Richard, So what you're saying is that you have no cents in New Zealand? :) Good point on uniformity of the 4 mil traces !! Dave > > From: "richard moffat" <richard.moffat@xxxxxxxxxxxxxxxxxxx> > Date: 2006/07/27 Thu PM 04:13:28 CDT > To: <icu-pcb-forum@xxxxxxxxxxxxx> > Subject: [PCB_FORUM] Re: How-to? [Impedance] > > Likewise - good idea to have it consistent. However, 4mils is harder to > achieve a constant impedance. The uniformity of the trace width and the > closer proximity to the reference plane are the two bigger problems. > > 5.68 down to 5 isn't that big a jump, and it will only be a short distance > (1/2 an inch?) that has a slightly higher impedance. Personally, I'd opt for > that. > > On a different note, you may have to look at a 10% tolerance for fine traces > such as these. 5% is more commonly used for wider traces such as 34 ohm used > in Rambus. > > Just my 5 cents. (We don't have 1 or 2 cent coins in New Zealand anymore.) > > Kind regards, > Richard > > > > >>> Dave Schaefer <dave.schaefer@xxxxxxx> 28/07/2006 7:44 a.m. >>> > Good idea from a tool useage standpoint, but you'll create an Impedance > "bump" - really depends upon the design as to if this is an issue. However, > Controlled Impedance is normally employed to prevent these "bumps". > > For example, a design with 5 mil traces requiring neck down to 4 mils in fine > pitch areas results in a 20% Impedance change ... why not just design > features and stackup to use 4 mil throughout? > > Just another opinion to consider ... > Dave > > > > From: "Feehan, Stephen \(Com US\)" <Stephen.Feehan@xxxxxxxxxxx> > > Date: 2006/07/27 Thu PM 02:14:10 CDT > > To: <icu-pcb-forum@xxxxxxxxxxxxx> > > Subject: [PCB_FORUM] Re: How-to? [Impedance] > > > > Hi William, > > > > Add an area constraint around the bga and set the width to the size you > > need. > > > > Here's an example: > > Area constraint = Net_Physical_Constraint = BGA_AREA > > Create new Net_Physical_Constraint = 5_mil_width > > > > Then under the assignment table set no_type in the BGA_AREA to 5_mil_width > > constraint. > > > > When you route into the bga it will automatically change to 5 mils then > > change back > > to 5.68 when you exit the bga area. Assuming you have the default width set > > to 5.68 for > > the 50 ohm nets. > > > > Regards, > > Stephen Feehan > > Siemens Network Convergence > > > > > > ________________________________ > > > > From: icu-pcb-forum-bounce@xxxxxxxxxxxxx > > [mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx] On Behalf Of William Billereau > > Sent: Thursday, July 27, 2006 1:19 PM > > To: icu-pcb-forum@xxxxxxxxxxxxx > > Subject: [PCB_FORUM] How-to? [Impedance] > > > > > > Hello All. > > > > We are actually fighting with impedances! > > all:all:50 ohm:5% > > > > Allegro routes with an autocalculated line width of 5.68mils. > > This is not possible to route inside the BGA which has an area with minimum > > line width set to 5 mils. > > small lenght routed with 5mils have impedance DRCs. > > > > I try to route them without the area using neck mode. The neck mode off the > > line is still 5mils. It does not switch again to 5.68mils... > > but it is not even a solution because the neck has also DRCs.. grrrrr. > > > > How do you generally proceed in such cases? > > > > Thanks in advance! > > > > William. > > > > =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= > > | Billereau William | PCB Designer | > > | | Tel: (+4122) 76 73403 | > > | CERN TS/DEM | william.billereau@xxxxxxx | > > | 1211 Geneve 23 Switzerland | Société: AMEC-SPIE/Electrotech | > > =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= > > > > > > ----------------------------------------------------------- > To subscribe/unsubscribe: > Send a message to icu-pcb-forum-request@xxxxxxxxxxxxx > with a subject of subscribe or unsubscribe > > To view the archives of this list go to > //www.freelists.org/archives/icu-pcb-forum/ > > Problems or Questions: > Send an email to icu-pcb-forum-admins@xxxxxxxxxxxxx > ----------------------------------------------------------- > > NOTICE: This message contains privileged and confidential > information intended only for the use of the addressee > named above. 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