Rewarming: Solder paste is usually refrigerated in a refrigerator, and the refrigerating temperature is preferably 5-10 degrees. Therefore, when the solder paste is taken out from the refrigerator, the temperature is much lower than the room temperature. If the bottle cap is opened without returning the temperature, the moisture in the air is easily condensed and adhered to the solder paste. Moisture is rapidly vaporized due to strong heat, causing “explosive tin” phenomenon, producing tin beads, and even damaging components. Solder paste reheating method: Under the premise of not opening the cap, it is naturally thawed at room temperature, and the temperature is returned for about 4 hours. Note: Do not open the cap without sufficient temperature recovery. Do not use heating to shorten the temperature recovery time.
Stirring: The solder paste is thoroughly stirred before use after warming. Purpose: To make the flux and tin powder evenly distributed, give full play to various characteristics; stirring method: manual mixing or machine stirring; mixing time: manual 4 minutes or so, machine 1-3 minutes; determination of stirring effect: scraping with a scraper Part of the solder paste, when the blade is tilted, if the solder paste can slip smoothly, the effect is achieved.
Printing reflow: After the solder paste is printed, it should be reflowed within four hours. If the standing time is too long, the solvent will evaporate and the viscosity will decrease, resulting in poor solderability of the parts or a weld after moisture absorption. Especially for the circuit board of the silver conductor, if the solder paste is printed at a temperature of 30 degrees Celsius, 80% humidity, high temperature and high humidity, and then placed aside, the soldering force after reflow will become extremely low. Solder paste is affected by humidity and temperature, so it is recommended that the working environment be between 23 and 25 degrees Celsius and 60% humidity. The viscosity of the solder paste can be adjusted to an appropriate viscosity at 23 to 25 degrees. Therefore, if the temperature is too high, the viscosity will be too low, and if the temperature is too low, the viscosity will be too high, so that the perfect effect cannot be achieved after printing. Due to the moisture absorption of the solder paste, in a high temperature and humid environment, the solder paste absorbs moisture in the air, resulting in solder balls and splashes.
Drying problem: During the process of re-disposing the solder paste, the solvent is not selected correctly, and the solvent with too strong volatility is too much, which causes the solder paste to dry out. Generally speaking, the good quality solder paste printing will not dry for 8 hours. If it is only open, it can be put longer; the storage condition of solder paste is generally maintained at 5~10 degrees, the temperature should be 20~25, and the temperature is 30% to 60%, the temperature is back for 4 hours. Drying, can not heat and accelerate the return temperature so that the evaporation of the solvent will also cause drying.