With the rise of high-end applications such as 5G communication, artificial intelligence, and automotive electronics, PCB boards have increasingly more layers and more complex structures. For multilayer boards like 6-layer, 8-layer, or even 22-layer and beyond, the stability of the lamination process directly determines the performance and yield of the circuit board. Among these, an overlooked material—the lamination buffer pad—plays a crucial role in enhancing lamination quality.

Multilayer PCB is made by bonding multiple copper-clad laminates and pre impregnated resin layers (PP) through a lamination process. As the number of layers increases, the thickness of the board increases, the requirements for alignment accuracy improve, and the accumulation of thermal stress increases, resulting in a geometric multiple increase in manufacturing difficulty.

The lamination process mainly includes the following stages: laminated assembly: according to the design structure, the inner layer board, semi cured sheet, copper foil and other materials are stacked in order; Preheating stage: Slowly raise the temperature under vacuum or pressure, releasing water vapor and volatile substances; Pressure curing: Softening, flowing, and curing the resin at a set temperature and pressure; Cooling demolding: After cooling to room temperature, release the pressure and remove the formed multi-layer board.

During this process, any loss of control at any stage may lead to fatal defects such as blistering, delamination, warping, and crushing of the board. At this point, the "buffer pad" sandwiched between the hot press plate and the PCB stack plays a crucial role in regulating, protecting, and stabilizing.

The primary function of a cushion pad is to provide pressure relief and balance: through a flexible structure, it automatically fills gaps and bridges the height difference between the hot plate and the sheet metal; Effectively disperse pressure to avoid leaving marks on the copper surface or causing wiring breakage; Reduce resin accumulation or voids caused by uneven stress. For example, when using an un-cushioned pressing process to produce 12 layer copper-clad laminates, the finished product often experiences local pressure damage or inner layer displacement; After introducing 0.8mm high elasticity composite pad material, such problems were almost eliminated, and the yield increased by about 10%.

Multi layer PCB lamination requires melting the resin inside the PP, allowing it to flow and fill the gaps within a controlled time, and then completing the curing process. The temperature responsiveness of resin directly determines the bonding effect. The second major function of the buffer pad is to serve as a thermal conduction medium, assisting in the transfer of heat from the hot plate to the PCB layers and improving temperature uniformity. Some high-performance cushioning pads, such as PI composite pads or high thermal conductivity silicone pads, have good thermal conductivity, which can make the entire pressing process heat up more evenly;

For the phenomenon of "thermal gradient" (excessive temperature difference between upper and lower layers) in high-rise boards, cushioning pads can alleviate it to a certain extent; At the same time, it can also avoid the occurrence of voids or delamination in certain areas due to insufficient heating causing resin to not flow properly.

During the lamination and cooling process, multilayer boards are prone to warping deformation due to differences in thermal expansion and contraction of materials, particularly in cases such as large panel dimensions, irregular structures, and metal core composite boards. The fourth key function of buffer pads is to provide deformation compensation during hot pressing and cooling: by moderately "yielding to deformation" during heating or cooling stages, buffer pads can offset a portion of thermal stress; reduce stress differential transmission between core boards and copper foils, thereby improving board flatness; and are especially suitable for high-Tg and low-CTE material combination boards, helping to mitigate the effects of thermal expansion and contraction.

It is worth noting that the buffer pad cannot completely eliminate warping issues caused by structural asymmetry, but it is indeed an effective auxiliary means for optimizing deformation control. By selecting cushion materials with appropriate elastic coefficients and combining them with precise temperature control procedures, the bonding deformation range can be maximally controlled within ±0.5mm.