高导热低介电损耗聚合物基复合材料的设计与制备

随着微电子集成技术的进步，电子设备中的热管理也变得越来越重要。在电子封装系统中，聚合物基复合材料得到了广泛的应用，如封装基板、印刷电路板、模塑料等。传统聚合物基复合材料的热导率低、热膨胀系数和介电损耗高，不能满足高性能电子设备的要求。因此研制高导热、低介电损耗的聚合物基复合材料十分必要并充满挑战。本工作选择高导热的氮化硼（BN）、流动性好的球形氧化铝（Al2O3）作为填料，以低介电损耗的改性聚苯醚（PPO）作为树脂基体，设计、制备、表征了兼具高导热、低热膨胀和超低介电损耗等性能的聚合物基复合材料。研究了多个对材料性能有影响的因素，并对相关机理进行了探讨。主要内容如下：

本工作以片状氮化硼为导热填料，三烯丙基异氰脲酸酯（TAIC）交联的PPO为树脂基体，制备了单一填料体系的PPO复合材料。研究结果表明，复合材料的热导率在氮化硼含量为40wt%（25.3v%）时达到1.26 W·m-1K-1，接近纯PPO树脂基体的6倍。此时的介电损耗为0.0021，热膨胀系数为65.3 ppm/℃，分别显著低于树脂基体（0.0035和89.6 ppm/℃）。为了解决填料的分散以及聚合物基体的界面相容性问题，本文采用多巴胺和硅烷偶联剂作为填料的表面改性剂，设计了效果较好的改性方案。

为了解决单一填料体系带来的高填充量时粘度高、导热性能提升有限、制备成本高等问题，本工作通过氮化硼和氧化铝混杂的方式制备了混杂填料体系的复合材料。另外，将树脂基体换成了介电损耗更低的不饱和烯烃共聚物（Ricon 100）交联的PPO。研究结果表明，随着混杂填料体积分数增加，球形氧化铝和片状氮化硼相互协作，构建了大量导热通路，更加有效地提高了材料的热导率，降低了热膨胀系数和介电损耗。当BN：Al2O3的体积比为1：4时且总体积分数为50v%时，热导率为1.45 W·m-1K-1，热膨胀系数为48.1 ppm/℃，介电损耗为0.0012。总之，复合材料的高导热、低热膨胀和超低介电损耗性能可以通过不同填料之间的混杂在较低填料总量的情况下同时实现。

With the advancement of microelectronics integration technology, thermal management in electronic equipment is becoming more and more important. In electronic packaging systems, polymer-based composites have been widely used, such as packaging substrates, printed circuit boards, molding compounds, etc. Traditional polymer-based composites have low thermal conductivity, high thermal expansion and high dielectric loss, which cannot meet the requirements of high performance electronic devices. Therefore, it is necessary and challenging to develop polymer-based composites with high thermal conductivity and low dielectric loss. In this work, polymer-based composites with high thermal conductivity, low thermal expansion and ultra-low dielectric loss were designed, prepared and characterized with high thermal conductive flake boron nitride and high fluidity spherical alumina as the fillers, modified polyphenylene oxide (PPO) with low dielectric loss as the resin matrix. The factors that influencing materials properties were studied and the related mechanisms were explored. The main contents are as follows:

A PPO composite system with single type of filler was prepared by using flake boron nitride as the thermally conductive filler and PPO crosslinked with TAIC as the resin matrix. With 40wt% (25.3v%) of BN, the thermal conductivity of the composites achieved at 1.26 W·m^-1K^-1, which is almost 6 times of that of pure PPO resin. Meanwhile, the dielectric loss and the coefficient of thermal expansion (CTE) decreased to 0.0021 and 65.3 ppm/℃, respectively, which are much lower than that of pure PPO (0.0035 and 85.6 ppm/℃). In order to improve the dispersion of fillers and the interfacial compatibility between fillers and the matrix, dopamine and silane coupling agents were applied as modification reagents. A modification scheme with good effect was designed.

To solve the problems of high viscosity caused by high filler loading, limited improvement of thermal conductivity and high cost of single filler system , hybrid systems were prepared by using both boron nitride and alumina as the fillers. In addition, the resin matrix was replaced an unsaturated olefin copolymer (Ricon 100) crosslinked PPO with lower dielectric loss. Along with the increase of filler volume fraction, spherical alumina and flake boron nitride synergistically built plenty of thermal conducting paths, which more effectively enhanced thermal conductivity while further lowered down CTE and dielectric loss of the material. When the volume ratio of BN/Alumina is 1:4 and total filler content is 50v%, the thermal conductivity reached 1.45 W·m^-1K^-1, while the CTE and dielectric loss were low as 48.1 ppm/℃and 0.0012, respectively. In summary, high thermal conductivity, very-low thermal expansion and ultra-low dielectric loss of composites can be simultaneously achieved at relatively low overall filler content through optimization of hybrid filler systems.

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