What is the Thermal Conductivity of Different PCBs [Solved]

Thermal conductivity is an important factor to consider in designing a PCB. The PCB thermal conductivity varies with different substrate materials and different amounts of copper. For example, an IMS PCB has better thermal conductivity than an FR4 PCB. Besides, PCB vias boost the PCB thermal conductivity.

What is the thermal conductivity of an FR4 PCB and other different PCBs? You can find answers in this article.

Part 1: What is PCB Thermal Conductivity

PCB thermal conductivity evaluates the time rate of heat flow through the surface of the printed circuit board in the z-axis (PCB thickness) direction. It is measured by the coefficient k, and the unit is W/m·K.

The formula of PCB thermal conductivity is:

K = (Q·L)/(A·ΔT)

Where,

Q is the amount of heat transferred through the PCB in Joules/second or Watts

L is the thickness between the two isothermal planes

A is the area of the surface in square meters

ΔT is the temperature difference in Kelvin

Or the formula can be:

K=1/(1/h1+δ/λ+1/h2)

Where,

h1 and h2 are the surface heat transfer coefficients of the two isothermal planes

δ is the thickness between the two isothermal planes

λ is the thermal conductivity of the material

PCB thermal conductivity is a parameter depending on the properties of PCB substrate and dielectric materials, the amount of wiring circuit copper, and the PCB vias.

You can refer to the thermal conductivity of the PCB materials or things below.

From the below data, you can find that an aluminum nitride PCB has better thermal conductivity than an aluminum oxide PCB; a copper-base PCB has better thermal conductivity than an aluminum PCB; an IMS PCB has better thermal conductivity than an FR4 PCB.

Besides, in a PCB, the amount of copper boosts the PCB thermal conductivity of PCBs. Because the PCB vias are electroplated with copper, the larger via aperture and more vias, the better PCB thermal conductivity.

Part 2: FR4 PCB Thermal Conductivity

The thermal conductivity of FR4 is only 0.1W/mK to 0.5W/mK, but thanks to the copper in the PCB, the FR4 PCB thermal conductivity is better than that of FR4.

The FR4 PCB thermal conductivity is mainly decided by the copper-clad laminate type you choose for your FR4 PCB. You can check out the thermal conductivity of the available PCB laminates from the PCB manufacturer PCBONLINE.

It is worth mentioning that the thermal conductivity of the Rogers 92ML in the z-axis direction at 23℃ is 1.7W/mK, and that of the Shengyi ST115G is 1.6W/mK.

Usually, in an FR4 PCB, if it is a two-layer single-mounting-sided, the thermal conductivity path is an electronic component pin > copper > prepreg > copper > prepreg > the FR4 substrate > the mechanical box and air.

Unless it uses a high thermal conductivity FR4 laminate, FR4 PCBs can't bear the heat of high-power applications. However, thermoelectric separation technology can help FR4 PCBs be used in high-power fields.

Thermoelectric separation means the heat transfer network is independent of the electrical function networks. The thermal conductivity path is an electronic component pin > copper > the mechanical box and air.

You can refer to the below FR4 PCBs designed and manufactured by PCBONLINE that use thermoelectric separation.

In the middle of the dual-mounting-sided FR4 PCB, a 1mm thick copper foil is embedded, which is insulated from the top and bottom circuits but connected with the LEDs' heat dissipation pads. When the LEDs work, thermal quickly dissipates through the copper foil (which can also be aluminum or AlN) to the external environment, and the FR4 areas that play the electrical functions won't be affected by the heat.

In this way, the thermal conductivity of the FR4 PCB is close to about 400W/mK copper thermal conductivity. And don't worry about the thermal management design, as the manufacturer PCBONLINE can help you design the PCB design and LED light parameters according to the requirements of your products.

Part 3: Aluminum PCB Thermal Conductivity

Aluminum PCB thermal conductivity is from 1W/mK to 9W/mK, which is much better than that of FR4 PCBs. Most aluminum PCBs have a thermal conductivity of 1W/mK to 2W/mK. Currently, aluminum PCBs are mainly used for LED lights in automotive, industrial, business lighting, etc.

You may wonder why the thermal conductivity of aluminum PCBs is much smaller than that of copper and aluminum. Well, you need to keep in mind that the aluminum PCB conductivity is mainly decided by the properties of the dielectric between the aluminum substrate and the copper circuit layer.

The thermal dissipation of a single-layer aluminum PCB is an electronic component pin > copper > dielectric > aluminum substrate > the mechanical box and air. The more dielectric layers that thermal has to flow through, the worse the thermal conductivity of the aluminum PCB. For this reason, aluminum PCBs are only single-layer, double-layer single-mounting-sided, double-layer dual-mounting-sided, and four-layer dual-mounting-sided.

The aluminum PCB manufacturer PCBONLINE already achieves fully automatic aluminum PCB fabrication, and we have our aluminum laminate factory called Yugu. Without any quality sacrifice, you can order bulk aluminum PCBs with a thermal conductivity from 1W/mK to 9W/mK at only $39 per square meter.

Part 4: Ceramic and Other PCB Thermal Conductivity

Apart from FR4 and aluminum PCBs, you may also want to compare the thermal conductivity of copper-base PCBs, AlN PCBs, and alumina PCBs.

Without thermoelectric separation, the thermal conductivity of copper-base PCBs is 1W/mK to 8W/mK. It is times better than aluminum PCB thermal conductivity (1W/mK to 2W/mK in most cases).

Without thermoelectric separation, ceramic PCBs have the best PCB thermal conductivity. Besides, they have stable mechanical and chemical characteristics.

Among ceramic PCBs, there are BeO PCBs, AlN PCBs, and alumina PCBs. At very high temperatures, the thermal conductivity of BeO PCBs is even better than AlN PCBs, but BeO is toxic and dangerous to fabricate.

The thermal conductivity of AlN PCBs is about 180W/mK, and that of alumina PCBs is about 20W/mK.

Besides, AlN PCBs have a close thermal expansion coefficient to ICs. The only drawback is that an AlN PCB with a large surface area may break in PCB fabrication. If you have doubts about the strength that AlN PCBs can withstand, please contact PCBONLINE.

Part 5: PCB Thermal Management One-Stop Manufacturer

Thermal management is always a challenge in PCB design. However, you can solve thermal management problems and have PCB/PCBA fabrication at one stop from PCBONLINE.

PCBONLINE is a reliable terminal manufacturer from PCBs to box build assembly. Founded in 1999, with two large advanced PCB manufacturing bases and one PCB assembly factory, we provide PCB fabrication, PCB assembly, and value-added services with thermal management solutions.

Regarding PCB thermal conductivity, PCBONLINE has these advantages:

Besides the above PCBs, PCBONLINE also fabricates flexible PCBs, rigid-flex PCBs, HDI PCBs, and high-frequency PCBs and solves thermal management problems for them. If you have needs for PCB, PCBA, and box-build assembly for power applications, please feel free to send your inquiry to PCBONLINE by email at info@pcbonline.com.

Conclusion

This article illustrates what PCB thermal conductivity is and lists the thermal conductivity of common PCB materials. Besides, it reveals the thermal conductivity range of FR4 PCBs and aluminum PCBs. PCB thermal conductivity is a critical parameter to consider in PCB design, especially for high-power applications. Apart from thermal conductivity, you may also want to know other PCB parameters, such as how much strength can different PCBs bear. You can chat with us online or by email at your convenience.

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