Solder balls often appear in wave soldering. There are two main reasons: First, when the printed board is soldered, the moisture near the through hole on the printed board is heated and turned into steam. If the metal coating on the hole wall is thin or there are gaps, the water vapor will be removed through the hole wall. If there is solder in the hole, when the solder solidifies, the water vapor will create a gap (needle hole) in the solder, or extrude the solder on the front of the printed board. produce solder balls. Second, the solder balls generated on the  side of the printed board (that is, the side that touches the wave crest) are caused by improper setting of some process parameters in wave soldering. If the amount of flux coating is increased or the preheating temperature is set too low, it may affect the evaporation of the components in the flux. When the printed board enters the peak, the excess flux is evaporated by high temperature, and the solder is splashed out of the tin bath. Irregular solder balls appear on the printed board.

For the above two reasons, Shanghai Hanhe Electronics usually takes the following corresponding solutions: First, the proper thickness of the metal coating in the through hole is very critical, and the minimum copper coating on the hole wall should be 25um, and there is no gap. Second, apply the flux using a spray or foam application. In the foaming mode, when adjusting the air content of the flux, keep the smallest bubbles as possible, and the contact surface between the foam and the PCB is relatively reduced. Third, the temperature setting of the preheating zone of the wave soldering machine should make the temperature of the top surface of the circuit board reach at least 100°C. Proper preheating temperature can not only eliminate solder balls, but also prevent circuit boards from being deformed by thermal shock.

There are many reasons for solder balls in wave soldering, but generally speaking, it is mainly due to the moisture of the material. In addition, the coating method of the flux is also very important. The ultrasonic spraying effect is very good. If water-based flux is used, The length of the preheating zone is three sections, 1.8 meters is very important, and the preheating zone should use hot air. In addition, the humidity of the production environment should also be strictly controlled.