With the rise in technology, PCB plays a significant role in modern electronics. It helps to provide the necessary connections and integration between all the required electronic components and allows them to work together. In addition to this rapid technological advancement, selecting PCB materials is the most important task. The proper selection of the suitable PCB materials ensures the electronic devices’ overall performance, longevity, and reliability. Thus, it is one of the most crucial steps in the PCB industry.
In this article, you will know about PCB materials, their properties, and factors to consider while selecting the best PCB materials according to your requirements.
Basics of PCB Designs
When designing a circuit board, the choice of materials is based on the electrical and environmental properties required for its operation. The circuit’s schematic determines the number of layers and the size of the board. The PCB supplier provides a stack-up of selected materials based on the design.
The substrate is the material that supports the components and traces on the PCB. Copper is used to create conductive paths for electrical signals. Solder mask is a protective coating applied to the board, except for areas where soldering is needed. Silkscreen printing adds decals and reference designators on the PCB, helping with component identification, test points, and more. The ink used is typically white, sometimes black for white substrates.
There are additional technical terms related to PCB construction. The annular ring is the copper ring around the drilled holes. Design rule check is a verification process for manufacturability. Blind and buried vias connect layers in the PCB without holes. Traces are conductive paths for signals. The surface mount refers to components placed and soldered using automated equipment. Plated-through holes are drilled holes with added copper plating.
When building a PCB, the selection of materials is crucial based on the electrical requirements. The substrate supports components and traces, while copper creates conductive paths. Solder masks and silkscreen printing provide protection and component identification. Various technical terms relate to specific aspects of PCB construction, such as connections, verification, and drilling.
Properties of PCB Materials
The major property of any PCB material is its properties to conduct electricity. The base material copper, used as PCB material, is a popular choice because of its higher conductive nature. Other electrical properties like dielectric, constant, and loss tangent also impact the PCB performance and the signal transmission in the circuit board.
Below are all the electrical properties that must be considered while selecting the PCB materials.
|The dielectric constant of a PCB material affects its impedance and signal integrity. It should remain constant over various frequencies, especially for applications including high-speed and high frequency.
|Relative permittivity is another term for the dielectric constant.
|Surface resistivity measures how well a dielectric material resists the flow of charge on its surface. It can changeable with respect to moisture and the temperature. Higher surface resistivity is desirable for having a better level of signal integrity.
|Volume resistivity refers to the resistance to electric current within the volume of a dielectric material. Higher volume resistivity keeps isolation between various layers.
|The dissipation factor determines the signal loss within the circuit board. It is a major concern for high-frequency analog signals as it is directly proportional to frequency.
|Electrical strength measures a PCB’s ability to withstand electrical breakdown in the z-direction (perpendicular to the layers).
During the working operations, PCB dissipates heat; thus, thermal management system is an important and crucial aspect of PCB materials. The rate of heat dissipation directly depends on the nature of PCB materials. The materials, with low coefficient of thermal expansion and good thermal conductivity, ensure their stability under various temperatures. Besides, other factors like glass transition temperature and thermal decomposition temperatures also affect the thermal properties of PCB materials.
|Glass Transition Temperature
|In this temperature, the PCB substrate changes from a hard to a soft state. It should be minimum than the temperature of the solder.
|In this decomposition temperature, PCB substrate permanently decomposes. For the PCB materials, it should be minimum compared to solder temperature.
|Coefficient of Thermal Expansion
|The rate at which a PCB expands or contracts with respect to change in temperature. It is preferable to have a low coefficient of thermal expansion.
|The measure of a material’s ability to conduct heat. Conductors generally have higher thermal conductivity compared to insulators.
The mechanical properties determine the longevity and durability of PCB. Mechanical properties like high tensile strength, impact resistance, and flexural strength affect the withstand nature of PCB. Below are some of the popular mechanical properties of PCB that are crucial in PCB materials.
|Bending (Flexural) Strength
|Bending strength refers to a PCB’s ability to resist deformation or breakage when subjected to bending stress. It is important to adhere to the standards outlined in IPC-6013C for rigid, flex, and rigid-flex boards.
|Time to Delamination
|Time to delamination measures how long the layers of a PCB will remain attached when exposed to temperature changes or moisture.
|Density is the measure of the amount of mass per unit volume for a dielectric material used in a PCB.
|Peel strength refers to the ability of the copper layers and dielectrics in a PCB to remain bonded even under thermal and chemical stress.
Finally, chemical properties are important for PCB performance, requiring materials resistant to chemicals, moisture, and corrosion to maintain integrity during manufacturing, assembly, and everyday use.
When selecting materials for PCBs, consider factors such as moisture absorption, flammability rating, and chemical resistance to ensure optimal performance.
|Methylene Chloride Resistance
|Typically, dielectrics have an MCR of less or equal to 0.2%.
|Water Absorption (in terms of %)
|Water absorption represents the moisture a PCB material can absorb when submerged. Most materials have a water absorption value of ≤ 0.2%. This can impact the both thermal and electrical properties of the dielectric.
|PCB materials must meet the requirements of the Standard Flammability of Plastic Material, which limits the burning time to 10 seconds per specimen with respect to combustion.
Types of Materials Used in PCB
FR-4, commonly known as FR4, is a cost-effective and highly adaptable material. It is manufactured from prepreg layers, consisting of fiberglass matting infused with epoxy resin. FR-4 is regarded as the industry standard due to its ease of drilling and metallization. Moreover, it enables the economical production of PCBs while delivering satisfactory performance, particularly at RF/microwave frequencies.
FR4 offers better electrical insulations with higher dielectric strength. It has a high strength-to-weight ratio. Besides, it is lightweight and one of the best choices.
Rogers Corporation is a well-known company that produces top-quality materials for printed circuit boards (PCBs). They have a diverse selection of products designed to meet different applications’ unique needs. Among their popular materials are the RO4000 and RO3000 series. These are particularly applicable that require high frequencies, higher temperatures, and better reliability.
Roger PCB provides robust mechanical strength, making them suitable for applications requiring rigidity and durability. Rogers materials minimize signal loss and distortion at high frequencies due to their low dielectric constant (Dk) and low loss tangent (Df) values.
These materials have high thermal stability, with high glass transition temperatures (Tg) and low coefficients of thermal expansion (CTE). It ensures consistent performance even at higher temperatures. Rogers provides a diverse range of materials useful for specific applications, including high-temperature and high-frequency.
Teflon PCB is gaining popularity in the PCB industry as it is high-performance PCB material. It is quite famous among PCB materials because of its excellent electrical properties with a lower dielectric constant (DK). This property has helped the Teflon PCB to be used in high-frequency and microwave applications.
Teflon PCB offers lower signal loss even at high frequency because of its low dielectric constant and low-loss tangent nature. Besides, it also offers a high glass transition temperature that helps to maintain its structural integrity at extreme temperatures. It offers a wide range of chemicals that make it suitable for extreme environments. On the other hand, Teflon PCBs are expensive compared to other PCB materials like CEM-3 and FR-4. In addition to this, Teflon PCBs are difficult to process during the fabrication process of PCB. This is due to its unique properties that result in its longer lead time and higher manufacturing costs.
It is a top-notch material for PCBs best for its exceptional properties like chemical, mechanical and thermal. It is widely used in applications where flexibility, reliability, and high temperature are crucial. This thermosetting polymer helps in dimensional stability. It offers high thermal stability. Therefore, it helps to maintain performance and structural integrity even at extreme temperatures.
The other contribution of this polyamide material is its flexible nature, because of which it is one of the perfect choices for flexible circuit boards. It is resistant to various chemicals. Thus, it is better for extreme environments also. There are some backsides of this polyamide material, and it is quite expensive compared to other PCB materials like FR-4. It is challenging to process the PC using this polyamide material because of its resistance to high temperatures and unique properties.
In terms of composition and performance, CEM-3 is a well-liked PCB material. It provides great mechanical strength, thermal stability, and electrical insulation since it is made of glass fibers embedded in an epoxy resin. It is sometimes used as an affordable substitute compared to FR-4
The benefits of CEM-3 is its overall strong performance and its suitability for a variety of applications due to its similar qualities of mechanical, and electrical to those of FR-4. Additionally, it offers a less expensive alternative to FR-4, making it ideal option with limited budgets.
There are restrictions to take into account, though. Because CEM-3’s Tg is lower than FR-4’s, its usage in extreme temperature applications may be constrained. Additionally, similar to FR-4, because of its dielectric constant it might not perform at its best in high-frequency or high-speed applications.
Particular PCB Materials
It is specially developed for applications that demand precise signal integrity at high frequencies. These materials are specifically designed with low-loss tangent and dielectric constant enabling them to reduce distortion and uphold signal integrity.
These materials are designed to withstand extreme temperatures without compromising reliability or performance. They have a low coefficient of thermal expansion and high glass transition temperatures. R04835 is one example of high-temperature PCB material.
The major property of this kind of PCB material is exceptional thermal stability and enhanced reliability. These kinds of PCB materials are designed to bear harsh operating environments and thus provide reliability and longevity in extreme conditions.
Metal Core PCB (MCPCB)
It incorporates a metal base layer that offers mechanical strength and superior thermal management. It is commonly made of copper/aluminum and efficiently dissipates heat from electronic components. This also finds extensive use in various applications, including automotive electronics, LED, etc.
It provides a better thermal management system. The core metal dissipates the heat from the CPB components. Thus, it results in better reliability and lower operating temperatures with better reliability. Besides, it provides mechanical strength that provides enhanced strength and rigidity.
It is a special type of PCB material that is designed and used in specific applications. It consists of multiple layers of flexible PCBs like polyamide. They are attached to a rigid PCB layer. These kinds of PCBs are used in aerospace, military and medical applications. The popular flexible circuit materials include R03000 and RO4000 since they have lower dielectric losses at microwave frequencies.
In a rigid-flex PCB, the rigid sections provide support and stability for components, while the flexible sections allow the PCB to bend or flex during operation or when fitted into tight spaces. This flexibility eliminates the need for connectors and wiring, reducing assembly time and potential points of failure.
Factors to Consider While Selecting PCB Materials
Choosing the appropriate PCB material is essential for achieving electronic devices’ best performance, reliability, and cost-effectiveness. When selecting a PCB material, various factors come into play, and each factor impacts the overall performance of the end product.
Below are some factors to consider while selecting PCB materials:
Electrical qualities must be taken into account when choosing PCB materials. First, You must ensure that the material you select can withstand the necessary electric current. Since different materials have different conductivity levels, it’s critical to choose one that can withstand the maximum current that will pass through the PCB.
You must take the material’s dielectric constant into account in addition to its capacity to handle current. The material’s capacity to store electrical energy when an electric field is applied depends on its dielectric constant. It is a crucial factor in figuring out how well the PCB will conduct electricity, especially regarding signal integrity and transmission effectiveness.
Depending on the application, a different dielectric constant will be appropriate. A lower dielectric constant is frequently desired for high-frequency PCBs to reduce signal loss and attenuation. Conversely, a greater dielectric constant might be preferable for power applications to boost capacitance and energy storage capability.
It can be easier to guarantee dependable performance and ideal functioning by properly analyzing your PCB materials’ electrical needs.
Glass transition temperature (Tg) and thermal conductivity must be considered when evaluating an electric device’s thermal performance.
The ability of a PCB material to dissipate heat produced by electrical components is greatly influenced by its thermal conductivity. The material lowers the possibility of thermal breakdowns and increases the device’s lifespan by effectively dispersing heat.
A PCB material’s glass transition temperature is also significant. The ability of a material to resist high temperatures without losing its mechanical stability is indicated by a greater Tg. Because of this, it is especially well suited for applications that operate in extremely hot or hot settings.
Thus, considering the selected PCB material’s thermal conductivity and glass transition temperature is necessary to evaluate a device’s thermal performance. These elements guarantee effective heat dissipation and the capacity to tolerate extreme temperatures.
Some key mechanical properties of PCB materials include tensile strength, impact resistance, and flexural strength. Tensile strength measures the ability of materials to bear the stretching forces. While impact resistance evaluates the ability of materials to bear sudden impacts. The mechanical strength is tested under thermal stress, chemical exposure, and high temperatures.
Flexural strength evaluates the ability of a dielectric material to withstand physical stress without breaking, while the tensile modulus (or Young’s modulus) measures its resistance to stress and strain. Density is quantified by grams per cubic centimeter (g/cc) or pounds per cubic inch (lb/in^3). The time to delamination indicates how long it takes for the layers of a PCB to separate when exposed to high temperatures, thermal shock, or moisture.
While it is essential to prioritize the electrical, thermal, mechanical, and chemical performance of PCB materials, it is equally important to find a balance between meeting performance requirements and managing costs.
When evaluating the cost and availability of PCB materials, it is crucial to consider the whole process of electronic device, including factors such as manufacturing, assembly, and maintenance costs. Choosing a material that is cost-effective and readily accessible can ensure a smooth project execution and reduce the likelihood of delays or exceeding the budget.
Environmental Considerations in PCB Material Selection
When choosing materials for PCBs, it’s crucial to consider their environmental impact throughout manufacturing. It requires sustainable and eco-friendly practices. Some of the key environmental points to consider includes:
Waste management is a crucial process in minimizing the environmental impact on PCB production and disposal systems. Electronic waste is also a global concern that releases hazardous substances into the environment. Thus, e-waste should be managed and disposed of properly.
Particularly in terms of the materials’ toxicity, the composition of materials can considerably impact the environment. Thus, while selecting PCB materials, choose those free of hazardous substances, like halogen-free and lead-free. Be aware of local and international regulations regarding the use of hazardous substances. And finally, make sure to work with a PCB manufacturer committed to less use of toxic materials.
By considering these factors, we can make more environmentally conscious decisions in selecting and using PCB materials.
A crucial step in designing and manufacturing electronic products is selecting the proper PCB material. It greatly impacts the finished product’s performance, dependability, and price. Engineers can make well-informed decisions that guarantee the best results for their projects by understanding the various PCB materials. The selected materials should have the properties like electrical performance, thermal performance, mechanical strength, chemical resistance, and environmental considerations. To meet the constantly changing demands of the electronics industry, it will be crucial to develop new and specialized PCB materials.
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