I have just finished reading the EE- 352 Engineering note regarding E-pad packages and mounting techniques. One thing I am not clear of is you don't say whether or not you use thermal relief's or direct connects on the ground plane connecting via's. Obviously direct connection would give you better electrical connection and lower thermal resistance to the ground plane but would it alter the temperature profile needed for reflow ? ie which would be better from the point of view of manufacturability ?
I use a 2.2mm center hole. This is sufficient for hand soldering. A 5mm hole is much too big.
On the 100 pin 21489, I used 24 sounding vias with 0.2mm holes
For hand soldering, we start with a small heater, Hakko FR-830. This preheats the board for better solder reflow.
It is possible to use solder, but we usually opt for paste. We solder a few outside pins on the LQFP first to insure alignment, and then use either a good iron or hot air.
A similar process is used for switchers. These are actually a little more difficult. Layout is critical for switchers. There is a small triangle area that includes the switch, inductor and output capacitor that should be very low impedance as well as the high current grounds.. You also want to avoid noise on the voltage divider and compensation. Read the datasheet many times and look at similar devices. They all have similar layout issues.
The ADI ADP2119 or ADP2120 is excellent for the core. It eliminates the need for external FETs.
Of course, all these hand soldering tricks are less than ideal compared to using a stencil and reflow. It's OK for prototyping, etc. but not what I would want to do in production.
We have never had a process problem with 21489 or 21479 devices in production. The profile is not that special. Any good contract manufacturer should get it right.
I have never heard of preheating parts for 24 hours before using. I doubt it a real big issue.