How to Handle Solder Paste Thinning

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Watering-out or separation of paste means the powder and flux system have split and the rheology has broken down. For mild watering-out, reseal, stir per procedure, and check viscosity; if homogeneity returns, run a small-batch test. Severe watering-out — remaining separated after stirring, with off-odor or caking — means the paste has degraded: discard it. Watering-out usually comes from excessive storage temperature, overlong shelf life, or repeated thermal cycling. Do not force-dilute with solvent; it destroys the flux system and causes soldering defects.

The occurrence of liquefaction in Solder Paste during use is usually closely related to storage conditions and ambient humidity. Especially in high-humidity environments, the Flux components in solder paste easily absorb moisture from the air, leading to a decrease in viscosity or even stratification.

After discovering liquefaction, first check whether the solder paste has passed its shelf life, and simultaneously inspect whether the seal remains intact after opening. If it has been stored for too long or the packaging is damaged, stop using it immediately and replace it with a new batch.

In practical operations, measures such as reducing workshop humidity, adding dehumidification equipment, and controlling the usage time of opened solder paste can be taken to prevent performance changes caused by moisture absorption.

For solder paste that has already liquefied, physical separation can be performed using a centrifuge, but this method is only applicable to mild liquefaction cases. If severe stratification or abnormal fluidity occurs, it is recommended to directly scrap the material.

In the printing process, appropriately adjusting the squeegee pressure and angle, and reducing the residence time of solder paste on the stencil, can also effectively mitigate the impact of liquefaction on printing quality. Meanwhile, it is necessary to ensure that the Reflow Soldering process is carried out promptly after printing to prevent the solder paste from being exposed to air for extended periods.

The core of solder paste liquefaction treatment lies in prevention. Strict control must be exercised at every stage from procurement to use, especially in warehouse management and the operational standards of personnel. Only by getting these details right can the adverse effects caused by solder paste liquefaction be fundamentally reduced.

For production lines that frequently experience liquefaction issues, it is recommended to communicate with suppliers to understand the formulation characteristics of the solder paste. If necessary, try switching to a more stable product model to adapt to the current production environment.

Solder paste liquefaction treatment requires a combination of environmental control, process optimization, and material management to truly achieve efficient SMT production.