Make sure to try these methods before using this guide:
1. Reset Network settings
2. Restart iPhone
3. Restore iPhone to factory settings
4. Go to Settings, Date and Time, change date and time to manual, and restart iPhone
5. Disconnect and reconnect the battery
If these procedures fail, proceed to the next section.
To make this guide, I tried to repair a common problem with the iPhone 4S. After using the freezer method and hairdryer method, the WiFi began working for briefly. I disassembled my iPhone, removed mother board, and used aluminium foil to protect it. I left only the WiFi chip unprotected. I used a heat-gun at 300 degrees to heat up the chip for 5 to 10 seconds and left it to cool down. I reassembled the iPhone and voila, it works.
Insert wisdom here.