Very fast development of modern microelectronics technology is driving electronic systems and equipment towards large-scale integration, miniaturisation, great efficiency, and high dependability. The growing integration of electronic systems will result in higher power density and more heat produced overall by the functioning of the electronic components and systems. Consequently, efficient electronic packaging has to handle the heat dissipation issue of electronic systems. As a basic electronic component, electronic packaging ceramic substrate materials mainly provide mechanical support, airtight protection, and heat dissipation for electronic components and their interconnections.
Kinds of substrate materials
Plastics, metals and metal-based composite materials and ceramics are the three primary divisions into which common electronic packaging substrates fall: One often used material for electronic packaging substrates is ceramic ones. Their benefits over plastic packaging materials and metal substrates stem from:
excellent dependability and insulating performance. The most fundamental demand of electronic components for substrates is high resistivity. Generally speaking, the package dependability increases with increasing substrate resistance. Usually covalently linked compounds with improved insulating ability are ceramic materials.
The high-frequency properties are good; the dielectric constant is modest. Low dielectric constant and dielectric loss of ceramic materials can help to shorten signal delay time and raise transmission speed.
Low thermal mismatches rate and small thermal expansion coefficient. Usually with great melting point properties are covalent bond chemicals. Generally, the thermal expansion coefficient of ceramic materials is minimal since the melting point determines the smaller coefficient.
strong thermal conductivity Traditional heat transfer theory holds that cubic BeO, SiC, and AlN ceramic materials have theoretically thermal conductivity no less than that of metals.
Consequently, in high-reliability, high-frequency, high-temperature resistant and airtight product packaging in aviation, aerospace and military engineering, ceramic substrate materials are extensively used. Among common ceramic substrates include Al2O3 ceramic substrates, AlN ceramic substrates, BeO ceramic substrates, Si3N4 ceramic substrates, SiC ceramic substrates, etc.
Ceramic substrates for Al2O3
Al2O3 ceramics are a collection of several ceramics with Al2O3 as the main raw material, α-Al2O3 as the main crystal phase, and Al2O3 content more than 75% (mass fraction). Among their several benefits are plentiful raw material sources, inexpensive price, strong mechanical strength and hardness, good insulating performance, thermal shock resistance and chemical corrosion resistance, high dimensional precision, and good adherence to metal. It is a reasonably comprehensive performance ceramic substrate material. With 90% of all the ceramic substrates used in the electronics sector, Al2O3 ceramic substrates have become an integral component for this sector.
Currently in use most of the Al2O3 ceramic substrates are multi-layer substrates; the Al2O3 composition ranges from 85.0% to 99.5% (mass fraction). The Al2O3 content will raise sintering temperature and manufacturing costs at the same time as it improves the electrical insulation performance, thermal conductivity and impact resistance. Often adding a certain amount of sintering aids, such B2O3, MgO, CaO, SiO2, TiO2, Nb2O5, Cr2O3, CuO, Y2O3, La2O3 and Sm2O3 helps to lower the sintering temperature and guarantee the mechanical and electrical properties of the Al2O3 ceramic substrate.
AlN ceramic platform
AlN crystal has a lattice constant of α=0.3110 nm, c=0.4890 nm, hexagonal system characterised by wurtzite-type covalent bonds with [AlN4] tetrahedron as the structural unit. Its outstanding mechanical, electrical, and thermal qualities are found by this construction.
The key is to choose the suitable sintering aid since the sintering process of AlN ceramics requires dense sintering, low impurity content, low temperature, and low cost reduction. Experimentally, Y2O3, CaO, Li2O, BaO, MgO, SrO2, La2O3, HfO2 and CeO2 may efficiently promote the sintering of AlN ceramics; the ternary system Y2O3-CaO-Li2O is a very excellent sintering assist system.
BeO ceramic substrates
Among alkaline earth metal oxides, BeO crystal has a lattice constant of α=2.695Å, c=4.390Å, so it is the only hexagonal wurtzite structure available. BeO has quite good thermal conductivity because to its wurtzite type and strong covalent bond structure as well as relatively low relative molecular mass. One order of magnitude above Al2O3 ceramics, BeO has the highest thermal conductivity among the Ceramic material used nowadays at room temperature.
BeO has a great disadvantage: it is quite poisonous. Furthermore, BeO's melting point is (2570±20) ℃ and the production cost of pure BeO ceramics is significant as their sintering temperature exceeds 1900 ℃. The following causes restrict its manufacturing and utilisation as well as its marketing. Still employed, though, occasionally in satellite communications and avionics equipment, in order to achieve high thermal conductivity and high frequency properties, BeO. Ceramic substrate.
Ceramic substrate Si3N4
Comprising silicon and nitrogen, covalently linked compound are silicon nitride ceramic (Si3N4). Mechanical qualities of silicon nitride ceramic substrate are excellent. Its two to three times that of aluminium nitride and aluminium oxide are bending strength and fracture toughness. It also boasts great heat cycle resistance and thermal conductivity as well as great thermal radiation. It is acknowledged as a high thermal conductivity, highly reliable ceramic substrate material.
Si3N4 is a strong covalently linked molecule with a robust structure, so solid phase diffusion finds it difficult to sinter thickly. Adding sintering aids, including metal oxides (MgO, CaO, Al2O3) and rare earth oxides (Yb2O3, Y2O3, Lu2O3, CeO2), etc., helps to promote sintering; densification is accomplished via liquid phase sintering process.
With a thermal expansion coefficient of Si3N4 almost the lowest among ceramic materials—except from SiO2 (quartz—3.2×10−6/℃, roughly 1/3 of Al2O3). Its dielectric qualities are somewhat low (dielectric constant is 8.3, dielectric loss is 0.001~0.1), and its high production cost limits its utilisation as an electronic packaging ceramic substrate.
SiC ceramic substrates
SiC single crystal has rather good heat conductivity. While polycrystalline SiC ceramic has only 67W/(m·K), pure SiC single crystal at ambient temperature has as high as 490 W/(m·K) due to grain orientation variance. SiC is not fit as a packaging substrate material also because of low degree of insulation, significant dielectric loss, and poor high-frequency properties. Studies have revealed that adding a specific quantity of BeO to SiC-based materials can significantly increase their dielectric and insulating characteristics. Particularly as a substrate material with outstanding performance, the altered SiC material can be used as an insulating substrate material and heat sink for big-scale integrated circuits.
Unipretec say
A fundamental part of electronic packaging, the kind and performance of ceramic substrate materials directly influence the dependability and performance of electronic devices. By means of its competent R&D and production capacity in the field of ceramic substrate materials, Unipretec offers the market a range of ceramic substrate solutions. Unipretec will keep innovating and supporting the development of ceramic substrate materials towards higher performance and wider applicability as electronic packaging technology develops, so helping to shape the electronic packaging sector.