I received nice gift from fellow hacker yesterday - my nice, shiny, homemade PCB. Double sided PCB, with no soldermask, but I can live without it.

I didn't enjoy it very long, as I had a lot of work to do.

Soldering QFN AVR

It is not that hard as it may look, even without professional tools. I took the AVR and bit of flux

and solderer the pads. Notice the difference between soldered AVR (left) and virgin one (right).

I soldered the PCB as well

applied more flux to PCB and placed the chip on it.

reflowed with hot-air gun and here we go:

Nicely soldered QFN chip, using those crude tools (homemade soldering iron on left, cheap chinese hot-air gun on right)

I repeated the same process for 12MHz resonator

Then I took DMM and checked if the pads are correctly soldered. I checked the internal protection diodes on IO pins on diode check against ground

Yes, this one looks good. Approximately 600-800mV is fine. Supply pins do read lower values, something like 400-500mV. This way you can tell between short to ground (zero value), OK value or unconnected (unreflowed) pad (infinite value). Of course, this isn't complete test, but as first-round check it's OK.

I soldered the other trinket pro components and made smoke test:

No blue smoke released, so far so good.

As I populated other components, I noticed I forgot to add pull-ups on I2C bus. D'oh! I greenwired (literally) the pull-up resistors and made the use for "breadboard" areas I included on the PCB.

Another smoke test, all voltages do look reasonable.

Now, the FLASH memory of AVR is empty, as expected. I need to get the trinket bootloader into the chip, somehow. For this purpose I used the "breadboard" area again and soldered pin headers for all ISP signals.

I flashed the bootloader (for testing purposes, I took another arduino, flashed arduino ISP sketch and with a little help of avrdude I flashed the bootloader in.

And then, I flashed fuses and the ATmega328p on the board went alive as trinket pro

Whoo-hoo!

Using the manual from adafruit I set up the arduino IDE for trinket pro and flashed blinky example

Awesome! it works!

Now I'm going to port the software from my protoboard version of pavapro