The reasons for rough soldering during the PCB manufacturing process are numerous. 

Issues such as incorrect soldering temperature and improper solder composition can both lead to rough soldering on the substrate. 

Rough soldering can adversely affect the performance of the components on the PCB board, 

so it should be avoided as much as possible. Below are three scenarios to illustrate this:

Firstly, the temperature factor in PCB soldering. Rough soldering caused by welding at inappropriate temperatures accounts for more than 40% of cases.

Therefore, manufacturers must strictly control the soldering temperature and time.

To address this issue, designers and manufacturers can adjust the preheating temperature of the soldering process by modifying the conveyor belt speed to establish an appropriate relationship and avoid rough soldering.

Secondly, incorrect solder composition. Before soldering, manufacturers must strictly inspect the composition of the solder to determine the type of solder and the appropriate soldering temperature for a particular alloy, and ensure that the solder is not contaminated. 

In addition, the PCB board should remain stable before the solder cools. If vibration occurs during this time, it can also lead to rough soldering. The substrate should be kept stationary.

Thirdly, during the PCB manufacturing process, if rough soldering is accompanied by issues such as soldering in blocks and protruding solder, designers must quickly check if the board surface is contaminated or if there are other issues such as a low secondary soldering waveform or low solder temperature.

These factors are also important reasons for the occurrence of rough soldering.