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PCB Ni/Au electroplating crack

2006

We are microelectronics contract manufacturer. Major product is PCB assembly.

Recently, we found PCB Ni/Au electroplating crack on the conductor trace after pass thermal process (Pb-free reflow solder or Multiple eutectic reflow solder) with 1-2% defect rate. From cross section, the crack line do not go thru Cu layer.

Which area of electrolytic Ni/Au finishing process do we need to review?

Thank you in advance.

Wacharapong
electronics - Lamphun, Thailand

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2006

I would start by reviewing the activation cycle prior to nickel plate. Nickel activators are cheap enough to make up new. If the problem still persists, you may want to address your nickel bath. Have the bath analyzed for inorganic contamination (metallic impurities). Dummy plating at low current densities(2-4 ASF) will help reduce unwanted metallic impurities. These impurities can cause brittle deposits. Another cause that comes to mind is the lack of a wetting agent in the nickel bath. You may have hydrogen gas bubbles present on the conductor trace preventing the nickel from plating, this can actually appear as a crack. Check the manufacturer's tech data sheet on the nickel to see if the bath does indeed contain a wetting agent. It may be time for a small addition. Your supplier can give you a proper addition rate. Good Luck!

Mark Baker

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2006

My experience in Ni cracks is that, most of the time, it is coming from an ORGANIC pollution of your Ni bath. An H2O2 or permanganate treatment can solve your problem. Be careful: the crack can go through the copper too from time to time... As you did only thermal stress, try to bend the PCB on a 30mm cylinder while you observe the behavior of you tracks with a microscope. It is a cheap mean to control the ductility of your Ni.

Cousyns Martin
PCB assy - Bangkok