Phil in any way do you feel that this cracking has gotten worst since 
     MDA was taken out of the polyimide resins?
                                                Jim Spendow 
                                                Smiths Industries
                                                PH 616-241-8413
                                                FAX 616-241-8686

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Subject: Re: polyimide bd, failure 
Author:  [log in to unmask] at SMTPpost1
Date:    3/31/96 10:48 PM


The failure of this type is not uncommon when using the high temp. 
polyimides, Keramid 601, (and some of the loweer temp ones) which tend to be 
brittle especially when the resin is not reinforced in power/ground  planes 
where the lands have been removed and unreinforced resin from the prepreg 
fills the area between the hole wall and the copper cladding on the ground 
plane.  A careful horizontal microsection often reveals radial cracks 
extending from the hole wall to the ground plane in these resin rich areas 
and after electroless plating these partially fill with copper and if not 
initially shorted will form a path for migration.  The thicker the copper 
cladding, the more likely for this to happen.  And when getting into thin 
metal core, 0.007in. thick,  and using the brittle resin, it is sure to 
happen. 
     
Phil Hinton 
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