Which solder paste is used for CPU reballing on Honor X10?

A

Reballing the CPU of a Honor X10 is a phone-rework job; prefer 5# fine-powder, medium-temperature SAC305 paste with a 217℃ melting point, which prints well and gives reliable joints, with a rework-station peak around 240℃. If the board has been reworked many times or you are concerned about overheating the CPU, use low-temperature bismuth-based paste with a 138℃ melting point and a 160~180℃ peak to reduce thermal damage to the CPU and board, though low-temperature paste joints are weaker than medium-temperature ones. Use paste flux during reballing to keep the spheres even, and ramp the rework station slowly to avoid cold joints and CPU damage.

In the CPU reballing process of Honor X10, the selection of Solder Paste directly affects the soldering effect. In actual operation, the specific model must be determined in combination with Reflow Soldering equipment parameters, pad size and component characteristics, to avoid insufficient solder joints or cold solder joints caused by poor fluidity of the solder paste.

On the production site, we usually give priority to solder paste with high thermal conductivity and low residue characteristics. Such products can effectively reduce the difficulty of cleaning after soldering, while ensuring the mechanical strength of solder joints and the reliability of electrical connection, but small batch trial soldering verification is required in advance.

The viscosity index of solder paste is an important reference basis. Excessively high viscosity will lead to broken lines or bridging problems during printing, while excessively low viscosity will easily cause solder paste collapse, which will affect the melting uniformity of subsequent reflow soldering. Therefore, it must be adjusted according to the usage range recommended by the manufacturer.

In practical applications, it is found that some batches of solder paste are prone to form oxide layers in high-temperature environments, which will significantly reduce the wettability, and further lead to burrs or voids at the edges of solder joints. At this time, it is necessary to immediately replace with qualified batches and check whether the storage environment meets the standards.

For precision soldering scenarios such as CPU reballing, it is recommended to use solder paste with low silver content to reduce the impact of thermal stress on the chip, while controlling the particle size of the solder paste between 35-75 microns to ensure printing accuracy and solder joint quality after melting. However, it must be noted that differences in activator content of different brands of solder paste may lead to increased residues after soldering.

In daily maintenance, the opening time and service life of solder paste need to be strictly controlled. Solder paste that has not been used for more than 24 hours should be re-evaluated for its applicability. Especially when the ambient temperature and humidity fluctuate greatly, the service time limit should be shortened to prevent performance degradation, otherwise it may cause batch soldering defects.

Finally, the storage conditions of solder paste cannot be ignored. It must be placed in a cool and dry place, avoiding direct sunlight and high-temperature environments, otherwise it will lead to the decomposition of Flux components, which will further affect the wettability during soldering and the integrity of solder joints. These details need to be monitored emphatically in production line management.