Products > Test Equipment
Hioki IM3570 LCR & Impedance Analyzer
<< < (18/26) > >>
KungFuJosh:

--- Quote from: Martin72 on September 14, 2024, 11:04:51 pm ---It looks like a nutcracker. ;)
And that should have some advantage over the “normal” SMD fixtures?

--- End quote ---

The traces are separated so it's 4-wires all the way to the DUT.
mawyatt:

--- Quote from: KungFuJosh on September 14, 2024, 10:08:34 pm ---Mike, help!

I built your cool SMT fixture, but I don't have a 3D printer, and the rubber clamp tip doesn't work at all for 805 parts.

What do you suggest I use instead to secure the SMT parts to the fixture?

Thanks,
Josh

--- End quote ---

Keep the large rubber tip, you'll need it for larger SMD components like power inductors or large chip caps. On the other bolt end add a tapered plastic tip, just about anything will work. You could get a plastic or wooden rod/dowel and turn down the tip, then drill and tap the other side for the bolt. However you do this, don't engage the bolt too deep into the tip as it distorts the fields more than the plastic tip.

Edit: The nylon screw/bolt is a good idea as you can easily taper the end to a dull point. Also did you add a internal shield within the box? This is worthwhile if you didn't.

Experiment with the Plunger base height above the PCB, we found ~10mm works with the Tip & Plunger fixture we have (there are a few types), and most of the SMD stuff we work with. You can fine tune the height with the bolt adjustment for different similar physical size SMD components.

When you use the fixture don't use too much force, often just a light pressure from the tip is enough. Get yourself some precision (0.5% if possible) 1, 5, 10, 15, 20, 30, 40, 50 and 100 milli-Ω 2512 resistors, start off with these larger SMD components and study the profile of the SMD components, some of the SMD resistors have the contact area recessed and often they make better contact flipped over face down.

We've found the larger more expensive quality SMD components seem to be easier to work with, altho we've tested some 0603 and 0805 components with patience.

Make sure the SMD and Fixture surface area is clean, we often clean with IPA and a cotton swab. Play around with how to engage the contacts (Hc, Hp, Lp, Lc) on the two SDM end conductive surfaces. Sometimes you'll get ridiculous readings, either way too high, low or negative, this is due to not having all 4 contacts engaged.

Don't forget to make a good Zero Ohm Shunt, critical for quality low Z measurements.

Best,
KungFuJosh:

--- Quote from: mawyatt on September 15, 2024, 12:26:10 am ---The nylon screw/bolt is a good idea as you can easily taper the end to a dull point. Also did you add a internal shield within the box? This is worthwhile if you didn't.

--- End quote ---

I think I will try the nylon screw first, as it's the simplest answer. I have a laser cutter, which I used to cut a 6mm thick piece of acrylic for the spacer.

I ground the paint off at contact points so the whole box is a better shield (and has continuity to the PCB ground plane), but I'm guessing you're asking if I added a shield plate between the H and L sides? I didn't do that yet.

mawyatt:

--- Quote from: KungFuJosh on September 15, 2024, 12:04:00 am ---
--- Quote from: Martin72 on September 14, 2024, 11:04:51 pm ---It looks like a nutcracker. ;)
And that should have some advantage over the “normal” SMD fixtures?

--- End quote ---

The traces are separated so it's 4-wires all the way to the DUT.

--- End quote ---

Correct, the actual SMD component conductive ends make the Hcur to Hpot connections and Lcur to Lpot connections.

This reduces contact measurement variations which are pronounced in low Z DUTs with the normal SMD fixture. If you look at the simple model we made for the normal SMD fixture, the Hcur and Hpot connections are made at the thin brass bolt end which screws into the plunger base, same for Lcur and Lpot on the other plunger.

So from this point to the plunger tip is un-sensed on each plunger by Hpot and Lpot respectively. The plunger tip to DUT  impedance variations are also un-sensed on each DUT end which produces a significant measurement uncertainty for low Z components that can't be compensated by the Zero/Short Calibration. A little experimentation with known precision low Z components like low mill-Ω 2512 precision resistors for example will show this uncertainly, at least it certainly did with us, which is why we developed this Split-Kelvin SMD Fixture.

The two resistors on the PCB are for providing a known resistance between Hcur and Hpot and same for Lcur and Lpot. This allows easier Open Cal but has some effects on such. Think we discussed this elsewhere, but can illustrate again if needed.


Edit: Just noted that you don't have a ground wire from Plunger Fixture to Case. You want Plunger Arm at Ground potential for better HF measurements. Also wrt to internal case shield, just a thin Cu sheet or FR4 between the H and L sides works, if you don't have any Cu sheet or FR4 then cut a section out of a Tin Can and solder to a BNC terminal or terminal wire running along the BNCs.

BTW Fixture looks good, nice work Josh :-+

Best,
mawyatt:

--- Quote from: KungFuJosh on September 15, 2024, 12:01:59 am ---
--- Quote from: tautech on September 14, 2024, 10:36:13 pm ---Hmmm, or machine the existing rubber foot to something more conducive to working with tiny parts......

--- End quote ---

The biggest problem with the existing rubber foot is that it's too soft. It doesn't firmly press well, and tends to move the DUT off the traces. Then the DUT is stuck to the foot and needs to be pulled off.

The traces need precision placement of the DUT, but the rubber foot has moved it in every attempted use. I can't do short correction because the 0Ω resistor fails to short the traces when the foot is applied. At best, I've had 2 of 4 traces shorted. Even using a piece of copper gets pushed out of the way.

--- End quote ---

Try raising the Plunger fixture a little higher so the plunger tip engages the SMD at ~90 degrees with the Plunger "Arm" ~parallel to the PCB surface.

It's difficult to see the DUT slide with the larger rubber tip, so a thin tip should help. Adjust the heights until the DUT doesn't slide and is pressured almost vertically. As mentioned in our case ~10mm was about right. A small amount of sliding isn't bad as it "scrubs" the surfaces which helps with contact.

Also, start off with larger SMDs like 2512 resistors to get familiar with the way this fixture works best.

Best,
Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod