Different type LCR SMD Fixture - Page 1
Forum section: electronics / projects

author: mawyatt
author_rank: Super Contributor
timestamp: September 15, 2023, 01:06:47 am
content: 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,

author: moffy
author_rank: Super Contributor
timestamp: September 15, 2023, 01:13:30 am
content: It is always pleasing to come up with a novel and simple solution.

author: mawyatt
author_rank: Super Contributor
timestamp: September 15, 2023, 01:14:08 am
content: More images.

author: mawyatt
author_rank: Super Contributor
timestamp: September 15, 2023, 01:23:56 am
content: 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,

author: mawyatt
author_rank: Super Contributor
timestamp: September 15, 2023, 01:28:34 am
content: Another view.Best,

author: Swake
author_rank: Frequent Contributor
timestamp: September 17, 2023, 06:24:46 pm
content: Really interesting topic and interesting application of the clamps.What is the diode sign for? It seems reversed with the cathode on the +.

author: mawyatt
author_rank: Super Contributor
timestamp: September 17, 2023, 09:18:29 pm
content: Quote from: Swake on September 17, 2023, 06:24:46 pmJust 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 simpleAnother 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,

author: mawyatt
author_rank: Super Contributor
timestamp: October 30, 2023, 06:59:25 pm
content: Mounted onto a cheap LCR fixture, works well.Best,

author: mawyatt
author_rank: Super Contributor
timestamp: October 30, 2023, 07:00:46 pm
content: Another view.Best

author: mawyatt
author_rank: Super Contributor
timestamp: February 28, 2024, 12:42:57 am
content: 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,

author: djerickson
author_rank: Regular Contributor
timestamp: February 29, 2024, 10:22:35 pm
content: 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.htmlDave

author: cosmicray
author_rank: Frequent Contributor
timestamp: March 06, 2024, 07:40:58 pm
content: 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 !

author: mawyatt
author_rank: Super Contributor
timestamp: June 05, 2024, 05:36:04 pm
content: Created some 3D printed standoffs and a plunger with narrow tip.Considering ordering a set of PCBS with gold plating as well as the DC Bias Adapter and Tek Curve Tracer Adapters if folks are interested.Best,

author: mawyatt
author_rank: Super Contributor
timestamp: July 13, 2024, 09:04:18 pm
content: Had a few moments today and thought about a way to improve the contact area for the SMD on the fixture. Our plan was later sometime when we ordered some PCBs we would also include this fixture PCB but with gold contact area.One thought that came to mind was to increase the roughness of the contact surface by means of adding some small conductive "particles" to the surface.So we mixed up a small amount of solder paste with extra flux and added some copper wire filings by filing some #12 copper wire. This slurry was smeared across the PCB contact area and slightly heated so the flux would flow, then evenly distributed across the contact area as best we could. Using an air gun we slowly heated the PCB surface around the contact area until the solder melted and flowed leaving a nice rough texture!!After a through cleaning and reassembly, seems this worked and get better SMD contact with less finagling than with the smoother surface. Getting good, repeatable low Z results under 100 milli-ohms with less effort now!!BTW for those that don't know how these Lab Grade LCR meters work, they have both Force and Sense for the Hcur and Lcur inputs, thus 4 inputs like DMM Kelvin Inputs. The fixture we've created with this PCB doesn't connect the Force and Sense together like most fixtures do, but rely on the DUT SMD contact ends to make the connections which should improve results with very low Z components. During Open Calibration our two Lab Grade LCR meters will "bark" at you since these Force and Sense aren't connected. A couple solutions are available, one is to include a small shunt resistor between the Force and Sense (see PCB layout earlier or image below, it has these footprints as R1 and R2), the other is to use a very high value (impedance) SMD like a high R resistor or low C cap and do the Open Cal with this component (for low Z measurements this shouldn't have much effect). Lastly one can just use 2 SMD devices and place them back to back but not touching so the ends make the Force and Sense connections (this is what we usually do).Anyway, just thought that others might this fixture and tips useful.Best,

author: RoGeorge
author_rank: Super Contributor
timestamp: July 14, 2024, 09:13:09 am
content: Nice finding!Looking for similar properties (rough contact surface, combined with some plasticity/elasticity) maybe solder-wick, too, might make a good enough contact pad.

author: tszaboo
author_rank: Super Contributor
timestamp: July 14, 2024, 12:21:19 pm
content: It's the first time I see this. Quite interesting and clever, good integration of different parts.I've some contribution, it's about the hold-down force of these clamps. They can go crazy high, bending and breaking everything. I've started using clamps, that have a small screw to set the hold-down force in my JIGs.

author: mawyatt
author_rank: Super Contributor
timestamp: July 14, 2024, 01:59:16 pm
content: The Lever Arm has a threaded rod with the Rubber Bumper (Black) on the end, see previous posts for details. This rod is fixed with two hex nuts and thus adjustable, allowing the DUT pressure to be adjusted.We've been thinking of replacing the hex nuts with Wing Nuts to allow easier pressure adjustments, but haven't done so just yet.We also placed a 3D printed cone shaped Bumper (Green) on the other end of the threaded rod, so can use either by flipping over.Best,

author: tszaboo
author_rank: Super Contributor
timestamp: July 14, 2024, 02:04:18 pm
content: Quote from: mawyatt on July 14, 2024, 01:59:16 pmThat's not the adjustment kind I was talking about.Take a look at this:https://nl.rs-online.com/web/p/clamps/1253863At the bottom of the lever, there is a small bolt, where the clamping force can individually adjusted from the clamping height.

author: mawyatt
author_rank: Super Contributor
timestamp: July 14, 2024, 02:12:30 pm
content: Quote from: cosmicray on March 06, 2024, 07:40:58 pmYou want to have 4 SMD devices for the bridge, and each SMD selectable?Interesting idea, are you going for a custom PCB for this?We've found various SMD devices have more or less difficulty in making good contact with the pads. This even shows with the concept of splitting the Force and Sense connections to the DUT end terminations, where contact effects should be minimized.This was the reason we created the rough conductive surface mentioned above, so you might want to consider such if you are going for custom PCBs for your Bridge.Anyway, interesting idea, please show your setup and results when you can.Best,Best,

author: mawyatt
author_rank: Super Contributor
timestamp: July 14, 2024, 02:17:15 pm
content: Quote from: tszaboo on July 14, 2024, 02:04:18 pmYes, that's a much better plunger fixture than what we are using, and should be a better overall setup, but also more expensive!!Post some images and results from your setup, curious to see what others are doing!!Best,

author: tszaboo
author_rank: Super Contributor
timestamp: July 14, 2024, 03:32:50 pm
content: Quote from: mawyatt on July 14, 2024, 02:17:15 pmI'm using it for different purpose. It's a hold-down clamp for the PCBs for ICT testing, or fixture for the assembly process.This clamp is quite big. And yes it's more expensive. I'm guessing there will be a supplier in the far East making similar parts.

author: mawyatt
author_rank: Super Contributor
timestamp: July 25, 2024, 03:48:08 pm
content: While doing some LCR measurements for a member we encountered the typical uncertainty when using Kelvin Clips for small capacitance measurements.https://www.eevblog.com/forum/testgear/lcr-cal-test-pcb/https://www.eevblog.com/forum/testgear/sensitive-lcr-meter-measurements/We then utilized Guard capability (Hioki IM3536) with a conducting plate (PCBite Base) for the effective "Work Bench" this improved the small capacitance measurements considerably.This effort caused us to think about a means to utilize the Guard Function with other LCR Measurement "Tools" than just the Kelvin Clips.Here's the result, with the Guard Function enabled on the SMD Fixture shown in previous posts here. The area underneath the upper surface "Contact Area" was void of any conductors in the previous design, now that area is filled with conductor surface which can be driven by the LCR Meter Guard Function via the Guard 2 pin connector. Also added another 6 pin connector for the wires from the enclosed case.Will probably be sending this off soon for PCB fabrication.Best,

author: mawyatt
author_rank: Super Contributor
timestamp: August 10, 2024, 09:14:25 pm
content: PCBs V5A finally arrived. Made up a slurry of Cu fillings, solder and flux to coat the contact area surface to increase roughness. Then swapped out the previous PCB version 4R, and put everything back together.Results were outstanding. Here's some showing the 1 to 100 milli-ohm 2512 SMD devices captured with the IM3536 and Th2830 @ 1KHz with 16 average.Note date is wrong, should be 8/10/24Best,

author: Nominal Animal
author_rank: Super Contributor
timestamp: August 10, 2024, 09:25:51 pm
content: I would consider using silicone rubber (Sugru, perhaps?) to form a more pliable bumper, forming it at the end of a suitable threaded rod.Or print a bumber cone with the tip removed, and squirt a (spherical) droplet of low-durometer electrically safe silicone for the tip.

author: mawyatt
author_rank: Super Contributor
timestamp: August 10, 2024, 10:07:27 pm
content: Actually the Green tip is 3D Printed (PLA tho), along with the Grey Standoff box (also PLA) for the Plunger assembly. With the setup as shown there is just enough pliability between the Tip, plunger arm, box and spring tensioned screws underneath the PCB. You can adjust tension and range with lever arm nut arrangement.Silicone rubber would be better for the Plunger tip, but the 3D printed PLA Tip seems to work well for nowBTW this fixture even holds up to 8MHz even for higher Z components, just measured our 0603 C0G 4.7pF Ref Cap. Getting (4.6874pF @ 8MHz) 4.6991pF @ 100KHz with IM3536, agrees well with this posting here (see # 119), results @100KHz. Edit just measured with the TH2830 @ 100KHz with 4.68012pF!!https://www.eevblog.com/forum/testgear/east-tester-et3502-lcr-bridge/msg5597001/#msg5597001Just for fun we grabbed a 2512 SMD 1.0 ohm and these are the results Rs + Ls (milli-ohms/nH) with the IM3536.1K 10K 100K 1Meg 8Meg995.66/ 995.61/0.23 995.49/0.67 994.42/0.99 959.91/1.55Best,

author: EC8010
author_rank: Frequent Contributor
timestamp: August 11, 2024, 09:26:49 am
content: Interesting stuff. At the moment I don't have a need to measure SMD parts accurately, but the principles are nice to see - especially the roughened surface trick.By the way, it appears to be an informal standard that the BNCs on LCR analysers are all on the same spacing. Very convenient. My (cheapy) Hameg 8118 talks about guarding in its manual, but with only four BNCs and all of them bonded to chassis inside the instrument (let alone my jigs), I don't see there are enough electrical connections to use a guard. Or maybe I'm missing something?

author: mawyatt
author_rank: Super Contributor
timestamp: August 11, 2024, 01:16:14 pm
content: The surface "trick" really helps as we were having much more difficulty in getting contact with the DUT SMDs. This works well and the "trick" is getting the mixture of fine Cu fillings mixed with flux and solder right, we've trashed a few PCBs and still don't have an exact formula but found ChipQuick Sn63/Pb37 T3 with Mechanic Uv559 Flux works well whereas the Mechanic NS83 Solder Paste with said flux didn't.The Hioki IM3536 has all the 4 BNCs "floating" wrt to chassis ground, and a Guard Terminal (Banana 4mm) next to the Lcur BNC. The Tonghui TH2830 has the Guard Terminal on the instrument rear panel and is also isolated wrt chassis ground but apparently not as well "isolated" as the IM3536.We reported measurement improvement when using Kelvin Clips using the Guard connected to a large (300 by 200mm) conductive plate (PC Bite). After some thought this made sense as all the Kelvin Clips we own have the clip tip as a long blade thur the handle and this entire length is unshielded which is one reason for measurement variations when using the Kelvin clips handheld!! With the fields so exposed with the Kelvin Clips, having a large area at the Guard potential to terminate the fields helps reduce their effect and this directly shows in the measurements.Our quality Kelvin Clips from Tonghui (TH260011CS) are only rated to 100KHz, the common cheap types have no rating. We don't put much faith even in the quality clips when using higher frequencies since even a slight cable movement changes the readings, but do get better results using the Guard plate approach mentioned.Best,

author: Nominal Animal
author_rank: Super Contributor
timestamp: August 11, 2024, 03:24:44 pm
content: Quote from: mawyatt on August 10, 2024, 10:07:27 pmYep!I'm only worried about fracturing thin film resistors and multi-layer ceramic capacitors when the lever goes past the switchover point: if the tip is too hard, it might exert a very short spike of pressure, akin to tapping with a small hammer. I worry about this kind of stuff because I'm an uncle bumbleduck (in AvE's vernacular) who somehow manages to break things quite often, so playing it safe lets me use more of my small budget fornewstuff. (I like to do things like use rubber paint (the kind used to coat the bed on a truck) on the insides of my Hammond cast-aluminium enclosures, to avoid accidental shorts due to things shifting about... So do consider my suggestions as pretty firmly on the paranoid side. In my hands, stuff just seems to, uh,failoften. Me too.)

author: mawyatt
author_rank: Super Contributor
timestamp: August 11, 2024, 03:47:19 pm
content: There is a flexible 3D filament called TPU, we haven't used this so might be worthwhile to take a look.Understand the issue with concern about fracturing delicate SMD chips, having seen some of the fractured SMD chip caps like the one Dave had light up when testing a cheap PS.What's interesting about this approach with the split Kelvin Force and Sense approach where the "connection" between them is on the DUT end terminations rather than the at the fixture to DUT interface, is this requires minimal DUT contact pressure.We can't get any reasonable repeatability with sub 10 milliohm SMD with the Standard SMD fixture, but have little problem with the split Kelvin approach.Best,

author: gitm
author_rank: Regular Contributor
timestamp: August 12, 2024, 05:42:51 pm
content: Quote from: mawyatt on August 11, 2024, 01:16:14 pmI’m confused by this statement. When I view the mfg’s picture of the TH2830 back panel, it shows a connector marked with a ground symbol. I don’t see a “guard terminal”. Is the “ground” an actual ground or does it carry a guard signal?What is the resistance between the rear panel “ground” to mains ground on the power cord? I’m wondering, if it is really a ground, how much improvement you get connecting it to the guard on your fixture?BTW, very nice work on the fixture. I need one of these.

author: gitm
author_rank: Regular Contributor
timestamp: August 14, 2024, 01:22:14 am
content: Wondering what happened to this thread?

author: mawyatt
author_rank: Super Contributor
timestamp: August 14, 2024, 02:19:12 am
content: Quote from: gitm on August 12, 2024, 05:42:51 pmOn the TH2830 the BNCs and rear terminal are directly connected, from the rear terminal to the earth ground on the AC measured to one of our PS with earth ground terminal we get 3~4 ohms. So not a true Guard, maybe a choke involved but don't know. The Hioki IM3536 Guard is basically galvanically isolated from the earth ground.We haven't used the Guard on the TH2830 yet, but the the Guard on the Hioki provides an improvement in measurements when using Kelvin Clips & Cable as mentioned with a Guard Plate, however the Split-Kelvin SMD Fixture it's not as pronounced if any. Honestly we need to do more detailed testing to verify the improvement, if any, and how much. Time is limited as today was spent building up another DC Bias Adapter which uses a pair of ultra-high "Q" C0G capacitors to improve the high frequency performance and we need to see how well this works.BTW our lab is far from "electrically quiet" and we should be receiving some clip-on chokes for the Power Cords, Hioki recommends these for "noisy environments" and we'll see how well these work.Best,

author: tszaboo
author_rank: Super Contributor
timestamp: August 14, 2024, 11:30:45 am
content: Quote from: gitm on August 14, 2024, 01:22:14 amThere are two similar threads with the same pictures on this forum, that were recently active.I was also wondering, as I seemed to remember more pages.

author: mawyatt
author_rank: Super Contributor
timestamp: August 14, 2024, 11:58:40 am
content: Quote from: tszaboo on August 14, 2024, 11:30:45 amMaybe the links in post #21?Or this one: "Cheap SMD LCR Fixture, the Good , Bad and Ugly!" We used an "!" in title which causes a link issue, so do a search.Best,

author: mawyatt
author_rank: Super Contributor
timestamp: September 02, 2024, 07:30:16 pm
content: The Split-Kelvin SMA Fixture also works with a DMM requiring 4 BNC to Banana Adapters allowing Hcur, Hpot, Lpot and Lcur to be routed to the 4 Banana inputs of a DMM as shown.Here a 40 milli-ohm 1% 2512 SMD Current Sense Resistor is being measured with the 4 Wire Ohms capability of the Keithley DMM6500.Best,

author: mawyatt
author_rank: Super Contributor
timestamp: September 03, 2024, 12:02:50 am
content: Few more 1, 10, 15, 20, 25, 50 milli-ohms 1/2 and 1% 2512 Resistors.Best,

author: mawyatt
author_rank: Super Contributor
timestamp: September 03, 2024, 05:46:52 pm
content: Using same Split-Kelvin Fixture with DMM6500 as shown above, we used a KS34465A and made some measurements with same DUT Precision 2512 Resistors. Compare with aboveThink these agree well with DMM6500 measurements, and show the ability of this unique SMD fixture.Best,

author: mawyatt
author_rank: Super Contributor
timestamp: September 15, 2024, 02:19:57 pm
content: We've had some requests for the Gerber files for this fixture, and included the updated original (V4) and latest which has the Guard capability (V5), both work. Also included are the 3D files for the Plunger Tip, Base and Bottom Supports.If you intend to copy this PCB and fixture, be sure to study this entire thread to understand how the fixture operates and how it interfaces with a Bench type LCR Meter, also how to "roughen up" the contact surface for better connectivity. Note how the Plunger Mechanism is attached and operates, and the 3D custom tip and standoff which places the Plunger base above the PCB Surface.One should study the various LCR Meter threads related to this special Custom Split-Kelvin SMD Fixture and it's use, as this provides a good vision of the usefulness and capabilities.Anyway, hope some folks find this unique SMD fixture worthwhile, we're here to help if needed.BTW plans are to publish this unique fixture soon, stay tuned!!Best,

author: KungFuJosh
author_rank: Super Contributor
timestamp: September 15, 2024, 10:51:49 pm
content: The nylon screw was a success. No modifications, and the screw is flexible enough I can safely position it on 805 SMT stuff with no trouble.I did order the V5 PCB since I like the contact design better.Thanks,Josh

author: mawyatt
author_rank: Super Contributor
timestamp: September 15, 2024, 11:43:40 pm
content: Nice work JoshThat setup sure looks like it belongs on the IM3570What size nylon screw did you get?Best,

author: KungFuJosh
author_rank: Super Contributor
timestamp: September 16, 2024, 12:41:37 am
content: Quote from: mawyatt on September 15, 2024, 11:43:40 pmThanks! It is nice. Now that I have the nylon screw, it's very simple to use.I bought a 6-32 1" nylon screw set. This one:https://www.amazon.com/dp/B00NQR0GAIBought that one because next day delivery and my impatience get along well enough. 😉You would want a longer one if you're keeping the 10mm spacer.Thanks,Josh

author: KungFuJosh
author_rank: Super Contributor
timestamp: September 28, 2024, 10:14:58 pm
content: Today I built version 5A of Mike's SMT fixture. It looks great, I really like the new contact pad design.This time, instead of the cheap aliexpress clamp, I used the Adafruit 2459, and it's significantly better. The 2459 is smooth and easy to move, and holds its accuracy better.With a single finger and very little force, the 2459 can easily move through its full range. The other one stops pretty short before a second finger is needed to convince it to move further:With the Adafruit clamp, I used a 3mm spacer instead of a 6mm spacer.Thanks for the awesome design, Mike!

author: mawyatt
author_rank: Super Contributor
timestamp: September 29, 2024, 03:18:57 pm
content: Looks great, did you get a gold plated PCB?The Adafruit Lever Arm does look good, as the nylon bolts...good jobBest,

author: KungFuJosh
author_rank: Super Contributor
timestamp: September 29, 2024, 05:24:06 pm
content: Thanks! Yes to gold plate.I'm glad I bought that extra fixture from that link you sent me. I bought the kelvin clips and the slightly cheaper tweezers. The 5A is on the tweezer fixture.

author: Randy222
author_rank: Frequent Contributor
timestamp: September 30, 2024, 05:50:46 pm
content: The test fixtures look nice.Just for educational purposes, does the measurements using compression forces (smd to fixture, banana leads pushed into bnc adapter, bnc insertions, etc) show the same results vs soldering the ends of test leads directly to the DUT?

author: mawyatt
author_rank: Super Contributor
timestamp: September 30, 2024, 06:44:06 pm
content: Our experience suggest any type soldering causes DUT small changes due to applied heat. With this fixture the light pressure required doesn't seem to have any effect, likely due to the actual measurement technique since DUT contact impedance effects are highly attenuated, thus high DUT pressure not required.WRT the BNC and/or Banana connectors, these don't have any affect we can detect assuming quality connectors of courseBest

author: gitm
author_rank: Regular Contributor
timestamp: January 22, 2025, 04:55:02 am
content: @mawyatt: I just made a SMD testing fixture using your pcb gerbers and am pleased with the repeatability and stability of the measurements. Very nice design.I used a cheap $38 Aliexpress fixture as a donor for the box and BNC connectors with the plastic ears. I ground off the paint, added grounding wires, copper tape at edges and covering holes, and RG405/U coax to connect from the BNCs to the PCB board.I made repeated measurements on 50 different resistors (603 and 805 size) using a 3065X, CKT515A, and a BM789. Repeatability was very satisfying even when removing the resistors from the fixture and then putting them back in to measure again; measurements usually landed either with the last digit of the display the same or off by less than a milliohm. I was using each instrument with the highest precision settings it offered and took care to insert resistors the same every time. The 3065X statistics showed standard deviations on repeated measurements of 0.00017 to 0.00020 ohms on 29.40.1%, 620.1%, and 5600.1% resistors. For 2500.01% resistors, the standard deviations were consistently 0.0000008 to 0.0000010 ohms.This was a tremendous improvement over my previous attempt to measure these resistors with the unmodified Aliexpress fixture, where the contact resistance from the spring loaded contacts varied substantially, often changing by 10’s to 100’s of milliohms.Hats off to your excellent design.

author: mawyatt
author_rank: Super Contributor
timestamp: January 23, 2025, 03:12:46 am
content: Good looking fixture you've created, you went all out on the shieldingThat's some impressive results with the 250Ω 0.01% resistors with SD of just 1uΩ!!! If you want get some 2512 milli Ω level precision resistors, this also highlights the fixtures benefits. We couldn't get good repeatability with other fixtures/clips but did find this fixture gave excellent repeatability in the mill Ω regions. Did you "roughen up" the contact surface or just use the surface as is from PCB fab?Josh replaced the plunger with a nylon bolt which should reduce the parasitic capacitance due to the plunger bolt if you're going to measure small capacitance values (also ground plunger lever case). We haven't done this yet but likely will in future, need to remember next time we're in Ace Hardware to get a nylon boltBTW do you have a bench type LCR meter available? Edit: See your picture shows a Tonghui type LCR, but now model.Anyway, glad you found this fixture useful, hopefully others will tooBest

author: gitm
author_rank: Regular Contributor
timestamp: January 23, 2025, 02:32:51 pm
content: Quote from: mawyatt on January 23, 2025, 03:12:46 amWell, yes and no and back to yes. The PCB finish on the DUT pads were not flat from the factory due to the FR4 fiberglass construction/weave. This definitely caused connectivity variance when placing SMD components onto it. I started with your suggestion of how to roughen up the pads, but I couldn’t get copper filings to distribute evenly on a test copper pcb causing me to abandon this technique. I went to fine copper powder with a #320 mesh size (looks just like red flour.)I experimented awhile with different techniques and ended up using this: tinned the DUT pads with lead solder and lightly dusted the pads with the copper powder. This left a relatively uniform coating, but the molten lead solidifies with a rounded surface due to surface tension. I remelt and, using tweezers, thendraga piece of woven copper desoldering wick, wetted with liquid flux, across the whole pad without stopping, trying to remove as much molten lead as I can. This leaves a relatively flat, rough surface with the PCB’s FR4 fiberglass hills and valleys filled in. If I was unhappy with the finish (like stopping and leaving a ridge) I would just remelt and drag again. Or add more lead and dust again. This technique reminds me of the old method of auto body work using a molten lead mixture to fill seams and imperfections.Pics didn’t work as expected, so attaching at the end. IMG_1638 is the factory PCB finish and IMG_1634 is the final result.ETA: IMG_1642 is a better pic of the final result.I have another experiment to do where instead of dusting the copper powder directly (actually using bulb to blow it), I put a fine metal mesh over the pads and dust over the top of the mesh. I’m waiting for the mesh to arrive.Quote from: mawyatt on January 23, 2025, 03:12:46 amI haven’t broken the LCR meters out yet; I really wanted repeatable resistance measurements for a project of mine. What you’re seeing is the CKT515A precision resistance meter, made/branded by Changzhou Chuangkai Electronic Co., Ltd. However, I have just bought a EUCOL U2832 LCR meter, which appears to be a very close relative to the Tonghui TH2832 with almost identical specifications. CKT has some kind of relationship to Tonghui, as CKT's web site does list Tonghui products, but it’s all a bit nebulous.

author: mawyatt
author_rank: Super Contributor
timestamp: January 23, 2025, 03:49:41 pm
content: Interesting, the fine Cu powder seems like a better solution than our Cu filings approach. Where did you get the fine Cu powder?Josh got his 2nd batch of PCBs with Gold, would be interesting to see which approach produces better repeatability.BTW most folks don't know how difficult getting repeatable results in the mill Ω region with small SMD can be. Your results are certainly impressive!!Best

author: gitm
author_rank: Regular Contributor
timestamp: January 23, 2025, 04:20:18 pm
content: Quote from: mawyatt on January 23, 2025, 03:49:41 pmAmazon.https://www.amazon.com/gp/product/B0CZ9SGDG7/ref=ppx_yo_dt_b_asin_title_o00_s01?ie=UTF8&th=1Thought about gold too, but it would have to be hard gold and not ENIG.

author: ZGoode
author_rank: Frequent Contributor
timestamp: January 23, 2025, 06:09:44 pm
content: I've been trying out copper powder from our LPBF printer for this. Currently, I'm waiting on a new batch of PCB's to apply this to before I take some measurements. If anyone is interested I could try and send some to people for testing (just pay for shipping (and probably USA only, not sure how customs would handle this)). This stuff has pretty tight size tolerances and is nearly pure. I don't remember the exact metallurgical compound, but I do know it is 40um particle size +/- 5um.

author: mawyatt
author_rank: Super Contributor
timestamp: January 23, 2025, 08:21:49 pm
content: This is getting interesting indeed!!How these various Copper filings and powders improve surface connectivity to the SMD end terminals vs the standard PCB surface prep should be of interest too many folks.For the Short Calibration we use a cut piece of thin Copper plate same size as 2512 Resistor, this has worked well and has good repeatability.Best

author: Kean
author_rank: Unknown
timestamp: January 24, 2025, 06:29:23 am
content: The copper powder seems like it would just get "absorbed" into the solder, but I guess some gets left behind after the wicking to leave a rougher surface.Another option that might be worth a try is gold plated SMD pads used for probing. I have some, but not yet ordered any of Mikes SMD fixture PCBs.Look on Digikey under Spint Loaded Contact Pad. This link might work for you, then filter by type Contact Pad. Many different sizes.https://www.digikey.com/en/products/filter/contacts-spring-loaded-pogo-pins-and-pressure/311

author: mawyatt
author_rank: Super Contributor
timestamp: January 24, 2025, 03:02:33 pm
content: Quote from: Kean on January 24, 2025, 06:29:23 amThose gold plated contact pads look interesting, seems one could use such for the Zero Ohm Calibration DUT!!Best,

author: Nominal Animal
author_rank: Super Contributor
timestamp: January 24, 2025, 11:20:04 pm
content: Harwin S70 series of contact pads for pogo pins are rated at 0.15mΩ max contact resistance. Mouser lists them underPassive Components>EMI Filters / EMI Suppression>EMI Gaskets, Sheets, Absorbers & Shielding; for exampleS70-125161545R(2.5×1.6×0.15mm, 6.0A max, 0.050µm gold over 2µm nickel over beryllium copper;Harwin product page).I wonder if these are too hard? The gold layer is definitely shallow; a thicker layer of pure gold with a fine pattern would be quite soft and malleable as a contact. Gold leaf is too thin also (typically on the order of 0.1µm).Here's an utterly crazy idea: Use short lengths of pure gold (99.9%, 24 karat) #18 to #28 gauge wire. These are sold in jewelers' supplies, and aren't as expensive as one might think (about 2€ per mm, depending on the gauge).

author: gitm
author_rank: Regular Contributor
timestamp: January 28, 2025, 01:44:56 am
content: Just closing off the copper screen comment I made above. For those wanting a more evenly distributed, finer grain but rough finish on the PCB SMD pads , I tested the following modification to the technique described above, producing pretty good results.Changed from lead solder to ChipQuick NC191LTA10 Sn42/Bi57/Ag1 No-Clean T4 and ChipQuick CQLF4 No-Clean liquid solder flux.Make a powder dispenser using an empty bottle, e.g. old pill bottle, partially fill with #320 mesh size copper powder and put a #200 mesh size copper screen over the top, secure with a rubber band. You could use a finer screen for more control at the expense of time.Wet pads with solder flux. My PCB was HASL finished.Lightly dust pads with copper.Touch soldering tip (400C) to pad letting heat move through the pad.Add a tiny dab of solder paste, melt with iron and let it spread across the tab. If it looks like there’s excess solder, use a wetted solder wick to remove excess.Wipe with IPA to clean loose copper and flux before repeating.Repeat the above steps to get the desired surface finish you’re looking for.Picture of finish after 4 iterations is attached. EZ-Peasy.With the above said, I haven’t tested whether this finish will produce more repeatable measurements than my first board, which produced excellent results (I’ll post those once I type them up.)

author: RoGeorge
author_rank: Super Contributor
timestamp: January 28, 2025, 07:50:37 am
content: Would be interesting to see if the surface ruggedness can survive after repeatedly pressing components against it.I wonder if self-adhesive foil, copper or aluminium, laid on a rubber substrate (instead of FR4) would work.The hope with that would be to get the equivalent of a "rubbery" metal, but I didn't try.

author: mawyatt
author_rank: Super Contributor
timestamp: January 28, 2025, 03:08:14 pm
content: The pressure involved is very slight since the end terminals of the DUT make the Force and Sense connections on each end of DUT, thus the DUT Contact pressure/resistance for the Force current signal becomes much less critical. The Sense terminal has such a high relative impedance that the DUT Contact pressure/resistance is also much less critical.These effects make the wear on the physical DUT contact area on the PCB much less critical than a normal measurement. If wear does take a toll on the measurements then one can just resurface the area again, but haven't had to do this yet after many thousands of engagements/measurements.The PCB design is such that one could use a connector (it's laid out for this), but we just soldered the 4 wires directly. This appears the same for gitm and Josh uses as well. The only component on the PCB is just the connector which is a cheap JST type, so one could just swap out the PCB after surface wear out as they are throw away cost-wise.Josh used a gold plated process for the PCB which could wear thru and require PCB replacement but suspect this would be after many many uses and then the PCB could simply be replaced as mentioned, the PCB would cost more but still in the throw way price range.For those that have a quality bench type LCR Meter or quality DMM and want highly repeatable measurements with SMD DUTs, this "Split-Kelvin Technique" just works, and even more so with low Z milli Ω DUTs.Best

author: gitm
author_rank: Regular Contributor
timestamp: January 28, 2025, 09:15:34 pm
content: Repeatability with low Z resistors:=====================I wanted to know, in general, how repeatable are measurements using the fixture in both time and position of the DUT on the SMD pads. That is, knowing what to expect and how much attention is needed to what details? Of the things I could control were measurement setup, warm up time, and the environment as found. Although tested in a “controlled” environment, I only have limited, indirect control of instrument repeatability through it’s configuration and warmup.I imagined a big part of repeatability is consistent contact resistance which would vary depending on SMD pad flatness/contact area with the DUT and where the DUT ended up on the pads. So the testing was setup to explore this point.Procedure:Use 4 “precision” low Z resistors: 1 milliohm, 10 milliohm, 100 milliohm, 2.4 ohm, all in 2512 size. Note: the 100 milliohm “metal element” resistor’s tappered contacts required a bead of solder to be layed down on the resistor’s underside; without this bead, there was no contact made with the SMD pads at all.Use a “precision” low resistance meter CKT515A and SDM3065X (a.k.a., use what you got) The 3065X is not really suitable for measurements 100 milliohms and below due to a +/- 0.005% of range specification, but still informative for measurement variations; it’s 200 ohm minimum range translating to +/- 10 milliohms deviation and still in specification. Due to this, measurements were grouped only once for each milliohm resistor on the 3065X, while CKT515A had many more measurements.Measurement “groups” would be made alternating between the CKT515A and 3065X to require the fixture be repeatedly detached and attached from one to the other. After all, this would happen in the real world.3 hours warmup with both machines powered on during testing across 48 hours.Each instrument was configured for high(er) accuracy, e.g. 16 averages, 100 NPLC, statistics turned on with 25+ measurements, relative on, etc., ensuring stable readings and no drift.The 1, 10, 100 milliohm resistors would be measured at various times over two days in groups of 6 measurements, with each measurement in a differing location from the last. The locations were named “center”, “right”, “down”, “up”, and “left”. “Center” placed the 2512 resistor centered directly over where the four corners of the pads meet so that equal resistor dimension were over all four pads. “Up” and “down” were horizontally centered but 2/3 of their height placed above or below, respectively, of the horizontal center line with the 1/3 on the other side. Similarly, “right” and “left” were 2/3 to the right or left, respectively, of the vertical center line.The sequence of resistor placement was center, right, down, up, left, and back to center, for 6 measurements. This gives some insight into location dependance on the reading value and direct comparison for the center to center measurement variance. For CKT515A measurements, each resistor had the group of 6 measurements repeated twice on the same day but 6 hours later.2.4 ohm readings were performed immediately before and after each of the milliohm resistor groupings across the 2 days. No significant attention was placed on placement other than what one might when casually inserting into the fixture. This 2.4 ohm resistor has been measured many times before this test and it’s value well known, averaging 2.4078 ohms previously measured overnight with +15k readings.Compile measurements and compute basic stats.Results:To me, the most telling metric on repeatability is the extreme spread (span) on the milliohm resistors since contact resistance variation would be a more significant value when compared to the actual resistor value and be more readily apparent. The tables below show the span and % of the mean for the milliohm measurements. The attached screenshot also shows each’s position readings one above the other which helps in showing (or not) of any patterns due to position.———————————1 milliohmCKT515A 20 mΩ range => 0.1%*Rd + 0.0025%*Rg => +/- 0.0015 mΩCKT515A 1 mΩ max span:0.0060 mΩCKT515A 1 mΩ min reading:0.9809 mΩCKT515A 1 mΩ max reading:0.9869 mΩCKT515A 1 mΩ mean reading:0.9830 mΩCKT515A 1 mΩ span as % of mean:0.6104 %———————————10 milliohmCKT515A 20 mΩ range => 0.1%*Rd + 0.0025%*Rg => +/- 0.0105 mΩCKT515A 10 mΩ max span:0.0210 mΩCKT515A 10 mΩ min reading:9.9792 mΩCKT515A 10 mΩ max reading:10.0002 mΩCKT515A 10 mΩ mean reading:9.9900 mΩspan as % of mean0.2102 %———————————100 milliohmCKT515A 200 mΩ range => 0.1%*Rd + 0.002%*Rg => +/- 0.1040 mΩCKT515A 100 mΩ max span:0.0530 mΩCKT515A 100 mΩ min reading:100.0010 mΩCKT515A 100 mΩ max reading:100.0540 mΩCKT515A 100 mΩ mean reading:100.0197mΩspan as % of mean0.0530 %———————————For the 2.4 ohm resistor, the 3065X was not nearly as hindered by it's accuracy specification of 0.005% * 200 ohm range; it performed very well with an extreme spread of only 0.5 milliohms for 7 measurements over 2 days.CKT515A readings on 2.4 ohms had a span of 2.3 milliohms or +/- 1.15 milliohms. It’s accuracy spec for the 20 ohm range is 0.02% of reading + 0.002% of the 20 ohm range, or +/- 0.880 milliohms, putting it some 270 micro ohms above it’s spec.To be honest, I think this test was a worst case scenario but still relevant to understand how well the fixture works. And I am very pleased with it. Great design.Attaching screenshot of measurements taken and resistor specifics along with two pictures. One picture being the testing pads after some 100+ measurements. There doesn’t appear to be signs of wear, not that I was expecting any. The second picture is a more oblique picture of the new PCB fixture pads to get a better perspective of the new rougher texture; I feel the close up posted above in my other post doesn’t convey how subtle yet rough it actually is — very grippy on the finger.

author: Nominal Animal
author_rank: Super Contributor
timestamp: January 29, 2025, 12:44:53 am
content: Quote from: gitm on January 28, 2025, 09:15:34 pmNote that it would be more useful to use median (50th percentile; the value where half the measurements are below, and half above) here, as usual: mean is unduly affected by outliers.

author: gitm
author_rank: Regular Contributor
timestamp: January 29, 2025, 02:05:24 am
content: Quote from: Nominal Animal on January 29, 2025, 12:44:53 amGood thought which I had too. Between using median and using mean, I chose mean because the distribution on the data was pretty symmetrical. Median would have been my choice if the distribution was skewed. But being pretty symmetrical, using mean would highlight a small number of outliers, if present, which, to my mind, is more descriptive.ETA: The reason it’s more descriptive is that the testing is looking for some noticeable change in a reading that should be fixed and might show up only in a minority of or even just 1 sample. I.e., the sample that gives information about the fixture’s repeatability, like where a location had inconsistent contact resistance. Mean, as you note, isunduly affected by outliers, but medianignores those few or even 1 outlierthat I’m looking for. Hope this clears up my point.See next post.As a practical matter, it’s moot as the calculation using either mean or median return essentially the same results with the distribution being as symmetrical as it was.For example:1 milliohm: mean=0.9830, median=0.9826, and span as % = 0.6104% and 0.6107% respectively.10 milliohm: mean=9.9900, median=9.9904, and span as % = 0.2102% and 0.2102% respectively.100 milliohm: mean=100.0197, median=100.0310, and span as % = 0.0530% and 0.0530% respectively.I also considered comparing the span to the anticipated span (I won’t use “expected” due to its mathematical definition) based on the accuracy specifications for each range, but the calculations were a bust with 2 out the 3 results having essentially the same span either way. The third was only 3 micro ohms over with the measured span of 6 micro ohms. I might have had to make many, many more measurements to pull out any difference. In the end though, I think it all points to the fixture enabling very repeatable measurements.

author: gitm
author_rank: Regular Contributor
timestamp: January 29, 2025, 02:26:06 pm
content: Quote from: Nominal Animal on January 29, 2025, 12:44:53 amThank you Nominal Animal.Having slept on this, I’m going to reverse myself and agree with you.Median would be more useful. The outliers I’m looking for are captured in the extreme spread (span). Ideally, I want to compare this value against the resistor’s “true” value. But we don’t have a “true” value, we have only mean and median values. In this testing, the median does appear to be closer to the “true” value than the mean.Why? All measurements would have contact resistance included. The key aha moment was to realise there’s a practical lower limit on contact resistance, but the upper limit is essentially unbounded. In a perfect world with perfect contact on all measurements, mean and median would be equal and the measured resistance would be at a minimum within the uncertainty of the instrument’s capability. But as reality creeps in and contact resistance inexorablyincreasesin an almost random pattern, it still can’t go below the lower limit. The measurements would thus be skewed above resulting in the median trending lower than the mean and closer to the “true” value.It boils down to wanting the outliers in the extreme spread but not in the estimate of the “true” value. In this context, median is more useful. Thus outliers would be more apparent using median over mean.Took me a while to see it. Thanks.

author: Nominal Animal
author_rank: Super Contributor
timestamp: January 30, 2025, 05:08:04 am
content: Well, I can accept both arguments myself, as it really is about what information you consider most useful and important to convey to others.I mostly deal with noisy datasets (with obviously erroneous measurements), especially microbenchmarking results for various algorithms (where events external to the benchmark will occasionally affect the measurement, and such errors are always relatively large, as there is a minimum duration for any kind of interruption in the benchmark), and have found the most useful report to be ofk'th percentiles; as in, 97% of all runs completed within timeT. The percentile I choose reflects my trust in the measurement setup; the higher, the more repeatable/reproducible (and thus better) the setup.For other kinds of measurements, giving the actual distribution (or histogram) of measurement is best, of course; that way one can best compare reproduced measurements, and any asymmetry and deviation from standard/Gaussian distribution tells something about the measurements and the values being measured. The next best thing, in my opinion, is form \$m^{+a}_{-b} ~ (p\%)\$, where \$m\$ is the median, and \$a\$ and \$b\$ are the symmetric \$p\$'th percentile error bounds. That is, \$p\%\$ of all measurements were between \$m-b\$ and \$m+a\$, inclusive; with \$(100-p)/2\$ percent of measurements below \$m-b\$, and \$(100-p)/2\$ percent of measurements above \$m+a\$. While the standard 68.3% error bars are well suited for standard/Gaussian distributions, one can choose a much larger \$p\$ to describe ones confidence in the testing methodology: the higher the \$p\$, the fewer measurements are rejected, and therefore the better the confidence in the implementation of the measurements.I'm not a metrologist, I only watch an occasional Oxtools and Joe Pie videos on Youtube. In all my posts in this thread, by "useful" I have meant "useful to those like myself, who use the reported numbers to build up an intuitive understanding of the properties and limits of this method/apparatus/approach". If I've understood correctly, the numbers you/gitm have reported, \$p = 100\%\$, with \$\text{span} = 100\% \cdot (a - b) / m\$, and \$m\$ also reported. To get a correct mental picture of the limits of the distribution, leaving its shape unspecified, and what kind of measurements one would "expect" if constructing similar setup, itwouldbe intuitively easier if \$m\$ refers to median, and not the mean. If you think about it,for that purpose, using mean for \$m\$ makes it quite difficult to wrap ones mind around what it means to the entire distribution of measurements.Furthermore, if \$m\$ is mean, then all comparisons to the result someone else got from duplicating the measurements,mustbe based on the mean also. (Having distributions/histograms, and knowing the median, is then useless information and not worth gathering.) Which is okay, if that is the way the equipment works, or how it has to be done in practice (by convention, or for some other reason).Mean differs from median only when the distribution is asymmetric (wrt. median). For all symmetric distributions, mean = median. The difference between mean and median depends on the asymmetry and width (deviation) of the distribution. Thus, if you repeat an experiment (getting a set of results you wish to compare), and your errors have a different distribution than the one you are comparing to, the two mean will differ from the median by different amounts. Then, the error bars will also include different portions of the two distributions, neither centered on the middle of the distribution! Essentially, you are comparing apples to oranges. And without knowing the median on both, we cannot even tell we're comparing apples to oranges, because we don't know how much each mean differs from the median. Essentially, the entire distribution becomes un-useful information, and we can only compare the two means.Which, again, is acceptable if metrologists always work with mean/average, and never even look at the actual measurement distributions/histograms and consider those non-useful. If everything you can compare to is mean/average-based, then having a histogram or distribution –– or thinking in such terms! –– is useless and extra unneeded work for nothing.

author: gitm
author_rank: Regular Contributor
timestamp: January 30, 2025, 03:01:44 pm
content: Your point is well taken.

author: Nominal Animal
author_rank: Super Contributor
timestamp: January 31, 2025, 07:03:20 am
content: Of course, when using \$p = 100 \%\$ as you have, my "only part of the distribution" argument does not hold. Then, if mean is what is typically used, then it makes more sense to use that, to keep results comparable. Median does have the benefit of describing the "center" of the distribution, unlike mean, so median-based results from completely different distributions are still directly comparable.Don't let my excess verbosity look like certainty! It's just an affliction I'm working on.

author: gitm
author_rank: Regular Contributor
timestamp: January 31, 2025, 01:39:10 pm
content: Yes, but it did help understand the distinction between how you were using “useful” and how I used it. It’s good to have these discussions otherwise I wouldn’t have thought twice about mean vs. median.For my purposes, I believe I have an understanding of how the fixture helps with repeatable measurements. Did I mention I like it very much?

author: mawyatt
author_rank: Super Contributor
timestamp: January 31, 2025, 04:17:41 pm
content: We found the Vishay WSL2512 Zero Ohm (Mouser 71-WSL251200000ZEA9) as a good Zero Ohm Reference with our Split-Kelvin Fixture. These have shown as good as the solid Copper thin plate cut to a 2512 size that we normally used in the past.The WSL routinely produces <10uΩ (SD ~6uΩ) residual with the Fixture on our DMM6500 without any meter compensation.What Zero Ohm Reference are you using, and what uncorrected residual do you see?Best

author: gitm
author_rank: Regular Contributor
timestamp: January 31, 2025, 09:30:30 pm
content: Neat part! Didn’t know it came in “0”.My “zero ohm reference” is solid 16 AWG copper wire, flattened in a press, trimmed to 2512 size, and then finished on both sides with 2000 grit diamond stones at 0.0227” thickness. This was to match the 2.4 ohm 2512 resistor (0.0238”). Final dimension is 0.250”x0.120”x0.0227”. Picture attached with it next to 2.4 ohm resistor.As for uncorrected measurements (CKT515A again): N=20, median=7.7µΩ (I’ve seen the light), mean=8.2µΩ, ES (span)=3.3µΩ, sigma=1.1137µΩ, min=6.9µΩ, max=10.2µΩ.Screenshot of actual measurements attached. Order of measurements is left-to-right, top-to-Bottom. Each measurement was taken by removing the 0 ohm reference and re-placing in a slightly different position.

author: mawyatt
author_rank: Super Contributor
timestamp: February 15, 2025, 09:32:31 pm
content: Here's our latest rendition of the Split-Klevin Adapter tailored for 4-Wire Bench DMM use. Initial test results are good, altho we are considering direct wiring to the Banana Jack rather than to a Spade Lug.Best

author: mawyatt
author_rank: Super Contributor
timestamp: February 16, 2025, 01:36:56 am
content: After thinking about using the spade lugs to attach to the Banana Jacks we decided to consider soldering wires directly to the Jacks rather than use the lugs. Reasoning was that the lugs only made electrical contact to the Jacks on one side since the Jack "Bolt" snugs up against the PLA plastic of the 3D Printed case, whereas normally the lugs make contact on both sides. The cheap Banana Jacks accept solder (claim Gold plated ??) and this seemed an easy improvement since it should also reduce the electrical interfaces of wire to lug to Bolt to Banana Jack to simply wire to Bolt to Banana Jack.Anyway, here's what it looks like, note the Green Wire Ground with Black Banana Plug plugged into LF. Too early to tell if any of this is worthwhile since the best solution for low Z components is high test currents like the specialized Lab Grade Bench type Milliohm Meters. Higher is better because the sense voltage is higher with better SNR and less uncertainty.Edit: After a few measurements last night and this morning of a Precision 1.00mΩ 2512 SMD Resistor we see repeatability within ~4uΩ on the DMM6500 on 1Ω Scale. We also see good repeatability on our 3 KS34465As on 100Ω Scale within ~10uΩ, and the 3 agree within ~50uΩ with each other and ~55uΩ with the DMM6500. If the older KS (Tan Case) is removed, then the 2 other KS (Black Case) are within ~15uΩ readings, and within ~25uΩ of the DMM6500. Not scientifically rigid measurements but good enough to show how this SMD fixture helps with low Z DMM measurement repeatably, even with DMMs not known for good low Z measurements.Best

author: Kean
author_rank: Unknown
timestamp: February 17, 2025, 05:05:14 am
content: Nice work.I was going to ask for a link to those banana posts/plugs, but I grabbed a snippet of your image of just the "gold plated" parts, and pasted it into AliExpress image search to get some useful results.It is actually amazing the accuracy and speed of the search results, both listing near identical items and some very similar brass refrigeration/AC fittings. It is not like they can index things like with a word search.

author: mawyatt
author_rank: Super Contributor
timestamp: February 17, 2025, 01:48:11 pm
content: That's interesting about the AliX Image search, did not know about that...thanks!!WRT to the Banana Plugs, only the blades are magnetic. Not sure what metals or plating are used on the plugs but they are solderable. The threaded parts seems to be cast rather than machined threads, sort of sloppy, but intended to engage stranded wires. Also you can engage another 4mm Banana plug into the threaded "Bolt" open end. Not Metrology grade, but good enough for our needsIf you decide to construct one of the Split-Kelvin Type Fixtures, we're sure you'll be impressed with the results.Best