MCU Factory Rejects

I must admit that sourcing for STM32F405RG is an issue. I have bought batches from China and I am rejecting a lot of MCU’s. The worst is actually the time to solder them on before I can test, so I seriously need the tester shown in my last article.

This is worst as I like now deal with a new board. I have soldered on 3 different MCU’s that all show up with failing memory sectors, and it’s a lot of stress on the PCB so you can only solder on/off so many times. After 3 fails on a new PCB I also start questioning other possibilities – do I as an example have a bad SWD on this board? SWD is a bit sensitive so if you have a bad SWD connector it might show up in various forms.

I managed to find a good tester for 44.- USD, so I am looking forward to that one. As much as I would like to test new boards I don’t want to waste more time on MCU unsecurity, so I will wait for the tester. I want to know that my MCU is good before I put it on.

I do however still need to sort out sourcing for STM32F405RG because this is unacceptable. But, with a tester I can actually test the batches I receive and slam down on bad sellers instantly to get my money back. I don’t expect the MCU’s to be perfect, but I expect them to work. This is prototyping and you can’t use my sources in production. But, I am getting rather pissed of with fraud schemes of selling factory rejects through Aliexpress! STM32F405 is specially bad for some reason.

I do however see that Farnell/Element14 sell this MCU for ca 9.- USD each in quantity of 10 delivered “next day” inside Norway – it is 2x my current cost, but it is tempting because of the time I waste on this.

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