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Guide to FR4 Thermal Conductivity for Printed Circuit Board

In the past days, light-emitting diodes were a common part of indicator lamps. As the technology advanced, PCBs served thousands of consumers in the electronics sector. Besides, with the changes in technology, the electronics produced are higher in power density. 

The size of these electronics is small, which results in boosting the flux through a particular electronic device. Therefore, a viable solution is important to regulate thermal conductivity. It will benefit in protecting the devices from facing possible damage as well. 

A fine example of this solution is FR4 PCBs that perform the same way. In this discussion, we will explore these PCB variations in detail to see how they basically work to regulate thermal conductivity. 

Properties of FR4 Thermal Conductivity

FR4 is a special material that is important for regulating thermal conductivity. Electronics that need to stabilize their performance according to thermal conductivity can benefit from this substance. There are some special attributes of this material that make it different from the rest. Let’s find them out below!

1.     Flame retardant

Now, this material is suitable for flame resistance. Due to this reason, this substance can easily resist fire in PCBs and eventually save electronics from undergoing more damage. Such substances are easy to adjust and are multipurpose. 

2.     Low moisture absorption

FR4, among all the substances, is good with moisture absorption. It is beneficial to use while producing PCBs as it will enhance their performance due to its minimal moisture absorption ability. 

3.     Good electrical properties

A fine material like FR4 offers remarkable electrical properties. It regulates and controls impedance to a large extent. The purpose is to maintain the number of electrical charges within a fixed range to ensure the flawless performance of PCBs. 

4.     Thermal conductivity

Thermal conductivity means the movement of heat from a hot part of a PCB to a cold part. There can be no better conductor of heat than FR4. It ensures that heat transfers within different parts of PCBs without any interference. 

5.     Radiation resistant

Radiation resistance is an important concept of PCBs in the field of telecommunication. FR4, used for resisting radiation, comes in handy.  

Not only this, it can protect the electronics from thermal fluctuations as well. The electronics that are always in contact with radiation mostly contain this substance. 

6.     Glass transition temperature (Tg)

The glass temperature of a polymer substance directly relates to CTE. When the glass temperature exceeds its limit, CTE will increase as well. Many PCBs can only work in an optimum environment where their temperature is below glass temperature. Fluctuations in temperature can lead to damaging the PCBs on the whole. 

Factors Influencing FR4 Thermal Conductivity

The PCB manufacturers must not ignore thermal conductivity during the production process. It determines how efficiently PCBs can convey heat to their components. Keep in mind that a PCB has different components, and each of them varies in its thermal conductivity. 

Below are some factors that affect the thermal conductivity of FR4:

·       Thermal vias

Thermal vias are hole-like structures in PCBs. Their purpose is to allow smooth heat dissipation. If a PCB has a large number of thermal vias, its thermal conductivity will be larger than those having less number of thermal vias. 

·       Copper Traces in PCB

Copper traces can also affect thermal conductivity. If a PCB has complete traces, it will have more thermal conductivity. The purpose of copper traces is to act as a bridge between different parts of PCBs. 

In any case, if traces break, they would fail to maintain thermal conductivity and would result in faulty performance. 

·       Internal layers

The internal layer relates to heat dissipation. The inner layers have to be less in order to produce more thermal conductivity. 

·       Management of FR4 Thermal Conductivity

You cannot overlook Thermal Conductivity Management when using FR4 for PCBs. It can make or break the performance of the PCBs on the whole. 

If you don’t pay attention to TCM, the PCBs will not function properly.

 Following are the problems that PCBs might have to suffer from due to pooer TCM:

  • Undergoing delamination
  • Abrasive mechanical damage
  • Complete failure of the devices
  • Electrical glitches
  • Excessive power losses

To save your PCBs from the abovementioned setbacks, there are some viable methods to ensure accurate TCM. Let’s explore them in this section one by one!

·       Designing PCB Better

While you are designing PCBs, make sure to isolate high-power conductors and signal conductors. Now, you can add more thermal vias on the thermal path. You can either use plated thermal vias or non-plated. 

It would not compromise the performance of PCBs at all. The purpose of these thermal vias is to allow full heat dissipation and circulate airflow at the same time. If the arrangement of these vias is accurate, it will boost the heat dissipation in the end. 

You can also increase the space between the tracks to ensure proper heat dissipation. It prevents creating extra areas that can cause damage. However, one issue is that you cannot rely on this method if your PCB is small. 

Now comes the geometry tracks. These are responsible for cooling down PCB parts only if they are small. 

·       Embed Copper Wire into FR4 PCB

There are many firms that have different takes on embedding copper wires into FR4 PCBs. However, this process is useful for the fields of aviation and automotive. It is because the devices used in these domains have more current flow. Copper wires in FR4 PCBs are only helpful when there are large amounts of current flowing within the system. 

·       Thermal Resistance in PCB

Heat control is important if you don’t want to overheat the PCB parts. There is no doubt that FR4 is a typical PCB substrate used in designing. It offers really low thermal conductivity. Due to this, the heat cannot escape the system and might overheat the components. 

Such overheated parts can lead to complete device failure. You can also use heat sinks instead of FR4 to make sure a large amount of heat is dissipating properly. The thermal resistance of this substance relates to its thermal conductivity.

 Substrates like FR4 are excellent with effortless heat transfers within the system. All parts of PCBs are variable in producing heat. Some generate more heat and some less. In order to find out the total thermal resistance of PCB, first, get the thermal resistances of all the PCB components.

 The thermal resistance of FR4 and copper combined are the thermal conductivity of a PCB. The copper parts in a PCB are useful to get the thermal resistance of PCBs. 

Constraints of FR4 Thermal Conductivity in PCB


The benefits of using FR4 for your PCBs include affordability and perfect electrical insulation. There are some downsides to this substrate as well. One major problem with FR4 is its extreme thermal conductivity. It means you cannot use it for those electronics that work at a fast pace. 

Below are some definite downsides of using FR4 in PCBs:

·       Controlled impedance

Now, this substrate lacks a fixed Dk value, unlike others used for fast-paced gadgets or devices. When the frequency of this substrate increases, it will also increase the Dk value. The Dk of FR4 can only endure changes up to a certain extent.

 If this happens often, it can clearly create a negative impact on the impedance values. Never rely on FR4 substrate if you are willing to produce devices that function on controlled impedance. 

·       Temperature stability

FR4 is not an option to look for if the device endures hot temperatures while working. Another issue with this substrate is that it does not fit well with lead-free soldering. The reflow soldering has extreme temperatures that can disrupt the normal functioning of FR4 on the whole. 

·       Insulating stability

The substrate under discussion is not reliable for working in high temperatures. Since it can break down due to excessive heat. However, the insulating ability of FR4 is impressive. 

·       Signal losses

Signal losses are common when you are designing PCBs. It mostly happens when the device is complex. The heat dissipation ability of FR4 is high. Now the frequency of this substance is always much higher than other PCB parts. Due to this reason, the lower frequency leads to power losses. 

Factors to Consider When Selecting FR4 Thermal Conductivity

There are some factors that you must keep in mind when dealing with FR4. You can rely on its dielectric properties on all counts. Not only this, there is a recent application of FR4, which is a mineral filler that is used to work with resins. Now FR4 has proved to be a good alternative for resins in this aspect. 

Below are some factors that will help you choose the best FR4 substrate each time:

·       Thickness

The thickness of FR4 matters a lot. Keep in mind this thickness is different for the type of PCB you are working on. It can directly relate to the width of PCBs as well. An appropriate thickness is important to make sure the PCB is working efficiently. Use thin FR4 substrates if the PCB is small. 

·       Cost

The substrate FR4 is an affordable option. Different PCB producers use this material since it is accessible and comes within their budget. It can help in the fine production of high-paced devices as well. 

·       Temperature management

When working with FR4, you cannot ignore temperature. Temperature regulation will make FR4 work at its best. However, you can replace it with laminates as they are useful in producing high-paced devices. 

·       Operational environment

There is always an optimum environment for FR4 to work normally. An optimum environment for FR4 is one with a fixed range of humidity and heat. If you consider laminates instead of FR4, they are much better than this substance in terms of resistance ability, heat, and moisture. 

How to Enhance Thermal Management via FR4 Thermal Conductivity? 

There are different researches on improving the thermal management of PCBs. Now each study has its own guidelines and factors to make sure the PCBs are excellent in their performance. 

However, there are important factors that can help you enhance thermal control regarding PCBs:

  • Thick Copper PCB: Such PCBs are good with excessive heat dissipation. Due to this, you don’t have to worry about cooling down PCBs and their components at all. 

The main areas that contribute to this process are thick copper layers and the inner layers of PCBs. Such printed circuit boards are useful when it comes to those devices that need thermal regulation and are complex. 

  • Metal Core -IMS: Such PCBs are also useful to allow a higher degree of heat dissipation. Due to these reasons, producers use IMS instead of FR4 for most LED devices. 

These work on a thermal paste that is highly conductive that combines with heat sinks to dissipate more heat. 

  • Trace Geometries: When using copper traces, it is clear that there will be more chances of a higher degree of thermal conductivity within PCBs. 

Now if you break the contact of these traces, it will reduce the heat dissipation as well. Trace geometries are important for the fine performance of PCBs. 

  • Thermal via array: Those PCBs that are slim and come with two sides contain an arrangement of thermal vias to dissipate large amounts of heat. You can use two different types of vias for this process.

 These can be regular vias and capped vias. Now these two types only enhance the process of heat dissipation, which results in quickly cooling down the PCB in case of overheating. 

The purpose is to give enough room to heat to escape the system. It is obvious the amount of thermal vias is directly proportional to the heat dissipation. More vias result in more heat dissipation. 

  • Ground and power planes: It is important for complex PCBs. For instance, an HDI board will work on fine ground and power planes. These two planes are useful for heat dissipation as well.

 However, their performance is much more impressive than the heat dissipation ability of ceramic boards. It is because the temperature difference between such boards is lower than other substances. 

  • Component size: Smaller PCB parts result in more heat dissipation. There are different devices that work on the same phenomenon. So the size of the components is crucial to consider when you are willing to allow more heat dissipation.  


FR4 is a huge asset for PCB manufacturers due to its benefits. However, there are some limitations of FR4 that can disturb the natural functioning of PCBs on the whole. Sometimes the drawbacks of this substrate override its attributes while designing PCBs. 

There are other materials like ceramics and metals that you can use instead of FR4 for thermal regulation. The need for using such material to regulate temperature for PCBs is only possible due to such substrates. We hope that you learned about FR4 keenly in this post. Now you can easily evaluate FR4 with other materials without any hustle. 




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