Screen printable epoxy/BaTiO3 embedded capacitor pastes with high dielectric constant for organic substrate applications

In this article, embedded capacitor pastes (ECPs) with various BaTiO₃ (BTO) powder contents were formulated and screen‐printed on PCBs to fabricate capacitors. The material properties of the ECPs that included their rheology, curing behavior, and dielectric constant were investigated. Embedded capacitors were fabricated for reliability tests related to the thermal cycling and high temperature and humidity potential of optimized ECPs. Additionally, changes in the dielectric properties were discussed. ECPs were formulated with various powder contents from 0 to 70 vol %. ECP resin was cured at temperatures ranging from 130 to 220°C. All ECPs had the viscosities below 30 Pa · s at a shear rate of 100 s^?1 to be easily screen‐printable. The dielectric constant of the cured ECPs increased to 60 at 70 vol %, and the dielectric loss was approximately 0.023 for all ECPs regardless of BTO volume content. For the reliability test, ECPs with 50, 60, and 70 vol % BTO powder contents were selected and embedded capacitors were fabricated. After a thermal cycling test with a temperature range from ?55 to 125°C for 1000 cycles, capacitance decreased by approximately 5 ～ 10%, but the dielectric loss did not change. After a 85°C/85RH% test for 1000 h, the capacitance and dielectric loss increased by nearly 20%. Cyanoresin (CRS) was used to form the high dielectric polymer/ceramic composite material. The newly formulated resin system had a dielectric constant that is double that of a conventional epoxy resin system. Additionally, the dielectric constant of the polymer/ceramic composite material increased 50% at 50 vol %. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

原位乳液聚合制备导电性聚苯胺/氯磺化聚乙烯复合材料及其性能

以十二烷基苯磺酸为乳化剂及掺杂剂,由二甲苯及水组成乳液,在氯磺化聚乙烯存在下,采用一步原位乳液聚合法制备了聚苯胺／氯磺化聚乙烯(PAn／CSPE)导电复合材料。研究了用熔融法(MP)或溶液法(SP)加工复合物材料的导电性及力学性能,并进行了表征。结果表明,MP法制得的复合材料在导电性及力学性能方面优于SP法制得的复合材料;当PAn质量分数为12％～18％时,MP法复合材料呈现热塑性弹性体行为,拉伸强度为6～8MPa,扯断伸长率大于400％,永久变形小于30％。当PAn质量分数小于18％时,SP法复合材料用闻甲酚二次渗杂后的导电率比原复合材料高出6个数量级,且其导电渗滤阈值由PAn质量分数22％降至3％。     

Preparation of conductive polypyrrole composites by in‐situ polymerization

Two kinds of conductive polypyrrole composites were prepared by in‐situ polymerization of pyrrole in a suspension of chlorinated polyethylene powder or in a natural rubber latex using ferric chloride as oxidizing agent. The preparation conditions were studied and the results showed that it is better to swell the chlorinated polyethylene powder with the monomer first, followed by addition of the oxidant, than to add the oxidant first, and that conversion can reach 98% for 6 h at room temperature. The conductivity percolation threshold of the composite is about 12%. The composites can be processed repeatedly, exhibiting a maximum tensile strength over 9 MPa and a maximum conductivity near 1 S cm⁻¹. The polypyrrole/natural rubber composites were prepared successfully by using a nonionic surfactant (Peregal O) as stabilizer at pH less than 3 with a molar ratio of FeCl₃/pyrrole = 2.5 below 45 °C. The latter composites show a low conductivity percolation threshold about 6%, a maximum tensile strength over 10 MPa and a maximum conductivity over 2 S cm⁻¹. The composites were characterized by FTIR and TGA. The polypyrrole/chlorinated polyethylene composites are very stable in air and almost no decrease of conductivity was observed for over 10 months examined. © 1999 Society of Chemical Industry     

Expanded graphite–epoxy composites with high dielectric constant

Composites of an expanded graphite/diglycidyl ether of bisphenol A (DGEBA) were prepared by a simple melt blending method, and their dielectric and mechanical properties were investigated. During observations of fractured surfaces of the composites, the graphite sheets were seen to be homogeneously dispersed in the epoxy matrix. Moreover, the composites presented an enhanced dielectric constant (～ 180) and a low loss factor (～ 0.05) at 50 Hz, suggesting their potential suitability for embedded dielectric applications. The enhanced dielectric constant can be explained by the percolation theory and the relatively low loss factor was attributed to strong interfacial interactions between the polymer molecules and the ? OH/? COOH groups of the expanded graphite, which constrained the orientational polarization of the polarons. Furthermore, dynamic mechanical analysis of the composites showed a restricted macromolecular relaxation and improved mechanical properties. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preparation of conductive polyaniline/chlorosulfonated polyethylene composites via in situ emulsion polymerization and study of their properties

The conductive composites of polyaniline (PAn) and chlorosulfonated polyethylene (CSPE) were prepared by polymerization of aniline in the presence of CSPE, using a direct, one‐step in situ emulsion polymerization method. The polymerization of aniline was performed in an emulsion comprising water and xylene containing CSPE in the presence of dodecylbenzene sulfonic acid, which acts both as a surfactant and a dopant for PAn. The composites can be processed by either melt method (MP) or solution method (SP). Conductivity of the composites obtained by different processing methods shows different percolation thresholds: 14 wt % for MP samples and 22 wt % for SP samples. At the same content of PAn, the conductivity of MP composites is higher than that of SP composites. The relationships between mechanical properties and PAn content obtained by the two different processing methods were also investigated. When PAn content of MP samples is between 12 and 18 wt %, the composites behave like a thermoplastic elastomer with tensile strength at 6–8 MPa, ultimate elongation > 400% and permanent set < 30%. The conductivity of composites obtained by SP method after secondary doping with m‐cresol is about 6 orders of magnitude higher than the original at below 18 wt % PAn content and the percolation threshold for conductivity is lowered to 3 wt % PAn content. The composite shows no electrochromic activity in acidic solution of LiClO₄ in propylene carbonate, but after secondary doping exhibits electrochromic activity even in neutral electrolyte. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 845–850, 2000     

Novel polymer–ceramic nanocomposite based on high dielectric constant epoxy formula for embedded capacitor application

Embedded capacitor technology can increase silicon packing efficiency, improve electrical performance, and reduce assembly cost compared with traditional discrete capacitor technology. Developing a suitable material that satisfies electrical, reliability, and processing requirements is one of the major challenges of incorporating capacitors into a printed wiring board (PWB). Polymer–ceramic composites have been of great interest as embedded capacitor material because they combine the processability of polymers with the high dielectric constant of ceramics. A novel nanostructure polymer–ceramic composite with a very high dielectric constant (ε_r ～110, a new record for the highest reported ε_r value of a nanocomposite) was developed in this work. A high dielectric constant is obtained by increasing the dielectric constant of the epoxy matrix (ε_r >6) and using the combination of lead magnesium niobate–lead titanate (PMN–PT)/BaTiO₃ as the ceramic filler. This nanocomposite has a low curing temperature (<200°C); thus, it is multichip‐module laminate (MCM‐L) process‐compatible. An embedded capacitor prototype with a capacitance density of 50 nF/cm² was manufactured using this nanocomposite and spin‐coating technology. The effect of the composite microstructure on the effective dielectric constant was studied. This novel nanocomposite can be used for integral capacitors in PWBs. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1084–1090, 2002     

Interfacial in situ polymerization of single wall carbon nanotube/nylon 6,6 nanocomposites

An interfacial polymerization method for nylon 6,6 was adapted to produce nanocomposites with single wall carbon nanotubes (SWNT) via in situ polymerization. SWNT were incorporated in purified, functionalized or surfactant stabilized forms. The functionalization of SWNT was characterized by FTIR, Raman spectroscopy and TGA and the SWNT dispersion was characterized by optical microscopy before and after the in situ polymerization. SWNT functionalization and surfactant stabilization improved the nanotube dispersion in solvents but only functionalized SWNT showed a good dispersion in composites, whereas purified and surfactant stabilized SWNT resulted in poor dispersion and nanotube agglomeration. Weak shear flow induced SWNT flocculation in these nanocomposites. The electrical and mechanical properties of the SWNT/nylon nanocomposites are briefly discussed in terms of SWNT loading, dispersion, length and type of functionalization.     

Flexible BaTiO3/SiC@PbTiO3/epoxy composite films with enhanced dielectric performance at high frequency

Flexible polymer composites with high dielectric constants and low dielectric losses at high frequencies are highly desired in microwave and RF applications. However, a high dielectric constant is often obtained at the expense of flexibility because a high loading of filler is needed. In this work, we synthesize a core-shell structured 1D filler by coating high-dielectric-constant PbTiO₃ onto the surface of low-thermal-expansion-coefficient SiC nanofibers, which are then incorporated into the epoxy matrix together with BaTiO₃ nanoparticles to form the multi-phase BaTiO₃/SiC@PbTiO₃/epoxy composite film. A high dielectric constant (35 at 100 Hz and 20 at 5 GHz) and a low dielectric loss (0.023 at 100 Hz and 0.13 at 5 GHz) are achieved as the filling content of SiC@PbTiO₃ and BaTiO₃ is 5.24 wt% and 80 wt%, respectively. Prediction models of the effective dielectric constant of polymer-based composites reveal that a continuous polarization network is constructed in the composites owing to the physical contact between BaTiO₃ and PbTiO₃. The construction of the multi-phase filler provides a feasible way to effectively adjust and improve the dielectric properties of polymer-based composite films.     

原位聚合法制备聚苯胺/改性羰基铁粉复合材料

采用正硅酸乙酯(TEOS)对羰基铁粉(CIP)表面改性,通过原位聚合法制备了聚苯胺(PANI)/改性CIP复合材料。傅里叶变换红外光谱验证了SiO2和CIP表面形成了化学键。耐酸性实验表明:TEOS可在较长时间内保护CIP不被酸腐蚀,保证了制备PANI/CIP复合材料过程中CIP处于SiO2的有效保护下。所得复合材料为CIP表面包覆直径约20 nm均匀致密的PANI微粒,复合效果明显改善。复合材料电导率与CIP未改性前处于相同数量级。     

Preparation of polyaniline/vermiculite clay nanocomposites by in situ chemical oxidative grafting polymerization

BACKGROUND: Recently, conducting polymers have attracted much attention, since they have interesting physical properties and many potential applications, such as in conductive coating charge storage. Hence the synthesis of conducting polymer nanocomposites is also an area of increasing research activity. RESULTS: Vermiculites (VMTs) were successfully delaminated using an acid treatment. Polyaniline (PANI)/VMT nanocomposites were prepared by in situ chemical oxidative grafting polymerization. CONCLUSION: The chemical grafting of PANI/VMTs was confirmed by Fourier transform infrared and UV‐visible spectroscopy. The percentage of grafted PANI was 142.7 wt% as a mass ratio of the grafting PANI and charged nano‐VMTs, investigated using thermogravimetric analysis. In addition, characteristic agglomerate morphology of PANI was observed in the composites using scanning electron microscopy. Thermal analyses indicated that the introduction of VMT nanosheets had a beneficial effect on the thermal stability of PANI. The electrical conductivity of the nanocomposites was 3.9 × 10^?3 S cm^?1, a value typical for semiconductors. Copyright © 2009 Society of Chemical Industry     

Efficient preparation of isotactic polypropylene/montmorillonite nanocomposites by in situ polymerization technique via a combined use of functional surfactant and metallocene catalysis

In order to promote efficiency of the preparation of isotactic polypropylene (i-PP)/montmorillonite (MMT) nanocomposites by in situ polymerization technique, a strategy was laid out to enhance both the intercalative selectivity and the catalyst activity of the in situ polymerization by a combined use of a functional surfactant for MMT modification and a metallocene catalyst system for isospecific propylene polymerization. Thus, (2-hydroxylethyl) hexadecyl diethylammonium iodine was involved in the ion-exchanged organic modification of MMT, leading to an implantation of catalyst-anchoring reactive sites (hydroxyl, OH) in the interlayer galleries of MMT (OMMT). By treating the OH-intercalated OMMT successively with excessive methylaluminoxane (MAO) and rac-Me₂Si(2-Me-4-Ph-Ind)₂ZrCl₂, the metallocene catalyst typical for i-PP polymerization was stabilized inside the interlayer galleries with a catalytically benign environment. The MMT-borne catalyst, upon further activation by MAO, released fairly high activities for propylene polymerization. The effective intercalative polymerization ensured an efficient preparation of i-PP/MMT nanocomposite. A series of i-PP/MMT nanocomposites containing completely disordered MMT at a loading range of 1.0-6.7 wt% (TGA measurement residue at 600 °C) were obtained in high yields.     

EVA/PBT nanostructured blends synthesized by in situ polymerization of cyclic cBT (cyclic butylene terephthalate) in molten EVA

Poly(ethylene-co-vinyl acetate) (EVA)/poly(butylene terephthalate) copolymers were synthesized by the in situ polymerization of cyclic butylene terephthalate monomer (cBT) in the presence of molten EVA copolymer.Titanium phenoxide Ti(OPh)₄ which leads to the highest degree of grafting compared to the more classical titanium system was used as the initiator for the ring-opening polymerization of the cBT monomer. The corresponding copolymer was characterized fully by ¹H NMR after selective extraction from the blend. As a result, a maximum of 11.3 wt% of EVA-g-PBT copolymer was synthesized by this method. Examination of morphology by transmission electronic microscopy (TEM) showed a fine dispersion of PBT phase with size ranging from 100 to 500 nm in diameter. This gave evidence for a crown structure of the PBT phase that is coated by EVA-g-PBT copolymer.Finally, rheological and mechanical studies highlighted a specific behaviour of this material with improved mechanical properties at room temperature.     

Synthesis by in situ chemical oxidative polymerization and characterization of polyaniline/iron oxide nanoparticle composite

Polyaniline (PANI) is a well‐studied material and is the pre‐eminent electrically conducting organic polymer with the potential for a variety of applications such as in batteries, microelectronics displays, antistatic coatings, electromagnetic shielding materials, sensors and actuators. Its good environmental as well as thermal stability and electrical conductivity tunable by appropriate doping make PANI an ideal active material for several applications. In this paper, we report the synthesis of water‐dispersible colloidal PANI/iron oxide composite nanoparticles using an in situ chemical oxidation polymerization method in a micellar medium of sodium dodecylsulfate, where the cores (iron oxide) are embedded in a PANI matrix layer. Transmission electron micrographs showed evidence of the formation of an iron oxide core/PANI shell composite with a thin layer of PANI over the iron oxide cores. The results of thermogravimetric, Fourier transform infrared and UV‐visible analysis indicated that the iron oxide nanoparticles could improve the composite thermal stability possibly due to the interaction between iron oxide particles and PANI backbone. We believe that the synthetic route described can also be adapted for the assembly of hierarchical structures of other metal oxides or hydroxides onto various cores. Copyright © 2010 Society of Chemical Industry     

Enhanced dielectric constant and breakdown strength in dielectric composites using TiO2@HfO2 nanowires with gradient dielectric constant

To investigate the influence of modification of ceramic fillers on the dielectric properties of polymer-based composites, TiO₂ and core-shell structured TiO₂@HfO₂ nanowires were synthesized, and investigated in this study. TiO₂ nanowires/polyvinylidene fluoride (PVDF) and TiO₂@HfO₂ nanowires/PVDF nanocomposites were prepared using the solution casting method. The experimental results showed that the TiO₂@HfO₂ nanowires/PVDF composites had improved dielectric properties compared with that of the TiO₂ nanowires/PVDF composites. Owing to the enhanced interfacial polarisation by the multilevel interface, the composites with 10 wt % TiO₂@HfO₂ nanowires achieved the highest permittivity of 12.56 at 1 kHz, which was enhanced by ～72% compared to the PVDF matrix. The electric field was evenly distributed by building the fillers with a gradient dielectric constant. The characteristic breakdown strength of the composite with 5 wt % TiO₂@HfO₂ reached 377.76 kV/mm, compared with that of 334.37 kV/mm for the composite with 5 wt % TiO₂ nanowires. This study initiated a novel strategy for preparing dielectrics with high dielectric constant and improved breakdown strength.     

原位聚合法制备环氧树脂/石墨复合材料的性能研究

采用原位聚合法制备了环氧树脂/石墨复合材料,并对其进行热重(TG)、扫描电镜(SEM)和力学性能分析。结果表明,环氧树脂/石墨复合材料的邵氏硬度和抗弯强度随石墨含量而变化,当其含量为17.44%(质量分数)时,两者出现最大值,抗弯强度达到22.4 MPa,邵氏硬度达到5.21 HD;石墨的加入也使复合材料的电性能和热性能得到提高,其耐热温度可达350℃。     

Rheological and mechanical properties of PVC/CaCO3 nanocomposites prepared by in situ polymerization

Poly(vinyl chloride) (PVC)/calcium carbonate (CaCO₃) nanocomposites were synthesized by in situ polymerization of vinyl chloride (VC) in the presence of CaCO₃ nanoparticles. Their thermal, rheological and mechanical properties were evaluated by dynamic mechanical analysis (DMA), thermogravimetry analysis (TGA), capillary rheometry, tensile and impact fracture tests. The results showed that CaCO₃ nanoparticles were uniformly distributed in the PVC matrix during in situ polymerization of VC with 5.0 wt% or less nanoparticles. The glass transition and thermal decomposition temperatures of PVC phase in PVC/CaCO₃ nanocomposites are shifted toward higher temperatures by the restriction of CaCO₃ nanoparticles on the segmental and long-range chain mobility of the PVC phase. The nanocomposites showed shear thinning and power law behaviors. The ‘ball bearing’ effect of the spherical nanoparticles decreased the apparent viscosity of the PVC/CaCO₃ nanocomposite melts, and the viscosity sensitivity on shear rate of the PVC/CaCO₃ nanocomposite is higher than that of pristine PVC. Moreover, CaCO₃ nanoparticles stiffen and toughen PVC simultaneously, and optimal properties were achieved at 5 wt% of CaCO₃ nanoparticles in Young's modulus, tensile yield strength, elongation at break and Charpy notched impact energy. Detailed examinations of micro-failure micromechanisms of impact and tensile specimens showed that the CaCO₃ nanoparticles acted as stress raisers leading to debonding/voiding and deformation of the matrix material around the nanoparticles. These mechanisms also lead to impact toughening of the nanocomposites.     

Preparation of highly conductive reduced graphite oxide/poly(styrene-co-butyl acrylate) composites via miniemulsion polymerization

Polymer/reduced graphite oxide (rGO) composite nanoparticles with a high electrical conductivity were synthesized using the miniemulsion polymerization technique. The rGO was modified with a reactive surfactant, 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS), to facilitate monomer intercalation into the rGO nanogalleries. The AMPS-modified rGO was emulsified in the presence of styrene (St) and butyl acrylate (BA) monomers, and the stable miniemulsion was polymerized to form poly(St-co-BA)/rGO composite latex nanoparticles. The transition in the composite nanoparticles from an electrical insulator to an electrical conductor occurred at an rGO content of 10 wt% (relative to the monolayer content), yielding an electrical conductivity of 0.49 S/cm. The electrical conductivity of the composite nanoparticles reached 2.22 S/cm at 20 wt% rGO, yielding a much better conductivity than other polymer composites prepared using a GO filler. Importantly, the miniemulsion polymerization method for fabricating poly(St-co-BA)/rGO composite nanoparticles is easy, green, low-cost, and scalable, providing a universal route to the rational design and engineering of highly conductive polymer composites.     

Effect of acrylic copolymer dispersants bearing epoxy groups on rheological and dielectric properties of carbon black‐filled epoxy system

In this article, the use of copolymeric dispersants with an acrylic backbone and epoxy side groups for formulating carbon black (CB)‐epoxy composites are described. Six epoxy‐containing acrylic copolymer dispersants were prepared from hexyl methacrylate (HMA), poly(ethylene glycol) ethyl ether methacrylate (PEGMA), and glycidyl methacrylate via a group transfer polymerization technique. The epoxy‐containing acrylic copolymer of the highest concentration of PEGMA showed a desirable passivation effect on CB, and was found to lower the viscosity of the CB‐epoxy paste, leading to the well‐cured composite after heat treatment. The thick composite film prepared by employing the [CB/acrylic dispersant/epoxy] paste was built up on a Cu plate by a screen printing process followed by thermal curing. The dielectric properties of the 3.1 vol % CB‐filled epoxy film showed us high dielectric constant (Dk 4900) and rather low dissipation factor (Df 29%) at 1 MHz. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Prediction of the effective dielectric constant in SWNT polyimide nanocomposites using the Bruggemann model

The Bruggemann model is used in this work to predict the effective dielectric constant of two kinds of single‐wall carbon nanotube (SWNT) polyimide nanocomposites. Electrical conductivity and dielectric constant exhibit a dramatic enhancement at low content of SWNT fillers with a percolation threshold at 0.06 vol %. Results of the Bruggemann model are compared with the experimental values of the dielectric constant in CP2/SWNT and βCN/SWNT polyimide nanocomposites. A reasonable agreement for SWNT contents under the percolation threshold and a SWNT dielectric constant of 2000 was found between the Bruggeman model modified by Giordano and the experimental values. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009