Current location:Home > News > Industry

Preparation of high thermal conductivity silicon nitride ceramics and its application in electronic packaging substrates

Release time:2020-07-15
  Silicon nitride ceramics have excellent properties such as high strength, high toughness, corrosion resistance, high temperature resistance, oxidation resistance, low specific gravity and thermal shock resistance. In addition, silicon nitride ceramics have relatively high theoretical thermal conductivity, which makes them considered as a potential heat dissipation and packaging material for high-speed circuits and high-power devices.
Selection of raw material powder for the preparation of high thermal conductivity silicon nitride ceramics
Si3n4 has two crystal types: -Si 3 N 4 and -Si 3 N 4. The phase is unstable at high temperature and can be easily converted into phase at high temperature. It is found that the thermal conductivity of si3N4 ceramics increases linearly with the content of phase in the range of 40%-100%. Therefore, high purity phase is the key factor to obtain high thermal conductivity si3N4 ceramics. -Si 3 N 4 and -Si 3 N 4 powder can be used as raw materials to prepare -Si 3 N 4 ceramics.
With -Si 3 N 4 powder as raw material, the → phase transformation was promoted by the dissolution and precipitation mechanism in the sintering process. Beta phase and used as raw material to obtain pure beta phase silicon nitride ceramics, the sintering process of no phase change, driving force is small, sintering is relatively difficult, and as a result of Si 3 N 4 in 1800 ℃ or more prone to decomposition, in order to ensure the sintered density, with pressure sintering, a driving force in order to improve the sintering and its decomposition temperature, so the production cost to improve more.
Silicon nitride ceramic belongs to the strong covalent bond compound, relying on the solid phase diffusion are hard to sintering density necessary to add sintering additives, such as MgO style, Al 2 O 3, CaO and rare earth oxides, etc., in the sintering process, sintering additives can be added with the native oxide on the surface of the silicon nitride powders, forming low melting eutectic liquid, using liquid phase sintering mechanism to realize densification. Grain boundary phase formed by sintering additives, however, its low thermal conductivity, thermal conductivity of silicon nitride ceramics has adverse effects, such as silicon nitride ceramic commonly used Al 2 O 3 sintering additives, at high temperatures and silicon nitride and its oxide formation on the surface of SiAlON solid solution, causing the lattice distortion near the grain boundary, impeded the phonon heat transfer, so as to reduce the thermal conductivity of silicon nitride ceramics. Therefore, the key ways to improve the thermal conductivity of si3N4 are to select the appropriate sintering agent and formulate a reasonable formula system.
Oxide type of sintering additives is silicon nitride ceramic sintering additives commonly used system, the most common is the combination of metal oxide and rare earth oxides, Y 2 O 3 - MgO style system of sintering additives is high thermal conductive silicon nitride material applied more extensive system of sintering additives, in addition, Yb 2 O 3 is also a kind of common rare earth oxide sintering additives. In addition to common oxide sintering auxilaries, in recent years, one of the research hotspots in the preparation of Si3N4 ceramics, especially si3N4 ceramics with high thermal conductivity, is the study of non-oxide sintering auxilaries.
The advantage of non-oxide sintering agent is that it can reduce the extra oxygen introduced, which is of great significance for purifying silicon nitride crystal lattice, reducing grain boundary glass phase, improving thermal conductivity and high temperature performance. In addition to the studies in which rare earth oxides are replaced by rare earth non-oxides as sintering AIDS, some studies also use Mg non-oxides to replace MgO as sintering AIDS, so as to reduce the oxygen content in the crystal lattice and improve the thermal conductivity. However, non-oxide sintering auxilaries also have some problems, such as rare raw materials, high cost, difficult sintering and high conditions. Therefore, at present, non-oxide sintering auxiliaries have not been widely used in mass preparation of high thermal conductivity si3N4 materials.
Application of Silicon Nitride ceramics in electronic packaging substrates
With the rapid development of modern microelectronics technology, electronic systems and equipment are developing towards large-scale integration, miniaturization, high efficiency and high reliability. The improvement of electronic system integration will lead to the increase of power density and the increase of heat generated by electronic components and the overall work of the system. Therefore, effective electronic packaging must solve the heat dissipation problem of the electronic system, and the thermal conductivity of the substrate material within the electronic packaging is the key to affect the heat dissipation of the entire electronic system. Silicon nitride ceramics are structural ceramics with the best comprehensive performance. The theoretical thermal conductivity of single crystal silicon nitride can reach 400W/(m·k), and it has the potential to become a high thermal conductivity substrate. In addition, the thermal expansion coefficient of Si 3 N 4 is about 3.0× 10-6 /℃, which is well matched with Si, SiC, GaAs and other materials, making Si 3 N 4 an attractive substrate material of electronic devices with high strength and high thermal conductivity.