PCB board during the deformation caused by the process
PCB board processing process of deformation is very complex can be divided into thermal stress and mechanical stress caused by two kinds of stress. The thermal stress mainly occurs in the process of pressing, the mechanical stress mainly produce plate stacking, handling, baking process. The following is a simple discussion in the order of the process.
CCL material: CCL are double-sided, symmetrical structure, no graphics, copper and glass cloth CTE is almost the same, so in the process of pressing almost no damage caused by the different CTE. However, CCL press size, hot plate in different regions there is a temperature difference, will lead to different areas of the process of curing resin curing the degree and degree of subtle differences, while the different heating rate of the dynamic viscosity is also a big difference, it will also produce Due to the local stress caused by the difference in curing process. Generally this stress will maintain balance after pressing, but will gradually release in the future processing to produce deformation.
Pressing: PCB pressing process is the main process of generating thermal stress, in which the deformation due to the different material or structure is discussed in the previous section. Similar to the copper cladding, there are local stresses caused by the difference in the curing process. The PCB stress is more difficult to eliminate than the CCL due to the thicker thickness, the pattern distribution, the more prepreg and so on. The PCB board in the presence of stress, in the subsequent drilling, shape or barbecue and other processes released, resulting in deformation of the plate.
Resistance, welding, character, etc. Baking process: As the solder resist ink can not be stacked on each other, so PCB board will be placed in the shelf baking curing, welding temperature of about 150 ℃, just over the low Tg material Tg point, Tg Point above the resin for the high elastic state, the plate easily in the weight or oven under the action of strong wind deformation.
Hot air solder leveling: ordinary board hot air solder leveling temperature of the furnace temperature of 225 ℃ ~ 265 ℃, time 3S-6S. Hot air temperature of 280 ℃ ~ 300 ℃. Solder leveling plate from the room temperature into the tin furnace, after two minutes and baked at room temperature after the washing. The entire hot air solder leveling process for the sudden hot quenching process. As the circuit board material is different, the structure is not uniform, in the hot and cold process will inevitably appear thermal stress, leading to micro-strain and the overall deformation Alice area.
Storage: PCB board in the semi-finished product storage are generally insisted in the shelf, the shelf is not appropriate to adjust the elastic, or stored in the process of stacking plate and so will make the plate mechanical deformation. Especially for 2.0mm below the impact of the sheet is more serious.
In addition to the above factors, there are many factors that affect PCB deformation.