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Pretreatment for electrolytic Ni

We are doing electroless NiP / Au plating on electrolytic Ni. We do package shear test to assess the adhesion strength between Ni and NiP. In most of the occasion, we can see the NiP is separated from the Ni after the shear test. This indicates poor adhesion between Ni and NiP. We are using HNO3 as a pretreatment chemical for the Ni before NiP plating. Is this HNO3 (15%) is the suitable chemical to be used or there is other chemical which can treatment the Ni more effectively ?

LK Ong
Plating shop employee - Melaka , Malaysia
May 19, 2009

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Hi, LK. I've never heard of using nitric acid for that. I believe you need a Wood's Nickel Strike.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
May 19, 2009

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First of two simultaneous responses --

Hi LK.
I concur. Activation of nickel surface does not involve nitric acid. Get a copy of ASTM B343 - Standard practice for Preparation of Nickel for Nickel Plating. It describes several methods of activation involving immersion/anodic / cathodic etch treatment to the nickel surface prior to nickel plating. Woods Nickel strike is one method described in ASTM B343. Good luck.

SK Cheah
- Penang, Malaysia
May 20, 2009

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Second of two simultaneous responses --

Nitric with ammonium bifluoride added might be used as an etch/activator, but not just nitric. You then need to rapidly go to the Woods strike after good rinsing and then rapidly into the EN.
Why not just do the EN immediately after the electrolytic nickel and save all of the hassle?

James Watts
- Navarre, Florida
May 20, 2009