5.1Picking is the appearance of excess needle-like solder at the end of the solder joint, which is a peculiar defect in the wave soldering process.

Causes: improper PCB transmission speed, low preheating temperature, low tin pot temperature, small PCB transmission inclination, poor wave crest, flux failure, and poor solderability of component leads.

Solution: adjust the conveying speed until it is appropriate, adjust the preheating temperature and tin pot temperature, adjust the PCB conveying angle, optimize the nozzle, adjust the shape of the wave peak, replace the new flux and solve the lead solderability problem.

5.2 Causes of virtual soldering: poor solderability of component leads, low preheating temperature, solder problem, low flux activity, too large pad hole, lead board oxidation, board surface pollution, too fast transfer speed, low tin pot temperature .

Solution: Solve the lead solderability, adjust the preheating temperature, test the tin and impurity content of the solder, adjust the flux density, reduce the pad hole in the design, remove the PCB oxide, clean the board surface, adjust the transmission speed, and adjust the temperature of the tin pot .

5.3 Reasons for thin tin: poor solderability of component leads, too large pads (except for large pads), too large pad holes, too large welding angle, too fast transmission speed, high tin pot temperature, and poor flux coating. All, the solder contains insufficient tin。

Solution: Solve the solderability of the leads, reduce the pads and pad holes in the design, reduce the welding angle, adjust the transmission speed, adjust the temperature of the tin pot, check the pre-coating flux device, and test the solder content.

5.4 Causes of missing soldering: poor solderability of leads, unstable solder wave crest, flux failure or uneven spraying, poor local solderability of PCB, jitter of conveyor chain, incompatibility of pre-coating flux and flux, unreasonable process flow.

Solution: Solder the lead solderability, check the wave crest device, replace the flux, check the pre-flux device, solve the PCB solderability (cleaning or return), check and adjust the transmission device, use the flux uniformly, adjust the process flow。

5.5PCB solder mask blistering after soldering

After SMA is welded, light green bubbles will appear around individual solder joints, and in severe cases, there will be bubbles the size of fingernails, which not only affect the appearance quality, but also affect the performance in severe cases. This defect is also a reflow soldering process. Problems that often occur in wave soldering, but most often when wave soldering.

Cause: The root cause of solder mask blistering is the presence of gas or water vapor between the solder mask and the PCB substrate. These trace amounts of gas or water vapor will be entrained into it during different processes. When encountering high welding temperatures , the gas expansion causes the delamination of the solder mask and the PCB substrate. When soldering, the temperature of the pad is relatively high, so the bubbles first appear around the pad.

One of the following reasons can lead to the entrainment of moisture on the PCB:

5.5.1PCBs often need to be cleaned and dried before doing the next process during processing. For example, after etching, they should be dried and then paste the solder mask. If the drying temperature is not enough at this time, water vapor will be entrained into the next process. Bubbles appear at high temperatures.

5.5.2 The storage environment before PCB processing is not good, the humidity is too high, and it is not dried in time during welding.

5.5.3In the wave soldering process, water-containing flux is often used. If the PCB preheating temperature is not enough, the water vapor in the flux will enter the inside of the PCB substrate along the hole wall of the through hole, and the water vapor will first enter around the pad. When the soldering temperature is reached, air bubbles are formed.

Solution:

5.5.4 Strictly control each production link, the purchased PCB should be put into storage after inspection, usually the PCB should not have blistering phenomenon within 10s at 260 ℃ temperature。

5.5.5 PCB should be stored in a ventilated and dry environment, and the storage period should not exceed 6 months;

5.5.6The PCB should be pre-baked in an oven at (120±5)℃ for 4 hours before soldering.

5.5.7The preheating temperature in wave soldering should be strictly controlled. Before entering wave soldering, it should reach 100~140℃. If a flux containing water is used, the preheating temperature should reach 110~145℃ to ensure that the water vapor can evaporate completely.