Multilayer PCB - What is pcb substrate made of?

What is pcb substrate made of?

First, the basic composition of the PCB printed circuit board (PCB) is a copper-clad substrate (Copper-clad Laminate, referred to as CCL) as a raw material for the manufacture of electrical or electronic components of the important institutions. Mainly by the copper-clad laminate (CCL), semi-cured sheet (PP), copper foil (Copper Foil), solder resist (Solder Mask). The structure is shown in the figure below.

1, Copper Foil Substrate

Copper Clad Laminate (CCL), referred to as Copper Clad Laminate (CCL) or Copper Clad Laminate (CCL), is the basic material for the manufacture of printed circuit boards, is a composite material consisting of a dielectric layer (resin, glass fibre) and a high purity conductor (copper foil). Now used more FR1, FR4, CEM3, ceramic boards and so on.

2, semi-cured sheet (PP)

semi-cured sheet, also known as PP sheet, is one of the main materials in the production of multilayer board. Mainly composed of resin and reinforcing materials, reinforcing materials are divided into glass fibre cloth (referred to as glass cloth), paper-based, composite materials and special materials and other types. The production of multilayer printed circuit boards used in the semi-cured sheet (bonding sheet) most of the glass cloth as a reinforcing material.

3, copper foil

Copper foil is deposited on the substrate layer of the circuit board is a thin, continuous layer of metal foil, which serves as a conductor of PCB, is bonded to the insulating layer, after etching to form the circuit pattern. Commonly used copper foil can be divided into two categories of calendered copper foil (RA) and electrolytic copper foil (ED).

4. Soldermask

Soldermask refers to the part of the printed circuit board that has soldermask ink. Soldermask ink colours are green, red, black and blue, etc. It is the protective layer of the printed circuit board.

Second, PCB board classification 1, to material points.

What is pcb substrate made of

What is pcb substrate made of?

Organic type of substrate: with reinforced materials, dipped in resin binder, through drying into a blank, and then covered with copper foil made of high temperature and high pressure. Phenolic resin, glass fibre / epoxy resin, polyimide resin, BT epoxy resin, etc. are organic materials.

Inorganic class substrate: mainly take its heat dissipation function. Aluminium, ceramic plate and enamel covered steel substrate.

2, to distinguish between hard and soft

Hard board: non-bendable, such as FR-4, ceramic substrate, used for most of the rigid PCB.

Soft board: bendable, such as PI, polyester (PET) substrate, used for FPC.

Combination of hard and soft boards: a combination of rigid and flexible materials, used for complex circuits that require partially bending and partially fixing (such as mobile phone camera module connecting lines).

3、Classified according to application scenarios

General-purpose substrates: FR-4, FR-2 and other epoxy resin substrates: suitable for most conventional electronic equipment.

High-frequency and high-speed substrates: PTFE, PPO, PI substrates: to meet the needs of 5G communications, millimetre-wave radar and other high-frequency signal transmission, reducing signal loss.

Heat dissipation substrates: metal-based (aluminium, copper), ceramic substrates for power devices, LEDs and other scenarios that require rapid heat dissipation.

Flexible Substrates: PI Flexible Substrates: Bendable and foldable, used for flexible screens, wearable devices FPC.

High Temperature Resistant Substrates: Ceramic Substrates, High Tg Epoxy Resin Substrates (Tg>170℃), PI Substrates, used for automotive engines, industrial high temperature equipment and other environments.

4、Classified by flame retardant grade

UL94 V-0 grade: excellent flame retardant performance, such as FR-4 substrate.

Non-flame retardant grade: such as phenolic resin substrate (FR-1, FR-2, etc., flammable, need additional processing).

5, with or without halogen

Halogen: the use of materials containing halogen elements (such as chlorine, bromine), common brominated flame retardants.

Halogen-free: the use of materials not containing halogen elements made of common alternative materials such as ammonium phosphate, nano-graphite, nano-magnesium hydroxide.

6, other special types of substrates

Buried capacitance / buried resistance substrate: integrated capacitance or resistance inside the substrate, reducing the size of the PCB, to improve integration, for high-density circuits.

Mixed material substrate: combining organic resin and inorganic filler (such as glass fibre, silicon micropowder) to optimize the dielectric properties and mechanical strength, such as composite substrates (CEM-1, CEM-3, etc.).

1、Glass transition temperature (Tg)

The glass transition temperature refers to the transition temperature corresponding to the change of the mechanical state of the substrate resin due to the increase of the ambient temperature, and the transition from the glassy state to the high elasticity state (rubbery state) under the condition of being heated.

High-performance boards with many layers, thick thickness and large area size should have better heat resistance or higher Tg temperature than conventional PCBs.

Increasing the Tg is one of the main ways to improve the heat resistance of FR-4. In general FR-4 resin formulations, the introduction of some trifunctional groups and multifunctional groups of epoxy resin or the introduction of some phenolic epoxy resin, to increase the Tg value to about 160-200 degrees.

FR-4 general Tg value of 130-150 ℃, Tg value of 150-170 ℃, high Tg value of 170 ℃ or more.

2, the coefficient of thermal expansion CTE

The coefficient of thermal expansion refers to the substrate material in the heat, its unit temperature rise between the linear change in the size of the substrate material caused.

Generally high Tg resin substrate material also has a low coefficient of thermal expansion.

The dimensional stability of copper-clad laminates depends mainly on the three raw materials that make up the laminates: resin, reinforcing materials, copper foil. Usually take the method is: to modify the resin, such as modified epoxy resin; reduce the proportion of resin content, but this will reduce the electrical insulation properties and chemical properties of the substrate; copper foil on the dimensional stability of copper-clad laminates have a relatively small impact.

what is pcb substrate made of

3, resistance to ionic migration (CAF) performance

Ion migration is between the positive and negative electrodes in the circuit board along the surface of the glass fibre conductive filament growth and insulation damage occurs, may cause a short circuit occurs.

With the PCB lines and holes are becoming more and more dense, the insulation distance is even shorter, which requires higher insulation performance of the insulating substrate. Especially in the humid environment, due to the moisture absorption of the substrate, glass and resin interface bonding for the weakest point, the substrate can be hydrolysed free ions slowly gathered, these ions in the electric field under the action of the electrodes to move between the formation of conductive channels, if the distance between the electrodes the smaller the formation of the channel the shorter the time, the faster the substrate insulation damage.

Hazards of ion migration:

Poor signal, performance and reliability of electronic products;

- Shorten the service life of electronic products;

- Increased energy consumption; insulation damage.

- Possible short circuit and fire safety issues.

4, dielectric constant DK

The dielectric constant determines the speed at which an electrical signal travels through a medium. The speed of electrical signal propagation is inversely proportional to the square root of the dielectric constant. The lower the dielectric constant, the faster the signal transmission speed. This parameter affects the impedance of the alignment on the PCB.