Electroless Nickel Plating Tutorial
Electroless Nickel Plating can be a simple and effective way of applying a nickel plate over steel, iron, copper, brass, zincated aluminum and copper alloys.
Electroless Nickel is applied by heating the nickel bath to 195°F, and then immersing the part to be plated into the bath for 15-60 minutes, depending on the desired thickness. No rectifiers or DC power are required - an autocatalytic reaction takes place that applies the nickel coating.
The tricky part about electroless plating is that you must keep at least 80% of the nickel in the plating solution at all times. Letting the amount of nickel get below 80% will cause the bath to crash, rendering it useless. Commercial platers have full time chemists on hand to monitor and make additions to their large and expensive nickel tanks. On our small scale, this is not possible, so we monitor this using a balance sheet, like a checkbook register.
NOTE: Thanks to one of our ingenious customers, we can now offer a small piece of Windows software to help you work out and track your credits. Download it here.
Plating Copper and Copper Alloys
Parts made from copper and copper alloys need to be in contact with a piece of steel, in the solution, for approximately 5 minutes so that the autocatalytic reaction will start. Once the reaction starts (part will start to gas), you can remove the steel. Some customers prefer to hang these parts into the solution from a piece of steel wire.
Nickel credits are a term we use to keep track of the nickel level in the tank.
Depending on the volume of plating solution, you start out with a number of credits. In our mini kit (5 pint), you have 1800 credits to start.)
Credits are used when you plate a part. To calculate credits used, you multiply the surface area in inches by the time you are plating.
The time you are plating, determines the plating thickness. 30 minutes of plating time give a coating that is 1/2 mil thick (0.0005")
Let's practice a few calculations:
- You have a part that is 5"x5" square, and flat, that you need to plate. That's 25 square inches per side, or 50 square inches total.
- You want 0.0005" of nickel plating on the part, requiring a 30 minute plating time.
- You will use 50 x 30 = 1500 nickel credits
- You have a cube shaped part that is 3"x3"x3". That's 54 square inches in area.
- You want 1 mil of thickness, requiring 60 minutes plating time.
- You will use 54 x 60 = 3240 nickel credits
Ok, so we understand how credits are used, but how are they replenished in the plating system?
In our Standard Electroless Nickel Kit (10 pint bath), we start out with 3600 nickel credits. This is based on the volume of chemicals in the tank. A kit twice the size would have twice the credits to start.
Using Example 1 above, we would use 1500 nickel credits during plating, so 3600-1500 = 2100 nickel credits left after plating. Easy, right?
BUT - we MUST remember that at no time can the amount of nickel credits in the bath get below 80% of their initial level, or the bath will crash. 80% of the original 3600 = 2880 credits.
So, if we plated this part for the entire 30 minutes, the bath would have crashed and would be useless.
So, how can we plate this part? Simple.....we must add replenisher during the plating.
- Using Example 1 above, we know that we will use 2100 nickel credits during the 30 minute plating time.
- We know that we must replenish after we use up 80% of the original credits (80% of 3600 = 720)
- We know that credits are calculated as time x area.
- We can work out that if the part is 50 square inches, we will lose 720 credits after 14 minutes. (720/50=14.4)
- Therefore, we must add replenisher every 14 minutes to bring the bath back up to it's original level. (To replenish 720 credits, we add 1floz of part A and 2floz of part C)
- We will need to do this every 14 minutes, so during a 30 minute plating cycle, you will replenish twice.
Ok, let's try with Example 2:
- In a Standard Electroless Nickel Kit we start with 3600 credits.
- Your part is 54 square inches in area.
- How many credits will you use during the entire plating time of 60 minutes?
- At what credit level do you need to replenish?
- After how many minutes should you replenish?
- How many times?
- 60 mins x 54 sq in = 3240 credits
- 80% of the beginning 3600 = 720 credits
- 720 credits, divided by 54 sq inches = 13.3 minutes (13 is ok)
- 3240 credits used / 720 credits each time = 4.5. If you replenish 4 times, once every 13 minutes, you'll have added 2880 credits out of the 3240 used, so at the end, add half a replensiher to give you back the balance of 360 credits.
Another consideration when electroless plating is Maximum Load. A certain volume of electroless plating solution can only plate a part that is a certain area or less. Parts bigger cause the autocatalytic reaction to fail.
In the mini 5 pint kit, the max load is 75 sq inches. If your part is bigger than that, you'll need a larger volume of plating solution to plate it.
|Plating Solution Volume||Max Load|
|5 pint||75 sq in|
|10 pint||150 sq in|
|20 pint||300 sq in|
|40 pint||600 sq in|
Making Up The Bath
Electroless Nickel Kits come with two enamel tanks. One for the electroless plating solution and one for the degreaser. Both are placed on a hotplate, stovetop, BBQ grill etc and heated to 195°F (glass thermometer included)
- To mix the degreaser, add 1 lb of powder to 2 gallons of distilled water and stir. Adjust these ratios for smaller kits.
- To mix the electroless solution, mix the chemicals using the ratio:
- 1floz Part A, 3floz Part B, 16floz distilled water (Makes 1.25 pints)
- ie. for a 5 pint kit (5 pints / 1.25 pints = 4 batches), so 4floz Part A, 12floz Part B and 64floz distilled water
- DO NOT ADD Part C or the END solution. Part C is used to replenish. END is used to make the kit drain safe for disposal.
- Add the entire bag of plastic balls. These help retain heat in the tank and reduce evaporation.
The Plating Process
Ok, so now that we've understood the nickel credits and how to ensure your electroless nickel kit won't be ruined during plating, it's time to plate a real part.
The look of your plated part is completely dependant on the look of your part before it's plated. A shiny part will be shiny when plated. A dull part will be dull when plated. This can be useful if you require a matte, or butler nickel. Just scotchbrite or bead blast the part, then plate it.
Assuming you want a shiny plated part, the steps are as follows:
- Buff and polish the part to a high shine
- Degrease the part in the SP Degreaser and do a waterbreak test. If the part fails the test, clean again until it passes.
- Calculate the number of credits you'll use and mix up your replenisher beforehand, so it's ready.
- Check Max Load - is your part too large?
- Heat the plating solution to 195F. Check the temperature with your thermometer and adjust your heat source so temp is maintained.
- Check for copper alloy - hang from a piece of steel if required.
- Hang the part into the plating bath
- Replenish if required during the plating cycle.
Electroless plating can be highly convenient because of the elimination of a power source, and very useful if you need to plate inside tubes, into heavily recessed areas, or when you have hundreds of small parts to plate (they can be dumped into a basket instead of having to be hung from wires), but a thourough understanding of the replenishment process is required.
Because of the "approximate" nature of our replenishment process (both area and times are approximate), the system has a maximum replenishment cycle of ten replenishes. At this stage, the credit level becomes unreliable. Because of this, Caswell Electroless Systems are is not suitable for larger operations where the monetary loss should a bath crash would be considerable. In these situations, industrial suppliers and nickel level titration calcuations should be sought.