We found that when the relative humidity in the workshop exceeds 60% for two consecutive hours, an unseaLED Solder Paste will develop a micro-condensed water film on its surface within 15 minutes. If the Solder Paste after temperature recovery is exposed to air for more than 30 minutes, its viscosity can decrease by up to 18%, directly causing the printing offset rate to rise to 7.3%. Therefore, humidity sensors must be embedded in three key locations: inside the solder paste temporary storage cabinet, at the outlet of the temperature recovery zone, and next to the stencil printer material rack, and an automatic linkage response mechanism for the dehumidification unit must be triggered when limits are exceeded.

Solder paste protection is not a problem that can be solved simply by tightening the lid. In our production line tests, we found that after 4 hours in an 85%RH environment, the internal cavity humidity of a standard PE sealing lid still reached 72%. After switching to a dedicated container with a double silicone ring and vacuum-assisted locking structure, the internal cavity humidity could be reduced to 41% under the same conditions. Therefore, all solder paste opening operations must be completed in a nitrogen atmosphere glove box, and 0.03MPa of nitrogen must be filled immediately after each use, with pressure maintained to detect a leak rate below 0.1kPa/min.

The most typical printing defects of moisture-absorbed solder paste are edge stringing and pad voids, which are often not caused by the quality of the solder paste itself, but by uncontrolled temperature recovery. We require that all solder paste taken out of the cold storage must be placed in a 25±1℃ constant temperature room for more than 120 minutes, flipped every 15 minutes to balance the internal and external temperature difference. It is strictly forbidden to use an oven or warm air to accelerate temperature recovery, otherwise the active components of the Flux will decompose in advance, causing the solder wetting angle to increase to more than 32°.

Printing parameters must be dynamically adjusted according to ambient humidity. When the humidity rises from 50% to 65%, the squeegee pressure must be synchronously increased by 0.8N/mm2, the printing speed reduced by 12mm/s, and the release rate increased to 3.5mm/s. Otherwise, the amount of solder paste remaining at the bottom of the stencil opening will increase by 23%, leading to bridging and tombstoning defects. At the same time, the first piece of each day must be tested for halogen residue on solder joints using XRF. Once the Cl? content exceeds 85ppm, the batch of solder paste is determined to have undergone irreversible moisture absorption degradation.

All solder paste batches are subject to dual-label management. The main label includes the production date, cold storage start time, and cumulative exposure minutes. The secondary label is a red, yellow, and green color-coded temperature-sensitive sticker, where the green range corresponds to 20–25℃ and humidity ≤55%, yellow triggers an early warning and shortens the subsequent process interval, and red forces isolation pending re-inspection. This mechanism has reduced the misuse rate of moisture-absorbed solder paste from the original 4.7% to below 0.3%.