Electrodeposition
The part plated is the cathode, and the anode is made of the metal plated on the part. Both are submerged in an electrolyte, with a rectifier to supply direct current to the anode, oxidizing the metal molecules in solution, which allows them to dissolve into the solution. At the cathode, the dissolved metal ions in the electrolyte solution are reduced, such that they "plate out" onto the cathode. The rate at which the anode is dissolved is equal to the rate at which the cathode is plated, when current is flowing through the circuit. In this manner, the ions in the electrolyte bath are continuously replenished by the anode.

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June 28, 2004

If the nickel solution is allowed to fall out of specification, the resultant stampers will vary in thickness, surface roughness, flatness (TTV), and will exhibit some of the well known cosmetic defects.

It is therefore mandatory to measure certain parameters on a routine basis. Daily measurements of the sump level, pH, temperature, baume, and wetting agent, along with daily monitoring of flow and voltage, are necessary. Packing the anode pellets, once every shift, and sometimes after every part, is also advised. Weekly cleaning of the anode pellets, mesh, and the internal metal parts of the backplates, along with the titrations for Nickel and Boric acid, are also necessary.

Some of these measurements are easy to do:

1. Sump Level - Using a pre-marked Dipstick, measure the level in the sump daily. If the level is low add DI Water. The level must be kept as it was set in the original makeup (between 7 & 7 1/2 inches). If the level is high, open all covers, and evaporate the excess water.
   
2. pH - Each shift the pH must be checked, even if no stampers are grown. The pH must be maintained between 3.8 - 4.2, using Sulfamic acid, added in small amounts (100 gram dosage), until the pH is within specification. It is also important to make sure the pH meter is freshly calibrated before every use.
   
3. Temperature can be measured using the pH meter, if it has the temperature reading function. It is important to compare the temperature in the cell, where the stampers are being grown, to the temperature in the sump. If these two values vary, a number of problems may appear on the stampers.
   
4. Baume - A Daily measurement, of the Specific Gravity of the Nickel solution is recommended. Using a hydrometer, you will be able to monitor the nickel metal content in the solution, without having to perform the more accurate, but more time consuming nickel titration process.
   
5. Flow - Knowing the flow value as it passes the front of the cathode is important. Without proper, and consistent flow, the backside of the stamper will exhibit pits, roughness, and/or nodules.
   
6. Voltage - Knowing what the voltage value is, during the plating cycle, especially at the peak current is important. As the solution ages, the cell will get dirtier. The dirt will be either soluble Sulfur compounds, or boric acid residue. These compounds will plug the mesh, which raises the resistance between the anode and cathode. You will see this problem, as the voltage increases to compensate for the higher resistance.
   
7. Dummy Compartment voltage check - Once a week a manual check of the dummy compartment is recommended. Using a voltmeter, place the leads across the anode and cathode, to verify that the system is pulling 0.6-1.0 vdc. This system is important as it plates out the stray metals, which are introduced from the water, and from the anode pellets.

Some of these measurements, require more technically designed equipment:

1. Nickel and Boric analysis, require titration equipment. Digital Matrix offers a Hanna Instruments - Nickel/Boric Titrator that is fairly easy to use for these applications.
   
2. Stalagometer - Used to measure Surface Tension, or the amount of wetting agent in the solution. This apparatus may purchased from DisChem.
   

A full detailed analysis of the bath chemistry may require an outside lab service. Thi skind of analysis can test for many metals which are not normally present, but can sometimes contaminate a bath. Copper or zinc are examples. A lab analysis can also measure ammonia content which can often approach problematic levels in old soutions. The cost of doing this type of lab analysis is minimal as compared to the benefit. Therefore, Digital Matrix recommends a yearly nickel bath analysis.

DisChem, Inc., located in Pennsylvania, USA, can perform the lab analysis. Basic analytical measurements are made in addition to metalic impurities and ammonia. If problems are found with the bath sample, then specific recommendations are made.

This will be covered in more detail in Part III.

In Part II, Nickel Component Analysis and Upkeep
In Part III, Nickel Impurities
In Part IV, Stress Issues and corrections.