2026-04-10 11:20 AM - last edited on 2026-04-10 11:37 AM by mƎALLEm
Hello everyone.
I have recently made my own STM32 board based on the STM32F405. After soldering all the components and testing all pads and connections, finding them to be wired correctly and checking that the 3.3V is being supplied to all the correct pins, I tried to upload some code but to my shock the STM32F405 isn't establishing a connection via the ST-Link V2 nor the USB cable. After trying multiple fixes, I suspect the issue might be the STM32F405 chip that I got off AliExpress itself.
So before I took any further steps to replace it, I decided to post my schematics on here for review in case the problem was in my PCB design. If you have any remarks on what might have caused this problem, please share them.
NOTE: The -B label is referring to ground, and P is the VCC.
schematics:
Solved! Go to Solution.
2026-04-10 2:15 PM - edited 2026-04-10 2:23 PM
Don't rely on the CubeMx figure, it's just a photo.
Please check the datasheet / Figure 76. LQFP64 - Outline
And this is pin 1:
.
In CubeMx: VBAT is indeed pin 1. But your reference of the package on the PCB is wrong.
2026-04-10 11:24 AM
Schematic looks okay.
Is VCAP around 1.2 V?
Is the chip oriented correctly? Show a picture of the board.
2026-04-10 11:45 AM
VCAP at 1.2V? Do you mean the voltage across it? If so, I can't check it anymore since I just removed those caps to use them in a PCB that I need urgently done. As for the orientation, it's oriented correctly; I triple-checked. Here is a picture:
2026-04-10 12:36 PM - edited 2026-04-10 12:37 PM
I suspect Pin 1 is at the lower right corner in this picture, not the lower left like it needs to be.
Which way is the text on the MCU oriented?
2026-04-10 12:54 PM
Oh no, I clicked on "accepted as solution" instead of "reply." How do I undo this?
The PCB is oriented correctly; the text is just flipped 180 degrees since it's intended to be read from that orientation:
2026-04-10 12:58 PM
Look at this post.
2026-04-10 1:01 PM - edited 2026-04-10 1:01 PM
If the MCU labeling (text printed on the chip) is not right side up in your photo, pin1 is not at the lower left corner.
2026-04-10 1:15 PM
> VCAP at 1.2V? Do you mean the voltage across it? If so, I can't check it anymore since I just removed those caps to use them in a PCB that I need urgently done.
Yes.
> As for the orientation, it's oriented correctly; I triple-checked.
How exactly did you check?
The part is oriented wrong, *and* it is now missing VCAP capacitors. Both of these are showstoppers. You will have to fix both of those. It is possible there are other issues. The soldering does not inspire confidence, but the picture is too blurry to spot any particular issues.
2026-04-10 2:01 PM
Yeah, the VCAP will have to wait until I buy more since I urgently need them, and I only had those 2. But when they were still on this board (4 hours ago), the problem mentioned was still persisting.
For the orientation, I followed this schematic I found:
Over here we can see that pin 1 is VBAT:
Following this schematic, pin 1 is directly above the smaller identifier:
According to my PCB layout, pin 1 is to the bottom right of the stm32F405 lable:
And that means it's the bottom left first pin in this picture since it's turned on its right side, and we can see the smaller identifier is under that row of pins, so I think it's oriented correctly unless the first schematic is wrong:
2026-04-10 2:03 PM
I followed this pinout diagram. Is it wrong?
VBAT is pin 1.