A Brief Discussion on Sedimentation, Stratification, and Oil Separation in Solder Paste

Solder paste sedimentation typically refers to the separation of components and oil separation that occurs during storage:

Separation of Solder Paste Components and Remedial Measures

Separation of solder paste components is commonly observed in cases of improper storage or use, with organic resins being one of the primary contributors to this phenomenon. Organic resins provide binding strength and shape retention in solder paste, but their stability can be affected by environmental factors such as temperature and humidity. When the properties of organic resins change, they may lose their ability to uniformly disperse other components, leading to separation. Additionally, factors such as unstable properties of fillers or additives, changes in component solubility with temperature, and temperature fluctuations during preparation or use may also trigger separation.

Steps for Handling Separation:

Preliminary Mixing: Upon discovering separation, manually stir for 5 minutes to perform preliminary mixing.

Mechanical Stirring: Then use a mechanical mixer to stir at low speed for 10 minutes until no liquid flows when the container is inverted.

Assessment and Action: If stratification is severe (flux layer thickness > 5 mm), discard the paste to prevent compromising soldering quality.

Preventive Measures:

Select stable organic resins: When preparing solder paste, choose organic resins that are reliable and stable.

Ensure thorough mixing: During preparation, ensure all components are thoroughly and uniformly mixed.

Strictly control temperature and humidity: Strictly control temperature and humidity conditions during preparation and use.

Standardize the warming-up procedure: After removing the solder paste from the refrigerator, keep the can upright and let it stand at room temperature for 4–6 hours until the temperature difference is <2°C to prevent metal powder sedimentation caused by horizontal placement.

Avoid repeated freeze-thaw cycles: Use the solder paste within 24 hours of thawing to avoid repeated freeze-thaw cycles.