How to Handle Hardened Solder Paste

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When solder paste hardens or dries out, the flux solvent has evaporated and the paste has aged. For slight hardening, seal it back and extend stirring time per the procedures; some of it can recover softness—check the viscosity and test in a small batch, and confirm printing and reflow are normal before use. Severe hardening, clumping, an off odor, or separation means the paste has degraded and must not be used—discard it. Do not thin it on your own with alcohol or rosin water, as this destroys the flux system and causes cold joints, voiding, and corrosion. Hardening is mostly caused by overdue open time, high workshop temperature, or poor storage, so tighten controls to keep the paste from drying out and being scrapped.

Solder Paste hardening is a common problem in SMT production, usually caused by improper storage or prolonged disuse. In such cases, you should first confirm whether the solder paste has passed its shelf life, and check whether the storage environment meets the standard temperature and humidity requirements. If the solder paste has already clumped or hardened, avoid using it directly; instead, soften it through appropriate methods.

In practice, you can first try taking the solder paste out of its container and letting it stand at room temperature for a period of time to allow it to naturally return to a suitable state. However, note that this method is only applicable to slightly hardened solder paste; its effect is limited if the hardening is severe. In such cases, you should consider replacing it with a new batch of solder paste to avoid subsequent product failures caused by poor soldering.

For hardened solder paste that must be used, a dedicated solder paste softener can be used for treatment, but you must strictly follow the instructions in the product manual to prevent improper use from affecting the solder joint performance of the solder paste. Also, keep the work area clean during the softening process to avoid impurities mixing in and affecting soldering quality.

The printing parameters of the solder paste also need to be adjusted, such as the squeegee angle, pressure, and the gap between the stencil and the PCB, as these factors all affect the fluidity of the solder paste. Therefore, when handling hardened solder paste, you should optimize the printing process based on actual conditions to ensure good printing results.

In daily management, it is recommended to establish a comprehensive solder paste management system, regularly check the status of solder paste in inventory, and use it according to the first-in-first-out principle. This can effectively reduce hardening problems caused by improper storage and improve overall production efficiency.

Regarding the treatment of solder paste hardening, it should also be noted that different brands and types of solder paste may have different handling methods. Therefore, in practical applications, priority should be given to referring to the supplier's technical documentation, and technical support can be contacted for professional advice if necessary to ensure the safety and effectiveness of the treatment process.