Reballing the GPU with stencil

[jackinthexbox]

I removed the GPU and applied 0.6 solderballs onto cleaned GPU with paste flux and stencil.
Everything looks perfect.
But when i start applying heat some solder balls start grouping together. What might be causing this? Bad flux/old pasteflux? Wrong heat profile?

[bonzo pl]

http://www.youtube.com/watch?v=RwMIFtWiAR8&feature=player_embedded

[dc_away]

depends on your stencil, but from the sound of it, your using a non direct heat stencil? if you are, you have to use tacky flux, and low air pressure (3.5-4 on mine). also pre heating the gpu a bit helps, around 80c seems to do the trick.

[jackinthexbox]

Jeps, non direct.
Airflow does not seem to be the problem. I will try preheating.
Flux is very tacky at low temp but heat it up a bit and its very fluid. if preheating does not do the trick i will start looking new flux.

[pkmz]

What exacyly is needed to reball? Like hot air station and what not.