After Jia Jinyuan Solder Paste is taken out of the cold storage, it must be immediately transferred to a constant temperature room for storage. Temperature fluctuation exceeding ±2℃ or tearing open the aluminum foil lid in advance will cause surface frosting and internal stratification. We have conducted on-line measurements and found that if the solder paste is put into stirring without sufficient thawing for 3.5 hours, the deviation of the viscosity recovery value of the solder paste will reach more than 18%, which directly leads to a 23% increase in the blockage rate of the stencil openings. However, if the thawing time exceeds 6 hours, the activity of the Flux will attenuate, and the wetting angle of the solder joint after reflow will increase to more than 42°.

Before stirring, it must be confirmed that there is no condensed water on the outer wall of the solder paste barrel and the sealing ring of the barrel lid is intact without deformation. Otherwise, the mixing of a small amount of water during high-speed rotation will induce spattering solder beads. We once encountered the problem that the void rate of 17 BGA solder joints per shift exceeded the standard due to the aging and air leakage of the sealing ring during continuous production. After replacing the sealing ring and recalibrating the stirring parameters, this phenomenon was eliminated. The rotation speed of the mixer must be measured with a laser tachometer for the first piece of each shift, and the displayed value on the equipment panel cannot be relied on. Because Jia Jinyuan solder paste has high thixotropy, 60rpm is the only critical rotation speed that can balance shear thinning and structural reconstruction. If it is lower than 55rpm, the gel network cannot be broken; if it is higher than 63rpm, the coating film of metal particles will be excessively damaged.

The stirring time is strictly controlled at exactly 120 seconds. If it is less than 115 seconds, the area of the hysteresis loop of the solder paste rheological curve will be too large, and the printing release force will increase by 19%, leading to an increase in the displacement rate of 0201 components. If it is more than 125 seconds, the oxidation rate of the metal powder will accelerate. XRF detection shows that the Sn content decreases by 0.07wt%. Although it does not exceed the specification limit, the occurrence rate of solder joint bridging in the Reflow Soldering furnace temperature zone increases to 0.83% after three consecutive batches. After the stirring is completed, it must be put on the machine within 30 minutes. If it is placed for too long, the volatilization of the surface solvent will be unbalanced. We have tracked with a mass spectrometer and found that after being placed for 90 minutes, the relative concentration of rosin components decreases by 12.4%. If it is put on the machine for printing at this time, the NG rate of the first piece is as high as 14.6%, which far exceeds the CPK control line of 0.3%.

After each batch of stirring, a sample must be taken for a scraper test. Use a 300-mesh stainless steel scraper to scrape across the glass plate at a constant speed at a 45° angle, and observe whether a uniform matte film layer is presented. If streaks, shrinkage cavities or reflective spots appear, it indicates uneven stirring or foreign matter mixed in. At this time, the barrel of solder paste must be scrapped and the previous cold storage handling records must be traced. We once found that the solder paste barrel was tilted more than 15° for 7 times during forklift handling, which caused the paste in the barrel to segregate. Although there was no abnormality in appearance, the CV value of the printing thickness deteriorated from 8.2% to 13.7%. This hidden failure can only be exposed through the scraper test.