X-Authentication-Warning: delorie.com: mail set sender to geda-user-bounces using -f X-Recipient: geda-user AT delorie DOT com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type:content-transfer-encoding; bh=ZOC/VCfkspHKyFBp8aTLhPVzIKUc8E7RtdMeLS3OtcU=; b=Za7wBfMnVOYIct2ESCqK4hH38amBLcvMwoo5khb3ZobbpSKQRXPPBFdEA7d5lfzD+T 1g5dUNvcdtEU04F9uucDWkLIZbTgF3B7kcN9TU0ReLaMD/cvGsU85dwMZfbZARSAwqkT NWpENIk6QBZ+/mKl4WZ99G6thbgLd5nZUa4MxbrULLyrJI6ol93iPHhIfOjmD41R4Zce 3qI7TNXMb3SutdzbRBCAOeVHxyDx+GR/g5b212tqByjOnmPYGRaIojDzvZgT+8vFSX1Y f5zNiLWcnaem8xvFSuo4By3Q9RCRnl08qKjX2Og88+jOZ7DSolUYx3TGpzOEfRQoWG53 0bRw== MIME-Version: 1.0 In-Reply-To: <20121023192443.GK524@fi.muni.cz> References: <20121023192443 DOT GK524 AT fi DOT muni DOT cz> Date: Wed, 24 Oct 2012 10:22:04 -0400 Message-ID: Subject: Re: [geda-user] Trace width - best practices? From: Bob Paddock To: geda-user AT delorie DOT com Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by delorie.com id q9OEM9UW027955 Reply-To: geda-user AT delorie DOT com Errors-To: nobody AT delorie DOT com X-Mailing-List: geda-user AT delorie DOT com X-Unsubscribes-To: listserv AT delorie DOT com Precedence: bulk On Tue, Oct 23, 2012 at 3:24 PM, Jan Kasprzak wrote: > Note that I don't want the whole net to be made from wider traces, > only connections between some of the pins of the same net should be made wider. These are better known as Fuses, and are generally a bad idea. Not saying it is not very common, just consider the Fuse aspect. > - this decoupling capacitor should be placed as close to this chip as possible > > or > > - these four connections together form a current loop, and the loop as a whole > should be made as short as possible It would be great to mark segments of the same net with attributes in both PCB and the schematic. As to the Autorouter being able to do it I don't think any Autorouter for any cost will be considering all issues that need thought about for a while. Autorouters are great for things like memory and digital buses, analog and power, not so much. What I have below here was written on a different list to a different question but the information is relevant to yours: ============================================ It has to do with the self-resonance of the package. Different capacitance values may have the same package self-resonance, for packages of the same size: http://www.sigcon.com/Pubs/news/1_17.htm Summed up in Intersil App. Note 1325: http://www.intersil.com/data/an/an1325.pdf "Since the same package was used for each of the capacitors, their high frequency responses are the same. Effectively, this negates the use of the smaller capacitors!" Articles by Howard Jonson on the subject: http://www.sigcon.com/Pubs/pubsKeyword.htm#bypass%20capacitors For anyone that is really into this kind of stuff I *STRONGLY* recommended subscribing to the Compliance Club, and reading all 102 (current issue) back issues: Journal Issue #55 and #56 2004 explains the issue and the issues of layout that I've never seen described anyplace else: http://www.compliance-club.com/journal_article.aspx?artid=138 section 2.6 to 2.9. [Note the pop-up at the bottom of the screen that forces you to check a box to allow cookies, if you don't you can't subscribe. It is free to subscribe.] Every layout I've ever seen puts the different values capacitors in the same physical orientation next to each other. This fails to account for magnetic flux interference between the packages. [If someone is going to tell me there is not magnetic flux then you have moved in the world of Scalar Potentials from the Aharonov–Bohm Effect & E. T. Whittaker .] Self-resonance (package), ESR, ESL, capacitance value, magnetic flux (layout), frequencies of interest, number of board layers, all have to be accounted for, which means it is not as easy as paralleled values [or changing trace widths in the middle of a net] is good or paralleled values is bad. Makes this job such fun...