What are PCB substrates

PCB substrate is composed of resin, reinforced material and conductive material. Resin is more common with epoxy resin and phenolic resin. Reinforcing materials include paper base and glass cloth. The most commonly used conductive material is copper foil and copper foil. For electrolytic copper foil and rolled copper foil.
According to different materials (most commonly used classification methods)
Paper substrate (FR-1, FR-2, FR-3)
Epoxy glass cloth substrate (FR-4, FR-5)
Composite substrate (CEM-1, CEM-3 (Composite Epoxy Material Grade-3))
 HDI (High Density Interconnet) Boards (RCC)
Special substrates (metal substrates, ceramic substrates, thermoplastic substrates, etc.)
According to the resin
Phenolic resin board
Epoxy resin board
Polyester resin board
BT resin board
PI resin board
According to the flame retardant performance
Flame Retardant (UL94-V0, UL94V1)
Non-flame retardant (UL94-HB)
Among them, the FR-4 material is the most used in the market, so we will learn about FR-4 sheet separately. The

FR-4 (Flame Resistance Grade 4) is a code for the grade of flame resistant materials. It means a material specification that the resin material must extinguish itself in the burning state. It is not a material name but a material. grade. An important parameter in the FR4 sheet is called Tg, which is the Glass Transition Temperature (Tg). The Tg of the most commonly used Normal material is 140°C, 150°C, and 180°C, where Tg150 is a middle Tg material and Tg180 is a High Tg material.

PCB common substrate materials can be divided into two categories: rigid substrate materials and flexible substrate materials.

An important class of generally rigid substrate materials is copper clad laminates. It is made of reinforced materials, impregnated with resin binders, dried, cut, laminated to form blanks, then covered with copper foil, and used steel plates as the molds, which were formed by high temperature and high pressure forming in a hot press machine. The prepregs for general multi-layer boards are semi-finished products of the copper clad laminates (mostly glass cloth impregnated with resin and dried and processed).

Paper based CCL
Phenolic resin (XPC, XXXPC, FR-1, FR-2, etc.)
Epoxy Resin (FE-3)
Polyester resin
Glass Fiber Cloth CCL
Epoxy Resin (FR-4, FR-5)
Bismaleimide Modified Triazine Resin (BT)
Polyimide Resin (PI)
Diphenylene ether resin (PPO)
Maleic anhydride imine-styrene resin (MS)
Polycyanate resin
Polyolefin resin
According to the classification of fire-retardant properties of CCL, it can be divided into flame-retardant (UL94-V0, UL94-V1) and non-flame-retardant (UL94-HB) categories. In the past year or two, with the increasing emphasis on environmental protection issues, a new type of CCL that does not contain bromine has been identified in the flame-retardant CCL, which can be referred to as “green type flame-retardant CCL”. With the rapid development of electronic product technology, there are higher performance requirements for CCL. Therefore, from the performance classification of CCL, it is divided into general performance CCL, low dielectric constant (ε) CCL (also known as high-frequency circuit CCL), high heat resistance CCL (general board Tg above 150°C), Low thermal expansion coefficient CCL (usually used on package substrates) and other types.