Cheap SMD LCR Fixture, the Good, Bad and Ugly

[dazz1]

That's an interesting idea, as it does move the connection point for the Force and Sense just inside the probe tip. This would remove most the impedance effects of the plunger, altho the resistance of plunger is very low as it's a solid chunk of plated brass. 

However, it doesn't help with the SMD DUT contact effects from the plunger tip to the DUT SMD end terminals. We've found this effect (DUT Terminals contact point) to be the most problematic in low Z SMD measurements and why we developed the Split-Kelvin SMD Fixture shown here:

https://www.eevblog.com/forum/projects/different-type-lcr-smd-fixture/

Here the Force and Sense connections are made by the DUT end terminals, on the DUT side of the connection. This Split technique works very well down to milliohm Z levels with excellent repeatability as we've done extensive testing with thousands of measurements, also holds up for higher frequency measurements as we've just built another using shielded coax from the BNC connectors to the PCB connection as shown in the attached image.

We don't have the capability to machine a plunger like you've shown, would be interesting to see how well it works 

Best,

Hi
From observation of your clamp-down design and information provided, it looks ideal for larger devices.  I'd blatantly copy it. 

My coaxial idea was intended to replace the existing probes for testing of smaller smd.  The problems you found with contact points could potentially be solved using V faces that would cut through surface oxides to get to bare metal, in exactly the same way wire wrap connects to square posts.  If the issue around DUT contact point variance could be solved, I suspect the coaxial probe would perform better than the standard probe.  The sense signal would be shielded from noise and the parasitics between the DUT and the sense wire would be very small.

I do have the materials and capability to make prototype coaxial probes but I don't have the fixture, a quality LCR meter or the need to accurately measure component values.  So it is likely the coaxial probes will remain a thought experiment. 

[TERRA Operative]

A larger design, but similar concept is the coaxial kelvin probes as used for battery testing etc.
I got some from Aliexpress but they are far too big for SMD, they are similar in design though.