| If the large amount of heat generated by the High-power LED cannot promptly and effectively dissipated, it will seriously affect the LED luminous intensity, stable performance of the packaging materials and shorten the life of the LED. At present, people's demand for green light is increasing day by day, which makes the application of LED more and more widely, but the heat dissipation problem of LED has been a big technical bottleneck which restricts its fast development. During the production process of the traditional LED packaging process, the thermal conductivity of the packaging materials has attracted much attention at home and abroad. But the current packaging materials cannot meet the heat dissipation requirements of High-power LED. So, how to effectively improve the thermal conductivity of the packaging materials has become the key to extend the life of High-power LED.Thermal conductivity of polymer matrix composites is related to many factors, which are mainly divided into two aspects: thermal conductive particles and polymer. At present, the method to increase the thermal conductivity of the packaging material is to add the thermal conductive particles into the polymer matrix. But, the increase of the thermal conductivity of materials is limited.In order to effectively improve the thermal conductivity of polymer matrix composites, this paper presents a method to improve the thermal conductivity of the composites by constructing a heat transfer channel in the interior of the material. In this paper, two methods are used to deal with boron nitride(BN) and iron powder(Fe) particles. Method one: the magnetic composite particles of BN coated iron powder were prepared by the method of surface treatment of boron nitride and iron powder by coupling agent. And then add the magnetic composite particles into the epoxy resin and placed under a uniform magnetic field curing, so as to prepare the orientation BN? Fe/Ep composite material. Due to the directional arrangement of the composite particles, the BN particles are contacted with each other, so the method constructed the phonon conduction channel in the material. Method two: the BN and Fe particles were aligned respectively in the uniform magnetic field by the BN-Fe-BN layer structure, to prepare the thermally conductive sheet with phonon and electronic double heat conduction channel. And then the orientation of BN-Fe-BN layered samples was prepared by overlapped the BN–Fe–BN thermally conductive sheet. The performance of the materials were characterized by optical microscope, BX53, SEM, thermal conductivity coefficient measuring instrument, broadband dielectric spectroscopy, XRD and so on. The main results are as follows:After BN and Fe particles were treated by coupling agent dry surface treatment, the composite magnetic particles of BN coated Fe powder were successfully prepared and after curing under the magnetic field, the particles inside the BN?Fe/Ep composite materials exhibit good orientation. When the mass fraction of particles composite filler was 50%, the thermal conductivity of materials reached 1.26 W/m?K, 6.3 times of the pure epoxy resin(0.2 W/m?K).When BN-F-BN structure under the magnetic field, BN particles can follow Fe powder together aligned along the magnetic field to reach the purpose of the BN and Fe particles are in contact with each other. So the phonon and electron double heat channels are constructed in the material. Also by the SEM observation, the results show that the particles in the direction of the magnetic field has a good consistency. XRD data representation I002/I100(I002/I100 represents the degree of orientation of BN) value reached 55.3, with a high degree of orientation. When the particle filled mass fraction is 50%. BN-Fe-BN structure oriented material thermal conductivity reached maximum 3.59 W/m?K, 18 times higher than that of pure epoxy resin thermal conductivity of 0.2 W/m?K.After the surface treatment of the coupling agent, the thermal conductivity particles obviously improved the dispersion of the particles and reduced the number of internal defects of the materials. The SEM diagram of the material section shows that the material surface treated by the coupling agent is smooth, the number and the width of the gap are obviously reduced, the phonon scattering problem is effectively reduced, and the thermal conductivity of the composite material is improved.In the frequency 10-1-106 HZ, the prepared orientation material has good electrical insulation properties. As to the aligned BN-Fe-BN, the dielectric constant and tan? do not show obvious change as compared with pure EP. The minimum resistivity of the sample was 6.52?106 ??cm in the frequency range 10-1–106 Hz. Meet the requirements of LED lamp, and in the field of microelectronics packaging also has a profound application prospects. |
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