[SOLVED] STM32F4 custom PCB design problem - Page 1
Forum section: electronics / general

author: can47
author_rank: Contributor
timestamp: January 24, 2021, 07:58:05 pm
content: I designed a pcb with STM32F411RE and a couple of sensors. Before, and after mounting components on the PCB, I checked the Vcc and GND pins for short circuit and I did not see any problem. I am using SWD programming and I connected my ST-Link V2 to my board, successfully loaded the program. Everything was normal until a few minutes. Approximately 3-5 minutes after, MCU disconnected from PC and then I checked the Vcc and GND pins and observed short circuit. Interestingly, as time goes resistance between Vcc and GND pin increased by itself.After that, I just mounted STM32F411RE, reset pin configuration and Vcap. I connected my board to PC and loaded the program successfully. However, after a while power pins shorted again. I just uploaded simple led blinking test program.My board schematic is below. Please help me to find my mistake.Schematic.png(132.77 kB. 4909x2254 - viewed 250 times.)In second experiment, I mounted only STM32F411RE, reset pin configuration and Vcap on an empty PCB and same thing happened again, after a while power pins are shorted. I supplied 3.3V from ST-Link V2. In second experiment I did not use any voltage regulator. Is there anything wrong with the power supply of MCU?? I checked from datasheet and did not see anything wrong.I also checked that schematic and pinout in layout matches.Eagle PCB files are also in the attachments

author: apurvdate
author_rank: Contributor
timestamp: January 25, 2021, 06:02:31 am
content: I did not check the pcb.But in schematic your PWR switch has net name '8.4+' on both side of switch, which makes the switch useless.

author: can47
author_rank: Contributor
timestamp: January 25, 2021, 06:55:12 am
content: Let me explain my last experiments on the PCB. For a second PCB I just mounted STM32F411RE, C5(Vcap), R9, C10, LED2, R11 and reset button. I did not solder any sensor, any voltage regulator etc. on second PCB. I used the power lines from ST-Link. I supplied only 3.3V to PCB. At the beginning I connected PCB via SWD to my computer and loaded simple LED blink program and everything works fine for a couple of minutes. After that I lost connection with PCB via ST-Link. I removed the power pins and see the short circuit.LED2 is connected to the PC2 GPIO output pin of the MCU there is also a 220ohm resistor. I think that the problem is in the microcontroller. Because in second experiment there is nothing than STM32 on the board. However, you are right I2C line should not be pulled up to 5V. In addition to that in second experiment where only STM32 on the board. The current consumption was normal it was about 10-20mA. But after a while it shorted again.

author: errorprone
author_rank: Contributor
timestamp: January 25, 2021, 02:11:59 pm
content: Are you using polarized capacitors and are they installed correctly? Does the short go away if you remove the capacitors or the MCU.

author: can47
author_rank: Contributor
timestamp: January 25, 2021, 08:52:59 pm
content: Probably I solved the problem finally. I removed the LEDs and did not use flux while soldering the STM32F411 and changed the ST-Link. As a result, the board is working fine, however I did not mount all of the components. For now, I mounted STM32F411, HC-06 Bluetooth and reset circuitry and it works without any problem.I think that the problem may be caused by the LEDs or the ports that connected LEDs or maybe the ST-Link that I used is damaged or there is something. In addition to that I doubt that maybe particles (dirt) in the flux may changed the conductivity of the flux.Tomorrow, I am going to complete the board.I will give a feedback from here. Thank you everybody for your contribution.

author: amwales
author_rank: Regular Contributor
timestamp: January 25, 2021, 11:07:32 pm
content: What flux did you use?This might interest youhttps://www.microchip.com/forums/m1151591.aspx

author: can47
author_rank: Contributor
timestamp: January 26, 2021, 05:37:23 pm
content: Friends today I completed the board and it works good finally. I did not used any flux and did not mount LEDs and changed the programmer ST-Link. Thank you all again for your precious contribution.