Root causes and solutions for iPhone 3g/3gs HOME key failure

Today, I went to Gu Li to find a sensor senior to have a meal. I did not know how to talk about the iPhone.
The Home Key fails. He said it must not be the sensor life problem in the Home key. It should be a mechanical design defect in the iPhone. It is the Home Key caused by stress strain.
Invalid. When I come back to my own rough calculation, if we use 100 home times a day, the life of any qualified button can be more than 5 years, and the performance can reach 100 years, really shouldn't
Such a wide range of failures may occur. My friend has a 3G iPhone with a home key that is not very clever. I am trying to split it and find out what is going on.

On the left is my normal blacklist, and on the right is my friend's home failed blacklist.

First, disassemble the machine. There are many tutorials on the Internet. First, remove two screws.

Then, a suction cup is used to suck the bottom of the screen and gently extract the whole screen.

When the screen is removed, do not press it too hard. There are three cables above the screen connected to the motherboard. Remove the labels marked as 1 to open the whole screen.

I learned from my brother who worked in the fruit that the three cables correspond to the signal transmission of the upper and lower half areas and the touch, and are not used to control the Home Key. So where is the control of the Home Key?

Zi
Let's take a look. There are still two small shrapnel at the bottom of the screen. After the screen is closed, it will be in contact with the metal pieces at the corresponding position on the motherboard. Is this the home key signal transmission channel? I did a small experiment,
Put my own iPhone
3G disassemble, stick the metal piece with tape, close the lid ...... Home failed. Take a closer look at the strip of the metal piece. There is no solid support below, with a slight indentation and bullet on the screen.
The film has been somewhat distorted-this is likely to be the culprit of Home key failure! (The figure shows the normal small black wire metal, and the broken metal film has obvious deformation)

Use the cone to slightly raise the shrapnel and cover the experiment. The Home Health sensitivity is greatly increased, but it is not perfect yet.

Next we will use my favorite Weller Solder! Use the Solder Pad to slightly point some solder on the two pieces of metal on the wire, so that the conductive part is raised upwards, and the contact with the screen is enhanced. The solder temperature is about F, so it should not be too high or too long. Otherwise, the cable will be burned out.

Today, my work is in bad shape.

Close the lid ...... The Home key came back perfectly!

overall
conclusion: the design of the iPhone 3G
Home Key cable must be a mistake. Pressing the Home key will cause the overall elastic deformation at the bottom of the screen, the stress in the soft contact area between the shrapnel and the strip increases. During long-term use, repeated pressing leads to
sag and plastic deformation, leading to poor contact between the cable and the screen, resulting in Home key failure. I think most home key failures are related to this design. About a few fruit workers in a short time
they may be able to gather together for dinner, so they may be able to get some insider information and update it later.
In addition, The shome key design is consistent with that of 3G, so this method should also be applicable to 3gs.
there is a risk in dismounting the machine, but it is not a good choice. (today is my first time to dismounting the machine. If you have confidence in yourself, go ahead ).