heat dissipation design

heat dissipation design

The performance and reliability of LEDs are greatly affected by temperature, so effective heat dissipation design is essential.
Here we will provide an easy-to-understand explanation of LED heat dissipation design.

Although LEDs have a higher luminous efficiency than incandescent bulbs, only about 30-60% of the input electricity is converted into light, with the remaining 40-70% becoming heat.

This heat can cause LEDs to fail to light, change in optical characteristics, and even shorten their lifespan. For example, if the LED junction temperature (Tj) increases, the light output decreases and the luminous efficiency deteriorates.
Furthermore, long-term exposure to high temperatures can cause the materials inside LEDs to deteriorate, shortening their lifespan. Because heat has such a large impact on LED performance and reliability, heat dissipation design to reduce heat generation is essential.

LED heat dissipation path

Heat generated from the LED chip is transferred to the substrate through the lead FRAMES. Therefore, it is important to accurately understand which TERMINALS the heat is concentrated on. Also, some LED products may have TERMINALS dedicated to heat dissipation in addition to the anode and cathode TERMINALS.
Especially with high-power LEDs, the heat flow tends to be complex, so a proper understanding of the heat dissipation path is fundamental to the design.

Horizontal and vertical heat conduction of the substrate

The design of the circuit board is key to efficiently dissipating heat from an LED. Here we will explain horizontal and vertical heat conduction.

Horizontal heat conduction
The most basic way to improve heat dissipation is to increase the copper (Cu) area on the board. Copper has high thermal conductivity, so heat can be dispersed efficiently by securing a large area. In particular, by placing sufficient Cu patterns around the LED, heat concentration can be prevented and heat dissipation can be dispersed throughout the board.
If the Cu area is spread too far, the effect will be reduced, so it is a good idea to get a rough idea of the area in advance by measuring it or conducting a thermal simulation.

Vertical Heat Conduction
Thermal vias (thermal conduction vias) are an effective method for transferring heat vertically. Thermal vias transfer heat from the front to the back of the board. This allows the heat dissipation area on the back of the board to be utilized, improving heat dissipation efficiency.
Increasing the number of thermal vias too much will reduce the effect, so it is a good idea to get a rough estimate by actual measurements or thermal simulations.

Selection of substrate material

One way to improve the heat dissipation of an LED is to select the substrate material.
In addition to the common paper substrate and glass epoxy substrate (FR4), there are also metal substrates, which have higher heat dissipation properties. This article explains the characteristics of metal substrates and points to note when selecting them.
The metal substrate has the following structure (see the diagram below).

Surface layer: Copper foil (for circuit formation)
Middle layer: Insulating layer (thermally conductive)
Base layer: Metal layer such as aluminum or copper

The type of metal used in the substrate layer affects the thermal conductivity of the entire board.
The general order of thermal conductivity is as follows:

FR4 < Aluminum board < Copper board

FR4 (glass epoxy board): A standard board material with low cost and low thermal conductivity. Suitable for low-heat-generating LEDs.

Copper substrate: It has very high thermal conductivity and is suitable for use with high-power LEDs and in high-temperature environments. However, its high cost and weight limit its applications.

When using a metal substrate, it is important to select one whose thermal expansion coefficient is close to that of the LED chip and lead FRAMES, as this reduces stress caused by temperature changes and improves the reliability of the LED.

LED heat dissipation design is an essential element for maximizing performance and reliability.
In this section, we have covered the following four points:

The importance of heat dissipation
It is important to understand the impact that heat generated by LEDs has on their performance and lifespan, and to implement an appropriate heat dissipation design.

Substrate Material Selection
Selecting the optimal board material for your application, such as FR4, aluminum board, or copper board, directly leads to improved heat dissipation performance.

How to measure Tj (junction temperature)
Accurately measuring and calculating Tj confirms the validity of the design and ensures the reliability of the LED.

By implementing these measures appropriately, you can maximize the performance of your LEDs and extend their lifespan.

We provide support for thermal simulations related to heat dissipation design.
By utilizing simulation, it is possible to consider efficient heat dissipation measures from the early stages of design.
If you have any questions or concerns, please feel free Inquiry.