In this scenario you have given what will be minimum annular ring to your
vendor. This will force them to lower the hole size from nominal.(They actually
drill about 2-3mils? larger than finished to allow for plating). You did not
indicate board thickness so I am unable to determine aspect ratio. This is
required info to assist in determining minimum hole size. Remember, the smaller
the drill the more cost associated as they break, need more sharpening, and
cannot stack and drill as many boards at once. Also with the small drill you
may get into plating problems depending on board thickness.

Adding fillets to pads is a good way to assure you have enough copper at where
trace and pad meet. This is probably a good idea in your case with 90 degree
break-out allowed. I would make sure the vendor does a 100% net list test on
all boards.

Vendors can typically handle this for you without any cost to you. We have run
into problems where we have a special required minimum spacing (RF) from
trace/trace or trace/ground. This could be a potential problem as vendors only
assure minimum spacing after fillet. Also, our system (Mentor) only allows
adding fillets at gerber generation and does not clear grounds (area fills) to
allow fillet.

Good luck Nevada,
Pt

--- Forwarded mail from [log in to unmask]

Resent-Date: Fri, 15 Mar 1996 11:42:15 -0800
From: [log in to unmask]
Date: Fri, 15 Mar 1996 09:01:33 -0800
Subject: Filleting of via pads
To: [log in to unmask]
Resent-From: [log in to unmask]

WE currently use vias with pads of .024" to .028" and holes of .014" to .018".
The spec on the holes is +0"/-closure.  There is no filleting allowed
presently,
but we to permit 90 degrees of breakout(not at the conductor junction).

My questions are as follows:

1)	What are the risks of the present specification?
2.)	What are the risks and benefits of filleting the via pads?  Can any
electrical problems arise from this?  If so, what?
3.)	If you recommend filleting the via pads, do you do it in house or do
you
	have your supplier add the fillets?  What do you recommend for existing
	designs where there is a cost to revise the artwork?

Tim Fowler
BENTLY NEVADA CORPORATION



---End of forwarded mail from [log in to unmask]