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PCB/PCBA knowledge
The Ultimate Guide to High-Speed PCB and Housing Materials

High-speed Printed Circuit Boards (PCB) and housing materials are specially designed to manage electrical signals traveling through a circuit board at lightning-fast speeds while simultaneously dissipating the heat generated by devices during operation.

They are essential when designing circuit boards that can withstand the demands of high-speed data transmission. These materials have been specifically designed to meet the needs of modern electrical engineering projects with increased frequencies, higher speeds, and lower profile components. It is essential to carefully consider their characteristics to make the right choice for each application.

This blog post will discuss different high-speed PCB and housing materials available today. We will explain how certain characteristics make them more suitable for specific applications than others so you can choose the right one for your needs!

Table of Contents

High-Speed PCB Materials

A. FR-4

fr-4

FR-4 is a versatile material used in PCBs. It has high mechanical strength and dielectric properties, making it perfect for printed circuit board substrates. This flame retardant popular choice also offers good heat resistance and is oxidation resistant, providing long service life even in challenging environments like those in aerospace and defense applications.

Dielectric Constant and Dispersion
The propagation speed of signals on a PCB is determined by the material’s dielectric constant and interconnect parameters, such as trace geometry. FR4 laminates have dielectric constants ranging from 3.8 to 4.8; computing an effective dielectric constant for signal fields between traces on a board involves factors like trace and plane arrangement.

Advantages of using FR-4
FR-4 is a beneficial material for those working with circuit boards due to its lightweight and sound resistance combination. It is also unaffected by moisture, ensuring the circuit board remains insulated against electrical shocks regardless of the environment.

It also maintains excellent mechanical strength in dry and wet conditions, making it invaluable in industries with fluctuating climates.

Disadvantages of using FR-4
FR-4 comes with a few built-in limitations. If too much power, voltage, or heat is applied to the circuit that uses FR-4, then its dielectric properties will degrade and cease functioning as insulation. This places certain restrictions on the kinds of electronic systems that can be created with it, as they must stay within their operating limits or risk an electrical breakdown.

Applications of FR-4
FR-4 has many uses due to its flame resistance and excellent electrical insulation properties, making it an ideal choice for various applications. One such use is industrial wear applications. FR-4 protects from flames and corrosion, which can be used in areas exposed to corrosive materials or spark ignition.

Another everyday use of FR-4 is for electrical insulation, including screw terminal strips, transformers, arc shields, washers, and busbars. By providing insulation from electrical currents, electricians can feel confident that devices are safe from shock when using components made with this material.

B. Rogers 4350B

Rogers 4350B

Rogers RO4350B is a good choice for reliable, high-performance solutions for electrical insulation with good mechanical strength and low CTE values. It’s widely used to manufacture circuit boards, making it a reliable and cost-effective choice. At operating temperatures up to 260°C and frequencies up to 4 GHz, its combination of woven glass reinforcement and hydrocarbon/ceramic matrix can provide physical stability and excellent electrical properties.

Dielectric constant and dissipation factor
Rogers ro4350b is a well-rounded dielectric material for microwave and RF circuit development. Its high dielectric constant of 3.48 +/- 0.05 makes it ideal for improving the capacitance density of circuits, while its dissipation factor, which can range from 0.0031 – 0.0037, ensures frequencies up to 40 GHz can be matched with suitable impedance.

Advantages of using Rogers 4350B
Utilizing Rogers AD350A insulated material in 4350B products has many advantages, including low thermal expansion, improved capacitance, low signal loss, and higher voltage transmission. As a result, this material helps create PCBs that work with higher-frequency components and have less overall distortion. The material also provides high thermal conductivity for heat dissipation and excellent dimensional stability for easier circuit board fabrication.

Applications of Rogers 4350B
Highly reliable and long-standing, Rogers 4350B laminates are popular for many application needs. The RT/droid series provides superior performance from aerospace to defense compared to other industry alternatives. These laminates provide unique properties, making them an ideal choice for applications such as microwave and RF assemblies, high-frequency circuits, and printed circuit components.

Their excellent dielectric and thermal qualities give users a lengthy list of reasons why Rogers 4350B has become widely used in their industries.

C. Isola IS620

Isola IS620

IS620i is the first material to combine the flexibility of digital design and supply assurance with conventional FR-4 processing techniques. Designed for high-speed applications ranging from 2 to 15 GHz, IS620i performs with low loss across frequencies and a flat response.

Furthermore, its unique resin matrix formulation is available in laminate, prepreg form, and all typical thicknesses and sizes. With these properties, designers and fabricators can be assured that IS620i provides the best possible combination for their specific product needs.

Advantages of using Isola IS620
Isola’s IS620 dielectric material is a RoHS-compliant polyimide product that offers a great range of performance attributes, enabling advanced product designs.

This material has a high dielectric constant and low dissipation factor at various frequencies, offering significant advantages regarding processing. It is also known for its UV-blocking capabilities, providing benefits in better selection of AOI fluorescence due to its unique properties. For these reasons, it has become a popular choice for those looking for excellent results from their applications.

Disadvantages of using Isola IS620
Isola’s IS620 is designed to provide superior signal integrity and maximize reliability, yet there are some things that could be improved to using this material. One disadvantage of the Isola IS620 material is its weak bonds, which drilling heat can easily affect. This melt-induced debris solidifying on the hole walls leads to poor heat dissipation, resulting in degraded signals due to increased insertion loss.

While through holes can improve overall heat dissipation, they also negatively affect signal integrity as the extra stub acts as a reflecting path and reduces signal quality.

Applications of Isola IS620
Isola IS620 is a highly flexible substrate increasingly used for various industrial applications. It is frequently employed in millimeter-wave applications because it can efficiently conduct high-frequency signals with minimal loss. Furthermore, its low moisture absorption and low Coefficient of thermal expansion make it an ideal choice for use in space satellite transceivers.

IS620’s excellent electrical properties also make it the perfect choice for setups like E-band point-to-point microwave links, personal or healthcare monitors, medical scanners (MRI, Ultrasound, CT, and more), power indicators and control devices, industrial and measuring equipment, and scientific instruments (photometers, microscopes, and control systems).

High-Speed Housing Materials

A. Liquid Crystal Polymer (LCP)

Liquid Crystal Polymer (LCP)

Liquid crystal polymers, or LCPs, are an exciting class of materials that are rising in popularity due to their unique properties. By combining a highly structured molecular formation with superior mechanical strength and temperature and flame resistance, LCPs offer great potential for use in various sectors. Because the molecules at their core remain consistent in both solid and liquid phases, engineers can work with LCPs using traditional melt processing methods like injection molding.

Dielectric constant and dissipation factor at different frequencies
The dielectric constant for liquid crystal polymer (LCP) materials is steady near 3.16, regardless of frequency. That being said, the dissipation factor for such materials varies depending on the material’s frequency and grade. For example, at 1 GHz, the DF of unfilled Vectra A resin is around 0.0019, much lower than other rates tested, which generally hovers closer to 0.0042.

However, when looking at higher frequencies such as 20GHz, the material’s DF appears to even out between 0.0022 and 0.007, depending on the grade and filler used in LCPs.

Advantages of using LCP
Liquid Crystal Polymer (LCP) possesses many beneficial properties, such as high heat resistance, flame retardant qualities, excellent chemical resistance, impressive dimensional stability, moldability capability, and even heat aging resistance.

In addition to these remarkable qualities, LCP offers a higher level of adhesion when compared to other types of materials. It has become an increasingly popular choice for combination parts used in the automotive and aerospace industries.

Disadvantages of using LCP
Liquid Crystal Polymer also comes with some significant drawbacks. It often forms weak weld lines when extruded, which can affect the strength of its end products. Additionally, LCP is highly anisotropic due to its molecular orientation. This property affects dimensional stability and requires extra caution during production by controlling mold temperatures and other processing conditions to ensure the part meets desired specifications.

Its molecular structure requires that all traces of moisture be removed before processing. This additional requirement adds complexity and costs to any process involving LCP materials.

Applications of LCP
Liquid Crystal Polymer (LCP) has excellent heat resistance, chemical inertness, electrical properties, dimensional stability, and hydrolytic stability, making it perfect for parts manufacturing and other uses.
The aerospace industry also uses the material’s durability for aircraft components like airframes, engines, and cabin interiors.

In addition to industrial applications such as these, food containers manufactured with LCPs offer a tamper-proof seal that conserves the freshly packaged consistency of foods longer than those using other plastics or composites.

B. Polytetrafluoroethylene (PTFE)

Polytetrafluoroethylene (PTFE)

Polytetrafluoroethylene (PTFE) is an excellent artificial material known for its strength, longevity, and ability to withstand harsh elements. It boasts a nonflammable property and an ultra-sleek surface thanks to the high melting point – which also makes it heat resist at temperatures up to 500°F – and PTFE does not corrode or react with most chemicals.

Additionally, its high melting point allows multiple uses, such as commercial roofing and industrial bearings. Due to these fantastic properties, PTFE is used in countless applications, including aerospace engineering, medical appliances, furniture fabrics, automotive products, and many more.

Dielectric constant and dissipation factor at different frequencies
The dielectric constant and dissipation factor of polytetrafluoroethylene (PTFE), commonly known as Teflon, have been measured over frequencies from 102 to 105 cis. At room temperature, the dielectric result for PTFE was approximately 2.1, and its dissipation factor was 0.001, indicating it was an excellent insulator.

As the temperatures increased, both values gradually decreased until just before the first-order transition point, which occurred at 327 °C. This is due to additional free charges entering the material, creating more significant losses at higher temperatures and affecting the performance of PTFE as an insulator.

Advantages of using PTFE
PTFE is an incredibly versatile material with many advantages that make it highly desirable. From low friction and inert properties to its self-cleaning, durable nature, and effectiveness in high and low temperatures, PTFE can be used in various industries – all while being nonflammable and corrosive resistant. This remarkable material offers the potential for new and improved product solutions in many applications, making it an invaluable resource.

Disadvantages of using PTFE
One of the main potential disadvantages of using PTFE is its cost. Because it is a high-end polymer, selecting PTFE can increase prices significantly. Additionally, due to the design complexities associated with the manufacturing process, PTFE isn’t the most accessible material to mass-production.

Its tendency to change shape with temperature or pressure changes is equally concerning, which can interfere with proper board operation. Lastly, because PTFE doesn’t weld easily, it isn’t suitable for boards requiring regular soldering operations.

Applications of PTFE
PTFE, or Polytetrafluoroethylene, is used in myriad applications. Aerospace industry professionals rely on PTFE’s remarkable chemical resistance and low Coefficient of friction when constructing an aircraft’s components. This material also finds use in medical appliances and implants due to its non-reactive properties; these qualities make it a safe choice for surgical tools and implants that must remain in contact with bodily fluids.

Domestic uses such as furniture fabrics, flooring tiles, carpet treatments, and automotive parts are prime uses of PTFE because of the material’s excellent stain resistance, durability, and waterproofing capability.

C. Liquid Silicone Rubber (LSR)

Liquid Silicone Rubber (LSR)

Liquid Silicone Rubber, or LSR, is an incredibly versatile and reliable material used in the elastomer industry. It can be injected into a mold cavity to produce a single part and then cured using a platinum catalyst, creating a permanently solid, flexible item ideal for various uses, from consumer products to medical devices.

Its durability has made it one of the most popular materials for producing high-quality parts with excellent longevity, especially in more demanding applications, making it an indispensable choice in manufacturing.

Dielectric constant and dissipation factor at different frequencies
Liquid crystal polymers (LCPs) are known for their unique dielectric properties, often containing values for the dielectric constant that range from 2.9 to 4. This feature provides superior electrical insulation performance and high signal transmission speeds on both internal and external components in electronics.

LCP’s dissipation factor also ensures that no heat is generated when used with electric machinery, as power losses are minimal due to low energy loss rates. Even when subjected to harsher conditions with higher electricity flow, LCP material can successfully maintain its optimal performance levels due to its excellent thermal stability and superior load-bearing capacity.

Advantages of using LSR
Liquid silicone rubber (LSR) is an incredibly versatile material with many advantages. Outstanding chemical inertness makes it useful for many applications where contaminant exposure is a concern. LSR has superior resistance to bacteria, UV light, ozone, and radiation compared to other materials.

The transparency and clarity provided by this rubber can improve lighting and illumination effectively, while the ability of gas permeability makes it an excellent choice for preventing deterioration quickly. The high elongation offered by this product means that it adequately maintains its shape and physical properties when used in different temperatures or weather conditions.

Disadvantages of using LSR
Some significant drawbacks to using liquid silicone rubber (LSR) need serious consideration before deciding to use it in a project. The most damning disadvantage is its lack of recyclability; once it is cured, one can not re-melt and collect the rubber for reuse.

Once cured, it cannot be re-molded, and if heated beyond the cure temperature, it will burn quickly. Fixing LSR takes a considerable amount of time, possibly up to three days, which adds costs to production and further delays the completion of any project that requires this type of rubber.

Applications of LSR
Liquid silicone rubber (LSR) is a vitally important material in many industries, as evidenced by its widespread application across various domains. In healthcare, it is one of the most sought-after materials for its potential applications, such as airway management devices, IV labeling systems, and feeding tubes.

On the automotive side, LSR is highly valued for its ability to form highly durable gaskets that facilitate heat transfer, whether for automotive or high-performance race car parts. LSR’s flexibility and strength have also made it ideal for producing electronics and consumer goods components, withstanding hours or continued use without showing signs of wear or tear.

Choosing the Right Material

How to choose the right material

A. Factors to Consider

Coefficient of thermal expansion
The glass transition temperature of a material indicates its maximum thermal expansion rate. Above this temperature, materials can expand at different coefficients depending on their composition. Knowing the Coefficient of thermal expansion (expressed in PPM) is, therefore, essential to make an informed decision when selecting PCB materials.

Decomposition temperature
Designers need to consider the decomposition temperature when selecting a material for printed circuit boards (PCBs), as it directly impacts the reliability of their products. The decomposition temperature (TD) of the laminate material is the point at which it will begin to break down, possibly leading to issues such as delamination.

Using materials with TD ratings of 340°C or higher is highly recommended for devices that demand higher reliability and work in more challenging environments. This way, designers can improve performance and ensure their PCB assemblies meet customer expectations.

Moisture absorption
When considering which material suits a printed circuit board, moisture absorption must be considered. In an ideal world, the chosen material should completely resist submerged moisture. Though this is unrealistic, minimizing moisture absorption should still be a priority. Most materials used for PCBs have an absorptivity of 0.01-0.2%, with higher quality products boasting lower rates. Items with low levels of moisture absorption boast better thermal and electrical properties, so it’s essential to consider how much the material will absorb when evaluating potential options.

Mechanical properties
The mechanical properties of a material play an important role in determining whether it is suitable for use in the production of printed circuit boards. While conducting tests on potential PCB materials, one should evaluate peel strength, flexural strength, density, and delamination time to assess its suitability.

Choosing a material with good mechanical properties is critical in avoiding flaws such as broken traces and delamination due to overloading. Moreover, higher flexural strength ensures longer service life making quality materials essential in producing reliable PCBs operating efficiently even under extreme temperatures or harsh environmental conditions.

B. How to Make the Right Choice?

When selecting the suitable material for your Printed Circuit Board (PCB) application, there are a few key factors to consider. The Coefficient of Thermal Expansion (CTE), Decomposition Temperature, Moisture Absorption, and Mechanical Properties of the PCB material should all be considered. Each of these characteristics will affect the performance and durability of the PCB itself and can impact its long-term feasibility.

To ensure you make the best decision possible, research each material thoroughly to evaluate its suitability for your specific needs. Compare different materials side-by-side to get an accurate picture of how each one performs and decide which is ideal for your project.

Conclusion

The key to making an informed decision based on the selection of materials in High-speed PCB and high speed housing lies in its ability to integrate with other components and electrical requirements. While different materials have specific features, strengths, and limitations, when choosing the suitable material for your application, it is essential to properly evaluate them according to their properties, such as the Coefficient of thermal expansion, decomposition temperature, moisture absorption, and mechanical properties. This will ensure a reliable and successful design for your Printed Circuit Board.

For a design team to make a well-informed decision when selecting materials for high-speed printed circuit board (PCB) designs, consideration must be given to the performance capabilities of each material while also weighing the cost implications of each option to ensure the best outcome.

The potential benefits of using High-speed materials cannot be overstated, as they enable devices to operate faster than ever before. Keeping these considerations in mind can ultimately mean the difference between success and failure during any High-speed PCB layout design project.

you asked we answer

High-speed PCB refers to a printed circuit board with a high layer and signal count. These types of PCBs often involve processor speeds, DDR signals, and many differential signals.

High-speed PCB design is any design where the integrity of your signals starts to be affected by the physical characteristics of your circuit board, like your layout, packaging, layer stack up, interconnections, etc.

A. FR-4
B. Rogers 4350B
C. Isola IS620

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