Interesting PCB not seen tracks like this before - Page 1
Forum section: electronics / general

author: tautech
author_rank: Super Contributor
timestamp: May 11, 2014, 09:24:49 am
content: Had a junk PCB given to me the other day with tracks that seem to be an additional overlay.This is a single sided PCB with very few TH components. But there are these track links/jumpers that look like an additional overlay. The manufacturer has gone to some trouble to keep it single sided.The longest track measures 180 ohms and a 10mm track measures 100 ohms.Every one seems to have a pair of test pads for post manufacture testing.Completely new technology to me.Can someone shed some light on this?EDIT new image

author: Niklas
author_rank: Frequent Contributor
timestamp: May 11, 2014, 09:30:11 am
content: Looks like printed carbon resistors.

author: ovnr
author_rank: Frequent Contributor
timestamp: May 11, 2014, 09:35:50 am
content: Yeah, those are "poor man's" 2-layer boards. They're constructed by screen-printing a layer of lacquer, then a layer of conductive carbon-filled polymer, then another layer of lacquer on top - that's why the resistance is so high. In some designs the inherent resistance is intentional (but the tolerances aredreadful), in others it's low enough to ignore.Obviously these are only used for low-current signals. Also, you might've noticed the SMD jumper links on the left side of the board; those are rather more expensive than through-hole wire links, and are used more sparingly (hence the film jumpers).

author: tautech
author_rank: Super Contributor
timestamp: May 11, 2014, 10:29:59 am
content: Quote from: ovnr on May 11, 2014, 09:35:50 amInteresting you call them "poor mans".Company is a small multi-national, that is more than capable of top PCB work. There must be good reason they have built it like this.Yes all the jumpers are used with thin tracks so presumably at logic or similar levels.Still I would like to know the terminology/name for this type of PCB work and what software if any supports it.

author: 128er
author_rank: Regular Contributor
timestamp: May 11, 2014, 10:35:35 am
content: I have seen this sort of jumper links quite often on PCBs for IR remote controls. Mostly they are single sided with a few of this links.

author: SeanB
author_rank: Super Contributor
timestamp: May 11, 2014, 11:02:25 am
content: It is used because it allows you to use a single sided cheap SRBP board, and this is very cheap in high quantity. As well drilling the board and routing it out is both faster and less wearing using simple HSS tools, instead of needing carbide cutters. As well you can simply use a punch and die to do a lot of the work, which cuts time per board a lot. Having to do the extra 3 screen printing steps onto the board for the lower layer, the resistive ink and the top layer adds little to the cost.That is why it is used for low cost mass produced boards.

author: tautech
author_rank: Super Contributor
timestamp: May 11, 2014, 11:18:54 am
content: Quote from: SeanB on May 11, 2014, 11:02:25 amThere is a section of blown mains track on the board and there is no discernible lip where the copper was. Can a milled board be that accurate? I believe it was etched.So "resistive ink", how would these tracks be generated in Altium for example and what is the manufacturing application process?

author: SeanB
author_rank: Super Contributor
timestamp: May 11, 2014, 11:38:51 am
content: Copper is etched, but the board outline and all the mounting holes are milled in the soft material, or you make a punch and die set to press it out of the large board after etching so you can mount components on it then solder.To make the tracks you simply make a new layer and use large vias to connect to it, then on the top surface you simply make those vias pads, and generate a set of masks for the other traces to give a screen printed insulating and conductive layer.

author: tautech
author_rank: Super Contributor
timestamp: May 11, 2014, 11:49:13 am
content: Screen printing. ThanksAs outlined byovnr.