Plastic, Then Aluminum, Now Glass: What Besides Looks Changed What Phones Are Made Of?

This time the change could not reverse the market's decline

The Pixel 3, Google's own-brand phone released on October 9, completes a turn in smartphone design.

It marks the point at which every major phone company has dropped aluminum from its new models. Google sold only 3.9 million phones last year, but it is still the company that controls the Android ecosystem. Like nearly everyone else, it chose glass over the metal body of its past two generations.

The move from metal to glass took about three years. Samsung put a glass back on the Galaxy S series in April 2015; the iPhone 8 and X settled the trend in 2017. This year Huawei's P20, the vivo NEX and OPPO Find X released mid-year, and then the Xiaomi 8, all came in glass.

Back in 2016, among the five largest smartphone brands by shipments as counted by the research firm IDC, almost every major model apart from Samsung's — Apple's iPhone 7, the Huawei Mate 9, the OPPO R9, the vivo X9 — was built on aluminum.

You can still buy a new phone with an aluminum shell, but they sit in the middle and low end. By the end of this year, according to the research firm Counterpoint Research, 26% of smartphones shipped worldwide will have glass backs; two years from now the figure will be 60%.

Metal was once the mark of a premium phone. When Tim Cook held up the iPhone 5 in 2012, its unibody aluminum shell was the outer limit of metalworking in consumer goods.

That was a manufacturing revolution Apple had been preparing since Steve Jobs's day. For a while everything Apple made was aluminum — computers, phones, iPods, mice, routers, even the walls of Apple Stores. So was Venus, the yacht Jobs had designed for him in the last years of his life.

From assorted plastics to aluminum to glass: in little more than a decade, phone bodies have already been through two big changes of material, and looks were not the only reason.

Glass went mainstream because of looks, and more because of 5G

Clear, refined — the words that attach themselves to glass. Even now, a huge glass façade is standard for a high-end shop.

On a phone the advantages are plain. Transparent glass shows the back panel underneath, which opens up colors, gradients, metallic finishes and much else.

The design also holds together better. The three bare white antenna bands across the back of the aluminum iPhone 6, there to let the signal out, no longer have to appear.

Glass is warmer to hold. It does not turn icy in winter the way metal does, and metal conducts heat so well that a few minutes of gaming leaves the phone hot. Glass resists scratches better, too: when Apple buffed the metal of the Jet Black iPhone 7 to a mirror finish like glass, the scratches came fast and in quantity.

Glass is not the best material for a phone. The things a phone is supposed to chase — lighter, thinner, tougher — it cannot deliver. Going from aluminum to glass costs the user something real.

Weight first. The iPhone 8 is 7% heavier than the model before it, the vivo X23 3% heavier, the Huawei P20 13.8% heavier.

Glass makes phones thicker too: the iPhone 8 by 4% over its predecessor, the iPhone 8 Plus by 2.7%, the Huawei P20 by 12.9% and the Mate 10 by 3.8%. None of the extra bulk went into battery life — the iPhone 8's cell actually lost 139 mAh. And glass is plainly easier to break than metal.

The gains and the costs are both obvious. Every maker's main phones still moved to glass in 2018, and the reason is that glass is the material that suits a 5G phone.

“What glass mainly solves is a metal body getting in the way of the signal. Next year 5G phones go on sale, and glass means fewer antenna strips on the body,” an industrial designer who worked on the Pixel line and now works at vivo told QDaily.

A 4G antenna is a long, thin strip — the three conspicuous white lines across the back of the iPhone 6 that people mocked from the day it shipped.

For 5G, keeping the signal steady means antennas shaped as square arrays instead of strips. A metal body can no longer use a few narrow lines on the back or a thin metal rail around the edge; neither is wide enough for an array.

4G, Wi-Fi and Bluetooth all carry their signals on electromagnetic waves, and those signals interfere with each other. In the 4G era, carriers around the world took up most of the spectrum between 1800 MHz and 2600 MHz. To get out of the way, the 5G standard went higher: international and Chinese rules currently put the top of the 5G high band at 30 GHz.

The higher the frequency, the shorter the wavelength, and an antenna works best at a quarter to half a wavelength. So a single antenna for high-band 5G comes down to between 5 mm and 2.5 mm.

Higher frequencies also lose strength far faster. The fix is more antennas — 4x4 or 8x8 arrays packed together — which needs a 10 mm by 10 mm patch inside the phone, and the mid-frame where antennas usually sit has no room for that.

A 10 mm square will not fit in the frame or anywhere along the edge; it can only go against the back. And metals such as aluminum block electromagnetic waves outright — a conductor reflects, absorbs and cancels them. To keep the signal strong, metal cannot be allowed to wrap the antenna.

Glass also lets the signal through and does not block wireless charging. Researchers at Beijing University of Posts and Telecommunications and the Telecommunications Research Institute under the Ministry of Industry and Information Technology have measured how much radio signal each material eats. Clear tempered glass costs about 10 dB or less; metal costs 25 dB, more than twice as much.

5G is not in service yet, but a jump as large as 4G to 5G takes phone makers and carriers a year or two to work out together. Carriers have to upgrade base stations for the faster network; phone makers have to commit to the hardware one to two years ahead, so they can test the 5G signal over and over before launch.

Taste in phone design varies. The technical limits do not. Every big change of material in the history of the phone has come from a new requirement like this one.

From plastic to metal to glass: phone materials have turned over several times

Like almost every consumer electronic product today, the phone started in plastic.

The first mobile phone, the Motorola DynaTAC 8000X, was born in New York in 1973. Martin Cooper, the engineer who invented it, held up the plastic-shelled brick and placed his first call to Motorola's rival of the day, the American Telephone and Telegraph Company.

It is not hard to see why plastic came first. When phones were still bulky, plastic was light, did not block the signal, was easy to manufacture and cost little.

Plastic is also easy to mold. Early phones existed to make calls and send texts; brands pushed sales by putting out dozens of shapes a year — clamshells, side-sliders, candy bars — and turned models over fast.

By 2005, Nokia alone was selling 61 differently shaped phone shells in a single year: candy bars with a nine-key pad, candy bars with a full keyboard, clamshells, side-sliders. For short sales cycles and dozens of models a year, plastic was the better material.

To tell the models apart, phones of those years were mostly a plastic structure with something else on the surface: metallic paint sprayed on Nokia's high-end N series, or, for a while, a layer of imitation leather glued to the back of BlackBerry's high-end 9 series.

What broke plastic's hold was the first iPhone — though not because of its aluminum shell, novel as that was at the time.

Metal had reached phone bodies before the iPhone. Motorola's classic Razr V8 used a stainless steel frame and aluminum hinges, and it looked expensive too.

The first iPhone mattered because it defined a shape: no keyboard, no lid, one large screen across the whole body. A phone's job moved from calls and texts to showing apps on as much screen as possible. Once that final form existed, every phone was designed toward it.

After the iPhone fixed that form, novelty in the outline of a phone dwindled. What was left to change was mainly screen size, shell material and color.

That is where the changes in material began.

The iPhone 4 of 2010 was the next big one. Stainless steel formed the mid-frame, with the antennas built into it, and two whole slabs of cut glass covered the front and the back — a world away from the all-plastic iPhone 3GS before it.

That glass did not last as a trend. On the iPhone 5 in 2012 Apple switched to a unibody aluminum body — again because of the screen.

“Apple kept pushing two ideas then: thin and light, and a body that feels like one piece. The MacBook was designed in the same style. Aluminum was a good way to keep the body strong and still thin,” said the industrial designer quoted above, who thinks Apple turned to metal because glass could not get thin and light enough.

The iPhone 4's glass was not today's glass. It was weaker, and its edges were vertical: the rim was as thick as the sheet. Later, starting with Nokia's N9, phones began using glass with a curved edge — so-called 2.5D glass — which looks thinner at the same thickness.

Sony and Samsung then tried glass backs, in 2014 and 2015. Sony launched the high-end Xperia Z3 with a glass back in 2014; Samsung, Xiaomi and others followed with double-glass designs on phones such as the Galaxy S9 and the Xiaomi 4S.

But glass was no longer the mainstream of design. The outsized success of Apple's iPhone 6 and 6 Plus turned the whole industry around. They are still the best-selling generation Apple has ever made, 220 million units in all over a two-year product cycle.

The unibody of the iPhone 6 cut down the seams and made the phone look like a single object. And after several rounds of tuning, the aluminum was strong enough to hold a large-screen phone together without adding thickness.

Going from a 4.7-inch screen to the 5.5-inch iPhone 6 Plus added only 0.2 mm of thickness. The 5.5-inch iPhone 6 Plus was even 2 g lighter than the 3.5-inch iPhone 4, and 2 mm thinner — 21.5% less.

Makers tried other things then. The first OnePlus phone, and later Motorola's Moto X, offered swappable back covers in bamboo, ceramic and other materials. Motorola went further and turned the back cover into a functional module: a new camera, say, or a bigger battery.

Apple tried polycarbonate on the iPhone 5C. Nokia had pushed the plastic earlier; it gave a shell a jelly-like finish and allowed brighter, more varied colors. In 2016 Apple also shipped the iPhone 7, which tried polishing a metal shell to the feel of glass.

None of it stuck. Until glass came back, the unibody aluminum body was the industry standard without exception.

By 2016, among the five largest phone makers by shipments, nearly every major model — Apple's iPhone 7, the Huawei Mate 9, the OPPO R9, the vivo X9 — was built on aluminum. In December 2016, 17 of China's 20 best-selling phones had unibody metal bodies: 85%.

Glass began coming back around 2016. Samsung, the industry's other reference point, did not follow Apple at the time: after years of plastic, it put a glass back on the S6 it released in February 2016. It later gave that glass the look of metal on its high-end models.

“Samsung actually used a film — a reflective film in a metallic tone that lets the glass read as metal,” vivo's industrial designer said of how the process works.

That is what distinguishes the new glass. Where the iPhone 4 had a whole square sheet laid on the body, the glass on the iPhone 8 and the Galaxy S8 is ground with a 3D curve; the edges are thinner and read as part of the body.

Among the top five makers today, only Xiaomi uses something else — ceramic, on the expensive MIX line. Every other maker's main models already have glass backs, and even Xiaomi uses glass on the higher-selling Mi phone series.

Behind any material lies a fortune, which is why makers are careful with design

A new process, a new material: the money behind them is large. The biography of Apple's chief designer, Jonathan Paul Ive, describes in detail what Apple spent on the aluminum unibody.

After it developed the metal unibody process, Apple began spending in earnest around 2007, buying every CNC milling machine it could find. It even booked three years of output from one Japanese factory. The machines cost $250,000 at the low end, and the dearest could run past a million dollars each.

By 2012, with the iPhone 5 and the iPad 3 — both unibody metal products — going into production, Apple's capital spending in this area reached $9.5 billion, most of it on tooling and process.

Apple spent $865 million on its retail stores, by comparison. Even with those stores in expensive, prime districts, manufacturing took 11 times as much — and Apple was not paying to build Foxconn's factories.

The Aluminum Association still carries a thank-you letter to Steve Jobs on its website. The title is “Thank You, Steve Jobs”; it credits him with pushing aluminum manufacturing forward.

Apple's aluminum unibody has governed the industry for years, but it was never the obvious choice. Aluminum-magnesium and titanium alloys were common in electronics before it.

Apple in fact tried several metals first — titanium, magnesium, chrome-plated steel. None could be used on a phone: they scratched, or were not hard enough, or weighed too much.

Personal taste entered into it. Jobs insisted the phone show the natural color of the metal; painted and chrome-plated finishes were unacceptable to him.

A phone takes about a year to go from design and choice of shell material to launch, with a run of use tests before it ships. Even after a process that long and testing that careful, aluminum caused two large problems.

The all-black iPhone 5 Apple launched in 2012 chipped badly on its metal body; the next year the iPhone 5s dropped black for space gray.

The iPhone 6 after it bent, because its aluminum was not strong enough; the iPhone 6s changed the alloy and fixed it.

In a few years, the iPhone's aluminum went from a way for Apple to beat its competitors to a process anyone in the industry could use. The companies that followed skipped the trial and error, and the money Apple sank into the wrong materials.

Getting the material wrong is expensive.

Apple invested in the sapphire company GT Advanced Technologies in 2012 and never managed to get sapphire glass onto a phone screen. It ended up only on iPhone camera lenses and on the low-volume stainless steel and gold editions of the Apple Watch. GTAT filed for bankruptcy in 2014; Apple had put in $600 million in all.

Apple also has to spend money investing in glass makers. In 2017 it put $200 million into Corning, which makes Gorilla Glass, to fund research on the most advanced glass processing and to buy equipment.

The same happened with the Jet Black iPhone 7, whose stainless steel was polished to the feel and the mirror finish of glass. Ive, the design chief, explained in a video that jet black took nine rounds of polishing.

The elaborate process cut output, and the jet black iPhone 7 was badly short of supply after launch. The bigger loss: Apple used a costly new process on that one generation of phone only. Afterwards it survived on a few watches and on the frame of the expensive iPhone X.

Small companies spend just as heavily. In 2014 Xiaomi, three generations into plastic, tried a stainless steel frame on the Xiaomi 4. Li Wanqiang said at the time that Foxconn and Hi-P had together added 1.9 billion yuan of CNC equipment — 1.2 billion at Foxconn, 700 million at Hi-P. All of it had to be spread over the life of Xiaomi's phone production.

The Xiaomi MIX of 2016 used a new ceramic shell. Two years on, ceramic — paid for by Xiaomi alone — has not gone mainstream; even Xiaomi can only use it on the low-volume MIX line, while the Xiaomi 8 stayed with glass and the cheap models are aluminum.

There are new designs beyond glass, and none has reversed the shrinking phone market

When the final form turns out not to be final enough, new designs begin.

The iPhone X was the first real change since Apple launched the iPhone. Face ID let Apple remove the Home button and run the screen across the whole face, but it still had to leave a 34 by 5 mm strip for the camera and the sensors face recognition needs.

That compromise on a full screen sent other makers off on their own experiments. Playing safe, most of them shipped something with an iPhone X-style top strip in the past year. But they also began making their own choices about the full screen.

Samsung kept an area at the top for the camera and the speaker. OPPO and vivo, both working on a new image, used a motorized slider and a pop-up camera to keep the front intact.

Xiaomi and Huawei each shipped a new phone with a manual slider. Every scheme costs something: the OPPO Find X and its motorized slider are 2 mm thicker than the iPhone X.

New technology is in test, too. A week ago, at Samsung's SDC 2018 developer conference in San Francisco, the company showed a foldable display panel called InfinityFlex Display for the first time. The product is nowhere near finished, but the line between phone and tablet is broken.

In the 11 years since the iPhone, every new smartphone technology has come to serve the apps on the screen: hold a thinner, lighter object, see a bigger interface, run it faster.

The shell and the frame now exist to be noticed as little as possible. Ive, Apple's chief designer, said of the iPhone X that “a phone of the future should look like a case attached to a display. The ultimate goal of iPhone design is to make the phone a single sheet of glass.”

Once the apps matter more than the hardware, it is not hard to see why everyone owns a smartphone and yet no new phone can make people trade up every year.

The industry once grew explosively on the smartphone itself. Then, from 2011, Samsung's first 5.8-inch Note started the run to big screens; three years later the iPhone 6 Plus made screen size a selling point and drove a wave of upgrades.

Now there is less and less to change on the outside. Apple's iPhone XS this year came with a new gold frame, another attempt to sell a color. vivo's NEX, OPPO's Find X, Xiaomi's MIX 3 — each maker's supposedly fuller full screen — none of them stirred enough people to trade up.

2017 was the first year the whole smartphone industry began to shrink; this year shipments have fallen year on year for four straight quarters. IDC data show that global smartphone shipments in the third quarter of 2018 were 35.52 million units, down 6% from a year earlier. Through September 2018 the Chinese market kept contracting as well: 35.03 million phones sold in September, down 7.7% year on year.

Apple's latest results confirm the decline. iPhone sales of 46.9 million came in under the 48.4 million analysts expected, and growth was close to zero.

Falling hardware sales wiped $200 billion off Apple's market value. Xiaomi's shares fell all the way through their IPO price.

The glass body will be with us for years. A crisis across an entire industry does not go away because the design changed.

Graphics: Feng Xiuxia

Cover image: Przemyslaw Marczynski on Unsplash