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I have mounted a STM32F446VETx on my PCB as shown on a picture of my PCB:

enter image description here

For me the pin 1 marker in the big mark at the top right of the picture, near C67.

But, after a lot of trial, I can't connect my ST-Link 3 to it. I checked the SWDIO, SWCLK, NRST and power signals. They are all connected to the right pin of the debugger and the 3V3 is nice and clean. This is the bare minimum to connect the St-Link. But, the ST-Link returns "Reason: No device found on target."

After a lot of digging, including testing my St-Link with another board that uses the same programming connectors, I came to the conclusion that I might have soldered my IC upside down!

Looking at the datasheet of the IC:

enter image description here

enter image description here

It seems that the Pin1 marking might have been the small mark at the bottom left of my picture and not the big one... But I haven't found any mention to some molding artifacts that I should pay attention for. I was confused when I soldered the chip and I may have concluded wrongly that the big fatty mark was the pin 1 marking. I don't know if the text orientation is always consistent with the pin 1 or if both are not related. According to the text orientation, the pin 1 mark is the small mark. unfortunately...

Has anyone worked with that chip before and know which marking is the pin 1 mark ?

Desoldering the IC to rotate it is a pain, and I don't want to do that if it is not needed....

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  • \$\begingroup\$ Nice soldering! \$\endgroup\$
    – Arsenal
    Apr 22 at 9:44
  • \$\begingroup\$ Solder paste, stencil mask and oven... it's cheating at this point... \$\endgroup\$
    – Blup1980
    Apr 22 at 13:24
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    \$\begingroup\$ I have had even professional PCB assembly companies fail with STM32 orientation. Nowadays I try to make the silkscreen extra-obvious (LQFP144 markings look a bit different than the 100-pin you have) \$\endgroup\$
    – jpa
    Apr 22 at 17:47
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    \$\begingroup\$ I haven't found any mention to some molding artifacts that I should pay attention for. Unfortunately, it is assumed that everyone knows about it :( To be an embedded engineer, it seems that you need to know the basics of plastic injection molding... \$\endgroup\$ Apr 22 at 21:23

4 Answers 4

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It's a bit unfortunate that the 2nd ejector pin mark from the injection molding process looks so similar to the pin 1 identifier.

In general, IC markings are always printed in the same orientation onto the package. In your case, pin 1 is indeed below the ST logo, and not near the large ejector pin mark. You've definitely got the chip soldered the wrong way around.

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The pin 1 mark is on bottom left.

What is even more confusing is that your PCB lacks pin 1 marking, and the U7 designator is on bottom left, which would indicate that the MCU pin 1 should be on bottom left near U7 print.

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Pin 1 now at bottom left of your picture. With high probability you have wrong orientation of MCU at PCB. Decoupling capacitors and SWD connector are placed for chip with pin 1 on top right corner of your picture.

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I also had this problem, the pin 1 marking is on the bottom left. Don't know why ST does that, its very confusing.

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    \$\begingroup\$ I don't think that only ST does it, assuming that ST even package these chips - many companies use an external packaging vendor. Unfortunately, people who design these packages have one foot in the plastic molding business, so obviously they know how molding process artifacts look. They haven't apparently paused to consider that not everyone sleeps next to a molding press... I've ran into a slight pin 1 uncertainty about 2 decades ago - not due to molding, but due to rather ambiguous package datasheet. A $500 FPGA turned into a paperweight. Ugh. The vendor was kind enough to replace it. \$\endgroup\$ Apr 22 at 21:25
  • \$\begingroup\$ They aren't the only ones, but I do remember having issues with them and more specifically manufactuers asking questions or loading them wrong. \$\endgroup\$
    – Voltage Spike
    Apr 22 at 21:27

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