Press cushion pads play several crucial roles in the PCB/CCL/FPC lamination process.

Press cushion pads play several crucial roles in the PCB/CCL/FPC  lamination process.

Uniform Pressure Distribution

Compensating for unevenness of hot press plates: In practical production, the surface of hot press plates is not perfectly flat, with slight irregularities or deformations. cushion pads are elastic and compressible. When pressure is applied by the hot press plates, the cushion pads can fill the gaps between the hot press plates and the PCB boards. For example, if there is a slight depression in a certain area of the hot press plate, the cushion pad will be compressed more in this area, thereby transmitting the pressure to this region and ensuring that the PCB board is uniformly stressed as a whole. Common paper press pads, with their uniform paper fiber structure, can effectively disperse the pressure and prevent defects such as indentations and delamination of the PCB board caused by uneven local pressure.

Balancing the pressure between multiple layers: During the lamination of multi - layer PCB boards, there may be slight differences in the thickness and material of each layer, which can cause deviations in the pressure transmission between layers. cushion pads can redistribute the pressure, ensuring that each layer receives appropriate and uniform pressure. For instance, in the lamination of rigid - flex PCBs, due to the different pressure - bearing and transmission characteristics of the flexible and rigid parts, cushion pads can adjust the pressure to ensure a tight and uniform bond between the flexible circuits and the rigid substrate, avoiding over - compression damage to the flexible parts or poor bonding of the rigid parts.

Thermal Conduction Regulation

Slowing down the heating rate: At the beginning of the lamination process, an excessively fast heating rate may lead to uneven heating of different parts of the PCB board, causing thermal stress concentration in the inner layers and resulting in problems such as inner layer slippage and blistering. cushion pads can act as a thermal cushion, reducing the speed at which heat is transferred from the hot press plates to the PCB board, allowing the PCB board to heat up slowly and evenly. Some cushion pads made of special rubber materials have a relatively low thermal conductivity and can effectively control the heating curve. In high - temperature lamination processes, when the temperature exceeds 260°C, ordinary materials cannot meet the requirements, while cushion pads with good high - temperature resistance (such as RCX - K 25 cushion pads made of specific fiber materials) can stably play the role of slowing down the heating process at high temperatures.

Promoting uniform temperature distribution: cushion pads can also promote the uniformity of the temperature on the surface of the PCB board during the heat conduction process. When heated, they can transfer heat relatively evenly to all positions on the surface of the PCB board in contact with them. For example, silicone cushion pads, with their good thermal conductivity and uniform texture, can ensure that heat is evenly distributed from the hot press plates to the PCB board, reducing the phenomenon of inconsistent local curing degrees of the PCB board caused by temperature differences, making the overall curing effect of the PCB board uniform, and improving the stability of electrical performance.

Protection and Isolation

Preventing mechanical damage: During the lamination process, relative displacement or friction may occur between the hot press plates and the PCB board, as well as between multiple PCB boards, which is likely to cause scratches, abrasions, and other mechanical damage to the circuits, copper foils, and other components on the surface of the PCB board. As an intermediate isolation layer, cushion pads can effectively avoid such direct mechanical contact. For example, during frequent lamination operations, red  silicone pads, with their soft and tough properties, separate the hot press plates from the PCB board,    protecting the fine circuits on the surface of the PCB board and reducing the risk of open circuits and   short circuits of the circuits caused by friction, thus extending the service life of the PCB board.

Avoiding chemical contamination: Some cushion pad materials are chemically inert, which can prevent impurities and chemical substances that may exist on the surface of the hot press plates from migrating to the PCB board, avoiding chemical contamination of the PCB board. This is particularly important for PCB boards used in high - end electronic products (such as aerospace, medical equipment, etc.) that are sensitive to chemical impurities. For example, cushion pads made of fluoroplastic release film not only play a cushioning role but also, due to their good chemical stability, can prevent prepregs from sticking and protect the prepregs from contamination, ensuring the purity of the PCB board during the lamination process and ensuring that its electrical performance is not interfered with by chemical impurities.