There were lots of definitions about Test Probe( Spring Contact Probe) on the web. But what we here to talk about is for In-Circuit Test, Function Test, and Semiconductor Test.
A Test Probe works as a terminal of an AVO meter, you might have ever had a good lesson in Physics, This terminal can carry the current and signal, and then pass over signals to the AVO meter to check the circuit. You can find the actual definitions at https://en.wikipedia.org/wiki/Test_probe
In somewhere, we called it Spring Contact Probe instead. But what is exactly composed of?
A Probe is usually made of three parts or four parts.
Starting with the plunger, a plunger is made of beryllium copper, high carbon steel, Pd silver alloy etc. It is cut by high precision CNC turning machine. Accordingly, to customer’s requirements, probe manufacturers will design a variety of functional tip styles, like the sharp dagger for via hole and dirty pads test based on its aggressive. The dagger tip could easily puncture the inside of the flux pad, and cut into the copper ring on PCB boards, a copper ring gets always hardcovers of oxygen. So is the pyramid head, all perform well in dirty PCB tests.
Probes experts also will make serrated crown tips for small pad tests and interfacing features. Dips are always fit by multiple points head tips, making sure to get in touch with the Dip Feet. We know the PCB board is covered with flux after the SMT process, so the probe always fights against flux, when PCB was soldering with all components before assembly, flux is not pure material, it is complex, composed of tin, pasta, dirts etc. Anyway it is sneaky and not electronic, and is very tough to move away. It will go with the PCB boards all the time, even when you get your iPhone or notebook, it is still there.
Come back, different tips are cut with relevant materials, BeCu is soft before heat treatment and easy to cut, with good performance on resistance, if there is no demand for puncture, copper is an optimized option, and always it can be shaped into big head tips. Another material high carbon steel for tips comes better on aggressive puncture.
The second part is the coil spring. spring is made of SUS or music wire, SUS has strong properties for high force, and music wire has well-compressed cycle times. There are many force choices for a probe, the canonical spring force is 100gram, 200gram, 300gram etc.
The final part containing spring inside is a barrel, which is always shaped like a tubular bar. Machines encase the mounting of the barrel for assembling the probe. coming along with the low resistance, barrels are made of some precious metal to keep a low resistance.
