Why the first iPhone screen was made from glass instead of plastic - Part 2/2: Gorilla Glass
You may recall early touchscreen smartphones, which utilised a soft plastic material over the display. These screens responded well to a stylus, but not so well to a finger.
Resistive touch screens respond to pressure: The screen is pressed; the outer layer is pushed into the next layer, which detects where it was touched. These screens are versatile because they can be operated with a finger, fingernail, stylus, or any other object. They are cheap to make, but do not work when damaged. Examples include old LG and Sony Ericsson phones, the Nintendo DS, cash machines, and self-checkout screens.
Capacitive touch screens sense conductive properties rather than pressure. This means that they are a lot more responsive to swiping and pinching gestures, and can detect several touch points simultaneously. They also allow for better colour reproduction.
Here we are testing a touch screen during an iPad repair.
Many of our elderly customers struggle to get to grips with the concept of a capacitive touch screen - pressing their fingers into the screen with tremendous force for several seconds at a time. A quick, gentle tap is all that's needed, Doris.
Now for the issue of fragility.
Glass is glass, and glass breaks. Fortunately, clever people use chemistry to ensure that our phone screens are more resilient than your typical untreated piece of glass.
Tempered glass is simply regular glass which has been subjected to extreme heat. When we temper glass, we make it harder. Tempered glass fractures into small shards, as opposed to regular glass, which breaks into big jagged shards. Windscreens use laminated glass, which involves a similar process, but with the inclusion of a transparent layer of plastic between two layers of glass.
Most modern smartphones use Gorilla Glass, which was developed by a company called Corning. Your phone screen looks like a normal layer of thin glass, but it has actually been chemically treated to make it tougher and more resistant to breaking. The glass is immersed into a hot potassium salt-bath. In here, sodium ions are exchanged for larger (stronger) potassium ions.
The result is a more resilient piece of glass, which is less susceptible to scratching or breaking. Crucially, it maintains its integrity when cracked. Think about normal glass: when it cracks, it quickly leads to further damage along the fault line, whereas Gorilla Glass maintains structural integrity by keeping damage localised. This is why people can often continue using a phone with a cracked screen for a long time.
Corning claims that Gorilla Glass can survive 2 metre drops on to hard surfaces, and is 4x more resistant to scratching compared with the next best alternative - aluminosilicate glass - which will typically break when dropped from just 0.8 metres.
Yes, your screen will break at some point if you keep dropping it - but consider how impressive it is that a lightweight, 1mm piece of touch-sensitive glass can withstand years of daily use. Try carrying a wine glass around with you all day; see what happens...
There is a trade off however. It seem likely that whilst harder glass is more drop-resistant, it is actually more susceptible to scratching.
Upon the release of the iPhone 12, Apple switched from Gorilla Glass to Ceramic Shield. An interlocking structure of small ceramic nanocrystals are embedded in the glass matrix. Apple claims that Ceramic Shield is much tougher than Gorilla Glass. However, there isn't really any evidence to support this claim.
One thing we can say for sure it that it is significantly more susceptible to cracking during screen removal. Removing the screen from an iPhone 12 is like peeling an egg or transplanting a spider web.
Most modern smartphones utilise glass backs instead of the previously favoured aluminium or plastic. This is because glass is non-conductive, and so radio frequencies can transfer through it with minimal disruption. This makes glass a better solution for wireless charging and 5G connectivity. Most manufacturers state that they use Gorilla Glass on the back of their devices as well as the front.
More glass, means more to break, means more to repair.
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