In the current large-scale application of high-density interconnect (HDI) boards, the lamination process has always been the top priority for quality control. Whether it's smartphone motherboards, car system control boards, or advanced communication base station equipment, HDI technology is irreplaceable in improving integration and signal integrity. However, many manufacturers frequently suffer from issues such as warping, bubbling, blind hole cracking, delamination, and copper surface damage during HDI board lamination. These problems are not uncommon. Where is the problem? Many times, it's not a big problem with the equipment or design, but rather you may have overlooked a key auxiliary material - the compression buffer pad. Today we will delve into why HDI board lamination is prone to problems, and how to effectively improve lamination quality and product yield by selecting suitable cushioning materials.

Why is HDI lamination more 'fragile'? ——The natural challenge of high-density structure: HDI board (High Density Interconnect) achieves more compact wiring density and smaller aperture through the use of blind holes, buried holes, laser drilling micro holes, layered structures, and other processes. Although it brings high-performance advantages, its manufacturing process also brings many challenges, especially in the pressing stage: multiple layers and complex processes: HDI often adopts a layered structure of 1-3 or more, and each stage needs to be independently pressed once; Blind hole structures are prone to compression damage: especially laser blind holes, their edges are prone to cracking under high pressure; The thickness difference of the board is large: the layered structure causes uneven local stress; Copper surface is dense and small: it is easy to cause copper foil compression damage or delamination during lamination; High difficulty in size control: Multiple hot pressing leads to thermal expansion and stress accumulation. These characteristics determine that the HDI board pressing process must be more "gentle", "balanced", and "precise", and this is exactly where the cushion pad can show its strength.

In order to meet the high-precision and high complexity requirements of HDI lamination, the use of cushioning pads has become a necessary configuration. Its key role in the compression process is mainly reflected in the following four points:

1. Relieve pressure on blind holes and release stress more evenly; A high elasticity cushion can absorb some stress during hot pressing, reducing problems such as cracks and bubbles caused by stress concentration in blind hole areas, especially during second-order and third-order HDI compression.

2. Promote resin flow and fill fine structures; PI composite or high thermal conductivity non-woven fabric cushion can help evenly transfer heat to the inner resin, allowing it to flow fully and fill the laser hole walls and microstructure gaps, effectively preventing delamination and voids.

3. Assist in exhaust degassing to avoid air entrapment; The buffer pad has a certain "flexible channel" function, which can assist in the discharge of air and water vapor from the stack during the preheating stage, avoid bubbles and black spot defects, and improve the interface adhesion.

4. Restrain deformation and warping, and improve overall flatness; Reasonable configuration of thickness and elasticity buffer materials can release stress gradient differences during the cooling stage, greatly controlling board warping, especially suitable for high-frequency HDI boards with extremely high dimensional stability requirements.