7 ms·

How to attach logic probes to tiny SMD components (2021)

99 points by dcminter 3y ago

dcminter 3y ago
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-printed-pcb-probing-jig-uses-accupuncture-needles/ https://hackaday.com/2019/11/15/needling-your-projects-3d-pr... Model for 3D printing: https://www.thingiverse.com/thing:3615910 https://www.thingiverse.com/thing:3615910
- dendrite9 3y ago
  Interesting, I liked the flexibility of his idea to use coolant hoses, or 3d printed parts to make coolant hoses. But It may be that I just want to toss something together real quick instead of asking for a second set of hands or eyes. I wonder why he updated his design to the newer one you posted? 2015: https://www.thingiverse.com/thing:801279 https://www.thingiverse.com/thing:801279
- sephamorr 3y ago
  Came to upvote this. The station works unreasonably well. The needles are pointy enough that they deform solder/copper a little bit and stay put once placed (you can flex the arm to preload the needle). You can buy it on the maker's website in the second link, with all the bits for ~50eur. Naturally this is no good for high frequency, but it has saved me countless hours of soldering and removing fine wire in the lab.
eschneider 3y ago
Hardware engineers who leave documented test points are my favorite people.
- analog31 3y ago
  You're welcome. ;-) Likewise to software engineers who leave "hooks" to internal functionality, so we hardware folks can create automated tests.
markild 3y ago
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/ https://sensepeek.com/
- adhesive_wombat 3y ago
  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 3y ago
  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 3y ago
    > 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 3y ago
    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.
nonrandomstring 3y ago
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 3y ago
I use 30AWG (Kynar wire) for most things I build. I have it in multiple colours which is helpful.
sebcat 3y ago
PUR-coated copper wire, .15mm diameter is pretty good. .1mm when needed. Use flux, good lightning and some (~10x) magnification.
onetimeuse92304 3y ago
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 3y ago
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 3y ago
  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 3y ago
    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 3y ago
    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 3y ago
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.html https://www.lcsc.com/product-detail/_BAT-WIRELESS-_C5137195.....
- kevin_thibedeau 3y ago
  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 3y ago
    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.
  - bsder 3y ago
    I would go further, adjust your footprints to accommodate a 30AWG wire being soldered to them. Too many people blindly accept generated footprints that are meant for machines and not humans. They are far too dense and have too little overhang. For QFNs, adding about .4-.6mm of exposed copper extension to all pins can make both testing and hand rework vastly easier. In addition, extending the thermal pad far enough that you can easily hit it with a soldering iron often makes heat gun rework tremendously easier. While this won't work for giant BGAs, you can often figure out how to extend exposed copper for up to about a 36 ball (6x6) BGA. For example, there are some wonky packages for power transistors that are basically 4 ball (2x2) BGAs. Running the traces out diagonally with some extra exposed copper helps for both soldering and testing.
akaij 3y ago
Tangentially, does anyone know if there are any off-the-shelf or DIY solutions to overcome hand tremors while soldering? I have read about micromanipulators: - off-the-shelf (https://www.singerinstruments.com/solution/mk1/specification/ https://www.singerinstruments.com/solution/mk1/specification...) - DIY (https://www.microbehunter.com/microscopy-forum/viewtopic.php?t=4800 https://www.microbehunter.com/microscopy-forum/viewtopic.php...) (https://retrotechjournal.com/2017/10/03/make-yourself-more-precise/ https://retrotechjournal.com/2017/10/03/make-yourself-more-p...) (https://www.sciencedirect.com/science/article/pii/S2468067218300415 https://www.sciencedirect.com/science/article/pii/S246806721...) They are very interesting, but don't seem to be suitable for soldering.

99 points by dcminter 3y ago

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-printed-pcb-probing-jig-uses-accupuncture-needles/ https://hackaday.com/2019/11/15/needling-your-projects-3d-pr... Model for 3D printing: https://www.thingiverse.com/thing:3615910 https://www.thingiverse.com/thing:3615910

dendrite9 3y ago
Interesting, I liked the flexibility of his idea to use coolant hoses, or 3d printed parts to make coolant hoses. But It may be that I just want to toss something together real quick instead of asking for a second set of hands or eyes. I wonder why he updated his design to the newer one you posted? 2015: https://www.thingiverse.com/thing:801279 https://www.thingiverse.com/thing:801279
sephamorr 3y ago
Came to upvote this. The station works unreasonably well. The needles are pointy enough that they deform solder/copper a little bit and stay put once placed (you can flex the arm to preload the needle). You can buy it on the maker's website in the second link, with all the bits for ~50eur. Naturally this is no good for high frequency, but it has saved me countless hours of soldering and removing fine wire in the lab.

eschneider 3y ago

Hardware engineers who leave documented test points are my favorite people.

analog31 3y ago
You're welcome. ;-) Likewise to software engineers who leave "hooks" to internal functionality, so we hardware folks can create automated tests.

markild 3y ago

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/ https://sensepeek.com/

adhesive_wombat 3y ago
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 3y ago
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 3y ago
  > 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 3y ago
  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.

nonrandomstring 3y ago

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 3y ago

I use 30AWG (Kynar wire) for most things I build. I have it in multiple colours which is helpful.

sebcat 3y ago

PUR-coated copper wire, .15mm diameter is pretty good. .1mm when needed. Use flux, good lightning and some (~10x) magnification.

onetimeuse92304 3y ago

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 3y ago

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 3y ago
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 3y ago
  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 3y ago
  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 3y ago

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.html https://www.lcsc.com/product-detail/_BAT-WIRELESS-_C5137195.....

kevin_thibedeau 3y ago
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 3y ago
  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.
- bsder 3y ago
  I would go further, adjust your footprints to accommodate a 30AWG wire being soldered to them. Too many people blindly accept generated footprints that are meant for machines and not humans. They are far too dense and have too little overhang. For QFNs, adding about .4-.6mm of exposed copper extension to all pins can make both testing and hand rework vastly easier. In addition, extending the thermal pad far enough that you can easily hit it with a soldering iron often makes heat gun rework tremendously easier. While this won't work for giant BGAs, you can often figure out how to extend exposed copper for up to about a 36 ball (6x6) BGA. For example, there are some wonky packages for power transistors that are basically 4 ball (2x2) BGAs. Running the traces out diagonally with some extra exposed copper helps for both soldering and testing.

akaij 3y ago

Tangentially, does anyone know if there are any off-the-shelf or DIY solutions to overcome hand tremors while soldering? I have read about micromanipulators: - off-the-shelf (https://www.singerinstruments.com/solution/mk1/specification/ https://www.singerinstruments.com/solution/mk1/specification...) - DIY (https://www.microbehunter.com/microscopy-forum/viewtopic.php?t=4800 https://www.microbehunter.com/microscopy-forum/viewtopic.php...) (https://retrotechjournal.com/2017/10/03/make-yourself-more-precise/ https://retrotechjournal.com/2017/10/03/make-yourself-more-p...) (https://www.sciencedirect.com/science/article/pii/S2468067218300415 https://www.sciencedirect.com/science/article/pii/S246806721...) They are very interesting, but don't seem to be suitable for soldering.