@dzungpham0703
I buy them on Aliexpress:
https://www.aliexpress.com/wholesale?catId=0&initiative_id=SB_20180706102504&SearchText=HTTM
If you apply hot air it is easy to take off the white "double sided tape" and the plastic.
@fets So far, I have only built the 5x5 board (but the others should be schematically identical). The only issue I have found so far is that I cannot get the ISP port to work. But I have checked and I have an identical setup on the 1.0 board and that worked, so I suspect the programmer is too weak to drive the net on this one. So it is not a board-issue per se, and might only be an issue on the 5x5 board as routing is the most complex on that one due to the size.
