PCB Technical - How to deal with PCB after expiration

Do you know "Why PCBs must be baked before they can be used in the reflow oven after the expiration date exceeds the shelf life"?

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.

In addition, after the PCB is produced and placed for a period of time, there is a chance to absorb moisture in the environment, and water is one of the main killers of PCB popcorn or delamination.

Because when the PCB is placed in an environment where the temperature exceeds 100°C, such as reflow oven, wave soldering oven, hot air leveling or hand soldering, the water will turn into water vapor and then rapidly expand its volume.

When the speed of heating the PCB is faster, the water vapor will expand faster; when the temperature is higher, the volume of water vapor will be larger; when the water vapor cannot escape from the PCB immediately, there is a good chance to expand the PCB .

In particular, the Z direction of the PCB is the most fragile. Sometimes the vias between the layers of the PCB may be broken, and sometimes it may cause the separation between the layers of the PCB. Even more serious, even the appearance of the PCB can be seen. Phenomenon such as blistering, swelling, bursting, etc.;

Sometimes even if the above phenomena are not visible on the outside of the PCB, it is actually internally injured. Over time, it will cause unstable functions of electrical products, or CAF and other problems, which will eventually cause the product to fail.