I'm trying to connect to a custom PCB made using an STM32L552ZET6Q using SWD and Cube Programmer, but I keep getting the "No STM32 target found!" error.

[ESpra.1]

I've gone over the hardware with a multimeter and all the pins have the right continuity, I've checked the design against the Nucleo-144 L552ZET6Q schematic and it checks out so far, and I've also checked the connections to the ST-LINK/V3 pins I'm using.

I haven't been able to program the MCU once yet via SWD or USB (I'm mostly sticking with SWD for now).

If anyone has any suggestions or thoughts, I'd appreciate any help I can get. If any additional information is needed from me, I'll do my best to provide

[Tesla DeLorean]

Basically a STRONG indicator that the chip isn't functional in the design.

Assume power and orientation being high up there.

Q vis non-Q parts with different pin outs and powering expectations.

Check the obvious things like the VDD, VDDA, VSS, VSSA connections. (I've posted check lists dozens of times)

VCAP as appropriate, check voltage and caps.

State of NRST pin.

For ST-LINK connections that VTarget is present when need to power buffers.

[ESpra.1]

I hope that's not the case. I've rechecked the connections like you mentioned, and while I haven't attached a voltmeter to each pin, I have checked for continuity on each one and they all come back fine.

As for NRST, I checked it with a logic analyzer and got this back. It looks like its working to me, at least in terms of the NRST line.I'll see what else I can find.

[Tesla DeLorean]

I was thinking in the more free-standing sense.

The alternate signs-of-life test is with BOOT0 HIGH trying to send the data patterns to one of the supported UARTs (See AN2606)

At 9600 8E1 send 0x7F data pattern, and watch for 0x79 response.

[ESpra.1]

If I wanted to do that with ST-LINK on SWD, USB or UART though, I'd have to establish a connection through the ST-LINK tool, right? That isn't happening right now.

[Tesla DeLorean]

The UART / Boot Loader method is entirely independent, and doesn't involve the ST-LINK at all.

It can be done from something like RealTerm, in Hex mode.

There aren't many other signs-of-life indications as the chip tri-states all its pins, and doesn't start or use external clocks normally.

For SWD not to work generally points to a design flaw, or construction issue.

You've shared no materials that would advance my understanding of the design

[ESpra.1]

No, it's not getting finger-burning hot. As for the layout, here's the layout regarding the microcontroller (Board and schematic) as well as the MX layout.

[ESpra.1]

I realize that the brd file image is a bit much and I'll get a better one. In the meantime, the bottom-left corner is pin 1, then it continues right.

[Tesla DeLorean]

Can you get a picture of the PCB section with the part on it?

Schematic looks reasonable enough, SWD traces look Ok.

[ESpra.1]

Will do. In the meantime though, I might have found something. There's an 100k ohm resistor between the NRST pin, and the rest of the SWD connection. The SWD side of the resistor is being pulled low, but is it possible that the MCU side of it is still being held high by the internal pull-up? It looks that way based on the multimeter I'm using, but it could just as easily be too slow to pick it up.

Edit: Here's the photo you asked about. The resistor I mentioned is R6