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) --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 -----------------------------------------------------