[HN Gopher] How to attach logic probes to tiny SMD components (2...
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How to attach logic probes to tiny SMD components (2021)
Author : dcminter
Score : 80 points
Date : 2023-11-12 11:08 UTC (11 hours ago)
(HTM) web link (reddit.com)
(TXT) w3m dump (reddit.com)
| dcminter wrote:
| Sharing this reddit thread because I was looking to solve this
| problem myself and thought that the needle-probe approach linked
| was terrific!
|
| Hackaday summary: https://hackaday.com/2019/11/15/needling-your-
| projects-3d-pr...
|
| Model for 3D printing: https://www.thingiverse.com/thing:3615910
| eschneider wrote:
| Hardware engineers who leave documented test points are my
| favorite people.
| analog31 wrote:
| You're welcome. ;-) Likewise to software engineers who leave
| "hooks" to internal functionality, so we hardware folks can
| create automated tests.
| markild wrote:
| As is mentioned in the post, there are very sleek off the shelf
| solutions.[0]
|
| I find their oscilloscope probes especially enticing.
|
| [0]: https://sensepeek.com/
| adhesive_wombat wrote:
| These really are lovely things. I only have the DMM ones, and
| rigged up a scope probe holder, but I'll be getting more of
| them.
|
| The use of M4 screws on the older models at least is very
| helpful for DIYing custom fittings (even without the real SMD
| nuts, brass nuts can be soldered to PCB stripboard)
|
| The stands are great too.
| YiraldyGuber wrote:
| I have a bunch of these. They're great, except for being
| frustratingly "floppy" at times. Imagine huddling over a PCB
| carefully positioning all these probes, not daring to
| breathe... only for the slightest brush to send them all
| tumbling over like dominoes. More than a few curse words have
| been let loose over this gear, but I couldn't do without them.
|
| It looks like they have new ones that address this: "The new SQ
| series of handsfree probes from Sensepeek have a lower point of
| gravity making them even more stable compared with the original
| SP series of handsfree probes."
| ofrzeta wrote:
| > making them even more stable
|
| Not related to the topic but it seems this marketing blurb
| has become the norm: They can't say they fixed something
| without claiming that it was already very good. I've come to
| hate this. No, they are not now "even more stable", "we made
| them more stable" because honestly they weren't that stable
| to begin with.
| ghosty141 wrote:
| We have them at work too, like you said they are too floppy
| and you gotta be extremely careful not to touch anything,
| especially if the point you are testing is very tiny. Apart
| from that they are great but yeah, there needs to be a way to
| fix them in place.
| anymouse123456 wrote:
| I'm considering buying these. Are you saying they're floppy
| as in, the bendable part doesn't hold it's shape? or floppy
| as in, the magnet isn't strong enough and the whole thing
| falls down?
|
| I'm assuming there's a magnet. I hope these aren't just using
| weight to hold their position....
| kedikedi wrote:
| One side has a magnet, and it firmly attaches the base
| board (steel). But the other side just has the pogo and is
| fixed there just by the weight of the thing. It works good
| if there's enough "bite" and the rest of the system applies
| force the right way. If not, we'll, it slides off.
|
| In my case for example, it is excellent for test points but
| somewhat challenging with soldered SMD component pads and
| very challenging if the density is high.
| adhesive_wombat wrote:
| If you're able to solder on and the signal can stand the
| stub, a little dot of copper tape on top of the IC and a
| tiny wire down to the lead in question and soldered on
| can help give an easier "hitbox". You can add the ground
| pad as well next to it and use the spring for the probe.
| adhesive_wombat wrote:
| I find the magnet is usable but weaker then I'd like if the
| steel is under an ESD mat, which are usual 2mm thick. If
| anything they're a just little bit too long which means
| they can be slightly floppy in the cross-wise direction.
|
| Thinking about it I might try a piece of low-profile bike
| chain and a copper wire and see if I can do better.
| YiraldyGuber wrote:
| The magnet is very strong, no issue there.
|
| I mean the 'bendable' part. The nearest consistency I can
| think of would be a bag of sand. They are weighty but not
| rigid. They are not designed to hold their shape.
| Unfortunately this means that it takes very little sideways
| force to make them "flop" over.
|
| Still, I can't recommend them highly enough. I use them
| _all the time_. Seriously, a PCBite plate with probes on-
| hand is now a permanent fixture on my main desk. If you do
| half as much fiddly electronics stuff as I do, they will
| pay for themselves. But you will also occasionally find
| them infuriating.
| The_Double wrote:
| I have bought the new SQ probes and went back to only buying
| the older version.
|
| The new ones are heavier, but that makes it harder to put
| them at an angle, they fall over more quickly. And the probe
| heads are bigger so you can't put as many close together.
| jdietrich wrote:
| I would strongly recommend adding a couple of dial indicator
| stands to your kit. They are rather more bulky than the
| included arms, but as they're designed for holding precise
| mechanical measurement instruments they are rigid, stable and
| can be very finely adjusted.
|
| https://www.mcmaster.com/products/dial-indicator-stands/
|
| For more complex probing, it is now remarkably
| straightforward to 3D print a bed-of-nails test jig.
| eschneider wrote:
| I saw that and it's like...take my money!
| atoav wrote:
| Honestly I would just replace those flimsy arms with magnetic
| measurement stands/articulated holders as they are used in
| precision manufacturing:
| https://www.noga.com/Products/hold/Holding%20System
|
| But at that point you could also just put your own pogo pins on
| somewhere.
| calamari4065 wrote:
| 200 euros for 4 100MHz and two logic probes and the entire
| fixturing kit. Not too bad. I'm sure I can convince my boss to
| buy these
| nonrandomstring wrote:
| Once I had a bunch of boards to test and rigged up a little
| temporary "bed of nails" ________________ o
| / ____________ o <-- connector | / _________o
| | | / | ---T---T---T---T----[] Where T
| = sewing pins and --- = thick polystyrene sheet Use finest
| 30+ SWG wirewrap
|
| The polystyrene gives a little bit of necessary springiness and
| as long as you have two (preferably three) reliable anchor points
| near the corners the pins will reliably find test points or the
| contact points of SM resistors or caps.
|
| It's good for about 10 contact points and 50 uses
| beardyw wrote:
| I use 30AWG (Kynar wire) for most things I build. I have it in
| multiple colours which is helpful.
| sebcat wrote:
| PUR-coated copper wire, .15mm diameter is pretty good. .1mm when
| needed. Use flux, good lightning and some (~10x) magnification.
| onetimeuse92304 wrote:
| Personally, I find the critical is to use good wire (the type
| used in transformers), use a good soldering station with right
| kind of tip, and plan a way to connect to your wires without
| destroying entire setup.
|
| I solder the wires to a short piece of FFC tape ending with a
| connector. The tape and the connector are attached somewhere with
| apiece of double sided adhesive tape. The end of the tape with
| the wires is suspended in air nearby. I then individually solder
| the wires to the test points.
|
| I can then connect my test tools (scope / logic analyser / PSU /
| DMM) directly to FFC connector easily. If I need more than one
| tool, I would usually use one of my breakout boards with
| connectors that make it easy to connect multiple test tools at
| the same time (for example supply power AND connect the scope, or
| maybe inject external signal to the chip on the board).
|
| I would like to mention I don't do it frequently. This usually
| only happens when I am having fun with an existing device. My own
| devices usually have built in enough test points / test
| connectors to not require this kind of shenanigans. I would
| usually plan for one or more surface mount connectors that I will
| only solder if I need it for some reason.
| flyingcircus3 wrote:
| Hot glue is good for strain relief. 30 gauge wire on tiny pads is
| going to be extremely fragile. Shifting the mechanical stress to
| the glue will make all of this more durable.
| tverbeure wrote:
| I prefer the UV hardening glue. Hot glue is a bit too messy for
| my taste, the glue gun takes too much space on my already full
| desk, and you need to wait for the thing to warm up.
| analog31 wrote:
| Ah, but you can peel it off. However, I agree that it's
| messy. Do take precautions when working with UV. It's both an
| eye and skin hazard.
| bogantech wrote:
| The trick is to ditch the glue gun - cut off a piece of glue
| stick, place it where you need it and hit it with the hot-air
| tverbeure wrote:
| Instead of regular test points, I'm now adding u.fl/ipex
| connectors to my PCBs. They're small enough to not be in the way
| for most cases, and it's so much easier to just plug in a
| connector instead of messing around with probes.
|
| They're around 3 cents (yes, $0.03) a piece on LCSC:
| https://www.lcsc.com/product-detail/_BAT-WIRELESS-_C5137195.....
| kevin_thibedeau wrote:
| I make my vias large enough to accept a 30AWG wire (15 mil
| hole). Slip in a precut/stripped wire, tack it with solder,
| trim to length, and you have an instant testpoint in a usually
| optimal location near the point of interest. Advantages are
| that you can't accidentally rip a pad off the board, it's
| accessible from both sides, and minimal board area is consumed.
| kurthr wrote:
| If you're doing anything more than 2-4 layer PCBs, I'd make
| one more caveat... through-hole-via! It makes getting to test
| points much easier from both sides of the board, and if
| you're using pogo-pin testers, helps align the pins.
|
| Unfortunately, if you're doing anything highspeed (>100MHz)
| or differential, then such vias (except at connectors) are
| highly frowned upon since they increase loading, crosstalk,
| imbalance, and reflections.
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(page generated 2023-11-12 23:00 UTC)