Black/Brown stains on electroless nickel plating

A. I'll bet it's rust, Ms. Xu, and that your electroless nickel is not thick enough and your drying/displacement system is not functioning adequately. Kovar is not rust resistant.

A. David,

You can heat treat your parts at 590 °F. for 3 hours and get the hardness you need 60Rc +. the part may come with light brown stains on them if not covered with fiber glass cloth. All platers should be able to do this heat treating in house.

A. Suggest to:

1. Check if Ni bath metallic contamination such as Cu is high. If so, run dummy at 2-5 ASF for several hours;
2. Measure nickel thickness (too low?) and porosity (too high?)
3. Verify whether plating parts are completely dried after plating;
4. Storage condition such as temp and relative humidity is important also

A. Brown spots causes are existence of Fe3+; mechanical contaminations; overdosage of brightener/leveling agent; or pH value is too high. Best regards,

A. Hello Mark,
Can you pinpoint if the staining is coming from blind holes or corners on the part? If so, an air agitated DI rinse may be in order. I like to use a 2 to 3 counterflow rinse system with the last rinse being air agitated. As you probably know the last DI rinse should be the cleanest. Good Luck!

A. I THINK FINAL DI WATER RINSE SHOULD BE HOT TEMP. 60-70 °C.
IMMERSION TIME 2 TO 3 minutes WITH AIR AGITATION.
THEN DRY HOT AIR, OIL-FREE

A. Dear,

The quality of rinse water can cause brown stains. First make sure you use DM water for rinse. Second check silicate in rinse water. There are chemicals and color disk to check silicate in water. If you exceed 1 ppm of silicate, you are likely to get stains. A regeneration of DM plant will bring down silicate contamination. Check silicate and try. Best wishes.

A. Oscar,
I can only assume your electroless gold is a borohydride type. I have found that frequent bath analysis is necessary, prior to each running of parts. These baths are compatible with silicon, but not polyethylene. You also have to be very careful with your water source when you replenish the volume level, and the final rinse. City water should never be used in either case. Carbon polished DI water is a big help.
Because you are going over Ni, some Ni ions are lost to the bath in the reduction process. If the nickel concentration is too high in the bath, it will become unstable. This is probably why you suspect Ni oxide on the surface. Unless you are using complexing agents in the bath(which I won't get into), it may have a rather short life. You could perform a lab test with a liter of the gold solution to make sure you are getting the thickness of gold per minute that you should. If you don't get the thickness and the bath analysis is good, do a titration for Ni. I bet you find the concentration is too high for the bath. Good Luck!

A. Hello Mr Mehra,

Looks like your EN bath has metallic or organic contamination somewhere. You need to find out its source and eliminate it. The contamination may also be from leaded steel parts; assuming all other process parameters are adhered to and you ae using a good process supplier.

A. Aluminum contamination will start out as a dull then gray then a dark gray/black EN coating. Lead will normally stop the plating.

Hi, Mie. Are you from the same plating company in Cavite as JM Puguan, and is this a continuation of the same question? Several suggestions were already made. Can you frame your question in terms of those previous suggestions? Thanks!

Regards,

Hi cousin Nur.

Apologies, but nobody has replied to you yet. But if you have "the same problem" please read the suggestions for that problem

Please try to express your ongoing "same problem" in terms of those suggestions. Thanks! Good luck.

Regards,

A. Hi cousin Saritha. There are several good books which introduce electroless nickel plating. In addition to the three phosphorous contents of acid baths, EN-phosphorous can also be alkaline based, and there is a boron based electroless nickel too.

The type of electroless nickel is not chosen based on the substrate material, but based on the needs of the surface. Solderability (boron best, low phosphorous good); and ferromagnetism (low phos), or freedom from it (high phos) can be criteria; but often the principal consideration is corrosion resistance (low phos is usually best for alkaline conditions, and high phos for acidic) or wear resistance/hardness (heat treated high phosphorous is best). It's not always easy to choose, but books like Mallory & Hajdu list dozens of automotive, aerospace, oil & gas, and electronics applications and what type of EN is usually chosen for them. Good luck.

Regards,

A. Hi, Antonie,

I think first thing first is to verify those black stain area is EN plated or not. For aluminum base material, there is a test called Alizarin test (hopefully it's the right spelling), you might remove those stains by water or IPA then conduct this test. Pink color indicating poor coating coverage.
You might update us once the test is done. Thanks.

A. Hi Antoine,
As suggested by Raymond, first you need to check if the black stain area is EN plated or not.
In my opinion it is more likely that the surface is nickel plated and then oxidized, because nickel oxide has a dark color, unlike aluminum oxide that is clear.
Black stains near holes, especially blind and threaded holes, are due mainly to insufficient rinsing after nickel. This usually happens on medium phosphorous electroless nickel, while high phosphorous tends to stain less.
Trapped air does not allow nickel to be deposited in the hole but should not lead to black spots.

A. Hi cousin Antoine. I was wondering why you tried to post this continuation as a new thread rather than here, then it hit me that perhaps you never received our notification about where your thread and the two responses offered could be found :-(

Hopefully you'll see it this time and be able to say "We conducted the Alizarin test, and ... " or "Although we were unable to do that Alizarin test because ..." :-)

Luck & Regards,

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