Have you noticed that some boards are no longer flat after assembly? Or have you received bare boards that are not completely flat? PCB warpage is a common term used to describe the irregular shape of a PCB, independent of the shape itself (bending, folding, twisting, etc.). One major challenge is that during the soldering cycle, a board may transition from flat to warped, making it difficult to hold by hand. As a result, the original shape may not directly correlate with the shape of the PCB after soldering. Warpage in both PCBs and PCBA can cause issues during assembly or final implementation. We will delve into the causes of these two scenarios and discuss how to prevent this problem.

PCB Warpage When a bare PCB is populated, it goes into a picker that places components on it to prepare for the soldering process. The unevenness caused by warpage in the board can lead to improper placement or component detachment. Flatness is also important during the reflow process, where the boards are heated to high temperatures, which can alter the materials and cause warpage. This can result in components slipping, improper placement, solder bridging, or other soldering issues.

PCB warpage can result in poor product quality and low acceptability. Ensuring the flatness of the PCB is crucial in preventing assembly-related issues, including bridging or open connections, which can ultimately lead to product failure.

Causes and Prevention of PCB Warpage PCBs are composed of different substrate layers that allow voltage and signals to pass through. The manufacturing facility uses various materials suitable for our industry, which have good thermal stability, resistance to ion migration, low dielectric constant, good processability, and no substrate drift. Current PCB manufacturing technologies can ensure that the warpage of PCBs during the assembly process is kept below 0.5%.

The soldering process can be a catalyst for board warpage. In reflow ovens or wave soldering machines, the PCB is exposed to high temperatures, causing materials on the board to expand and contract. Due to the different coefficient of thermal expansion between copper and the substrate, unequal expansion and contraction may occur, resulting in the generation of internal stress. As a result, the board may warp as it cools and stabilizes to its static state. Improper storage and handling can also lead to warpage. If the circuit board absorbs moisture, it may undergo heating and cooling at different rates, resulting in warpage.

Other factors that can contribute to board warpage may lie in the actual design. During the design process, engineers must consider the balance between circuit area and conductor patterns, as well as the symmetry of the PCB stack-up. If the operating temperature of the PCB exceeds the rated temperature, it can also play a role. Furthermore, during the PCB manufacturing process, the PCB product undergoes multiple cycles of thermal drift and heat treatment. When the processing temperature exceeds the Tg (glass transition temperature) of the copper-clad laminate, manufacturers must heat both sides of the substrate uniformly and evenly while keeping the processing time as short as possible to minimize board warpage.

Conclusion on Warped PCBs Warped PCBs can cause issues during component picking and placement. SMT components may not land on the intended pads, components may not enter the expected holes on the board, components may slip off, or solder may bridge and cause short circuits. Irregular PCBA is difficult to install in a chassis, leading to reliability issues in the field. All of these make it crucial for all stakeholders to make diligent efforts to avoid PCB warpage. To eliminate this problem, ensure that the circuit boards come from.