Printed Circuit Board(PCB) Material Types and Comparison

PCB base material is an important part of PCB. It determines the PCB board performance and scope of application. Different products have different requirements on the PCB base material. With the development of electronic technology, PCB base material meet more and more challenges, which also push the development of copper clad laminate(CCL).

What is CCL?

The structure of CCL

Copper Clad Laminates (CCL), also known as cores, are sheets of rigid material made by impregnating glass fiber cloth or other reinforcing materials with resin, covering one or both sides with copper foil and laminating together in a hot press. They form the main structure of rigid printed circuit boards, giving PCBs their thickness and strength.The structure of the copper clad laminate can be divided into three layers: base layer, copper foil, copper clad laminate adhesive:

1.Baseplat

The substrate of the core is composed of polymer synthetic resin and reinforcing material. There are many types of synthetic resins. Commonly used are phenolic resin, epoxy resin, polytetrafluoroethylene and so on. There are generally two types of reinforcement materials: paper and fiberglass cloth.

2.copper foil

Copper foil is an important material for the manufacture of copper clad laminates, which must have high conductivity and good weldability. This helps reduce the impedance of the circuit and facilitate welding of components. It is required that the surface of the copper foil shall not have scratches, blisters and wrinkles, the metal purity shall not be less than 99.8%, and the thickness error shall not exceed ±5um.3.adhesive for the copper clad laminate

The adhesive is the key to whether the copper foil can be firmly covered on the substrate. The peel strength of the copper clad laminate mainly depends on the performance of the adhesive.

The role of CCL

CCL mainly plays the role of interconnection, insulation and support in the PCB, and has a great influence on the transmission speed, energy loss and characteristic impedance of the signal in the circuit. Therefore, CCL largely determines the performance, quality, processability, manufacturing level, manufacturing cost, and long-term reliability and stability of the PCB.

Types of CCL: Rigid CCL and Flexible CCL

Generally speaking, CCL can be divided into two categories: Rigid Copper Clad Laminate and Flexible Copper Clad Laminate.Rigid Copper Clad Laminate can be divided into different types according to different factors such as insulating material, thickness, and reinforcing material. There are also many different types of Flexible Copper Clad Laminate.

Rigid Copper Clad Laminate

Divided by insulating material and its structure

• Organic resin copper clad laminate
• Metal base (core) copper clad laminate

Metal-based copper clad laminates are generally composed of three parts: a metal substrate, an insulating medium, and a conductive layer (usually copper foil). That is, one or both sides of a metal substrate whose surface has been chemically or electrochemically treated are covered with an insulating dielectric layer and copper foil, and then composited by hot pressing.

• Ceramic base copper clad laminate

The ceramic base copper clad laminate is composed of a ceramic substrate, a bonding layer and a conductive layer (copper foil). There are many types of ceramics.

Divided by the thickness of the CCL

• Conventional board

The thickness of the conventional board is not less than 0.8mm.

• Thin board

The thickness of the thin plate is less than 0.8mm. However, the IPC standard defines the thickness of the thin plate to be less than 0.5mm. Epoxy resin glass fiber thin board can be used for punching processing, and glass fiber cloth thin board can be used for inner core board of multilayer PCB.

Divided by reinforced materials used by CCL

• Electronic glass fiber cloth base copper clad laminate

Electronic grade glass fiber cloth has the characteristics of good electrical insulation, fire retardant, waterproof, aging resistance, weather resistance, high strength and high modulus.

• Paper-based copper clad laminate

The paper-based copper clad laminate is made of impregnated fiber paper as a reinforcing material, impregnated with a resin solution and dried, then covered with glued copper foil, and then formed by high temperature and high pressure lamination. The most common paper-based copper clad laminates are: FR-1, FR-2, FR-3, (flame retardant) and XPC, XXXPC (non-flame retardant).

• Composite base copper clad laminate

Mainly refers to the insulating base material composed of two different reinforcing materials for the surface layer and the core layer. In addition, different copper clad laminates can also be divided according to the insulating resin used in the copper clad laminate or according to the flame retardant grade and other some special properties.

Flexible Copper Clad Laminate

• Polyester film type (flame retardant and non-flame retardant)
• Polyimide film type (flame retardant, non-flame retardant, two-layer method and three-layer method)
• Ultra-thin electronic glass fiber cloth type

Flammability of CCL

Flammability is an important reference for evaluating PCB performance indicators. It is necessary to classify CCL based on flammability. According to flammability characteristics, we can divide PCB into UL-94 VO, UL-94 V1, UL-94 V2, UL-94 HB.

UL-94 HB:

Normal cardboard (non- fireproof, the lowest grade material, cannot be made as power plate). The UL 94 standard is a test method standard for the combustion performance of materials developed by the American Underwriters Laboratory. “UL94 HB Class” is the lowest level of the classification of the combustion performance of materials in the UL94 standard.

UL-94 V0:

flame retardant cardboard, 22F: single-sided fiber glass board CEM-1: single-sided fiber glass board CEM-3: double-sided half-glass board.

CCL with high Tg

Tg is the vitrification temperature, you can treat it as melting point.

The circuit board must be resistant to burning. The board cannot be burned but it will be soft when heated. At this heated temperature point is called vitrification temperature.

The vitrification temperature (Tg point) is related to the durability of PCB. So what is the advantage of high-Tg PCB circuit boards? High-Tg PCB will be from the glass state into rubber state When the temperature rises to a certain degree. So the Tg number is referred to maximum temperature (℃) that PCB can still be rigid. Normal PCB base material at high temperature will become softening, deforming, Melting , also get much worse performance in the mechanical, electrical characteristics.

Normal PCB material Tg point is 130 ℃. Tg point for high Tg PCB is generally greater than 170 ℃. For medium Tg PCB, Tg point is around 150 ° C.

With high Tg point, high-Tg PCB has better heat resistance, moisture resistance, chemical resistance, stability and other characteristics. TG

In the lead-free processing, the high-Tg PCB get wider application because lead-free processing need higher temperature than processing with lead.

With the rapid development of the electronics industry, especially in the computer as the representative of the electronic products, electric engineers want PCB with the smaller vias, fine lines, lower thickness, it also need High-Tg material. High Tg PCB is significantly better than normal FR-4 base materials. But the price will be higher.

Aluminum board is a kind of metal base copper clad board with good heat dissipation ability. And the single layer panel is composed of three layers: circuit layer (copper foil), insulating layer and the metal base. The double-sided board is used in high-end design consist of circuit layer, insulation layer, aluminum based, insulating layer, circuit layer. Multilayer Aluminum board is rarely seen. Normally we recommend you to use single layer Aluminum board, 2 or more layers Aluminum board is very expensive.

For those who need to prototype pcb, if you want to customize your PCB material, you can contact Seeed Studio Fusion customer service for more information.