Every electronic technician has a different "best" way to solder surface mount components onto a PC board. My favorite method for the 64-pin PIC 18F6520 micro-controller is shown in the attached movie. First I use a circuit board with ample solder plating. Then I coat the surface pattern (solder pads) with liquid rosin flux that comes in an alcohol base. I line up the chip and pads by looking through a stereo-dissecting microscope. I use a very sharp temperature-controlled tip (700 F) and press the tip down at the junction between the chip leg and the PC board trace. I do not add any solder but depend on the solder plating on the chip and on the board to melt together. I observe the solder coating melt upward on the leg toward the chip and stop heating when most of the solder from the leg has been melted. When all legs are soldered, I test the connections by pushing sideways on each pin with a probe to see if it is solidly attached. If it moves, then I resolder it.
Different techniques are better for different size chips. You can use solder paste, stencils and ovens to melt the solder. Circuit board manufacturers may also offer an assembly service but I have never tried using it. It seem likely such service will be very expensive compared with doing it yourself.
Contributed by: Dr Steve Smith