Hello Ivan,

I find the technique that Leon described, of partial tenting, or via
encroachment works well. Applying a negative solder mask clearance to the
vias of a value that will cover the land of the via, but not the hole. If
you are worried about solder travelling up the vias and forming solder balls
if the board is wave soldered, then the best solution is to use peelable
solder mask on the solder side under the device. This is peeled off after
waving but before cleaning.
You can define this by using fills on one of the spare mechanical layers.
Certainly talk to you fab shop and assemblers about this.

regards,

Phil.

Phil Dutton C.I.D.
Senior CAD Technician
IPC Certified Interconnect Designer

Tenix Defence Pty Ltd 
Electronic Systems Division
Second Avenue, Technology Park,
Mawson Lakes.  SOUTH AUSTRALIA  5095

================================
Phone   (08) 8300 4400 (reception)
        (08) 8300 4481 (direct)
Fax             (08) 8349 7420
email           [EMAIL PROTECTED]
Internet Page   http//www.tenix.com
================================


-----Original Message-----
From: Bagotronix Tech Support [mailto:[EMAIL PROTECTED]]
Sent: Thursday, 13 September 2001 7:41
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



* * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
* To post a message: mailto:[EMAIL PROTECTED]
*
* To leave this list visit:
* http://www.techservinc.com/protelusers/leave.html
*
* Contact the list manager:
* mailto:[EMAIL PROTECTED]
*
* Forum Guidelines Rules:
* http://www.techservinc.com/protelusers/forumrules.html
*
* Browse or Search previous postings:
* http://www.mail-archive.com/proteledaforum@techservinc.com
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

Reply via email to