Hello si-list, I have a question concerning vias in flex circuits. A colleague of mine wants to use twisted pair lines on a double sided flex circuit. In order to twist the lines he wants to use vias to actually twist the lines. This kind of twisted pair lines is described in the literature as TDL (twisted differential line) and various configurations exist (TDL, O-TDL, V-TDL and OV-TDL) - see e.g.11th EPEP Oct 2002. However, the flex cable is flexed on a cyclic basis with following parameters: -1- number of cycles: >200.000 -2- bend angle: 180 degrees -3- minimum bend radius: 20mm Currently we are planning to use standard flex technology with a 25 or 50micron thick PI substrate and 25micron adhesives and 25 micron coverlayers. After a discussion with a flex manufacturer the idea of vias seems not a good idea because of reliability reasons - the vias are the week aspect in the idea of using TDL on the flex circuit. Actually the cable is about 20cm long and each twisted pair would need about 40 vias (if we use one twist/cm). Of course are there alternatives, we could do without the vias and just use a pair of lines - one o top and one of the bottom layer. So given the data above: would you recommend the use of vias in our flex design?? Kind regards, Jan Vercammen Agfa-Gevaert NV Mortsel, Belgium ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu