Ivan, we have found that the best solution is PARTIAL TENTING.
ie You need to cover the annular ring with mask but leave the hole free.
This allows the via to be flushed of any residual etching chemicals and will
still fill if wave soldered.
Depending on your fabricator and process allowance, typically an 18mil hole
could use a 22mil soldermask opening (set your mask expansion to -5mil). We
have not had any adverse feedback in our experience.
hope this helps
Leon Fonstin C.I.D.
Integrated CAD Technologies Pty. Ltd.
http://www.ict.net.au
IPC Certified PCB Designers
-----Original Message-----
From: Bagotronix Tech Support [mailto:[EMAIL PROTECTED]]
Sent: Thursday, 13 September 2001 8:11 AM
To: Protel EDA Forum
Subject: [PEDA] via tenting question
Hello, all:
I am wondering what to do about vias. I have a design for an 8-layer 0.090
in. PCB with about 700-800 vias 32mil pad, 18mil hole (no BGAs). Since the
vias can be very close (6 mil) to other vias and pads, I want to cover the
vias with either soldermask or tent them. What is the difference between
just covering them with soldermask, or tenting? I guess tenting is where
the via holes are filled with an inert material to plug them, right?
I have read in trade journals (such as PCB Design) that trapping residual
PCB etching chemicals inside vias can "eat them out" over time and result in
boards going bad after X years of service. If this is so, wouldn't
soldermask AND tenting both trap these chemicals inside the via holes?
Best regards,
Ivan Baggett
Bagotronix Inc.
website: www.bagotronix.com
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