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Application Of Diamond In New Electronic Packaging Substrates

June 03,2023

Modern microelectronics technology is developing rapidly, with electronic systems and equipment moving towards large-scale integration, miniaturization, high efficiency, and high reliability. The improvement of electronic system integration will lead to an increase in power density, as well as an increase in heat generated by electronic components and the overall operation of the system. Therefore, effective packaging must solve the heat dissipation problem of electronic systems.

Good device heat dissipation depends on optimized heat dissipation structure design, packaging material selection (thermal interface material and heat dissipation substrate), and packaging manufacturing process. Among them, the selection of substrate materials is a key link, which directly affects the cost, performance, and reliability of the device. Generally speaking, the application of electronic packaging materials needs to consider two basic performance requirements: firstly, high thermal conductivity to achieve rapid heat transfer and ensure that the chip can work stably under ideal temperature conditions; At the same time, packaging materials need to have adjustable coefficient of thermal expansion, so as to keep matching with chips and packaging materials at all levels and reduce the adverse effects of thermal stress. The development trajectory of electronic packaging materials is the continuous improvement and optimization of these two properties.

Of course, new packaging substrate materials also need to consider other properties, such as high resistivity, low dielectric constant, dielectric loss, good thermal compatibility with silicon and gallium arsenide, high surface smoothness, good mechanical properties, and easy industrial production. Therefore, the selection of new packaging substrate materials is a hot topic for research and development in various countries. At present, several commonly used packaging substrates include Al2O3 ceramics, SiC ceramics, AlN and other materials.

As early as 1929, Siemens of Germany successfully developed Al2O3 ceramics, but the coefficient of thermal expansion and dielectric constant of Al2O3 are higher than those of Si single crystals, and the thermal conductivity is not high enough, leading to the fact that Al2O3 ceramic substrates are not suitable for use in high-frequency, high-power, and large-scale integrated circuits.

Subsequently, high thermal conductivity ceramic substrate materials SiC, AlN, SI3N4, and diamond gradually entered the market.

The thermal conductivity of SiC ceramics is high, and the higher the purity of SiC crystals, the higher the thermal conductivity; The biggest drawback of SiC is its high dielectric constant and low dielectric strength, which limits its high-frequency applications and is only suitable for low-density packaging.

AlN material has excellent dielectric properties and stable chemical properties, especially its coefficient of thermal expansion is better matched with silicon, which makes it a promising semiconductor packaging substrate material. But the thermal conductivity is low, and with the increasing demand for heat dissipation in semiconductor packaging, there are also certain development bottlenecks for AlN materials. Finally, diamond stands out. Diamond has good comprehensive thermophysical properties. Its thermal conductivity at room temperature is 700~2200W/(m · K), and its coefficient of thermal expansion is 0.8 × 10-6/K has many excellent characteristics in semiconductor, optical, and other fields, but a single diamond is not easy to be made into packaging materials and has a high cost. According to the mixing rule, the diamond/metal matrix composite prepared by adding diamond particles into high thermal conductivity metal matrix such as Ag, Cu and Al is expected to become a new electronic packaging material with both low thermal expansion coefficient and high thermal conductivity. Based on the excellent electrical conductivity and high thermal conductivity of copper, diamond/copper composite was developed as the substrate material for electronic packaging, and it was confirmed that diamond/copper composite has good plating and solderability, which meets the performance requirements of electronic packaging substrate materials with low thermal expansion coefficient and high thermal conductivity. Compared with Mo/Cu alloy, it has smaller density and lighter weight, so diamond is used as the reinforcement

Diamond/copper composite materials with copper as the matrix material can be used for chip packaging, which can improve the performance of electronic equipment systems and help reduce equipment weight. With the continuous tackling of various technical issues such as materials and devices, diamond has become a substrate material that combines advantages such as high thermal conductivity and good heat dissipation. It has broad application prospects in higher temperature environments and is the best semiconductor material for manufacturing low-power and high-power density devices. Its enormous potential has attracted more and more researchers to invest in it. The potential of diamonds will gradually be developed to meet the needs of the future semiconductor industry and occupy a place in semiconductor electronic packaging materials.

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