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Reply To: | DesignerCouncil E-Mail Forum. |
Date: | Tue, 24 Apr 2001 19:14:15 -0500 |
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Hello Jack I see that you are with ADC. Are you in the group in Beaverton
Oregon? I am with tmp.worldwide here in Portland and work with board
designers. I have placed many good designers on contract. I thought I
would mention that one of my clients in Beaverton will need a few designers
in the near future. Would you happen to know any designers that like to
work contracts? The tool of preference is Mentor, for this position. Just
doing a little networking. Thanks for your time.
Sharon K. Gheen
Account Executive
[log in to unmask]
tmp.worldwide
(Parent company of monster.com)
4900 SW Meadows Road, Suite 100
Lake Oswego, OR 97035
Toll Free 888-278-2272
Phone: 503-635-4658
Fax : 503-635-6067
-----Original Message-----
From: Olson, Jack [mailto:[log in to unmask]]
Sent: Tuesday, April 24, 2001 4:44 PM
To: [log in to unmask]
Subject: [DC] Minimum Via Size for .093 Thick PCB
As a result of some discussion with our in-house manufacturing,
we decided to re-evaluate our minimum via size for .093 board thickness.
Just for fun (grin) I decided to look everything up in the latest IPC specs.
If anyone enjoys poking holes in IPC logic, here is the result:
(see below for supporting references)
calculated IPC minimum via size = 19.7 mil drill with 41.4 mil land
Can anyone think of a way to design PCBs to meet IPC with a smaller via?
-=-=-
Our initial parameters are:
Design for Class 2 (no one is going to die if the product fails)
Assume Level C producibility but prefer Level B (ha!)
Many designs are >12" long
Many designs are >8 layers
According to IPC-2222 Table 9-6,
a plated through via on a board >2mm thick for Class 2 is .5mm minimum
Result: the minimum drill size is 19.68mils
According to IPC-2221 Table 9-1,
For a Level C board up to 450mm dimension (<18inches)
and with note 2 to add .05mm to .45mm for >8 layers is .5mm minimum
Result: Minimum Fabrication Tolerance is 19.68mils
According to IPC-2222 Paragraph 9.1.1
minimum land = a + 2b + c
where
a = maximum drill diameter (19.68mils)
b = minimum annular ring (1mil)
c = fabrication allowance (19.68mils)
Result: minimum land diameter is 41.37mils
A 20 mil hole with a 42 mil pad is difficult to design with.
To meet IPC even at Level C, the only thing I can see to reduce is
the minimum annular ring to allow breakout, are ya kiddin me?
Am I missing something?
Any comments are greatly appreciated!
Jack
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