The WHY and HOW to repair the Wifi and Bluetooth issue with iPhone 4S
*** forum admin deleted this post when i first posted it. I assure you all this is the proper solution. I repair hundreds of iphones. This is information that iphone 4S users need so don't delete it please ***
The problem is a hardware issue, NOT software.
The reason your wifi goes from working in one version of iOS to failing after an update is because the new iOS version checks the wifi chips functionality before allowing the OS to use it. If it doesn't pass ALL tests, it will not allow wifi to switch on in iOS. The older version of iOS will simply not check the wifi chip for faults and just go ahead and use it.
The problem is the solder joints connecting the Wifi IC to the circuit board fracturing *some* pins. But it often has enough connected pins to allow iOS to operate it without passing all tests. It just won't work with iOS7 which will reject it if any diagnostic pins are not connected or fractured.
Why does it fracture? well, this is a common problem with BGA mounted ICs on a lot of electronics since the banning of lead content solder. The non-leaded solder is more prone to fractures under heat. So we have gone "greener" but sacrificed reliability in the process.
How do we fix this without reballing it with LEADed solder?
REFLOW the Wifi IC
the best way is to use an infrared rework station, but that is uber expensive and out of reach for most people.
An alternative is to use a hot air reflow. While it will do the job, I feel it is not actually the best way as it uses more heat than is necessary and is prone to damaging surrounding components and warping.
The best practical method available to the average person is to reflow it in an oven.
I use a small electric toaster oven, which I use to reflow laptop motherboards, PS3s, graphics cards, DRAM modules, phone and tablet boards and so on.
remove the 4S motherboard and wrap it in Aluminium foil leaving only the wifi chip exposed. Remove the black sticker shield on the wifi chip. The Wifi chip is the large square IC near the headphone socket.
Put the wrapped motherboard in the oven and, HERE IS THE SECRET SAUCE, put a small strand of solder about 5mm long and bend it into a 3D roundish S-shape. This is your temperature guage! Put it on the insulated foil near the area to be reflowed.
The biggest problem with reflowing is getting the temperature and timing right and using a piece of solder as an indicator gets the best results.
the Solder will melt at around 220deg C so set the oven to around 230-240.
after 5 to 10 minutes depending on the power of the oven, you will see the solder slowly melt and fuse into a ball.
start a stopwatch when it turns into a ball blob and give it 60 seconds and turn the oven off and open the door.
this allows the right temperature range to hit the spot to reflow the solder joints without overheating anything.
everything on the motherboard can withstand this temperature range because all of it had to be mounted at manufacture with AT LEAST this temperature.
DO NOT MOVE THE ITEM WHEN IT'S HOT
allow it to cool down to room temperature.
after it has cooled, unwrap it and put it back into the 4S.
Wifi and Bluetooth will now work without resetting anything or restoring.
There is no magic special way around it, the Wifi Chip needs to be reflowed. It is not a software problem.
And it will work after the next iOS update or restore unlike the blowdryer method which is just a temporary workaround to bypass the IC testing. With regards to freezing,all it does is contract the unfractured pins and try to pull the fractured pins together to temporarily press the fracture together. Freezing can fracture more joints than it can repair so it should be avoided unless it is the only method available. You want to repair it for use at room temperature, not for use in the antarctic.
If this is useful, I can start a new thread and write up a proper step by step with pictures.
