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I have a STM32L432KS circuit with this 0.5mm pitch UFQFPN32 package:

Photo of Package

I have to take a look at some pads but with which kind of oscilloscope probe could I use?

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    \$\begingroup\$ You can always break out the pins to test points which you can make of arbitrary size. \$\endgroup\$ – loudnoises Oct 12 '17 at 9:24
  • \$\begingroup\$ @loudnoises how do you do this? \$\endgroup\$ – Lemaitre Cedric Oct 12 '17 at 10:01
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    \$\begingroup\$ @LemaitreCedric - I've fixed the broken datasheet link, but FYI I can't find evidence that the STM32L432KS exists; only the B and C suffixes. Although not directly relevant to your question, please update the part number for accuracy and to avoid later questions. Thanks. \$\endgroup\$ – SamGibson Oct 12 '17 at 12:11
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    \$\begingroup\$ Adding a photo would make this question much easier to understand. Here is a link to a 28pin QFP: upload.wikimedia.org/wikipedia/commons/2/23/… \$\endgroup\$ – Frosty Oct 12 '17 at 21:51
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    \$\begingroup\$ @Frosty - Good idea about adding a photo but you made an unfortunate typo - that photo (and the OP's question) are about QFN-type package, not "QFP" as you said. The reason why some of the current answers are not applicable, is that their recommendations rely on having the exposed leads of QFP-type packages, which QFN-type packages don't have (as shown in the underside IC package photo that you kindly linked). Therefore to avoid confusion, it's vital not to mix-up those acronyms, IMHO :-) \$\endgroup\$ – SamGibson Oct 12 '17 at 22:35
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**I misread the initial question, my below recommendations are for an IC with exposed leads/legs. An interposer is our best guess at this point: https://www.arieselec.com/products/data/24007-high-frequency-interposer-socket.htm **

Dean already mentioned it, but I spoke with our probes expert and he mentioned 3 options:

  1. Use a wedge adapter with an N287xA passive probe and dual lead adapter or an N2795A/96A active probe with a dual lead adapter. The adapters we have are the E2613A (0.5mm, 3 signal), the E2614B (0.5mm, 8 signal) or the E2643A (0.5mm, 16 signal) (replace the "x" in N287xA with a 0,1,2,3,4 for different bandwidths).

  2. Use an IC clip like the 10467-68701 0.5mm IC clip

  3. Every one of our N287xA passive probes comes with 5 different IC caps for IC lead pitches.

Hope that helps!

Passive probes here: http://www.keysight.com/en/pc-1659288/oscilloscope-passive-probes?nid=-32557.0.00&cc=US&lc=eng

Single ended active probes here: http://www.keysight.com/en/pc-1659295/oscilloscope-single-ended-active-probes?nid=-32556.0.00&cc=US&lc=eng

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  • \$\begingroup\$ Daniel - Hi, please check again that you're looking at the correct IC package type. I haven't reviewed all of your recommendations, but as I commented to Dean, the wedge adapters which you mentioned (for example) are for QFP-type packages with visible leads, and the OP's package is not one of those. Therefore, as far as I know, they are not suitable for the OP's requirement. Can you please re-check and guarantee that your recommendations really are suitable for the QFN-type of package that the OP is asking about? \$\endgroup\$ – SamGibson Oct 12 '17 at 20:29
  • \$\begingroup\$ Good point, I believe you are right - I'll check. \$\endgroup\$ – Daniel Bogdanoff - Keysight Oct 12 '17 at 22:56
  • \$\begingroup\$ Thanks Daniel, I look forward to an update. I've now checked the recommendations (2) and (3) too (in addition to the wedge adapters mentioned in (1) that I've already mentioned) and both the micrograbbers in (2) and the IC caps in (3) also seem to rely on having the exposed leads of QFP-type packages. Therefore I believe that none of those 3 types of probes / accessories have any features which are specific to avoiding shorts between the pins on QFN-type packages, as QFN-type packages have no exposed lead to "grab onto", nor for the plastic IC cap to "sit over". \$\endgroup\$ – SamGibson Oct 12 '17 at 23:10
  • \$\begingroup\$ So, I did some more digging and my my initial recommendations were incorrect. Sorry for the mixup and thanks for catching it. We'll play around with it here, but my probes guy says the best bet is to to try to find some sort of interposer arieselec.com/products/data/… \$\endgroup\$ – Daniel Bogdanoff - Keysight Oct 13 '17 at 20:51
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For this I solder a very fine wire (like wrapping wire) to the pin and then use the scope's grip tip on the other end. It works quite well.

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    \$\begingroup\$ Yes - though wire wrap wire is actually rather large on the scale of these pins. \$\endgroup\$ – Chris Stratton Oct 13 '17 at 1:29
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You can get probes with a plastic shield at the end that helps align the probe pin with the IC pin without shorting to adjacent pins. You can also get wedge probes that probe two adjacent pins by wedging in between them.

Keysight's offerings: http://literature.cdn.keysight.com/litweb/pdf/5989-6162EN.pdf?cmpid=zzfindkeysightprobes

I assume you already have a board so it is too late to add test pads, but either test pads you can probe, or full-on debug connectors you can connect to a logic analyzer or oscilloscope make life much easier.

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  • \$\begingroup\$ Yes, the guy who make the circuit not place test place to put easily a probe… \$\endgroup\$ – Lemaitre Cedric Oct 12 '17 at 9:59
  • \$\begingroup\$ like N287xA model at page 5 of the document? \$\endgroup\$ – Lemaitre Cedric Oct 12 '17 at 10:06
  • \$\begingroup\$ Take a look at the E2613A (They are not cheap) \$\endgroup\$ – Dean Franks Oct 12 '17 at 17:23
  • \$\begingroup\$ @Dean - Hi, Note that you're recommending probes (like the E2613A wedge probe adapter) which are only suitable for QFP-type packages i.e. the ones with visible external leads. However the OP's device is not in that package! Instead, it has a version of the QFN. See page 148 of the datasheet which they linked in the question. \$\endgroup\$ – SamGibson Oct 12 '17 at 18:04
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When I had to probe a 0.5mm QFN28 the other day, I just put the oscilloscope behind the SMT microscope - I looked through the microscope to position an ordinary cheap scope probe by hand, then looked past it at the scope's screen to see what was there.

Even if the IC doesn't have metalization on the sides, usually there's some exposed solder on the PCB trace, though yes, it's possible to design a board where there's not much gap between the soldermask and the package.

The microscope isn't even strictly necessary, though it helps get the right pin without mistakes (and if you are designing with QFNs and similar, you really should get one to diagnose assembly faults). Obviously, if you know the same signal is available elsewhere on a lower density connection, grab it there instead.

Granted, direct manual probing is harder if you need multiple signals. I also spent quite a while preparing fine enamel wires to solder in to break out an entire SPI bus from the adjacent pins on the side same of that QFN28 to a logic analyzer - in the end I got enough signals to see what was being sent, but MISO wasn't actually connected - fortunately I learned enough without that.

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