We have now received our first control board PCBs from ITead Studio. It took two weeks from placing the order to receive the boards. ITead provides quite cheap services. You can get a 5cmx5cm 2-layer PCB at less than 2$ per piece and it includes the shipping costs. At those prices you can’t expect highest quality but we wanted to see if it would be good enough. The smalles used wire width in the design was 12mil and it looks good on the board. Also the drill holes are where they are supposed to be. The biggest quality problems are in the silk screen. In most boards we received it’s a bit off and quite smudged. Outline of the board is 96mmx48mm
As this was a completely new desing for us we were quite eager to see what works and what doesn’t. The board assembly is quite easy. Soldering the STM32 LQFP64 cased chip might require some skills or a microscope.
After assembly we could see that the board starts up and works. So far we have found one bigger issue when using the USB to power the board. The 5V from the USB is connected to PB13 for detecting the USB client mode. The problem is that the used PB13 pin works properly only after setting the pinmux correctly in the software. Before that the 5V leaks through the chip and 5V can be measured from the power rail. This is not nice. I tested that with the F4 discovery board and PB13 pin the same behaviour can be verified. The difference with F4 discovery design is that instead of PB13 the PA9 is used for detecting the USB 5V. Possibly the PA9 pinmux defaults internally differently so the problem can’t be seen on that pin.
Otherwise the issues we found where more SW related. ChibiOS got F4 support just recently and it runs on our board nicely despite some missing tweaks.