No STM32 Target Found - Custom board

[TEsli.1]

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
  • 
  •  
• 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

MCU Schematics

VDD 

External Clocks

[TDK]

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.

[TEsli.1]

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​

[TDK]

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.

[TEsli.1]

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