Have you noticed that some boards are no longer flat after assembly? Or is the bare board you received not completely flush? PCB warping is a general term used to describe the irregular shape of a PCB, independent of the shape itself (bending, bending, twisting, etc.). A major challenge is that during the welding cycle, a board may transition from flat to warped, so it cannot always be held by hand. Therefore, the original shape may not be directly related to the shape of the PCB after welding. The warping in PCB and PCBA can cause problems during assembly or final implementation. We will delve into the reasons behind these two situations and how to prevent them.

PCB warping

When the exposed PCB is filled, it will enter the picker, which places the component on top of it to prepare for the welding process. When using warped boards, this unevenness may lead to improper placement or parts falling off. When a circuit board passes through a reflow soldering furnace, flatness is also important. These machines heat the board to a high temperature, which may alter the material and cause the board to warp. This may also lead to parts slipping, incorrect placement, welding bridges, or other welding issues.

PCB warping can lead to poor quality and low acceptability of the final product. Ensuring the flatness of the circuit board is crucial for preventing assembly related issues, including bridging or open connectors, which may ultimately lead to product failure.

The causes and prevention of PCB warping

The PCB is composed of different substrate layers that allow voltage and signals to pass through. The processing workshop uses many materials suitable for our industry. These materials have good thermal stability, resistance to ion migration, low dielectric constant, good processing performance, and no substrate drift. The current PCB manufacturing technology can ensure that the PCB warpage in all states during the PCB assembly process remains below 0.5%.

The welding process may be the biggest catalyst for plate warping. In reflow soldering furnaces or wave soldering machines, PCBs are exposed to high temperatures, causing material on the board to expand and contract. Due to the different coefficients of expansion between copper and the base material, there may be unequal amounts of expansion and contraction between the two, leading to the generation of internal stress. As a result, the board may warp when cooled and stabilized to its stationary state. Incorrect storage and handling can also lead to warping. If the circuit board absorbs moisture, it may cause the area to heat and cool at different rates, resulting in warping.

Other factors that may cause board warping may be actual design. In the design process, engineers must consider the balance between circuit area and conductor patterns, as well as the symmetry of circuit board stacking. If the working temperature of the PCB exceeds the rated temperature, it may also take effect. Finally, during the PCB manufacturing process, PCB products undergo multiple thermal drifts and heat treatments. When the processing temperature exceeds the Tg of the copper clad plate, the manufacturer must heat both sides of the substrate evenly and evenly, while keeping the processing time as short as possible to reduce substrate warping.

Conclusion on Warped PCB

A bent PCB can cause problems when picking and placing components. SMT components will not fall on the expected pads, components will not enter the expected holes on the board, components may slip off, or solder may bridge and short circuit. Irregular PCBA is difficult to install into the chassis, and reliability issues may arise on-site. All of these make it crucial for all stakeholders to make every effort to avoid PCB warping. To eliminate this issue, please ensure that the circuit board comes from a high-quality store, and the warehouse should pay attention to the handling and storage of circuit boards, especially in damp places. In addition, engineers can pay attention to ensuring the balance of the board in the design, or specify materials with higher Tg to better withstand different stresses. The circuit board processing factory explained that engineers shared the reasons for the warping of PCBA and PCB components, as well as solutions for PCB and PCBA warping.