How to avoid shorting when sampling signals on an IC  - Page 1
Forum section: electronics / projects

author: Hgspine
author_rank: Contributor
timestamp: October 31, 2019, 09:02:25 pm
content: How does one put a probe tip on the leg of an IC to check a waveform without risking the probe falling in the space between two IC legs shorting them out together and causing damage? Special probe? Electric tape placed between the IC legs? Some other method? Thanks.

author: teksturi
author_rank: Regular Contributor
timestamp: October 31, 2019, 09:12:35 pm
content: Quote from: Hgspine on October 31, 2019, 09:02:25 pmMaybe take your time and turn power off and insert hook. If it is your design you can anticipate and make testpoint for every pin you may want to look at. And one way is to probe else where. Signal has to go some other place also and maybe you can probe there without risking making short.

author: AndyC_772
author_rank: Super Contributor
timestamp: October 31, 2019, 09:19:41 pm
content: What kind of IC package?For something like a 0.5mm QFP, I just use a good quality, sharp probe tip and a magnifying glass. If it's in an area where shorting adjacent pins really could cause damage, then turn off the power and solder a wire to the signal you're interested in, then probe that instead.

author: Someone
author_rank: Super Contributor
timestamp: October 31, 2019, 11:38:26 pm
content: There are accessory tips for some probes that align the sharp point. Lecroy, R&S, Keysight all call them "IC Cap":https://cdn.teledynelecroy.com/files/accessories/pp007_pp008_accessorydiagram.pdfCould be an interesting investigation to find the OEMs and produce a compatibility chart for different probe accessories.

author: MosherIV
author_rank: Super Contributor
timestamp: November 01, 2019, 07:51:37 am
content: My tip is to use very sharp and hard probe tip, push the tip hard into the solder of the chip leg to leave an indentation. The indentation will help to stop the tip moving.Not always possible though.

author: rstofer
author_rank: Super Contributor
timestamp: November 01, 2019, 07:24:42 pm
content: The bigger issue is to keep the board from moving around while you glance away. The board knows you're not looking and it takes that opportunity to mess you up.Sharp points, considerable force and a board that can't move.

author: thm_w
author_rank: Super Contributor
timestamp: November 02, 2019, 12:23:55 am
content: Quote from: Someone on October 31, 2019, 11:38:26 pmVery nice, $25 is not too bad for 10pc:https://www.digikey.com/product-detail/en/teledyne-lecroy/PK007-008/PK007-008-ND/3587098But anyone find any clones? 3D print is possible but you'd have to do it on a SLA (potentiallyhttps://dirtypcbs.com/store/print3d)

author: dicky96
author_rank: Regular Contributor
timestamp: November 02, 2019, 11:58:37 am
content: Thesehttps://www.aliexpress.com/item/32951465926.html?spm=a2g0o.productlist.0.0.35511ea02MBiyP&algo_pvid=e7f34827-c27e-4fff-a40a-baadd779f834&algo_expid=e7f34827-c27e-4fff-a40a-baadd779f834-0&btsid=20b779ab-1b66-454a-a230-b5d08413b8f3&ws_ab_test=searchweb0_0,searchweb201602_8,searchweb201603_55https://www.aliexpress.com/item/32955514788.html?spm=a2g0o.productlist.0.0.35511ea02MBiyP&algo_pvid=e7f34827-c27e-4fff-a40a-baadd779f834&algo_expid=e7f34827-c27e-4fff-a40a-baadd779f834-1&btsid=20b779ab-1b66-454a-a230-b5d08413b8f3&ws_ab_test=searchweb0_0,searchweb201602_8,searchweb201603_55I've never tried them but was thinking of buying some. Did anyone else try them? I seem to recall reading a review that said they work very well, the only limitation being you can't clip to two adjacent pinsI've also looked for something like a set of these to fit the all most common QFP packages, but the ones i have managed to find cost £££ each!https://www.adapters.com/prod_serv/em_clip.htmhttps://www.adapters.com/catalog/test_clips.pdfI would have thought some chinese manafacturer could make these cheap enough.It would be a nice crowd fund project if someone wanted to take it on

author: dicky96
author_rank: Regular Contributor
timestamp: November 03, 2019, 01:37:54 pm
content: I've ordered these todayhttps://www.aliexpress.com/item/33039250212.html?spm=a2g0o.productlist.0.0.51321b78evJdw9&algo_pvid=ee90e604-220e-4f3b-a8ce-a0b08796b7ad&algo_expid=ee90e604-220e-4f3b-a8ce-a0b08796b7ad-0&btsid=edfb4d7a-aaf6-4e8c-a9b5-3ff46598f50c&ws_ab_test=searchweb0_0,searchweb201602_7,searchweb201603_52I don't know if I can use them on 0.5mm QFP so I will try them and post hereIt also occurred to me that it would be good if someone made something that I can only describe as a square plastic 'comb' that had tines of the correct pitch to fit between the legs of a QFN. It would only need to be a few mm high and it would act as an effective shield to prevent the scope probe from slipping. It could have colour coded tines to make it easy to count the pins to the one you wanted to probe. Now that would be really useful. Can somebody make something like that please - I would buy itI also came across this when I was buying the QFP clips off Aliexpress, a link just popped up and it looked interesting so.... you know the resthttps://www.aliexpress.com/item/32825672697.html?spm=a2g0o.detail.1000013.10.2f615628piet9I&gps-id=pcDetailBottomMoreThisSeller&scm=1007.13339.146401.0&scm_id=1007.13339.146401.0&scm-url=1007.13339.146401.0&pvid=0ee65116-a281-4858-ad1d-2d42687be1c1I've not seen one of those before and I'm not totally sure exactly what it is meant to do - it's apparently something to do with programming car ECU but couldn't that be repurposed for general electronics diagnosis/repair?

author: China NewBoy
author_rank: Regular Contributor
timestamp: November 03, 2019, 02:35:15 pm
content: Quote from: AndyC_772 on October 31, 2019, 09:19:41 pmagree

author: magic
author_rank: Super Contributor
timestamp: November 03, 2019, 08:42:56 pm
content: https://sigrok.org/wiki/Probe_comparison

author: thm_w
author_rank: Super Contributor
timestamp: November 04, 2019, 10:38:17 pm
content: Quote from: dicky96 on November 03, 2019, 01:37:54 pmI think defpom or another got those recently but didn't do testing yet (I can't find the video), to me it looked like they were too big and would short out the pins on 0.5mm. But one of the ali reviews says: "It's working up to SSOP, QFP 0.5mm pitch, lower You can grab only one pin." Either way its less than a cost of a single high end probe on that sigrok page so worth trying.

author: dicky96
author_rank: Regular Contributor
timestamp: November 06, 2019, 03:11:14 pm
content: Quote from: thm_w on November 04, 2019, 10:38:17 pmYes I read that too. I'll happily do a video review when they arrive - they are already on the plane to Spain according to the tracking :-)Rich

author: ptricks
author_rank: Frequent Contributor
timestamp: November 06, 2019, 04:09:45 pm
content: I don't probe on the chip if the pins are too close , I find a point on a trace connected to the chip.

author: graybeard
author_rank: Frequent Contributor
timestamp: November 07, 2019, 03:33:40 pm
content: tack a small piece of thin sold wire on with a soldering iron. I keep a spool of wire wrap wire with my soldering supplies for just that.