The other side of the coin is conductor or trace thickness tolerance. For commercial applications the applicable criteria can be found in IPC-RB-276 (page 13). It takes into account the starting base foil and sets criteria for minimum finished conductor thickness. Also plating/coating thickness of exposed copper on non-solderable surfaces is permitted to be 1% for class 3 (Microwave). I understand your concerns regarding possible degraded electrical performance. You might want to try your worst case scenario and see what effect electrically these surface anomalies may have. If nothing is effected and it meets the other thickness criteria than the minor exposed copper spots should not effect your long term reliability any more than the possibility of any exposed copper edges along traces. (Provided the surface finish is that type that has exposed copper along edges.) Hadco Printed Circuits Tech Center Two / Watsonville _/_/_/_/_/_/_/ _/_/_/_/ _/_/_/_/_/_/ _/_/_/_/_/_/ _/_/ _/ _/_/ _/_/ _/_/ _/ _/_/ _/_/ _/_/ _/_/_/_/ _/_/_/_/_/_/ _/_/_/_/_/_/ Dave Hoover (408) 728-6677 Senior Process Engineer (408) 728-1728 Fax [log in to unmask] ______________________________ Reply Separator _________________________________ Subject: Pitting Condition on PTFE PWB's Author: [log in to unmask] at SMTPLINK-HADCO Date: 9/27/95 9:59 PM To someone familiar with PTFE Microwave Application PWB's: We are looking at some very small pits (1-5 microinches) located sporadically on conductor traces. The pits were obviously created by some minute contamination on the plated copper surface which left small voids in the tin-lead electroplate. In most cases, copper is exposed at the bottom of the pit. The etching process may have attacked the copper to varying degrees but we are unable to determine the depth of these pits into the copper conductor. Specifications allow +/- 10% conductor width variation. Nominal conductor widths are .088" on traces that exhibit these pits. I mention this fact as it relates to controlled impedance. The amount of copper loss due to the pitting condition could in no way add up the amount allowed by this specification (10% .088 = .0088 x conductor length) when on the low side of the tolerance. What effect will these pits have on performance and long term reliability? Will it create difficulties in 'tuning' the board for it's end use application? Will the small amount of exposed copper pose any long term reliability problems? In advance, Thanks Ralph Malloch - Process Enginnering