Explained
How a smartphone works.
Inside a smartphone
Open up a modern phone and most of the space is battery. The rest is a carefully layered sandwich. At the front is the cover glass with its touch sensor. Below it is the display, then the frame, which holds the logic board, cameras, speakers and haptic motor. At the back are the wireless charging coil and the back glass. This model is generic and unbranded, but the layout is typical.
The logic board is the phone's computer. To save space, many phones stack two boards on top of each other, with the processor, memory, storage and modems spread across both. The main chip combines the CPU, the graphics processor and dedicated circuits for photos and machine learning on one piece of silicon. Thin flex cables join it to the display, cameras and buttons.
Glass, display and touch
The cover glass gets its strength from chemistry. The finished glass is soaked in a bath of molten potassium salt, and larger potassium ions swap places with smaller sodium ions near the surface. They squeeze into the surface, putting it into compression, so a crack has to overcome that squeeze before it can grow. A grid of transparent electrodes under the glass senses the small change in capacitance when your finger comes close.
Most flagship phones use OLED displays, where each pixel is a tiny light-emitting diode that makes its own light. That is why the blacks look truly black: those pixels are simply off. The display connects to the board through a folded flex cable.
Water resistance, battery and charging
Water resistance comes from seals, not magic. An adhesive gasket bonds the glass to the frame all the way round, the buttons have rubber rings, and the speaker and microphone openings are covered by fine meshes. Ratings like IP68 come from a standard code: the first digit is protection against dust, the second against water. Try the water test in Play mode to see the seals light up.
The battery is a lithium-ion pouch cell, the technology that earned John Goodenough, Stanley Whittingham and Akira Yoshino the 2019 Nobel Prize in Chemistry. Wireless charging works by magnetic induction: a coil in the charger makes a changing magnetic field, and the coil in the phone turns it back into current. That's why the back is glass rather than metal. Open the layers one by one in Play to see the order a repair technician would follow.
Parts glossary
- Cover glass
- Chemically strengthened glass protects the display and carries the touch sensor. Its toughness comes from a squeezed outer layer made by ion exchange. Fun fact: In ion exchange, small sodium ions in the glass are swapped for larger potassium ions, which squeeze the surface into compression.
- OLED display
- In an OLED panel every pixel makes its own light, so black pixels are simply switched off. A thin flex cable connects it to the logic board.
- Seals and gaskets
- An adhesive gasket bonds the glass to the frame, and small rubber rings seal the buttons and ports. These are what stop water getting in. Fun fact: In an IP68 rating, 6 means dust-tight and 8 means protection against continuous immersion in water.
- Frame
- The metal frame is the phone's backbone. Antenna bands are separated by plastic gaps so the radio signals can escape.
- Logic board
- Stacked circuit boards hold the main processor, memory, storage and modems. They fold a computer into the space of a few postage stamps.
- Camera module
- Each camera is a tiny lens stack over an image sensor, with motors for focus and stabilisation.
- Speaker
- A sealed speaker box at the bottom edge pushes sound out of the grille. The earpiece at the top doubles as a second speaker.
- Haptic motor
- A linear motor shakes a small mass back and forth to make crisp taps and buzzes.
- Charging port
- The port carries power and data. Its gasket and coatings keep moisture out of the circuits.
- Battery
- A flat lithium-ion pouch cell takes up most of the inside. Pull-tabs or special adhesive hold it in. Fun fact: The 2019 Nobel Prize in Chemistry went to Goodenough, Whittingham and Yoshino for developing the lithium-ion battery.
- Wireless charging coil
- A flat copper coil picks up energy from a matching coil in the charger by magnetic induction.
- Back glass
- The back is glass, not metal, so the charging field and radio waves can pass straight through it.
