[Hardware Hacking General] AnArChYm:
Hi,

If the imei is available (null), it could be the case that it needs repairing rather than actually chaging the eMMC chip , however you'll need a special tool to do this, which honestly do not know which exactly is as I'm more into hardware repairs rather than software.

Another possible issue could be that the phone can also have corrosion around critical components, ie around the main baseband supply, which is stopping from the baseband switch on, thus no signal or any radio communication from starting up. It would be best to have a microscope and inspect each part of the board for bad components, rather than rushing to the eMMC replacement.

It's very important to read this post very carefully and understand it as it is not easy to be done, but it is very much possible. And find a lot of youtube videos before even trying so you'll be more familiar with the process and different techniques.

Anyways for the most interesting part :)

Basically the eMMC chip is a 14 by 14 bga, ball grid array chip which is fairly easy to reball comapred to other complex ones, like baseband processor or the main application processor, You'll also be needing a reballing stencil to put the balls on top of the solder pins, and solder paste to paste the solder onto the holes and a hot air gun to melt that solder into balls. (Basically the solder paste will melt between those holes inside the stencil and will form nice silverish balls.

The chip also has got a lot of not connected pads (aka dummy pads) so do not worry when removing the chip as you'll be more then likely to lift pads from the board especially if this your first reball job.

First of all, you'll need to clean the surrounding glue around the chip by using around 200C and with a needle scrape off the glue, be very gentle not to scrape any tracks or board layers.

Then to remove the chip from the board use around 350C (always ramping up the temp), very important to use kapton tape around the surroundings to reduce heat stress. Personally I use the following temperatures: (do not use any nozzle with the heat gun as the chip is large and you need the heat to dispersed all over the chip)

1st min 180C full air

2nd min 280C full air

4th min 350C full air until the surrounding components turn silverish and are easy to lift, at that time get a very sharp needle and gently (very gently) start to pry up with ease the chip from one side, until it is fully lifted.

Then you'll need to clean the board, basically put flux and with a fine tip soldering iron clean the pads gently until all underfilled glue is no more remaining and the pads are nice and shiny and set the board aside.

If you'll buy a new eMMC chip most probably you'll have it reballed from the supplier. If not pre reballed, you ll need to reball it using a reballing stencil and solder paste.

Finally align back the eMMC chip over the board in the correct way, always note where is pin A1 and solder it back by ramping up heat again, same process as removing the chip.

The last process is all based on software, basically you'll have to copy the bootloader from a good working S3 phone to this one, as the new eMMC chip is empty of data, and obviously without the bootloader so the phone wouldn't be able to switch on.There is a process somewhere on the net how this is exactly done.

Ryan