All,
The basic problem I'm having is the formation of bubbles in PI-2611
after the hard bake. The bubbles are only forming over aluminum pads and
appear to be within my 3micron thick polyimide, not at the metal, PI
interface. Here are my process steps:

Starting with a SiO2 and patterned aluminum substrate I prebake at 150C
for 5min, then spin VM-651 (0.5% in DI), cure again at 150C for 5min.
Then spin down 2611. Next the PI is soft baked from 50C to 200C on a
hotplate at a ramp of 2C/min. Then the final cure is done in a tube
furnace in nitrogen from 200C to 350C and we hold at 350C for 1hr.

Any advice appreaciated,
   Mike Martin
   University of Louisville
   502-852-1572