What your board house is referring to is the symmetry of the copper plating pattern when making OL circuits. Variations in the symmetry of the plating pattern cause variations in the electrical field across the surface of the panel. The electrical field variation results in differing amount of copper plating on the surface. If you fabricator uses panel plating, the "plating" image is solid copper. Very symmetric, uniform electrical field and uniform copper thickness on the surface. But with panel plating, you have to etch back down through all that copper and that introduces variation in etch feature sizes. Fluid transport of fresh etch solution to the copper interface being etched can make it difficult to etch narrow spaces. If you have 4 mil lines on your OL board and some of them are way off on their own with no adjacent while others are run at 4 mil spacing from adjacent lines or other copper features, it will be difficult to make both the isolated and dense traces have the same width. They'll have the same height (that's the beauty of panel plate), but the isolated features will be narrower than the dense ones. In pattern plate, you have essentially the opposite effect occurring. The resist image pattern induces asymmetry to the copper plating pattern. The isolated features are now in areas of higher current density and the copper plates faster (thicker) in these areas compared to the dense areas. Etching is simpler than panel plate because you are only etching through the base foil plus a thin layer of strike copper plate. This is the reason your trusty board fabricator comes back and asks you if it's OK to add "robbers" (non-functional copper fill added to areas of high current density to level out the image symmetry) to the outer layers of your panels. To avoid this, my always unpopular recommendation is don't rout critical, narrow traces on OL. If you must, try to make the copper pattern as uniform as possible. Mike McMaster RF Product Engineer Merix Corporation 503-992-4263 > ---------- > From: JaMi Smith[SMTP:[log in to unmask]] > Reply To: TechNet E-Mail Forum.;JaMi Smith > Sent: Tuesday, October 08, 2002 10:43 PM > To: [log in to unmask] > Subject: [TN] definition question > > When a board house states the following: > > "Tolerance on track widths is +- 0.008mm or better depending on the design > and uniformity of copper distribution." > > How should I understand "depending on the design". > > How should I understand "uniformity of copper distribution". > > Thanks, > > JaMi Smith > -------------------------------------------------------------------------- > ------- Technet Mail List provided as a free service by IPC using LISTSERV > 1.8e 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/html/forum.htm for additional > information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 > ext.5315 > -------------------------------------------------------------------------- > ------- > --------------------------------------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8e 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/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------------