The trick is to establish where and when the void occurred; poor
metalization (black-hole in this case), poor electroplating, or poor Sn(pb?)
plating and thus an etched void.
Shop history and a keen read of the micro-sections will provide the biggest
clues.

Ian




-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Sandy Kumar
Sent: Thursday, January 25, 2001 5:14 PM
To: [log in to unmask]
Subject: [TN] Circumfrential Void


I am looking for information on the possible causes of circumfrential voids
(occuring inside the hole barrel), that I am seeing in the cross sections of
multilayer FR4 boards with 10 mil holes with aspect ratio of 10. After
drilling, these boards go through Blackhole graphitic carbon / Cu flash /
image / Cu pattern plate with Sn as etch resist / strip dry film, etch Cu
and strip the Sn/ LPI and HAL.

I would like to find out the cause for these voids. I deeply appreciate any
valuable advice on how to fix this problem.

Thanks.
Sandy