Why do PCB circuit board processing need to be baked?

Why do PCB circuit board processing need to be baked? The main purpose of PCB baking is to dehumidify and remove moisture, and to remove the moisture contained in the PCB or absorbed from the outside, because some materials used in the PCB itself are easy to form water molecules. First of all, the purpose of drying the board before china pcb assembly drilling is mainly to dehumidify, and the drying board before PCB drilling is to remove moisture from the board and reduce internal stress. There is also printed solder mask after pressing, including characters, etc., which need to be baked. Before shipping and packaging, there is also a process of baking the pressing plate, which is also to remove moisture, and the warpage of the baked printed circuit board has been greatly improved. Secondly, after baking, the moisture in the pad can be dried to strengthen the welding effect and reduce the false welding and repair rate. However, baking will cause a little change in the color of the PCB board, which will affect the appearance.
 

 

Usually, the baking time is generally 100-120°C, and the baking time is about 2H. Don't bake for too long! So, what are the requirements for baking conditions and time settings for circuit board processing?
1. PCB is well sealed within 2 months of the manufacturing date. After unpacking, it is placed in a temperature and humidity controlled environment (≦30℃/60%RH, according to IPC-1601) for more than 5 days. Bake at 120±5℃ for 1 hour.
2. The PCB is stored for 2-6 months beyond the manufacturing date, and it needs to be baked at 120±5°C for 2 hours before going online.
3. The PCB is stored for 6-12 months beyond the manufacturing date, and it must be baked at 120±5°C for 4 hours before going online.
4. PCB is stored for more than 12 months from the manufacturing date, basically it is not recommended, because the bonding force of the multilayer board will age over time, and quality problems such as unstable product functions may occur in the future, which will increase the market for repairs. In addition, there are risks of plate bursting and poor tin eating during the production process. If you have to use it, it is recommended to bake at 120±5°C for 6 hours. Before mass production, first try to print a few pieces of solder paste and make sure that there is no solderability problem before continuing production. Another reason is that it is not recommended to use PCBs that have been stored for too long because their surface treatment will gradually fail over time. For ENIG, the industry’s shelf life is 12 months. The thickness depends on the thickness. If the thickness is thinner, the nickel layer may appear on the gold layer due to the diffusion effect and form oxidation, which will affect the reliability, so you should not be careful.
5. All PCBs that have been baked must be used up within 5 days, and unprocessed PCBs must be baked at 120±5°C for another 1 hour before going online.
 
The baking time varies with the thickness and size of the PCB. For thinner or larger PCBs, you have to press the board with a heavy object after baking. This is to reduce or avoid the PCB The tragic occurrence of PCB bending deformation due to stress release during cooling after baking. Because once the PCB circuit board is deformed and bent, there will be offset or uneven thickness when printing solder paste in SMT, which will also cause a large number of solder short circuits or empty soldering defects during subsequent reflow.
 
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