> I thought that the following stackup was prefered because then every > signal is one layer from a ground plane. > > 1 signal > 2 gnd > 3 signal > 4 pwr > 5 pwr > 6 signal > 7 gnd > 8 signal
But then you don't have as good decoupling between your pwr and gnd planes, since they are farther apart. My stackup (as mentioned in an earlier post, and repeated below) gives you copper balance, better decoupling, and your signals are still only 1 layer away from a pwr or gnd plane. And since the pwr and gnd planes are effectively the same thing to high frequencies, a signal being next to a pwr plane is the same as that signal being next to a gnd plane. sig gnd1 pwr1 sig sig gnd2 pwr2 sig While we are on this subject, I like to use 0.01 uF caps for decoupling, not the 0.1 uF caps you frequently see on digital circuits. The reason is that 0.01 uF caps have a higher self-resonance frequency than 0.1 uF caps, which makes them better able to decouple the high-speed transients that are so common in today's circuits. Also, 0.01 uF caps are less expensive and take up less space (0805 vs. 1206). One last comment: DO NOT put vias within your pads. Some folks advocate this in order to reduce the track inductance from the part pin to the via. The problem is that this causes hell for manufacturing. During the reflow process, solder flows down into the via barrel, away from the part pin/pad junction, resulting in insufficient solder at the junction. Sorry if the previous 2 paragraphs are obvious, but there might be some folks lurking on this list who are new to PCB design and need a rehash of "da rules". Or should I say "(e)da rules". Whaddaya know, I was on topic this time... Best regards, Ivan Baggett Bagotronix Inc. website: www.bagotronix.com ----- Original Message ----- From: <[EMAIL PROTECTED]> To: "Protel EDA Forum" <[EMAIL PROTECTED]> Sent: Tuesday, June 03, 2003 11:02 AM Subject: Re: [PEDA] six or eight-layer (or more?) stackups > >> The "text book" standard that is > >> > >> 1 signal > >> 2 gnd > >> 3 signal > >> 4 gnd > >> 5 pwr > >> 6 signal > >> 7 pwr > >> 8 signal > >> > > > I thought that the following stackup was prefered because then every > signal is one layer from a ground plane. > > 1 signal > 2 gnd > 3 signal > 4 pwr > 5 pwr > 6 signal > 7 gnd > 8 signal > > Any comments? > > Also anyone else losing messages, or is it just my IT department and Lotus > Notes? > > Robert D. LaMoreaux > MTS Systems Corp. > Powertrain Technology Division > 4622 Runway Blvd. > Ann Arbor, MI 48108 > 734-822-9696 > Fax 734-973-1103 > Main Desk 734-973-1111 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * To post a message: mailto:[EMAIL PROTECTED] * * To leave this list visit: * http://www.techservinc.com/protelusers/leave.html * * Contact the list manager: * mailto:[EMAIL PROTECTED] * * Forum Guidelines Rules: * http://www.techservinc.com/protelusers/forumrules.html * * Browse or Search previous postings: * http://www.mail-archive.com/[EMAIL PROTECTED] * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
