I am in need of some help regarding kapton coverlay (or covercoat or soldermask, whatever you wish to call it) applied on multilayer flex boards.

I am wandering if there is a different procedure that should be followed when bonding a coverlay sheet as opposed to a "normal" cycle for Kapton. Here is what's happening. I'm making a six layer flex board with 3 cores of 1 mil kapton (with adhesive) press cycle 360F for 90 minutes. After I bond the coverlay and a stiffner (same cycle 360F for 90 min) on the board and go through hot air leveling I get severe delamination between the board and the coverlay. Cross sections show that the three cores that make the 6 layer board stick together perfectly but the coverlay blisters in several places both over copper and over clear areas.