PCB News - Why should PCB be baked?

During the production of China's aerospace products, PCBs are baked for 24 hours. So why bake for 24 hours? First of all, we know that if an aerospace product is launched into space, its maintenance and inspection is an impossible task, so we strive for perfection in any detail. So the question is, why should PCB be baked?

Dehumidification and dehumidification of PCB is the main purpose of baking, because there will be water molecules in the air. The produced PCB has not been produced in the future for a long time, which may cause the circuit board to absorb external water and gas. Moreover, the materials used by many PCB circuit boards are easy to form condensation and invasion of water molecules, and the content of water molecules exceeds the relevant regulations, In the process of reflow furnace, wave welding furnace, hot air leveling or hand welding with an instantaneous temperature of more than 200 degrees, these internal water molecules will be heated and atomized into water vapor.

With the increase of temperature, the volume of water vapor will expand rapidly. The higher the temperature, the larger the volume of atomization. At this time, when the water vapor cannot escape from the PCB immediately, it is very likely to support the PCB, Breaking the via between the layers of the PCB may sometimes cause the interlayer separation of the PCB. More seriously, blistering, swelling, plate explosion and other phenomena can be seen even on the surface of the PCB. Sometimes even if the above phenomena can not be seen on the surface of the PCB, it has been internally injured. With the passage of time and aging, the function of electrical products will be unstable and eventually lead to product failure.

When PCB is welded, it will cause popcorn or delamination.

In fact, the PCB baking program is very troublesome.

1. When baking, remove the factory packaging before putting it into the oven, and then bake at a temperature exceeding 100 degree Celsius,

2. The temperature is mostly set at 120 + / - 5 degree Celsius to ensure that water vapor can really evaporate from the PCB body. Only the circuit board after baking can be printed on SMT line and welded in reflow furnace.

3. The baking time is set according to the thickness and size of PCB.

4. The thin or large PCB needs to be pressed with heavy objects after baking to reduce or avoid the tragedy of PCB bending deformation caused by stress release during PCB cooling after baking.

Once the baked PCB is deformed and bent, there will be offset or uneven thickness when printing solder paste on SMT patch, which will cause a large number of welding short circuit or empty welding during subsequent reflow.