I've always wondered about this, from both the design and manufacturing standpoint, how is a via-in-pad any different from a via with a non-circular capture pad? Why would you use a microvia instead of lets say a 14 mil via in the center of a 40x40 mil 0603 pad which would practically be a large via capture pad with corners? Why would a fab house worry about the shape of the capture pad, they don't seem to handle octagonal capture pads for through hole vias differently? Or plane stitching vias with practically board size capture pads? Thanks a lot for your help. Best, Vincenzo -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Sol Tatlow Sent: Tuesday, April 06, 2004 7:23 AM To: cchalmers@xxxxxxxxxxx Cc: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] AW: Vias on decoupling pads Hi Chris, >Is it ok to put vias actually on the pads of >a ceramic decoupling cap in terms of manufacture? >Do other people do this? yes, you CAN do this, BUT it can require technologies (micro-via or via-plugging techniques) that are otherwise not needed - this can make the PCB more expensive, as well as extending delivery times, plus can limit your choice of PCB manufacturers: it is NOT simply a case of placing normal vias in pads at the layout stage and end of story (solder paste disappears into the holes=3Dbad/no joints, solder paste application difficulties on other side, etc.). Obviously, via-in-pad CAN give you the best technical result/performance with very small decoupling caps, where there is no space to put the vias for the individual pads BETWEEN the pads (0603 and smaller), and in the case of micro-vias allows the placement of caps directly under full matrix BGAs where it might otherwise not be possible (good against 'bounce'), but needs to be weighed against cost requirements. On a more detailed level, before you use something like micro-vias, you perhaps also need to do analysis (comparison) of the impedances of the various possibilities of connecting the pads to the planes, since micro-vias are (obviously!) small. Plus, micro- vias (normally) only connect between neighbouring layers - stacking is possible, but EXPENSIVE! - which means they are perhaps ok for GND (L1-L2) but not for PWR (L1-Lx). Plugging is yet another different story, with different methods and (plugging) materials. If you want more info, let me know, and I can give you more info on manfg. techniques that will help you evaluate the pros and cons. Hope this helps! ____________________________________ Sol Tatlow, M.Eng. (Oxon) ProDesign Electronic & CAD Layout GmbH Product Developer Albert-Mayer-Str. 16 D-83052 Bruckmuehl Phone: +49 (0) 8062-808-302 Fax: +49 (0) 8062-808-333 Mailto:sol.tatlow@xxxxxxxxxxxxxxxxxxxx www.prodesign-europe.com ____________________________________=20 -----Urspr=FCngliche Nachricht----- Von: Chris Chalmers [mailto:cchalmers@xxxxxxxxxxx]=20 Gesendet: Dienstag, 6. April 2004 12:48 An: si-list@xxxxxxxxxxxxx Betreff: [SI-LIST] Vias on decoupling pads ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl List technical documents are available at: http://www.si-list.org List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl List technical documents are available at: http://www.si-list.org List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu