Homebrew PCBs

Hi,

Well I've had the opportunity now to try both the budget hot-air 
soldering system using the fish tank bubbler and radio-shack 
desoldering system (as seen in the links section) as well as a 
Xytronics system that I just got that includes a hot-air pencil.

Firstly, using either system without preheating the board is an 
exercise in futility. While the budget system did ultimately melt 
the solder paste, it took forever. The Xytronics system never even 
got hot enough to melt the paste! Add to that the strength of the 
air flow and the parts just flew off the board. So I stopped using 
that system for hot-air work. I did ask the vendor about it and they 
said the hot-air pencil was really meant for shrink wrap and other 
apps and that I should buy the full hot-air rework system if I 
wanted to solder with it. No thanks...

Continuing with the budget system, which has a nice gentle flow, I 
had very good results on IC's when preheating the board to 150-200F. 
That really worked pretty nicely. The tiny caps were still tough 
though as they seem to blow away at the slightest provocation. 

I also had problems with shorts under caps. Are there any tips about 
this? The problem is that the paste starts running and wicks under 
under the chip (even a little dab) leading to shorts. With the hot 
air, I can't seem to get that to melt effectively under the cap. Any 
hints?

For a budget preheater, I got a free-standing heater that looks like 
the top of an electric range, maybe 8" in diameter for the entire 
unit. I then took a cast iron frying pan, turned it upsidedown and 
put it over the entiire unit so the inside of the pan rested on the 
heating elements. This seems to provide a nice uniform heat. A 
cooking thermometer was used to measure the temperature roughly.

I'd heard the 200F number for preheating before, is this the right 
number? Also, how long is it safe to heat the board and components? 
From chip specs, it seems like 200F is ok indefinitely, but I'm not 
sure.

-Ted