Why is the  Copper-clad Laminate  Hard?

There are 6 main reason for the hardness of the copper-clad laminate (CCL)

The hardness of the CCL is determined by six factors: resin system, filler content, glass fiber cloth, copper thickness, pressing process, and board specification. The harder the board, the better its rigidity, heat resistance, and dimensional stability. However, its toughness and drilling processing performance will decrease.

1. Resin system (the most critical factor)

High Tg high heat-resistant resin (hard)

FR-4, high Tg, FR-5, polyimide PI, BT resin, ceramic resin, halogen-free high rigidity resin have extremely high cross-linking density, with tightly packed molecular chains, and after curing, they have extremely strong rigidity, and the feel is noticeably harder.

The lower the resin content, the harder the board.

Resin is a flexible carrier, and glass fiber + filler is a rigid framework. Thin sheets / thick core boards with a resin content of 30% or less are very hard; boards with 45% or more high adhesive resin have a soft feel and can be slightly bent.

2. The addition amount of inorganic fillers (the main source of industrial hard boards)

To reduce the coefficient of thermal expansion CTE, improve heat resistance, flame retardancy, and dimensional stability, manufacturers will add a large amount of inorganic powders such as silica, alumina, aluminum hydroxide, and talc.

High-filler boards (high CTI halogen-free, high thermal conductivity copper-clad boards, vehicle boards) have a filler content of 20% to 50%, which are as dense and hard as cement; they are soft when the resin content is 45% or more and can be slightly bent.

Ordinary low-filler boards have less fillers and are dominated by resin, with a softer texture.

3. Specifications of glass fiber cloth

Glass fiber cloth is the framework of the board and directly determines its rigidity:

Thick glass fiber, high-density glass fiber are harder

1080 thin cloth is soft; 7628, 2116 thick glass fiber yarn, with a large weaving density, have a significant increase in rigidity under the same resin;

More layers of thick core boards (4 sheets of 7628 glass fiber pressed together) are much harder than a single 1080 thin core board.

4. Board thickness and copper foil thickness

Under the same material, the thicker the board, the harder it is: 0.8mm and 1.6mm thick boards have much greater rigidity than 0.05mm and 0.1mm thin cores;

Thick copper foil (2oz/3oz copper) increases the overall bending hardness of the metal layer, while thin copper 1/3oz board is softer.

5. Production pressing process

High temperature and high pressure for full curing

High pressing temperature and long holding time result in complete cross-linking of the resin, increasing the hardness; partially cured semi-finished boards are softer due to insufficient pressure and low temperature curing.

High pressing force

High pressure extrudes excess resin, making the board dense, high in density, and with a hard feel; low-pressure boards have more pores and excess resin, making them softer.

6. Classification of special functional hard boards

High thermal conductivity copper-clad boards (aluminum-based / ceramic-based CCL)

Ceramic fillers, alumina-based materials, have a hardness much higher than ordinary FR-4, and are almost impossible to bend;

Military / high-frequency PTFE, BT resin boards have a dense cross-linked structure, high rigidity, and low deformation;

Vehicle, high-frequency, halogen-free, high-filler boards, with a large amount of flame-retardant inorganic fillers, have a hard feel and are easier to drill and chip edges; ultra-thin ultra-thin core boards with an extremely high glass fiber ratio are hard and brittle, and a slight bend causes them to turn white and delaminate.