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How to Choose Blank Circuit Board Material

How to Choose Blank Circuit Board Material

Blank circuit board material must match its application needs. That’s because different materials have different characteristics. For instance, FR4 offers excellent mechanical strength. However, it has higher dielectric losses than high-frequency boards, such as ceramics. Read on for more, including selecting the best material for your project.

What are Blank Circuit Boards Made of?

As its name suggests, a blank circuit board has no components. In the electronics world, we call it a PCB (printed circuit board) and a PCBA (printed circuit board assembly) when mounted with parts.

The board only has the primary material — the substrate — and the copper pattern that forms the conductive pathways. It’s also commonly coated with a solder mask, silkscreen, and conformal coating for added protection.

FR4 blank circuit board
FR4 blank circuit board
Resource: https://www.researchgate.net

Blank Circuit Board Material Types

The core of a blank PCB can be of different materials, such as FR4, glass, or a flexible plastic film like polyimide (Pi) or Teflon (PTFE). These materials, together with their properties, are listed below. They include:

FR4

FR in FR4 means flame retardant, denoting the material’s ability to “self-extinguish” and prevent fire propagation. It’s typically an epoxy resin strengthened with glass fibers.

Paper-backed FR variants, such as FR1, FR2, and FR3, are also available. These offer lower-level properties, making FR4 the most popular blank circuit board material. Below are its main characteristics.

  • Good rigidity and other mechanical characteristics
  • A high glass transition (Tg) temperature of between 130 and 140 (and up to 180 for high-Tg variants)
  • Low dielectric losses between 0.015 and 0.035
  • Stable dielectric constant of 4.4
  • Low thermal conductivity

CEM

CEM (Composite Epoxy Material) combines woven glass fabric with resin and a paper core. Like FR, CEM has variants, including CEM1, CEM2, and CEM3.

CEM is a lower-grade material. However, it’s a less expensive alternative to FR4 and suitable for less demanding applications and single-layer circuit boards. It has the following properties.

  • It has a Tg value of between 135 and 140
  • Lower thermal conductivity than FR4 at 0.25-0.35 W/(m K)
  • A dielectric constant of 4.6
  • Higher dielectric loss than FR4 ranging from 0.02 to 0.0035

Ceramics

Ceramics are a group of materials made from aluminum compounds, such as aluminum oxide and aluminum nitride. Others include silicon carbide, beryllium oxide, and boron nitride.

With a higher ability to withstand heat, ceramics present a good option when manufacturing a blank circuit board for high-temperature uses. Their primary properties include:

  • High dielectric constant that makes them an excellent choice for high-frequency circuits
  • Exceptional thermal conductivity for high-temperature applications
  • Remarkable insulation for electrical leakage prevention
  • Good resistance to chemicals

Polyimide

Polyimide belongs to a group of flexible PCB materials. Others include Teflon (PTFE) and polyester film (PET). Polyimide and Teflon are the most popular types. Starting with polyimide, here are its fundamental characteristics.

  • High flexibility without breaking
  • High resistance to chemicals
  • Low dielectric losses of between 0.003 and 0.006
  • A dielectric constant of 3.3
  • High glass transition temperature of above 250
  • Low thermal conductivity of 0.12-0.15 W/ (m K)

Teflon

Teflon, or PTFE, is a heat-resistant material that can also be flexible, making it a great choice when manufacturing flexible circuit boards. Here are its other qualities.

  • High Tg value that ranges from 160 to 280 C
  • Remarkable heat resilience, from as low as -196 to over 250
  • Low thermal conductivity ranging between 0.44 and 0.95 W/ m K
  • Chemical resistance allowing use around corrosive materials
  • Superior insulation properties and low dielectric losses
  • Stable dielectric constant (2.1 to 2.6) across different frequencies

Metal Core

A metal core blank PCB material has a metal core beneath its dielectric layer. The metal is typically aluminum or copper. Copper has the best properties; however, it’s a more costly option, making aluminum a better choice.

Metal offers exceptional thermal conductivity, heat dissipation, and higher rigidity and structural integrity than other materials. Metal-backed substrates have these properties.

  • Exceptional mechanical strength (up to 4 times stiffer than standard resin substrates)
  • Remarkable dimensional stability in different environments
  • Excellent thermal performance with a conductivity rate of up to 7 W/m K
  • Longer lifespan than most other substrates

Glass

A glass circuit board has a glass base instead of the usual FR or CEM series and metal types. The glass can be of different types, including borosilicate, aluminosilicate, or fused silica. Glass circuit board material has these characteristics.

  • Up to 3-5 times the thermal conductivity of FR4
  • High heat resilience of above 200 C
  • Low CTE (coefficient of thermal expansion)
  • Superior chemical and moisture resistance
  • Superb insulation and low dielectric losses even at high frequencies
  • High flexural strength
Aluminum blank circuit board
Aluminum blank circuit board
Resource: https://www.youtube.com/watch?v=6N_E6Uv7GyE

How to Choose Blank Circuit Board Material

Choose your blank circuit board material based on your project needs. As we have seen, each material has unique characteristics that make it suitable for specific applications. When selecting your blank PCB material, consider the following.

Mechanical Strength

Mechanical strength measures the board’s robustness and indicates its ability to withstand manufacturing and application stress. It also shows its durability level.

Mechanical properties include tensile strength (stretch resistance), flexural strength (ability to resist bending), and peel strength – or how firmly the copper layer attaches to the substrate.

Rigid materials won’t bend or stretch easily, while flexible types like polyimide and Teflon can absorb shock and vibration better. Higher peel strength means a more durable board in high heat and moisture conditions.

Electrical Performance

A PCB is an electrical device. As such, you want its material to have good electrical properties for better power and signal transmission. Ask yourself these critical questions:

Does the material’s impedance remain stable with frequency increase? This property is a measure of its dielectric constant. How quickly does it lose power (dissipation factor)?

What is the material’s resistivity within its structure and along the surface? Electrical strength measures how well the material can hold up in high voltages and must be used to select the best material for your needs.

Thermal Performance

Evaluate your blank circuit board material for the following thermal properties based on your project’s needs: CTE, Tg, and decomposition temperature.

CTE (or coefficient of thermal expansion) refers to the material’s heat expansion rate. Tg (glass transition temperature) refers to the temperature at which the material will become rubbery and pliable.

Decomposition temperature is the temperature level that can cause the material to decompose. It indicates the PCB’s ability to withstand extreme heat without failing.

Chemical Resistance

Various chemicals, such as fluxes and cleaning solutions, can damage PCBs during production. Application environments may expose it to corrosive materials, including gases and fluids.

Blank circuit board materials undergo tests to check their ability to resist methylene chloride absorption (MCA). It should also adequately resist moisture, depending on whether you need it for low or high-humidity conditions.

Cost Consideration

Some materials cost more than others. Depending on your project’s budget and board use requirements, choose a material that will cost you less without compromising performance.

For instance, polyimide has better qualities than Teflon. However, it’s a more expensive option and only necessary if you’re making a PCB for extreme conditions involving high temperatures, bend cycles, and more.

Rigid-flex blank PCB
Rigid-flex blank PCB
Resource: https://www.youtube.com/watch?rvo_APqPmGw

Rigid Vs. Flex Blank PCB

When making a blank PCB, the choice between a rigid and flexible material will usually arise. Flexible boards use a bendable base. Rigid types do not. When choosing between the two, you need to understand the benefits and drawbacks of each.

Rigid boards offer higher mechanical stability but can only fit larger spaces. Flexible circuit boards can fold to a desired shape, allowing you to install them in a confined space. They also excellently resist vibrations and shocks.

It’s also good to understand that flex PCBs are more expensive to fabricate than their rigid counterparts and will cause additional costs if you intend to use them.

You may also need to combine rigid and flexible boards on your blank PCB. Your blank PCB board supplier can guide you on the best choices for your project based on its specific requirements.

Conclusion

Choosing a suitable material for your blank circuit board is crucial to your project’s success. As we have seen, the material can be rigid or flexible. Other essential characteristics include its mechanical, thermal, and electrical properties. You also want the material to be reasonably priced and aligned with your project requirements and budget.

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