There is a crucial point in every iFixit phone or tablet teardown where the future is about to take a drastic turn. It’s like right before the river card in poker, or a triple axel in figure skating, or clicking on a self-involved friend’s Instagram story: will there be stretch release adhesive under the battery, or (sigh) something else?
Gadgets that keep their batteries in place with stretch release adhesive are the next best thing to not using any adhesive at all. What makes stretch release so notable to us is what stretch release is not: sticky, hard-to-remove glue that practically forces you to bend and poke at a lithium-ion battery (which is a terrible, really bad idea). Battery removal is a big part of a smartphone’s repairability score—not a whole point’s worth by itself, but it could easily move a score one point higher or lower. Using an adhesive that a regular person can remove without special tools or chemicals is a big deal.
I’ve learned all this in my year and a half working at iFixit. But I wanted to know more. What are the physics, what is the chemistry, behind stretch release? Why doesn’t every device maker use stretch release adhesive? And what’s the best way of using it, either going on or coming off? Let’s dig in.
How stretch release tape works
iFixit is lucky to have friends among the adhesive gurus at Tesa, a giant global provider of adhesives for industry and trade markets with nearly 5,000 employees, but still able to send a few folks to our small-city office. We filmed their experts for a video tutorial for our Pro customers about how to apply tape and which tape to use, and they spoke with our staff about the details and science behind stretch release.
There are three important properties to any tape: adhesion, cohesion, and tack. They form a triangle: you can add or take away from any one property, but it alters the other. Adhesion and cohesion are the most contradictory, and crucial to designing and choosing an adhesive. Put very simply:
- Adhesion is the attraction between the adhesive and the substrate (the surface you want the adhesive to stick to). It improves with pressure, and usually with a brief period of time. It’s the ability to stay attached to something.
- Cohesion is the inner strength of an adhesive, its ability to stay intact. It’s how an adhesive resists being melted, pulled sideways, picked at, or otherwise disrupted. It’s the ability to stay together.
- Tack is an adhesive’s ability to first grab onto something, during the very first application. It’s especially important when applying adhesive to adhesive-resistant surfaces, such as rough planes. It normally doesn’t matter much after the adhesive is applied and under pressure or time (that’s adhesion), but note those italics there. It’s the ability to grab onto something when applied or moved.
Normally, what you care about in tape is how well it holds two things together. You want it to resist the force that might detach those two things, usually coming from a parallel direction: gravity, hands, whatever. But here’s where some weird science comes in. Stretch release adhesive is made with polymers that realign themselves when the material is stretched parallel to the surface it is on. The tack reduces drastically, the adhesive bond is broken, and the substance (which is still intact, thanks to its cohesion) can slide across surfaces it would normally grab onto. It leaves no residue behind because it wasn’t pried or rubbed away, it just politely left the scene, like the best party guest.
Just to reiterate: it’s adhesive that changes its molecular properties if you pull it like Laffy Taffy. It’s amazing stuff.
I wish I could give you more about the exact science of how stretching the tape realigns its polymers, but it’s … a lot. There are a number of posts on open-question forum Quora asking how 3M’s wall-hanging Command Strips work, but the closest thing to an answer is a former 3M employee saying, actually, it’s a secret. He does reference how that Command adhesive has “extremely high tensile strength, but pretty low shear strength.” As with many big concepts, there is an xkcd comic that helps explain that, and then an explainer for the explanation (warning: comic contains one swear, but much science).
One of the oldest U.S. stretch release patents, granted to Johnson & Johnson in 1976, says the stretch release magic is “a unique film forming composition comprising elastomeric and thermoplastic A-B-A block copolymers.” What kind of A-B-A block copolymers, you ask? “[T]he A-blocks are derived from styrene or styrene homologues and the B-blocks are derived from conjugated dienes or lower alkenes.” Ah, well, there we go. You can try 3M’s 1999 patent for stretch release tape with an integrated pull-tab, too, but it assumes you understood the chemistry of the 1976 patent.
3M does explain how their pull-tab Command Strips work—just a little bit—in a blog post about … holiday decorating. Expert scientist Margaret Sheridan offers a layperson explanation of the chemistry behind Command Strips, which she helped develop:
“The adhesive has adhesive strength, which is the strength between the strip and the substrate, or the surface you’re sticking the strip to. It also has cohesive strength, which is how strong the adhesive is internally,” explains Margaret. “We want that cohesive strength to be greater than the adhesive strength, so when you stretch it, it comes off cleanly.”
Note: If you know of, or can provide, a good plain-language explanation of how stretch release chemistry or physics works, we’d love to include it here! Email email@example.com.
iPhone XR Akku
Ersetze einen kaputten Akku durch diesen 2942 mAh Ersatzakku.
$39.99 On Sale
The best way to remove stretch release strips
Load up any of our iPhone battery replacement guides (and a few others, including , and you’ll get iFixit’s advice on working with stretch release adhesive. For example:
- Avoid wrinkling or twisting the strips
- Go slow and apply even pressure, so there is no slack or bunching
- Pull at as low an angle as possible (lower than 60 degrees if possible), without snagging it on other things
- If it breaks, grab the end and keep going
- If you can’t get the end back, try heat or isopropyl alcohol, string, and patience.
The Tesa experts emphasized to us that smooth, constant pressure is the key to efficient removal. Try never to let up on your pressure, while occasionally re-grabbing the adhesive closer to the battery.
Experienced phone-openers might notice that in some of our guides, we instruct you to remove the Taptic Engine or other parts of the iPhone, parts that might not seem strictly necessary to get at the battery. Now you can understand why: we’re removing objects that can potentially snag the adhesive, or prevent you from pulling at that nice low angle.
When you pull it off, you have a battery that’s ready to slide right out, and no leftover adhesive on the case. With a quick isopropyl cleaning of the phone surface, you’re ready to re-apply new stretch release strips. This begs the question …
Why doesn’t every device maker use stretch release?
The folks at Tesa, which sells both stretch release and other adhesives to device makers, told us that there are some trade-offs in designing for an easy battery removal.
A device maker has to not only add a smidgen of thickness for the strips themselves (you laugh, but every micrometer counts), but also design for accessing the tabs. That can mean moving components around so that your fingers, or blunt tweezers, can get at the release tabs, and putting no pieces above or below the height of your pulling that might snag the tape. Some device makers, especially those who don’t see any profit or gains in repair work, may not want to invest the time or space in designing for stretch release.
Then again, even Google, which previously glued down batteries, switched to stretch release tabs starting with the Pixel 3. And inside the Pixel 4a, they went so far as to cut little windows out of the middle frame, putting the tabs on the other side and giving you a very shallow angle for pulling.
Why do batteries need tape/glue in the first place?
It’s a paradox of modern phone design that phones are as thin as possible, yet the batteries inside them need to be held in place with adhesive. Shouldn’t the tight space inside be enough to keep the battery in place?
If it was the kind of battery that you once had inside your 2000-era phone, sure. The hard case kind of battery that you could grab from the back of your phone could withstand some knocking around. But modern smartphone batteries are thin and have soft foil cases. This allows them to fit better, and shove more battery life, into a smaller space. But, as iFixit’s Kyle Wiens wrote in WIRED about the Galaxy Note 7 debacle:
The industry’s obsession with slimmer gadgets requires slimmer batteries. So they increasingly turn toward lithium polymer batteries. Such batteries are incredibly delicate, and encased in a flexible foil-like case. This reduces bulk, making the batteries easy to package. But it means essentially wrapping a potentially incendiary device in tinfoil.
And then pasting it into a device people hold near their face.
Modern lithium-ion batteries, the thin, foil-backed kind, are adhered into place so that they do not get pinched, punctured, or otherwise damaged by other phone bits. The long, flat battery, glued into place, can also act as reinforcement for the phone itself in certain designs. It’s not likely that batteries will go back to hard shells any time soon, so for now, we’re … stuck with adhesive.
How to reapply stretch release
We provide a film template for applying adhesive after a battery swap, because improperly placed adhesive can interfere with the wireless charging coil. It speaks to one real disadvantage of stretch release tape: once you put it down, you can’t reposition it.
Our guide to applying stretch release adhesive assumes that you are applying adhesive to a brand-new battery, fresh out of its packaging. When you’re applying adhesive to the phone itself, however, you want to clean the surface thoroughly, preferably with isopropyl alcohol. I’ve found this to be a deciding factor in whether a Command Strip holds a picture frame to a wall, or whether I hear a loud crashing sound in the middle of the night.
Finally, avoid air bubbles, wrinkles, and other deformities at all costs. Having any kind of gap in the contact between the adhesive and surface seriously weakens the bond, and can lead to unexpected release. You don’t want your battery loose inside your device. Trust us.