What to Look for When Choosing High-Frequency PCB Materials

October 5, 2022
What to look for when choosing high-frequency PCB materials

One of the most important things to consider while constructing a printed circuit board (PCB) is the type and quality of the materials you are using. After all, your PCBs will only operate without issue and support the performance of a high-speed design when they are formed from the right selection of materials.

On the other hand, when you use the wrong materials for PCB construction, your outcome will have considerable differences, and there will be problematic gaps in your PCB’s overall performance.

Circuit boards are made up of non-conductive dielectric substrate core layers, as well as dielectric laminate layers. The laminate layers are the base for the copper foil that forms your board’s power planes and metal traces.

A PCB’s many layers are all made out of various materials that are designed to meet specific dielectric constants and other property requirements.

Since high-frequency circuits have tighter signal integrity requirements, the materials’ dielectric properties in a circuit board are a more significant part of the overall signal integrity equation.

Of course, the materials you use to construct a circuit board should meet a variety of criteria, including cost-effectiveness, ease of use, sturdiness, and insulation capabilities. If any of these criteria are not met, it could compromise the effectiveness of your PCB and contribute to the deterioration of the board or signal loss.

Necessary Attributes of High-Frequency Materials for Circuit Board Construction

There are several attributes that you should pay particular attention to while selecting materials to use during the construction of your PCB. If you want to have a fully functional PCB that performs optimally, you should keep the following attributes in mind:

1. Dielectric constant (DK)

It is essential for most high-frequency materials to have a dielectric constant with a high level of consistency. That consistency should exist both within the circuit material sheet and between lots. When such consistency is offered by the materials’ dielectric constant, your board’s electronic circuitry will offer the same performance in large batches.

If you want your application to extend over a significant range of frequencies, the dielectric constant’s value must be consistent over that entire range. The materials’ dielectric constant must also withstand a range of temperatures without fluctuating since the application is likely to operate at various temperatures while in use.

2. Coefficient of thermal expansion (CTE)

A circuit board material’s coefficient of thermal expansion is another critical thing to consider when you are constructing a PCB. Whenever your PCB’s ambient temperature rises, it will want to expand. If your board’s materials have a CTE that is very different from the copper on your board, there will be an increased amount of stress placed on your board’s solder joints.

That could become a particularly significant problem if your PCB’s thermal changes dynamically cycle up and down. As the various materials expand and shrink in differing amounts, eventually, it may lead to a separation from the solder that connects the circuits.

If your board has materials with vias, their CTE is most important along the z-axis, since a higher z-axis CTE could damage the board’s plating and, consequently, degrade the electrical connection.

3. Moisture absorption

For a high-frequency operation to be possible, your PCB materials must exhibit minimal moisture absorption. Without minimal moisture absorption, the material will be unable to maintain a consistent dielectric constant. That is because the electric performance of your board can be affected by even the smallest amount of moisture ingress.

Various circuit board materials come with different moisture ratings. For instance, the moisture absorption rating of traditional FR-4 can be as high as 50%. On the other hand, materials like PTFE can have a moisture rating as low as 2%. Consider these ratings carefully while choosing the right materials for your PCB.

Which high-frequency PCB materials meet these requirements?

Although you can likely find several materials on the market that claim to be suitable for high-frequency PCB construction, there are only a few that meet the requirements mentioned above.

1. FR-4

FR-4’s material is flame retardant, highly insulating, and rigid. Its substrate is made from a woven glass-reinforced epoxy laminate, which typically forms a PCB’s base material. Standard FR-4 may have inconsistent dielectric stability across higher frequencies, a higher dissipation factor, and higher insertion loss at microwave frequencies. However, you can avoid such problems by using high-performance FR-4.

2. 370HR

ISOLA’s 370HR is a high-performance FR-4 material with advanced properties like improved dielectric and thermal properties, higher CAF resistance, and UV blocking. It is made from E-glass fabric that is reinforced with multifunctional epoxy resins, which provides it with a low CTE and high Tg, while maintaining the high processability of FR-4. The 370HR is best for multi-layer, high-performing PCB applications.

3. FR408HR

FR408HR boasts an impressive 30% improvement regarding z-axis expansion, and it also has upwards of 24% electrical bandwidth when compared to other competitive products. It also has a superior moisture resistance at reflow, which helps it to bridge the gap from electrical and thermal perspectives.

FR408HR uses E-glass fabric reinforced with ISOLA’s patented high-performance multifunctional resin system, which allows it to offer a low dielectric constant of 3.39. This means that wider trace widths are possible, as well as a reduction in the skew caused by dielectric constant differences between glass and resin.

4. RO4000 Series

The RO4000 series materials are made from reinforced hydrocarbon/ceramic laminates instead of PTFE, allowing for low dielectric tolerances and a low loss factor. Therefore, RO4000 series materials can offer excellent performance even at higher operating frequencies and are ideal for broadband applications.

How Circuits Central Can Help With All Your High-Frequency PCB Material Needs

If you are thinking about putting together a PCB with high-frequency materials, Circuits Central can certainly help you. Our team is full of seasoned experts in electronics manufacturing and PCB assembly, so we can offer any guidance you may require during your materials acquisition and assembly process.

You can benefit greatly from our reliable, flexible-by-design production facility, which will make the construction of your PCB easier no matter what your expected range of volume or design complexity is.

Circuits Central is capable of handling all aspects of assembly, including material management, PCB Assembly, cable assembly, and product testing and integration. Throughout your product’s development process, you can make use of our top-quality Electronic Manufacturing Solutions. Even if you have an incredibly intricate design, we can still confidently guide you through the entire process.

Our PCB assembly team is also constantly improving as we review and modify our operation regularly to maintain quality control. During this process, we consistently integrate new processes to overcome the challenges that tend to come with cutting-edge PCB electronics. If you want to be competitive in a global market, Circuits Central can help you achieve that goal without a doubt.

For more information about our state-of-the-art PCB assembly line and production facility, call Circuits Central at 1 (888) 602-7264 or email us at info@circuits-central.com.

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