Preparation and properties of Si3N4/PS composites used for electronic packaging

A kind of polymer composite was fabricated using polystyrene as the matrix and Si₃N₄ powder as filler employing the method of heat press molding. Microstructure, thermal conductivity and dielectric constant of the Si₃N₄ filled composite were evaluated. The effect of the volume fraction of Si₃N₄, the particle size of the polystyrene matrix and the silane treatment of Si₃N₄ filler on the thermal conductivity of the composite was investigated; dielectric constant of the composite was evaluated. The main factors that affect the thermal conductivity of the composite were confirmed through theoretical analyzing of the experimental data and the thermal conductivity model. Experimental results show that with the filler content increasing, a thermally conductive network is formed in the composites, thus the thermal conductivity of the composite increases rapidly. The composites experience a highest thermal conductivity of 3.0 W/m K when the volume fraction of the filler reaches 40%. The increasing of thermal conductivity is dominated by the ease of forming a thermal conductive network. A larger polystyrene particle size, a higher Si₃N₄ filler content and the silane treatment of the filler have a beneficial effect on improving the thermal conductivity. The dielectric constant increases with the content of Si₃N₄ filler, however, it remains at a relatively low lever (<4, at 1 MHz).     

Fabrication of a polymer composite with high thermal conductivity based on sintered silicon nitride foam

A novel route was developed to fabricate Si₃N₄/epoxy composite. In this route, the Si₃N₄ particles were constructed into the foamed shape by using protein foaming method, firstly. Then the Si₃N₄ foams were sintered to bond these Si₃N₄ particles together. Finally, the Si₃N₄/epoxy composite was fabricated by infiltrating the epoxy resin solution into the sintered Si₃N₄ foams. This route was proved to be an efficient way in enhancing the thermal conductivity of epoxy matrix at a low loading fraction. For example, the thermal conductivity of the as-prepared Si₃N₄/epoxy composite with a loading fraction of 22.2 vol% was up to 3.89 W m⁻¹ K⁻¹, which was about 17 times higher than that of neat epoxy.     

Enhanced thermal conductivity of Cu matrix composites reinforced with Ag-coated β-Si3N4 whiskers

Cu matrix composites reinforced with 10 vol.% Ag-coated β-Si₃N₄ whiskers (ASCMMCs) were prepared by powder metallurgy method. With the aim of improving the thermal conductivity of the composites, a quite thin Ag layer was deposited on the surface of β-Si₃N₄ whiskers. The results indicated that thermal conductivity of ASCMMCs with 0.30 vol.% Ag (0.30ASCMMCs) reached up to 273 W m⁻¹ K⁻¹ at 25 °C, which was 98 W m⁻¹ K⁻¹ higher than that of Cu matrix composites reinforced with uncoated β-Si₃N₄ whiskers (USCMMCs). The Ag coating could promote the densification of composites, reduce the aggregation of β-Si₃N₄ whiskers and enhance the Cu/Si₃N₄ interfacial bonding, therefore it could efficiently enhance the thermal conductivity of Cu matrix composites reinforced with β-Si₃N₄ whiskers (SCMMCs).     

High conductive ethylene vinyl acetate composites filled with reduced graphene oxide and polyaniline

A conductive network composed of reduced graphene oxide (RGO) planes and polyaniline (PANI) chains was designed and fabricated by in situ polymerization of aniline monomer on the RGO planes. It was further used for fabrication of conductive composites with a polymer matrix–ethylene vinyl acetate (EVA). The composites achieve improved conductivity at a low filler loading although the host polymer–EVA–is of insulator. For instance, compared to the pure EVA polymer, the conductivity of the composite filled with 4.0 wt.% RGO and 8.0 wt.% PANI increases from 1.2 × 10^?14 S cm^?1 to 1.07 × 10^?1 S cm^?1. In addition, thermal stability of the composites is also enhanced by the filler loading.     

An innovative process to fabricate copper/diamond composite films for thermal management applications

Diamond dispersed copper matrix (Cu/D) composite films with strong interfacial bonding were produced by tape casting and hot pressing without carbide forming additives. The tape casting process offers an original solution to obtain laminated materials with accurate thickness control, smooth surface finish, material net-shaping, scalability, and low cost. This study presents an innovative process of copper submicronic particles deposition onto diamond reinforcements prior to densification by hot pressing. Copper particles act as chemical bonding agents between the copper matrix and the diamond reinforcements during hot pressing, thus offering an alternative solution to traditionnal carbide-forming materials in order to get efficient interfacial bonding and heat-transfer in Cu/D composites. It allows high thermal performances with low content of diamond, thus enhancing the cost-effectiveness of the materials. Microstructural study of composites by scanning electron microscopy (SEM) was correlated with thermal conductivity and thermal expansion coefficient measurements. The as-fabricated films exhibit a thermal conductivity of 455 W m^?1 K^?1 associated to a coefficient of thermal expansion of 12 × 10^?6 °C^?1 and a density of 6.6 g cm^?3 with a diamond volume fraction of 40%, which represents a strong enhancement relative to pure copper properties (λ_Cu = 400 W m^?1 K^?1, α_Cu = 17 × 10^?6 °C^?1, ρ_Cu = 8.95 g cm^?3). The as-fabricated composite films might be useful as heat-spreading layers for thermal management of power electronic modules.     

Study on tribological behavior of electrodeposited Cu–Si3N4 composite coatings

Cu–Si₃N₄ composite coatings were prepared by electrolysis from a copper sulphate solution containing dispersed Si₃N₄ particles of 0.4 or 1 μm mean size. Wear behavior of Cu–Si₃N₄ composite and pure copper coatings were evaluated using a pin-on-disc test machine under dry condition sliding. Effects of current density and particle concentration on the incorporation percentage of Si₃N₄, the preferred orientation of copper crystallites, the microstructure, the microhardness and the wear resistance of the coatings were determined. Si₃N₄ particles in the copper matrix resulted in the production of composite deposits with smaller grain sizes and led to change the preferred orientation growth from [1 0 0] to [1 1 0]. It was proved that the presence of Si₃N₄ particles decreases the wear loss and the friction coefficient of the coating. According to the results, the friction coefficient decreased dramatically from 0.52 to 0.26 for pure copper coatings to 0.16–0.24 for Cu–Si₃N₄ composite coatings. In addition, fluctuation of friction coefficient values for Cu–Si₃N₄ composite coating was lower compared with the pure copper coating. The wear properties of Cu–Si₃N₄ composite coatings were shown to depend on the weight fraction, the size and the distribution of co-deposited particles.     

Microstructure and properties of the Si3N4/silica aerogel composites fabricated by the sol–gel method via ambient pressure drying

Si₃N₄ particle reinforced silica aerogel composites have been fabricated by the sol–gel method via ambient pressure drying. The microstructure and mechanical, thermal insulation and dielectric properties of the composites were investigated. The effect of the Si₃N₄ content on the microstructure and properties were also clarified. The results indicate that the obtained mesoporous composites exhibit low thermal conductivity (0.024–0.072 Wm^− 1 K^− 1), low dielectric constant (1.55–1.85) and low loss tangent (0.005–0.007). As the Si₃N₄ content increased from 5 to 20 vol.%, the compressive strength and the flexural strength of the composites increased from 3.21 to 12.05 MPa and from 0.36 to 2.45 MPa, respectively. The obtained composites exhibit considerable promise in wave transparency and thermal insulation functional integration applications.     

Electrical properties and thermal expansion of cobalt doped apatite-type lanthanum silicates based electrolytes for IT-SOFC

The thermal expansion and conductivities have been investigated for Co³⁺ doped lanthanum silicates. The apatite-type lanthanum silicates with formula La₁₀Si_6?xCo_xO_27?x/2 (x = 0.2, 0.4, 0.6, 0.8, 1.0, 1.5) were synthesized by sol–gel process. The thermal expansion coefficient (TEC) of La₁₀Si_6?xCo_xO_27?x/2 was improved with increasing cobalt content because of the lower valence and larger radius of Co³⁺ ion compared to Si⁴⁺. Analysis of AC impedance spectroscopy showed that conductivity increased first and then decreased with increasing cobalt content. There is an optimum doping amount of cobalt and La₁₀Si_5.2Co_0.8O_26.6 exhibits the highest conductivity of 3.33 × 10^?2 S/cm at 800 °C. When x ≤ 0.8, the local distortion caused by doping with Co³⁺ can significantly affect the oxygen channels and assist the migration of the interstitial oxide ions, resulting in the improvement of ionic conductivity. However, excess Co³⁺ dopant (0.8 < x ≤ 1.5) reduced the number of interstitial oxide ions and decreased the conductivity.     

The effect of interfacial state on the thermal conductivity of functionalized Al2O3 filled glass fibers reinforced polymer composites

Rapidly increasing packaging density of electronic devices puts forward higher requirements for thermal conductivity of glass fibers reinforced polymer (GFRP) composites, which are commonly used as substrates in printed circuit board. Interface between fillers and polymer matrix has long been playing an important role in affecting thermal conductivity. In this paper, the effect of interfacial state on the thermal conductivity of functionalized Al₂O₃ filled GFRP composites was evaluated. The results indicated that amino groups-Al₂O₃ was demonstrated to be effective filler to fabricate thermally conductive GFPR composite (1.07 W/m K), compared with epoxy group and graphene oxide functionalized Al₂O₃. It was determined that the strong adhesion at the interface and homogeneous dispersion of filler particles were the key factors. Moreover, the effect of interfacial state on dielectric and thermomechanical properties of GFRP composites was also discussed. This research provides an efficient way to develop high-performance GFRP composites with high thermal conductivity for integrated circuit packaging applications.     

Thermal conductivity of epoxy composites with a binary-particle system of aluminum oxide and aluminum nitride fillers

Aluminum oxide and aluminum nitride with different sizes were used alone or in combination to prepare thermally conductive polymer composites. The composites were categorized into two systems, one including composites filled with large-sized aluminum nitride and small-sized aluminum oxide particles, and the other including composites filled with large-sized aluminum oxide and small-sized aluminum nitride. The use of these hybrid fillers was found to be effective for increasing the thermal conductivity of the composite, which was probably due to the enhanced connectivity offered by the structuring filler. At a total filler content of 58.4 vol.%, the maximum values of both thermal conductivities in the two systems were 3.402 W/mK and 2.842 W/mK, respectively, when the volume ratio of large particles to small particles was 7:3. This result was represented when the composite was filled with the maximum packing density and the minimum surface area at the same volume content. As such, the proposed thermal model predicted thermal conductivity in good agreement with experimental values.     

Effect of polymer modifier chain length on thermal conductive property of polyamide 6/graphene nanocomposites

The influence of polymer modifier chain length on the thermal conductivity of polyamide 6/graphene (GA) nanocomposites, including through-plane (λ_z) and in-plane (λ_x) directions were investigated. Here, three chain lengths of double amino-terminated polyethylene glycol (NH₂–PEG–NH₂) were used to covalently functionalize graphene with graphene content of 5.0 wt%. Results showed that λ_z was enhanced with the chain length of NH₂–PEG–NH₂ increased, but λ_x reached a maximum value at a certain chain length of NH₂–PEG–NH₂. The maximum λ_z and λ_x of GA are 0.406 W m⁻¹ K⁻¹ and 9.710 W m⁻¹ K⁻¹, respectively. This study serves as a foundation for further research on the thermal conductive property of graphene nanocomposites using different chain lengths of polymer modifier to improve the λ_z and λ_x of the thermal conductive materials.     

Structure and thermal conductivity of powder injection molded AlN ceramic

AlN powders doped with Y₂O₃ (5 wt.%) were compacted by employing powder injection molding (PIM) technique. The binder consisted of paraffin wax (PW, 60 wt.%), polypropylene (PP, 35 wt.%) and stearic acid (SA, 5 wt.%). The feedstock was prepared with a solid loading of 62 vol.%. The binder was removed through debinding process in two steps, solvent debinding followed by thermal debinding. At last, the debound samples were sintered in flowing nitrogen gas at atmospheric pressure. The result reveals that thermal debinding atmosphere has significant effect on the thermal conductivity and structure of AlN ceramics. The thermal conductivity of injection molded AlN ceramics thermal debound in flowing nitrogen gas is 231 W m^?1 K^?1.     

Polysaccharidic binders for the conception of an insulating agro-composite

The objective of this study is the formulation of a natural polysaccharidic binder for the conception of an insulating bio-based composite made with sunflower stalk particles. The formulation was performed using chitosan cross-linked with Genipin and mixed with alginate, guar gum and starch. A fractional factorial experimental design within 32 essays was established to find the formulation leading to composites with the best combination between good mechanical properties and limited amount of chitosan in the binder. Composites with a thermal conductivity (κ) of 0.07 W m⁻¹ K⁻¹ and a maximum tensile stress (σ_max) of 0.2 MPa were obtained with a total binder ratio of 5.5% (w/w). The results of this study show that the insulating bio-based composites evaluated have competitive mechanical and thermal performances compared with other eco-friendly insulating materials available on the market.     

Porous high entropy (Zr0.2Hf0.2Ti0.2Nb0.2Ta0.2)B2: A novel strategy towards making ultrahigh temperature ceramics thermal insulating

Transition metal diborides based ultrahigh temperature ceramics (UHTCs) are characterized by high melting point, high strength and hardness, and high electrical and thermal conductivity. The high thermal conductivity arises from both electronic and phonon contributions. Thus electronic and phonon contributions must be controlled simultaneously in reducing the thermal conductivity of transition metal diborides. In high entropy (HE) materials, both electrons and phonons are scattered such that the thermal conductivity can significantly be reduced, which opens a new window to design novel insulating materials. Inspired by the high entropy effect, porous HE (Zr_0.2Hf_0.2Nb_0.2Ta_0.2Ti_0.2)B₂ is designed in this work as a new thermal insulting ultrahigh temperature material and is synthesized by an in-situ thermal borocarbon reduction/partial sintering process. The porous HE (Zr_0.2Hf_0.2Nb_0.2Ta_0.2Ti_0.2)B₂ possesses high porosity of 75.67%, pore size of 0.3–1.2 μm, homogeneous microstructure with small grain size of 400–800 nm, which results in low room temperature thermal diffusivity and thermal conductivity of 0.74 mm² s⁻¹ and 0.51 W m⁻¹ K⁻¹, respectively. In addition, it exhibits high compressive strength of 3.93 MPa. The combination of these properties indicates that exploring porous high entropy ceramics such as porous HE (Zr_0.2Hf_0.2Nb_0.2Ta_0.2Ti_0.2)B₂ is a novel strategy in making UHTCs thermal insulating.     

Development of electromagnetic shielding materials from the conductive blends of polystyrene polyaniline-clay nanocomposite

Electromagnetic interference shielding composite materials were developed from the conductive blends of nanostructured polyaniline-clay composite (PANICN) and Polystyrene (PS) by a one step host matrix assisted emulsion polymerization of anilinium salt of 3-pentadecyl phenol-4-sulphonic acid (3-PDPSA) in clay. 3-PDPSA was derived from cashew nut shell liquid, a low cost renewable resource based product. These blends were characterized using Uv–visible and FT-IR spectroscopy, XRD, electrical conductivity, thermal property, dielectric property and electromagnetic shielding efficiency. The interactions between the primary particles and host matrix were elucidated from the studies made through spectroscopy and rheology. The key finding of the research is that this low cost PANICNPS blend with superior electrical conductivity (7.6 × 10^?1 S/m), excellent thermal stability and EMI SE of 10–20 dB at 8 GHz makes them as a promising candidate for application in EMI shielding and antistatic discharge matrix for the encapsulation of micro electronic devices.     

Investigation of thermal conductivity and dielectric properties of LDPE-matrix composites filled with hybrid filler of hollow glass microspheres and nitride particles

The hybrid filler of hollow glass microspheres (HGM) and nitride particles was filled into low-density polyethylene (LDPE) matrix via powder mixing and then hot pressing technology to obtain the composites with higher thermal conductivity as well as lower dielectric constant (D_k) and loss (D_f). The effects of surface modification of nitride particles and HGMs as well as volume ratio between them on the thermal conductivity and dielectric properties at 1 MHz of the composites were first investigated. The results indicate that the surface modification of the filler has a beneficial effect on thermal conductivity and dielectric properties of the composites due to the good interfacial adhesion between the filler and matrix. An optimal volume ratio of nitride particles to HGMs of 1:1 is determined on the basis of overall performance of the composites. The thermal conductivity as well as dielectric properties at 1 MHz and microwave frequency of the composites made from surface-modified fillers with the optimal nitride to HGM volume ratio were investigated as a function of the total volume fraction of hybrid filler. It is found that the thermal conductivity increases with filler volume fraction, and it is mainly related to the type of nitride particle other than HGM. The D_k values at 1 MHz and microwave frequency show an increasing trend with filler volume fraction and depend largely on the types of both nitride particles and HGMs. The D_f values at 1 MHz or quality factor (Q × f) at microwave frequency show an increasing or decreasing trend with filler volume fraction and also depend on the types of both nitride particle and HGM. Finally, optimal type of HGM and nitride particles as well as corresponding thermal conductivity and dielectric properties is obtained. SEM observations show that the hybrid filler particles are agglomerated around the LDPE matrix particles, and within the agglomerates the smaller-sized nitride particles in the hybrid filler can easily form thermally conductive networks to make the composites with high thermal conductivity. At the same time, the increase of the value D_k of the composites is restricted due to the presence of HGMs.     

Thermal and electrical properties of magnetite filled polymers

By the addition of metal-oxide particles to plastics the electrical and thermal conductivity of polymers can be increased significantly. Such particle filled polymers can substitute metals and metal oxides in applications like radio frequency interference shielding. Furthermore, particle filled polymers with higher thermal conductivity than unfilled ones become more and more important in applications with decreasing geometric dimensions and increasing output of power, like in computer chips.Therefore, thermal and electrical properties of polypropylene and polyamide with metal-oxide particle filler (magnetite, Fe₃O₄) are investigated. Different particle sizes of magnetite and types of additives were added in various proportions to a standard polypropylene and polyamide in an extrusion process. Samples were prepared by injection molding to investigate thermal and electrical properties systematically.The thermal conductivity increases from 0.22 to 0.93 W/(m K) for a filler content of 44 vol% of magnetite, whereas the electrical resistivity decreases more than seven orders of magnitude from an insulator (0% of magnetite) to 10 kΩ m (47 vol% of magnetite).The experimental results of thermal and electrical conductivity were correlated to the amount and particle sizes of magnetite filler. Electrical resistivity shows a significant drop at the theoretical percolation threshold (∼0.33) and for filler contents exceeding 33 vol% the magnetite particles have point contacts and are surrounded by the polymer matrix.     

Fabrication,mechanical properties and microstructure analysis of Si3N4/SiC nanocomposite

Ceramic nanocomposites, Si₃N₄ matrix reinforced with nano-sized SiC particles, were fabricated by hot pressing the mixture of Si₃N₄ and SiC fine powders with different sintering additives. Distinguishable increase in fracture strength at low and high temperatures was obtained by adding nano-sized SiC particles in Si₃N₄ with Al₂O₃ and/or Y₂O₃. Si₃N₄/SiC nanocomposite added with Al₂O₃ and Y₂O₃ demonstrated the maximum strength of 1.9 GPa with average strength of 1.7 GPa. Fracture strength of room temperature was retained up to 1400 as 1 GPa in the sample with addition of 30 nm SiC and 4 wt% Y₂O₃. Striking observation in this nanocomposite is that SiC particles at grain boundary are directly bonded to Si₃N₄ grain without glassy phases. Thus, significant improvement in high temperature strength in this nanocomposite can be attributed to inhibition of grain boundary sliding and cavity formation primarily by intergranular SiC particles, besides crystallization of grain boundary phase.     

Thermal conductivity of Cu–Zr/diamond composites produced by high temperature–high pressure method

Copper matrix composites reinforced with about 90 vol.% of diamond particles, with the addition of zirconium to copper matrix, were prepared by a high temperature–high pressure method. The Zr content was varied from 0 to 2.0 wt.% to investigate the effect on interfacial microstructure and thermal conductivity of the Cu–Zr/diamond composites. The highest thermal conductivity of 677 W m⁻¹ K⁻¹ was achieved for the composite with 1.0 wt.% Zr addition, which is 64% higher than that of the composite without Zr addition. This improvement is attributed to the formation of ZrC at the interface between copper and diamond. The variation of thermal conductivity of the composites was correlated to the evolution of interfacial microstructure with increasing Zr content.     

Characterization of mechanochemically synthesized MHSO4–H4SiW12O40 composites (M = K,NH4, Cs)

Anhydrous proton conductive MHSO₄–H₄SiW₁₂O₄₀ (MHS–STA) composites were successfully synthesized using mechanochemical treatment. 80MHS·20STA (mol%) composite, for example, showed very high anhydrous proton conductivity above 10^?3 S cm^?1 in a temperature range from 160 to 60 °C under ambient pressure. From the X-ray diffraction study, it was confirmed that the mechanochemical treatment induced chemical interactions via ion-exchange between M⁺ ion in MHS and H⁺ ion in STA. Furthermore, phase-transition of raw substances, such as melting, dehydration and superprotic phase-transition, was suppressed in mechanochemically synthesized MHS–STA composites, indicating that improvement of anhydrous proton conductivity for MHS–STA composites is caused by the changes in protic conduction behavior.