The Ultimate Guide To Circuit Board Material Selection

PCBs are as good as the materials used in manufacturing them. Therefore, this implies that the performance and functionality of a printed circuit board depends on the type of material they are made from. With the increasing demand for miniaturization of devices and cutting-edge technology, it is incredibly important to choose the right type of circuit board material.

There are a huge range of circuit board materials that can meet your performance requirements. Quality circuit board materials don’t only offer great functionality, but also have great durability. In addition, proper material selection is good way to start your PCB manufacturing.  Also, there are parameters and factors that determine the type of material to use for your PCB project.

This comprehensive guide will help you discover the best quality and most common types of printed circuit board materials.

What are Circuit Boards Made of?

Selecting a board material requires considering certain things.  PCBs comprise some crucial layers. What are circuit boards really made of?

Substrate layer

The substrate layer is the foundation of the printed circuit board. It is usually manufactured from fiberglass. Fiberglass is a very rigid materials, hence, it offers PCB rigidity. However, there are other materials used for substrate. This includes epoxies, CEM-1, G-11, insulated metal substrate, FR-1, and polyimide. Substrates are specially made to meet some requirements like dielectric constant and glass transition temperature. Fiberglass, which is popularly known as FR-4, is the most commonly used material for substrates.

Conductive layer

The copper layer is the conductive layer that makes signal traces. These signal traces conduct electricity in the circuit. Also, copper is a common material used for the conductive layer of a printed circuit board. Other materials like gold and silver can also be used. However, the conductive layers of PCBs are mostly made of copper. This is because copper is a good conductor of electricity.

Solder mask layer

Solder mask comprises a thin layer of polymer. It is on top of the copper clad laminate. Also, the solder mask gives the printed circuit board the green color. This layer prevents the formation of solder bridges by helping PCB manufacturers to solder the appropriate areas on the board. Also, the solder mask prevents conductive copper traces from having contact with metal, solder, and other conductive materials.

Silkscreen layer

Silkscreen is an epoxy ink usually printed on the board. Also, it is a reference designator that indicates where to place components on the circuit board. Furthermore, it helps in detecting some warning symbols. A silkscreen helps to detect manufacturer marks and test points. Also, silkscreen is mostly white in color.

Types of PCB Substrate Materials

FR-4

FR4 is the most commonly used PCB substrate material. It is an epoxy resin laminate sheet reinforced with glass. Also, the epoxy of this material is flame retardant and water resistant. The “FR-4” simply means flame retardant level 4. Also, FR-4 has a high tensile strength and glass transition temperature. Therefore, this substrate can reach about 1180oC. Furthermore, this material is ideal for rigid PCBs.  

FR-2

This substrate material has the lowest performance. FR-2 means flame retardant level 2. It comprises phenolic material. Also, FR-2 is commonly used in simple consumer electronics like small low cost radios.

FR-1

FR-1 is ideal for single-sided PCBs. It is a flame retardant level 1 material which is paper-based. It is similar to FR-2 as they both have identical properties. . However, FR-1 features a higher temperature value.

Teflon (PTFE)

Teflon is an extremely flexible material that provides no resistance and as such, it is ideal for high speed signals. Also, Teflon is a type of plastic that features high mechanical strength, high degree of insulation,  and flame resistance.

Flexible substrates

Flexible substrates can foldable and bendable materials that can form desired shapes. Also, these substrates enable designers to create circuit boards that can fit into the smallest enclosures. Rather than using epoxy resin or fiberglass, flexible substrates integrate plastic films.

 These substrates are usually made with materials like liquid crystal polymer (LCP), polyimide, and polyester. In addition, polyimide is the most common material used for flexible substrates.

Metal substrates

Metal substrates are commonly made of aluminum. They offer great thermal and high dielectric properties. Also, aluminum can withstand temperatures of 350 degrees Celsius. These substrates provide exceptional high frequency performance. Therefore, it is ideal for applications like wireless communication base stations, RF sector, and LED lighting.

Other PCB Substrate Material Types

Asides from the materials mentioned above, there are other types of PCB substrate materials.

Fine ceramic

Examples of fine ceramic substances include aluminum nitride and aluminum oxide. Fine ceramic features great endurance when used in environments with high temperature. Also, ceramic compounds feature low CTE, high decomposition temperature, and high glass transition temperature.

CEM1

The composite epoxy material 1 (CEM1) has a whitish color and is usually integrated in printed circuit boards with a conductive layer. CEM1 is a material sandwiched between phenol substances and a glass fiber epoxy layer. Also, CEM1 features similar dielectric properties with FR-4. However, this material is cheaper than FR-4.

LTCC

Low temperature co-fired ceramics (LTCC) is commonly used for multilayer PCB manufacturing. Also, this circuit board material comprises burnt aluminum oxide. It is possible to burn LTCC substrates at temperatures of about 900oC by simply adding glass materials to aluminum oxide. Also, LTCC substrates are ideal for high frequency RF modules.

Types of Solder Mask Material

Solder mask is a crucial layer in a printed circuit board.  It protects the exposed area of the copper. Also, solder mask is usually green in color. However, there are other colors like white, red, yellow, and blue. There are different kinds of soldermask materials based on how they are applied to the copper.

Epoxy liquid

This is a thermosetting epoxy usually applied through the silk screening method.  The epoxy liquid is not commonly used due to its low resolution and accuracy.

Dry film photoimageable

A dry film is ideal for flat PCBs having a uniform topography. You can use vacuum lamination to apply a dry film before development and exposure. Also, a dry film will always offer a uniform surface thickness. However, this type of soldermask is only suitable for flat boards.

Liquid photoimageable

The liquid photoimageable soldermask is ideal for circuit boards having unusual topography. You can apply a UV curable ink with the use of different coating techniques. This soldermask doesn’t offer a consistent layer, but it offer better contact with the copper traces. Also, it offers a better coverage. It is ideal for circuit boards with very complex surface features.

Types of Materials Used in PCB Conductive Layers

The three main materials used as a conductive layer in PCBs are copper, iron, and aluminum. Copper is the most commonly used material for conductive layers. This is a major reason most printed circuit boards are copper clad.

Copper foil

Copper foil is a highly conductive material and as such, it is widely used as a conductive layer in a PCB. Also, copper has good electrical conductivity and ductility. Also, the copper layer as a conductive layer offers exceptional thermal properties and tensile strength. Copper layer thickness is usually measured in ounces.

This conductive material plays a crucial role in PCB manufacturing as it features great thermal and electrical properties required for heat dissipation and signal transmission. Also, this material is more resistant to corrosion compared to iron and aluminum.

Aluminum

Aluminum serves as a good conductive layer in a printed circuit board. This material features high durability. Also, aluminum is a sturdy material with great thermal and electrical characteristics. The use of aluminum as the conductive layer of a printed circuit board eliminates accidental breakage risk. Accidental breakage can occur during manufacturing or handling.

Aluminum is a very easy to solder material. The thickness of aluminum ranges between 1 ounce to 10 ounces. Also, aluminum offers a conductive path for electronic components.

Iron

Iron is also a type of metal used as a conductive layer of a circuit board. This material features a good shielding effect and is ideal for surface mounting. Also, iron offers good heat dissipation and stability.

Dielectric and Electrical Properties of PCB Materials

The substrates and materials integrated in PCB manufacturing should feature excellent dielectric and electrical properties.

Dielectric constant

The dielectric constant measures the ability of a material to store electrons in an electric field. This property is crucial for substrates utilized in electronic devices. Also, dielectric constant refers to relative permittivity. Most circuit board materials feature a dielectric constant between the range of 2 and 4.6. The dielectric constant of a substrate helps in determining the performance of the printed circuit board in high frequency applications.

Volume resistivity

This defines the ability of a material to resist insulation. Also, it measures the resistance of an insulating material to leakage current via its body. High volume resistivity refers to low leakage current. Materials with high volume resistivity are less conductive.

Surface resistivity

This property measures the ability of the circuit board materials’ surface  to resist the transfer of electrical charge. Surface resistivity and volume resistivity are similar in measure, but their location of measurement is different. Temperatures and moistures are factors that affect surface resistivity.

Dissipation factor

Dissipation factor of PCB materials measures how inefficient an insulating material is. Also, it measures the amount of electrical energy lost and obtained when you apply electrical current to an insulating material. It describes the inefficiency of a printed circuit board material to act as an insulating material.

Thermal and Mechanical Properties of PCB Materials

Co-efficient of thermal expansion (CTE)

CTE measures the change in the size of a PCB material in relation to temperature. In other words, it measures a material’s expansion rate in response to temperature. A substrate that features high CTE will easily expand. Also, this property is crucial in multilayer boards. There could be a detachment between layers during temperature cycles if the substrates of these layers have various CTEs. A high CTE PCB material can expand with much greater force than the mechanical strength. This could cause chips or cracks.

Glass transition temperature (Tg)

The glass transition temperature is a thermal property that measures the temperature at which a circuit board material transforms into a ruber-like state. The material returns to its initial state when the temperature is below Tg.  This property helps in determining if a PCB material is ideal for rigid or flexible applications.  

Thermal conductivity

This is a thermal property that describes the ability of a printed circuit board material to transmit heat. A PCB material with low thermal conductivity has limited heat transfer capacity. Also, a material with high conductivity can transmit thermal energy.

Furthermore, thermal conductivity aids heat dissipation in a printed circuit board. High thermal conductive material can improve the PCB performance.

Peel strength

Peel strength describes the strength of the bond between a substrate material and conductive layer. This property measures the amount of force required in breaking a material bond. A peel strength test is usually carried out under certain conditions. You must expose the sample to molten solder at above 250oC to cause thermal stress.

Moisture absorption

Moisture absorption measures the ability of a PCB substrate to absorb moisture content. High moisture absorption affects the thermal and electrical properties of a PCB.

Factors to Consider when Choosing Printed Circuit Board Materials

The materials used in printed circuit boards are crucial in determining their performance. Circuit board materials should have exceptional mechanical, thermal, and electrical properties. Since there are a wide range of circuit board materials, it could be very challenging to determine the ones to opt for. Therefore, you should take some factors into considerations. These factors help you make right decisions.

Purpose of the PCB

When designing a board, you will need to know the requirements of the PCB application. Also, you should consider signal integrity requirements. What type of board will you need for the application? What purpose is it serving? Will the board need to tolerate high temperatures? It is important to answer these questions when choosing a PCB material.

Cost

Cost is one of the factors that determine the type circuit board material to use. Also, the type of PCB you will be designing will determine the type of material. PCBs that feature buried vias, gold surface finish, and via filling will require more expensive materials. However, some PCB manufacturers opt for cheaper alternatives when choosing circuit board materials.

Stackup

Stackup determines the design of the circuit board. Some materials aren’t ideal for double layer or multilayer boards. For instance, FR-1 and FR-2 are only ideal for single sided boards. On the other hand FR-4 and teflon are ideal for both single sided and multilayer boards. Therefore, the amount of layers on your PCB will determine the choice of your PCB material.

Signal integrity and mechanical strength

Some applications require materials that have electrical and mechanical strength. In high frequency applications, high power or high frequency PCB materials like FR-4, aluminum, and Teflon are ideal materials.

How Does Heat and Power Impact the Choice of PCB Materials?

Heat and power affect the choice of PCB materials in the following ways:

Thermal conductivity

Thermal conductivity is a crucial factor when choosing PCB materials. Materials that can dissipate heat faster are highly preferred in some applications. Ceramic substrates have better thermal conductivity than FR-1 and FR-4 materials.

Moisture absorption

The moisture absorption of a material will impact its electric and thermal properties. Most times, dielectric materials feature moisture absorption between the range of 0.01% and 0.20%. Printed circuit boards with low moisture absorption perform better

Methylene chloride resistance

This is also known as chemical resistance. It measures the capacity of a dielectric material to resist the absorption of methlyene chloride. Also, the methylene chloride of most dielectric materials ranges between 0.01% and 0.20%.

Brands of PCB Laminate Materials

Companies such as ISOLA, Taconic, Rogers, and Ventec manufacture PCB laminate materials. These materials can meet the requirements of high-speed and high performance applications. Let’s take a look at some of the PCB materials produced by these companies.

Rogers

Rogers PCB materials are widely used in high-frequency PCB manufacturing. They comprise properties that meet high frequency demands. Also, these PCB materials feature exceptional signal transmissions and electrical characteristics. Rogers printed circuit board materials are available in a wide range of dielectric constant. Below are some Rogers circuit board material options:

RO4000 Series

These materials are ideal for high frequency printed circuit boards. Also, they are primarily made from ceramic substances and hydrocarbon compounds. RO4000 series materials have similar processing procedures with FR-4. These materials are suitable for the fabrication of multilayer printed circuit boards and rigid PCBs.

Printed circuit boards comprising RO4000 series can operate at high frequency values with good impedance control.  Also, RO4000 series materials are widely used in applications like satellites, sensor and radar technology, and power amplifiers.

RO3000 Series

This series material comprises ceramic substances and polytetrafluoroethylene compounds. Also, these materials feature constant physical properties within a wide range of dielectric constant values. The CTE of these PCB materials is much lower than FR-4. As a result of mismatched CTEs, Rogers circuit boards suffer thermal strain. You will find RO3000 series in power amplifiers and surface mount technology RF components.

Isola

Isola PCB materials are available in various options.

FR406

This a fire retardant material that comprises epoxy-based laminate and a prepreg. Also, FR406 is widely used in multilayer PCB manufacturing. This PCB material offers improved board consistency in terms of size. Also, it features great thermal performance and CTE.  

G200

G200 material enables PCB manufacturers to produce printed circuit boards with high-efficiency and great reliability. Also, this Isola material is often integrated in panelization modes of multilayer PCB manufacturing.

IS415HR

This is an efficient PCB material used in the configurations of multilayer printed circuit boards. It is best suited for applications that require high signal quality. Its low reaction to temperature changes makes it an ideal material for multilayer PCB fabrication.

370HR

This is another flame retardant material by Isola. It is an FR-4 alternative for producing laminates and prepregs. Also, 370HR can function well at high temperature values with high glass transition temperature at above 170 degrees Celsuis. The integration of a glass fibre standard fortifies the resin-epoxy compound during the manufacturing process of this material. Also, the electrical, thermal, and mechanical properties of this material are better than FR-4 materials.

IS680-300

This is a PCB laminate material that features low dielectric loss. IS680-300 allows consistent performance levels within wider frequency limits and temperature. Also, this material is ideal for use in RF transmission circuits. It is a cheaper alternative for teflon.

Taconic

The Taconic Corporation manufactures PCB materials. Taconic materials vary in terms of their thermal, electrical, and physical properties. Also, these materials are usually based on fine ceramic substances, glass, and teflon. Examples of Taconic PCB materials include:

Taconic tly-5

This laminate material has a uniform dielectric constant and excellent dimensional stability. The dielectric constant of Taconic tly-5 measures at 2.20 while its dielectric thickness is 0.0050. Also, this materials is ideal for applications like cellular communications, amplifiers, and aerospace.

Taconic CER10

Taconic CER10 is a glass reinforced ceramic filled laminated. This material has uniform electrical properties. It is widely used in filters, couplers, and passive components. Furthermore, this PCB material features an interlaminar board. It is a dimensionally stable PCB laminate and as such, it is ideal for low-cost and high-volume applications.  Also, it features low moisture absorption and good flexural strength.

Taconic RF35

This is a ceramic-filled material with glass reinforcement. Taconic RF 35 is well suited for industrial applications like power amplifiers, passive components, and antennas. This Taconic material features low dissipation factor and efficient dimensional stability.

Conclusion

A standard printed circuit board comprises different types of materials. Electronic components are also materials used in PCB manufacturing process. Circuit boards comprise a huge variety of materials. However, there are certain factors that determine the choice of PCB materials. Such factors like electrical properties, thermal requirements, and mechanical features. Also, the application requirements will determine the type of material to use.