The first place I saw this stuff was a presentation by one of the people behind Chibitronics. Along with copper tape really useful for building up circuits on paper. Not sure if they still use it in any of the products but still pretty cool: https://chibitronics.com
3M tape with anisotropic z-axis electrical conductivity
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Re: 3M tape with anisotropic z-axis electrical conductivity
#12A while back I invested in 3M because it's a company that makes so many amazing and industry leading products and I thought they'd do well. A couple years later and the stock is just lagging. I guess they're dragged down by their environmental lawsuits these days.
As a human, I'm appalled at their environmental track record but as an engineer, wow they really do so many things so well.
Re: 3M tape with anisotropic z-axis electrical conductivity
#13Earlier quoted context omitted.
so the 3.4e14 is resistance along the tape, and .3 is vertically, right?
Yes, in plane (XY), it is many orders of magnitude more resistive than out of plane (Z-axis).
Interesting, how "designed for EMI shielding" (as written on the product page) works then. The charges in the shield should be able to move not just in Z but also in X&Y to actually work as a Faraday cage.
Re: 3M tape with anisotropic z-axis electrical conductivity
#14Earlier quoted context omitted.
Yes, in plane (XY), it is many orders of magnitude more resistive than out of plane (Z-axis).
Interesting, how "designed for EMI shielding" (as written on the product page) works then. The charges in the shield should be able to move not just in Z but also in X&Y to actually work as a Faraday cage.
> Z but also in X&Y to actually work as a Faraday cage.
The x-y could be done by the contiguous ground above and below the tape. For example a can/shield stuck onto a ground region of a PCB, with signal lines going up nearby. I imagine this is mostly used with flex PCBs.
Re: 3M tape with anisotropic z-axis electrical conductivity
#15For anyone looking for the interesting numbers: Insulation resistance: 3.4 x 1014 ohms/square Contact resistance: Direct link to datasheet: https://multimedia.3m.com/mws/media/66235O/3m-electrically-c...
I think you mean 3×10¹⁴ ohms/square.
Re: 3M tape with anisotropic z-axis electrical conductivity
#16What does that mean?
“Isotropic” means that something is the same in all directions, and “anisotropic” means that it _isn’t_ the same in all directions. In this case, the tape conducts electricity between its top and bottom surfaces, but not along its length.
Re: 3M tape with anisotropic z-axis electrical conductivity
#17This stuff is rad. I took a class on hardware implants with Joe Fitz a couple years back—on the heels of that wholly unsubstantiated Bloomberg article about China embedding rice grain-sized hardware implants into Supermicro motherboards that magically found their way only to select F100s and gov’t agencies—where we made a PCB to interface an ATtiny85 to an unpopulated UART header on some IoT device but instead of soldering it down we just taped it with this.
(The UART provided a root shell and enough power to “boot” the ATtiny which simply waited a few seconds and then ran some commands to initiate a reverse shell to a server under our control every time the device was powered on. Thanks to this tape and the device’s tool-less case (and convenient unpopulated header with space around it), it was enlightening how trivially easy it’d be to develop and deploy such an implant to an operating device (with the caveat that I wouldn’t consider the connection robust enough to survive transport).
It’s also useful to connect SMD EEPROMs to unpopulated/desoldered pads for testing without installing a socket.
Re: 3M tape with anisotropic z-axis electrical conductivity
#18What does that mean?
You could (in theory) put the tape over a circuit board and place components on tape and the circuit would function. It would not short circuit because it only conducts on the z-axis (up and down) not between things on the surface.
Re: 3M tape with anisotropic z-axis electrical conductivity
#19What does that mean?
Anisotropic -> not equal in all directions (isotropic would be equal in all directions). In this case, the tape is insulating in the X and Y direction (directions parallel to the adhesive "plane") but conductive in the Z direction (perpendicular to the adhesive "plane"). I put plane in quotes because the tape need not be applied to a flat surface.
Re: 3M tape with anisotropic z-axis electrical conductivity
#20What does that mean?
Imagine a tiled surface, where the tiles are conductive but the grout is not. So you have islands of conductive material which don't connect to each other. If you shrink that very small, and make it flexible and sticky, it's useful:
Suppose you have a glass LCD panel, like the kind used in clocks and watches. The traces are indium-tin-oxide (ITO), on the glass. This is fiendishly difficult to connect to, it doesn't take solder well, etc. And you want to connect it to some flexible ribbon cable which will carry the signals to the control board. But how to do that?
With Z-tape! By laying a strip of the tape over the ITO traces on the glass, and then smushing the flexible cable to it, the conductive spots in the tape now connect the cable traces to the ITO traces, without shorting them to each other.