode and run it as an anode and cathode at the same time? Do I have to have a separate graphite piece to act as a cathode for the reverse current? What current density should I use for this or should I use constant voltage and if so what voltage? Hoping someone with experience can provide some insight into this process.
Benjamin Hartford [returning]- Laurens, South Carolina USA
July 14, 2022
A. Hi again. If I am understanding your situation correctly, your pins are plating fine but the housing which is isolated from the pins and is not electrified, and is not supposed to be plated, inadvertently acquires an immersion deposit.
I am not familiar with that reverse current approach either, but surely it's easy enough (theoretically) to prevent an immersion deposit on the housing by running a low voltage, very low amperage reverse current to the housing though.
Luck & Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
⇩ Related postings, oldest first ⇩
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 LivingstonA. 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 Millsmetal finishing shop - Gorham, Maine
1998
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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 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 microwave & cable assemblies - Mesa (what a place-a), Arizona 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 Haatajahelicopters - Fort Worth, Texas 1998 |
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
Falls Township, Pennsylvania
1999
Need equipment for electrogravimetric measurement to analyze immersion gold solution
2002Q. 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
Ed. note: Sorry, this RFQ is old & outdated, so contact info is no longer available. However, if you feel that something technical should be said in reply, please post it; no public commercial suggestions please ( huh? why?)
Immersion Gold - not wetting Lead-Free Solder
2006Q. 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,
- Austin, Texas
A. Brandon,
How much Tin is in your solder?
- West Palm Beach, Florida, USA
2006
Immersion gold peeling from electroless nickel
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 ?
PCB - Bangkok, Thailand
2007
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"Gold Plating Technology"
by Reid & Goldie (hard to find & expensive; if you see a copy cheap, act fast) 
on eBay or AbeBooks or Amazon (affil links) 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 BakerProcess 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? - Singapore 2007 |
Multiple threads merged: please forgive chronology errors :-)
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
Process Engineer - Thailand
November 25, 2009
A. I have had the best success with a 10% sulfuric 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 BakerFellow Plater - Syracuse, New York, USA
November 25, 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.
- Toledo, Ohio
December 8, 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.
Fellow Plater - Syracuse, New York USA
December 9, 2009
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