Five Major Principles and Requirements for Solder Paste Control

A

Five key control principles for solder paste: 1. Storage control—refrigerate at 2~8℃ sealed, use first-in-first-out, and record times; 2. Warm-up control—let it return to room temperature while sealed, and never open early, to prevent moisture uptake; 3. Stirring control—stir thoroughly before use to restore even viscosity and avoid trapped bubbles; 4. Opening control—record the opening time, discard overdue material, and strictly limit workshop exposure; 5. Use control—hold workshop temperature and humidity, place and reflow promptly after printing, seal leftover paste, and discard any abnormal paste. Keep full traceability throughout to avoid batch soldering defects.

The core of Solder Paste control lies in full-process management from source to end. First, the storage conditions of solder paste must be clearly defined, such as temperature control at 4-10 degrees Celsius, avoiding direct sunlight, and paying attention to the shelf life. Expired solder paste is strictly prohibited from being used, otherwise it will lead to a decrease in Solder Joint Strength and affect product reliability.

During the unsealing and use of solder paste, the first-in-first-out principle must be strictly followed. After unsealing, the time should be recorded and used as soon as possible. If exposed to air for a long time, the Flux will volatilize, resulting in poor fluidity of the solder paste, and prone to cold solder joints or bridging, which is particularly critical in high-density PCB production.

In the printing process, the angle, pressure and speed of the squeegee need to be adjusted according to the stencil design. An excessively small angle will lead to insufficient solder paste filling, while excessive pressure may cause solder paste overflow, affecting subsequent placement accuracy. At the same time, it is necessary to regularly check whether the stencil holes are blocked to prevent the solder paste from being unable to be released evenly.

In the inspection stage, it is not enough to rely solely on visual inspection, but also should be combined with X-ray inspection and AOI equipment. Especially for fine-pitch components, insufficient solder paste amount or uneven distribution is often difficult to identify with the naked eye, while X-ray can clearly show the internal structure of solder joints, so as to detect potential defects in time.

Finally, the recycling and reuse of solder paste must follow specifications. The remaining solder paste should be sealed and stored to avoid contamination, but solder paste of different batches cannot be mixed at will, otherwise it may lead to chemical component imbalance and affect the soldering effect. At the same time, a complete solder paste usage ledger should be established to facilitate traceability and problem analysis.