In the manufacturing of multi-layer PCBs, the success or failure of the lamination process directly determines the yield and performance stability of the product. In the lamination process, a crucial auxiliary material that is easily overlooked is the compression cushion pad (Cushion Pad/Press Pad), which often determines whether the finished board is "flat, non foaming, and non pressure damaged". This article will systematically explain "how to choose a cushion pad" from five aspects: the principle of cushion pad, material selection, matching strategy, common problems, and selection suggestions. It will help you improve the quality of compression and make your multi-layer board more stable and flat!

The working principle of the compression buffer pad: the "pressure regulator" hidden in the hot pressing system 

The laminated cushion is located between the rigid hot press plate and the PCB stack during the lamination process. Its core function is to regulate pressure, evenly transfer heat, cushion displacement and stress, and assist resin flow and exhaust.

Especially in the production of special PCBs such as high layer numbers, HDI structures, embedded copper, and thick copper, there are large differences in material thickness and narrow compression parameter windows. A suitable buffer pad can not only effectively absorb stress and compensate for uneven thickness, but also reduce risks such as copper foil compression damage, core board delamination, and bubble inclusion. The specific functions are as follows:

Uniform pressure transmission: improve the consistency of the force on the upper and lower pressure plates, reduce local "hard pressure" or "suspension";

Improve interface adhesion: assist in the flow of resin inside the semi cured sheet, enhance interlayer bonding strength;

Buffer thermal expansion and contraction stress: reduce problems caused by thermal stress such as warping and cracking after lamination;

Protect the copper surface and circuit: avoid direct compression of the metal to prevent indentation or wire breakage.

In other words, the buffer pad is the "invisible pressure regulator" in the entire hot pressing system, especially suitable for multi-layer board and HDI board manufacturing scenarios that require high precision and complex structures.

In the face of complex and ever-changing PCB lamination requirements, selecting a suitable lamination buffer pad requires consideration of product characteristics, process adaptation, cost control, and stable delivery time from multiple perspectives. Here are some practical suggestions for PCB manufacturers:

Conventional 6-12 layer board: It is recommended to use aramid or non-woven cushioning pads to balance cost and performance;

HDI/High Layer Number Board (>14 layers): Use PI composite pads or high elasticity rubber pads to improve alignment and bonding effects;

Thick copper/embedded copper/irregular structural plates: Priority should be given to customized cushioning materials with strong buffering capacity and precise positioning;

Trial production sampling stage: using an adjustable thickness buffer pad combination with alignment holes for easy validation of the process window;

Environmental protection/dust-free requirements: Choose low volatility, powder free polymer cushioning materials to avoid contaminating finished products.

With the increasing demand for multi-layer, ultra-thin, and rigid flex composite boards, the future development direction of cushioning pads will evolve towards high elasticity, high thermal conductivity, low pollution, intelligent monitoring, and other directions. For example, the introduction of digital temperature control response materials or visualized pressure labels for cushioning pads is becoming a new trend in high-end manufacturing.