Types and Performance Characteristics of Ceramic Substrates in Electronic Packaging

Electronic packaging substrates come in a wide variety of types, typically categorized into plastic, metal, and ceramic substrates.
Plastic substrates are inexpensive but have low thermal conductivity and limited reliability, making them unsuitable for applications with high-performance demands.
Metal substrates, while offering excellent thermal conductivity, often suffer from mismatched thermal expansion coefficients and higher production costs.

Ceramic substrates, on the other hand, are widely adopted for electronic packaging due to their unique balance of properties. Compared with plastic and metal substrates, ceramics offer:

1. Excellent insulation and high reliability;
2. Low dielectric constant and superior high-frequency performance;
3. Low thermal expansion and high thermal conductivity;
4. Outstanding hermeticity, chemical stability, and strong protection for electronic systems.

These features make ceramic substrates ideal for aerospace, aviation, military, and other applications requiring high reliability, high-frequency operation, thermal resistance, and airtight packaging. Moreover, ultra-miniaturized electronic components used in mobile communications, computing, household appliances, and automotive electronics also frequently rely on ceramic substrate packaging.

Currently, the most commonly used ceramic substrate materials in electronic packaging include alumina (Al₂O₃), aluminum nitride (AlN), silicon nitride (Si₃N₄), silicon carbide (SiC), boron nitride (BN), and beryllium oxide (BeO).

Application Areas of Common Ceramic Substrate Materials

1. Alumina (Al₂O₃) Ceramic Substrate
Alumina substrates are produced in large volumes and used across diverse applications. However, their thermal conductivity, though higher than that of silicon, is still insufficient for high-frequency, high-power, or ultra-large-scale integrated circuits, which limits their use in advanced electronic systems.

2. Aluminum Nitride (AlN) Ceramic Substrate
The synthesis of AlN powder—the key raw material for AlN ceramics—is complex, energy-intensive, and costly. These factors restrict mass adoption, so AlN ceramic substrates are primarily utilized in high-end and precision electronic industries.

3. Silicon Nitride (Si₃N₄) Ceramic Substrate
Although Si₃N₄ offers good mechanical strength, its dielectric properties (dielectric constant ≈ 8.3, dielectric loss 0.001–0.1) are relatively poor, and its production cost is high. These limitations make it less favorable as a mainstream electronic packaging substrate.

4. Silicon Carbide (SiC) Ceramic Substrate
SiC possesses a very high dielectric constant—about four times that of AlN—and relatively low compressive strength. Consequently, it is suitable only for low-density packaging applications. Beyond integrated circuits and laser diodes, SiC is also used for conductive and structural components.

5. Beryllium Oxide (BeO) Ceramic Substrate
BeO ceramics exhibit exceptionally high thermal conductivity and desirable high-frequency characteristics. They are used in specific high-performance applications such as heat sinks for high-power transistors and semiconductor devices, emission and traveling wave tubes, lasers, klystrons, and avionics or satellite communication systems.

6. Boron Nitride (BN) Ceramic Substrate
Boron nitride offers excellent thermal conductivity that remains stable with temperature changes, a low dielectric constant, and strong electrical insulation. These properties make BN suitable for radar windows, high-power transistor bases, tube shells, heat sinks, and microwave output windows.

Performance of Ceramic Substrates of Various Materials: