PCB board deformation and warping refer to the shape changes that occur during the processing and use of the PCB board, mainly including bending, warping, twisting, etc. PCB board deformation and warping will affect the normal use of the PCB board and even cause damage to the PCB board. Therefore, in-depth analysis and research on the causes are required.
In PCB board milling, how to reduce or eliminate deformation and warping caused by different material characteristics or processing has become one of the problems faced by PCB board manufacturers.
The following are some of the causes of PCB board deformation and warpage:
1. PCB design is unreasonable
PCB board design is an important factor affecting its deformation and warping. If the design is unreasonable, it will cause the PCB board to deform and warp during processing and use. For example, if the length-to-width ratio of the board is unreasonable, or the layout of components on the board is unreasonable, it will cause the PCB board to deform and warp.
2. Improper data selection
The choice of PCB board material is also an important factor affecting its deformation and warping. Different materials have different characteristics, such as thermal expansion coefficient, density, etc. If the selected data does not match the application environment of the PCB board, it will cause the PCB board to deform and warp.
3. Improper PCB processing technology
The processing technology of the PCB board is also an important factor affecting its deformation and warping. If the processing technology is improper, it will cause the PCB board to deform and warp. For example, if the welding temperature is too high or the time is too long, it will cause the PCB board to deform and warp. If the drilling depth is too large or the hole diameter is too small, it will cause the PCB board to deform and warp.
4. Improper use environment
The usage environment of the PCB board is also an important factor affecting its deformation and warping. If the use environment is improper, it will cause the PCB board to deform and warp. For example, if the ambient temperature is too high or the humidity is too high, it will cause the PCB board to deform and warp. If used in a high-frequency electromagnetic field environment, it will cause the PCB board to deform and warp.
5. The weight of the PCB board itself will cause the board to dent, deform and warp.
Generally, reflow ovens use chains to drive the PCB board forward in the reflow oven. If there are overweight parts on the board, or the size of the board is too large, the center of the board will be dented due to its own weight, causing the board to be dented. bend.
6. The depth of V-Cut and the connecting strip will affect the amount of panel deformation and warping.
V-Cut is to cut grooves in the original large sheet, so the place where V-Cut appears is prone to deformation and warping.
7. Deformation and warping caused by PCB board processing
The causes of deformation and warping during PCB board processing are very complex and can be divided into two types of stress: thermal stress and mechanical stress. Thermal stress is mainly generated during the lamination process, and mechanical stress is mainly generated during the stacking, handling, and baking processes of panels.
The following is a brief discussion in process order.
Incoming copper clad laminate materials: The size of the copper clad laminate press is large, and there are temperature differences in different areas of the hot plate, which will lead to slight differences in the resin curing speed and degree in different areas during the lamination process, and will also produce local stress, which will be gradually released during future processing. Deformation board warping.
Pressing: The PCB board pressing process is the main process that generates thermal stress, which is released during subsequent drilling, shaping or grilling processes, causing the board to deform and warp.
Baking process of solder mask, characters, etc.: Since the solder mask ink cannot be stacked on top of each other when curing, the PCB boards will be placed vertically in the rack for curing. The boards are easily deformed and warped under their own weight or the strong wind of the oven.
Hot air solder leveling: The entire hot air solder leveling process is a sudden heating and cooling process, which will inevitably cause thermal stress, resulting in microscopic strain and overall deformation of the board warping area.
Storage: PCB boards are usually stored in a shelf during the semi-finished product stage. Improper adjustment of the shelf tension, or stacking of boards during storage, etc. will cause mechanical deformation of the board and warping of the board.
In addition to the above factors, there are many factors that affect the deformation and warping of the PCB board. Once you find that the PCB board is deformed and warped, you need to immediately check the cause and make improvements.
Preventive measures for PCB board deformation and warping
1. Reasonable design of PCB board
When selecting boards, you need to select appropriate boards according to the application environment. For example, if the application environment temperature is high, you need to choose a plate with a smaller thermal expansion coefficient. If the application environment has high humidity, you need to choose a board with better moisture-proof performance.
2. Reasonable layout of components
In order to avoid signal interference between components, the distance between components must be reasonable. If the distance between components is too small, signal interference will occur. If the distance between components is too large, the space utilization of the board will be reduced. The height of components should also be reasonable. If the height of the component is too small, it will cause signal interference. If the height of the components is too large, the space utilization of the board will be reduced.
3. Choose the appropriate processing technology
3.1. Select the appropriate welding temperature and time
During the welding process, it is necessary to choose the appropriate welding temperature and time. If the soldering temperature is too high or the soldering time is too long, it will cause the PCB board to deform and warp. If the welding temperature is too low or the time is too short, the welding may not be strong.
3.2. Select the appropriate drilling depth and hole diameter
During the drilling process, it is necessary to choose the appropriate drilling depth and hole diameter. If the drilling depth is too large or the hole diameter is too small, it will cause the PCB board to deform and warp.
In addition to the above factors, the causes of PCB board deformation and warping and the preventive measures for PCB board deformation and warping. There are many factors that affect the deformation and warping of the PCB board. Once you find that the PCB board is deformed and warped, you need to immediately check the cause and take improvement measures.