Remember, the reason for the thermal relief is to insure that the component leads can be soldered and unsoldered successfully, so all leaded components need thermal reliefs large enough to permit initial assembly and later rework. Worrying about the added inductance of the thermal ties often reminds me of looking where the light is good. The leads of these components have at least an order of magnitude more inductance than the thermal ties can ever create. Lee W. Ritchey Speeding Edge P. O. Box 2194 Glen Ellen, CA 95442 Phone- 707-568-3983 FAX- 707-568-3504 I just took the energy it took to be angry and wrote some blues. Count Basie > [Original Message] > From: steve weir <weirsp@xxxxxxxxxx> > To: <Gareth.Baron@xxxxxxx>; <jan.gillis@xxxxxxxxxxxxxx> > Cc: <si-list@xxxxxxxxxxxxx> > Date: 4/28/2004 5:42:40 PM > Subject: [SI-LIST] Re: thermal relief > > Gareth, I agree with your advice that thermal relief should only be used > where needed. But the effects are not as terrible for the leaded component > as you make them sound. > > You can estimate the effects rather easily by looking at the spreading > resistance and inductance for a solid ring with the via ID, and the spoke > width for the OD, and then just multiply that up by the area difference > between the ring and the spoke areas. Leaded components that would be > impedance sensitive like VRM modules are usually handled with a patch of > vias. In that case, relieving the component via has almost no effect. > > Regards, > > > Steve. > At 05:22 PM 4/28/2004 -0700, Gareth Baron wrote: > >My thoughts would be: > > > >Since you now have mini stubs going from the via [for thermal releifed = > >pads] > >to the reference plane you will be decreasing the skin-area for the = > >current > >return path at high frequencies - hence the impedance will go up at = > >higher > >frequencies. Ie the little stubs will act like series inductors. = > >You'll > >probably have to do some calculations using an inductance model to find = > >out > >how serious this is. > > > >My advice: Don't use thermal relief on vias for the following reasons: > > > >1) You add unnecessary inductance > >2) You're more likely to have isolations/islands on power planes since > >the thermal pads are easily cut-off from the power planes. > > > >Gareth. > > > >-----Original Message----- > >From: si-list-bounce@xxxxxxxxxxxxx > >[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of jan gillis > >Sent: Wednesday, April 28, 2004 4:09 AM > >To: si-list@xxxxxxxxxxxxx > >Subject: [SI-LIST] thermal relief > > > > > >Hi all, > > > >I am designing a four-layer microwave synthesizer. The second layer is=20 > >defined as a ground plane. For soldering purposes, it would be preferred = > >to=20 > >make use of thermal reliefs for the ground vias. But I wonder what would = > >be=20 > >the influence of the pin-to-ground plane impedance. Can anyone provide = > >some=20 > >guideline for this purpose? > > > >Thanks! > > > >------------------------------------------------------------------ > >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?Si-List_FAQ > > > >List technical documents are available at: > > http://www.si-list.org > > > >List archives are viewable at: =20 > > //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 > > =20 > > > >------------------------------------------------------------------ > >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?Si-List_FAQ > > > >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?Si-List_FAQ > > 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?Si-List_FAQ 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