1. When baking large-size PCBs, use a horizontal stacking arrangement. It is recommended that the maximum number of a stack should not exceed 30 pieces. The oven needs to be opened within 10 minutes after baking to take out the PCB and lay it flat to cool it. After baking, it needs to be pressed. Anti-bend fixtures. Large-size PCBs are not recommended for vertical baking, as they are easy to bend.
2. When baking small and medium-sized PCBs, you can use flat stacking. The maximum number of a stack is recommended not to exceed 40 pieces, or it can be upright, and the number is not limited. You need to open the oven and take out the PCB within 10 minutes of baking. Allow it to cool, and press the anti-bending jig after baking.
Precautions when PCB baking
1. The baking temperature should not exceed the Tg point of the PCB, and the general requirement should not exceed 125°C. In the early days, the Tg point of some lead-containing PCBs was relatively low, and now the Tg of lead-free PCBs is mostly above 150°C.
2. The baked PCB should be used up as soon as possible. If it is not used up, it should be vacuum packed as soon as possible. If exposed to the workshop for too long, it must be baked again.
3. Remember to install ventilation drying equipment in the oven, otherwise the steam will stay in the oven and increase its relative humidity, which is not good for PCB dehumidification.
4. From the point of view of quality, the more fresh PCB solder is used, the better the quality will be. Even if the expired PCB is used after baking, there is still a certain quality risk.
Recommendations for PCB baking
1. It is recommended to use a temperature of 105±5℃ to bake the PCB. Because the boiling point of water is 100℃, as long as it exceeds its boiling point, the water will become steam. Because PCB does not contain too many water molecules, it does not require too high a temperature to increase the rate of its vaporization.
If the temperature is too high or the gasification rate is too fast, it will easily cause the water vapor to expand quickly, which is actually not good for the quality. Especially for multilayer boards and PCBs with buried holes, 105°C is just above the boiling point of water, and the temperature will not be too high. , Can dehumidify and reduce the risk of oxidation. Moreover, the ability of the current oven to control the temperature has improved a lot than before.
2. Whether the PCB needs to be baked depends on whether its packaging is damp, that is, to observe whether the HIC (Humidity Indicator Card) in the vacuum package has shown moisture. If the packaging is good, HIC does not indicate that the moisture is actually You can go online without baking.
3. It is recommended to use “upright” and spaced baking when PCB baking, because this can achieve the maximum effect of hot air convection, and moisture is easier to be baked out of the PCB. However, for large-size PCBs, it may be necessary to consider whether the vertical type will cause bending and deformation of the board.
4. After the PCB is baked, it is recommended to place it in a dry place and allow it to cool quickly. It is better to press the “anti-bending fixture” on the top of the board, because the general object is easy to absorb water vapor from the high heat state to the cooling process. However, rapid cooling may cause plate bending, which requires a balance.
Disadvantages of PCB baking and things to consider
1. Baking will accelerate the oxidation of the PCB surface coating, and the higher the temperature, the longer the baking, the more disadvantageous.
2. It is not recommended to bake OSP surface-treated boards at a high temperature, because the OSP film will degrade or fail due to high temperature. If you have to bake, it is recommended to bake at a temperature of 105±5°C, not more than 2 hours, and it is recommended to use it up within 24 hours after baking.
3. Baking may have an impact on the formation of IMC, especially for HASL (tin spray), ImSn (chemical tin, immersion tin plating) surface treatment boards, because the IMC layer (copper tin compound) is actually as early as the PCB stage Generation, that is, it has been generated before PCB soldering, but baking will increase the thickness of this layer of IMC that has been generated, causing reliability problems.