I have seen the voids you describe caused by wet holes at the
image pre-clean process.  Moisture in the holes softens the
dry film resist over the hole and the vacuum from panel cooling
draws it into the hole.  The developer leaves a perfect ring of
resist in the hole just down from the knee.

-----Original Message-----
From: Julie Dixon [mailto:[log in to unmask]]
Sent: Tuesday, December 14, 1999 8:42 AM
To: [log in to unmask]
Subject: [TN] Ring Voids
Dear TechNet,
What would cause a perfect ring void just under the knee of the hole, with
the knee
intact? Drill, DML, Dry film, light scrub, Pre plate clean- acid cleaner &
Na
Persulfate Etch 10-15 micro inches, Acid CU, Acid bright Tin, Mono DF strip,
Ammoniacal
Etch. Job specific to 1 part # all other product running along side is
perfect.
All material Std. .062 Fr-4 1/1. Longtime runner w/ no probs in past.
Thanks,
Julie Dixon

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