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Next time you try to wipe a smudge off your iPhone screen, take a closer look. See if you can spot one of the two tiny QR codes etched into its glass.

Chances are you won’t be able to find them. Both codes are tiny—one is the size of a grain of sand and can only be seen with special equipment, while the other, roughly the size of the tip of a crayon, is laser-printed on the reverse side of the glass somewhere along its black border or bezel. The codes are placed on the glass at different stages of manufacturing to help Apple track and reduce defects. They represent the company’s obsessive attention to detail in manufacturing devices such as the iPhone, which has helped it squeeze costs in a traditionally low-margin business.

• Two tiny barcodes on the cover glass of iPhone help Apple track defects

• Apple struggled to get clarity on glass defect rates from suppliers

• Newest bar code has saved Apple hundreds of millions of dollars

“Apple has been granularly and singularly tracking many components in the iPhone for some time, but expanding that to the glass and doing it with a microscopic bar code is another level of obsessive attention to detail that few companies would do,” said Kyle Wiens, CEO of iFixit, a popular Apple gadget repair site. “I’ve never heard of serial numbers on the glass level, but if you’re throwing infinite money at improving your manufacturing knowledge, then why not?”

Apple added the smaller of the two QR codes—0.2 mm in width—to iPhone screens in 2020 so it can track precisely how many usable cover glass units its two Chinese suppliers, Lens Technology and Biel Crystal, are making and how many defective cover glass units they are throwing away during manufacturing. Lens and Biel have previously stymied Apple’s efforts to learn the true rate of defects, which can raise its production costs. Apple has paid millions of dollars to install laser and scanning equipment at Lens and Biel factories to both add the microscopic QR code and scan the cover glass at the end of the production process.

Apple, Lens and Biel didn’t respond to requests for comment.

That subsurface bar code, which comprises a matrix of 625 uniquely positioned dots, is embedded with tiny lasers and scanned with high-definition lenses that magnify its image, according to two people familiar with the matter. It isn’t in the same spot on every iPhone, although it was located just below the speaker receiver hole on the iPhone 12 and somewhere inside the black frame at the bottom edge of the screen in some later models, the people said.

Apple has long kept track of components such as metal parts in its supply chain using tiny printed bar codes to help it identify the source of leaks or trace the cause of defects. But developing the technology for the microscopic bar code was particularly complex. Initially the bar code, which is embedded with lasers inside the glass rather than on its surface, weakened the screen. In drop tests, for example, any crack in the iPhone’s cover glass would often originate from where the subsurface bar code was placed.

To prevent that from occurring, Apple engineers had to make sure the bar code wasn’t etched either too deeply or too shallowly beneath the glass’s surface. The company had to devise new techniques to scan the barcode, which involved pairing special microscope lenses with ring lights.

The work paid off. Before Apple introduced this bar code into iPhones, Lens and Biel had to toss out as many as three out of 10 pieces of iPhone cover glass because of defects, even late into mass production, when they had supposedly worked out manufacturing kinks. Since then, the number of errors has fallen to fewer than one in 10, according to one person with direct knowledge of the matter. Lower defects reduce the overall cost of making the component. Apple has saved hundreds of millions of dollars a year as a result.

The addition of the microscopic barcode highlights the complexities involved in making iPhone screens, which are actually two components—the cover glass and the display—joined together.

Apple contracts with several companies in at least four countries to handle the work. Corning, for example, makes the material used in cover glass in places including South Korea and Taiwan. The U.S. firm then ships the glass in large sheets mainly to Lens and Biel, whose factories in China are responsible for transforming the raw glass into the form-fitting screens that go on top of the iPhone’s displays. The two firms cut, grind, polish and chemically strengthen the glass, and add black ink to its border and hole- and pill-shaped cutouts, where the iPhone's front camera and sensors go. The smaller bar code is added at the beginning of this process to keep suppliers honest about their production levels.

The second, larger bar code on the cover glass tracks the units as they move further down the supply chain. It is added just before shipment of the finished cover glass to places such as Vietnam, where companies including Samsung and LG install it on top of displays they have made for the iPhones. From there, the screen goes back to China, where Foxconn and other vendors add the iPhone’s multiple sensors and front camera behind the screen’s cutouts. Apple relies on the second bar code to determine which supplier—Lens or Biel—is responsible for causing any defects that occur during screen assembly.

Cost of Innovation

Complaints about overheating in Apple’s newest iPhones, the 15 Pro and 15 Pro Max, which have spread across social media this week, are a reminder of the enormous complexities involved in making modern smartphones. Some observers attribute the overheating to the fact that Apple is using titanium—a new material designed to make the phones lighter—rather than steel in the top-tier version of the iPhone 15. The lesson is that every innovation has its drawbacks, something Apple has also found with the iPhone screens, which it regularly redesigns.

Former Apple employees said the brittleness of cover glass means it has one of the highest rates of defects—or lowest yields, in manufacturing parlance—of any iPhone component. When Apple introduced the iPhone X—a model that came with a completely redesigned screen—in 2017, Lens and Biel were initially throwing out one of every two pieces of cover glass they produced because of defects, which had become more noticeable due to the new model’s sharper displays. That meant the two firms were charging Apple more for production, given how expensive it was to make one usable piece.

Although these suppliers have an incentive to overstate the defects they’re encountering to pad their costs, they also don’t want Apple to order more of the cover glass from the other, which it might do if either producer is struggling with low yields. As a result, the manufacturers sometimes fudge the absolute number of glass screens they make. In 2018, for example, Biel overstated how much usable cover glass it produced for Apple, according to a former Biel employee. Apple dispatched two of its own employees to physically count the number of glass screens in a Biel warehouse, only to come up short of Biel’s claims, the employee said.

Apple has since tried other methods to check whether Lens and Biel are accurately reporting their production. At one point, it proposed weighing the raw glass coming in from Corning and others against the final weight of cover glass produced by Lens and Biel, one former Apple employee said. However, representatives from Lens and Biel objected to the practice, saying the grinding and cutting of glass during production produced enough waste to make the comparison meaningless, the former employee said.

Now Apple uses the equipment it installed in Lens and Biel factories to scan every piece of cover glass after it is cut, ground, polished and chemically strengthened. Uploaded and recorded on Apple’s servers, the data allow Apple to identify which company made the glass and on what day it was produced. This helps Apple keep tabs on the Chinese manufacturers’ production levels and yields.

By revealing their true yields, Apple has been able to exert pressure on Lens and Biel to reduce their prices, saving money for the iPhone maker while also cutting down on waste. Apple accounted for 71% of Lens’ $6.4 billion in revenue in 2022, according to Lens’ regulatory filings. (Biel is private and doesn’t disclose its finances)

Apple first added the subsurface bar code to the Apple Watch Series 5 in 2019 as part of a broader effort companywide to reduce costs. Rob York, an Apple vice president of manufacturing design, led the initiative. Early in his career, York worked in the auto industry, which tracks components closely due to the possibility of safety recalls. Adding the code to the Watch was easier because of its smaller display size and thicker glass. Within the next 12 months, Apple added the code to the glass screens of the iPad and MacBook before it made its way to the iPhone, Apple’s most profitable and highest-volume product, two former Apple employees said.