How long after mixing will solder paste fail if it is not used?

Failure management after solder paste mixing is a key quality control aspect. The following is a detailed analysis and summary of failure management after solder paste mixing: 

I. Failure time management

Routine expiration time:

At room temperature (20~25°C), the stirred solder paste is recommended to be used up within 48 hours.

Special solder pastes may have a longer open time, but the specifics need to refer to the technical specifications and data sheets provided by the manufacturer.

Factors affecting the expiry time:

Solder Paste Composition: Lead-free solder pastes may be more susceptible to failure compared to leaded solder pastes because the composition is more sensitive to environmental and storage conditions.

Ambient Temperature: High temperatures accelerate the flux evaporation and oxidation process, resulting in faster paste failure.

Ambient humidity: Excessive humidity can cause solder paste to absorb moisture, affecting soldering performance and paste stability.

Exposure time: The longer the solder paste is exposed to the air, the higher the volatilisation and oxidation of the flux, thus accelerating the failure.

Environmental airflow: solder paste to do in the environment if there is an air outlet above the airflow exchange port, air flow acceleration, flux volatilisation accelerated, affecting the quality of the solder paste.

Failure performance and detection

Flux volatilisation: the solder paste becomes dry, the fluidity deteriorates, the viscosity increases, and it is not easy to spread evenly on the printing plate.

Oxidation: hard lumps or crusts appear on the surface of the paste, and the colour may change.

Deterioration of soldering performance: the wettability becomes poor when soldering, and the solder joints may have problems such as false soldering, grape balls, voids, and weak soldering.

Third, the strategy to extend the service life

Sealed storage: unused solder paste should be immediately sealed and stored to reduce contact with the air to delay the volatilisation and oxidation of the flux.

Low-temperature storage: the solder paste stored in the refrigerator (0 ~ 10 ° C), can significantly extend its service life.However, make sure the solder paste is warmed back to room temperature before use to avoid changes in performance due to temperature differences.

Splitting: Split the paste according to the actual demand, to avoid waste and failure caused by mixing too much at one time.

Disposal of invalid solder paste

No longer use: Once the paste failure performance, should immediately stop using, in order to avoid adverse effects on the welding quality.

Environmental protection: Failed solder paste should be properly disposed of in accordance with local environmental regulations to avoid pollution of the environment.It is recommended to co-operate with professional waste disposal companies to ensure compliant disposal.

V. Summary and Suggestions

Regular inspection: Regularly inspect the storage and use of solder paste to ensure that it is in good condition.

Follow manufacturer's instructions: Strictly follow the technical specifications and data sheets provided by the manufacturer for operation and use to ensure solder paste performance and solder quality.

Train employees: Train employees in the use and storage of solder paste to improve their operational skills and quality awareness.

Record management: Establish a record management system for the use and storage of solder paste in order to track and monitor the status and use of solder paste.

By implementing these failure management measures, it is possible to ensure that solder paste is fully utilised within its stirred expiry date, while avoiding adverse effects on solder quality and the environment.