Making Flexible Circuit Boards?

Kirk Fraser

I have seen some sites offering flexible circuit boards. How can one either make one from scratch or specify details like this matrix pressure map sensor built with flexible board technology?

http://www.sensorprod.com/images/tactile-surface-sensor/tactile-surface-sensor2-lg.jpg

Here's a competing sensor. The problem is the vendors sell these for $12,000 and up, far beyond the money I have, just for one and I need several for my humanoid robot. Any suggestions? Or temporary employment to make that kind of money? Thanks.

https://www.youtube.com/watch?v=q6_iZwuK3cU

Heater.

You ask about Flexible Circuit boards. But you question is all about pressure sensors. Which do you want.

You may find a PCB house that can make flexible circuit boards for you, they won't be cheap, you will want to order thousands before the price of one becomes economical. They won't be making a pressure sensor for you.

Leon

The Pulsonix PCB software that I use has an option for flexi-rigid and flexible boards:

http://www.pulsonix.com/flex.asp

I have it, but I've never tried it.

Here is a UK company that makes them:

http://www.stevenagecircuits.co.uk/

They will be expensive.

Gadgetman

If you want flexible PCBs, you may want to look into the tech of the AgIC printing system...
https://www.kickstarter.com/projects/1597902824/agic-print-printing-circuit-boards-with-home-print
It will be capable of printing on some types of plasti film according to the creators.


The Kickstarter is over, but it can be preordered on http://agic.cc
($299 for a DIY kit, you supply the printer and they haven't yet said which models work, or $599 for a finished printer)

Or you could get a pen with conductive ink...

CuriousOne

I have manufactured without any problems several PCBs, which were curved for about 30%. Technique was easy - use thin laminate, orientate non square parts bend direction-wise, use jig which will hold PCB in desired shape during soldering and remove only when installing into specific device. This was about 3 to 4 years ago, will check if I have any photos remaining.

PropGuy2

Years ago I used flex boards for a government contract. Actually they are better for a wire harness, than a circuit board with components or ICs soldered on them. The traces tend to crack at edge connectors and around discrete components, then they are impossible to repair (for reliably). We ended up reinforcing the edge connectors and circular connector pins with a PCB backup strip epoxy bonded to the flex circuit. And they are expensive ($10 to 20 or more even in quantity) plus we lost a lot in the production line.

Genetix

Speaking of "Flex" circuits, is anyone familiar with bending and folding them?

Kirk Fraser

Thanks for the advice, experience, and tips. I am reminded of 3D printing technology. I hope the http://agic.cc link pans out meeting their August delivery schedule -- it sounds hopefully worth waiting for -- easier to experiment with than a PCB shop. Not sure about the content between the circuit layers - one Radio Shack book suggested graphite as a sensor which reminded me of the old telephone microphones that used carbon. Maybe I can get some carbon/rubber compound to work or print piezo crystals somehow. I have a desktop CNC so some kind of 3D printing ought to work. But I have tried using a tiny Dremel bit to cut copper traces and it doesn't work very well on rigid PCBoard so that won't do for flexible board. It has to be printed then aligned and glued. Further suggestions on printing carbon/graphite and or piezo crystals? Thank you.

Beau Schwabe

Kirk,

May I ask what the application is for? I have had first hand experience with Tekscan and various other pressure sensor vendor while I was in the Prosthetic industry. What I can tell you that they won't is that any kind of bend or curvature can create a reading, so for best results the sensing element must be flat and free from any wrinkles, creases, or bumps (a grain of sand in the wrong place can kill the sensor)

We tried to use the Tekscan sensor to measure real time pressure in the bottom of a prosthetic foot during gait analysis. In clinical trial studies, the sensors held up with mixed results, but in almost ALL cases, long term use was out of the question. We resorted to developing our own, and we also needed a flexible circuit board. In the Early 90's our only option was to ride on the success of others.... right in front of us was a printer with a flexible circuit delivering power to the Print head... So after a little digging we contacted the company that made the flexible ribbon cable and they obliged to making a custom flexible circuit.

To combat the sensors we stayed away from any kind of FSR (Force Sensitive Resistor) since in all cases that we tried, the shear stress involved within a Prosthetic foot would de-laminate the sensors very quickly. We created an inductive sensor, a Coil of wire if you will that was actually designed as part of the flexible circuit. To change the inductance with pressure, the coils were separated with a neoprene type material and a metallic foil mesh on the back side. As the neoprene compressed, the inductance of the coil changed due to the proximity of the metal foil mesh to the coil and a reading was able to be taken. While these sensors weren't without problems, they lasted 10's of times longer (several months) than the FSR sensors we originally used (a few days).

Kirk Fraser

Beau,

Thank you very much! My application is a humanoid robot described at www.reliablerobots.com for sensing hand and foot contact with the environment. I'm hoping to compete in the DARPA Robotics Challenge next June although my finances may not permit completion by then, I'm still going to work on it until I have a prototype to try to turn into a product. So I'll work on a flexible inductive sensor as your experience proved more long lasting. Thanks also for saving me further efforts in the wrong directions.

Kirk