The Role of PCB Board Baking in the Semiconductor Field

In the semiconductor field, PCB boards provide physical support and electrical connections for components such as chips, resistors, and capacitors. From smartphones and computers to industrial automation equipment, communication base stations, and even aerospace devices, PCB boards are indispensable. If PCB boards are not properly baked during the production process, they may experience delamination, bubbling, or cracking between layers. This is because PCB boards can absorb moisture from the environment during storage or transportation. When these boards are exposed to the high temperatures of reflow soldering, the moisture rapidly vaporizes and expands, leading to product failure. Additionally, the presence of moisture on the surface of unbaked PCB boards can cause oxidation of the soldering surface, affecting the wettability of the solder and resulting in poor or cold solder joints. This can reduce the reliability and performance of the product and may even cause failures during use.

I.The Role of PCB Board Baking

1.Moisture Removal: PCB board materials, especially the resin substrates and glass fiber cloth in multilayer boards, have a certain degree of hygroscopicity due to their natural microporous structures. During high-temperature processes such as reflow soldering, moisture can rapidly vaporize and expand, generating significant steam pressure that can cause delamination, bubbling, or cracking between layers of the PCB board. Baking can thoroughly remove moisture from the PCB board, preventing damage from water vapor during high-temperature soldering

2.Stress Relief: Various manufacturing processes can introduce internal stresses into the PCB board. Baking allows the board to undergo thermal treatment at a certain temperature, which helps to release these internal stresses. This stabilizes the dimensions of the board and reduces deformation that may occur during subsequent processing or use due to internal stresses.

3.Improved Soldering Performance: Moisture can cause oxidation of the soldering surface, affecting the wettability of the solder and leading to poor or cold solder joints. After baking, the moisture in the solder pads is removed, effectively improving the stability and reliability of the soldering process and reducing soldering defects such as cold soldering.

4.Prevention of Ionic Contamination:If moisture in the PCB board is not removed, it may form ionic contamination during subsequent high-temperature processes, increasing the risk of electrochemical migration around the solder joints, which can lead to short circuits or reduced product life. Baking reduces the likelihood of such ionic contamination, thereby enhancing the electrical performance and service life of the product.

II.Why Bake PCB Boards?

• Enhanced Reliability: By removing moisture and relieving internal stresses, baking significantly improves the reliability of the PCB board during high-temperature soldering and subsequent use, reducing failures caused by moisture and internal stresses.
• Improved Soldering Quality: The surface of a baked PCB board is drier, and the solder wettability is better, which improves soldering quality and reduces soldering defects such as cold soldering.
• Extended Service Life: By reducing ionic contamination and preventing board bursting, baking effectively extends the service life of the PCB board, enhancing the overall performance and stability of electronic devices.

III.PCB Board Baking Process

1.Preheating Stage: Generally, after placing the PCB board into the oven, preheating is performed first at a temperature of around 60°C for about 30 minutes. This step helps to evenly diffuse the moisture and reduces thermal shock during drying.

2.Main Baking Stage: After preheating, the main baking stage begins. The temperature is usually set at 120±5°C for constant temperature treatment. The specific baking time needs to be dynamically adjusted based on factors such as the storage period and thickness of the PCB board. For example, for PCB boards that have been unsealed for more than 5 days within 2 months of the manufacturing date, bake at 120±5°C for 1 hour; for those exceeding 2 to 6 months from the manufacturing date, bake at 120±5°C for 2 hours.

3.Cooling Stage: After baking is complete, the cooling stage begins. Forced air cooling is used, but the cooling rate must be controlled at ≤3°C/min to avoid thermal stress deformation.

IV.Suitable Ovens for PCB Board Baking

1.Hot Air Circulation Oven:

The hot air circulation oven heats the PCB board evenly through the circulation of hot air inside the oven. This type of oven is suitable for PCB boards that require high uniformity in baking and can effectively ensure baking quality.

2.Vacuum oven:

The vacuum oven performs baking in a vacuum environment, effectively reducing the impact of oxygen on the PCB board and avoiding oxidation issues. This is very important for PCB boards that are sensitive to oxidation or need to be used in high-vacuum environments.

3.Nitrogen Oven:

The nitrogen oven creates a low-oxygen environment by filling the oven with nitrogen, avoiding oxidation and contamination of the PCB board during high-temperature processing. This is particularly important for high-precision, high-performance PCB boards.

4.Infrared Oven:

The infrared oven uses infrared radiation to heat the PCB board, featuring fast heating speed and high efficiency. However, it is important to note that infrared ovens may have adverse effects on certain materials or components that are sensitive to infrared radiation. Therefore, selection should be based on the specific conditions of the PCB board.

In the semiconductor field, baking of PCB boards is an indispensable process. Through baking, moisture is effectively removed, internal stresses are relieved, soldering performance is improved, and ionic contamination is avoided. This enhances the quality and reliability of PCB boards and extends their service life. Different baking processes and oven types are suitable for different production requirements and PCB board characteristics, ensuring the quality and performance of PCB boards and thereby improving the reliability and service life of electronic products.