- FR4 material which is always used in printed circuit boards usually isolates neighboring copper planes. In this case, they don’t get short-circuited. Also, they can provide better flexibility for the structure.
- Another role of FR4 material is that it ensures PCBs are durable and usable.
- A reliable alternative to FR4 materials is CEMs (composite epoxy materials).
The expectations for modern circuit boards is that they should be multifunctional, high speed and able to maximize the tightest of spaces. Also, they are always expected to be of very high quality, easy to handle, and highly resistant to variations in temperature. Amongst the various PCB dielectric materials, some (like FR4 material) have been popularly used than others. In this post, we will be revealing some of the features of an FR4 material. We will also discuss some alternatives that you can take into consideration.
PCB Dielectric Material
When it comes to circuit boards functioning normally, the role of PCB dielectric material can hardly be ignored. This is very obvious in the aspects of integration as well as performance of such circuit boards. In most cases, the performance of a PCB can be affected by mechanical, chemical, electrical or electrical properties. One of the functions of PCB dielectric material is that it facilitates the formation between the circuit board’s base and conducting copper layers.
PCB dielectric material can also be called PCB substrate material. It is responsible for providing the platform which aids the soldering of electronic components. Its role is crucial in formation of electronic circuit. A major form of PCB substrate material that is popularly used is FR4.
This is crucial in establishment of PCB usability and durability. It is the acceptable standard for different types of PCBs. These could be double-sided, single-sided and multilayered circuit boards. Their requirements for mechanical strengths are usually very strict. FR4 material is characterized by properties that are fire-resistant. PCBs that are single and double-sided usually have top copper layer, bottom copper layer and an FR4 core. The core of multilayered PCBs is formed with FR4 material.
Also, they are covered using prepreg material on both sides prior to having the top as well as bottom copper layers placed. FR4 is ideal especially for high power density PCBs. This is due to its high glass transition temperature.
FR4 Material Properties
FR4 materials can have neighboring copper planes isolated without the need to get shorted-circuited. It can also provide the structure with flexibility. Talking about FR4 properties, there is something you should understand. This is the fact that they vary among manufacturers. However, it can be grouped into the following categories. These will be highlighted below.
- The cheapest FR4 material that many companies are using today is characterized by glass transition temperature of around 1300
- Another group is the FR4 material which is usually compatible with any technology related to lead-free reflow. This has a glass transition temperature of approximately 170°C – 180°C.
- Furthermore, there is another category of FR4 material which is halogen-free. This is also compatible with any technology related to lead-free reflow.
- Finally, there is an FR4 material which has a CTI (comparative tracking index) that is normalized. This is usually more than 400. CTI is the rate at which dielectric materials which are used in circuit boards are measured.
Some of the features/properties of FR4 are:
- PCB substrate flexibility
- Moisture or water-resistant
- High mechanical strength
- Temperature resistant
- High electrical insulation using high dielectric strength
Why FR4 Alternatives Are Required?
The truth is that there are circumstances or scenarios where FR4 may seem unsuitable. These are explained below.
- FR4 material can become defective when PCB gets exposed to high temperature for a long time. This is because its thermal conductivity is low. FR4 alternatives are popularly used in aerospace industry for PCB substrate.
- Lead-free soldering is a preferrable option especially for countries where RoHS compliance is strictly adhered to. Lead-free soldering requires high temperature maintenance. This makes FR4 material not to be a perfect option for these applications.
Boards which make use of FR4 material are not consistent when it comes to maintaining constant impedance as well as reflections. This makes it impossible for FR4 material to be used in high frequency applications.
Just as explained above, there are instances when FR4 material may not be ideal. In such case, designers are expected to choose other options. In this section, we will be explaining some of the most popular FR4 alternatives.
Composite Epoxy Materials
These materials are great when used in high density applications. It should be noted that they are of various types such as CEM-3, CEM-2, and CEM-1. CEM-1 material is usually a combination of phenol compounds, woven glass epoxy and paper. It can prove perfect once used in single-sided circuit boards. Apart from its affordable nature, it can ensure provision of dielectric properties.
CEM-2 is characterized by much higher glass transition temperatures in relation to that of CEM-1 material. CEM-3 seems to be perfect for double-sided PCBs that have plated holes.
Teflon or Polytetrafluoroethylene is used in coating of non-stick cookware. It consists of fluorine and carbon. Its glass transition temperature is around 1600C and 2800C. Its features are high moisture-resistance, thermal insulation, electric strength, flame resistance, dielectric strength and temperature stability. Polytetrafluoroethylene material is perfect for satellite, mobile communication systems, high frequency boards and high-speed PCBs.
Metal backed boards are also great FR4 alternatives. This is why they are mostly used in LED lighting industry. The reason is because they can extend the lifespan of LEDs. Some of their advantages are lightweight, durability, great heat dissipation, and cost-effective.
Based on the above, it is true that FR4 is probably the most popular material used in circuit boards. However, there are times when manufacturers or designers may need to explore other alternatives. This is based on factors like high temperature, frequency and power of applications.
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