Here's a quick list of things to look into:
Was the the board (especially the surface) completely clean and dry
before applying the coverlay?
Did you remove the release film from the coverlay before lamination?
(Believe it or not, I run into this one at least once a year.)
If you prebake the coverlay before lamination to control adhesive flow
was it too much?
Are you laminating with enough pressure?
Do you have enough adhesive thickness in the coverlay to avoid thin
spots?
Are your conformal materials compliant enough to accommodate the regions
of high and low pressure caused by the local thickness variations in the
multi-layer board?
Are you relaminating before HAL in an attempt to eliminate soda
strawing?
Did you prebake sufficiently before hot air leveling?

Andy Magee
Flex Guru - Consulting
[log in to unmask]
(937) 435-3629


Kiko wrote,

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 stiffener (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.
Any help would be greatly appreciated
Kiko

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