Nitride ceramics are ceramics with refractory compounds of nitrogen and metal or non-metal elements covalently bonded as the main component. The most widely used ceramics include silicon nitride (Si3N4), aluminum nitride (AlN), boron nitride (BN), and other ceramics. Among them, silicon nitride ceramics and aluminum nitride ceramics can be made into ceramic substrates for electronic packaging due to their excellent hardness, mechanical strength, and heat dissipation, and have good development prospects. In the preparation process of aluminum nitride and silicon nitride ceramic substrates, boron nitride ceramics play an important role.
Characteristics of Boron Nitride
Boron nitride is a binary compound composed of the same number of nitrogen atoms (N) and boron atoms (B), and its empirical formula is BN. According to the crystal form, boron nitride is divided into hexagonal boron nitride (hBN, also known as α-BN or g-BN), cubic boron nitride (CBN, also known as β-BN or z-BN), rhombohedral boron nitride (RBN) and wurtzite boron nitride (WBN).
Among them, cubic boron nitride and hexagonal boron nitride are more common crystal forms. The structure of cubic boron nitride is similar to that of diamond, which is extremely hard and widely used in industrial drilling and grinding tools. Hexagonal boron nitride is a white powder and an advanced ceramic material. Its crystal structure is very similar to that of graphite, and the physical and chemical properties of the two are also similar. Therefore, hexagonal boron nitride is also called “white graphite” and is the most commonly used form of boron nitride.
Characteristics of hexagonal boron nitride:
1 The expansion coefficient is equivalent to quartz, but the thermal conductivity is ten times that of quartz, the same as stainless steel. The high thermal conductivity of hot-pressed products is 50W/mK and the thermal shock resistance is excellent;
2 In terms of mechanical properties, it has the advantages of non-abrasiveness, good lubricity, and easy processing;
3 In terms of electrical properties, it has the advantages of good dielectric strength, low dielectric constant, low loss at high frequency, microwave penetration, and good electrical insulation;
4 In terms of thermal properties, it has the advantages of high thermal conductivity, high heat capacity, low thermal expansion, thermal shock resistance, high-temperature lubricity and high-temperature safety;
5 In terms of chemical properties, it has the advantages of chemical stability, corrosion resistance, oxidation resistance, low moisture, biological stability, and non-stick properties.
Application of Boron Nitride in Ceramic Substrates
1 Sintering Crucibles for Silicon Nitride/Aluminum Nitride Substrates
Boron nitride crucibles can be used for sintering silicon nitride substrates/structural parts, aluminum nitride substrates/structural parts, etc. The maximum operating temperature is 2100℃. They are resistant to repeated high and low-temperature impacts, carbon corrosion, non-reactive with metal and ceramic materials, non-adhesive, and have a long service life. They can replace graphite and alumina crucibles.
2 Boron Nitride Isolation Powder
Boron nitride isolation powder is used for green body isolation or buried firing during the sintering process of aluminum nitride/silicon nitride ceramic substrates. It can prevent the substrates from sticking to each other, and can easily separate the sintered substrate sheets without contaminating the product. It can also reduce the surface roughness of the substrate and improve the product qualification rate. The boron nitride layer on the surface of the sintered ceramic substrate can be removed by polishing and ultrasonic cleaning.