Solder paste is one of the important materials for bonding circuit board and components. It is a thixotropic fluid.The viscosity of solder paste is not only related to the percentage of alloy weight, particle size and particle shape, but also related to temperature. The change of ambient temperature will cause the fluctuation of viscosity.Therefore, it is best to control the ambient temperature at 23℃±3℃.Because most of the printing of solder paste is done in air, the environmental humidity will affect the quality of solder paste.General requirements of relative humidity control in RH45%~ 70%;In addition, the solder paste workshop of printed PCB should be kept clean and tidy, without dust and corrosive gas.
At present, PCB assembly density become higher and higher, printing is more and more difficult, must correctly use and keep solder paste.The main requirements are as follows:
(1) must be stored in the condition of 2-10℃.
(2) It’s required to remove solder paste from the refrigerator a day in advance(at least 4 hours in advance), opening the lid of the container until the solder paste reach room temperature , (1) must be stored in 2~10℃ conditions.To prevent condensation.
(3) Before using, stirring the paste evenly by using the stainless steel mixer knife or automatic mixer, the mixer knife must be clean, manual mixing should be in one direction, the machine or manual mixing time for 3~5min
(4) Covering the container cover after adding soldering paste.
(5) No cleaning solder paste cannot be used with recycled solder paste. If the printing interval is more than 1h, the solder paste should be wiped from the template and recycle the solder paste into the container used on the same day.
(6) Try to finish reflow welding within 4h after Pcb printing.
(7) Do not scrub the solder joints with alcohol if not using flux, but if using flux during repairing board by free cleaning solder paste, any residual flux outside the solder joints that has not been heated must be scrubbed away at any time, because unheated flux is corrosive.
(8) PCB products to be cleaned should be cleaned on the same day after reflow welding.
(9) During printing solder paste and smt operation, hold the edge of the PCB or wear gloves to prevent contamination of the PCB.
