Testing for small connectors - Page 1
Forum section: electronics / general

author: law
author_rank: Regular Contributor
timestamp: August 23, 2024, 05:10:48 am
content: I have a bunch of Molex PicoClasp connectors across my boards.They have a 1mm pitch.I do a 100% functional test on each board, where I currently manually plug in the connectors, then run a bunch of test scripts.I'm working towards removing manually plugging in each connector by use of a jig where all connections are made at the same time, rather than one at a time.Can anyone recommend any fine pitch pogo pins they have used before?I've also thought of taking a connector plug and shaving it down a bit so that the insertion force is much lower, then attaching this to a jig somehow.I imagine the connectors would flog out after repeated use, though.Any other suggestions?Thanks

author: thm_w
author_rank: Super Contributor
timestamp: August 23, 2024, 09:08:46 pm
content: https://www.isipkg.com/products/pogo-pins-spring-probes/Or add additional test points on your board, is another option.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: August 24, 2024, 03:59:17 pm
content: Those isipkg pogo pins claim to go down to 0.3mm pitch, but I doubt whether that is the spring loaded version.Spring loaded pogo pins are convenient because the layout for the test setup is the same as for the product. You can simply copy the PCB to a new project, replace the testpoints with pogo pin footprints and continue from there.When pitch needs to be small, then I have the layout in mind as used in semiconductor testing. There the test pins are (almost) horizontal needles, and contact force is ensured by pushing the bed with needles hard enough to the test subject that the needles bend a bit. You can get a very fine pitch this way (into the micrometers) but making the bed with nails is more complicated.

author: mtwieg
author_rank: Frequent Contributor
timestamp: August 25, 2024, 01:48:40 pm
content: It's not clear what you're asking for. Do you need to contact the connector pins directly (thereby verifying the soldering of the connector), or are you fine with bypassing the connector itself to test the rest of the circuitry?Are all these connectors facing the same direction?Quote from: law on August 23, 2024, 05:10:48 amAny test fixture will be expected to wear out after repeated use, so the part that mates with the UUT should be designed such that it can be replaced easily. This applies to pogo pins and cable assemblies.

author: law
author_rank: Regular Contributor
timestamp: August 25, 2024, 11:19:45 pm
content: Hey, thanks for the replies and suggestions.> It's not clear what you're asking for.I want to contact the pins directly to verify the soldering of the connector.The connectors are all on the top side of the boards, but not necessarily in the same orientation.I've used pogo pins before, but only in PCB contacting application. I have no experience using them to contact pins of connectors.> Any test fixture will be expected to wear out after repeated useI agree with this. PicoClasp connectors are rated for up to 30 cycles, so I'm not too convinced my fixture would last too long if I took this approach. I'm happy to be told otherwise though.Thanks again.

author: tooki
author_rank: Super Contributor
timestamp: August 25, 2024, 11:28:22 pm
content: Quote from: law on August 23, 2024, 05:10:48 amPicoClasp are rated for only 30 mating cycles, so I’d be leery of using them for your test jig since you’d have to replace them frequently, even if they exceed their rated mating cycles in practice. And alignment might be an issue too.Do you have room for either regular pogo pins, or for something like the Samtec One-Piece Interface “connectors” that just press against pads on the PCB?https://www.samtec.com/flex-stacking/standard/micro/I used the SEI model for thehttps://sengerm.github.io/Chubut_2_16CH/doc/230810_characterization/main.htmlmain board, which uses them to connect to the “disposable” carrier boards, which the end user designed himself for the different detectors he tests. They’re rated for 100 mating cycles, though I’d expect them to last longer.

author: law
author_rank: Regular Contributor
timestamp: August 26, 2024, 06:42:28 am
content: > Do you have room for either regular pogo pinsOnly if they are <= 1mm pitch! And I'm aiming to not change connectors...

author: tooki
author_rank: Super Contributor
timestamp: August 26, 2024, 07:00:05 am
content: FYI, I was envisioning adding extra test connectors, not actually trying to mate with the PicoClasp connectors.You mention that you want this process to verify the soldering of the connectors — is that actually necessary?? As in, has this been a problem in the past?

author: law
author_rank: Regular Contributor
timestamp: August 26, 2024, 09:29:46 am
content: > I was envisioning adding extra test connectorsAh, I understand! I'm not going to add extra test connectors. My boards are tiny and the smaller I can make them, the better!> As in, has this been a problem in the past?Maybe once or twice - it is early days still. I also don't have AOI and am only inspecting by eye at the moment.To perform my functional tests I need to interface with the signals in the connectors. It made sense to me, that since the connectors are directly available to the end user and I need the signals within to test, that I should just directly test the connector.I've had a bit more of a look around and it looks like the cup end pogo pins can be used to test connectors?Maybe I'm wrong, but it seems like it would be as easy (or as hard) to test the connector directly with a pogo pin as it would to test a pad on the PCB...I will have to manage misalignment of the connector as soldered onto the board.Thanks

author: mtwieg
author_rank: Frequent Contributor
timestamp: August 26, 2024, 01:01:43 pm
content: Quote from: law on August 25, 2024, 11:19:45 pmIf so, that makes things far more difficult...QuoteYou might be able to find cup-end pogo pins small enough for 1mm pitch. Actually using them to make a workable test fixture will be quite a mechanical challenge, especially if you have connectors facing different directions.If your only concern is durability of the test fixture, then I would stay with manually plugging in cables, and replace the cable assemblies every X boards you test.If your main concern is making the test faster and reducing labor, then I don't think pogo pins to the connector pins will get you much, as you would still be testing one board at a time. I would look into whether your connectors can be covered by AOI. If so, you can use more traditional test methods using test points on the PCB, like flying probe or ICT.

author: ajb
author_rank: Super Contributor
timestamp: August 26, 2024, 03:13:29 pm
content: Quote from: law on August 26, 2024, 09:29:46 amI've done this for JST ZH (1.5mm pitch) headers using standard 1mm dia cup point pogo pins, aside from the spacing being very tight it works fine. As you go down in pitch the size of the cup becomes more critical, since it needs to be big enough to reliably accept the pin on the DUT, but small enough to not cause a clearance issue between pins. The alignment of the board to the fixture also becomes more critical of course, so you might need to take extra measures there. Using pins in the fixture that align to tooling holes in the PCB would be a good idea rather than relying on the board outline to locate the PCB.Quote from: tooki on August 25, 2024, 11:28:22 pmSince the limiting factor on mating cycles is usually contact resistance exceeding a fairly low threshold, you can get quite a lot of tests out of a set of connectors if the current requirements are low enough. I don't think there's a likely mechanism for a worn out plug to damage a brand new header after one short use, aside from overloading a high resistance contact? And of course physical damage if the plug is REALLY beat up. It's also possible to incorporate a contact resistance test into the fixture/test procedure to catch a failing harness before it causes a problem. The downside is it requires a redundant connection for each monitored net, which could be the same net on a different connector/pin, or a test point on the board -- or some support from the DUT, maybe. But it might be a good option if the connectors are all low current signals plus power/ground.Quote from: law on August 23, 2024, 05:10:48 amI've done this as well, although just for manual plug-in tests. At least with ZH connectors IME, the first thing point of failure on small connectors that get cycled a lot is the contacts popping out, since the wires inevitably get tugged on while unmating the connector because there's so little connector to hold on to -- which would also make to hard to mount the connector in a fixture, especially in a way that can withstand the removal force. The other problem with using those connectors in a fixture will be aligning them to the headers. Remember that there is a certain amount of tolerance for the position of the connector on the board, so just mounting the connectors very precisely and very rigidly in the fixture won't work. The fixture connectors need to be able to 'float' and self-align to the header somehow. Maybe you can modify them with a lead-in chamfer on the front or something, but they'll still be somewhat consumable, and will be harder to replace if they need extensive modification.

author: thm_w
author_rank: Super Contributor
timestamp: August 26, 2024, 07:31:31 pm
content: Quote from: Doctorandus_P on August 24, 2024, 03:59:17 pmIt says "Spring force" right in the table and "Spring" in the URL, they are all spring pogo pins.

author: law
author_rank: Regular Contributor
timestamp: August 27, 2024, 01:16:59 am
content: Hey all,Just to clear up "The connectors are all on the top side of the boards, but not necessarily in the same orientation."The connectors are on the top of the board, all pointing vertically but just rotated differently.I've included a picture of one of my boards as an example.Thanks for the advice. I think I should be able to align off the screw holes. I'll have a scout around and see if I can find some fixture pins.As an aside, I am currently manually plugging in connectors for testing. I've cut the positive lock features off the connectors, but not shaved them down.It's been working alright for now, but I have experienced all the cable issues mentioned.Thanks again

author: mtwieg
author_rank: Frequent Contributor
timestamp: August 27, 2024, 11:40:57 am
content: Quote from: law on August 27, 2024, 01:16:59 amAh, that's not so bad then. But I see why you want to get away from cables.... 13 connectors...Even so seems challenging. A basic tolerance stackup:1. Final position of connectors on board2. Tooling hole tolerance3. Pogo pin to tooling pinNeed to keep that total to less than 0.5mm for all pins. Definitely possible, but since you have so many connectors you'll probably have to iterate several times to get everything aligned. Hope you have access to a good CNC.

author: Gribo
author_rank: Frequent Contributor
timestamp: August 27, 2024, 11:56:27 am
content: Both Ingun and QA tech offer probes for 1mm grid.To probe connectors, you would use something like this:https://ingun.com/en-GB/GKS-080-303-080-A-0805-E/GKS-080-0019

author: law
author_rank: Regular Contributor
timestamp: August 28, 2024, 09:52:47 am
content: Thanks - they look pretty good. They have an online store too

author: jmelson
author_rank: Super Contributor
timestamp: August 30, 2024, 03:43:08 pm
content: Actually, what you are trying to do is not likely to work. If you have a newly assembled board that has bad soldering on a few through-hole connectors, and you apply a bit of force to the connector pins, they will make good contact while the pressure is applied. So, the act of touching the pins with pogo pins or whatever, will likely cause the boards to pass just fine when they actually have soldering defects.I have experienced this on several occasions. Once, when a board was shipped out with a BUNCH of missed solder joints. VERY embarrassing!Jon

author: law
author_rank: Regular Contributor
timestamp: August 31, 2024, 07:19:31 am
content: Hey, that's pretty frustrating! What did you do to get around this?The connectors I'm interested in testing are all SMT. I can see that I could run into similar issues.Surely, testing signals coming in and out of connectors is a pretty common thing to do.Does everyone just use AOI to inspect the connector soldering, then pogo pin to the board elsewhere to test the actual signal?Thanks again

author: mtwieg
author_rank: Frequent Contributor
timestamp: August 31, 2024, 01:04:30 pm
content: Quote from: jmelson on August 30, 2024, 03:43:08 pmI think this might be a little too pessimistic... yes, bad solder joints can present themselves as intermittent depending on applied force, temperature, etc... but that doesn't mean doing x-ray inspection on every joint is necessary (these connectors are SMT, btw).It does, again, beg the question of what marginal benefit there is to probing the connector pins. I would only attempt this if I knew that these connectors were exceptionally prone to assembly defects (and had ruled out changing connectors as an option). I've never used pico-clasp, but at a glance they don't look challenging (main issue I assume is that they don't have board guides, so roughly handling the boards between placement and reflow could result in misalignment).