Many test engineers focus on Contact Resistance to keep the test line stable and fast transmitting.

What will contribute to the Contact Resistance of a test probe?

As the former probe definition essay said, a probe comprises plungers, a barrel, and a spring.

Let's have a detailed concept of the resistance of a contact probe.

We always confound the contact resistance with mechanical resistance, even with impedance.

What is mechanical resistance?

It equals probe resistance, only based on materials, length, cross-area, etc. 

But Contact Resistance is not a mechanical resistance but is included, furthermore, it is not the original resistance, let see the contact resistance for a double-ended probe and ICT probe.

So, we should focus on more probe-making, a good process will help a lot to reduce the resistance.

A good tube can keep R2 and R3 as low as possible,

Elaborate electroplating increases the electric conductivity of plungers,

Even if we never want the current to go from the plunger to the spring, a plating treatment for spring will be better. Nobody can work like a god, neither does a probe. ( Spring is always made of steel, and steel is a low electric conductivity material with high spring and lifespan )

Sometimes contact resistance is a key to test, like high speed.

Focus more, and keep the flux off.