David M. Ransier wrote: > Hello, all. > > I'm having to critique a board that is a very large flex circuit. It's kind > of funky in that it isn't a conventional board, but rather an array of 22 > resistive sensors spread over a (roughly) 18x24 inch area. The board looks > like like six 1/2 inch fingers extending, vertically, 24 inches from a 2 > inch, horizontal, section. The connector comes off the 2 inch part and each > sensor is mounted on the 1/2 inch stripes (either 3 or 4 sensors per strip.) > > The current version of the board appears to have fairly wide traces > (eye-balling, they appear to be 10-15 mils), This sensor array will be in a > constant state of movement (it will sit on a dense foam pad which will be in > a regular state of "flex" as heavy items are laid on the pad), there fore, > the flex circuit will be flexed, a lot, over time. > > Here are my questions: > > 1) How narrow can I make the traces on flex circuit? 15 mils is about the minimum track/space with carbon ink. You might want to usecopper on mylar if wear and tear is an issue Garry > > > Currently, the 2 inch horizontal part is full of 48 traces (2 per sensor) > and I'd like to re-spec that section to be narrower. > > 2) How much flex board material is needed to support the traces? > > The current design has about 1/4 (maybe 3/16) inch of flex material on the > board edge. That is, the routing outline is 1/4 inch inside the board edge. > Can this be reduced to 1/8 or 1/16 inch, or less? If I can go to 8 mil > traces (with 8 mil space) and use 1/16 inch between the board edge and the > routing outline, then the portion of the board that has only 2 traces would > be .149 inches wide ((.0625 X 2) + (.008 x 3)). > > Thanks, > David R > > -