Choosing the proper PCB materials is crucial for ensuring optimal circuit performance, and long-term reliability. The materials used in PCB construction directly influence electrical performance, thermal stability, manufacturing costs and product longevity. With the growing sophistication of electronic devices, knowing your PCB material becomes increasingly important to having a successful design. In this guide, we delve into the most common PCB materials used, with regard to unique properties and use performance characteristics. In addition to this, we’ll also discuss the key considerations to make when choosing materials to ensure you make informed decisions for the next PCB project.
Exploring the Materials Behind the Four Key Layers of a PCB
As you select materials for your PCB, it’s helpful to understand how each layer of the board contributes to overall performance. A typical PCB involves four basic layers that have different material requirement and functionality.
Silkscreen Layer: This is the top layer of a PCB, where labels, symbols and other identities are printed. This layer is usually made of epoxy ink or liquid photoimageable (LPI) ink, typically in white or other colors. It allows manufacturers to mark component placements, test points, and other details.
Solder Mask Layer: Beneath the silkscreen is the solder mask layer, which is made from a polymer-based material, typically green epoxy. This layer shields the copper traces from oxidation and helps prevent short circuits by covering most of the PCB’s surface.
Copper Layer: Made of high-purity copper foil, this conductive layer forms the circuit traces and planes. PCBs typically have one or more copper layers, depending on the complexity and type of the board. The copper is laminated onto the substrate and patterned to create traces, which serve as the pathways for electrical signals between components.
Substrate Layer: PCB substrate provides mechanical support, generally, it is made of FR4 (a glass reinforced epoxy laminate), known for its durability and insulation capabilities. Common other PCB substrate materials include FR2, Rogers, and Polyimide.
7 Common Types of PCB Materials
Getting to understand the different PCB material options is important in circuit board design. Here’s a comprehensive overview of the most important PCB materials and their applications:
FR-4
FR 4 is the most commonly used material that combines woven fiberglass cloth with an epoxy resin binder. It is both mechanically strong and electrically insulating with moderately good thermal resistance, all at an economical price. FR-4 is a common material used in general purpose electronics ranging from consumer devices to industrial equipment and works fine for both single and multi layer PCBs.
Polyimide
Polyimide is commonly chosen for high temperature and flexible applications, and is usually selected for aerospace, automotive and medical devices. Its thermal stability (up to 260°C), chemical resistance and remarkable mechanical flexibility make it very suitable for harsh environment as well.
PTFE (Teflon)
PTFE is specialized for RF and microwave applications, which has a low dielectric constant and minimal signal loss, thus ensuring stable signal transmission at high frequencies. Although more expensive and with more specialized manufacturing processes required, it is essential for use in high frequency applications where signal integrity is key.
Metal Core
Commonly used materials for metal core PCBs are aluminum and copper, both of them are featured with enhanced heat dissipation. Aluminum core PCBs are cost effective for thermal management of LED lighting and power supply, while copper core PCBs are more suitable fore applications that need to handle high power.
CEM Materials
CEM-1 and CEM-3 are cost effective alternatives to FR-4. CEM-1 employs paper based laminate for simple one layer applications while CEM-3 employs fiberglass reinforcement for better performance. For budget conscious project with basic performance requirements, these materials are ideal.
Ceramic Substrates
Ceramic PCBs (with aluminum oxide or nitride) are highly thermally conductive and electrical insulating, designed for the most extreme environments. Their superior thermal performance makes them suitable for military, aerospace and high power electronics applications where reliability under the most extreme conditions is required.
Rogers PCB Materials
Rogers materials have excellent consistent dielectric properties and minimal signal loss at high frequencies, making them invariable for advanced RF and microwave applications, telecommunications, radar systems, satellite communications. Even with higher costs, they are the first choice for applications needing high frequency characteristics.
To help you compare these PCB materials at a glance, the table below summarizes key properties of each type:
| Material | Tg (°C) | Dk (Dielectric Constant) | Df (Dissipation Factor) | Thermal Conductivity |
| FR-4 | 130-180 | 4.2-4.8 | 0.015-0.02 | 0.2-0.3 W/m·K |
| Polyimide | 200-260 | 3.5-4.2 | 0.002-0.008 | 0.12-0.28 W/m·K |
| PTFE (Teflon) | 200-260 | 2.1-2.5 | 0.0005-0.001 | 0.25 W/m·K |
| Metal Core (Al) | 150-180 | 4.0-4.2 | 0.015-0.02 | 1.0-3.0 W/m·K |
| Metal Core (Cu) | 150-180 | 4.0-4.2 | 0.015-0.02 | 5.0-7.0 W/m·K |
| CEM-1 | 110-130 | 4.5 | 0.03 | 0.15-0.2 W/m·K |
| CEM-3 | 110-130 | 4.5 | 0.03 | 0.2-0.25 W/m·K |
| Ceramic (Al2O3) | >200 | 9.5-10 | 0.0001-0.001 | 25-170 W/m·K |
| Rogers | 280-300 | 2.2-10.2 (varies by grade) | 0.001-0.004 | 0.5-1.5 W/m·K |
Key PCB Material Properties and Performance Impact
- Dielectric Constant (Dk)
The Dk value represents how much an ‘electric flux’ concentrates in a material. For high frequency applications lower Dk values (typically 2.5-4.5) are preferred because they reduce signal propagation delay and cross talk. The most commonly used PCB material, FR4 has a Dk around 4.2-4.8; high performance Rogers Materials can reach a Dk as low as 2.2.
- Thermal Conductivity
Thermal conductivity is the property that defines a material’s capacity to transfer heat through it, which is typically measured in Watts per meter-Kelvin (W/m·K) or W/m·°C. It can range from 0.2 W/m·K for standard FR-4 to greater than 3 W/m·K for thermal enhanced substrates. For applications that experience significant heat generation, higher thermal conductivity is necessary for efficient thermal dissipation and the protection against component failure.
- Glass Transition Temperature(Tg)
The temperature at which the material starts to soften, and lose its rigid properties, is called the Tg. Tg of standard FR4 is usually in the range of 130–140°C, and can be high as 170–180°C for high Tg materials. Above Tg, the PCB board may have issues including delamination, warpage, and even board failure.
- Moisture Absorption
Moisture absorbed can cause the board to swell, warp, delaminate, increase electrical leakage and decrease dielectric strength. Lower moisture absorption rates are a critical factor in preventing performance degradation and reliability problems. The standard FR-4 absorbs around 0.1 to 0.3 % moisture, high performance materials can get below 0.1 %.
- Dissipation Factor (Df)
This property indicates how much electrical energy a material loses during signal transmission. In simpler terms, it measures how well an insulating material can maintain electrical energy. This is something that must be considered when working with high speed digital and RF circuits. All PCB materials are going to absorb some energy when a signal moves thru. For FR4 material, this number is typically on the order of 0.015.
- Coefficient of Thermal Expansion (CTE)
CTE measures dimensional changes with temperature variations. For reliable PCB performance, the CTE should closely match that of copper (17 ppm/°C) to prevent stress on plated-through holes and component connections. FR-4 typically has a CTE of 50-70 ppm/°C in the x-y plane.
Factors to Consider When Selecting PCB Materials
- Circuit Function and Purpose
First, consider what you want to do with your PCB and how it will be used: what is the operating environment, durability needs, temperature tolerance, and limits on performance. Moreover, your prototype design should account for environmental stresses and performance demands specific to your application.
- Thermal Management
Modern electronic products have multiple functions, and it is undoubted that a lot of heat will be generated during the operation of the equipment. Therefore, when choosing PCB materials, it is important to consider thermal conductivity materials that are suitable for your power requirements, which is crucial for effective heat dissipation and ensuring that the equipment maintains normal operating temperature.
- Mechanical Strength
When selecting materials, it is vital to choose one that can keep the structural integrity throughout its operational life. So, before making the choice, evaluate both the electrical and mechanical strength needs. For micro-electronic applications consider Coefficient of thermal expansion.
- Signal Performance
Evaluate your application’s specific needs – does it involve high frequencies, substantial power requirements, dense component placement, or microwave signals? Each type of circuit demands materials with particular electrical characteristics that align with the signal specifications.
- Flexible or Rigid?
If your design needs to connect across multiple planes or fit into tight spaces, you might want to explore hybrid boards that combine both rigid and flexible sections. Consider whether your project would work better with conventional rigid boards or if it requires circuits that can flex and adapt to certain configurations.
- Material Cost
The choice of materials can greatly impact manufacturing expenses. Enhanced features such as gold-plated surfaces, complex via structures, or filled vias will raise costs. Consider alternative surface treatments that offer good protection at lower prices while meeting performance needs.
Start Your PCB Project Right: Consult UnityPCB’s Material Experts
Choosing the right materials is essential to the success of your PCB project. At UnityPCB, our experienced engineers partner with clients from the initial stages to recommend the best materials, stackups, and design practices to ensure seamless manufacturing. We have expertise in a broad spectrum of advanced PCB materials and offer cost effective solutions for every project unique requirement. With UnityPCB’s cutting edge facilities, rigorous quality control and skilled team, you get high quality PCBs fulfilling the toughest standards. To meet your PCB design and manufacturing requirements, contact us today and find out how we can help with your project.
