Causes and prevention methods of PCB bending and warping
PCB bending and warping are common problems in the production process. This phenomenon will affect the assembly and welding quality of the circuit board, and may even cause the circuit board to not work properly. Bending and warping are usually the result of multiple main effects. The following are the most common reasons:
1. Material problems
Uneven or poor quality of the material of the PCB substrate may lead to unstable thermal expansion coefficient, which in turn causes warping.
Uneven distribution of copper foil thickness and glass cloth layer, etc.
2. Improper temperature control during production
During the PCB production process, the temperature changes too quickly, especially in high-temperature soldering processes (such as reflow soldering and wave soldering), the heat may cause the PCB board to warp.
During the hot pressing process, if the pressure and temperature are uneven, warping is also prone to occur.
3. PCB design problems
The layout during PCB design is unbalanced, resulting in excessive local stress, or uneven component layout on the PCB.
Warping may also be caused by excessive board area or uneven component density.
4. Lamination process problems
During the PCB lamination process, if the pressure of the upper and lower heating plates is uneven, or the hot pressing time and temperature are improperly controlled, the board may be deformed.
5. Improper board storage
If the PCB is not protected during storage and transportation, it may be subject to humidity, temperature changes or physical pressure, which may cause the board to warp.
6. Welding process problems
During the welding process, if the heat distribution in different areas is uneven, it is also easy to cause the lining board to bend. For example, the temperature is too high or uneven during the reflow soldering process.
7. Mechanical processing problems
During the mechanical processing of the PCB spindle, cutting, etc., if the processing parameters are not carefully controlled, it may also cause concentrated voltage and cause warping.
So how to prevent PCB board bending and warping? The following effective methods can be used for reference:
1. Select PCB materials with reliable quality and meet the requirements to ensure the uniformity of chip thickness and structure.
2. Use materials with relatively consistent thermal expansion coefficients to avoid using substrates with unstable quality.
3. Strictly control the temperature changes during the production process, reasonably control the reflow soldering temperature, especially in the high-temperature treatment stage, and reduce the heating and cooling speed of the reflow soldering.
4. During the welding process, use gradual heating and cooling to avoid excessive local temperature differences.
5. In the design stage, reasonably plan the layout of the PCB and the distribution of components to avoid the similarity of overweight components concentrated on the circuit board.
6. For large-size PCBs, you can consider designing reinforcing ribs or other reinforcement measures to reduce the risk of board bending.
7. Give priority to high-Tg boards, which can withstand deformation caused by high temperatures to a greater extent.
8. Reduce the number of panels and reduce the size of PCB boards, because the panels and sizes increase, and after the high-temperature treatment of reflow soldering, the pressure on different areas of the board will be different, and due to the influence of the weight itself, it is easy to cause the middle part to have limits and deformation.
9. Use oven trays/jigs to reduce circuit board deformation.
What is the PCB warpage standard? In actual production, PCBs are usually not 100% flat, and there will be some bending more or less. What is the PCB warpage standard? The PCB warpage is mainly judged by "warpage".
According to the IPC standard, the warpage of the PCB to be mounted must be ≤0.75% to be a qualified product.
Dongxun PCB's standard for board warpage is 0.7%. If it exceeds this standard, we will use 150 degrees for 2 hours of furnace pressing to achieve a more ideal board flatness.
