PCB Baking

PCB baking condition setting

1. If the PCBs are well sealed within 2 months of the manufacturing date and placed in a temperature and humidity controlled environment (≦30℃/60%RH, according to IPC-1601) after unpacking more than 5 days, it should be baked at 120±5℃ for 1 hour before assembly.
2. If the PCBs are more than 2 to 6 months of the manufacturing date, before assembly they should be baked at 120±5℃ for 2 hours.
3. If the PCBs are more than 6 to 12 months of the manufacturing date, before assembly they should be baked at 120±5℃ for 4 hours.
4. If the PCBs are more than 12 months of the manufacturing date, basically not recommended to use, because the adhesive of multi-layer board will age with time, may occur product function instability and other quality problems. If they must be used, it is recommended to bake at 120±5℃ for 6 hours.  Before mass production, assembling samples for testing to check if they are qualified.
5. All baked PCB must be used within 5 days, the leftover PCBs must be re-baked at 120±5℃ for 1 hour before assembly.

Stacking of PCB when baking

1. When large-size PCB is baking, it is recommended that the maximum number of a stack is not more than 30 pieces. After baking, open the oven to take out the PCB and put it flat to cool, and press the anti-bending fixture after baking. Upright baking is not recommended for large size PCB, which is prone to board bending and warping.
2. When small and medium-sized PCB is baking, they can be placed flat stacked, the maximum number of a stack can not exceed 40 pieces; They can also be adopted upright, the number is not limited, after baking, open the oven to take out the PCB flat place to cool, and press the anti-bending fixture after baking.

Precautions for PCB baking

1. The baking temperature can not exceed the Tg point of the PCB, generally can not exceed 125℃.
2. The baked PCB should be used as soon as possible, if not used, they need re-vacuum packaging. If the exposure time is too long, it must be re-baked.
3. The oven should be equipped with ventilation drying equipment, otherwise the baked water vapor will remain in the oven to increase the relative humidity, which is not conducive to PCB dehumidification.
4. Whether the PCB needs to be baked, Depends on whether its packaging is damp. Observe the vacuum packaging HIC (Humidity Indicator Card), if the packaging is good, HIC does not indicate moisture, then they can be directly used for assembly.
5. Baking will accelerate the oxidation of PCB surface coating, and the higher the temperature and the longer the baking, the more unfavorable.
6. It is not recommended to bake the OSP surface board at high temperature, because the OSP film will degrade or fail due to high temperature.
7. Baking may have an impact on the generation of IMC (copper-tin compound), especially for HASL and ImSn surface boards, because its IMC layer has been generated before the PCB soldering, baking will increase the thickness of IMC, causing reliability problems.