Electronic – Cleaning filthy PCB pads

Rounded pads are better for lead-free surface mount assembly using reflow, because lead-free solder doesn't flow as well as leaded solder, and the higher temperature causes problems with the flux at the corners. They are recommended by IPC. Here is a reference I found.

This may be deemed a comment more than an answer, but just as important as which solvent (if any) to use -- we wash our boards with critical circuitry in RO (reverse-osmosis) water because it is free of salts + other contaminants -- make sure the boards are dried thoroughly.

Surface-mount chips often have a very thin gap between the chip and the board which can act as a capillary to retain water for days. So drying thoroughly is important. I'm not sure what works best, but in one case we put our circuit boards in a thermal chamber at a high temperature (probably 60-80 C; I forget) and low humidity for a day to drive off the water.