Sandy,
                    Check some panels after flash to be sure you have
complete hole coverage. Check your developing to be sure you have completely
developed all the resist in the barrel of the holes. Check your tin
coverage, is it enough or is the grain structure what it should be? Finally
the more difficult is have any of these panels seen "rework"? Reetch etc.

Hope this helps,

Mike Doty
P.E.
Sanmina TCE

-----Original Message-----
From: Sandy Kumar [mailto:[log in to unmask]]
Sent: Thursday, January 25, 2001 5:19 PM
To: [log in to unmask]
Subject: [TN] Circumfrential Voids



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
email: [log in to unmask] <mailto:[log in to unmask]>
phone: 847-290-9800, ext. 45
fax: 847-290-9823