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topic 20973

Problems & Solutions in ENIG (Electroless nickel / immersion gold) and ENAG Plating

Current question and answers:

December 7, 2020

Q. Is there are any differences between finishing processes called:

- Electroless Nickel Immersion Gold
- Immersion Gold
- Chemical Gold

Or they are completely the same processes and their valid name is ENIG ?

Mariusz Ciszewski
- Wroclaw Dolnoslaskie
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"Chemical (Electroless) Nickel Plating
G. G. Gawrilov"

from Abe Books

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December 2020

A. Hi Mariusz. Certainly ENIG is universally accepted to mean electroless nickel followed by immersion gold.

Unfortunately, the others are not so clear. When someone says "immersion gold", although they certainly mean immersion gold, we can't say whether they are envisioning electroless nickel first or not.

I haven't personally heard the term "Chemical Gold", but I have heard "Chemical Nickel" [in fact there is a good book titled Chemical (Electroless) Nickel Plating], so I'd assume that Chemical Gold means electroless gold rather than immersion gold -- but it's not a spec, it's just slang.

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey




Previous closely related Q&A's starting in:

1996

Q. I am looking for a brief description of processing and potential problems for immersion nickel and immersion gold. We are a manufacturer of printed circuit boards and have a need to install this process for one of our customers.

Thank you,

Jim Moritz
ES&D, Inc


1996

A. I have never heard of "immersion nickel", do you mean electroless nickel and electroless gold?
The Canning Handbook p. 640-641 is pretty brief on immersion gilding of gold:
1. hang the articles on 24 swg copper wire.
2. clean in the usual way ( ! ! )
3. well rinse in a swill.
4. cyanide dip, 50 g/l KOH, cold
5. "most neutral and acid gold solutions, if used hot, will produce an immersion deposit on copper nickel or brass", but the author cautions that the bath will become contaminated with the displaced base metal, and thus should not be used again in electroplating.
Note: I would check with some suppliers of gold plating solutions for further information. I just bought my 'Canning Handbook' at Sur/Fin '96 Cleveland last week -- I've always wanted one, and look, I'm using it already.

tom pullizzi monitor
tom pullizi signature
Tom Pullizzi
Falls Township, Pennsylvania 


1996

A. Jim,

I agree with Tom, never heard of immersion nickel, but there is immersion gold real easy to use, watch the adhesion though. Try Technic in R.I., ask for Ormerse.

Good luck,

David Guleserian
- Rhode Island


1996

A. Electroless Nickel-Immersion Gold is a popular finish in Europe to replace hot-air leveled solder, (HALS). Most of the major chemical suppliers have the process very well defined. Any of them can supply the whole process.

Richard Zuendt
- Garfield, New Jersey



1998

ENIG vs. ENAG

Q. Electroless gold users, what are some of the problems you have experienced using an electroless gold process?

Back some years ago, the early baths produced a deposit with terrible adhesion. Is this still a problem with the latest generation of Electroless Gold baths?

Bob S [last name deleted for privacy by Editor]
New Brunswick, New Jersey


2004

Q. I am evaluating the quality and reliability of two plating processes used in PCB manufacturing specifically at the plating process:

* What is the difference between Electroless Ni Immersion Au versus Electroless Ni Autocatalytic Au plating processes?
* What is the process flow and chemistry differences?
* What are the end result quality differences?
* What are the surface morphology differences?

Filmore A. Ochoco
laminate PCB user - Warren, New Jersey, USA


2005

A. Filmore: I'm a little out of the loop on progress in ENAG, but the biggest advantage of the autocatalytic process is that the thickness is not limited because you can build gold-on-gold rather than the operation coming to a halt as soon as no more nickel is exposed.

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey



To minimize search efforts and to offer multiple viewpoints, we combined previously separate threads onto this page. Please forgive any resultant repetition, failures of chronological order, or what may look like readers disrespecting previous responses -- those other responses may not have been on the page at the time :-)



2003

Skip Plating Problem

Q. Our company faces a serious skip plating issue with ENIG finishes. The skip plating all happened on isolated pad of BGA with no line connected. Need your help. Thanks.

Philo Young
electronics - Shanghai, China



2003

A. Hello,

I have experienced this issue a lot. There is a lot you can do to minimize this problem: The most common reason for this to occur is that you have micro-etch solution remaining in the holes. If one BGA pad is somehow connected to this hole it will skip. Even if the contact is through an inner layer. The actions you might take are:

1. Make sure you don't have SM residues in the holes (helps trapping solution).
2. Make a horizontal micro-etch outside the line (if the equipment is vertical); it improves rinsing of the holes.
3. Improve rinsing in the vertical line with heated rinses and vibrators in the rinses after the micro-etch.
4. Increase time in the activator (to make sure even the small surfaces is activated.
5. Increase activity in the Ni-bath, by lowering the stab.
6. Increase surface in the bath with dummies. Most important again, check the rinsing of the holes.

Peter Fogel
ReCoV - Sweden


April 13, 2013

A. This will be happen because in MASK you did not open small hole then it Si will be fully filled, a sort of mix of air and solder mask is in the hole. Then you do Ni/Au and the air in the hole will get bigger, due to heat, and push the SM out of the hole SM is coming onto a SMD-pad and on that place there will be no gold and this is called skip plating.

Vipul Desai
job - gandhinagar,Gujarat,india



2004

Can't Pass Solderability Test after Steam Aging

Q. Hello,

I need some help about ENIG thickness requirements for Steam age testing. (Solderability - after exposing to steam for 8 hrs).

My base layer is Silver and is coated with 100 - 150 µin. of EN (7% P) and my final finish is 3 µin. of Immersion Gold. The parts pass solderability test before steam aging. After steam aging we observe de-wetting of solder on the surface.

My Question is, What is the failure mechanism? What is the minimum thickness of gold I should apply. Unfortunately I cannot go for electrolytic process due to the nature of the component. Is there a way to solve the problem without going for a thick gold using Electroless Gold? Does EN thickness play a role? Thanks for your help in advance.

Karthik Thambidurai
electronic components - Norwood, Massachusetts


2004

A. Steam aging causes oxidation of the 7% P electroless nickel under-layer. It is very difficult to pass steam-aging using immersion gold. However, I have succeeded by using a high phosphorus Electroless nickel (it is more corrosion resistant) and long times in the immersion gold. The gold does not build thickness, it only covers the nickel by chemical replacement. The nickel should be active before using immersion gold. Very short rinse (but thorough), short transfer time to the gold (before oxidation can occur), and longer time in the gold solution.

don baudrand
Don Baudrand
Consultant - Poulsbo, Washington
(Don is co-author of "Plating on Plastics" [affil links to: Amazon ... AbeBooks ])


affil. link
"Electronics Manufacturing with Lead-Free ... Materials"
from Abe Books

or

2004

Q. Hello Don,

Thanks for your input. I will try High Phosphorous Nickel on some samples and put them for steam age.

I have a few more questions. Won't longer duration of EN Parts in Immersion Gold bath lead to Black Pads? And also High-Phosphorous is not good for soldering -- what is your experience on that.

Thanks

Karthik Thambidurai
electronic components - Norwood, Massachusetts

----
Ed. note: Soldering issues with electroless nickel are the subject of many other threads on the site; Don Baudrand discusses it on letter 34791 for one.



2005

Black spots on pads. Is rework possible?

Q. We are in the manufacture of PCBs with ENIG plating .

Recently we have experienced black spots on large size pads of 12 mm and 16 mm in Finished Board.
Question : How to remove this tarnishing . If we do any rework on ENIG, is it reliable ?

HARAGOPAL
ECIL - Hyderabad India


2005

A. Haragopal: I'm just the website operator not an ENIG expert, but if an area must be reworked, it would seem that you could use brush electroplating of gold; you might contact brush plating suppliers about that. But a good first step is to try to determine at what point in the process the black spots first appear.

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey



ENIG on PCBs vs. on Silicon Wafer Pads

March 27, 2012

Q. We have started to use the ENIG process to plate Nickel (3 µm thickness over the copper pad) then followed by immersion gold layer (~500 Angstrom thick) to protect the nickel layer bond pad. We encountered a few technical challenges dealing with this process as we have seen multiple defects such as black bond pad, skip plating, delamination of pad after mounting on PCB board and more. What are the key differences in term of ENIG control when we use it to plate on the Silicon wafer pad versus PCB board ENIG plate?

Edward Ng
- San Jose, California, USA



2002

Need cyanide-free non-toxic ENIG

Q. I want to ask a question: "I work on Electroless/Immersion Ni & Au plating. Since cyanide is very toxic, is there any option on chemicals for the process which is cyanide-free, and of course not more toxic?" Thank you very much for your advise.

Wymen Lee
- GeorgeTown, Penang, Malaysia


2002

A. Electroless nickel is cyanide free. It it usually based on hypophosphite or borohydride.

It isn't quite clear to me whether you electroplate gold onto the electroless nickel or if you are talking about an autocatalytic electroless gold process or an immersion gold process. Cyanide-free golds based on other complexes are available.

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey


2002

Q. Thank you very much Mr.Mooney. Yes, it's autocatalytic immersion gold onto the electroless plated nickel surface. I've surf some page and found some information regarding cyanide-free gold plating. What I've found there somebody said the substitute complex is more complicated to treat the solution before effluent to environment. Any comments on this?

Thanks again.

Wymen Lee
- GeorgeTown, Penang, Malaysia


2002

A. I don't know exactly what the complexing agent is, but yes, it probably requires some sort of "chelate breaker" chemistry. Remember that not much gold will dissolve in a simple alkali or acid and requires some complexer that probably will not allow metals to drop out via simple pH adjustment. But I suspect that for waste treatment the gold can be easily plated out or removed by ion exchange, and the complexing agent then destroyed/deactivated/occupied with a simple metal like iron, aluminum, or calcium. The water treatment is probably not a big deal.

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey


2002

A. Electroless Nickel followed by electroless Gold or immersion gold is now very common in both the semiconductor industry and the printed circuit industry. In many cases the newer technology does not use a cyanide type gold. The use of a variety of sulfite type gold solutions is now common.

Louis Hirbour
Anaheim, California, USA


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