i've been using a circuit-test SX500 variable temp soldering station, and using to 0.4 mm tips. i have also notice the tips build up crud very quickly, but had been using the same one for the past 5 months. the problem i seem to have with these very fine tips is they tend to jam into the metal iron holder cage, and i wind up bending the tips. although initially a pain with the bent angles, i later found it quite effective with the SSOP chips.

for a low cost hot air rework station, check out MPJA. they have a hot air rework station for around $150 USD. http://www.mpja.com/category/Solder_...N_15143_TL.asp