When discussing the repair of smartphone screens, we first need to have a general understanding of the basic structure of the screen. The screen structure of modern smartphones usually includes from the outside to the inside: protective glass (mirror) - touch sensing layer - polarizing film - liquid crystal display - backlight. For Apple's iPhone series, starting from iPhone 5, the structure of the screen has changed, in order: protective glass (mirror) - polarizing film - touch sensing layer - liquid crystal display - backlight. By analyzing the structure of the screen, we can know that most smartphone screen repairs can involve replacing the protective glass, touch sensing layer and backlight. However, for iPhone 5 and later Apple models, because its touch sensing layer is tightly attached to the liquid crystal display and difficult to separate, only the protective glass and backlight can be replaced. If the liquid crystal display (inner screen) is damaged or has problems such as leakage and display abnormality, it is usually impossible to repair it, and the entire screen assembly can only be replaced. Taking the iPhone 6 as an example, we can further explore the details of screen repair. Based on the above information, we know that the repair of the iPhone 6 is limited to the outer screen (protective glass) and backlight. The premise of replacing the external screen is that the touch function and display function (LCD screen) must be intact, otherwise the repair will lose its value. So, when do you need to replace the backlight? If the phone has backlight problems due to water ingress, such as the screen content can still be seen under strong light, the phone can be answered normally, and there are light spots or water stains on the backlight, these problems usually need to be solved by replacing the backlight.