Date: 2026-07-04 hits: 102
The deformation reasons in the PCB board processing are very complex and can be attributed to two types of stresses: thermal stress and mechanical stress. Thermal stress mainly occurs during the lamination process, while mechanical stress primarily arises from board stacking, handling, and baking processes. Below is a brief discussion in the order of the process flow.
Copper-clad laminate incoming material: Copper-clad laminates are all double-sided boards with symmetrical structures and no graphics. The CTE (Coefficient of Thermal Expansion) of copper foil and glass fiber is nearly identical, so deformation caused by different CTEs rarely occurs during lamination. However, due to the large size of the copper-clad laminate press, temperature differences exist in different areas of the heating plate, leading to slight variations in resin curing speed and degree across different regions during lamination. Additionally, there are significant differences in dynamic viscosity at different heating rates. This results in local stress caused by variations in the curing process. Such stress generally maintains equilibrium after lamination but is gradually released during subsequent processing, causing deformation.
Lamination: The PCB lamination process is the main source of thermal stress. Deformation due to differences in materials or structure is analyzed in the previous section. Similar to copper-clad laminate lamination, local stress from curing process variations also occurs. Due to reasons such as greater thickness, diverse graphic distribution, and more prepreg layers, PCB boards experience more and harder-to-eliminate thermal stress compared to copper-clad laminates. The stress present in the PCB board is released during subsequent processes such as drilling, profiling, or baking, leading to board deformation.
Solder mask and legend baking processes: Since solder mask ink cannot be stacked during curing, PCB boards are placed upright in racks for curing. The solder mask curing temperature is around 150°C, which exceeds the Tg point of medium and low Tg materials. Above the Tg point, the resin is in a highly elastic state, making the board prone to deformation under its own weight or strong airflow from the oven.
Hot air leveling: For standard boards, during hot air leveling, the solder pot temperature is 225°C~265°C, with a time of 3S-6S. The hot air temperature is 280°C~300°C. The board enters the solder pot from room temperature and undergoes post-treatment water washing at room temperature within two minutes after exiting. The entire hot air leveling process involves rapid heating and cooling. Due to differences in circuit board materials and non-uniform structure, thermal stress inevitably occurs during heating and cooling, leading to micro-strain and overall deformation or warpage.
Storage: During the semi-finished stage, PCB boards are generally stored vertically in racks. Improper adjustment of rack tightness or stacking of boards during storage can cause mechanical deformation. This is particularly severe for thin boards below 2.0mm.
In addition to the above factors, there are many other factors that affect PCB deformation.
