Scott, The last time I looked the positional accuracy of a laser photoplotter was about 1/4 mil (.00025"). Whatever feature to feature tolerance you're concerned about will NOT be a function of imaging. What it will be a function of is copper weight and etching/plating process control. Copper weight is a factor because as the copper gets thicker it gets more difficult to etch it extremely accurately. After etching, traces have a trapezoidal shape. The thicker the copper, the more the difference in width between the top of the trapezoid and the bottom. The etching/plating process will vary from chemical batch to chemical batch (as will the actual thickness of copper on the FR4). As a rule of thumb, assume your feature widths and spaces will vary by approximately the thickness of the copper they're etched in. That is, an 8 mil trace may vary between 6.5 - 9.5 mils, and an 8 mil space may vary by the same amount if etched in 1 oz/sqft (.0014" thick) copper. Most producers typically do much better, but don't bet the farm on it. Greater accuracy can be achieved in thinner copper weights or by paying more per piece. On the other hand, I may be misinterpreting the question. If your concern is with mechanical design tolerances, that's a different issue. The positional tolerance of components after they're mounted on the board will be related to pad shape and size, as well as the positional tolerance of the component leads. The larger the pad area the more the component can "drift", but the easier they are to assemble (and vice-versa). I don't think their are any hard numbers available for that since the number of uncontrollable factors is so large. Michael Hiteshew Lockheed Martin NE&SS Marine Systems 410-682-1259 > ---------- > From: Buscomb, Scott[SMTP:[log in to unmask]] > Reply To: TechNet E-Mail Forum.;Buscomb, Scott > Sent: Monday, July 09, 2001 6:07 PM > To: [log in to unmask] > Subject: [TN] Pattern to Pattern Tolerance > > I am looking for the standard industry locational tolerance of copper > feature to copper feature on a single sided PCB. Since PCB fabrication is > a > photographic process, I am assuming it is a function of gerber plotter and > artwork imaging. > TIA, > > Scott Buscomb > > -------------------------------------------------------------------------- > ------- > Technet Mail List provided as a free service by IPC using LISTSERV 1.8d > 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 delivery of Technet send the following message: SET > Technet NOMAIL > Search previous postings at: www.ipc.org > On-Line Resources & Databases > > E-mail 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 1.8d 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 delivery of Technet send the following message: SET Technet NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail 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 ---------------------------------------------------------------------------------