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topic 59721

Electroless nickel plating in through-hole structure

October 23, 2014

Q. Hi,
I am currently doing research on electroless nickel plating for through-hole structures (with hole size around 40 µm x 1 µm in rectangular shape), I have tried to use copper super filling method (with additives PEG or SPS independently), but it doesn't help much. It will have a seam in the middle (around 1 µm) as nickel film approaches from both sides.
It would seem the additive leveling agent would help in copper plated through-hole (i.e., JGB), any suggestion for which leveling agent is good for electroless nickel plating? And any comment about getting rid of the seam (may be due to narrow restricted area, lower mass reactant, and product transfer) in the middle as nickel film approaching from adjacent sides?

Anything helps. Thanks.

Kevin lee
- san jose, California

simultaneous October 24, 2014

A. I do not think that there is any silver bullet additive for this.
What will help is a stronger air agitation directly under the hole and slowing down the plate rate a bit by pH or temperature or concentration.
If these are small, you might look at barrel plating with 2/3 of a normal load, slow rotation and extremely strong air under the barrel.

James Watts
- Navarre, Florida

October 24, 2014

A. Hello Kevin,
Because Electroless Nickel is an autocatalytic process, I don't know or have ever heard of a leveler for EN. In baths I have used in the past we had to do the following to achieve even plating in small holes:
1) Side to side work bar movement to ensure the solutions are being "pushed" through the holes. This bar agitation must be used in all EN related tanks especially the activator which is key in proper EN coverage.
2) We also had to employ work rack vibration, portable air activated vibrators on the plating rack. This helped with trapped air bubbles that would form in the small holes.
3) Constant filtration which aids in solution movement and filtering out small Ni fines that can fall off plating racks. We also had air agitation behind the heater(s) to avoid heat localization thereby reducing the chance of premature plat-out.
4) We also had to keep a close eye on the concentration of our Pd activator with a few routine analysis per shift.
5) Dumping the bath just before the bath Metal Turn Over (MTO's) reached it's lower range. Frequent ph checks / adjustments also helped us. Good Luck!

Mark Baker
Process Engineer - Phoenix, Arizona USA

October 24, 2014

Q. Thanks for replying and providing useful information for my project.

I still have few more questions:

Would the additives used in copper electroplating such as SPS or PEG (both slow down plating rate in copper electroplating) work for electroless nickel plating or electroless copper plating? As well as other additives such as leveler JGB or BTA and others.

So additives won't work well in electroless plating in comparison to electroplating?

Thanks so much for help.

kevin lee [returning]
- san jose California

Electroless Plating
by Mallory & Hajdu
from Abe Books

October 26, 2014

A. I have never used it and have no knowledge of its makeup, but there is an electroless copper made for thru the hole plating of printed wiring boards.
You might try to come up with the EN book from several years back by Hajdu and another big name in EN plating.
Ted might put a link to it here.

James Watts
- Navarre, Florida

Ed. note: Will do, =>

July 24, 2018 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Electroless nickel plating small 316 stainless steel parts, approx. 1/4" square and .025 thick. There is a .037 hole in the part. We are getting really bad edge build-up but only in the hole. The hole closes up to .035 or less. The plating thickness measures .0003" on the flat surfaces.

Do you think the solution is not flowing into the holes, but is forming a small bubble that dries in the holes? I cannot think of any other cause for such a large edge build-up.

Stephen Oneufer
Designer - Elizabethtown, North Carolina USA

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