we place many BGA's by hand, in fact it can be fairly easy.  The
screenprinting is critical and the placement very important.  We build many
prototype assemblies that are not worth setting up on the placement machines,
the bga's are placed by hand.  in general we focus on the following:
- very fresh paste,
- place the part in a very well lit area
- use a very very low vision angle (almost lay your head on the table) and
using a vaccum pen to hold the part place it on while lineing up the rows of
balls with the rows of solder bumps.  this does take some practice.
- do not ever push down on the part
- look at the part from all four sides until all the balls line up with the
solder pads.
- try taking the part off  before reflow you will see that the solder will
generally hold
 up even after pushing the part around a bit (not too much though)
-take your time, some parts are trickier than others but we have put down
just about anything..

any questions send me a line
[log in to unmask]