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Why should the Pcb board be dried?

Why should the Pcb board be dried?

The board should be dried before being placed on the machine. During the pcb manufacturing process before the flux is applied, the PCB has been treated in the plating solution. If a certain amount of solution and water are absorbed due to its porosity, the liquid will be vaporized when the wave soldering operation is performed at a high temperature. This not only causes the solder itself to splash (that is, the moisture in the PCB evaporates during the wave soldering to spray the solder out of the welding seam), but also forms a large amount of steam. These vapors are trapped in the filler solder to form pores. In order to eliminate the residual solvent and moisture hidden in the PCB during the manufacturing process, it is recommended to dry the PCB before going on the line before inserting the components. The drying temperature and time can be refer to Table 1 as below.


Drying equipment Temperature (°C) Time (h)


Circulating drying oven 107-120 1-2
70-80 3-4
Vacuum drying oven 50-55 1.5-2.5


The temperatures and times listed in Table 1, it can be used for lower temperatures and shorter times for circuit board thickness below 1.5 mm, while high temperatures and longer times can be used for thick boards. PCBs with more than four layers require the highest temperature and the longest time in the table.


It is also advantageous to eliminate the residual stress formed during the PCB board fabrication process and to reduce the warpage and deformation of the PCB during the wave soldering by performing the drying treatment on the Pcb board before going on the line.