Clear, printable, flexible circuits? - Page 1
Forum section: electronics / projects

author: asgard
author_rank: Regular Contributor
timestamp: August 01, 2013, 04:27:07 pm
content: I have been going back a bit in time to take a look at some of the more intriguing technical developments. One area that seems ripe for development, but has been "orphaned" due to disinterest, or some unforeseen technical problem is ink-jet printed circuitry.It seems to me that the print heads are getting way more accurate (with better servo-ing transport mechanisms) and more capable of depositing more diverse materials than ever. For goodness' sake I have been seeing ink-jet printed replacement organs for experimental transplant, created with off-the-shelf printer parts.Therefore, it seems to me that it is a simple matter of getting a print head to deposit organic conducting materials. Has anybody heard of such a beast? Is there some fundamental impediment to getting a printer to deposit semiconductor junctions that are fully functional? If that ever comes to be I can foresee creating strips or sheets of transparent plastic sheeting that has entire screens of TFT pixel elements. Or is that too much to hope?J.R. StonerBTW I have worked up in prototype a simple design for a N-length double-buffered shift register with an LED at each latch output pin. If only I can print these into large arrays on a flexible substrate my place as a captain of industry is assured

author: Corporate666
author_rank: Unknown
timestamp: August 01, 2013, 06:26:37 pm
content: I remember the promise of clear flex PCB's as well, but I think the reason we have what we have now is that-You can plate copper on it-It can survive the reflow processI am not aware of any transparent and flexible plastic that would survive reflow temperatures. When you get to lead free, it gets worse.Which means you are looking at conductive adhesive bonding your components. I still have tubes of conductive epoxy I bought years ago - it was so expensive and long expired but I'll never toss it outIt is almost like solder paste - millions of tiny spheres in an epoxy solution. Except the spheres are made of almost pure silver. So it makes the stuff extremely expensive. I had only mixed results with it at best. It is most definitely not reliable in applications with vibration or bending stress.I think the same for printed conductive traces. You are probably talking about a matrix of densely packed conductive particles, so closely spaced as to have enough touching to be conductive. But I think by nature, that tends not to be reliable. Pure copper, OTOH is nice and flexible and can remain so long-term.I'm not expert on this subject at all - but that's my experience.

author: asgard
author_rank: Regular Contributor
timestamp: August 01, 2013, 11:26:13 pm
content: In my original post the idea is that there would be no reflow, since the devices are printed directly on the plastic substrate.J.R.

author: Rerouter
author_rank: Super Contributor
timestamp: August 02, 2013, 02:32:22 am
content: if you could come up with a clear and flexible substrate that could survive approx 1100C you could always print in pure copper,or to take the idea another way, print the copper design onto an intermeiatary plate, then adhere the design to your flexible material, pure copper, as long as you correct for shrinkage, but that should be possible in software,as for your nozzle for this beast, high speed steel melts 500C higher, so it should be possible to have it lathed up, same for the heating chamber,

author: asgard
author_rank: Regular Contributor
timestamp: August 02, 2013, 02:49:21 am
content: The interconnects would almost certainly be in conductive organo-polymer. A lot of the LCD panels are using that with the OLED's.I am attaching the elements I have around. I breadboarded it with simple 74C tiny logic, but the typical devices are shown here as raw transistors. I figured that these could be used directly on the substrate. The most hinky part of this is having resistors at each pixel. I would be happy to hear about any other method that uses less resistive materials, if it is as easy to address pixels individually.

author: Corporate666
author_rank: Unknown
timestamp: August 02, 2013, 03:18:39 am
content: Quote from: asgard on August 01, 2013, 11:26:13 pmAre you talking about mounting components on this substrate or simply an interconnect? I assumed the former, which is where conductive epoxy comes in... how else do you intend to connect components to traces?

author: asgard
author_rank: Regular Contributor
timestamp: August 02, 2013, 03:24:50 am
content: My thought was that there would be no discrete components mounted. I thought the entire circuit would be deposited with one or more passes with an inkjet style printer. The previous D flop design, you will note, has no capacitor charge storage. The parasitic charge would itself be the storage element. There is one complication in that one of the clock regions is electrically isolated from the boundary. That alone would require at least three passes to accomplish. First layer would be most of the circuit elements, the second pass would be a transparent insulator, then the third pass would be for just a "jump" of that interior clock to the outside tie point. That would also be where the LED's can be deposited, if the typical GaAsP or GaAsN materials can be fed into an inkjet print head. Sort of some kind of macro-epitaxy process, I think.

author: asgard
author_rank: Regular Contributor
timestamp: August 02, 2013, 03:31:08 am
content: Check that. The transistor next to the /Q "output" can be involuted so that the base is on the other side, so no jumper is needed. The /Q pin is not needed, and the R pin is just tied to Vcc.

author: Marco
author_rank: Super Contributor
timestamp: August 02, 2013, 10:26:03 am
content: Quote from: Rerouter on August 02, 2013, 02:32:22 amYou can use flash sintering to get around this, print powder and then use xenon flash to make solid tracks without destroying the substrate.Any way, it's a long time since I paid attention ... are RFID's made in production with inkjet printed semiconductors yet? (Doesn't have to be organic, nanoparticle silicon with sintering and zinc-tin-oxide have also been suggested.)PS. I've always thought Fluidic Self Assembly made more sense ... but not much happened with that either.

author: asgard
author_rank: Regular Contributor
timestamp: August 02, 2013, 02:32:35 pm
content: How about this: the first pass(es) with the printer could deposit either some enzyme or weak acid to etch micro channels into the substrate, which can then be flled-in with wet traces or sintering powder in a true epitaxial construction, just the way production CMOS was constructed. If a valid PN junction can be deposited this way and survive a xenon flash "fixing" process that might work.

author: free_electron
author_rank: Super Contributor
timestamp: August 02, 2013, 06:35:12 pm
content: your flipflop is too complex. I can do it with 5 transistors. ( ok , it will be a latch but for your applications this will work fine. you don't need edge triggering. you have a master shifter driving columns. the row latch is fired from a barrel shifter. these two shifters are outside the matrix. ) there is no need to have this inside each LED cell.the LED cell is a ring flipflop ( two inverters back to back ) and I use a mos as pass-gate to store the new state.6 transistors if you need a reset (why do you need a reset ? simply have a master reset for the column driver and have the barrel shifter for the row access activate all rows. this wipes the entire grid in one shot. you can do away with the rest transistor. it is one less line you need to route.)your grid consists of two horizontals and two verticals. : horizontal : row strobe and gnd. vertical column data and vcc. the vcc can be shared between two adjacent cells so you open up a gap to run the pwm line there.you want to minimize the number of traces in the grid.7 if you need PWM at the output stage ( I use a master pwm controlling all pixels simultaneously ) if you drop reset I can go back to 6 transistors per cell.( yeah , I did some memory cell generators in my time... so I know a trick or two... )

author: asgard
author_rank: Regular Contributor
timestamp: August 02, 2013, 07:09:35 pm
content: But must the whole array be row/column addressing? If you can get 300MHz or better clocking through the cells then the entire plane can be shoved whole in each retrace. Maybe even stack multiple planes for true 3D.I thought I could use a simple long shifter in serpentine layout in the entire plane. PWM not needed as it is only bistable. Reset not needed. Maybe example?

author: Odysseus
author_rank: Regular Contributor
timestamp: August 03, 2013, 07:05:00 am
content: If you want to use an ink-jet printer, I think this is relevant:

author: Marco
author_rank: Super Contributor
timestamp: August 03, 2013, 01:53:49 pm
content: Organic TFT's have not failed to take off by lack of trying or by problems in deposition/patterning AFAICS. RFID companies threw a lot of money at it. Deposition/patterning is the easy part too ... the lousy mobility and things like moisture sensitivity are larger problems.

author: asgard
author_rank: Regular Contributor
timestamp: August 06, 2013, 11:36:34 pm
content: I expect that environmental controls would (obviously) be critical with this. Clean-room conditions at the very least, to prevent particulate contamination. Dessicating conditions as well? The printer is getting much more modified as we think this through! I was just hoping that the same level of positioning accuracy for a high-end inkjet printer would be sufficient to deposit semiconductor junctions with interconnects. *sigh*.