The procedure for PCB baking is actually quite troublesome.
When baking, the original packaging must be removed before it can be put into the oven and then baked at a temperature of more than 100℃, but the temperature should not be too high to cause excessive expansion of PCB.
The general industry for PCB baking temperature is mostly set at 120±5℃ conditions to ensure that the moisture can really be eliminated from the PCB before the SMT soldering. Baking time varies with PCB thickness and size.
Chart1 Baking Oven
The Setting of PCB Baking Time
1. When a PCB is within 2 months of manufacturing date and sealed well, Unseal and place in a temperature and humidity controlled environment (≦30℃/60% RH).
And according to IPC-1601) for more than five days, Roast 120±5℃ for 1 hour before going online.
2. PCB storage exceeds the manufacturing date by 2~6 months, Roast for 2 hours at 120±5℃ before going online.
3. PCB storage exceeds the manufacturing date by 6~12 months, Roast 120±5℃ for 4 hours before going online.
4. PCB stored more than 12 months after the date of manufacture, Basically not recommended, Because the bonding force of the multilayer will age over time. There may be quality problems such as product instability in the future and increase the chance of market rework, and the production process also has the risk of PCB baking and bad tin waste.
5. All baking PCBs must be used within 5 days, and the unprocessed PCB must be re-baked for 1 hour at 120±5℃ before going SMT production line.
The precautions of PCB Baking
1. We recommend using a temperature of 105±5℃ to bake PCB because the boiling point of water is 100℃.
The PCB does not contain too many water molecules, it does not require too high a temperature to increase its gasification rate.
If the temperature is too high or the gasification rate is too fast, it is easy to make the water vapor expand rapidly, which is unfavorable to the quality and quality, especially for the multilayer board and the PCB with buried holes, 105℃ is just above the boiling point of water, and the temperature is not too high.
Not only dehumidification but also reduce the risk of oxidation.
2. Measuring PCB whether need baking or not we can observe its packaging to check if it’s damp, that is, whether the HIC in its vacuum packaging (Humidity indicator Card) has shown moisture, and if the packaging is good, HIC does not indicate that moisture can be directly online without baking.