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Why does internal-stress occur?

2000

Hi everyone! We are one of the biggest manufacturer of plastic products for electronics in Japan. By the way, could you let me know why internal-stress occurs?

I must reduce internal-stress of electroplated Ni on electrocircuit, made of copper.

I wish someone gives good knowledge or know-how.

Hitoshi Kawaguchi
- YOKOHAMA, KANAGAWA, JAPAN [please do not contact privately]

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Try using a sulfamate bath instead of watts or woods.

James Totter, CEF
- Tallahassee, Florida
2000

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A very technical subject. A simple explanation is the way that one atom of metal bonds to the atom below it.

Stress can be controlled to near zero in electroless nickel, but it takes work, a lot of testing and great attention to detail. Generic homebrew EN will seldom achieve it.

James Watts
- Navarre, Florida
2000

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2000

hi Hitoshi

nice to see a Japanese brain here...

Did you ever try to reduce the sulfur level in your bath.

Electroless Nickel could be a suitable substitute in such kind of scenario.

as per your basic question why it occurs:

Internal Stress refers to forces created within an electrodeposit as a result of the crystalyzation process itself. It may be due to the codeposition of impurities such as sulfur and other elements but mainly sulfur.

The forces are of two kind either tensile or compressive. I don't want to go in detail here but you can go through certain good books on this topic.

But I don't agree to James Watts that we can attain a zero level in internal stress. Also Sulfamate solution without chlorides and addition agents can produce deposits with the lowest internal tensile stress.

good luck

Hemant Kumar
- Florida, USA

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I'm not sure if you're saying that stress cannot be zero in electroless nickel or in electrodeposits, Hemant. Sulfamate nickel can absolutely be controlled to zero stress. I've seen large nickel electroformed cylinders made for space telescopes in thicknesses around 6 thousandths of an inch; if the stress were not zero they would wrinkle up, and they don't.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2000

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First of two simultaneous responses--

EN can be near zero. It may depend on who's definition of near. EN can be either Tensile or compressive, both near zero. The trick is to keep it there, which is virtually impossible, if you are going to try to get 15 metal turnovers. There are some vendors that are very proud of how close they can keep it. This is not done easily and very very few shops would even attempt it. It rarely brings enough of a premium to offset the extra work.

Sulfamate nickel, with chlorides, can be controlled very easily to tensile or compressive. It takes a little reading and a little thought and saccarin or its substitutes are not one of them. It takes automated equipment or a lot of lab work, the amount is how close do you want to keep it.

James Watts
- Navarre, Florida
2000

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Second of two simultaneous responses--

Dear Hitoshi

a zero level in internal stress can not be achieved, you can only reduce the internal stress to an level, where it does not have any effect of the elongation of your metal. Try to find out what kind of internal stress occurs in your bath (tensile or compressive), if you have tensile stress try to lower your current density, if you have compressive try a higher current density. Internal stress depends very strong on the used current density. If that does not work or you can not lower your current density, try to lower your chlorid concentration or use organics that you can buy from any firm that sells electroplating baths. One very useful and cheap chemical is saccharin (also used instead of sugar) that will decrease tensile stress or even will generate compressive stress if concentration is to high.. If you have compressive stress, I think you have too much organics in your bath.

To your question why IS occurs, there are many theories, but noone knows exactly.

Good Luck

Marcus

P.S. :The electroformed cylinders for telescope are electroformed while measuring internal stress at the same time so the IS can be hold on a minimum.

Marcus Hahn
- sachseln,Switzerland
2000

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2000

Dear Hitoshi, stress can be controlled and lowered to near zero values in sulfamate Ni, acid Cu and many other baths. The following reference will give you an overview of the problem and some pointers as to stress measurement and control: www.finishing.com/library/stein/stresspaper.html. Any questions? Please call or e-mail, I'll be happy to help. Best of luck from PlaterB

"PlaterB" Berl Stein
NiCoForm, Inc.

Rochester, New York

Our research with the electronics industry indicate that residual stresses in circuits can be reduced considerably by a proper cryogenic process.

F. J. Diekman
- Streamwood, Illinois, USA
2000