Hi Steve,
Sorry for the delayed response. I was out for the afternoon. It appears
that you have had a couple of good responses already. I was going to suggest
Happy Holden's free HDI book which has a clear and instructive chapter on
signal integrity by Eric Bogatin.
The pad will create some capacitance. From my experience, the impact will
not be large and that it will show up as a small discontinuity. However,
whether or not it would have major an impact on the signal would depend on
performance need and operating frequency. That said (and I am musing here),
it would be interesting to define the boundaries, beyond which there truly
be dragons. The difference between a blind via and a small plated through
hole of equal dimensions, for example. My gut says they will be different but
I don't know how much. I will leave that to the experts with the right
tools. Continuing to muse in the moment, however, it might be an interesting
task to create some sort of simple look-up chart of rules of thumb for
common design features for to provide generalized limits and where the clear
air, turbulence and "no fly" zones are at speed and altitude to help the
designer more quickly navigate their design.
All the best,
Joe
In a message dated 12/3/2009 12:37:07 P.M. Pacific Standard Time,
[log in to unmask] writes:
Hi Joe,
Characteristic impedance. Via is a .006 drill on a .012 pad- after plating
approx. .004 . Regards Steve
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Joe Fjelstad
Sent: December-03-09 2:33 PM
To: [log in to unmask]
Subject: Re: [TN] Impedance through a via
Hi Steve,
Are you looking for the electrical or the electronic impact? Current
carrying or characteristic impedance? Hole size and copper thickness will
likely
dominate the former and land dimensions the latter.
Best,
Joe
In a message dated 12/3/2009 10:28:09 A.M. Pacific Standard Time,
[log in to unmask] writes:
Good Afternoon,
Can someone please tell me how to calculate the impedance through a via?
Build is a flex - ½ oz. copper on both sides of .001 kapton. Thanks in
advance. Regards Steve Kelly
Steve Kelly (PLEASE NOTE NEW E-MAIL ADDRESS)
(416) 750-8433 (work)
(416) 750-0016 (fax)
(416) 577-8433 (cell)
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