What is the function of preheating the PCB prototype board?

Engineers use prototype PCBs to test the functionality of PCB-based solutions early in the design process. Before entering more complex designs, they often order multiple prototype runs to test redesigns or test individual functions. This allows them to discover elements that need to be corrected early in the process. The sooner these problems are discovered, the lower their costs will be. So what is the function of preheating the prototype board first?

Engineers use prototype PCBs to test the functionality of PCB-based solutions early in the design process. Before entering more complex designs, they often order multiple prototype runs to test redesigns or test individual functions. This allows them to discover elements that need to be corrected early in the process. The sooner these problems are discovered, the lower their costs will be. So what is the function of preheating the prototype board first?

① The solvent in the flux and the moisture that may be absorbed by the PCB assembly board will evaporate. The solvent and moisture will boil when the wave is over the peak and cause the solder splash (commonly known as “tin frying” phenomenon). Frying tin is like in a boiling oil pan If mixed with water, it will produce splashes, forming hollow solder joints, blisters, tin beads, missing solder, virtual solder, pores and other defects. Therefore, preheating before SMT chip processing can reduce soldering defects.

②The rosin and active agent in the flux require a certain temperature to decompose and activate. The activation reaction can remove the oxide film on the surface of the printed board pad, component tip and pin surface, and other contaminants.

③The prototype PCB and components are fully preheated to avoid thermal stress and damage to the printed board and components due to the rapid temperature rise during SMT soldering.

What is the function of preheating the PCB prototype board?

The preheating temperature and time of the printed board should be determined according to the type of flux, the activation temperature range, the size and thickness of the assembly board, the size and number of components, the number of mounted components, that is, the heat capacity of the assembly board. The length of the preheating zone of the wave soldering machine is determined by the output and the speed of the conveyor belt. The higher the output, the longer the preheating zone is needed to achieve the required wetting temperature for the assembled board.

The preheating temperature is 90~130℃ (referring to the surface temperature of the PCB). The upper limit of the preheating temperature is taken when the multi-layer board and more components are mounted. The preheating temperature of different PCB types and assembly forms is also different, but it must be combined The specific situation of pcba patch should be set after process test or trial welding. Like reflow welding, the real-time temperature curve must be measured.

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