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High-speed circuit boards can achieve high speeds in excess of 500 MHz, but they require various special HDI PCB materials and fabrication processes. The critical components of PCB design — the dielectric material and the conductor material — affect the electrical properties of the PCB and its ability to withstand high temperatures.
When people think of PCB materials and laminates, some of the first things that come to mind are FR4 or other rigid materials. But there are also highly flexible PTFE laminates that can be used for many applications. In this guide, we will cover what key factors you should look for choosing high-speed materials and laminates for PCB fabrication, as well as Megtron 6, EM-888, and I-Speed.
Key Considerations for Choosing High-Speed PCB Materials and Laminates for Fabrication
Find out Whether the Material Supports Layers or Bonding Wires
One of the most important criteria to consider when choosing a material is whether or not it supports layers and bonding wires. If you are creating a multilayer circuit board with many tracks and components, select a material that supports layers. The more layers you add, the more complicated your board becomes. Make sure the material you choose can support all of them.
Look at the Thickness of Each Layer
The thickness of each layer plays a vital role in determining how long it takes to fabricate your board. If you need to get it done quickly, look for materials with thin layers so that they take less time to process. You can also look for materials with single-sided laminates if you want faster processing times because these have fewer layers than double-sided laminates do. This way, you would not have to wait too long before starting work on other parts of your circuit board.
See How the Manufacturers Rate the Impact Strength of the Material
Impact Strength is crucial when selecting a material because it determines how much force your board can withstand before breaking. Impact strength measures how well a material resists impact loads, which can be caused by dropping or hitting the board with an object like a hammer.
Materials with high impact strength can absorb energy from impacts and prevent damage to the PCB. For example, if a component falls off a board during transport, impact-resistant material will prevent damage to the solder joints and pads on the board. Therefore the higher the number, the better the board will resist damage when dropped.
Beware Solder Mask Degradation
The solder mask is an essential component of the PCB design since it provides a layer of protection from moisture and other contaminants during use. It also prevents static electricity build-up during transport or storage. The solder mask layer is typically made from epoxy with high dielectric strength and low-temperature coefficient of expansion (TCE) so that it does not crack when exposed to extreme temperatures during reflow soldering processes.
A good solder mask should withstand temperatures up to 260°C, which is required in most reflow soldering processes like lead-free soldering. If the solder mask cracks or peels off after reflow soldering, it will cause short circuits between conductive tracks on the PCB board resulting in decreased performance and failure rate of electronic devices using these boards.
Track Width and Spacing
The track width is the distance between two parallel tracks. The minimum track width required for high-speed signals is determined by the signal propagation time and the period of the signal’s highest frequency component. For example, for a 1 GHz signal with a 50% duty cycle, the signal propagation time is 0.5 ns. Therefore, this signal’s period is 0.25 ns, or 250 ps (picoseconds).
The track spacing should be at least equal to twice the period of the highest frequency component of your signal. In this case, that would be 500 ps or greater than 500*10^6 seconds, which converts to 5 micrometers or more than 5 million nanometers! This can be reduced by using higher layer count PCBs and adding impedance control features such as vias with controlled impedance (Z-layers).
Consider Dielectric Constant and Loss Tangent
When choosing high-speed PCB materials, it is essential to consider dielectric constants and loss tangents because this will help determine how quickly you need your boards produced and how easy they are to manufacture.
The higher the dielectric constant, the better material will conduct electricity at high frequencies (measured in MHz). Similarly, a low loss tangent indicates little power dissipation in the material, which results in better signal transmission.
Reviewing Megtron 6, EM-888, and I-Speed for Fabrication of High-Speed PCBs
Megtron 6
Megtron 6 is a high-performance, low-cost FR-4 with improved mechanical and electrical properties. It has been designed to meet the need for high-quality boards with a wide range of applications in the industrial, commercial, military, and automotive sectors. Megtron 6 offers excellent dielectric properties and high mechanical strength, which results in improved product performance and reliability. Megtron 6 also has excellent moisture resistance and is, therefore, suitable for outdoor use.
Megtron 6 uses a proprietary formula that offers excellent adhesion to copper and other metals. It has been designed for use in standard through-hole technology (THT) or surface mount technology (SMT). Megtron 6 can also be used for flex PCBs where it has been shown to exhibit good flex life at temperatures up to 105°C.
EM-888
EM-888, a medium-density fiberboard, is an excellent alternative for the most demanding applications. It has an oil-resistant core layer that provides excellent moisture resistance and dimensional stability.
This material is easy to cut and glue with standard adhesives. EM-888 has a smooth surface with no visible tear-out when routed or milled. The material can be painted or finished with a variety of coatings.
I-Speed
I-Speed is an excellent alternative to Megtron 6, EM-888, and other high-speed PCB materials. It has the same high thermal conductivity, thermal shock resistance, and low coefficient of thermal expansion (CTE) as Megtron 6 and EM-888, but it is much less expensive.
I-Speed has a lower dielectric constant than Megtron 6, EM-888, and other FR4 materials, which means it can be used for thinner layers with better signal integrity at higher frequencies. Moreover, I-Speed has excellent moisture resistance, making it ideal for use in outdoor devices such as wireless base stations and cellular phones, which are exposed to extreme environmental conditions.
Final Verdict and Recommendation
Ultimately, it all comes down to the final product that you need to have. Are you just prototyping the project, and there is no time for thermal cycles? Then we would recommend Megtron 6 specifically designed for rapid prototype PCB, or EM-888 – which can be qualified as a high-temperature material, but later, when you can afford it, we would recommend going with I-Speed. If you are designing without any concerns about the lead time, we highly consider Megtron 6 – because of its resolution, especially with photoresist etch mask materials. And then we would probably use either EM888 depending on the surface finish tolerances you are looking for. To learn more about these Assembly specifications, visit Hemeixin.
