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FPC Research Blog
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When welding the large copper bar on the PCB, due to uneven heat or other factors, the thermal expansion coefficient of the copper bar and the surrounding material may be inconsistent, resulting in local thermal expansion and contraction of the welding area. This uneven thermal expansion and cold shrinkage process may lead to formation of local mechanical stress in the plate, and eventually cause the warping or deformation of the PCB.


Copper is a metal with a relatively high coefficient of thermal expansion, which expands at high temperatures, while other PCB materials (such as glass fiber reinforced substrates) have a relatively low coefficient of thermal expansion. During the welding process, the heat is concentrated at the copper bar, making the expansion rate of the copper higher than the surrounding material, so it may cause uneven contraction when cooling, resulting in mechanical stress and PCB warping or deformation.


What is PCB?


PCB refers to the Printed Circuit Board (printed circuit board), also known as circuit board or circuit board. It is a basic platform used to support and connect electronic components, usually consisting of a non-conductive insulating substrate covered with one or more layers of conductive copper foil. It is mainly used in electronic equipment, as a mechanical support of electronic components, electrical connection and signal transmission carrier. Electronic components, such as resistors, capacitors, integrated circuits, etc., are connected to the PCB by welding or inserting to form a complete circuit system.


What can be caused when PCB warping deformation ?


Circuit connection failure:


The warping deformation of the PCB can cause problems in the connection between the electronic components, and even cause a break or short circuit. This can cause the circuit to not work properly or fail completely.


Performance loss:


The warping deformation may affect the performance of the circuit board. In some cases, especially in high-frequency or high-precision circuits, deformation of the plate may result in loss of signal transmission, increased noise, or signal distortion.


Mechanical stability decline:


The warping deformation of the PCB may cause its mechanical stability to decline. This can make it difficult to install in the device and can also affect the overall stability and performance of the device.


Reliability issues:


Deformation can cause stress concentration in the PCB, which can affect its long-term reliability. This can lead to a shortened life of the PCB, increasing the risk of failure.


Maintenance difficulties:


If the PCB is severely deformed, a more complex repair process or PCB replacement may be required to solve the problem. This increases repair costs and time.


The factors which leading PCB warping deformation after welding large copper bars?


Thermal expansion coefficient difference:


The coefficient of thermal expansion of copper and PCB sheet is different. When welding large copper bars, high temperatures will cause the copper to expand, but the coefficient of thermal expansion of the copper and the surrounding substrate material (usually a glass fiber reinforced substrate) is different. This uneven expansion and contraction can cause mechanical stress during cooling, which can cause the PCB sheet to warp or deform.


Thermal stress:


During the welding process, high temperature will cause local thermal expansion, and when the plate is cooled, the temperature change rate is different in different areas, which may produce thermal stress. This thermal stress may cause the sheet to bend or deform.


Plate design and thickness:


PCB board design and thickness may also affect warping deformation. If the plate is thin or the impact of large copper bars on the plate is not considered in the design stage, it is easy to increase the risk of deformation of the plate.


Improper welding temperature and process control:


The temperature during welding is too high or uneven, which may also lead to local overheating of the plate, causing the expansion of the material around the copper bar, causing deformation




Optimize welding process:


Control the welding temperature and time to ensure uniform temperature distribution and avoid local overheating. The use of appropriate welding techniques and tools to ensure uniform heat propagation and reduce the possibility of thermal stress.


FPCWay social figure for PCB welding example



Design suitable support structures:


Designing support structures near large copper bars or reducing the area of the copper bars in the PCB layout can help mitigate the risk of warping after welding. These support structures disperse the pressure caused by thermal expansion, reducing the risk of sheet deformation.


Increase sheet thickness or strengthen support:


Increasing the thickness of the PCB sheet or strengthening the support structure around the large copper bar can help reduce warping deformation. Thicker sheets can withstand greater thermal stress and reduce the possibility of deformation.


Material and structure optimization:


Select materials with a lower coefficient of thermal expansion to reduce problems caused by differences in thermal expansion. In addition, considering the influence of large copper bars on the plate in the design stage can reduce warping deformation by optimizing the structure.


Temperature control and cooling process:


After welding is complete, a gradual cooling process is used to evenly cool the sheet, helping to reduce the risk of warping.


Using auxiliary tools:


During the welding process, temporary auxiliary support tools can be used to ensure that the copper bar and sheet remain flat during the cooling process, reducing the possibility of deformation.


In summary, by optimizing the welding process, designing the structure and support, increasing the thickness of the plate, optimizing the selection of materials and reasonable temperature control and cooling process, the warping deformation caused by welding large copper bars can be effectively reduced or avoided.


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