What solder paste is used for chip tin removal?

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For removing solder from chips and rework, ordinary solder paste is generally not used; prefer low-melting-point rework paste, or a solder wick plus solder paste flux. For BGA and QFN chips, medium-temperature SAC305 fine-powder paste can be used: heat it on a rework station to melt the old solder, then clean it off with a solder wick. For repeated rework or heat-sensitive chips, use low-temperature bismuth-based paste with a 138℃ melting point to reduce thermal damage. Always use paste flux when desoldering to improve wetting so the old solder gathers and cleans more easily. Do not apply high heat for long periods, to avoid damaging the chip and PCB.

In chip desoldering operations, selecting the appropriate Solder Paste directly affects the reliability of subsequent soldering. Using solder paste with high activity and low residue characteristics can significantly improve solder joint quality, while avoiding cold solder joints or short circuits caused by insufficient solder paste performance. The particle size, viscosity, and Flux composition of the solder paste must all be matched to specific process requirements.

In practical operations, if poor fluidity or caking of the solder paste is found, immediately check whether improper storage conditions or expiration are the cause, and simultaneously verify whether the solder paste has been opened beyond the recommended usage period. These factors all affect its soldering performance, and the use of solder paste must strictly follow the operating specifications provided by the manufacturer.

For the desoldering process of precision chips, it is recommended to use fine-particle solder paste to improve printing accuracy, while controlling printing pressure and squeegee angle to avoid poor soldering caused by uneven solder paste distribution. The solder paste also requires sufficient reflow time to ensure it reaches its optimal state during use.

When performing desoldering operations in high-temperature environments, the thermal stability of the solder paste is particularly critical. If oxidation or discoloration occurs after the solder paste is heated, it indicates potential quality issues and it should be replaced promptly. The storage environment for solder paste should be kept dry and at an appropriate temperature to prevent environmental factors from affecting its performance.

For different types of chips and substrate materials, the selection of solder paste must consider its thermal expansion coefficient and surface treatment process to avoid stress cracking after soldering caused by material incompatibility. The melting point and alloy composition of the solder paste must also match the target soldering temperature to ensure stability during the soldering process.

In mass production, the use of solder paste requires the establishment of a strict management process, including opening records, usage time monitoring, and remaining quantity statistics. This helps reduce waste and ensure product quality. Regular performance testing of solder paste, such as wettability tests and viscosity inspections, can also identify potential issues in a timely manner.

For chips with complex structures, the application method and thickness control of solder paste are particularly important. Excessive thickness may cause overflow or bridging, while insufficient thickness will affect Solder Joint Strength. The printing parameters of the solder paste need to be adjusted according to the actual process to ensure it can evenly cover the pads during the soldering process.

In daily maintenance, the cleaning of solder paste and equipment maintenance cannot be ignored. The stencil and squeegee of the printing machine need to be cleaned regularly to prevent residues from affecting the uniformity of the solder paste. The use of solder paste must also be combined with specific soldering equipment and process parameters to achieve the best results.