How does a home button break?
There are two main causes for a home button to stop working.
1) physical damage
Home buttons that suffer physical damage can stop working properly, for example cracked surface, torn flex cable etc.
2) water damage
There are electronic circuits on back of a home button. If electronic components are damaged by liquid/water, circuits can malfunction.
3) other causes
Connection between home button and screen
All accessories of a phone are connected to the motherboard directly or indirectly. For iPhone 7 / 7 Plus / 8 / 8 Plus, a home button is connected to motherboard with the bridge of the screen. If flex cables connection the screen and the motherboard is broken, the home button can also malfunction.
Home button repaired by replacing the screen
We have received an iPhone 7 which had a home button problem. The home button was said to be replaced 4 months ago in town and stopped working recently.
To repair a home button, the screen must be removed first and then a diagnose to it. After the screen was removed, we were surprised to see that the bracket to secure the home button was missing. We also found a lot of screws missing, which were used to hold brackets to secure covers for battery socket and front camera socket. What a irresponsible repair!
To figure out where the problem was, we replaced the home button but it turned out no good. But the new home button was a proven good one. Then we replaced the new screen as well, it worked alright. So the flex cable which bridges the home button to motherboard must be broken, it still displays and touches well though.
Irresponsible repair could be a nightmare
We continue to check the phone under microscope and shocked to find one component knocked off the motherboard as shown below. Fortunately it’s not an essential one. Image below shows two sockets, with the left one for display and the right one for touch and home button. The previous technician must have accidentally knocked the capacitor off.