Loss of brightness in nickel sulfamate bath

A. Maybe there was a proprietary ingredient in your initial run called "beginner's luck" and it has become exhausted.

Seriously, it is hard to tell why the quality of the deposit deteriorated so drastically, but I might make a wild guess that your pH went bad and your meter doesn't work, because I can't understand a tiny addition of saccharin causing the pH to actually plummet.

Low current dummying may remove copper and other impurities, but it's hard to know why you would have developed serious contamination in a short period of operation.

A leveling agent will help general brightness because it helps with micro-leveling, but it will not seriously improve metal distribution across the face of a part in nickel plating. PVC or polypropylene shields to divert current from the high current areas ought to work though.

A. Sulfamate nickel should be a very smooth matte surface. If it is shiny, it had a poison, either organic or inorganic, that plated out (or the equivalent), I.E.: the plate that you are now getting is normal (if I understood your description) For your final question, the rate of deposition is at the square root of the distance from the anode. You do not have a leveling problem, you have an anode placement problem. If you can not move the anode you will have to use a shield or a thief to reduce the high plating area. Using a lower current density (amperage) will also help slightly with the leveling. I have never used saccharin, but can not imagine, or ever heard of it having that pronounced effect on the pH.

A. I assume you are plating onto an organic or non conducting substrate and using the copper as a conducting layer. The photoresist is there to impart the desired pattern. It looks to me like you are using impure chemicals. The bath composition that you briefly describe may give a bright deposit with certain surfactants, but not all; since you do not know what it is, there is a problem here. Some surfactants can act as brighteners, but many do not, so you really need to know what you are using. Furthermore, if the initial solution contains impurities this too can act as a temporary brightener until it is depleted. I would suggest you make a new bath with known and pure chemicals. When you add the saccharin the bath will give a bright and hard deposit, but use sodium saccharin. Neither saccharin or sodium saccharin will reduce the pH, so I think the saccharin is either impure or totally mislabeled. As far as throwing power is concerned, you do not mention how big the cathodic surface area is, so you could be overloading the bath. Alternatively and more likely, the copper conducting layer is not as conducting as you hoped it was! It may have been burnt when you initially turned on the nickel current and contact has been jeopardized. Try using a much lower initial current (say 2-5 ASF) and slowly step-ramp it with time.

A. Boric acid is basically not consumed. The biggest loss is dragout or it precipitated out when the temp was lowered. Gray in the LCD is almost always copper contamination. With a stripped piece of corrugated steel, apply 1-2 amps per square foot of cathode. This will plate out the copper in the recessed areas and not take out too much nickel. Certainly you control the pH with sulfamic acid. How else did you plan to do it since the pH rises with use.