Typically I would always recommend that all grounds have thermal relief's at
the P.T.H.. This will also help you with your soldering process. Ground
planes tend to act as a heatsink. The more copper at the hole, the more heat
it will attract to the localized area. This excess of heat is the apparent
cause of this defect. The choice of laminate material will also contribute
to this problem. I would recommend a material with a higher Tg such as
polyimide. What type of board is this?

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Richard G Smith
Sent: Friday, December 19, 1997 3:10 PM
To: [log in to unmask]
Subject: [TN] heeelp - NON-THERMAL RELIEVED VIAS AND COPPER PLANES


     Been having some trouble with vias fracturing on plane layers of a
     PCB. The PCB is an eight layer board with four different voltage
     planes. On two of the planes the vias have thermal ties, the other two
     do not. The vias are fracturing on the two planes where a thermal tie
     is not utilized. It seems to be sporadic and only after the PCB is
     assembled which has at least three thermal excursions during assembly.

     The vias are .018 +-.003 and flooded with soldermask.

     Any comments/help/ideas why this is happening would be greatly
     appreciated.

     Thankyou,

     Rick

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