When Solder Paste is stored in its original sealed packaging in a dedicated refrigerated refrigerator without the lid opened, its nominal shelf life is 6 months. However, this value is valid only under the preconditions that the temperature control accuracy of the refrigerator is stably maintained between 0°C and 10°C, there is no frost inside the cabinet, and there are no sudden temperature fluctuations caused by frequent door opening and closing. Once a single power outage exceeds 15 minutes or the door seal ages and leaks cold air, the actual shelf life of the solder paste may be shortened to within 3 months, and this effect is particularly significant for lead-free solder pastes containing low-melting-point alloy components.

Opened solder paste must be immediately affixed with a label containing a timestamp, and used throughout on a constant-temperature workbench (22°C ± 2°C), with timing starting from the first opening. If the ambient humidity is higher than 60%RH and nitrogen protection is not enabled, it must be scrapped within 12 hours. Even if it still appears as a uniform paste visually, it must not be used further, because the active components of the Flux have already begun irreversible attenuation. At this stage, problems such as poor demolding, aggravated stencil clogging, and abnormally increased wetting angle after reflow are likely to occur after printing.

Our production line once put refrigerated solder paste that had been opened for 4 hours back into the refrigerator for secondary refrigeration, which led to dense solder beads on three consecutive boards during printing the next day. The root cause was that moisture condensed on the surface of the solder paste and mixed into the interior of the paste, which instantly vaporized during the reflow stage and formed micro-explosions. Therefore, refrigerated solder paste is strictly prohibited from being refrigerated a second time. Once opened, it enters one-way time limit control. Even if there is sufficient remaining amount, it must be used up on the same day or disposed of according to hazardous waste procedures.

Solder pastes from different brands vary greatly in their sensitivity to condensation. For example, the refrigerated solder paste of a certain Japanese manufacturer can still recover good rheological properties after standing at 8°C for 72 hours, while a certain domestic model shows obvious delamination after only one exposure to 25°C followed by returning to cold storage. Therefore, during procurement, the "Low-Temperature Cycle Stability Test Report" for the batch must be requested, rather than relying solely on the theoretical shelf life data on the instruction manual.

Solder paste stored in the refrigerator must be kept away from the evaporator air outlet and the condensation area on the cabinet wall. It is recommended to use dedicated Solder Paste Storage boxes with sealed silicone rings for compartmentalized placement, with each box holding no more than 200g, which both prevents cross-contamination and facilitates quick access. If yellowing on the solder paste surface, increased stringing length, or decreased thixotropy is found, it must be immediately discontinued regardless of whether it has reached the expiration date. Such phenomena often indicate that partial oxidation or hydrolysis reactions have occurred in the organic carrier.