Timeframe of diffusion of CU into gold Through Ni barrier
Here is my problem at my company we currently use beryllium copper for making plunger to test circuit boards as a base material which is plated with 50-100 Mils nickel and then 50 Mils of gold. Using the nickel as a diffusion barrier between the copper and the gold. Though after a while of sitting in the stock room the copper still diffuses into the gold. I am writing to you to learn the timeframe for appreciable diffusion at room temperature. I am also looking for new barrier plate options that would be low resistivity and non-magnetic properties. I have looked everywhere for the timeframe and can't find it anywhere. Thank you for taking the time to read this.Duncan Wallace
- Hampton, New Hampshire
Diffusion of copper through nickel at room temperature will be very, very slow. I am sorry that I do not have diffusion rates readily at hand. This makes me question what evidence that you have that the copper is diffusing through the nickel. And how long of a shelf life are you seeking.
FYI: I assume that your plating thickness values are millionths of an inch (0.00005 to 0.00010 in. nickel, 0.00005 in. gold). The term mil typically is used to indicate 0.001 in. and 50 mils of gold plating would be quite extraordinary. You may only need to to increase the nickel thickness slightly to reduce porosity in the thin nickel layer.
You may find Paul Stransky's notes on diffusion interesting.
Ted Mooney, P.E.
Pine Beach, New Jersey
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