Will the PCB/BMS expire?

　　PCB is the basic carrier of most electronic products. Even for battery products, there are circuit boards with protection and monitoring functions such as PCM or BMS.

　　PCB technology is very mature and has high stability, but PCBs stored for a long time do have the possibility of expiration. For PCBs that have been stored for a long time, they must be baked before they can be used.

　　The main purpose of baking is to remove moisture and 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 absorb water molecules or form water molecules. Water is one of the main killers of PCB popcorn or delamination. Because when the PCB is placed in an environment with a temperature exceeding 100°C, such as a reflow oven, wave soldering oven, hot air leveling or hand soldering, the water will turn into water vapor and then rapidly expand. When the water vapor cannot escape from the PCB immediately, there is a good chance of swelling the PCB, which may break the vias between the layers of the PCB, or cause the layer separation of the PCB. More serious, blistering, swelling, and plate bursting can be seen even on the outside of the PCB.

　　Sometimes, even if the above phenomena cannot be observed on the outside of the PCB, there are already unpredictable internal damages. With the passage of time, this will cause the function of electrical products to become unstable and eventually cause the product to fail.

　　The baking process is actually quite troublesome. The first is to remove the package before putting it in the oven. The second is to bake at a temperature exceeding 100°C, but the temperature should not be too high to avoid excessive expansion of water vapor during baking. Instead, it blows up the PCB.

　　Most of the PCB baking temperature in the industry is set at 120±5°C to ensure that moisture can really be eliminated from the PCB body. The baking time varies with the thickness and size of the PCB, and for thinner or larger PCBs, you have to press the board with a heavy object after baking to avoid the PCB from cooling down after baking. The stress is released and the PCB is bent and deformed.

　　At present, the industry generally sets the conditions and time for PCB baking as follows:

　　1. The 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 to 6 months beyond the manufacturing date, and it must 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 to use it, because the adhesive force of the multilayer board will age with time, and quality problems such as unstable product functions may occur in the future.

　　5. All PCBs that have been baked must be used up within 5 days

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