Related knowledge: The circuit board should be pre-baked in an oven before welding. Usually, the oven is used to pre-bake at 105℃ for 4h~6h.
Why do circuit boards have to be baked?
Circuit board drying refers to the process of removing moisture and curing the completed circuit board through pipes such as heating and ventilation during the circuit board manufacturing process. This step helps ensure the quality and performance of the circuit board and prevents problems caused by moisture. Commonly used drying methods include hot air oven, infrared drying and hot plate drying. The specific drying time and temperature will be determined according to the material and thickness of the circuit board and the manufacturing technical requirements.
The baking process of circuit boards is mainly divided into two stages: drying and preheating. Drying is to put the board into the oven and evaporate the moisture inside the board through a certain temperature and time; preheating is to improve the adhesive force and avoid other problems during the patching process.
So what are the specific steps for baking a circuit board?
The first step is preparation. Before baking, the circuit board to be baked must be cleaned and processed. Because the surface of the circuit board is easily contaminated with some dust and impurities, these substances will affect the adhesion between the circuit board and the patch. Therefore, before baking, the circuit board needs to be cleaned with clean alcohol or water.
The second step is drying. Place the circuit board in the preheated oven and bake according to the set temperature and time. During this process, the moisture on the circuit board will slowly evaporate. It should be noted that the drying time and temperature depend on the material, size and thickness of the circuit board.
The third step is to warm up. After drying, the moisture in the circuit board has evaporated, and a thin, clean oxide layer will form on the surface of the circuit board. This step is called preheating. The purpose of preheating is to make the circuit board easier to fit during patching and to avoid oxidation.
The fourth step is baking. After the circuit board is preheated, the circuit board can be placed in the SMD oven for baking. When baking, you need to heat according to the set temperature and time. Normally, the temperature and time of the oven need to be set in the process file of the SMT patch.
In the fifth step, after the above processing, the circuit board has completed the baking work and can then be processed by SMT. By baking the circuit board, the quality and accuracy of the patch can be ensured, and the product can operate normally.
Pre-baking precautions for multilayer circuit boards
1. If an oven is used for the circuit board, it must be equipped with air blast and constant temperature control to ensure uniform pre-baking temperature. Moreover, the oven should be clean and free of impurities to avoid falling on the board and damaging the membrane surface.
2. Do not use natural drying, and the drying must be complete, otherwise it will easily stick to the film and cause poor exposure.
3. After circuit board processing and pre-baking, the multi-layer circuit board should be air-cooled or naturally cooled before film alignment exposure.
4. After pre-baking the multi-layer circuit board, the time from coating to development should not exceed two days at most. When the humidity is high, try to expose and develop within half a day.
5. Different models of liquid photoresist have different requirements. You should read the instructions carefully and adjust the process parameters, such as thickness, temperature, time, etc., according to production practice.
It is important to control the pre-baking temperature and time. If the temperature is too high or the time is too long, it will be difficult to develop and remove the film. If the temperature is too low or the time is too short, the drying will be incomplete and the film will be pressure-sensitive, which will easily stick to the film, causing poor exposure and damage to the film. Therefore, if the multi-layer circuit board is processed and pre-baked properly, the development and film removal will be faster and the graphics quality will be good.
Although circuit board baking is only a small part of the SMT part processing process, it plays a vital role in the quality and performance of the product. Only through scientific and reasonable circuit board baking processing can we produce higher quality PCBA products.