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
>
> -