4 wire measurement of a 0402 chip resistor - Page 1
Forum section: electronics / general

author: DeepLink
author_rank: Regular Contributor
timestamp: October 30, 2023, 07:16:47 am
content: I need to measure the resistance of a 0402 chip resistor - before and after reflow solderingThe resistor will not be soldered to a PCB, just go through the oven to be heatedI need it done by a 4 wire measurement, as the resistance is low and I need the accuracyMy kelvin clips are to big for a reliably connection on such a small componentAre there any fixtures that can be used for this task?

author: Psi
author_rank: Super Contributor
timestamp: October 30, 2023, 08:30:52 am
content: Do you want like a ZIF socket for a 0402 part with 4wire measurement ?I suspect any difference you detect caused by the oven process will be smaller than the difference you get just having it mounted vs not mounted on a PCB, ignoring the heating involved in doing that.

author: wraper
author_rank: Unknown
timestamp: October 30, 2023, 08:33:45 am
content: Make PCB test pads for 4 wire measurement.

author: PartialDischarge
author_rank: Super Contributor
timestamp: October 30, 2023, 08:35:14 am
content: Quote from: wraper on October 30, 2023, 08:33:45 amExactly, in the final application the resistor will be soldered so best to mimic the same conditions

author: DeepLink
author_rank: Regular Contributor
timestamp: October 30, 2023, 05:39:01 pm
content: Quote from: Psi on October 30, 2023, 08:30:52 amYes, a "ZIF" socket would fit my needs, but I can't find anyIt is not possible to solder the resistor to a PCB to measure, as I need to measure before solderingThe resistor is a 49.9 Ohm 0.1% TC10According to the datasheet "Resistance to Soldering Heat - ΔR±0.2%"In production we are seeing some PCB's where the resistors are outside these tolerances, so we need to figure out weather it is the initial resistance or the reflow process that are giving us problemsWe have the temperature under control and the equipment to measure correctly, but simply need a fixture

author: mendip_discovery
author_rank: Super Contributor
timestamp: October 30, 2023, 05:39:55 pm
content: Make smaller kelvin clips.Or buy something like this,https://uk.rs-online.com/web/p/lcr-meter-accessories/1235980It is for an LCR meter but should also do the job neatly for you.I have seen some of Ali for less and from Rohde for a lot more.

author: coppice
author_rank: Super Contributor
timestamp: October 30, 2023, 05:43:35 pm
content: If your resistor is a low enough value to worry about the effects of the copper traces try looking athttps://www.analog.com/en/analog-dialogue/articles/optimize-high-current-sensing-accuracy.html

author: Nanitamuscen
author_rank: Contributor
timestamp: October 30, 2023, 06:32:25 pm
content: It is possible to make a 4-wire seat on the printed circuit board, covered with gold, on which the investigated resistor is easily pressed from above.

author: mawyatt
author_rank: Super Contributor
timestamp: October 30, 2023, 06:52:41 pm
content: Might be possible with something like this.https://www.eevblog.com/forum/projects/different-type-lcr-smd-fixture/Altho we haven't measured any 0402 components, works OK for larger SMD devices.Best,

author: Psi
author_rank: Super Contributor
timestamp: October 30, 2023, 09:46:48 pm
content: Maybe you could modify this 0402 flip top capacitor aging test jig to be a 4 wire resistor tester by linking one of the other 0402 channels together at the right spot to be the measurement circuit.https://www.aliexpress.com/item/4000129421329.htmlOr maybe message that seller and ask if he has any 0402 4-wire measurement jigs. He look to be in that industry of 0402 jigs. Only 85.7% positive feedback though, so YMMV

author: PartialDischarge
author_rank: Super Contributor
timestamp: October 31, 2023, 06:01:53 am
content: Quote from: DeepLink on October 30, 2023, 05:39:01 pmThis is actually an interesting problem that probably few have taken a look at. Maybe even the small size of 0402 makes them more prone to variations compared to 0603 or 0805.Let us know what you find.

author: guenthert
author_rank: Frequent Contributor
timestamp: October 31, 2023, 07:38:52 am
content: Quote from: DeepLink on October 30, 2023, 05:39:01 pmWhat does that mean? Is here with 'R' truly the electrical resistance meant?

author: DeepLink
author_rank: Regular Contributor
timestamp: October 31, 2023, 08:51:51 am
content: Quote from: mendip_discovery on October 30, 2023, 05:39:55 pmWe do have such a fixture for our LCR meter, that is a 2 wire connection to the DUT

author: DeepLink
author_rank: Regular Contributor
timestamp: October 31, 2023, 08:58:12 am
content: Quote from: guenthert on October 31, 2023, 07:38:52 amThis simply means that the resistance can shift +/- 0.2% from its initial value, after being reflowed

author: Psi
author_rank: Super Contributor
timestamp: October 31, 2023, 08:58:45 am
content: Could you make a 4-wire test PCB that you solder the part to before hand using ultra low melt solder, like 118°C stuff.Then expose to full reflow temp and retest after.

author: JodelJonny
author_rank: Contributor
timestamp: October 31, 2023, 09:11:29 am
content: Wouldn't all kinds of clamping pressure affect the resistance as well?Mercury would qualify as ultra low melting point solder, wouldn't it?

author: Psi
author_rank: Super Contributor
timestamp: October 31, 2023, 11:21:19 am
content: Quote from: JodelJonny on October 31, 2023, 09:11:29 amGallium maybe, i think you're pushing it with mercury.

author: Kleinstein
author_rank: Super Contributor
timestamp: October 31, 2023, 12:47:52 pm
content: Getting a proper 2 wire contact to the small pads is tricky. This applies also to the PCB the resistors are used in. The solder and exact position on the PCB can effect where exactly the current flows or voltage is taken from. The same applies to the test jigs , the one at the manufacturer to trim / test the parts and the 2nd jig for the test before soldering.The idea with essentially all solders is getting some alloying to the material. So it can be undone fully. Mercury and also gallium are quite keen to react with other metals.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: October 31, 2023, 06:44:48 pm
content: I'd just make the connections very close to the probe tip and not worry about trying to get separate connections right on the resistor.

author: mawyatt
author_rank: Super Contributor
timestamp: October 31, 2023, 06:48:04 pm
content: An 0402 will be a challenge for 4 wire resistance measurements, and maybe the best approach is to use the SMD fixture for LCR meters.Best,

author: jbb
author_rank: Super Contributor
timestamp: October 31, 2023, 07:09:19 pm
content: Quote from: Nanitamuscen on October 30, 2023, 06:32:25 pmQuote from: JodelJonny on October 31, 2023, 09:11:29 amHmm, sounds like some kind of squishy conductor might help. Maybe some Z-axis tape would help? These have little metal conductors and conduct through the tape (Z direction). But not across the tape (XY directions).Possible option:https://www.adafruit.com/product/1656

author: coromonadalix
author_rank: Super Contributor
timestamp: October 31, 2023, 07:13:42 pm
content: https://www.ebay.co.uk/itm/Four-Wire-Kelvin-Test-Tweezers-with-4x-BNC-for-LCR-Meters-Component-Testers-/264074739210

author: mawyatt
author_rank: Super Contributor
timestamp: October 31, 2023, 07:23:27 pm
content: Quote from: coromonadalix on October 31, 2023, 07:13:42 pmWe got an equivalent of these long ago, they tended to be very difficult to use. Later acquired the Tonghui TH26009B style, these were much easier to use, but more expensive.Best

author: mawyatt
author_rank: Super Contributor
timestamp: October 31, 2023, 07:50:33 pm
content: Quote from: JodelJonny on October 31, 2023, 09:11:29 amThat's a good question and one we had awhile back wrt to measuring SMD very low impedance values. The LCR fixtures and tweezers we have all suffer form the variations in applied pressure, including the "Zero" ohm calibration.When we set out to develop the "Plunger" type SMD fixture shown (see above link), one of the goals was to achieve better repeatability than what we had seen with the LCR SMD fixture and tweezers (even the better Tonghui ones mentioned) with low Z DUTs.This is still an ongoing developement, but highly encouraging results have been achieved. We've been able to measure quality low impedance (milliohm levels) with very good repeatability, even into the sub-milliohm regions. The main reason for this level of repeatability is that the Force and Sense leads from the LCR meter aren't terminated at the fixture connection point like conventional fixtures, but the connection between Force and Sense is made with the DUT SMD end terminations. So in effect the DUT itself is making the connection between the Force and Sense which dramatically reduces the contact impedance, pressure, surface, and orientation sensitivity of the fixture to the DUT.Still need to perform more work and get gold plated PCBs, will provide more details if folks are interested.Best,

author: DeepLink
author_rank: Regular Contributor
timestamp: November 01, 2023, 06:38:21 am
content: Quote from: coromonadalix on October 31, 2023, 07:13:42 pmUnfortunately, this is still a 2 wire connection to the DUT. We do have such a tweezer, but readings are quite unstable and very dependent on applied pressure

author: PartialDischarge
author_rank: Super Contributor
timestamp: November 01, 2023, 07:55:15 am
content: Quote from: DeepLink on November 01, 2023, 06:38:21 amThis is why you should make a test board with the resistor soldered. I would use first the lowest temp possible and then apply heat with a gun and see how reversible or not the effect of heat is.

author: coppice
author_rank: Super Contributor
timestamp: November 01, 2023, 01:31:25 pm
content: I don't think the OP has defined what they mean by a low resistance. What works well for hundreds of milliohms can work very poorly for the one milliohm or less resistors people widely use as things like shunt sensors. At a milliohm or less EVERYTHING is significant part of the impedance. I've never successfully measured an SMD resistor that small without is being soldered to a PCB that is tracked to make a 4 wire connection, following the guidelines inhttps://www.analog.com/en/analog-dialogue/articles/optimize-high-current-sensing-accuracy.html. We did our own research, and came to the same conclusions as those guys at Analog Devices, but they published their note just before we published ours, making our pointless. We had covered exactly the same ground, probably for similar reasons, and got exactly the same results.

author: mawyatt
author_rank: Super Contributor
timestamp: November 01, 2023, 02:42:31 pm
content: Quote from: coppice on November 01, 2023, 01:31:25 pmThat's an excellent article, must read for anyone trying to achieve high accuracy low Z SMD measurements/uses.Thanks for posting!!BTW the crude SMD fixture mentioned earlier isn't too bad wrt to low value SMD resistor measurements. We have a few somewhat precision 2512 SMD resistors used to check things, of course these are 2512 and not 0402 the OP referenced. This is just used for sanity checks, and the fixture still needs additional effort as it's not totally foolproof!!Anyway, here's a few measurements just for reference, and related to earlier measurement from over a month ago, mainly to show some repeatability and consistency between various instruments and repeat measurements.All in milliohms:Resistance TH2830(10/31/23) TH2830 (9/27/23) IM3536 (9/28/23) DMM6500 (9/28/23)5 4.99910 10.001 9.949 10.04 10.026215 14.919 14.97 14.86820 20.003 20.06 20.01640 39.965 39.848 39.90 39.91650 50.107 49.993 50.03 50.065Best,

author: mendip_discovery
author_rank: Super Contributor
timestamp: November 01, 2023, 07:01:06 pm
content: Quote from: coppice on November 01, 2023, 01:31:25 pmQuote from: DeepLink on October 30, 2023, 05:39:01 pmLow ohm but not low low ohm.btw looking at the AD article, I found it interesting that the method used before was considered a good way to do it. I had a chat with an old Marconi chap once about shunts and he talked about thinking about the flow of electrons across the shunt and how you need the point where you take the voltage reading to be in a good flow part of the shunt otherwise you get errors. The way I thought about it was to imagine water flowing through a void in the shape of the shunt.

author: coppice
author_rank: Super Contributor
timestamp: November 01, 2023, 07:11:42 pm
content: Quote from: mendip_discovery on November 01, 2023, 07:01:06 pmThe big deal is to get every last scrap of high current carrying copper out of the path over which you sense, or the horrible temperature coefficient of copper wrecks accuracy as the temperature changes.

author: mawyatt
author_rank: Super Contributor
timestamp: November 01, 2023, 07:40:36 pm
content: In the case of the SMD fixture we mentioned, the "assumption" was the conductive end caps of the SMD DUT were at equipotential on each end wrt the current flowing thru the SMD DUT.https://www.eevblog.com/forum/projects/different-type-lcr-smd-fixture/Weren't sure just how valid this "assumption" was but the idea was to let the SMD DUT conductive end caps make the sense connection in the 4 wire Kelvin measurement process. Thus the DUT is making the Force/Sense connections on each end of the SDM DUT, which should help with the connection uncertainties involved.So far measurements indicate this wasn't too bad an assumption for making a low Z SMD measurement without soldering the component. Of course one could argue all sorts of "reasons" why this isn't a good approach, and the real "proof" would be to solder the test DUT SMD onto a proper PCB with the optimum layout as shown in the ADI article, and then compare the mounted and soldered results with the fixture results. We may give this a try someday when time permits, but so far reasonably happy with the results we've been able to glean from this crude SMD test fixture.Should mention also in application trying to keep the 2 sense points at the same temperature helps with the TEMF of Cu and the other conductive metals involved.BTW find it interesting that the ADI article also chose the 2512 size, seems popular for low value resistors.Anyway, as always YMMV.Best,

author: coppice
author_rank: Super Contributor
timestamp: November 01, 2023, 07:44:49 pm
content: Quote from: mawyatt on November 01, 2023, 07:40:36 pmPeople using really small shunt values are usually dealing with large currents, so this is not surprising. People generally cop out with lower currents, and use a bigger shunt resistance, even if careful design could have kept it lower.

author: mawyatt
author_rank: Super Contributor
timestamp: November 01, 2023, 11:16:28 pm
content: Quote from: coppice on November 01, 2023, 07:44:49 pmYes, and the I^2R resistor heating with the TC, along with Thermal EMF issues, not a simple Ohm's Law direct solution!!Best,

author: Aheld
author_rank: Regular Contributor
timestamp: December 02, 2023, 08:20:14 am
content: Hi,Think about a simple Waferprober setup with chuck, microscope and 4 simple manipulators.With applied needles for contact your can measure direct at the resistors contact areas in real kelvin mode.If the chuck is not large, used equipment is quite cheap. Or if you already have some microscope, you simply need some manipulators or needle holders.This really depends on the sample count you want to measure on regular base.For first impression how it can looks like, watch homepage from HPPI in Germany. They‘re also offering a small, simple prober.Br. Axel

author: lugaw
author_rank: Regular Contributor
timestamp: December 02, 2023, 12:36:10 pm
content: Just calibrate it after soldering.

author: mendip_discovery
author_rank: Super Contributor
timestamp: December 02, 2023, 01:43:28 pm
content: Quote from: lugaw on December 02, 2023, 12:36:10 pmI think the OP is trying to work out an issue they are having.Are the resistors incorrectly specified?Is there a process issue such as too much heat during soldering?Have they a bad batch?Reducing time spent faffing about soldering and desoldering faulty parts could save a lot of time.

author: gamalot
author_rank: Super Contributor
timestamp: December 02, 2023, 04:43:44 pm
content: For the measurement of 49.9 ohm 0.1% resistance, a LCR meter with an SMD fixture is enough.The picture shows my LCR measuring a 1 ohm 1% resistance in 0402 package.