Jack,
I've got some little diddly board houses doing 8mil vias
(at no extra cost) Thats what I've found to be the minimum
drill for most board houses.
Now how thick are the boards that would cause drill wander
to that extent?
I agree if you do teardrops (if your software allows it
easily) the breakout isn't a problem. I'm running 1mil
annular ring (per IPC) and an additional 9mil for MFG
tolerances. That's 22over the hole size. Is that effectively
what your are running on the pad? I don't allow braekout with
this and generally run a 4mil (from pad center) registration.
Not debating it I just want to find out what annular ring
you are using? (collecting data)
Chris Robertson
[log in to unmask] <mailto:[log in to unmask]>
Senior Designer
Lockheed-Martin Services Inc.
4912 Research Dr.
Huntsville, AL 35805
(256) 722-2626
Sorry for the long delay!
I mis-spoke in my email, kind of embarrassing...
I meant we are using 1.27mm pitch on .093mil thick boards with no trouble.
For those designs we use .013mil via holes +.003/-.013
(so they can be plated closed, we don't care) and they have .025 pads
For 1mm pitch, our vendor says we can use 20mil (or.5mm for dual trace)
with 10mil holes.
In order to make this manufacturable, we have to state that:
1) holes can be plated closed.
(the aspect ratio is too high, and our concern is getting the plating
all along the barrel. who cares what the finished hole size is, right?)
2) breakout is ok
(the drill wander through a thick board may break the annular ring
requirement. which means the drill can cut the edge of one side of
the pad. the result is that a trace on that side of the pad may be
disconnected by the drill, which leads to the all-important last
item number 3)
3) teardrop the pads!
(since this adds copper at the point where a trace joins the pad,
even if the drill "breaks out" at that spot, there is extra copper
to keep the connection)
I have never heard anyone complain about this method, and it has been posted
before on various forums.
I don't know how we are going to handle finer pitch devices on .093 boards,
without using microvias. (haven't had to yet, but only a matter of time,
eh?)
Good luck,
Jack
-----Original Message-----
From: ANDERSON, Corky [mailto:[log in to unmask]]
Sent: Tuesday, April 03, 2001 1:09 PM
To: Olson, Jack
Subject: RE: [TN] [DC] Blind and Buried Vias
Hi Jack,
Can you tell me what size vias and pads you are using for 1MM BGAs-
We are currently doing some via size tests with different pitch BGAs and
trying to avoid special processes.
Thanks,
Corky
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