Fabrication And Properties Of Polyimide Composite Films With Low Thermal Expansion

With the development of the integrated circuit industry, high-performance microelectronic packing technology has formed high-tech industries compatible with IC industry. In terms of electronic packaging materials, low thermal expansion coefficient and good high frequency characteristics (ie. low dielectric constant and dielectric loss) are two important indicators. Polyimide (PI) has good prospects in electronic plastic packaging materials for its excellent mechanical,dielectric,electrical insulation,marked thermal stability and corrosion resistance properties.In this study, the high purity zirconium tungstate (ZrW2O8) powders have synthesized by two methods:direct solid-state reaction and step by step solid-state reaction, with the average size of 5～10μm and the average coefficient of thermal expansion of -9.604×10-6K-1.And then selecting the synthetic ZrW2O8 and n-SiC as fillers, ZrW2O8/PI and n-SiC/PI composite films were prepared by in-situ dispersive polymerization separately. The surface morphology, thermal expansion, dielectric properties and thermal stability of ZrW2O8/PI and n-SiC/PI composite films were studied by scanning electron microscopy (SEM), thermal mechanical analysis (TMA), impedance analyzer and thermal gravimetric analysis (TG) respectively. The following are the results:(1) ZrW2O8 particles are dispersed in the PI evenly, and the input of ZrW2O8 decreases the CTE of composite films. The higher ZrW2O8 content, the smaller the CTE; number of thermal cycles has little effect on the CTE, so the prepared PI films has good dimensional stability. The dielectric constant of ZrW2O8/PI composite films increases slowly with the content of filler, and the dielectric loss changes little with increasing content of filler, remaining in the lower range, and both of them are stable in a wide frequency range and have little dependence on temperature. With the increase of ZrW2O8 content, the thermal stability of composite films increases, while the mechanical properties of composite films decreases slightly, and still remaining in the higher range. Using KH550 to modify ZrW2O8, the modified ZrW2O8 disperses in the PI matrix more uniformly, resulting in smaller CTE,lower dielectric constant,lower dielectric loss of ZrW2O8/PI composite films.(2) n-SiC particles are dispersed in the PI matrix evenly by employing the in-situ polymerization. The coefficient of thermal expansion (CTE) of n-SiC/PI composite films decreases with the increasing the SiC loading, while the experimental data could be analyzed by Kerner model closely. The CTE of PI with n-SiC mass fraction of 15% is about 11% decrease than that of the pure PI. The dielectric constant and dielectric loss of films increase slowly with the content of n-SiC fillers, remaining in the lower range and stable in both a wide frequency range and a wide temperature range. Compared with the pure PI, the thermal stability of n-SiC/PI composite films has improved.Both PI composite films have low coefficient of thermal expansion, low dielectric constant, low dielectric loss (temperature,frequency stability), high thermal stability and other performance characteristics, can be well applied in electronic packaging materials.