What you describe is a common occurrence in dry film solder mask
lamination. There could be a number of causes. I will list a few for you to
check out.

1. Uneven heat distribution during lamination. Heat circles can be caused
by "hot spots" on the platen surface. If you are running a high temp during
lamination, you could be aggravating the problem.

2. Improper clearance/spacing during the lamination cycle. This could
cause uneven pressure from the bladder during the "slap down cycle".

3. The bladder could have increased in durometer from age/use, causing
area's in the bladder to become hard and exert excessive pressure
during the "slap down" cycle.

4. Improper handling of the film prior to lamination. I have seen cases
where pressure applied to the film unevenly during handling could result
in heat circles.

There are certainly other possible causes as well. Hope this is helpful. If
you need further assistance, give me a call.

Bob Metcalf
Morton Electronic Materials
714-730-8356

>>> <[log in to unmask]> 02/20/97 09:34am >>>
Hello Technet,
We have been experiencing problems with our soldermask lamination
process.  We 
use Dupont's Vacrel 8140 dry film soldermask, and apply with an EH2400
vacuum 
laminator.  Upon removal from the laminator, we frequently see that rings
have 
formed in the soldermask.  The rim of the ring is darker green, and the
area 
confined by the ring is lighter green than the surrounding soldermask.  We

have requested help/suggestions from mfg of both laminator and film, but
as 
often happens, each says the problem is not with their product.
Has anyone else experienced this problem while vacuum laminating dry
film 
soldermask?  Any suggestions on how to eliminate this problem would be
greatly 
appreciated.
cbh

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