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