Frank, Are you certain the board shop didn't symmetrize your asymmetrical design? After demanding our board shops return a stack up proposal for our approval, we found our impedance controlled 'asymmetrical' boards were coming back as 'symmetrical'. In the board shop's defense, asymmetrical stack ups are not entirely reasonable. After questioning various boards shops concerning this, I always got one of two responses: 1.) it's impossible, 2.) you can have it, but you will have to really pay for it! Meaning, rather than utilize the whole panel, only the center portion of the panel is used due to warping. Now that we're better educated, we make compromises we're willing to live with at the design stage instead of unknown compromises the board shop will make in order to manufacture the board. Ioan, Assuming your stack up is symmetrical, you can flip flop the panels. However, keep in mind that the board shops will use a 'trick' of running the ground plane of a core facing up and the controlled impedance signal side facing down. This gives a more predictable and consistent etching rate since etchant can drip off the bottom of the panel instead of rolling across the top before dripping off as it is sprayed onto the panel. If you flip flop, make sure the that the signal and grounds don't both end up on the same side of a core. (Although it is still workable to have signals on both sides of a core...) In the case you stated below, grounds and signals will still properly match when you flip flop. Thanks, Ryan -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Frank Kimmey Sent: Friday, March 02, 2007 12:32 PM To: [log in to unmask] Subject: Re: [TN] Flip-flop panels Ioan, You've listed the biggest of the Pros here, but could also add the evener distribution of coppers (less warping). Unfortunately it looks like from the impedance requirements you listed this particular design will not work well with flip-flop panelizing. You need to have matched impedance layer for layer if you want to flip flop and you will need to assure the distance between layers is consistent top to bottom (symmetrical stackup). The Design you describe might work, but sounds a little risky and probably should be experimented with prior to taking to volume. Flip-flop panelization usually works best with the simpler boards that have a low enough part count to load in a single pass. I don't know how comfortable I would be if I found out my CM was doing flip-flop with my controller impedance designs (most of my multilayers are asymmetrical due to design requirements). Hope it helps, FNK Frank N Kimmey CID+ Principal PCB Designer PCB Programs Powerwave Technologies Inc Office 916-941-3159 Fax 916-941-3195 Mobile 916-670-0645 -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Tempea, Ioan Sent: Friday, March 02, 2007 11:16 AM To: [log in to unmask] Subject: Re: [TN] Flip-flop panels John, Steve is right on the money. Best solution for JIT, one piece flow. When the mechanical-test-packing cell is almost out of boards, you just flip the boards half assembled, with no down time for changeover, and start supplying again. Regards, Ioan -----Original Message----- From: TechNet [mailto:[log in to unmask]]On Behalf Of Steve Gregory Sent: Friday, March 02, 2007 2:09 PM To: [log in to unmask] Subject: Re: [TN] Flip-flop panels Hi John, I've built panels that had flip-flopped boards before, (small narrow double-sided SMT boards for a bar code reader pen), and it made things so easy. One stencil, one SMT set-up, to do both sides of the panel on one line. After they come out of the reflow oven from the first side (and they've cooled down of course), you just stick them right back in the screen printer for the other side without so much as missing a beat...pretty cool, eh? -Steve Gregory- -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of John Parsons Sent: Friday, March 02, 2007 12:51 PM To: [log in to unmask] Subject: Re: [TN] Flip-flop panels Ioan, Why would you want to design an array like this? John Parsons -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Tempea, Ioan Sent: Friday, March 02, 2007 10:23 AM To: [log in to unmask] Subject: [TN] Flip-flop panels Hi Technos, the flip-flop nickname actually comes from the Technet, I heard it right here some time (years) ago. What I mean is the panels made up by arrays of alternating top-bottom patterns. I know that the layer stackup has to be symmetrical, that the copper weight has to be symmetrical, but what about the controlled impedance boards? Let's say a 12 layer PCB, that calls for: 4.0 mil lines: 56 ohm trace impedance +/- 10% layers 2,4,5,8,9,11 6.5 mil lines: 50 ohm trace impedance +/- 10% layers 4,9,11 8.1 mil lines: 45 ohm trace impedance +/- 10% layers 4,8,9 8.0 mil lines: 56 ohm trace impedance +/- 10% layers 1,12 Is this PCB a good candidate for flip-flopping? And it is just now that I realized it has 12 layers? Any limitations coming from layer count? And even better, I have one other board with microvias and blind/burried vias. Can this be flip-flopped? Thank you, Ioan --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 -----------------------------------------------------