Hey Austin, You know, I've wondered about that. Luckily I haven't had to deal with it yet. One reason is that lately I only have top and bottom as routing layers. I think the last time I had inner layers, the stack-up was designed to have the trace widths/spaces the same for inner and outer for all impedances. Here's how I handle it now for only outer routing layers, on 15.5.1: - I set up the diff pairs using Logic -> Assign Differential Pair, Auto Generate - I set the trace width, spacing etc. for the pairs in CM - I create a Spacing Constraint Set for each impedance (i.e. "90DIFF" for USB) with the "Line To Line" set to the spacing required pair to pair I'm not sure how to handle a different trace width and spacing within the pair for inner layers as opposed to outer layers. I would suggest, if you can, to design the stack-up to have the widths and spacings the same for outer and inner. That's the easy way out! Maybe setting up constraints, including diff pairs, is easier in 16, I hope so. Good luck, I'm curious to see if anyone has the solution to this. Gary E. MacIndoe PCB Design Engineer Fort Collins, Colorado amd.com gary.macindoe@xxxxxxxxxxxxxxxxxxxx Message----- From: icu-pcb-forum-bounce@xxxxxxxxxxxxx [mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx] On Behalf Of Austin Franklin Sent: Wednesday, March 26, 2008 12:39 PM To: icu-pcb-forum@xxxxxxxxxxxxx Subject: [PCB_FORUM] Using an "Electrical CSET" vs a "Constraint Set" for diff pairs... Hi, There appear to be two ways to get the diff pair spacing and gap, but only one allows differing them by layer. Setting up an "Electrical CSET" only seems to allow one overall (as in for all layers) space/gap. But, the advantage of using the ECSET is you can assign it to a net or multiple nets using the Constraints Manager spreadsheet using a pulldown menu. Or, I can setup a "Constraint Set" and select each layer's space/gap...but I then have to attach this as a property to each and every net manually by selecting the nets and attaching this Constraint Set name as a NET_PHYSICAL_TYPE attribute. I prefer the Constraint Set, since it gives me the per layer control...but the thing that seems to be missing, is the ability to assign a given Constraint Set to the nets using the Constraint Manager spreadsheet. I'm on 15.2. Am I missing something? If not, has this improved on 15.7 or 16? Regards, Austin ----------------------------------------------------------- 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 -----------------------------------------------------------