Archive of the former Yahoo!Groups mailing list: Homebrew PCBs

I did play with some CSP chips a while back to see if I could solder
them with my hotplate, and it worked - although you have to be careful
about lead-free solder balls on those, they melt at a higher
temperature. IIRC I used a flux pen both on the pcb and on the solder
balls, to make sure they'd adhere properly since as you note you can't
see under them. If you're going to use the "dab of solder" trick, use
lead-free solder. Also, be wary of flux under the chip - water clean
is hard to get out, and no-clean conducts electricity! It's like a
100k resistor between the balls.

The board worked, but one chip popped off when I flexed the board - I
use thinner than average boards, and it ripped the solder balls right
out of the chip! So if you're going to do bga, use as stiff a board
as you can fab.