EEVblog #335 - Carbon Printed Resistors

[nitro2k01]

[EEMarc]

I've seen triac dimmers with axial carbon resistors that someone took a Dremal to in order to increase the resistance. Of course they were too cheap to put a diac on the triac input to make it operate better at lower end of the dimmer range.

[G7PSK]

I saw a pick and place machine in the early to mid 80's. all the component were in a single tray and there was one arm that picked up each component in turn, the travel speed of the arm was quite slow as well. The whole machine was no bigger than a large fridge or stove laid over on its back and the boards had to be put in and taken out by hand as did the components in the tray.

[mikeselectricstuff]

Around the early 80's Sharp went through a phase of using silver ink and printed resistors on the top sides of single layer PCBs in consumer audio gear.  They had some reliability  issues, in particular with board flexing.

[tramjoe]

Funny, I just noticed the wikipedia resistor page edit done yesterday from a mysterious Telstra IP address adding a section on carbon-printed resistors illustrated by a picture of a Psion II board ;-)

I wonder who that could be 

[EEVblog]

Funny, I just noticed the wikipedia resistor page edit done yesterday from a mysterious Telstra IP address adding a section on carbon-printed resistors illustrated by a picture of a Psion II board ;-)
I wonder who that could be 

Whilst searching around a bit I did notice that to be an oversight. The world know knows about carbon printed resistors 

Dave.

[tramjoe]

Whilst searching around a bit I did notice that to be an oversight. The world know knows about carbon printed resistors 

 

[PuterGeek]

Wow Dave, you're really straining my gray matter!

I was at my second EE job in the early 80's using surface mount and for the life of me I can't remember what chip resistors cost. Placement was a significant cost at that time since the pick and place machines were pretty slow. Probably the only parts taped were the R's and C's. The SOIC's were usually in sticks back then and the QFP's were in tray's. Tape feeders were mostly 8 mm and occasionally 12 mm.

Panelized boards were uncommon then because of the slow pick and place machines and large boards were more challenging. Many contractors couldn't build our 'large' 12 by 12 inches boards strictly because of size.

A side note on the printed resistors, my first job was with an automatic test equipment manufacturer that evolved out of their laser trim business. The laser trim systems trimmed the value of printed resistors on modules to as close as 0.1%. The system was a mounted on a 6" thick granite slab for vibration isolation and had a small trim area. The computer was a Data General Nova minicomputers (6U 19" rack mount, 8 to 16 kbytes of core memory, 8" floppy drive) and the control language was similar to Basic (the interpreter was written using FORTRAN). By the early 80's the laser trim business was dead so the measurement infrastructure became the basis for high accuracy analog testing (1 mv absolute accuracy in a few racks of equipment).

Ah the 'good old days'!

[PeteInTexas]

I'm wondering if its because of that ribbon cable:  what if, for whatever reason, the two boards had to be joined first and as a result the head of the pick and place machine can no longer get in that close.  You notice that orientation of the caps (?) also close to the ribbon cable are oriented 90 degrees, thus, maybe allowing the pick place to get close to the cable.  Just thinking out loud...

[ciccio]

I remember than in the 1980's a representative of Japan's NOBLE company (the one that is still manufacturing potentiometers and switches) presented us with a similar process that was available (resistors printed over PCB).  They could even produce a dual side PCB without metalized holes: the conductive ink could fill the holes, and carry signals from one side to the other. The minimum quantity required was not very high (if I remember well it was in the order of  5 to 10 thousand pieces) and we could use it in the input channels of our audio mixers, with a good cost reduction,  but the whole operation (including PCB production) had to be carried out in Japan and this was against the "all built in Italy by a supplier near us" Company's politics.
In those years I bought a Technics cassette deck that used the same technology, and it worked very well.
Best regards

[SeanB]

Printed resistive tracks are common on remote controls, saves the cost of making a double sided board, and they can use a thin SRBP board as well. The conductive traces are even used for carrying power to the controller, though the high current leads to the IR emitters mostly are copper, though they might use multiple vias to the conductive  track to make a jumper.

[kcozens]

This is a reply to a comment made by Mike Whitenton on YouTube to EEVblog #335. I couldn't post the URL's there so here they are. The first DIY Pick and Place machines I discovered on the net is the redFrog Pick and Place machine. The project site can be found at
    http://buildyourcnc.com/PickandPlaceMachineTheredFrog.aspx

A second machine I recently discovered is the one at
    http://hairyraho.com/home-made-pick-place-smt-machine

[drm1]

An old topic, but just came across this from a PCB maker in Ireland and Canada:

http://www.shipcircuits.com/embedded-resistors/

and their supplier of materials for embedded resistors:

http://www.ohmega.com/technology/

[Gribo]

The Xerox PE120 has printed carbon resistors and jumpers. They use it on a single sided PCB with 2 solder masks (They have an extra solder mask "pad" below the carbon jumpers).