3M tape with anisotropic z-axis electrical conductivity | Hacker News Reader

3M tape with anisotropic z-axis electrical conductivity

3m.com

244 pointsarsalanb140 comments

This 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.

Yep! But it sadly cannot replace soldering for denser pinout layouts, unless a lot of pressure is applied. Someone tried though;

https://tomverbeure.github.io/2019/11/21/Z-tape.html

(A bit off topic but that Bloomberg story is still such a mystery to me. It went into quite a bit of details and claimed it had tons of sources, so even if it was a completely false story whoever fabricated it must have put insane amounts of efforts/identity fraud into the set up)

It was also quite a plausible hack. The faker, if indeed anything was faked, knew more than most. Enough to have done the thing for real.

It was completely implausible - the chip that was identified could not possibly carry enough processing ability to do anything useful as far as espionage goes, had no connectivity to networking, and there was never any evidence of communication from these devices to anything suspicious or unknown.

> processing power; networking

Could the device not simply get the host to do these things for it, by e.g. rootkit-ing the server’s BMC? A “hardware virus”, per se.

>> It was completely implausible - the chip that was identified could not possibly carry enough processing ability to do anything useful as far as espionage goes, had no connectivity to networking, and there was never any evidence of communication from these devices to anything suspicious or unknown.

> Could the device not simply get the host to do these things for it, by e.g. rootkit-ing the server’s BMC? A “hardware virus”, per se.

IIRC, that's exactly what was alleged in the article. It was an implant that sat on the BMC ROM bus, fiddling with bits as the ROM was read during bootup. No need for any networking or processing ability beyond what was needed to that. This guy actually did a POC of that: https://trmm.net/Modchips/.

So totally plausable.

Not at all implausible, it was reported to be connected to the BMC which are often notoriously insecure and which could conceivably grant it network access.

No adding components activates different hardware features on the chipset its connected to. I.e. remote debug access via a reserved data line when pinX is high/low... all that would need is a single surface mount resistor or frankly tin-foil.

My understanding was that it sat between the BMC and its boot flash and (assuming it was real) was designed to bit-twiddle regions of the firmware as it flew past over SPI. So basically streaming strpos() (or maybe even counting bytes) and then sending some alternate sequence of data.

That would require some processing chops to handle whatever speed the SPI bus ran at, and a bit of space to store the replacement bytes. Firmly within the margin for plausibility with even basic off-the-shelf kit. Honestly depressing really.

Had me fooled, I got quite excited reading it, ashamed to admit.

The Bloomberg story, my thinking is that it was probably true, but someone from national security forced them to clam up.

Yep. For the CIA or NSA or whomever quashing that story is a good short-term solution (protecting your spy IP - spy P?) and also medium-term (harming Bloomberg's reputation), but the longer term side-effects (harming media's reputation in general) probably ended up doing far greater harm to the US. Trust is so easy to destroy, and takes a very long time to build up again.

UART pins! That is such a good idea!! I need to get some of this stuff and make some stick-on connectors so I don't have to solder pins whenever I need a UART for 30 seconds to unbrick a router or something

Springy pogo pins are what you want.

Hold them on with one hand while you type a few commands over the serial connection with the other.

If you have more in depth debugging to do, get a 'helping hand' to hold it in place.

A 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.

3M is an awesome company. I've worked with them to produce custom adhesives for us ($MM orders). Their products have exceptional quality, reliability and performance. What you see in a datasheet is what you're going to get (or better).

3M's consumer products (Scotch, etc.) are also excellent. Anytime you use 3M products, you don't need to worry. I like that consistency and it brings peace to the mind. I'll pay more for it.

Japanese equivalent is Nitto: https://www.nitto.com/us/en/products/

Not just that, but (at least when last I needed this specific service) they had a great phone support system where you could call up and say "I need an adhesive to connect $A to $B and have these curing properties and this strength" and someone would go through their database and make a list for you.

Most companies with such a huge array of subtly different products are nowhere near so clear.

One cool thing now is that 3M releases finite element data packages for adhesive tapes, digital prototyping!

https://www.3m.com/3M/en_US/bonding-and-assembly-us/resource...

3M’s consumer abrasives are also remarkably good. Not only are they more effective during use, but they last longer as well, with a much later falloff in abrasion quality. In fact, they last so long that their price (nearly double the price per pad in my case) easily justifies itself.

I have no idea what kind of black magic makes it possible but I’m so glad I gave them a try.

3M, Johnson Johnson, Church Dwight, and a bunch of really householdy name companies are all smack in the middle of NJ. It's a sweet spot if you want to hop a few big corporations in your lifetime and work your way up the chain.

Just hold your breath while you're doing so......

Yeah, plus in last week's thread, we learned that basically all of these CPG and domestic manufacturers (including some of these blue chip companies were the ones polluting these superfund sites!

Good luck finding and collaring those shot-callers at this point!, they're all in New Zealand having a pint.

The product quality is awesome. The company has some bad history with chemical dumping and caused at least one superfund site. And used the standard tobacco playbook after finding health concerns with PFAS chemicals in the 1970s to delay the rest of the world from finding out how bad it was. They only started phasing them out in 2000 and paid off at least one academic researcher for another decade to prevent or slow the release of studies showing negative affects.[1]

[1] https://www.smh.com.au/lifestyle/health-and-wellness/toxic-s...

> A 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.

The relevant question isn't whether they make great products, but whether their stock is undervalued.

We in the tech world are used to "great products" -> "stock price always goes up", but in the "real world" there's no reason for that to be true. "Stock price goes up" should, from an efficient-markets PoV, reflect new information.

And an efficient-market-PoV should, from an investor PoV, be put back on the shelve together with the other econ fairy tales like general equilibrium, rationality,... There's a reason funds prefer to hire STEM PhDs over economists.

No. An "efficient-market-PoV" isn't equivalent to the statement "the market is always 100% efficient", and in fact the entire concept of speculative investing is in fact predicated on this. If you want to beat the market, you must find the place where the market is inefficient, and the only way you can do that is if you know something that everyone else does not know.

The "efficient-market-PoV" in this instance is simply - is an observation that 3M makes good products likely to constitute information that is not already factored into the stock price?

It's a good idea to read up on the history of the efficient market hypothesis, and how Fama came to it. There's also different tiers with different layers of credibility.

Base tier (and the one pretty much everybody can agree on): The expected value of the error of the market is zero. This means that the market does not always fundamentally overvalue or undervalue assets, and that, over time, it will overvalue things as often as undervalue.

(... many intermediate forms ...)

Strong efficient market hypothesis: The market price always reflects all accessible information, and every market movement is driven by new information.

The strong efficient market hypothesis is pretty evidently wrong (the existence of all the various quant funds that are generating outsize returns is strong evidence; it would also mean there are no stock bubbles. Having lived through 2 bubbles in my life, I can tell you: Bubbles exist, and there are many forces outside of new information that lead to them inflating and popping).

New great products, in blue-ocean markets, creating new revenue sources, aren’t enough? For companies the size of 3M that “do everything”, do market traders just price in a certain stable rate of predicted innovation leading to geometric revenue growth / monopoly positioning / etc?

The current price is based on the predicted earnings growth. Everyone expects 3M to have earnings growth and that expectation is already baked in. The price is only going to spike if something unexpected happens. Growth would have to exceed expectations.

I'm surprised they didn't do well during the pandemic. Their Aura masks were, like, weirdly better than every other mask I tried (at least in terms of comfort).

I feel like they just had an odd look to them, they are a KF94 design recertified as N95. But if you find them comfy when they make a good seal, that's what counts.

Some of the comfort may also be the breathability, Auras have a pretty low pressure diff between the inside and outside when in use. If you want that low pressure difference in a traditional N95 style, Indiana Face Mask makes some top notch high-filtration high-breathability N95s that are similar. Both they and the Auras usually test above 99.5% filtration, the Auras usually have a little bit of a petroleum smell but if it's bad enough that it makes the mask deeply unpleasant to wear, you probably have a fake (sometimes factory rejects get resold etc.).

Agreed, they're the most comfortable ones I found without an exhalation valve. Conveniently they also fold flat. Only downside is that they go behind the head instead of using ear loops.

I can't stand ear loops anyway, they hurt my ears. It helps that my hair has grew out during the whole "don't get close to people" thing. Ponytail + around-head straps is a great combo for maximum snugness (you can loop the top one under and the bottom one over).

I think it just varies, but I'm with you. It might be because I also wear glasses, do you? I feel like the ear loops press my glasses harder into my ears, preventing longer term wear (they're great for a half hour, not so good for six hours straight).

I mostly use behind the head but foldable ones now, the ones to TC-84A-9315 spec (H95W) are pretty good for me but my nose is a bit too pointy to fit right at the nose. They seem to work really really well for people with slightly flatter features, the little nose metal form doesn't quite hold well enough.

No glasses for me. Interestingly, my SO who wears glasses prefers some random behind the ear looped kn-95s. No accounting for comfort I guess.

In all honesty, I've yet to find a flexible N-95 of any kind that doesn't seem to leak like a sieve around the nose. If someone is cool with that wearing it fairly loose is pretty comfortable... this is how I almost always see people wearing them, they're obviously not sealed at the upper edge.

I imagine it still helps some, but I'm very attentive to leaks at the top because glasses. If you wear it loose enough the gaps at the top are so big it doesn't fog your glasses anymore, I go the opposite direction and fiddle with it all day long trying to get the nose piece rigid enough to stop the leak. I'm not sure which approach is more risky... touching your mask is a nono too.

I guess a good mask with leaks is better than a surgical mask maybe, dunno if it's better than a rigid mask with an exhalation port TBH though, at least if you're not exhaling strongly there are no leaks and it's good for personal protection -- and since we've as a country decided it's everyone for themselves I feel pretty okay wearing a vented rigid N95 in an environment with a bunch of unmasked people.

Auras are great. I gave some to family and friends, and they became the go-to good masks for a decent portion of them.

My personal favorite is the 3M V-Flex N95. Super comfortable, great seal, and relatively large interior volume (great breathability). It's pretty close to a perfect mask. I also gave some of these away, and they were similarly popular.

In general, Aura seemed to be liked more for smaller faces, and V-Flex for larger faces. So, nowadays, my go-to recommendations are V-Flexes and Auras.

If you didn't already know, 3M shareholders can sign up for an annual holiday box. It costs money to order, but it's still much cheaper than buying the individual components (although if you don't need command hooks or post-it notes it might not be worth it for you)

Full disclosure: I am the proud owner of one share of MMM.

Proud, but only one?

What's the calculus there, and why proud — if you don't mind me asking?

It was a slightly tongue in cheek comment :) You need to own at least 1 share to be eligible for the annual gift box, so I own one share. I think it's a solid dividend stock if you're into that kind of thing, but I'm not. I try not to have too much of my portfolio invested in individual stocks, or do anything else that would make the late Jack Bogle disappointed in me.

> he preached investment over speculation, long-term patience over short-term action, and reducing broker fees as much as possible. The ideal investment vehicle for Bogle was a low-cost index fund held over a lifetime with dividends reinvested and purchased with dollar cost averaging.

Wow, pretty cool guy for a banker — wonder what his "catch" was!

What’s in it and what is the cost?

What's important is not only the amazing products, but also that they solve problems and that they can actually be bought by people who need solving those problems.

My anecdotal experience is that every time I run into some amazing 3M product, it costs $300/liter.

Nile Red recently posted this cool video of extinguishing a book with this fancy 3M liquid. Looked, yup, that's about the price.

If you wanted to experiment with fancy computer cooling, Fluorinert is also an arm and a leg in the quantities that'd be needed. It was apparently used in the Cray waterfall, but it seems after more than 30 years the stuff is still bloody expensive.

And so on.

it seems after more than 30 years the stuff is still bloody expensive

Fluorinert is a super niche product. The price reflects that. I imagine the cost to produce it has dropped dramatically in 3 decades. 3M just make more profit from it now.

As products mature there's no reason to believe the production process and efficiency savings will always be passed on to the consumer.

> Fluorinert is a super niche product.

I mean, that goes both ways. At that price it will always be a super niche product, and never graduate to "plain niche".

Look at the enthusiast market, there's no lack of fancy water cooling gizmos out there. They're bought by a small segment, but there's still a market for fancy gizmos to provide the best cooling for overclocked high end hardware.

And that's exactly what I'm getting at -- it's not enough to make cool stuff. The cool stuff also has to reach the people interested in using it.

Every ARM Server SoC failed to make their chips available. They do deals with "hyperscalers" and then wonder why nobody wants their chips or the hyperscaler just designs their own chip and makes a dedicated SoC vendor that only sells to "hyperscalers" obsolete.

I suspect some of these products have a funny price curve.

If Fluorinert costs $300/litre today and you cut the price to $100/litre - that's still far too expensive to become a mainstream PC coolant. It's not like there's a proven market for mineral oil PC cooling.

Could be, if you cut the price of Fluorinert by 2/3rds, you'd just be giving a discount to your existing customers, for whom price is no object anyway.

Mineral oil is _very_ messy, which really doesn't help at all. And the one company that sold the tanks had to stop due to some patent nonsense.

According to https://en.wikipedia.org/wiki/Fluorinert#Toxicity Fluorinert has to be limited to closed systems because it has "high global warming potential", it can decompose into a highly toxic gas, and "care should be taken to avoid contact with eyes and skin" (I'll admit I'm not sure how all this squares with the 'inert' in the product's name)

To me this sounds more difficult to use than mineral oil, not easier.

It does, yes. Seems like they have another product that fixes that issue, but it also sounds toxic. Not something I'd want to play with.

Isn't Flourinert a PFC and thus really dangerous/impactful in terms of accelerating global warming? I think we do well to keep its use to niche applications.

Yep. https://en.wikipedia.org/wiki/Fluorinert:

“As perfluorinated compounds (PFCs), all Fluorinert variants have an extremely high Global Warming Potential (GWP),[1] so should be used with caution”

That page also says

“Although Fluorinert was intended to be inert, the Lawrence Livermore National Laboratory discovered that the liquid cooling system of their Cray-2 supercomputers decomposed during extended service, producing some highly toxic perfluoroisobutene. Catalytic scrubbers were installed to remove this contaminant.”

Perfluoroisobutene is a schedule 2 substance, in the sense of the Chemical Weapons Convention (https://en.wikipedia.org/wiki/List_of_Schedule_2_substances_...), so it’s a substance that “can either be used as chemical weapons themselves or used in the manufacture of chemical weapons but that have small-scale applications outside of chemical warfare and so can be legitimately manufactured in small quantities”.

The question that we should ask in those cases is: how are their dividend payments going?

The stock market has nothing to do with the performance of a company; they are unrelated. Investing means betting on other investors to want to bump up the stock; it turned out to be really effective for e.g. Tesla where a lot of gullible amateurs got on top of it as well.

(I am one of those btw, I've sold what I had left early in the year and made a nice profit. Didn't get rich because you need to have money to make money, but it was a nice extra).

That's speculating, rather than investing. Not to denigrate the practice, just to be clear on the terminology.

At least part of the reason 3M stock price doesn't rise as much is because they distribute a dividend.

3M being innovative is already priced in

For anyone looking for the interesting numbers:

    Insulation resistance: 3.4 x 1014 ohms/square

    Contact resistance: < 0.3 ohms

    Minimum gap: 0.4mm

    Minimum overlay area: 3.2mm^2

Direct link to datasheet: https://multimedia.3m.com/mws/media/66235O/3m-electrically-c...

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.

> 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.

Thanks. This is exactly what I was looking for, and it was annoying this wasn’t in the specification or details section.

I think you mean 3×10¹⁴ ohms/square.

What people should also know is that every single display, and that includes every single cell phone touch screen has ACF (Anisotropic Conductive Film) in them. They aren't the same contact adhesive as this 3M film, and some are moderately expensive (e.g. >$0.25/inch @1mm width) for those displays, which is at least comparable (>10%) to the display ICs attached to them.

Why is so much ACF used? Because it is the most cost effective and compact way to connect dissimilar high density connections from one substrate to another. Displays typically require thousands of connections so you're looking at linear densities of 1 contact per mil (~25um) with resistances measured in ohms (for less than 0.01mmsq). The reason that IC packages (internally wire bonded or electroplated CSP) don't use ACF is a combination of cost, self alignment (solder pulls it into place), and much lower resistance.

The way that almost all of these ACFs are made is embedding conductive beads (often spherical of controlled diameter) which can compress when the adhesive is pressed/bonded to the two substrates. If the aerial density of the beads is right, you'll only get a few beads in contact and none will short any neighboring contacts. For displays the ACF material is typically a ~25um thick B-stage epoxy, which is tacked down and then "snaps" when heated and compressed permanently pulling together the two contact regions and compressing ~10um gold coated polystyrene balls between gold "fingers" on each glass/PCB/COF/COP side after the epoxy flows.

3M tried to get into these higher end ACFs, but now it's mostly Japanese and Korean suppliers.

To clarify, those figure are after bonding right? I understand that means it must be heated and compressed between conductors to reach those values.

This stuff confused the hell out of me as a 6-yr old electronics hobbyist (read unskilled-tear-downer). Took apart a non-functioning lcd calculator. Everything looked normal, except the lcd display itself was just pressed onto a rubbery tape like thing which seemed to be stuck to a line of pads in the pcb.

I expected a flex cable connecting the lcd to the PCB but couldn't find one. I 'knew' rubber was an insulator, so no matter what that rubbery thing was (I guessed it was simply a spacer) it wasn't the connection between the two.

Didn't learn about the existence of z-tape for another decade or so and immediately the light bulb in my brain flashed, solving a childhood mystery.

The clue would also be the clear doping of the conductive layer...

It's a shame your 6yo self didn't have a microscope around, or even a decent magnifying glass!

Zebra-strip is incredibly distinct once you're viewing it up close, and I bet its function would've immediately clicked upon seeing the structure.

Oh, I had a cheap magnifying glass; And I had access to a "Community Science Center" where they would have let me use a high-school-class microscope if I begged enough* . The problem was it didn't even occur to me to take that tiny rubbery strip that seriously. True shame really - by that time I had taken apart enough LCD calculators for there to be nothing surprising in any of them. This was the first surprise, in a while. I really should have focused on figuring it out. Just never occurred to me that the 10mmx1mmx1mm thingy was such an awesome thing.

*for free too; It was my favorite Saturday hangout spot - watching lab demonstrations, animal dissections etc, playing with the ever-changing interactive science demos).

Oof. Yeah. I have my own "I could've done something amazing if I'd just realized I needed to push on that thing that didn't look like a button" moment as a kid. A little nudge of guidance would've gone a long way.

The prowess of materials science in companies like 3M and Dupont never ceases to amaze me. Just when I think I've seen it all with fiberglass tape and kapton tape...

Their "prowess" saw DuPont give cigarettes laced with new toxic chemicals they made to their employees to test the chemicals effects.

Every human on earth has Dupont chemicals in their blood that will never go away, but accumulate over the course of our lives. These are "forever chemicals" that never break down. When you die you pass them on. They are in the animals you eat, in the beverages and water you drink, they are in the vegetables you eat. Your descendants a millennium from now will be eating them still, plus all the new ones produced between now and then.

This is the result of American capitalism and the worlds most corrupt banana republic legislature where bribery is so bad they made it legal.

Those absolutely evil bottom dwellers at Dupont you admire so much produce hundreds of toxic chemicals, and your bribed government allows them to produce and market these chemicals and spread them around the world without consequence.

Fuck Dupont and Fuck 3M. They are poisoning the planet.

https://www.netflix.com/title/81192027

That Netflix link is not available everywhere and also quite time-consuming to review. Obviously it is also a dramatic piece rather than a (semi-)scientific. I had a brief look at the PFAS wikipedia page (https://en.wikipedia.org/wiki/Per-_and_polyfluoroalkyl_subst...), which is what that Netflix movie seems to be about, but it's also quite wordy and the claims you make can not be found on there as-is. Maybe you want to consider adding a better source.

https://www.popsci.com/story/environment/dark-waters-chemica...

Basically, the US government allows companies to sell new chemicals they invent, completely unregulated. You could make a toxin today that kills everyone who touches it 10 years after they ingest it, and you would be free to market and sell this product. The chemical is presumed safe until evidence to the contrary comes to the knowledge of the govt.

That's how Dupont poisoned people all over the world. They sold unregulated chemicals they invented that nobody but them knew about.

One report by the Centers for Disease Control and Prevention’s National Health and Nutrition Examination Survey (NHANES) found PFAS in the blood of 97% of Americans... The number of new PFAS chemicals appear to be increasing, and exposure is difficult to assess. - https://www.niehs.nih.gov/health/topics/agents/pfc/index.cfm

There is now REACH in EU.

https://echa.europa.eu/regulations/reach/understanding-reach

Not sure if you'll consider this a more scientific source, but John Oliver also did a piece about PFAS: https://m.youtube.com/watch?v=9W74aeuqsiU.

The list of issues that the wiki article claims are "high certainty" is also quite concerning to me: https://en.m.wikipedia.org/wiki/Per-_and_polyfluoroalkyl_sub...

At the very least, seems that the production is being ramped down - quick skim of the article yielded this quote: "Their [PFASs'] production has been regulated or phased out by manufacturers, such as 3M, DuPont, Daikin, and Miteni in the US, Japan, and Europe."

John Oliver is a comedian, so also not a very good source. It's written for entertainment rather than being informative.

I think it can be both entertaining and informative, but it definitely feels like they try too hard to be funny at times. Do you have an example where the information they stated in the show was factually incorrect about PFAS?

Oliver is often correct at some core level but wrong on the details to play to the audience. Or "lies by omission" where a false narrative is produced without actually saying anything false.

That's not true, John Olivers show is extremely well researched. Sometimes his lack of references make it hard to use him as a source, but you can use the show as a starting point and validate his claims from there. They hold up very well.

The intercept brought a lot of this to light: https://theintercept.com/search/?s=pfas

Your post comes across as being written by someone who is unhinged rather than someone trying to make a convincing argument.

> This is the result of American capitalism and the worlds most corrupt banana republic legislature where bribery is so bad they made it legal.

And things like that just sound silly and trying to string a bunch of buzz words together.

What about that did you not understand? You have a corrupt government, where no law gets passed without input from corporations via their lobbyists. They have this access because they pay bribes for the privilege. That's banana republic levels of corruption.

The reason this is relevant is because your FDA and EPA are both captured organisations, which is what allows Dupont and these other environmental terrorists to go about their business unhindered https://en.wikipedia.org/wiki/Regulatory_capture

The US government is very far from "the most corrupt" legislature in the world.

I agree it's quite corrupt, though.

When you use corruption in the sense of committing corrupt illegal acts, the US looks fairly clean. But if you define it in the general sense and include lobbying and sacrificing the public interest for private interests as corrupt, then in terms of the dollar values, US legislative systems are some of the most corrupt anywhere.

Maybe so, but if so, only because the USA has the biggest economy in the world.

Whatever the reason, the statement holds up.

Can you name another country where you can bribe legislators and get away with it?

"Most corrupt" definitely fits.

That's true in many, many countries. To pick one: Pakistan.

The US government is not corrupt though. There is some small amount of corruption but largely works correctly.

DuPont is now also the owner of Union Carbide whose carelessness caused one of the biggest industrial disasters in Bhopal in '84, killing over 3k people, and causing lasting injuries for many 10s of thousands. IIRC, some IITs even disallowed DuPont from participating in their campus-placements for this reason.

India's craven political dispensation accepted the pittance of damages paid by UC, but it barely covered anything. Such disgrace.

(like I said..) I'm impressed with the prowess of the MATERIALS SCIENCE in companies like 3M and DuPont, certainly not the business ethics.

Please don't conflate admiration for the fascinating engineering work with endorsement of an entire company's impact on the world!

3M certainly do good some science, they just had(?) a terrible engineering ethics problem.

The issue is that when you remove social and environmental ethical constraints, a lot of companies would become impressive in a technological, financial or managerial sense. But if you include them and measure 3M's, Dupont's etc. performance in a strong regulatory environment with good compliance, they earn decidedly unimpressive overall scores and can be seen as bunch of greedy, clever, selfish parasites, gaming the system.

That's why narrow statements praising one aspect of their performance paints half a picture. Like calling a war criminal an effective tactician - technically correct, but against the big picture, so what?

Years ago I had the idea to use this tape to make solder-free PCB kits to teach electric circuits (the tape would connect the chip pins to the board, without shorting sideways). I bought a roll, and printed some boards for LEDs and 555 timers and such.

Unfortunately it didn't make reliable contact for the chip pins unless you were constantly pushing down on it. As I recall the datasheet states as much. That seems like a solvable material science problem, but alas perhaps not valuable enough.

Ben Krasnow used this for his DSKY replica [0] - its a very interesting product.

[0] - https://youtu.be/Z2o_Sp2-aBo

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

This is sometimes used to connect rigid touch panel electrodes (on glass) to flex cables, bypasses having to do lots of soldering…

Seems like it would be a good replacement for zebra strips. Not in existing vintage devices that need multi-mm of height but just in principle like if you were making something new.

What 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.

well said.

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.

I take it the tape would go in the middle between the circuit board and components?

"I take it the tape would go in the middle between the circuit board and components?"

Let me see...

"place the tape on a circuit board and place components on the tape"

Thanks, without your constructive comment I would've never known that I was asking a dumb question.

Perfect for easily removable/replaceable surface mount components (as long as there is no G/shock requirement), but even that could be mitigated with a pressure plate over the components.

I don’t quite get how that’s useful.

You can place BGA components on a board without soldering, which for BGA requires an oven, a hotplate or a heat gun. Also ribbon cables without a housing.

Besides an occasional process improvement over soldering, this can be applied in cases where soldering cannot, for example with very heat-sensitive components such as OLEDs.

Perhaps also on stress-sensitive components such as high-stability voltage references.

It's useful in certain special circumstances where it's useful. It's probably not useful to you or most people.

It's just a very exotic and strange thing that does make some things possible which would otherwise be difficult or impractical some other way.

It can do essentially the same job as a zebra strip, with the following differendes:

Zebra strips are typically very thick blocks of silicone rubber. This is very thin tape.

Zebra are generally not adhesive. They're usually just a chunk of rubber that conducts electricity in two dimensions and insulates in one dimension, but the 3-part sandwich of pcb+zebra+part must be held in place mechanically (metal frames around lcd screens). This is double-sided adhesive tape.

Zebra conduct in two directions and insulate in one. They are useful in only one dimnsion. You can take a line of contacts and lay a zebra strip across them. The line can be curved or straight but it's sill essentially a single dimension which is along the line. IE the row of contacts could be say radiating lines and you could lay a zebra in a circle to cross tbose. What you can't have is a grid of dots or any other random arrangement of contacts, just a line. This tape however insulates in two dimensions and only conducts in only one dimension. It's like a tiny carpet of vertical conductors all insulated from each other. You can lay an inch square sheet of it right over a footprint of any random arrangement of contacts, and it conducts an exact image vertically up from each contact, but does not short between the contacts.

Some uses for that could be prototyping where you want to test components temporarily and conveniently without soldering. You just stick the components to the pcb with the magic tape and they actually work.

More likely uses are to connect things where soldering would be difficult or impossible. For instance connecting displays or ribbons to pcbs where the part may be glass with no metal to solder to, or delicate plastic film that would be destroyed by heat, etc. You can do that with zebra strips now, but this would allow packing in a whole lot more contacts into a smaller space. Or allow sticking components directly onto materials they can't be soldered to. Like sticking a chip directly onto the back of a glass display with no ribbon and no pcb.

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.

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.

This is a great answer. I guess the "tiles" are so small that there's no way they could bridge even the tiniest IC packages?

The article has several pictures in which you can see that conductive grains in the tape are relatively sparse in the tape, such that any given grain isn't in contact with any other grains.

Directly above and below a point on the tape conduct to each other (along the thickness), and no where else.

If y'all have never been on McMaster-Carr, you are in for a treat: https://www.mcmaster.com

All kinds of stuff like this can be explored with a pretty decent UI.

I went to look at this expecting it to also have excellent thermal conductivity (due to the low resistance z-axis conductivity through silver particles). To my surprise, it does not. The published range is 0.16-0.20 W/mK, which is pretty much what you get for most tape products.

We use specialized thermally conductive tapes in a range >= 1 W/mK. I am always looking for interesting developments in this domain.

Unless I'm misreading this, it's $19.78 / yard for 4" wide size at digikey.

If the link doesn't work (lots of tokens in there) try searching for "9703 3M tape conductive" as a starting point.

https://www.digikey.com/en/products/detail/3m/9703-4-X36YD/6...

Could this be used for CPU (or some other truckload-of-pins chip) "reballing"? Does it do well under a bolted-on radiator / pressure plate?

For instance, many old Playstation 3 systems go faulty because of the poor quality solder on the CPU/GPU that tends to crack over time. Being a normie, it's really hard to fix something like that at home. But this tape seems like it could save the day.

There's no way you could have good enough signal integrity. The frequency is high and there's no clever signal processing.

I have never tried it but it seems implausible.

> Could this be used for CPU (or some other truckload-of-pins chip) "reballing"?

The datasheet[1] says the minimum gap between conductors is 0.4mm, so based on that it should work for 0.5/0.65mm BGA.

Also would clearly affect the speed you can run things at due to introducing parasitics. But would certainly be fun to try.

[1]: https://multimedia.3m.com/mws/media/66235O/3m-electrically-c...

Getting the chip lined up accurately enough might be a bit trickier. With soldering, you can normally rely on the solder's surface tension to pull the pads into alignment.

What's Z-axis on this tape? is it thickness?

It's conductive only in the z-axis. So you can, for example, tape components to your circuitboard instead of having to solder tiny pieces.

I think they were asking… what is the z-axis? What’s the canonical co—ordinate system for tape? You just repeated that it’s conductive in the z-axis.

Yes, z-axis is the direction of the tape's "thickness" so electricity passes only from the thing stuck to the top to the thing stuck to the bottom (directly through the tape) without shorting the rest of the contacts.

I misread the question to be "what makes this 'z-axis' tape" rather than "which axis is the z-axis of the tape".

Yes, the z axis is the thickness direction.

Oof, a roll of this stuff is ~$180

Would be extremely useful to get an explanation of what 3M means is the "Z-axis" of the tape. Along the tape plane? Across the tape plane? Through the tape plane?

I can see uses for all, but how you'd apply it would certainly differ if depending on which one is Z....

z-axis is the thickness of the tape

It's been pretty entertaining to watch the stocks of this stuff on Amazon dwindle minute by minute

Neat. Elastomeric materials like that are widely used, made from alternating insulating and conductive layers. They need external compression. An adhesive tape is a clever variation.

Is there a less technical term for anisotropic? Polarized?

Anisotropic means “depends on direction”. This tape has conductivity that is different in one direction than the other two directions. This is unique because many materials have a conductivity that is the same regardless of the direction of current flow.

Polarized is not the right word.

Directional, though anisotropic is a better description.

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