1. Research on Thermal Conductive Filler Technology

1.1 Development History of Thermal Conductive Filler Technology in China

As early as the 1970s, packaging resins had become the mainstream of microelectronic packaging materials, occupying over 95% of the entire packaging material market due to their simple production process and low cost. In order to improve the comprehensive performance of packaging resins and meet the requirements of modern and increasingly developing microelectronic packaging, the proportion of thermal conductive fillers in packaging resins will also be increasing. So to a certain extent, thermal conductive fillers play a decisive role in the performance of packaging resins, and the study of thermal conductive fillers has become an important component of the research and development of thermal conductive materials. Nowadays, the addition technology of thermal conductive fillers has become the core technology of thermal conductive material manufacturers.

The new generation of microprocessors requires thermal conductive materials to have higher thermal conductivity and better long-term reliability. Some application fields also need to consider functions such as insulation, vibration reduction, and fixation. Using in-situ solidified low modulus thermal conductive silicon gel as thermal conductive material is one of the effective ways to achieve this goal. Developing low-cost high thermal conductivity fillers to replace commonly used alumina fillers can reduce the amount of fillers added without reducing the thermal conductivity of the thermal conductive material, thereby improving the wetting performance of the thermal conductive material on the surface of the contact material, and achieving the goal of reducing contact thermal resistance and improving heat transfer efficiency. The use of surfactants to treat the surface of fillers and the design of particle size and distribution ratios can also improve the thermal conductivity of thermal conductive materials to a certain extent. Due to its low cost, this approach has been widely used.

Compared to foreign thermal conductive material production enterprises such as Shinyue in Japan and Dow Corning in the United States, the scale of Chinese thermal conductive material production enterprises is generally small, and the proportion of high-end products is relatively small. To improve the overall production technology level of thermal conductive materials in China, it is necessary to increase research and development investment in upstream raw materials, form a complete industrial chain, and follow the path of professional scale development, in order to meet the rapid development needs of China's electronic industry.

1.2 Current Status of Technical Research on Thermal Conductive Fillers

1.2.1 Research progress of thermal insulation materials

(1) Inorganic non-metallic thermal insulation materials

Usually metals (such as Au, Ag, Cu, Al, Mg, etc.) have high thermal conductivity, but they are all conductors and cannot be used as insulation materials. Some inorganic non-metallic materials, such as metal oxides Al2O3, MgO, ZnO, NiO, metal nitrides AlN, Si3N4, BN, and SiC ceramics, not only have high thermal conductivity, but also excellent insulation, mechanical, high-temperature, and chemical corrosion resistance, Therefore, it is widely used as a high heat dissipation interface material and packaging material in the fields of motors, electrical appliances, and microelectronics.

Ceramic packaging has the advantages of good heat resistance, less cracking, no damage after thermal shock, high mechanical strength, low thermal expansion coefficient, high electrical insulation performance, high thermal conductivity, high-frequency characteristics, high chemical stability, and good airtightness. It is suitable for packaging products with high reliability, high-frequency, high temperature resistance, and strong airtightness required by aerospace and military engineering. Due to the excellent comprehensive performance of ceramic materials, they are widely used in hybrid integrated circuits and multi chip modules. In situations where high sealing is required, ceramic packaging can be chosen. Japan is the leading foreign ceramic packaging material, accounting for 90% to 95% of the US ceramic packaging market and 95% to 98% of the US defense (military) ceramic packaging market. The traditional ceramic packaging material is Al2O3 ceramic, which has good insulation, chemical stability, and mechanical properties. Doping certain substances can meet the requirements of special packaging, and the price is low. It is currently the main ceramic packaging material. The thermal conductivity of SiC is very high, more than ten times that of Al2O3, and the thermal expansion coefficient is also lower than Al2O3 and AlN. However, the dielectric constant of SiC is too high, so it is only suitable for packaging with lower density. AlN ceramics are the most promising packaging material by domestic and foreign experts, with high thermal conductivity similar to SiC, lower thermal expansion coefficient than Al2O3, higher fracture strength than Al2O3, and Vickers hardness half of Al2O3. Compared with Al2O3, the low density of AlN can reduce weight by 20%. Therefore, AlN packaging materials have attracted more and more attention from the packaging industry at home and abroad.

(2) Polymer based thermal insulation materials

Due to the excellent electrical insulation, corrosion resistance, mechanical properties, and easy processing properties of polymer materials, people are gradually replacing traditional electrical insulation materials with polymer materials. However, most polymer materials have low thermal conductivity and cannot be directly used as thermal conductivity materials. It is necessary to add thermal conductivity substances to make them thermal insulation materials. According to the method of obtaining thermal conductivity, polymer thermal insulation materials can be divided into bulk thermal insulation polymers and filled thermal insulation polymers. Bulk thermal conductive insulating polymers improve their thermal conductivity by altering their molecular structure and condensed state during polymer synthesis or processing, resulting in high regularity. The filling type improves its thermal conductivity by adding thermal insulation fillers to polymer materials.