Clever ways to hold multiple probes: Please Share - Page 1
Forum section: electronics / testgear

author: rx8pilot
author_rank: Super Contributor
timestamp: June 25, 2018, 05:17:32 pm
content: One of the slowest elements of setting up a test is getting the scope, logic, and DMM probes all placed in a way that is stable enough to get the measurements, safe enough to avoid a tiny slip that shorts out something important.I have bootstrapped a number of super janky methods that sort-of work. The professional probe placement rigs are wildly expensive. Is there any modest cost option to precision placement of probes?Additional notes:In the early stages of design, I incorporate various test friendly features on the PCB. As the design gets into production form factor - most of those go away in favor of high-density layout. The tests on the final design get harder and harder.The spring clips and clothespins in the photo are a weak solution.

author: kony
author_rank: Regular Contributor
timestamp: June 25, 2018, 05:20:17 pm
content: Dial indicator magnetic base stands. Highly suggested to have the probe holder springloaded, otherwise you are risking damage to the probe tip.

author: lukier
author_rank: Unknown
timestamp: June 25, 2018, 05:22:14 pm
content: Sometimes I use these cheap magnetic dial indicator stands, like these:https://www.ebay.co.uk/itm/252577436299Not a real positioner, but even without a steel plate under the ESD mat to use the magnetic function it is fairly heavy on its own and probes can fit where the dial indicator goes with some padding or a 3D printed adapter.

author: tautech
author_rank: Super Contributor
timestamp: June 25, 2018, 11:19:56 pm
content: Bed of nails test fixture.https://www.electronics-notes.com/articles/test-methods/automatic-automated-test-ate/ict-in-circuit-test-fixture-bed-of-nails-probes.phpPogo pointshttp://www.testelectronics.com/Probes/probes.php

author: all_repair
author_rank: Frequent Contributor
timestamp: June 25, 2018, 11:33:31 pm
content: Suspend 2 pieces of plastics with holes, like those screwdriver holder. Misaligned holes maybe better as the probe can come in at an angle. The probe shall rest on the PCB, and guided and held by the plastic sheet on top. Narrow probe shall be better, and DIY from metal post, etc.Not my idea. It is from hobbyist from China. You can buy this from Taobao.

author: Dubbie
author_rank: Unknown
timestamp: June 25, 2018, 11:37:44 pm
content: You could buy the $15 mag-base indicator stands from ebay and get a thin sheet of steel and glue some antistatic mat to it.I'm sure you could machine up an adapter to hold the probes from nylon or something.I think I might do something similar!

author: tautech
author_rank: Super Contributor
timestamp: June 25, 2018, 11:59:41 pm
content: Thing is RX8, on your last spin of the PCB you need spin up a bed of nails PCB too that carefully aligns pogo pin points onto your test points, set it into a alignment fixture and add some hold down HW and you're all set to go.This all presumes you can add some trace thickening or pads for landing points for the pogo pins or does your final density prohibit this ?

author: nctnico
author_rank: Super Contributor
timestamp: June 26, 2018, 12:05:27 am
content: I usually just solder a thin piece of wire to a test point which I can then grab with the hook of a probe.

author: rx8pilot
author_rank: Super Contributor
timestamp: June 26, 2018, 12:47:37 am
content: Quote from: Dubbie on June 25, 2018, 11:37:44 pmThis is about the level of complexity and expense I was hoping for. The only real effort is machining the bits that grab the probes - a rather small project. My guess is that this kind of thing could cover a lot of scenarios - reducing my stress and frustration trying to balance 4 probes.Quote from: nctnico on June 26, 2018, 12:05:27 amThat is a tried and true method...just getting harder and harder with 0201 parts and lack of space for a pad. If I can find a reasonable way to just place the probe directly - sure would save some time and improve the quality of the measurement on the more challenging (fast and/or low-level analog) signals.Quote from: tautech on June 25, 2018, 11:59:41 pmI keep promising myself that I would take the time to do this, yet have not yet tried. My density is still probably loose enough to make this practical - especially if it is part of the plan from the very beginning. I am guilty of trying to figure out a test plan after it is mostly too late in the game. This approach will work well for the power electronics projects I do. There are dozens of points that simply need to go to the logic analyzer. Fewer that connect to critical analog signals that require some effort to keep them from being damaged by the test efforts.

author: rx8pilot
author_rank: Super Contributor
timestamp: June 26, 2018, 12:48:33 am
content: Quote from: all_repair on June 25, 2018, 11:33:31 pmDo you happen to have a link or photo? Can't quite picture this.

author: helius
author_rank: Super Contributor
timestamp: June 26, 2018, 12:59:39 am
content: I know this kit has been discussed here before:https://pcbgrip.comMaybe it could give you some ideas.

author: tautech
author_rank: Super Contributor
timestamp: June 26, 2018, 01:07:37 am
content: Quote from: rx8pilot on June 26, 2018, 12:47:37 amAre your test needs for each produced PCB or only on the final prototype spin ?Are IC's programmed after production ?

author: rx8pilot
author_rank: Super Contributor
timestamp: June 26, 2018, 01:20:57 am
content: Quote from: tautech on June 26, 2018, 01:07:37 amThe immediate goal is to exhaustively test the final spin of a new design. It would be nice to be able to accomplish automated test of production PCB's - but I feel like that is a totally separate effort. The last 5-6 designs I have done were quite a challenge. Soldering little 30 and 34 gauge wires, delicately balancing probes, etc.Essentially - I am trying to speed up prototype tests through final validation stage.

author: KaneTW
author_rank: Frequent Contributor
timestamp: June 26, 2018, 01:39:36 am
content: PCBgrip looks cool, and I'm tempted. How well does it probe fine-pitch packages?

author: tautech
author_rank: Super Contributor
timestamp: June 26, 2018, 01:46:49 am
content: Quote from: rx8pilot on June 26, 2018, 01:20:57 amSounds like you need 30+hrs/day and a little time on your mill to build a universal test fixture for use with scope probes......something that you can use for other than just this project. The link Helius provided will indeed give some ideas of ways to move forward.Of course you've got both sides of the PCB to play with in order to gain connection to the rails/nets you need to connect to but of course we don't need to tell you which you shouldn't bring out on the other side just to gain connection.A little trick I've used is SMD test points that are later replaced with zero ohm resistors. Even when really tiny you can still get hold of them with any SMD grabber and break out to a short lead with a loop for your scope probe grabbers.These came up in a very quick search but maybe there's smaller available:https://www.digikey.co.nz/product-detail/en/keystone-electronics/5015/36-5015CT-ND/278886

author: all_repair
author_rank: Frequent Contributor
timestamp: June 26, 2018, 06:09:06 am
content: See picture

author: bitseeker
author_rank: Super Contributor
timestamp: June 26, 2018, 06:53:38 am
content: Mount a PCB holder to the center of the base of one of these?https://www.aliexpress.com/item/Third-Hand-Soldering-Tool-6-Flexible-Arms-Six-Arm-Soldering-Station-With-Swiveling-Alligator-Clip-USB/32831133451.html

author: Dubbie
author_rank: Unknown
timestamp: June 26, 2018, 09:07:30 am
content: Thats pretty cool All_Repair.

author: lukier
author_rank: Unknown
timestamp: June 26, 2018, 10:01:49 am
content: I didn't expect bed of nails fixtures here, this is rather for production testing, especially in volume, than just debugging a circuit.Anyway, another thing I really like for probing is well, SMD probes, Tek used to make these, up to 500 MHz:https://nscainc.com/wp-content/uploads/pdf/TEK_P6562A.pdfWith various adapters, micro-grabbers and so on these are good for 0.5mm QFPs and are small enough that often no holding is needed.Like some active probes which have interchangeable leads (sometimes even soldered-in), so it usually doesn't matter if the probe body is held or not.Typical passive scope probes for me are more of "electrician" tools than something for highly integrated SMD electronics.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: June 26, 2018, 12:20:36 pm
content: You can glue a 0.1" header somewhere on the board (double sided tape or hot snot) and then solder enameled wires between that connector and the test points.

author: Hydron
author_rank: Super Contributor
timestamp: June 27, 2018, 06:53:01 am
content: I've used these guys when I needed a bed-of-nails fixture for development work in a hurry:http://www.merifix.com/Not hobbyist-cheap but is compared to getting a proper custom bed-of-nails tester built (note that you need to pay a little more for the plate to be pre-drilled). Look elsewhere for high volume testing or large numbers of test points, but it worked well for a 100mm dia PCB with ~a dozen test points that we wanted to test/program in small volumes.If you have room for some test point pads and could deal with the parasitics of pogo-pins then getting something like that made may be practical - while the clamping forces get high if you populate a lot of pins (more than a couple of dozen) you could get everything drilled but only populate pins you need for a particular measurement.

author: bson
author_rank: Unknown
timestamp: June 27, 2018, 07:39:32 am
content: I leave little pads for test points and if needed populate them with Keystone 5015 SMD micro test points. Also makes it easy to solder if needed. They recommend an overly large footprint IMO, I use 2.6x1.2mm; their suggestion is 3.4x1.8mm which is way big I think.

author: exe
author_rank: Unknown
timestamp: June 27, 2018, 12:15:40 pm
content: I have pcbite and this kit:https://www.eevblog.com/forum/buysellwanted/high-precision-needle-pcb-probing-system-quick-magnetic-holders-low-profile/.Sadly, nether of them I tried in a real scenario. But I'd say both are a bit harder to use than I expected. I'd love to have some micro-grabbers instead of needles, but those are super-expensive (those that are suitable for fine-pitch ICs).

author: nanofrog
author_rank: Super Contributor
timestamp: June 27, 2018, 02:13:48 pm
content: Instead of using the single base for segmented CNC hose as is the case in the photo frombitseeker, you can attach strong magnets to the threaded end (epoxy a nut to the magnet) and place a piece of thick sheet metal beneath the ESD mat (paint the metal).Not only is this effective, but it's inexpensive as well.

author: bitseeker
author_rank: Super Contributor
timestamp: June 27, 2018, 04:27:32 pm
content: Neat mod to that, nanofrog. The whole bench becomes a base for "helping hands."

author: rx8pilot
author_rank: Super Contributor
timestamp: June 27, 2018, 06:43:46 pm
content: Quote from: bitseeker on June 26, 2018, 06:53:38 amThe Loc-Line holders are handy for non-precision stuff. They have too much spring. Maybe good for managing probe cables.Making contact on a 10mil via that is adjacent to a number of other 10mil vias is pretty hard. The Noga arms on mag bases are rigid enough for this I think. Maybe the best solution is to have both the Noga arms and the Loc-Line working together. Could probably be done for around $100 per channel - a huge improvement from the commercial solutions that are around $700-1500 per channel.Quote from: Hydron on June 27, 2018, 06:53:01 amThe pogo pin based bed of nails are a bit of a commitment compared to just positioning 4 probes directly to the board. I have to deal with a number of designs that never make it to production - therefore hoping to have a solution that focuses on holding standard passive and active probes onto a PCB. Bed of nails is the next level.....the next step.

author: all_repair
author_rank: Frequent Contributor
timestamp: June 27, 2018, 11:24:37 pm
content: https://www.thingiverse.com/thing:2609385Going to print this to try myself. 3D printing the test jig (pogo bed-of-nails) maybe one way if you have a 3d printer. Once you have a base design, each new one shall be a slight customisation. Search for "pogo", "test jig", "programming", etx on thingiverse for other ideas. If you do, look forwards to your sharing of design.

author: andyzoo
author_rank: Newbie
timestamp: June 28, 2018, 01:08:10 am
content: I thought test leads are just held and tip-touch to PCB like my profile photo, never thought it's a fixture-structure!Maybe some company could design a better gadget to do testing...

author: rx8pilot
author_rank: Super Contributor
timestamp: June 28, 2018, 02:47:17 am
content: Quote from: all_repair on June 27, 2018, 11:24:37 pmThat is about the right idea. Minor changes and it could hold any probe or pin.

author: nanofrog
author_rank: Super Contributor
timestamp: June 28, 2018, 11:51:12 am
content: Quote from: bitseeker on June 27, 2018, 04:27:32 pmExactly.It would also work for the magnetic base dial indicator holders as well. And there happens to be anadjustable gimbal swivelattachment that *could* be better suited to holding DMM or oscilloscope probes (not sure how large the hole diameter is though). Still looks usable as a clamp though for say PCB material.Quote from: rx8pilot on June 28, 2018, 02:47:17 amYou could swap the segmented CNC line for a suitable dial indicator holder that would replicate the basic configuration of the 3D printed item linked above.Such as the following (Magnetic Pull Base Holder Dial Indicators 170 lbs.):It shouldn't be too much effort or expense to modify the knurled bolt end to something you'd find suitable. For example, you could add the above gimbal clamp to/were the knurled bolt is, and use that to hold a bit of PCB with a pogo-pin soldered to it.Quick, easy, and inexpensive (i.e. 4x of them coming in under $100).Hope this inspires an idea or two.

author: JPortici
author_rank: Super Contributor
timestamp: June 28, 2018, 04:36:22 pm
content: Hi carlos, today i was at a power electronics convention. Tektronix was doing a seminar on measurements techniques (which of course was just to promote their new TIV high bandwidth optically isolated probes *drooling* ) and somwthing caught my eye. I then was talking to the rep, they are suggesting to use MMCX connectrs for test points, they are also selling or will soon sell probes wich don't have the classical tip, but have MMCX connector at the end, and adapters for other 'classic' probes so they can mate with the MMCX. The result was a steady connection, probe is held in place very tightly.They also had this neat little gadget that i obviously forgot to take a photo of, some sort of plastic tripod with holes to insert the probe. They will add it as an accessory soon but i think you can 3d print one...I did a sketch, sorry for my bad sketch skills :/Indeed, not that much of a probe holder, esp if you need many probes at one but it should be easy to make one from 3d printing...

author: tautech
author_rank: Super Contributor
timestamp: June 28, 2018, 07:55:15 pm
content: Quote from: nanofrog on June 28, 2018, 11:51:12 amThe last fitting on the solid arm clamps both to the arm and the small stub shaft with the knurled nut and that can be removed to leave a hole in the last fitting in which a probe could be inserted. It might need to be nylon bushed to fit the hole better and protect the probe.For only 4 probes I agree with nanofrog these might be the most secure solution.And you can use this stuff in the metalwork shop too.

author: rx8pilot
author_rank: Super Contributor
timestamp: June 28, 2018, 09:01:22 pm
content: Quote from: JPortici on June 28, 2018, 04:36:22 pmThose are a great idea for test layouts - a step up in performance from the low-tech probe holders. The only downside is the size for very space sensitive layouts on production pcbs. For prototyping, I wonder if anyone makes adapters for common probes - definitely a good idea when space allows. I have seen a number of commercial and DIY efforts at making probe sockets. All of them are better than handholding for sure....if space allows.The Alan Wolke version.....Quote from: JPortici on June 28, 2018, 04:36:22 pmYour manual sketch skills are better than mine.....A common challenge I face is trying to probe many points in a small area. It requires the probes to be angled considerably adding to the challenge of placement. Grounds are yet another challenge - the spring grounds are hard to manage, especially at an angle. I try to consider the placement of vias or pads in critical areas as much as possible. Some efforts work better than others.A straight down holder seems limiting overall.I found this on Makezine....just need probe holders instead of long pins (for higher BW) and better physical precision to get a sharp probe tip on a tiny via or QFN pad.Here is the fancy configuration for the 3D printed holders posted earlier.....The pin setup is BW limiting, but no reason it could not handle the probes directly. I like that the PCB holder is part of the structure, allowing the user to move it as a unit with less chance of messing up the probe positions.

author: bitseeker
author_rank: Super Contributor
timestamp: June 28, 2018, 10:17:54 pm
content: Quote from: rx8pilot on June 28, 2018, 09:01:22 pmYeah, that's pretty cool.

author: exe
author_rank: Unknown
timestamp: June 29, 2018, 06:06:17 am
content: I always wondered why probes are so big so they need support, etc. I'd like to have small probes small handpiece. Or no handpiece at all, but a cable with small plug.

author: bd139
author_rank: Super Contributor
timestamp: June 29, 2018, 06:08:18 am
content: Small children are pretty good at holding probes. Especially if you bribe them.

author: JPortici
author_rank: Super Contributor
timestamp: June 29, 2018, 06:21:06 am
content: Quote from: rx8pilot on June 28, 2018, 09:01:22 pmwhich is exactly what i said, as i have the same problem although my boards are far less complex, but luckily for me most of the signals i have to deal with are very low in bandwidth and i can get away with regular probinng, once it's assured that the signal IS fine. but for some key signals it may be a very good solutionQuotethey had a thing that plugged on a regular probe tip so in theory they make the adapter

author: all_repair
author_rank: Frequent Contributor
timestamp: June 29, 2018, 12:01:09 pm
content: https://www.thingiverse.com/thing:2427726This is the latest version. He is selling his kits. Others have designed adapter to fit this to hold scope probe, and crocodile clip