Gold plating custom electronic switch

[dfro]

I have a project where I am making a 5 volt electronic switch out of a small, .063" diameter, 1" long, zinc plated spring and a 1/32" brass rod. The brass rod is bent like a staple and soldered to the circuit board on both ends.

One end of the spring is attached to a moving lever arm. When the lever arm is in the up position, it pulls the spring up against the horizontal part of the brass rod, thus closing the switch. When the lever arm is pushed to the down position, the spring releases contact with the brass rod, thus opening the switch.

Here are my questions:

1. Does Caswell sell a plating solution that will put a thick enough coat of gold on these parts? There will be some wear and tear from the slight rubbing of the spring against the brass rod over time. A local jewelery supply store told me that their solutions are designed only for flash plating and they did not think that it would withstand the repeated action of the switch. Any thoughts?

2. What cleaning solutions and other methods should I use to ensure a hard, thick enough coat? I have a rectified power supply.

3. Also, is there any extra plating I may need to do first over the zinc or brass before plating gold?

I would rather do the plating in-house rather than send such a small job to a plating company.

Thanks for any help,

dfro

[CarWiz]

If I understand your switch correctly, the spring rubs against the brass rod to make contact. (Pinched between a coil.) I don't think any plating will stand up to the wear for very long. Especially gold. Chrome and Nickel may stand up but carry a high resistance for contact switches. The zinc on the spring will wear off pretty quick and brass rod will wear at the sliding points.

If the switch design is fixed, I would be more inclined to use a Beryllium Copper spring and skip the plating all together.

[dfro]

CarWiz

Thanks for the reply. I understand your points. This is a switch for a keyboard instrument. I am following a design that was used for decades by electronic keyboard companies before they started making conductive, molded, rubber domes that compress when the key is pressed.

One end of the spring is attached to the instrument key and is pulled up against the horizontal beam part of the brass staple form. It touches the brass staple form in the middle of the spring. This switch design allows the key to travel past the contact point with no effect on the feel of the key. The spring just bends a little against the brass bar. Also, the spring is tightly wound, so the coils do not separate and pinch the brass bar - the pressure is very slight, also. There is a little friction, but many vintage keyboards seem to still be going with no problems.

The old Hammond organs did not bother with any plating of the steel contacts on a similar design to mine. Over time the contacts would oxidize and effect the triggering of the notes.

I have also noticed that many of the keyboards have the spring silver plated instead of gold plated. The manufacturers did not seem to be concerned about the silver oxidizing.

Could I get a thicker. more durable plate with silver?

Thanks,

dfro

[dfro]

I have been reading more throughout the site and I think I should plate both the zinc plated springs and the brass bars with copper, then nickel ,and then gold plate.

I like the idea of doing all three plating steps with the Plug 'N Plate kits. The parts I want to plate are tiny.

The Pick-a-kit helper says I should use the Flash Copper kit over pot metal/zinc, but would the Plug 'N Plate copper kit suffice?

And I think I will try Soft Scrub or Bon Amie or just baking soda to clean the parts.

[lcaswell]

Plug N Plate Copper is Flash Copper, so you will be fine there.

Soft Scrub would certainly be ok.

[dfro]

Thanks for the information! I have put in my order.

dfro

[NOL4154]

dfro,
Gold is not design for constant wear. If I was asked to plate the brass rod I would do the following:
1. Clean & active brass.
2. Apply electroless nickel or electroplate nickel sulfate layer ~ 100-200 micro-inches.
3. The gold layer would be a Type II which is a acid alloy gold containg nickel, cobalt
and some iron (~0.4 % mass). Gold thickness would be 100-200 micro-inches.
Type II is recommended by Military and ASTM specifcation.
4. Copper "strike or flash" which in plating world there is a difference.
5. The layer provides a layer for the following:
a. Corrision barrier.
b. Layer to build the following plated layer.
c. Improve adhesion bewteen plated layers.
6. A nickel layer is needed because of inter-metalic formations bewteen disimiliar metals.
Inter-metallic formation will cause brittle comdition. For more information of inter-
metallic formation. Check web sites!
7. No zinc layer! Cause a serious problems with inter-metallic formation.

I have been in the plating industry for over 25 years and have plated from a-z, etc...

Nol4154

I have a project where I am making a 5 volt electronic switch out of a small, .063" diameter, 1" long, zinc plated spring and a 1/32" brass rod. The brass rod is bent like a staple and soldered to the circuit board on both ends.

One end of the spring is attached to a moving lever arm. When the lever arm is in the up position, it pulls the spring up against the horizontal part of the brass rod, thus closing the switch. When the lever arm is pushed to the down position, the spring releases contact with the brass rod, thus opening the switch.

Here are my questions:

1. Does Caswell sell a plating solution that will put a thick enough coat of gold on these parts? There will be some wear and tear from the slight rubbing of the spring against the brass rod over time. A local jewelery supply store told me that their solutions are designed only for flash plating and they did not think that it would withstand the repeated action of the switch. Any thoughts?

2. What cleaning solutions and other methods should I use to ensure a hard, thick enough coat? I have a rectified power supply.

3. Also, is there any extra plating I may need to do first over the zinc or brass before plating gold?

I would rather do the plating in-house rather than send such a small job to a plating company.

Thanks for any help,

dfro

[dfro]

NOL4154,

Thanks for the information. These zinc plated springs are the only ones I could find that suit my purpose. Maybe if I kept looking I could find a spring this size that is not zinc plated. I will be plating over the zinc first with copper and then plate with nickel and then gold.

I expect the gold layer to wear, but I am hoping that the nickel layer resists oxidation enough to make good enough contact to switch 5 volt logic integrated circuits. I hope the gold keeps the keys I do not play that much from oxidizing. I hope the keys I play more often will keep the nickel plate polished from the slight bit of rubbing.

Maybe I should skip the gold all together and leave a nickel surface finish. What to you think?

Also, how long do you think I should leave the spring in the Plug 'N Plate nickel solution to get a 100-200 micro inch thick plate? The wire thickness is .008 inch and the springs are .063 inch diameter by 1 inch long.

Thanks,
dfro

[NOL4154]

Dear dfro,
I recommend that you do not copper plate over zinc plating because you are setting up a perfect intermetallic formation zone that in time will become brittle and crack.
I would remove the zinc plating with about 20-30 % muratic acid rinse and quickly plate copper (100-150 micro-inches) because you want to avoid flash rust. You then can follow with nickel and gold.
Give it a try, can not go wrong.
Now, how long to leave in nickel bath, I recommend to refer to Caswell manual because you need surface area information and what type of rectifer you have. Caswell should have a chart for this in your kit.
Nol4154

NOL4154,

Thanks for the information. These zinc plated springs are the only ones I could find that suit my purpose. Maybe if I kept looking I could find a spring this size that is not zinc plated. I will be plating over the zinc first with copper and then plate with nickel and then gold.

I expect the gold layer to wear, but I am hoping that the nickel layer resists oxidation enough to make good enough contact to switch 5 volt logic integrated circuits. I hope the gold keeps the keys I do not play that much from oxidizing. I hope the keys I play more often will keep the nickel plate polished from the slight bit of rubbing.

Maybe I should skip the gold all together and leave a nickel surface finish. What to you think?

Also, how long do you think I should leave the spring in the Plug 'N Plate nickel solution to get a 100-200 micro inch thick plate? The wire thickness is .008 inch and the springs are .063 inch diameter by 1 inch long.

Thanks,
dfro