Aluminum Nitride - The Most 'Trendy' Substrate Material

Since entering the 21st century, with the rapid development of electronic technology, the level of integration and assembly density of electronic components has been continuously improved, making heat dissipation a key factor affecting the performance and reliability of devices. Taking high-power LED packaging as an example, only about 20% to 30% of the input power is converted into light energy, while the remaining 70% to 80% is converted into heat. The accumulation of this large amount of heat can lead to serious consequences.

By utilizing packaging substrates to导出 heat from the chip (heat source), thermal exchange with the external environment is achieved to fulfill the purpose of heat dissipation. Among these, ceramic materials, with their high thermal conductivity, excellent heat resistance, high insulation, high strength, and compatibility with the thermal characteristics of chip materials, have become commonly used materials for power device packaging substrates.

With its high thermal conductivity and comprehensive performance, is truly captivating

For a long time, commonly used ceramic substrates have included Al₂O₃, SiC, and BeO. Al₂O₃ ceramics were developed first, with the most mature preparation technology, the lowest cost, and the widest application. However, the thermal conductivity of Al₂O₃ ceramics is only 17-25 W/(m·K), and their thermal expansion coefficient is poorly matched with that of semiconductor materials such as Si and GaAs, which limits their use in high-frequency, high-power, and high-integration circuits. Although SiC ceramic substrates have high thermal conductivity and a thermal expansion coefficient closely resembling that of Si, they exhibit poor dielectric properties, high sintering losses, and high costs, along with the difficulty of producing dense products, which restricts their mass application. While BeO has thermal conductivity comparable to that of AlN, its thermal expansion coefficient is excessively high, and BeO powder is toxic; inhalation can lead to chronic beryllium disease, resulting in most countries around the world having ceased its use.

What is the performance of aluminum nitride? Let's take a look:

1. Exceptional Thermal Conductivity: AlN exhibits high thermal conductivity, with a theoretical maximum at room temperature reaching 320 W/(m·K) – approximately 8 to 10 times higher than alumina ceramics. Commercially produced variants readily achieve thermal conductivities as high as 200 W/(m·K).

2. Favorable Thermal and Lattice Matching: AlN possesses a low coefficient of thermal expansion (CTE), with a theoretical value of 4.6 × 10⁻⁶/K. This CTE is comparable to silicon (Si) and gallium arsenide (GaAs), and its temperature dependence closely mirrors that of silicon. Furthermore, AlN exhibits lattice matching with gallium nitride (GaN). This thermal and lattice compatibility ensures robust bonding between chips and substrates during high-power device fabrication, which is critical for device performance and reliability.

3. Wide Band Gap and High Insulation: With a band gap of 6.2 eV, AlN ceramic offers excellent electrical insulation. This inherent property eliminates the need for additional insulation layers when used in high-power LED applications, thereby simplifying the manufacturing process.

4. Robust Mechanical Properties, Thermal Stability, and Chemical Resistance: AlN crystallizes in the wurtzite structure, characterized by strong covalent bonding. This structure confers high hardness, high strength, and overall good mechanical performance. Additionally, AlN demonstrates excellent chemical stability and high-temperature resistance. It remains stable in air up to 1000°C and exhibits good stability in vacuum environments up to 1400°C, facilitating high-temperature sintering processes. Its corrosion resistance is also sufficient to meet the demands of subsequent processing steps.

In summary, these exceptional properties collectively make Aluminum Nitride (AlN) an outstanding choice for substrate material in demanding applications like high-power electronics.

Key roles in numerous fields

Currently, the demand for Aluminum Nitride Substrates is steadily increasing in the fields of power semiconductor devices, hybrid integrated power circuits, antennas in the telecommunications industry, solid-state relays, power LEDs, and multi-chip modules (MCMs). The end markets are directed towards automotive electronics, LEDs, rail transportation, communication stations, aerospace, and military defense.

Antenna
The antenna can convert the guide wave propagating on the transmission line into electromagnetic waves propagating in free space, or convert electromagnetic waves into guide waves, and its essence is a converter. Antennas are used for a wide range of purposes and need to work well in any environment, so their components require high and extremely reliable quality. Ordinary circuit boards can not meet the basic requirements of antennas, and the closest to all aspects of antenna requirements at this stage is the ceramic-based circuit board, among which the AlN ceramic-based circuit board has the best performance, which is mainly reflected in:
(1) Small dielectric constant, so that the high-frequency loss can be reduced and the signal can be transmitted completely.
(2) Low resistance and good adhesion metal film layer. The metal layer has good conductivity and generates less heat when the current passes through.
(3) The ceramic base has good insulation. The antenna generates high voltage electricity during use, and the breakdown voltage of ceramic substrates is high.
(4) High-density packaging is possible.

Multi-Chip Module (MCM)

Multi-chip modules are advanced microelectronic components that offer high performance, high reliability, and miniaturization to meet the stringent requirements of aerospace, military electronics, and other applications. With the increase in component power and the improvement of packaging density, effective heat dissipation is a critical technology that must be prioritized. The MCM-C packaging substrate materials typically employ a multilayer ceramic structure, utilizing AlN ceramic for its high thermal conductivity within MCM technology, significantly reducing the internal heat of microelectronic components and enhancing operational stability.

High-Temperature Semiconductor Packaging

SiC, GaN, and diamond-based wide bandgap semiconductor materials and devices can operate at high temperatures, with Sic Technology being the most mature. SiC can stably operate in high-temperature environments of 600°C due to its excellent physical and chemical properties, making it extremely important for high-temperature electronic systems in the aerospace field. Currently, high-temperature electronic packaging substrates primarily use Al2O3 and AlN ceramic substrates, with AlN ceramics exhibiting thermal conductivity several times greater than that of Al₂O₃ ceramics and a coefficient of thermal expansion that matches that of SiC, making it the preferred material for high-temperature electronic packaging.

Power Semiconductor Modules

Power semiconductor modules are integrated assemblies of power electronic components that are packaged according to specific patterns and functions. These modules can have components selected for packaging based on the required functionality, commonly including Insulated Gate Bipolar Transistors (IGBTs), Power Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs), and Power Integrated Circuits, among others. Power semiconductor modules have very high heat dissipation requirements. As one of the main core components, the ceramic circuit board is also the first point of contact for heat. Therefore, high thermal conductivity AlN ceramic substrates are undoubtedly an ideal choice, especially for automotive electronic IGBT modules.

Power LED Packaging

LEDs are semiconductor chips that convert electricity into light. Scientific research indicates that only 20%-30% of electrical energy is effectively converted into light energy, with the remainder dissipated as heat. If there is no suitable method for rapidly dissipating this heat, it can cause the operating temperature of the lighting fixture to increase sharply, significantly shortening the lifespan of the LED. The emergence of ceramic circuit boards has effectively addressed this heat dissipation issue in LED lighting, particularly through the application of AlN ceramic substrates. In LED packaging, the heat generated is quickly transferred to the high thermal conductivity AlN ceramic substrate, achieving rapid heat dissipation, which can effectively reduce device damage and better maintain lifespan.

Summary

Compared to aluminum oxide ceramic substrates, the application range of aluminum nitride ceramic substrates in China is currently relatively narrow due to factors such as high production process requirements and higher costs, primarily being used in high-end electronic fields. However, with the continuous upgrading of technology in the electronic information industry, the trend towards miniaturization and functional integration of PCB substrates is emerging. The market's demand for the thermal conductivity and high-temperature resistance of heat dissipation substrates and packaging materials is constantly increasing, making it difficult for materials with performance comparable to ordinary substrates to meet market requirements. Thus, the aluminum nitride ceramic substrate industry is presented with opportunities for development. Consequently, aluminum nitride has become the most关注ed packaging substrate material at present.