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PCB Tech

PCB Tech

PCB Tech

PCB Tech

Recommendations for PCB baking
2021-09-09
View:26
Author:Frank

 

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 rapidly, which is actually not good for the quality, especially for multilayer boards and PCBs with buried holes. 105℃ 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 been improved a lot.

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 that it has been damp. If the packaging is good, HIC does not indicate that the dampness is actually It can be put directly on the line without baking.

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3. When PCB baking, it is recommended to use "upright" baking with intervals, 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 jig" on the top of the board, because the general object is easy to absorb moisture from the high heat state to the cooling process. However, rapid cooling may cause plate bending, which requires a balance.

7. Disadvantages of PCB baking and matters to be considered

1. Baking will accelerate the oxidation of the PCB surface coating, and the higher the temperature, the longer the baking, the more unfavorable.

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 generation 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, and baking will increase the thickness of this layer of IMC that has been generated, causing reliability problems.