Properties investigation on electrically conductive adhesives based on acrylate resin filled with silver microsheets and silver plating carbon fibers

The introduction of highly electrically conductive fillers (Ag microsheets and silver plating carbon fiber) can functionally improve the electrical conductivity of acrylate resin. In this study, Ag microsheets and Ag/CF were thus introduced into acrylate polymer via solution blending method under ultrasonication in order to improve the electrical conductivity of the acrylate resin. The properties and microstructures of Ag microsheets, CF, Ag/CF and ECAs were performed by scan electron microscope (SEM), X-ray diffraction analysis (XRD), etc. SEM images and XRD results illustrated that the impurities in carbon fiber could be completely removed after the adequately alkali treatment. The SEM images showed that large numbers of metallic silver particles were uniformly and densely coated on the surface of the carbon fibers and hybrid fillers (silver microsheets and Ag/CF) could homogeneously disperse in acrylate resin. Electrical conductivity measurements demonstrated that the electrical conductivity of ECAs increased with the increasing content of hybrid fillers and the percolation threshold of ECAs was 5 wt%. The electrical conductivity of ECAs at its percolation threshold was 15.79 S/cm, which was two orders of magnitude higher than that of the ECAs based on acrylate resin filled with silver microsheets. The increment in Ag/CF contents may decrease 180° peel strength and raise shear strength with low content of Ag/CF. The overall performance of ECAs was optimum with 2 wt% Ag/CF. The TGA analysis indicated that ECAs possess excellent thermal stability.     

The Sintering Behavior of Electrically Conductive Adhesives Filled with Surface Modified Silver Nanowires

Electrically conductive adhesives (ECAs) filled with sintered silver nanowires were prepared and the effect of different curing conditions on the electrical property of the ECAs was discussed. Silver nanowires with a diameter of 50–60 nm and a length of 2–3 μm were successfully synthesized through a polyol process and surface functionalized with dicarboxylic acid. Morphology studies showed that surface modified silver nanowires began to sinter at 200°C and became shorter and thicker, and eventually formed large chunks at higher temperatures. The conductive adhesives filled with 75 wt% of silver flakes and nanowires (3:2 weight ratio) were cured at different temperatures using two kinds of catalysts. The volume resistivity of the conductive adhesives cured at 300°C without a catalyst reached 5.8 × 10 ^–6 Ω cm. The dramatic improvement in the conductivity of the ECA is due to the sintering of silver nanowires and the high solid content resulting from the partial evaporation of polymer components.     

Novel flexible electrically conductive adhesives from functional epoxy,flexibilizers, micro‐silver flakes and nano‐silver spheres for electronic packaging

In this study, five different flexibilizers were added into a matrix resin to improve the flexibility of electrically conductive adhesives (ECAs). The flexible ECAs were fabricated from the matrix resin and electrically conductive fillers. Their curing was fixed at 150 °C for 30 min. Of the five flexibilizers, 1,3‐propanediol bis(4‐aminobenzoate) (PBA) had the best effect on the electrical, mechanical and thermal properties of the ECAs. During curing, PBA reacted with the functional epoxy in the matrix resin. The soft ether segments in PBA were grafted into the crosslinked epoxy network to form an orderly spaced mesh structure. This led to high‐temperature stability, with the pyrolysis temperature being above 350 °C. Flexible ECAs with a 10% weight ratio of PBA in the matrix resin had the best properties. Their viscosity and bulk resistivity were the lowest. Their flexibility and electrical conductivity were the highest. They also had low storage modulus which could effectively dissipate or reduce the residual shear stress generated by the mismatch of thermal expansion coefficient between chip and substrate. Their impact strength was the lowest, and the toughening effect was so significant that the improvement was about 48% compared to ECAs. © 2013 Society of Chemical Industry     

酚醛树脂/镀银碳纤维导热复合材料的制备与性能

采用化学镀的方法在碳纤维(CF)上镀一层银膜,然后采用搅拌混合的方法制备了酚醛树脂/镀银碳纤维(Ag-CF)导热复合材料,通过扫描电子显微镜(SEM)、X射线衍射仪(XRD)、X射线能量色散光谱仪(EDS)等方法对其结构和性能进行表征。结果表明,大量的银粒子均匀分布在CF表面;酚醛树脂/Ag-CF导热复合材料的导热系数、冲击强度和拉伸强度随着Ag-CF含量的增加而逐渐增加;Ag-CF的含量为7.0 %时,酚醛树脂/Ag-CF导热复合材料的综合性能最优,此时其导热系数为1.25 W/(m·K),冲击强度和弯曲强度分别为66.7 kJ/m2和139.2 MPa;残炭率为30 %时,添加量为7.0 %的复合材料对应温度为 500 ℃,高于纯酚醛树脂的 450 ℃。     

Sintering behavior and effect of silver nanoparticles on the resistivity of electrically conductive adhesives composed of silver flakes

In this paper, silver nanoparticles with size of 30–50 nm were synthesized by reducing silver nitrate with sodium borohydride and sodium citrate and using PVP as an adsorption agent in the ethanol solution. The experimental results indicate that the morphologies and sintering behaviors of both kinds of silver nanoparticles are impacted by glutaric acid and sintering temperature. The electrically conductive adhesives (ECAs) filled with micro-sized silver flakes and silver nanoparticles as hybrid fillers were fabricated and the electrical properties were investigated based on the fraction of the silver nanoparticles of the total of silver flakes and the curing temperature, etc. The incorporation of the untreated/treated silver nanoparticles into the polymer matrix with 65?wt% silver filler the resistivity increased in almost all cases, especially the high fraction and the low curing temperature. The curing temperature has influence on the resistivity of the ECAs filled with micro-sized silver flakes and the silver nanoparticles due to the sintering of the silver nanoparticles. The addition of 10% treated silver nanoparticles into the ECAs with 60?wt% silver fillers, the resistivity is slightly lower than that of the ECAs with micro-sized silver flakes. In the system of the ECAs with the high loading of silver fillers, the untreated/treated silver nanoparticles have little effect on the electrical conductivity. The results suggest that the morphology and distribution of silver fillers are the key to affect the conductivity of ECAs when nanoparticles are included in the system.     

镀银纳米石墨微片/丙烯酸酯导电压敏胶的研究

以天然EG(膨胀石墨)为原料,采用超声分散法制得NanoG(纳米石墨微片);然后采用化学镀法制备导电填料Ag-NanoG(镀银纳米石墨微片);最后采用溶液共混法制备丙烯酸酯类Ag-NanoG/PSA(镀银纳米石墨微片/导电压敏胶)。研究结果表明:NanoG表面镀上了一层均匀紧凑的金属Ag,Ag层厚度为250 nm左右,其质量分数为50.04%;导电填料Ag-NanoG已均匀分散在丙烯酸酯PSA基体中,并形成了导电网络;当w(Ag-NanoG)=40%时,Ag-NanoG/PSA的综合性能相对最好,其180°剥离强度为0.25 kN/m,剪切强度为0.133 MPa且电导率为2.5×10-2S/cm。     

High performance electrically conductive adhesives from functional epoxy,micron silver flakes,micron silver spheres and acidified single wall carbon nanotube for electronic package

To develop high performance electrically conductive adhesives (ECAs), bi-modal ECAs were prepared by a matrix resin, micron silver flakes and micron silver spheres, and tri-modal ECAs were prepared by a matrix resin, micron silver flakes, micron silver spheres and acidified single wall carbon nanotube (ASWCNT). With the increase of nano silver spheres, the bulk resistivity of bi-modal ECAs decreased firstly and then increased while tri-modal ECAs' bulk resistivity firstly increased and then decreased with the increase of ASWCNT due to different electrically conductive channels were formed in them. After aged for 500 h under humid and thermal cycle of constant humidity level of 85% relative humidity at 85 °C, the contact resistance shift of bi-modal ECAs was more than 20% and that of tri-modal ECAs was less than 15% showing tri-modal ECAs had lower and more stable contact resistance. The humid and thermal surroundings had bad effect on the mechanical properties of bi- and tri-modal ECAs, after aged for 500 h, they both were reduced about 50–65%. And a bi-modal ECAs and a tri-modal ECAs were optimized and investigated in detail which can be used in electronic packaging.     

环氧树脂/镀银纳米石墨微片导热复合材料的制备与性能

以膨胀石墨为原料,采用超声分散法和化学镀法制得镀银纳米石墨微片,然后将其填充在环氧树脂基体中制备环氧树脂/镀银纳米石墨微片复合材料。结果表明,银粒子均匀镀覆在纳米石墨微片上,银层厚度为100 nm,有利于在环氧树脂基体中形成导热通路;与环氧树脂相比,环氧树脂/镀银纳米石墨微片复合材料的力学性能和热导率能都得到提高;当镀银纳米石墨微片含量为3 %时,复合材料的热导率为1.827 W/(m·K),比纯环氧树脂热导率提高了近5倍。     

Application of nitrogen-doped graphene nanosheets in electrically conductive adhesives

Nitrogen-doped graphene nanosheets (N-GNSs) were used as a conductive filler for a polymer resin adhesive and as a performance improver for a silver-filled electrically conductive adhesive (ECA). The N-GNS samples were prepared by the chemical-intercalation/thermal-exfoliation of graphite followed by a thermal treatment in NH₃. Only 1 wt.% of N-GNSs was required for the adhesive to reach a percolation threshold, and the performance using N-GNSs was much better than that obtained using carbon black or multi-walled carbon nanotubes (MWCNTs). The effect of N-GNS or MWCNT additives on reducing the electrical resistivity of Ag-particle filled ECAs at low Ag loading ratios was also investigated. With 30 wt.% of Ag filler, the polymer resin was still non-conducting, while a resistivity of 4.4 × 10⁻² Ω-cm was obtained using an Ag/N-GNS hybrid filler fortified with only 1 wt.% of N-GNSs due to large specific surface area, high aspect ratio, and good electrical conductivity of the doped graphene.     

Synthesis and properties of electrical conductive and antibacterial siloxane-modified carbon fiber–silver–acrylate nanocomposites

First, silanized carbon fiber (SCF) was synthesized, then silanized carbon fiber–silver (SCF-S) was obtained. Finally, silanized carbon fiber–silver–acrylate (SCF-S-A) electrical conductive and antibacterial composites were prepared. The structures of CF, SCF, SCF-S, and SCF-S-A were characterized by X-ray photoelectron spectroscopy, FTIR, scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and UV spectra. The electrical conductive and antibacterial properties of SCF-S-A nanocomposites were studied. The results showed that electrical conductive and antibacterial activity properties of SCF-S-A nanocomposites were improved. When the content of SCF-S was 50%, the conductivity of SCF-S-A nanocomposites was maximum. The SCF-S-A nanocomposites will have promising application in high-performance electrical conductive and antibacterial materials.     

Effect of surface modification of aluminum nitride on electrical and thermal characterizations of thermosetting polymeric nanocomposites

Thermally conductive composites and nanocomposites composed of epoxy resin as base matrix and aluminum nitride (AlN) as micro and nanofiller have been studied at variable temperatures and loading of AlN. To improve the dispersion of the filler within the polymer matrix, AlN was surface modified with silane‐coupling agent. Thermogravimetric analysis confirmed the interfacial bonding of epoxy‐ and silane‐modified AlN. The dielectric properties of epoxy/AlN composites and nanocomposites have been studied at variable percentage of filler. Test result indicated an increase of thermal conductivity of the composites at 20 wt% of AlN. Also, silane‐treated composites exhibited improved electrical conductivity properties, whereas the electrical insulation property decreased in terms of dielectric strength and resistivity. POLYM. COMPOS., 2013. © 2012 Society of Plastics Engineers     

Processing and shape effects on silver paste electrically conductive adhesives (ECAs)

Various amounts of silver flakes and dendrites were used as conductive fillers in an electrically conductive adhesive (ECA) resin with DPM, BCA and xylene as diluent to help uniform distribution of filler particles in the matrix. Due to the fact that the higher the temperature, the higher the shrinkage rate of the polymer resin and, consequently, the larger the connecting area in-between fillers, a better curing condition for processing silver filled ECA was found to be a relatively higher curing temperature. The mechanism of conductivity achievement in conductive adhesives was analyzed by comparing processing conditions, resistivity and microstructures. In addition, the influence of adding nano-sized silver particles on the resistivity of the conductive adhesives was also investigated and the addition of nano-sized silver particles resulted in a lower percolation threshold for ECAs.     

The role of a third component on the conductivity behavior of ternary epoxy/Ag conductive composites

Conductive adhesives, based on highly filled silver particles dispersed in a liquid epoxy resin, with an aliphatic amine [diethyltriamine (DETA)] as a curing agent, were investigated. A third component was added to the epoxy/Ag system to obtain composites of better conductivity, or similar conductivity but at lower silver contents, to modify the conductive adhesive properties, and also to reduce cost. Epoxy/Ag/carbon black (CB), epoxy/Ag/carbon fibrils (CF), epoxy/Ag/SiO₂ and epoxy/Ag/dispersant composites were thus studied. The effect of high curing temperature on the uniformity and resulting conductivity level was also studied. The studied systems, excluding the epoxy/Ag/CB composite, exhibited enhanced conductivities. The microstructure of most of the systems was studied by scanning electron microscopy (SEM). The micrographs produced have served to establish structure‐property relations for better understanding of the observed phenomena.     

聚氨酯/镀银纳米石墨导电胶的制备与性能研究

以聚氨酯(PU)预聚体为基体,以镀银纳米石墨为导电填料,采用共混法制备PU/镀银纳米石墨导电胶,并与PU/纳米石墨导电胶进行电学性能、力学性能和热稳定性能对比。结果表明:PU/镀银纳米石墨导电胶和PU/纳米石墨导电胶的导电渗流阈值分别为3%和9%,此时对应的电导率分别为0.044 S/cm和0.012 S/cm;前者的力学性能(最大剪切强度为5.76 MPa)高于后者(最大剪切强度为3.65 MPa),并且前者的起始分解温度比后者提高了近10℃,说明前者的应用前景比后者更广阔。     

Preparation and adhesive performance of electrical conductive epoxy-acrylate resin containing silver-plated graphene

The epoxy-acrylate (EA) was mixed with Ag-plated graphene (Ag-G), which was used as the conductive filler, to prepare the dual-curable electrical conductive adhesive (ECA). The characterization of Ag-G has been carried out by transmission electron microscope, X-ray diffraction, Raman spectrum, and X-ray photoelectron spectroscopy. Results showed that the Ag-G has been successfully prepared and the relative amount of Ag nanoparticles was 11.25?At%. The mechanical and conductive properties together with thermal stability of ECA have also been investigated. The shear strength reached to 4.67?MPa and the electrical conductivity of ECA reached to 0.41?S/cm when the content of conductive filler was 25?wt%, respectively. This content was regarded as the optimum. And, thermal analysis indicated that ECA exhibited better thermal stability than EA.     

聚苯胺/镀银四氧化三铁复合材料的制备与表征

以聚苯胺（PANI）为基体,Fe3O4为磁性能给体,通过化学镀的方法在Fe3O4表面包覆一层银单质制备Ag/Fe3O4,并通过化学原位聚合的方法将PANI与Ag/Fe3O4复合,制备导电聚合物电磁双复型复合材料PANI/Ag/Fe3O4。结果表明,当Ag/Fe3O4的添加量为PANI质量的20%时,PANI/Ag/Fe3O4复合材料的电导率为0.85 S/cm,饱和磁化强度为 16.34 emu/g,复合材料的电磁性能得到很好的匹配;Ag/Fe3O4的加入阻碍了PANI的分解,PANI/Ag/Fe3O4复合材料的分解温度升高,热稳定性加强。     

Thermal conductivity and electromagnetic shielding effectiveness of composites based on Ag‐plating carbon fiber and epoxy

Thermally conductive and electromagnetic interference shielding composites comprising low content of Ag‐plating carbon fiber (APCF) were fabricated as electronic packing materials. APCF as conductive filler consisting of carbon fiber (CF) employed as the structural component to reinforce the mechanical strength, and Ag enhancing electrical conductivity, was prepared by advanced electroless Ag‐plating processing on CF surfaces. Ag coating had a thickness of 450 nm without oxide phase detected. The incorporation of 4.5 wt % APCF into epoxy (EP) substrate yielded thermal conductivity of 2.33 W/m·K, which is approximately 2.6 times higher than CF–EP composite at the same loading. The APCF–EP composite performed electromagnetic shielding effectiveness of 38–35 dB at frequency ranging from 8.2 to 12.4 GHz in the X band, and electromagnetic reflection was the dominant shielding mechanism. At loading content of APCF up to 7 wt %, thermal conductivity of APCF–EP composites increased to 2.49 W/m·K. Volume resistivity and surface resistivity decreased to 9.5 × 10³ Ω·cm and 6.2 × 10² Ω, respectively, which approached a metal. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42306.     

Properties of Phenolic-Based Ag-Filled Conductive Adhesive Affected by Different Coupling Agents

In this study, a phenolic-based Ag flake-filled electrically conductive adhesive (ECA) was investigated in terms of rheological, electrical, and mechanical properties. To clarify the effect of various Ag flake filler content and silane coupling agents on the characteristic of the ECA, rheological properties of the Ag flake-filled ECA paste, electrical resistivity, and shear strength of the cured ECA were investigated. Results showed that an increase of Ag flake content leads to an increase in both viscosity of the ECA paste and electrical conductivity of the as-cured ECA. Silane coupling agents-treated Ag flakes have a significant effect on the electrical resistivity and shear strength in the ECAs.     

Hybrid laser processes for thick silver coating fabrication on AlN substrate

Aluminum nitride (AlN) are particularly suitable as integrated circuits (ICs) substrates due to its high thermal conductivity and excellent electricity insulation. However, its poor weldability with metals limits its usage. Recent research on surface metallization of AlN provides possible solutions to tackle this defect. Nevertheless, these solutions show some shortages such as complicated processes or insufficient electrical conductivity. In this paper, we report a method that consists of laser induced surface metallization and laser sintering of silver (Ag) coatings. A nanosecond laser was applied to induce a 10 μm thick aluminum (Al) layer from the AlN substrate. Afterwards, laser sintering of Ag layers was implemented, which could enhance the conductivity and the bonding performance between layers. With optimized laser parameters applied, both the electrical conductivity and the bonding tests demonstrated excellent physical properties. Finally, simulation and EDS analysis illustrated the melting evolution and confirmed a metallurgical combination of Al and Ag, thus enhancing bonding strength. Thanks to the small size of focused laser spot, electrical circuits width could be greatly narrowed if these findings were applied; hence highly dense ICs on AlN substrate become potentially available.