In Apple's introduction to iPhone 11, their web page promotes their new strengthen glass by stating: "Creating tougher glass isn’t rocket science. It’s molecular science. The toughest glass in any smartphone, front and back." Apple highlighted that it used a Dual ion-exchange process.

Today the US Patent & Trademark Office published a patent application from Apple that relates to asymmetric chemical strengthening of a glass article. More particularly, the present invention relates to patterned asymmetric chemical strengthening having an increased depth of compression over at least one localized region.

Apple points to a dual ion process beginning in their patent claims by noting: "forming the first compressive stress region comprises: immersing the cover sheet into a first bath comprising sodium ions; and subsequent to immersing the cover sheet in the first bath, immersing the cover sheet in a second bath comprising potassium ions.

This is followed by: "The first bath includes a sodium concentration of greater than 30% mol; and the second bath includes a potassium concentration of greater than 30% mol.

Technically Speaking

Digging down and cutting to the chase, the heart of the patent, Apple's' patent FIG. 3 illustrates one embodiment for strengthening a glass article #300. A glass article #302 in need of glass strengthening is immersed in a first bath 304 that contains a sodium solution 306 comprising sodium ions.

The enhanced strengthened glass article is then removed from the first bath #304 and immersed in a second bath 308 that contains a potassium solution #310 comprising potassium ions. A glass article treated using this method of strengthening would have little or no warpage and have little or no control over the direction of impact initiated crack propagation.

The level of glass article enhancement is generally controlled by the type of glass (glass articles can, for example, be alumina silicate glass or soda lime glass, and the like); the sodium ion or sodium salt concentration of the bath (e.g., sodium nitrate, typically 30%-100% mol); the time the glass article spends in the bath (typically 4-8 hours); and temperature of the bath (350.degree. C.-450.degree. C.).

Strengthening of the glass article in the second bath is controlled by the type of glass, the potassium ion concentration, the time the glass spends in the solution, and the temperature of the solution. Here, the potassium ion or potassium salt concentration (e.g., potassium nitrate) is in the range of 30-100% mol, but the glass article would remain in the bath for about 6-20 hours at a bath temperature of between about 300.degree. C.-500.degree. C.

Generally, chemical strengthening processes rely upon ion exchange. In each solution or bath, the ions therein are heated to facilitate ion exchange with the glass article. During a typical ion exchange, a diffusion exchange occurs between the glass article and the ion baths. For example, sodium ions in the sodium solution #306 of the first bath may provide an exchange enhancement process. In particular, the sodium ions may diffuse into the surface of the exposed glass, allowing a build-up of sodium ions in the surface of the glass.

In embodiments, the sodium ions replace other ions found in a silicate (e.g., aluminosilicate) or soda lime glass. In embodiments, sodium ions may exchange for smaller lithium ions in the glass. The ion exchange during immersion in the first bath may take place at a first temperature below a glass transition temperature of the glass.

Upon immersion of the enhanced glass article into the potassium solution of the second bath, the sodium ions of the enhanced glass article are replaced by potassium ions in surface areas to a greater extent than sodium ions found more toward the interior or middle of the glass article. The ion exchange during immersion in the second bath may take place at a second temperature below the glass transition temperature of the glass. After exchange of sodium ions in the glass for potassium ions, a compression layer is formed near the surface of the glass article (for example, the larger potassium ions take up more space than the exchanged smaller sodium ions). The sodium ions that have been displaced from the surface of the glass article become part of the potassium bath ion solution.

Touch ID for Future iPhone Highlighted

In Apple's patent figure 1A below, Apple interestingly illustrates a future iPhone with an optical sensor that is covered by a face glass that will act as the next-generation of Touch ID under the display.

The patent filing reveals that "A transparent window region may extend over a display component, a camera, an optical sensor, or another optical or visual device #120. The feature of #120 is represented by a virtual outline of a Touch ID system.

The positioning of the ID area is not officially limited to being a virtual circle. It's just an indication of a touch ID system in general that could be placed anywhere under the display.

Apple's patent application 20200017406 that was published today by the U.S. Patent Office was filed back in Q1 2019. As far as the dual ion process on glass is concerned, this is now a patent fulfilled.