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 irregular PCB shapes, independent of the shape itself (bending, bending, twisting, etc.). A major challenge is that during the welding cycle, a plate may transition from flat to warped, so it cannot always be grasped by hand. Therefore, the original shape may not be directly related to the shape of the PCB after welding. Warping in PCBs 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 enters the handler, 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. The flatness is also important when the circuit board passes through the reflow soldering furnace. These machines heat the plates to high temperatures, which may alter the material and cause the plates 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 that are 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 largest catalyst for plate warping. In the reflow soldering furnace or wave soldering machine, the PCB is exposed to high temperature, resulting in the expansion and contraction of the materials on the board. Due to the different coefficients of expansion between copper and base metal, 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 resting state. Improper 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 pattern, as well as the symmetry of circuit board stacking. If the working temperature of the PCB exceeds the rated temperature, it may also have an effect. Finally, during the PCB manufacturing process, PCB products have undergone multiple thermal drifts and heat treatments. When the processing temperature exceeds the Tg of the copper clad plate, the manufacturer must evenly and evenly heat both sides of the substrate while keeping the processing time as short as possible to reduce substrate warping.