Wayne,
I agree with Richard's response in separate email and to an extent with you,
Wayne. Teardropping is regarded as "best practice" by many and normally
comes as an automatic, semi -automatic or manual process on layout tools.
I'd rather do it in-house as the design rule checks can still be made and
track entry adjusted to maximise coverage. Where compromises occur, they can
be managed. Remember also, on very high speed designs, the signal integrity
characteristics will be altered by addition of the teardrop and this needs
to be verified by appropriate simulations - at very high speeds, vias can
look like band-pass filters due to inductive/capacitive effects above
certain frequencies/bit rates. Additions at PCB fab house cannot account for
this and may upset operation electrically.
Barbara,
The enhancement of track entry with teardrops at feature sizes you describe
will help, but nothing protects against any fab house's bad process if
they're drilling is not up to par (i.e. the pad annulus to adjacent copper
features on non-teardropped layers - the barrel could be closer than you
want). And there's nothing wrong with being an "old-fashioned girl" - would
that there were more ;-)
Kind Regards,
Phil.
-----Original Message-----
From: Wayne Thayer [mailto:[log in to unmask]]
Sent: 06 July 2006 14:32
To: [log in to unmask]
Subject: Re: [TN] Validy of Teardropped vias?
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Barbara-
That's usually a job done in CAM--the PCB fab usually will contact you
if they feel like doing it. Teardropping drastically reduces the
probability that minor breakout due to layer stackup lamination issues,
over etching, or drill mis-targeting will cause a continuity failure.
But if your annular ring is 5mils or greater, the probability is
probably pretty darned small anyway.
Wayne Thayer
>>> [log in to unmask] 7/6/2006 9:17 am >>>
Hey Y'all,
It is my habit to teardrop a trace coming into a through-hole pad if
the
trace is 5 mils or less and the annular ring of the pad is 5 mils or
less.
Does this improve manufacturability of the bare board, protect against
drill-out, and fracturing of the point where the trace enters the pad
under shock and vibration?
Or am I an old-fashioned girl?
Barbara Burcham, C.I.D.
Sr. PCB Designer
RFTrax a Fairfield Co.
[log in to unmask]
281-276-5916
281-276-5950 fax
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