Rice husk‐derived porous carbon/silica particles as green filler for electronic package application

Bio‐based porous carbon/silica particles (denoted as RH‐carbon/silica) were successfully prepared from agricultural waste rice husk by using acid‐hydrothermal treatment and pyrolysis under nitrogen condition. As green filler, the cure behavior, thermal‐mechanical properties, and thermal conductivity of the epoxy‐carbon/silica biocomposites at different filler contents (5, 9, 17, 29 wt %) were characterized. Because of superior surface properties (surface area, porosity, and silica segment) and high content of carbon component in the RH‐carbon/silica, the characteristics of the biocomposites were significantly improved with the increase of the filler content. At 29 wt % of filler content, the epoxy biocomposites exhibit lower curing temperature (148 °C), lower CTE (42 ppm/°C), higher T_g (123 °C), higher storage modulus (4059 MPa), and higher effective thermal conductivity (0.29 W/mK). In brief, the RH‐carbon/silica particles that can serve not only as reinforcing agent but also as thermal transport medium used in epoxy composite, is a green and high‐performance filler for this purpose. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44699.     

BN填充PA6基导热绝缘复合材料导热性能研究

以聚酰胺6（PA6）为基体, 氮化硼（BN）作为导热填料,经双螺杆挤出机熔融共混,模压成型制得导热绝缘复合材料。研究了BN含量、粒径、形状和不同BN粒径复配对复合材料导热性能的影响,并研究了BN含量和粒径对复合材料绝缘性能的影响。结果表明,在各种粒径下,复合材料热导率均随BN填充量的增加而增大;在BN粒径为5 μm、填充量为25 %（体积分数,下同）时,复合材料热导率达到1.2187 W/(m·K);在BN填充量相同时,填料粒径对复合材料热导率的影响不是简单的单调规律,呈现50、100 μm时较小,1、5、15 μm时较大,150 μm时最大的规律;片状BN填料比球状BN填料更有利于提高复合材料的热导率;2种不同粒径填料复配所填充的复合材料的热导率大于单一粒径填充的复合材料;5 μm与150 μm粒径BN复配,在填充量为20 %,配比为1:3时,复合材料的热导率最大,达到1.3753 W/(m·K),为纯PA6的4.9倍;在不同BN含量和粒径下,复合材料体积电阻率均能达到10000000000000 Ω·cm以上,满足绝缘性能。     

A Study of Encapsulation Resin Containing Hexagonal Boron Nitride (hBN) as Inorganic Filler

Preparation and property characterization of encapsulation resin contained hexagonal boron nitride (hBN) as inorganic filler were carried out in this work. The dielectric properties, coefficient of thermal expansion (CTE), thermal conductivity, curing kinetics, adhesion strength and viscosity of the resins with the load of hBN filler ranging from 9.2 to 25.7 vol.% (20–70 wt.%) were evaluated. It was found that the dielectric properties of resin containing SiO₂ filler are inferior to that containing hBN. Also, the resins possessed lower CTE and the higher T _g when the hBN contents were high (>15 vol.%) and the resin containing 25.7 vol.% hBN exhibited the largest thermal conductivity of 1.08 W/m K. Adhesion strength of the composite resins decreased with increase of hBN content and the adhesion strength on various substrates was found to be in the order of: alumina > Si wafer > eutectic PbSn solder. An erratum to this article can be found at     

Thermal conductivity of polyimide/boron nitride nanocomposite films

The thermal conductivity of polyimide/boron nitride (PI/BN) nanocomposite thin films has been studied for two sizes of BN nanofillers (40 and 120 nm) and for a wide range of content. A strong influence of BN particle size on the thermal conduction of PI has been identified. In the case of the largest nanoparticles (hexagonal‐BN), the thermal conductivity of PI/h‐BN (120 nm) increases from 0.21 W/mK (neat PI) up to 0.56 W/mK for 29.2 vol %. For the smaller nanoparticles (wurtzite‐BN), PI/w‐BN (40 nm), we observed two different behaviors. First, we see a decrease until 0.12 W/mK for 20 vol % before increasing for higher filler content. The initial phenomenon can be explained by the Kapitza theory describing the presence of an interfacial thermal resistance barrier between the nanoparticles and the polymer matrix. This is induced by the reduction in size of the nanoparticles. Modeling of the experimental results allowed us to determine the Kapitza radius a_K for both PI/h‐BN and PI/w‐BN nanocomposites. Values of a_K of 7 nm and >500 nm have been obtained for PI/h‐BN and PI/w‐BN nanocomposite films, respectively. The value obtained matches the Kapitza theory, particularly for PI/w‐BN, for which the thermal conductivity is expected to decrease compared to that of neat PI. The present work shows that it seems difficult to enhance the thermal conductivity of PI films with BN nanoparticles with a diameter <100 nm due to the presence of high interfacial thermal resistance at the BN/PI interfaces. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42461.     

Development of a ceramic-based composite for direct bonded copper substrate

In the present paper, a computational approach is presented to design alumina-based composite with tailored properties that could replace commercial alumina used in Direct Bonded Copper (DBC) substrates for applications in power electronic modules. A mean-field homogenization and effective medium approximation (EMA) using an in-house code is used for predicting potential optimum thermal and structural properties for DBC substrates by considering the effect of filler type, volume, and size in the alumina matrix. The primary goal for designing such alumina-based composites is to have enhanced thermal conductivity for effective heat dissipation and spreading capabilities together with a coefficient of thermal expansion (CTE) value that is close to the silicon chips in electronic circuits in order to avoid interface layers. At the same time, other functional properties like elastic modulus and electrical conductivity have to be maintained. Our strategy incorporates thermal and structural properties of composites as a constraint on the design process. Among various metallic and carbon-based fillers, chromium, silicon carbide and diamond fillers were found suitable candidates that could enhance the thermal and structural performance of the alumina-based substrates. As a validation, we developed alumina-silicon carbide (Al₂O₃-SiC) composites in line with the designed range of filler size and volume fraction using Spark Plasma Sintering (SPS) process. Thermal and structural properties including thermal conductivity, CTE, and elastic modulus are measured to complement the computational design. It is found that the developed computational design tool is accurate enough in predicting the desired properties of composite materials for DBC substrate applications.     

复合绝缘导热胶粘剂研究

以增韧的酚醛环氧树脂为基体树脂,氮化铝、氮化硼、氧化铝混杂粒子为导热填料制备了-新型绝缘导热胶粘剂。研究了填料用量对胶粘剂热导率、热阻、介电常数、体积电阻率等性能的影响,发现填料用量为40％时胶粘剂的热导率为O．99 W／mK,热阻为0．70℃／W,介电常数6,体积电阻率4．6×1012Ω·cm,20℃、200℃、250℃下的剪切强度分别为13．0MPa、10．0MPa、5．65MPa。研究结果表明该胶具备良好的电绝缘及力学性能,可以长期在150℃温度下使用,与不加导热填料的相同胶粘剂相比,具有良好的导热能力。     

环氧树脂/玻纤/BN导热绝缘复合材料制备研究

采用高温模压成型法制备环氧树脂/玻纤/BN导热复合材料,探讨了BN用量对复合材料力学性能、导热性能和电性能的影响,结果表明.当BN用量为10%时,复合材料的冲击强度和弯曲强度较佳;导热性能随BN用量的增加而提高,当BN用量为20%耐.热导率为0.7438 W/mk,此时复合材料仍保持较好的绝缘性能.     

Thermo-mechanical behaviors and moisture absorption of silica nanoparticle reinforcement in epoxy resins

An investigation of the thermo-mechanical behavior of silica nanoparticle reinforcement in two epoxy systems consisting of diglycidyl ether of bisphenol F (DGEBF) and cycloaliphatic epoxy resins was conducted. Silica nanoparticles with an average particle size of 20 nm were used. The mechanical and thermal properties, including coefficient of thermal expansion (CTE), modulus (E), thermal stability, fracture toughness (K_IC), and moisture absorption, were measured and compared against theoretical models. It was revealed that the thermal properties of the epoxy resins improved with silica nanoparticles, indicative of a lower CTE due to the much lower CTE of the fillers, and furthermore, DGEBF achieved even lower CTE than the cycloaliphatic system at the same wt.% filler content. Equally as important, the moduli of the epoxy systems were increased by the addition of the fillers due to the large surface contact created by the silica nanoparticles and the much higher modulus of the filler than the bulk polymer. In general, the measured values of CTE and modulus were in good agreement with the theoretical model predictions. With the Kerner and Halpin-Tsai models, however, a slight deviation was observed at high wt.% of fillers. The addition of silica nanoparticles resulted in an undesirable reduction of glass transition temperature (T_g) of approximately 20 °C for the DGEBF system, however, the T_g was found to increase and improve for the cycloaliphatic system with silica nanoparticles by approximately 16 °C. Furthermore, the thermal stability improved with addition of silica nanoparticles where the decomposition temperature (T_d) increased by 10 °C for the DGEBF system and the char yield significantly improved at 600 °C. The moisture absorption was also reduced for both DGEBF and cycloaliphatic epoxies with filler content. Lastly, the highest fracture toughness was achieved with approximately 20 wt.% and 15 wt.% of silica nanoparticles in DGEBF and cycloaliphatic epoxy resins, respectively.     

The effects of expanded perlite aggregate, silica fume and fly ash on the thermal conductivity of lightweight concrete

Thermal conductivity coefficients of concretes made up of mixtures of expanded perlite and pumice aggregates (PA) were measured. To determine the effect of silica fume (SF) and class C fly ash (FA) on the thermal conductivity of lightweight aggregate concrete (LWAC), SF and FA were added as replacement for cement by decreasing the cement weights in the ratios of 10%, 20% and 30% by weight.The highest thermal conductivity of 0.3178 W/mK was observed with the samples containing only PA and plain cement. It decreased with the increase of SF and FA as replacement for cement. The lowest value of thermal conductivity, which is 0.1472 W/mK, was obtained with the samples prepared with expanded perlite aggregate (EPA) replacement of PA and 70% cement+30% FA replacement of cement. Both SF and FA had a decreasing effect on thermal conductivity. EPA (used in place of PA) also induced a decrease of 43.5% in thermal conductivity of concrete.     

环氧树脂/氧化锌晶须/氮化硼导热绝缘复合材料的研究

以环氧树(脂EP)为基体,分别以氧化锌晶(须ZnOw)和ZnOw/氮化硼(BN)混合物为导热填料,制备了EP导热绝缘复合材料。研究了填料含量对复合材料导热性能、电绝缘性能及力学性能的影响,并利用扫描电镜对复合材料的断面形貌进行了观察。结果表明:随着导热填料含量的增大,复合材料的导热系数和介电常数增大,体积电阻率下降,而拉伸强度呈先增大后减小的趋势;在填料含量相同的情况下,EP/ZnOw/BN复合材料比EP/ZnOw复合材料具有更好的导热性能;当填料体积分数为15%时,EP/ZnOw/BN复合材料的热导率为1.06W/(mK)而,EP/ZnOw复合材料的热导率仅为0.98W/(mK)。     

Thermal properties of diamond/Ag composites fabricated by eletroless silver plating

Thermal management in microelectronic technology has become an important issue due to the increase of device power and integration levels. Diamond and silver were selected for the fabrication of composites with high thermal conductivity and low coefficient of thermal expansion (CTE). Diamond reinforcement powders with varied types, shapes and sizes were electroless plated by silver. Then these powders were hot-pressed in air at 600 °C, 500 MPa for 30 min to produce bulk silver matrix composites. The thermal conductivity and the CTEs of the composite at 20 vol.% are 420 W/m K and 12 ppm/K, respectively. These diamond/Ag composites have potential applications for the high integration electronic devices.     

Wire electrical discharge machinable SiC with GNPs and GO as the electrically conducting filler

SiC based composites filled with graphene nano-platelets (GNPs) or graphene oxide (GO) prepared by rapid hot-pressing exhibit sufficient electrical conductivity for their machinability by wire electro-discharge machining (WEDM). Composites microstructure anisotropy caused by graphene alignment as a consequence of rapid hot pressing was confirmed by measuring of electrical conductivity and thermal diffusivity. Electrical conductivity increased significantly with increased weight fraction of graphene in both measured directions. Highest value of 2031 S/m was obtained for composites with 15 wt. % of GNPs in parallel direction and only 1246 S/m in perpendicular direction to aligned GNPs. Thermal diffusivity is 63.3 mm²/s in parallel and only 23.3 mm²/s in perpendicular direction. The increase of the electrical conductivity has resulted in successful WEDM. The MRR was almost doubled when the filler concentration increased from 5 wt. % GNPs/GO to 15 wt. % GNPs. At the same time, the surface roughness decreased.     

Crystallization and thermal conductivity of poly (vinylidene fluoride)/boron nitride nanosheets composites

ABSTRACT

In this work, boron nitride (BN) and exfoliated boron nitride nanosheets (BNNs) were employed as thermal conductive fillers to improve the thermal conductivity of poly(vinylidene fluoride) (PVDF) composites. Results suggested that the thermal conductivity of PVDF increases significantly with an increase in loading content of functional fillers. When the mass ratio of fillers was more than 30 wt%, the heat conduction network was formed. BNNs were capable of forming denser heat conduction network as per the SEM observations. In this scenario, PVDF/BNNs composites demonstrated excellent thermal conductivity. For example, the thermal conductivity of PVDF/BNNs (60/40) was 0.82 W/mK, which was 2.4 times and 17% higher than that of neat PVDF and PVDF/BN (60/40) counterpart, respectively. The non-isothermal crystallization of corresponding composite was studied by Mo method. Combining with XRD results, both BN and BNNs acted as the nucleation agents but had no effect on crystal forms.     

Solvent-free fabrication of thermally conductive insulating epoxy composites with boron nitride nanoplatelets as fillers

A solvent-free method for the fabrication of thermally conductive epoxy-boron nitride (BN) nanoplatelet composite material is developed in this study. By this method, polymer composites with nearly any filler fractions can be easily fabricated. The maximum thermal conductivity reaches 5.24 W/mK, which is 1,600% improvement in comparison with that of pristine epoxy material. In addition, the as-fabricated samples exhibit excellent overall performances with great mechanical property and thermal stability well preserved.     

Polymer composites with enhanced thermal conductivity via oriented boron nitride and alumina hybrid fillers assisted by 3-D printing

Herein, oriented boron nitride (BN)/alumina (Al₂O₃)/polydimethylsiloxane (PDMS) composites were obtained by filler orientation due to the shear-inducing effect via 3-D printing. The oriented BN platelets acted as a rapid highway for heat transfer in the matrix and resulted in a significant increase in the thermal conductivity along the orientation direction. Extra addition of spherical Al₂O₃ enhanced the fillers networks and resulted in the dramatic growth of slurry viscosity. This, together with filler orientation induced the synergism and provided large increases in the thermal conductivity. A high orientation degree of 90.65% and in-plane thermal conductivity of 3.64 W/(m∙K) were realized in the composites with oriented 35 wt% BN and 30 wt% Al₂O₃ hybrid fillers. We attributed the influence of filler orientation and hybrid fillers on the thermal conductivity to the decrease of thermal interface resistance of composites and proposed possible theoretical models for the thermal conductivity enhancement mechanisms.     

Thermal properties of polytetrafluoroethylene/Sr2Ce2Ti5O16 polymer/ceramic composites

Polytetrafluoroethylene (PTFE) composites filled with Sr₂Ce₂Ti₅O₁₆ ceramic were prepared by a powder processing technique. The structures and microstructures of the composites were investigated by X‐ray diffraction and scanning electron microscopy techniques. Differential scanning calorimetry showed that the ceramic filler had no effect on the melting point of the PTFE. The effect of the Sr₂Ce₂Ti₅O₁₆ ceramic content [0–0.6 volume fraction (vf)] on the thermal conductivity, coefficient of thermal expansion (CTE), specific heat capacity, and thermal diffusivity were investigated. As the vf of the Sr₂Ce₂Ti₅O₁₆ ceramic increased, the thermal conductivity of the specimen increased, and the CTE decreased. The thermal conductivity and thermal expansion of the PTFE/Sr₂Ce₂Ti₅O₁₆ composites were improved to 1.7 W m^?1 °C^?1 and 34 ppm/°C, respectively for 0.6 vf of the ceramics. The experimental thermal conductivity and CTE were compared with different theoretical models. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

氮化硼/碳纳米管对乙烯基聚二甲基硅氧烷导热性能影响的研究

分别采用氮化硼和氮化硼/碳纳米管(CNTs)复配物制备导热乙烯基聚二甲基硅氧烷(PDMS)材料,并对其导热性能进行研究。结果表明:随着氮化硼和CNTs用量的增大,材料的热导率和热扩散系数逐渐增大;氮化硼用量足够大时,能够形成导热通路进而促进填料网络的形成;CNTs在填料中将氮化硼粒子之间形成的平面结构连接起来,从而形成三维网络结构;填料越多,形成的导热网络结构越强;氮化硼在网络中起主要作用,CNTs起到辅助增强的作用。     

Preparation of flexible transparent acryl/alumina nano-hybrid materials exhibiting low thermal expansion coefficient

In this study, flexible transparent hybrid films with low thermal expansion coefficient were prepared by combination of alumina fillers and polymerizable/non-polymerizable surface modifiers with carboxyl group. Four types of alumina fillers with different shape and size were used in this study, and could modify with surface modifiers containing carboxyl groups by electrostatic interaction and disperse homogeneously in resulting hybrid films regardless of the shape and size. So the hybrid films obtained showed high transmittance around 90%T, and it was considered, from transmission electron microscopic analysis, alumina fillers were dispersed at near original filler size, without aggregation. Moreover, thermal mechanical analysis cleared that the use of pillar or fiber type filler is more effective to reduce CTE compared with plate type fillers, especially CTE of hybrid film prepared with fiber type filler was drastically decreased to 17 ppm/K, while the influence by the difference of filler shape/size was not observed on tensile properties, surface hardness. By use of fiber type alumina filler and combination of polymerizable surface modifier and non-polymerizable surface modifier which seems to interact with matrix, for optimizing of the crosslink density, it was possible to reduce CTE, while the good mechanical properties was kept. Finally, hybrid film indicating low CTE value as 19 ppm/K, high flexibility (windable against 0.4 mm radius steel bar), and good tensile properties and surface hardness which were equal to or higher than those of matrix could prepared.     

Effective surface treatments for enhancing the thermal conductivity of BN‐filled epoxy composite

To improve the thermal conductivity of BN‐filled epoxy composite, admicellar polymerization was used to coat polystyrene and polymethyl methacrylate on the BN surface to improve the interfacial adhesion in the composite. The treated surface was characterized by FTIR and contact angle measurements. The results show that the admicellar treatment led to improved wettability of epoxy resin on the treated surface. Thermal conductivity of the composite increased from 1.5 W/mK for untreated BN to 2.69 W/mK when the admicellar‐treated BN was used, indicating improvement in the interfacial adhesion between BN and epoxy resin in the composite. The mechanical properties of the composite also improved significantly. The surfactant : monomer molar ratio of 1 : 10 was found to be the optimum condition for the admicellar polymerization process. The solubility parameter concept was used to explain the difference in the effectiveness of polystyrene and polymethyl methacrylate. When compared to the more conventional silane treatment, admicellar treatment was found to be more effective in improving the interfacial adhesion between the BN particles and epoxy resin. SEM micrographs of the fractured surface of the composite further confirm the improvement in the interfacial adhesion after the admicellar treatment. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Preparation and properties of thermally conductive photosensitive polyimide/boron nitride nanocomposites

A new thermally conductive photoresist was developed. It was based on a dispersion of boron nitride (BN) nanoflakes in a negative‐tone photosensitive polyimide (PSPI) precursor. 3‐Mercaptopropionic acid was used as the surfactant to modify the BN nanoflake surface for the dispersion of BN nanoflakes in the polymer. The thermal conductivity of the composite films increased with increasing BN fraction. The thermal conductivity of the PSPI/BN nanocomposite was up to 0.47 W m⁻¹ K⁻¹ for a mixture containing 30 wt % nanosized BN filler in the polyimide matrix. Patterns with a resolution of 30 μm were obtained from the PSPI/BN nanocomposites. The PSPI/BN nanocomposites had excellent thermal properties. Their glass‐transition temperatures were above 360°C, and the thermal decomposition temperatures were over 460°C. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011