In order to meet the electronic products development requirements of light, thin, short, small and multi-functional, highly reliable, the electronic product structure using PCB hybrid assembly process is increasing the proportion. Not only THC / THD and SMC / SMD hybrid assembly more common, and even the phenomenon of a PCB mixed with THC, THD, SMC, and SOIC is not uncommon.

PCB assembly usually uses more than 95% of the SMD devices and a small number of different parts, such as connectors, transformers, etc. These devices are assembled by SMT equipment and processing systems in addition to the wave soldering line complement completion. High energy consumption and a lot of flux, solder and nitrogen consumption, making the wave soldering process at this time is very affordable, but also in the wave soldering double-sided PCB board, solder trough solder temperature often make the top device solder joints secondary remelting occurs. At the same time lead to PCB bending deformation. Therefore, we must use the following methods to solve.

1. Try not to use artificial iron welding
In the field of assembled circuit boards requiring high quality and high reliability, which is not allowed when using manual welding. Poor process reproducibility makes manual welding as a concern for quality.

2. The use of solder mask to protect the PCBA
Use a complex solder mask to protect the PCB solder surface of the device, to avoid contact with flux and solder. In today's electronics, PCBs are protected by strict quality standards, especially those left on the PCB after soldering, which can lead to PCBA contamination, which can permanently reduce the surface impedance of the board.

3. Selective welding process
Selective soldering process for through-hole components of the welding, SMT components are dominate, and through-hole components just occupy on little part in PCBA on all components in a small proportion, but this installation method will be continue for a period of time.