The HUAWEI Mate 20 Pro is a powerful device, but improper charging habits or environmental factors can lead to serious hardware issues. In this case, the phone was charged overnight and placed under a pillow, only to fail to boot the next morning. A fixed current reading during testing suggests that the CPU’s connection to the PCB may be compromised. Thankfully, this is a repairable issue.
Devices Details
Model: HUAWEI Mate 20 Pro
Announced: 2018, October 16
This guide will show technicians and DIYers how to tackle poor CPU soldering—an increasingly common issue in Android phones, especially with high-performance chips like the Kirin 980 in the Mate 20 Pro.
Defect Phenomenon
After charging the phone overnight, the device won’t boot. Connecting it to a charging multimeter reveals a 0mA current, confirming that the phone is not charging.
Troubleshooting Steps
1: Disassemble the Phone
- Begin by carefully disassembling the phone. Protect the camera lenses with stickers, and remove the motherboard.
2: Test Boot Current
Connect the motherboard to a DC power supply and attempt to trigger the boot process. The current is fixed at 97mA, indicating the phone cannot boot. Based on repair experience, this can be caused by:
- CPU overheating, leading to poor soldering between the CPU and the PCB.
- A broken inner PCB rail, disrupting the connection between the CPU and related circuits.
Since the phone has no signs of water damage or physical drops, the most likely cause is CPU poor soldering.
How to Repair Huawei Mate 20 Pro Won’t Turn On
1: Remove the CPU
- First, remove the shielding cover to access the Kirin 980 CPU.
- The Kirin 980 is prone to poor soldering, so we need to rework it. Start by removing the glue surrounding the CPU chip using a hot air gun set to 290°C. Be cautious not to overheat any specific area.
2: Disassemble the CPU Layers
The CPU is composed of two layers: the upper RAM layer and the lower core CPU layer.
- Remove the upper RAM layer first.
- Next, slightly heat the lower CPU layer until the solder melts, and carefully pry it up from the PCB.
3: Inspect the PCB Pads
- After removing the CPU, inspect the PCB. Some pads may have turned black due to corrosion, leading to poor connections.
4: Clean and Reball the CPU
- Clean the PCB pads using solder paste flux, a hot air gun, and a soldering iron. Use solder wick to remove excess solder and ensure the pads are flat.
- Carefully remove the hard black glue from the PCB, especially around the corners, under a microscope. Ensure the pads are spotless and flat to ensure proper CPU re-soldering.
5: Reball the CPU Chips
- Reball the CPU’s upper and lower layers using a stencil. Be patient, as this process requires precision.
6: Resolder the CPU
- Align the lower CPU layer with the cleaned PCB and reflow the solder using the hot air gun. Heat the board evenly until the solder melts, allowing the CPU to seat itself onto the PCB.
- Afterward, resolder the upper RAM layer using a similar method.
7: Reassemble and Test
- Reassemble the phone and test it. The phone should now boot normally, and charging, along with other functions, should work perfectly.
Conclusion
CPU poor soldering is a frequent issue in Android devices, and the Kirin 980 in the HUAWEI Mate 20 Pro is no exception. By carefully removing, cleaning, and resoldering the CPU, Huawei Mate 20 Pro boot issue can be successfully resolved. Proper handling and repair skills, especially in CPU rework, can fix up to 90% of boot issues caused by soldering problems.
Tips for Prevention
To avoid future soldering issues caused by overheating or improper charging:
1: Adopt Better Charging Habits
- Avoid using the phone while it’s charging.
- Use a certified charger and USB cable.
- Charge the phone in a well-ventilated, cool area.
- Try to keep the battery between 30% and 90% rather than allowing it to drop to 0% or charge fully to 100%.
2: Avoid Overnight Charging
- Charging the phone overnight, especially under a pillow or in hot environments, can contribute to CPU overheating, which may weaken solder joints.
By following this step-by-step guide, you can resolve most HUAWEI Mate 20 Pro boot issues caused by poor CPU soldering. This comprehensive solution can help you avoid unnecessary motherboard replacements, saving both time and money. If you have any questions or need further assistance, feel free to leave a comment below!
English 
Español 
Français 
Deutsch 
Italiano