Different type LCR SMD Fixture

[mawyatt]

We have and use the typical SMD fixtures for our lab grade LCR meters, and these work well for most SMD devices except the larger types. Typical large value SMD inductors, Tantalum SMD capacitors and large Polymer & Electrolytic SMD capacitors have been difficult to measure with these fixtures, and we've had to resort to handheld Kelvin Clips which isn't their intended use as they are for leaded devices not SMD devices.

Awhile back we developed a DIY SMD fixture for our Tek 577, shown here.

https://www.eevblog.com/forum/projects/smd-test-fixture-for-the-tektronix-576-curve-tracer/

This was based upon using the Lever Arm Clamp devices intended for clamping and holding down items. It worked so well we decided to try these Lever Arms for a custom DIY LCR Meter fixture and created a few custom PCBs to give this a try.

It works treat!! We tested a few SMD components that we couldn't test at all with the conventional LCR SMD Fixtures, and we did a couple devices we could test with the conventional LCR SMD Fixture for comparison. The comparison results were very good and we now have a fixture we can rely on for larger SMD devices!!

The first PCB uses both sides with different SMD DUT connection patterns, one for larger contact areas and one for smaller. We added the two Lever Arm assemblies, one on each side. You simply flip over the fixture to use the other side, and maybe do another Short/Open Calibration, altho we've found this isn't necessary unless one is interested in very low or very high impedances.

Also have another type PCB which employs a split SMD contact area which brings the Kelvin connections right up to the SMD DUT and even uses the SMD DUT to make the Kelvin Force and Sense connections, which we'll give a try later when time permits.

Anyway, hope some folks find this interesting and useful, certainly works for us!!

Best,

[moffy]

It is always pleasing to come up with a novel and simple solution.

[mawyatt]

More images.

[mawyatt]

Here's the Tek 577 SMD fixture that provided the inspiration for these LCR SMD fixtures. Note the PCB to the right, this has the Kelvin Type connection moved to the SMD actual pad contacts. Will be interesting to see how this works!!

Best,

[mawyatt]

Another view.

Best,

[Swake]

Really interesting topic and interesting application of the clamps.

What is the diode sign for? It seems reversed with the cathode on the +.

[mawyatt]

Really interesting topic and interesting application of the clamps.

What is the diode sign for? It seems reversed with the cathode on the +.

Just to remind of the polarity of applied DC bias when using such. So if one is measuring a diode for example, then with a + bias and the diode in the indicated direction it will be reversed biased, this would be the "usual" measurement for reverse bias diode capacitance.

We first used these clamps for out Tek 577 custom fixture, and they work so well decided to try with the LCR meter which also works really well!! Before we couldn't measure larger SMD devices with the standard SMD fixtures, now it's simple

Another possibility is to split the fixture contact surface area into a Kelvin like measurement where the DUT SMD makes the actual Force and Sense connection by means of the SMD contact surface. Here's a close up of the fixture contact area.

Making a lever arm tip from teflon or another plastic with smaller pressure area will reduce the tip capacitance, and something we've considered (maybe just glueing on a plastic tip to the arm tip). Of course gold aa a contact area would be better than the standard PCB plating, lots of options.

Best,

[mawyatt]

Mounted onto a cheap LCR fixture, works well.

Best,

[mawyatt]

Another view.

Best

[mawyatt]

Update, seems some interest in this PCB from over here.

https://www.eevblog.com/forum/testgear/cheap-smd-lcr-fixture-the-good-bad-and-ugly!/

Best,

[djerickson]

Nice work, thanks for sharing it!

My favorite impedance fixture is the HP 16092A Spring clip fixture, usable up to 3GHz! Very clever design, it handles down to 0402 parts, even leaded parts! It is not 4 terminal though. 

I used it up to 500MHz with an HP3495A analyzer. It is always impressive to see a little $0.02 part operating nicely at 500MHz. It does use 7mm and N connectors to the instrument, but a similar type fixture could be used at lower frequencies.

https://www.keysight.com/th/en/product/16092A/spring-clip-fixture.html

Dave

[cosmicray]

Do you mind if I riff a little off your concept ?

I want to make a whetstone bridge, with four DUT positions, so that I can qualify matched pairs of common SMD devices. The board under the clamps was a random 100x100 mm board that I was using to make sure it would all fit.

thanks !