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No STM32 Target Found - Custom board

TEsli.1
Associate II

Hi guys,

I recently made a design based on nucleo wb55 dongle using STM32WB55CGU (48-UFQFN), but I cannot connect to it using SWD.

I believe it is not a schematic problem, so I am a bit stuck for debugging the situation. I soldered it using hot air station (< 250/260 deg celsius). The joints look okay, but I am not an expert on soldering QFN. So, my main guess is that I broke it while soldering.

  • Is it really feasible to solder it using hot air station ? or a reflow oven is a must ?
  • I compared the voltage on the dongle with my custom board, and the difference I find is on pin VLXSMPS, and VFBSMPS. It is 3.3V on dongle, but 0V on mine. What could be the reason ?
    • It is not shorted to GND.
    • I tried to short it to VDD, but it didnt help
    • 0693W00000Dq0DGQAZ.png
    •  
  • NRST is at 3.24V
  • I use the ST-Link V2 to program it, same as what I use on the dongle

Thank you very much for your time

SWD

0693W00000Dq0TsQAJ.pngMCU Schematics

0693W00000Dq0D6QAJ.pngVDD0693W00000Dq0D1QAJ.png 

External Clocks0693W00000Dq0CwQAJ.png

13 REPLIES 13
TDK
Guru

Soldering a QFN with a hot air gun is very doable, but takes some amount of skill/experience. STM32 chips are quite robust. It's hard to damage them from temperature. Use flux, you should see it shift into place when solder begins to flow.

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TEsli.1
Associate II

Thank you for your message. That's how i did it actually. Would you mind having a quick look at my schematic if you have some time please ?

Thanks again​

I did. Seems fine to me but I'm not an expert with SMPS configuration. I would assume a fresh chip is configured to run in LDO mode for any relevant option bytes.

If you feel a post has answered your question, please click "Accept as Solution".

Thanks, any review is precious ahah. There are not so many STM32WB55CG left on sale online..