Brad,
I cannot recall ever seeing anything from IPC coordinating track widths
to a preferred or suggested via size. I Glanced through IPC-2221 and couldn't
see anything specified. The only statement in IPC-2221 states to use the
largest via sizing that can be accommodated in your design, duh!
For the minimum via size, it is really a question of your fabricators
capabilities. They will have their standard technology minimum hole size (no
premium charged) and their reduced producability or higher technology minimum
hole size (where there will be some premium charged). Then they will have a
minimum annular ring and fabrication allowance for both cases as well.
For your minimum via size in either case, take the minimum hole size
and add two minimum annular ring sizes and your fabricators fabrication
allowance. The fabrication allowance will vary between single/double layer and
multilayer-layer layer counts.
minimum Hole + 2*(annular ring) + fabrication allowance = minimum via pad size
For small width tracks (maybe 6 mils or less) it would be suggested to
add tear-dropping to your track/via, track/pad, entries in order to reduce the
possibility of tracks cracking at the edge of vias/pads during thermal cycles.
Sincerely,
Brad Velander
Senior PCB Designer
Northern Airborne Technology
1925 Kirschner Rd.,
Kelowna, BC, V1Y 4N7.
tel (250) 763-2329 ext. 225
fax (250) 762-3374
-----Original Message-----
From: Brad Kosiance [mailto:[EMAIL PROTECTED]
Sent: August 2, 2005 9:03 AM
To: [email protected]
Subject: [PEDA] Vias.
Any recommendations for via/pad size for 10mil tracks?
I have a dense PCB and require the smallest via/pad size that won't violate
manufacturability of the PCBs.
The signal lines are low voltage and low current.
I assume there is a rule of thumb for 10mil, 20mil, 30mil. track widths?
Thanks,
Brad.
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