Green stains on electroless plated brass components

We make low volume / high value electronic assemblies for a number of different applications and have recently received some turned brass components from a US supplier that have electroless nickel plating on them that appears under a microscope to be slightly porous with evidence of green stains in some places. I suspect from other questions and answers that the green staining could be acidic salt residue from the plating process, but would like to know if this is a correct suspicion, if something else could have caused it and what to do about it on the components we have and how to prevent it in future. Also, is it likely to be linked to porosity?

Many thanks.

Unless your brass part is a casting, the green stain that your are seeing is probably the corrosion product from brass coming through the pores in the EN coating. To solve it, you need to stop the porosity in the coating. Porosity can be due to a number of causes, including substrate defects, contaminated or excessive old baths, inadequate pretreatment, inadequate bath (i.e., using a mid phos bath when a high phos is needed), inadequate thickness, etc.