Hi all With all due respect, we may as well explain WHY this is not true, and give a model answer for the homework assignment! Argument #1: Electrons will fly off the end of an acute angle trace. There are essentially two electron velocities: the Fermi speed and the drift velocity. The Fermi speed is the actual electron speed, and is in the order of 106 ms-1 for copper. It is not related to voltage or the change in voltage over time (the voltage rise time). The electron drift velocity is the velocity that an electron travels along the medium, and is related to the voltage, is approximately of 0.004 ms-1 for one volt in copper. It also is not dependant on the voltage rise time. Argument #2 : Acute traces can radiate This can happen due to impedance mismatch, but at a scale that is not important. Referring to Fig.1, The corner-to-outside radius of a right-angled trace is approximately 21% larger than the trace width, and it is correct that this will cause an impedance mismatch. However, the distance that the mismatch occurs is less than the trace width itself. (Very large traces, ie, in high RF, this will _start_ to have an effect.) Assuming my maths is correct: A rise-time of 100ps will give a first-harmonic wavelength of approximately 60mm. This is far greater than the mismatch distance, and combined with only approximately 20% impedance difference, any radiation will be extremely negligible. Impedance mismatches from pad-trace or pin-trace will far exceed the value from acute angle traces. Cheers, Richard __________________________ Richard Moffat PCB CAD Manager Allied Telesyn Research Ltd, NZ. ph. +64 (3) 3393000 richard.moffat@xxxxxxxxxxxxxxxxxxx >>> "Lee Ritchey" <leeritchey@xxxxxxxxxxxxx> 31/08/2004 4:38:52 a.m. >>> This is one of the pieces of misinformation that circulates about right angle bends. It is simply not true. Those who repeat it need to do their homework. Lee W. Ritchey Speeding Edge P. O. Box 2194 Glen Ellen, CA 95442 Phone- 707-568-3983 FAX- 707-568-3504 I just used the energy it took to be angry to write some blues. Count Basie > [Original Message] > From: Kanakaraj <k.kanakaraj@xxxxxxxxxxxxx> > To: <pcb_user@xxxxxxxxxxx>; <si-list@xxxxxxxxxxxxx> > Date: 8/30/2004 7:17:42 PM > Subject: [SI-LIST] Re: 90 degree bend > > Hi, > The simplest thing is that when you make 90 degree turns on the pcb track, > the electron moving in it cannot make sudden turns..( remember inertia of > direction in physics and a bus making a 90 degree turn at full speed)... so > some of the electrons will jump out of the pcb track and will cause emi > issues.. > > and Andy, Andrew, Ray anderson and the seniors will give you more inputs on > that. > Well I am too like you. a beginner :-) > Kanak > > ----- Original Message ----- > From: "New Bee" <pcb_user@xxxxxxxxxxx> > To: <si-list@xxxxxxxxxxxxx> > Sent: Monday, August 30, 2004 5:19 PM > Subject: [SI-LIST] 90 degree bend > > > > Hi > > > > I am a new PCB designer. > > > > I have a silly doubt - really do not know if I ask it in this forum. > > > > > > why is it suggested not to have 90 degree bends for the traces while > routing ? > > > > If some one can give me the electrical/electronics and manufacturing > reasons I will be greatful to them > > > > If this is not the right forum to address this please let me know where > can I ask > > > > Thanks in advance > > Kam > > > > Yahoo! India Matrimony: Find your life partner online. > > > > > > Yahoo! India Matrimony: Find your life partneronline. > > > > ------------------------------------------------------------------ > > 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 NOTICE: This message contains privileged and confidential information intended only for the use of the addressee named above. 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