What causes pinholes in electroless nickel deposits? C.Y.
Here are a few general areas to investigate. Your EN bath may contain organic impurities or have suspended matter. Organic impurities can end up in your bath from a couple of sources, such as the air used for agitation, dragin or incorrect tank materials. Using better filtration can reduce suspended matter.
Your base metal may have pits or other imperfections on the surfaces. Zinc diecasts are a good example of this type of problem.
The chemical balance of your tank may be out of control. If your bath is not under good control, larger than normal amounts of hydrogen may be formed on the surface of your parts giving rise to pinholes and/or pits.