Solder paste is a paste-like stable mixture of solder powder and paste flux. It acts as a bonding component in the PCB printed circuit board, promotes solder wetting, removes oxides, sulfides, micro magazines and adsorption layers, protects the surface of the board pad from re-oxidation, and forms a strong metallurgical bond.
The stickiness in the solder paste is the ability of the solder paste to adhere to the PCB assembly components after positioning and reflow soldering. The stickiness of the solder paste is the standard for verifying that the working life has disappeared. If the adhesion test indicates that the solder paste has exceeded its working life, it will not be able to position the component during the placement process and prior to reflow. From the point of view of use, a good quality solder paste should have the following characteristics:
(1) The printing performance is good, the PCB can be printed continuously, the holes of the steel mesh plate will not be blocked, and the unnecessary pcb solder paste will not overflow on the reverse side of the steel mesh plate;
(2) Good thixotropy, no collapse during placement or preheating, no solder joint bridging; very good solderability, no solder ball splashing (solder paste after soldering to the soldering station) Short circuit caused by tiny solder balls splashing around;
(3) The solder paste is well preserved, and the solder paste is stored for 3-6 months under refrigeration (5~10 °C, refrigerator freezer), and the performance should be unchanged. Remove the solder paste from the refrigerator two hours before use, and return to the room (4) temperature before use; the printed circuit board is placed for a long time, generally can be placed at room temperature for 12~14h;
(4) The residue after welding should have high insulation resistance and good cleaning property; non-toxic, odorless and non-corrosive.