Many people believe that ceramic substrates are the future trend of the electronics industry, and this trend is irreversible – this is mainly due to the fact that ceramic substrates can solve the increasingly serious heat dissipation problems of electronic packaging compared to other substrate materials, Therefore it is valued.
At present, ceramic substrate materials mainly include alumina, beryllium oxide and aluminum nitride, of which alumina ceramics are the most mature type, and are widely used for their good thermal shock resistance and electrical insulation properties, as well as mature manufacturing and processing technology. widely used.
However, it should be noted that “widely used” is not the same as “lower-end application”, and the two are often easily confused. In fact, although ceramic substrates have been maturely used in LED high-power lighting, high-power modules, refrigeration chips, automotive electronics and other fields, due to the difficulty of production and few production enterprises, product prices have been high, and the market is highly dependent on external high.
Take the alumina substrate as an example, it can be divided into different models such as 75 porcelain, 85 porcelain, 95 porcelain and 99 porcelain according to the purity. The biggest feature is low dielectric loss, little relationship between electrical properties and temperature, high mechanical strength, good chemical stability – and with the increase of alumina content, the above advantages will be further amplified, so 99.5%, or even The market for 99.9% alumina ceramic substrates is considerable. However, it is not easy to do high-purity alumina substrates well. Elastic modulus, elastic deformation cycle times, service life and reliability are all indispensable. Therefore, there are not many companies that have the ability to do well.
Performance comparison of alumina substrates with different purities
|Mmaterial||99.9% Al2O3||99.5% Al2O3||96% Al2O3|
|Bending strength (MPa)||660||440||300|
|Thermal conductivity (W/m・K)||33||32||23|
|Relative permittivity (25℃ 1MHz)||–||–||9.6|
|Relative dielectric constant (25℃ 10GHz)||10||9.9||–|
|Dielectric loss (25℃ 1MHz)||–||–||2*10-4|
|Dielectric loss (25℃ 10GHz)||1*10-4||1*10-4||–|
|Volume resistance (Ω・cm)||1015||1015||1014|
The Magical Use of High Purity Alumina Substrate
When it comes to the application of alumina substrates, we have to mention high-frequency circuit substrates. In recent years, the electronic communication market dominated by 5G communication is developing rapidly, product technology is constantly innovating, and the requirements for high-frequency and high-speed signals on materials are also increasing. In terms of material selection, high-purity alumina ceramics are the first choice because they can well meet the characteristics of high-frequency signals (high-frequency: above 300MHZ, that is, the short-wave frequency range with a wavelength of more than 1 meter).
Why do you say that? This is because as high frequency signals (which are constantly shifting between positive and negative phases) pass through the dielectric layer, the molecules in the dielectric try to orientate according to these electromagnetic signals, although in reality, since these molecules are cross-linked, they cannot really be Orientation. However, the change of frequency makes the molecules move continuously, generating a lot of heat, resulting in the loss of energy, which is also called “dielectric loss”. The dielectric loss of high-purity alumina ceramics is in a wide frequency range (including ultra-high frequency), and the loss value is small, and it does not change much with the increase of temperature, and has good thermal conductivity, strength and insulation. It is very suitable for use in high frequency bands.
In addition, substrates for optical communication devices, relay substrates and circuit substrates for other communication devices are also the advantageous application areas of high-purity alumina ceramics.
Preparation of alumina substrate
At present, the preparation process of alumina substrate can be divided into the following steps: raw material selection, mixing and crushing, defoaming, substrate forming, punching, sintering, cutting processing, finishing, and inspection.
Needless to say, the importance of raw material selection, in addition, the molding and sintering process is also a key factor in determining success or failure. In terms of molding technology, injection molding, dry pressing molding and tape casting are commonly used. However, although the injection molding efficiency is high, it is difficult to make large-sized sheets; dry pressing products have high density, and the flatness of the substrate is easy to ensure, but the production efficiency is low , high cost, and it is difficult to prepare ultra-thin substrates; tape casting has the dual advantages of high production efficiency and ultra-thinness, but due to the low density of the green body, it is easy to deform during sintering. Therefore, in order to improve the quality rate of large-sized substrates, the industry is currently focusing on the optimization of sintering methods and the selection of sintering aids.