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    Precautions for using solder paste

    Pay attention to the following points in the process of using solder paste:

    (1) When using, take it out of the refrigerator at least 4H in advance, write down the time, number, user and applied product, seal it at room temperature, and open the bottle cap when the solder paste reaches room temperature. If it is opened at low temperature, it is easy to absorb water vapor, and solder beads will be produced during reflow soldering. Note: do not place solder paste beside hot air heater and air conditioner to accelerate its temperature rise.

    (2) After unsealing, it is necessary to mix at least 30s with mixer or 5min by hand to make the components in solder paste uniform and reduce the viscosity of solder paste.

    (3) After the adjustment of the first printed board or equipment on duty, the solder paste thickness tester shall be used to measure the solder paste printing thickness. The test points shall be selected at five points, including the upper, lower, left and right and middle of the test surface of the printed circuit board, and the value shall be recorded. The solder paste thickness range shall be - 10% - + 15% of the screen board thickness.

    (4) If it is not used for more than 30min, it should be stirred with the stirring function of screen printing machine before use. If the interval is longer (more than 1 h), the solder paste should be put back into the tank and the bottle cap should be tightly closed. After the solder paste is used again, it should be stirred at least with a mixer or by hand to make the components in the solder paste uniform.

    (5) The amount of solder paste added to the screen board for the first time is determined by the amount of solder paste added to the screen board for the first time. Generally, 200-300g is added for the first time. After printing for a period of time, a proper amount of solder paste is added to ensure that the solder paste rolls clockwise along the forward direction of the scraper, and the thickness is about 1 / 2 to 3 / 4 of the height of the metal scraper. (6) After printing the solder paste, it should be pasted in the shortest possible time to prevent the volatilization of flux and other solvents. In principle, it should not exceed 8h. If the time is exceeded, the solder paste should be cleaned and re printed.

    (7) In principle, the solder paste should not be used more than once in the same day. Solder paste scraped back from the screen should also be sealed and refrigerated.

    (8) The optimum temperature of printing time is 25 ℃± 3 ℃, and the optimum temperature is 45% - 65%. When the temperature is too high, the solder paste is easy to absorb water vapor and produce tin bead during reflow soldering.

    (9) Do not put fresh solder paste and used solder paste into the same bottle. To prevent the solder paste from being contaminated when the solder paste is replaced.

    (10) It is suggested that 1 / 4 of the old solder paste and 3 / 4 of the fresh solder paste should be mixed together to keep the new and old solder paste in the best condition.

    (11) In the production process, 100% inspection of solder paste printing quality is conducted, the main content is whether the solder paste pattern is complete, whether the thickness is uniform, whether there is solder paste tip phenomenon.

    (12) Clean the mesh plate according to the process requirements after the shift.

    (13) After the printing experiment or printing failure, the solder paste on the printed circuit board should be thoroughly cleaned and dried with ultrasonic cleaning equipment to prevent solder balls from appearing after reflow due to residual solder paste on the board during reuse.