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Snapdragon 888 is one of the most popular processers in recent years. However, from phones under the rule of Snapdragon 888, there has been so much criticism on the overheating problem. The Xiaomi Mi 11 is one of the first devices powered by a Snapdragon 888 processor. Today we will share how to fix common problems of Snapdragon 888 with a Mi 11 repair case.
Press the power button and the phone won’t turn on. Plug in the power cable and the phone is still dead.
The next step is to take out the motherboard for further testing. Place the phone back down on the heating pad at 90 °C for 2 minutes. Insert a plastic card and slide it through. Apply some alcohol to facilitate separation.
As the back cover is separated, remove the camera and motherboard shielding covers.
Disconnect the flex cables and then remove the motherboard. Detach the back camera module.
Hook the motherboard to a direct current supply and prompt a boot-up with tweezers. The boot current jumps between around 100 mA and 200 mA.
According to the current jump and our experience, devices powered by Snapdragon 888 tend to have problems like no power, no wifi, no sound, etc. due to the pseudo soldering of the CPU. The general repair solution is to reball the CPU.
In order to remove the CPU, we need to cut a gap first. Remove adhesive with a hot air gun at 300 °C and airflow 80.
Then heat the RAM with a hot air gun at 380 °C and airflow at 120. While heating, try to pry up the RAM with a pry blade. You can remove the RAM once it becomes loose.
Keep heating to remove the CPU. Then we apply some middle-temperature solder paste to the bonding pads. Neutralize the temperature of the bonding pads with soldering iron at 380 °C.
Clean tin on the bonding pads with solder wick. Remove underfill adhesive with a hot air gun at 300 °C. Clean the bonding pads with PCB cleaner.
Use the same method to clean tin and adhesive on the CPU. During cleaning, some capacitors will be erased. Please note that these are filter capacitors and do not influence the use of the phone.
Clean tin and adhesive on the RAM with desoldering braid. Remove residual adhesive with a hot air gun at 300 °C.
Reball the CPU. Apply some middle-temperature solder paste. Heat with a hot air gun to form the solder balls. Then recall the RAM.
The next step is to solder the CPU. Apply some paste flux. Align the CPU. Solder the CPU with a hot air gun at 350 °C and airflow at 100. Touch the CPU gently with tweezers. If the CPU returns to position, the CPU is soldered well.
Then we solder the RAM. Clean with PCB cleaner. After the motherboard cools, connect the motherboard with the direct current supply and trigger the boot-up with tweezers. The current jump becomes normal.
Then we put back the camera module to the motherboard. Apply thermal paste to the CPU. Install the motherboard. The phone turns on and other functions work well.
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