- Email: [email protected]
Al2O3 ceramics for LTCC application
G Model
ARTICLE IN PRESS
JECS-11036; No. of Pages 7
Journal of the European Ceramic Society xxx (2017) xxx–xxx
Contents lists available at www.sciencedirect.com
Journal of the European Ceramic Society journal homepage: www.elsevier.com/locate/jeurceramsoc
Fabrication of a high-performance film based borosilicate glass/Al2 O3 ceramics for LTCC application Luchao Ren a,b , Xianfu Luo a,b , Yunsheng Xia a,b , Yongkang Hu a,b , Hongqing Zhou a,b,∗ a b
College of Materials Science and Engineering, Nanjing Tech University, Nanjing Jiangsu, 210009, China Jiangsu Collaborative Innovation Center for Advanced Inorganic Function Composites, Nanjing Tech University, Nanjing Jiangsu, 210009, China
a r t i c l e
i n f o
Article history: Received 27 November 2016 Received in revised form 20 January 2017 Accepted 21 January 2017 Available online xxx Keywords: High-performance film Polymeric dispersant Tape casting LTCC application
a b s t r a c t The present work was initiated aiming at developing a high-performance film for LTCC application using a kind of polymeric dispersant in tape casting process of borosilicate-based glass/Al2 O3 ceramics. The dispersion mechanism of the polymeric dispersant with the powders was analyzed in detail and the optimal amount of the dispersant addition was also determined through the sedimentation experiment. Its effects on the compactness, tensile strength and surface roughness of the films were analyzed. In addition, the sintering and microwave properties of the composite fired at 850 ◦ C were also determined. For the application of tape technology, the co-firing compatibility between the composite and Ag electrodes at 850 ◦ C was also verified. After testing and verification with different qualitative and quantitative instruments, a flexible film optimized by 1.5 wt% polymeric dispersant achieved the best overall performance. © 2017 Published by Elsevier Ltd.
1. Introduction The recent rapid developments in the microelectronic industry demand miniature microwave devices with high processing speed [1]. To meet this requirement, Low Temperature Co-fired Ceramic (LTCC) technology, which combines the use of low permittivity dielectrics with low loss glasses, has been developing rapidly [2]. Recently, glass/Al2 O3 composites have received much attention because they can meet a lot of requirements of physical, electrical and thermal properties [3,4]. Different glass systems are designed to cater to the specific purpose, such as B2 O3 -Bi2 O3 SiO2 -ZnO(BBSZ) [5], Li2 O-B2 O3 -SiO2 (LBS) [6], Li2 O–SiO2 –ZrO2 (LSZ) [7], CaO–B2 O3 –SiO2 -Al2 O3 (CABS) [8], etc. Among the different LTCC glass-ceramics systems, CABS glass/Al2 O3 has been reported as a promising material for using in microelectronic packaging because of its low firing temperature and low dielectric loss [9]. In our previous study [10], the CABS glass/Al2 O3 sintered at 850 ◦ C showed r = 7.87 and tan ␦ = 20 × 10−4 at 7 GHz. The composite is physically and chemically compatible with the common electrode material, silver. For practical applications, the ceramic should be in the form of thin sheets through tape casting. The development of such flexible LTCC films with smooth surface, high
∗ Corresponding author at: College of Materials Science and Engineering, Nanjing Tech University, Nanjing Jiangsu, 210009, China. E-mail address: [email protected] (H. Zhou).
density and high performance is the most important step in the fabrication of multilayer ceramic modules [11]. In this work, we introduced a kind of polymeric dispersant into slurry system instead of the common castor oil which dispersion mechanism was found to be steric hindrance [12–14]. This kind of polymeric dispersant belongs to the type of weakly cationic polymeric amine (WCPA). The physicochemical property of polymeric dispersant and castor oil are listed in Table 1. It is expected to disperse primary particles and to hold them in a homogeneous suspension by two methods, ionic repulsion and steric hindrance [15]. So the deflocculation of polymeric dispersant is better than that of castor oil in theory. We investigated the optimization results of the polymeric dispersant on the tape casting process of CABS glass/Al2 O3 composite, expecting to develop a smooth surface, high density and strong mechanical films for further tape processing of LTCC application.
2. Experimental procedures CABS glass with composition 15CaO:5Al2 O3 :16B2 O3 :64SiO2 was prepared by conventional glass quenching method. After being equally mixed, raw materials were melted in a platinum crucible at 1500 ◦ C for about 1 h. To prevent the occurrence of any crystallization, the melt was quenched into deionized water to form frits. Then, the glass frits were dried and milled in high speed agate mill, resulting in fine glass powders. The resulting glass powder (D50 = 3.8 m) was mixed with the Al2 O3 ceramic pow-
http://dx.doi.org/10.1016/j.jeurceramsoc.2017.01.031 0955-2219/© 2017 Published by Elsevier Ltd.
Please cite this article in press as: L. Ren, et al., Fabrication of a high-performance film based borosilicate glass/Al2 O3 ceramics for LTCC application, J Eur Ceram Soc (2017), http://dx.doi.org/10.1016/j.jeurceramsoc.2017.01.031
G Model JECS-11036; No. of Pages 7
ARTICLE IN PRESS L. Ren et al. / Journal of the European Ceramic Society xxx (2017) xxx–xxx
2
Table 1 Physicochemical property of polymeric dispersant and castor oil. Dispersant
Ingredient
Molecular weight
Decomposition temperature
Weakly cationic polymeric amine(WCPA) Castor oil
Substituted amino-terminal (-NR3 + ) group polycaprolactone Ricinoleic acid, glyceride
12000 933.26
500 ◦ C 265 ◦ C
der (D50 = 3.0 m) at the mass ratio [m(Al2 O3 ):m(glass) = 45:55] for about 20 h. According to our previous study[8], the melting point of CABS glass was 710.7 ◦ C with r = 5.99 and tan␦ = 1.4 × 10−3 at 7 GHz. Due to the solid state of the polymeric dispersant, it should, firstly, be dissolved in solvent. So the tape casting slurry was prepared in a three stage process. In the first stage, polymeric dispersant was ball-milled for 5 h in the solvent (isopropanol/xylene/ethanol) ensuring it was fully dissolved. In the second stage, CABS glass/Al2 O3 ceramic powder was added and ball-milled for 24 h. In the third stage, binder (polyvinyl butyral) and plasticizer (dibutyl phthalate) were introduced and ball-milled for another 24 h. The final slurry was then degassed in a vacuum desiccator for 10 min to remove air bubbles and cast using a tape casting machine (BHLY-011A). After that, the tapes were dried at room temperature. The thickness of the green tape was 160 ± 5 m and the green tape was cut into circular sheets with the diameter of 21.46 mm. For the microwave test, 60 layers of the green tape were stacked and laminated together to obtain the final cylindrical sample at 21 MPa for 10 min at 70 ◦ C. The thickness of the laminated sheets were about 6 mm. After binder burnout and sintering, dense LTCC composite could be obtained. Zeta potentials of CABS glass/Al2 O3 suspensions were calculated from the measured electrophoretic mobility using ZetaPALS (Brookhaven Instruments Corporation, USA). The chemical information of the powders and dispersant was measured by means of Fourier Transformation Infrared Spectrometer (Nexus-670, Nicolet, USA). Density of the film was the average of five sample datum through the density formula-mass divided by volume. Mechanical property of films was defined through electronic universal material testing machine (CSS-2205). Surface roughness of the film was measured using an Atomic Force Microscope (AFM) (Dimension Edge, Bruker, Germany). The microstructure was investigated by scanning electron microscopy (SEM) analysis (JSM-5900).The bulk densities of the sintered samples were evaluated by Archimedean immersion method using water as medium with the accuracy of
±0.001 g/cm3 . The microwave properties (dielectric constant r and quality factor value) were determined by the cavity method with a network analyzer (HP 8722ET, Agilent, U.S.A.) operating at 7 GHz at room temperature. The temperature dependence of dielectric constant was also measured by the same method by changing temperature from −5 ◦ C to 45 ◦ C. The coefficient of thermal expansion (CTE) measurements from 23 ◦ C to 300 ◦ C were carried out by dilatometer Netzsch 402E. The heating rates for dilatometric measurements were 5 K/min. 3. Results and discussion 3.1. Surface features and dispersion mechanism To identify the glass/Al2 O3 powder surface properties (surface electrical behavior and surface chemical groups), Zeta potentials of CABS glass/Al2 O3 suspensions with different pH values and infrared absorption spectrum of glass/Al2 O3 powder were measured. Fig. 1a showed the zeta potentials of the powder suspensions with different WCPA content at different pH values. The zeta potential was noticeably decreased with the higher content of polymeric dispersant. The isoelectric point (IEP) of the powder was also affected by addition of polymeric dispersant WCPA, but all within the pH range from 2 to 4. The used powder could be determined to carry negative charges on the surface. Moreover, distinct changes of surface charge in dispersed glass/Al2 O3 suspensions were due to adsorption of dispersant on the surface of the particles, inducing more negative charges to the particle double layer [16]. Infrared absorption spectrum of polymeric dispersant WCPA and CABS glass/Al2 O3 was depicted in Fig. 1b. After detailed analysis, the determination of functional group was as follows: for WCPA, a typical spectrum showed the NH group stretching vibration absorption bond at 2495.47 cm−1 . The −NH group bending vibration absorption occurred at 1552.27 cm−1 and 1648.80 cm−1 . The peak at 1724 cm−1 indicated the existence of carbonyl (i.e. C O) in amide groups (i.e. −CONH2 ). The peak at 3436.89 cm−1 indicated
Fig. 1. Powder surface properties. a. Zeta potential as a function of pH value (surface electrical behavior). b. Infrared absorption spectrum of the dispersant and powder (surface chemical groups).
Please cite this article in press as: L. Ren, et al., Fabrication of a high-performance film based borosilicate glass/Al2 O3 ceramics for LTCC application, J Eur Ceram Soc (2017), http://dx.doi.org/10.1016/j.jeurceramsoc.2017.01.031
G Model JECS-11036; No. of Pages 7
ARTICLE IN PRESS L. Ren et al. / Journal of the European Ceramic Society xxx (2017) xxx–xxx
3
Fig. 2. Dispersion mechanism of the polymeric dispersant with the powders in solvents.
the existence of OH group. The peak at 1397.85 cm−1 stands for the existence of C N. Considering a strong peak at 1190.48 cm−1 and a weak peak at 1046.59 cm−1 (corresponding to asymmetry and symmetry stretching vibration of C O-C- respectively), there was no doubt that the gender structures of WCPA were CONH2 group(anchoring group) and polycaprolactone (solvatable chain). For inorganic powder, besides the characteristic peak of glass and Al2 O3 , a stretching vibration peak at 3448.70 cm−1 was identified as the hydroxyl ( OH), which would react with WCPA [17]. A definite understanding about the powder surface properties and the gender structure of WCPA makes for the interpretation of the dispersion mechanism of polymeric dispersant WCPA. For the structure of WCPA, one part is anchoring group, which can be tightly adsorbed on the surface of powders through chemical bond, hydrogen bond or Van der Wals forces; while the other functional group is a solvatable chain, which can extend in the solvent medium and form an adsorption layer with certain thickness on the surface of the powders. The dispersion mechanism of the polymeric dispersant is illustrated in Fig. 2. As indicated in the Fig, the action process between dispersion and powders is divided into three stages. In the first stage (reaction stage), after dissolving in the solvent, the polymeric dispersant WCPA with cations is readily attached to the surface of powder by counter-ion attraction [18]. Furthermore, the strong polar group −CONH2 of WCPA, which can form hydrogen bonds with the OH on the surface of the powders, plays the anchor role In enhancing the adsorption force between the dispersant and powders [19]. In the second stage (formative stage), after the powders have been anchored with WCPA, the polycaprolactone side chain extends into the solvents system and forms the thick solvate layer. The solvate outer layer mainly plays a role of steric hindrance to prevent coagulation [20]. Meanwhile, the mutually exclusive cations also exist on the WCPA. In the last stage (stabiliza-
Fig. 3. Variation of relative sediment height as a function of time for different amounts of WCPA. The inset is an image of the process of sedimentation measurement.
tion stage), due to the combined effect of electrostatic repulsion and steric hindrance, the powders are well dispersed in the solvents. 3.2. Sedimentation analysis The amount of polymeric dispersant WCPA could be optimized by sedimentation analysis. A simplified model system was designed for the sedimentation test. These systems were composed of glass/Al2 O3 powder, different amounts of polymeric dispersant WCPA and organic solvent (the mass ratio of powder and solvent is 10:10). Fig. 3 showed the variation of relative sediment height (H/H0 , H is the powder height at time t, H0 is the initial powder
Please cite this article in press as: L. Ren, et al., Fabrication of a high-performance film based borosilicate glass/Al2 O3 ceramics for LTCC application, J Eur Ceram Soc (2017), http://dx.doi.org/10.1016/j.jeurceramsoc.2017.01.031
G Model
ARTICLE IN PRESS
JECS-11036; No. of Pages 7
L. Ren et al. / Journal of the European Ceramic Society xxx (2017) xxx–xxx
4
Table 2 Final organic formula of the tape casting slurry (wt% of powder). WCPA
Solvent
Polyvinyl Butyral
Dibutyl Phthalate
1 1.3 1.5 1.7 1.9
51 51 51 51 51
10 10 10 10 10
3 3 3 3 3
height) as a function of time for different amounts of polymeric dispersant WCPA. It could be seen that suspensions with 1 wt% and 1.3 wt% WCPA settled fastly and showed higher relative sediment height; whereas, suspensions with 1.5 wt%, 1.7 wt% and 1.9 wt% WCPA settled slowly and exhibited the same lowest relative sediment height. As described by Richard E. Mistler [21], the dual action of dispersion and deflocculation can be observed as the higher additive concentrations take longer to finish setting; the plateau is reached when the deflocculant concentration is adequate to fully deflocculate the powder. In addition, compared with the settlement result of cast oil dispersion, it was obvious that the final sediment height of suspension with WCPA was far below that of suspension with cast oil (for cast oil, 2 wt% is the best addition [22]). The lowest sediment height meant the highest package density. After detailed analysis, we could conclude that the dispersing ability of WCPA was much stronger than cast oil, suspension with 1.5 wt% WCPA was dispersed most uniformly and the superfluous WCPA like those with 1.7 wt% and 1.9 wt% did not contribute to the further promotion of the dispersion. 3.2.1. Characteristics of films and fired ceramic Table 2 showed the final organic formula of the tape casting slurry. The amount of each component was calculated as the mass fraction of glass/Al2 O3 powder. After tape casting, the crack free tapes were obtained. For further tape processing, investigating den-
Fig. 4. Bulk density and tensile strength of films with different WCPA content.
sity and tensile strength of films is very significant [22]. Green bulk density is vital to quality control of a cast, since it is directly related to the distance between ceramic particles in the tape. Changes in interparticle distance have a direct effect upon firing shrinkage and can also affect fired bulk density (FBD) in many cases. In addition, many tapes are further processed with automatic or semiautomatic handling equipment. Specifically, when the tape is processed separate from the carrier film, the tensile forces should be applied to the cast tape, which require the tape to have a certain level of tensile strength to avoid damages [21]. The bulk density and tensile strength of films with different WCPA content were illustrated in Fig. 4. It could be seen that the density and tensile strength of film exhibited the same variation trend. They both attained the maximum when the WCPA content was 1.5 wt%. Associating the result of the sedimentation in Fig. 3, we can summarize a rule that the most uniformly dispersed slurry was, the highest bulk density and
Fig. 5. Surface micro-topography of the film with 1.5 wt% WCPA. (a) Optical microscope image. (b), (c) the SEM images in different magnifications.
Please cite this article in press as: L. Ren, et al., Fabrication of a high-performance film based borosilicate glass/Al2 O3 ceramics for LTCC application, J Eur Ceram Soc (2017), http://dx.doi.org/10.1016/j.jeurceramsoc.2017.01.031
G Model JECS-11036; No. of Pages 7
ARTICLE IN PRESS L. Ren et al. / Journal of the European Ceramic Society xxx (2017) xxx–xxx
5
Fig. 6. 2D and 3D AFM images of the film with 1.5 wt% WCPA.
Fig. 7. Co-firing compatibility with Ag electrodes at 850 ◦ C of the film with 1.5 wt% WCPA. (a) Optical microscope image of the composite co-fired with Ag electrodes. (b) SEM image of the composites’ cross sections. (c) SEM image on the interface between glass/Al2 O3 composite and Ag electrodes. (d) XRD pattern of the composite co-fired with Ag electrodes.
tensile strength films possessed. It could be interpreted by the zipper bag theory [18] (if the powder is not first deflocculated and deagglomerated in the solvent vehicle, groups of agglomerates are encased in a polymer film (binder) along with entrapped air and act as a single unit for the remainder of the tape casting process after binder being added. It would be as if there were a number of these zipper bags full of agglomerated particles and entrapped air being mixed in a solvent-rich slip. This phenomenon will deteriorate the powder accumulation effect). It is a well-known fact that a welldispersed and deagglomerated slip settles to a denser packed bed than does a slip that is only partially flocced or agglomerated [23]. This could also explain why the density of the green tape prepared by cast oil was only 1.63 g/cm3 [22]. Surface micro-topography of the film with 1.5 wt% WCPA was measured to analyze the state of inorganic powder and verify the compactness of the film (in Fig. 5). Optical microscope image in Fig. 5 (a) showed that the inorganic powder was uniformly dispersed without any agglomerates. SEM images in Fig. 5 (b) and (c) demonstrated that the glass and ceramic powders were surrounded by latex binder particles (the glass, ceramic powders and latex binder were marked clearly in Fig. 5(c)), which were uniformly
distributed from the surface of the film. Moreover, the powders were accumulated closely with few pores, which meant that the film had a good compactness. The surface roughness of film has great impact while printing circuit patterns in LTCC devices. For better printing of patterns on LTCC tape roughness is necessary since it promotes adhesion. The AFM images of film were shown in Fig. 6. The average surface roughness was found to be 224 nm. Most of the commercial LTCC films offer a surface roughness <500 nm/square inch [24], and the present LTCC tape’s roughness was on a par with commercial requirements. To avoid the formation of cracks or warpages in laminated tapes during debinder period, the heating rate was controlled at 0.5 ◦ C/min from room temperature to 500 ◦ C and the temperatures were held for 1 h at 300 ◦ C, 350 ◦ C, 400 ◦ C and 450 ◦ C, respectively. The co-firing compatibility with Ag electrodes at 850 ◦ C (held for 15 min) of the film with 1.5 wt% WCPA was presented in Fig. 7. The film was compactly sintered with the Al2 O3 powder well packaged by glass phase and the air pores filled by liquid phase [25], which could be seen from Fig. 7 (b). The XRD patterns in Fig. 7 (d) showed that there was no other phase formation except ␣-Al2 O3 , anorthite and Ag. The optical microscopy and SEM results in Fig. 7 (a) and
Please cite this article in press as: L. Ren, et al., Fabrication of a high-performance film based borosilicate glass/Al2 O3 ceramics for LTCC application, J Eur Ceram Soc (2017), http://dx.doi.org/10.1016/j.jeurceramsoc.2017.01.031
G Model
ARTICLE IN PRESS
JECS-11036; No. of Pages 7
L. Ren et al. / Journal of the European Ceramic Society xxx (2017) xxx–xxx
6
tive instruments. Results showed that the film with 1.5 wt% WCPA possessed the best compactness and mechanical property with the density at 2.01 g/cm3 and the tensile strength at 2.1 MPa. In addition, the roughness of the film with 1.5 wt% WCPA was 224 nm. These properties were superior to that of the green tapes prepared by cast oil and very helpful to the further tape processing, including cutting, punching, printing and so on. Moreover, the sintered LTCC composite exhibited good properties with the density at 3.08 g/cm3 , r = 7.92, CTE = 5.6 and tan␦ = 1.6 × 10−3 at 7 GHz. Besides, after co-firing with Ag electrodes at 850 ◦ C, the glass/Al2 O3 composite could meet the shrinkage requirement of Ag electrodes and would not possibly react with Ag electrodes. Based on the above findings, we could therefore assert that this kind of polymeric dispersant WCPA acted the best promoting role in the tape casting process and the flexible borosilicate-based glass/Al2 O3 film we have studied could be suitable for LTCC application. Acknowledgments Fig. 8. Variation of dielectric constant with the increase of temperature. Table 3 Sintering and microwave properties of the composite LTCC-1 and LTCC-2 fired at 850 ◦ C.
LTCC-1 LTCC-2
Density(g/cm3 )
r (7 GHz)
tan␦ (7 GHz)
CTE (ppm/K)
3.08 3.06
7.92 7.90
1.6 × 10−3 1.9 × 10−3
5.6 5.4
(c) showed that the glass/Al2 O3 composites could match Ag electrodes well without any intervals or permeations on the interface between them. The composites and Ag electrodes were locked into each other, and the crystalline grains of Ag were assembled together to constitute the Ag line. The temperature variation of the electrical properties is very important for practical applications. The temperature coefficient of dielectric constant should be practically zero over the operational temperature range. Fig. 8 showed the dependence of dielectric constant with temperature ranging from −5 ◦ C to 45 ◦ C at 7 GHz. It was obvious that the dielectric constant increased slightly as the temperature rose within the limits of 7.82-8.0. And the temperature coefficient of the dielectric constant was found to be +106.4 ppm/K. Table 3 showed the sintering and microwave properties of the composite produced by 1.5 wt% WCPA (LTCC-1) and 2 wt% cast oil (LTCC-2) dispersion fired at 850 ◦ C. The result comparison showed that the sintering and microwave properties of LTCC-1 and LTCC-2 were similar. This mainly because that after the organic ingredients burning out, the subsequent performance of the composites relied largely on the flow of liquid glass phase and rearrangement of the particles. Due to LTCC-1 and LTCC-2 possessed the same glass and Al2 O3 powders, there was no wonder that they had the similar performance. The sintered LTCC composite exhibited good properties with the density at 3.08 g/cm3 , r = 7.92 and tan␦ = 1.6 × 10−3 at 7 GHz. 4. Conclusion We presented here a novel method to optimize the tape casting process of borosilicate-based glass/Al2 O3 ceramics using a kind of polymeric dispersant WCPA. The dispersion mechanism of the polymeric dispersant with the powders was analyzed in detail and the optimal amount of WCPA addition was also determined through the sedimentation experiment. To judge its effect on the properties of films and sintering ceramic, the characteristics of films, sintering and microwave properties of composite fired at 850 ◦ C were established by employing different qualitative and quantita-
This work was financed by the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD), the Program for Innovative Research Team in University of Ministry of Education of China (No. IRT 15R35) and Research and Innovation Program for College Graduates of Jiangsu Province (KYZZ16 0233). References [1] R.R. Tummala, Ceramic and glass-ceramic packaging in the 1990, J. Am. Ceram. Soc. 74 (5) (1991) 895–908. [2] K. Manu, M.T. Sebastian, Tape casting of low permittivity Wesselsite–Glass composite for LTCC based microwave applications, Ceram. Int. 42 (1) (2016) 1210–1216. [3] M.T. Sebastian, R. Ubic, H. Jantunen, Low-loss dielectric ceramic materials and their properties, Int. Mater. Rev. 60 (7) (2015) 392–412. [4] M.T. Sebastian, H. Wang, H. Jantunen, Low temperature co-fired ceramics with ultra-low sintering temperature: a review, Curr. Opin. Solid. St. M. 20 (3) (2016) 151–170. [5] C. Liu, H. Zhang, H. Su, T. Zhou, J. Li, X. Chen, et al., Low temperature sintering BBSZ glass modified Li2 MgTi3 O8 microwave dielectric ceramics, J. Alloy. Compd. 646 (2015) 1139–1142. [6] S. Duan, E. Li, H. Chen, B. Tang, Y. Yuan, S. Zhang, Influence of Li2 O–B2 O3 –SiO2 glass on the sintering behavior and microwave dielectric properties of BaO–0.15ZnO–4TiO2 ceramics, Ceram. Int. 42 (7) (2016) 7943–7949. [7] S. Arcaro, F.R. Cesconeto, F. Raupp-Pereira, A.P. Novaes de Oliveira, Synthesis and characterization of LZS/␣-Al2 O3 glass-ceramic composites for applications in the LTCC technology, Ceram. Int. 40 (4) (2014) 5269–5274. [8] M. Liu, H. Zhou, X. Xu, Z. Yue, M. Liu, H. Zhu, Sintering, densification and crystallization of Ca–Al–B–Si–O glass/Al2 O3 composites for LTCC application, J. Mater. Sci. Mater. El.24 (10) (2013) 3985–3994. [9] M.T. Sebastian, H. Jantunen, Low loss dielectric materials for LTCC applications: a review, Int. Mater. Rev. 53 (2) (2008) 57–90. [10] L. Ren, H. Zhou, X. Li, W. Xie, X. Luo, Synthesis and characteristics of borosilicate-based glass–ceramics with different SiO2 and Na2 O contents, J. Alloy. Compd. 646 (2015) 780–786. [11] S. Arcaro, M. Isabel Nieto, J.B. Rodrigues Neto, A.P. Novaes de Oliveira, R. Moreno, I. Reimanis, Al2 O3 nanoparticulate LZS glass-ceramic matrix composites for production of multilayered materials, J. Am. Ceram. Soc. 99 (11) (2016) 3573–3580. [12] Z. Jingxian, J. Dongliang, L. Weisensel, P. Greil, Deflocculants for tape casting of TiO2 slurries, J. Eur. Ceram. Soc. 24 (8) (2004) 2259–2265. [13] Y. Qiao, Y. Liu, A. Liu, Y. Wang, Boron carbide green sheet processed by environmental friendly non-aqueous tape casting, Ceram. Int. 38 (3) (2012) 2319–2324. [14] M. Yu, J. Zhang, X. Li, H. Liang, H. Zhong, Y. Li, et al., Optimization of the tape casting process for development of high performance alumina ceramics, Ceram. Int. 41 (10) (2015) 14845–14853. [15] G.C.R. Moreno, Oil-related deflocculants for tape casting slips, J. Eur. Ceram. Soc. 17 (1997) 351–357. [16] Q. Tan, Z. Zhang, Z. Tang, S. Luo, K. Fang, Rheological properties of nanometer tetragonal polycrystal zirconia slurries for aqueous gel tape casting process, Mater. Lett. 57 (16–17) (2003) 2375–2381. [17] Y. Zhou, J. Yu, X. Wang, Y. Wang, J. Zhu, Z. Hu, Preparation of KH570-SiO2 and their modification on the MF/PVA composite membrane, Fiber Polym. 16 (8) (2015) 1772–1780. [18] G.H. Hsiue, L.W. Chu, I.N. Lin, Optimized phosphate ester structure for the dispersion of nano-sized barium titanate in proper non-aqueous media, Colloid Surf. A 294 (1–3) (2007) 212–220.
Please cite this article in press as: L. Ren, et al., Fabrication of a high-performance film based borosilicate glass/Al2 O3 ceramics for LTCC application, J Eur Ceram Soc (2017), http://dx.doi.org/10.1016/j.jeurceramsoc.2017.01.031
G Model JECS-11036; No. of Pages 7
ARTICLE IN PRESS L. Ren et al. / Journal of the European Ceramic Society xxx (2017) xxx–xxx
[19] P. Barick, B. Prasad Saha, R. Mitra, S.V. Joshi, Effect of concentration and molecular weight of polyethylenimine on zeta potential, isoelectric point of nanocrystalline silicon carbide in aqueous and ethanol medium, Ceram. Int. 41 (3) (2015) 4289–4293. [20] J. Zhu, G. Zhang, G. Liu, Q. Qu, Y. Li, Investigation on the rheological and stability characteristics of coal–water slurry with long side-chain polycarboxylate dispersant, Fuel Process. Technol. 118 (2014) 187–191. [21] E.R.T. Richard, E. Mistler, Tape Casting Theory and Practice, Wiley, New York, 2000. [22] L. Ren, X. Luo, W. Xie, L. Qian, Y. Gu, H. Zhou, Optimization of tape casting process via surface modification of glass/Al2 O3 powder, J. Mater. Sci-Mater. E.27 (9) (2016) 9877–9884.
7
[23] James S. Reed, J.W. Laughner, Introduction to the Principles of Ceramic Processing, Wiley, New York, 1988. [24] I.J. Induja, P. Abhilash, S. Arun, K.P. Surendran, M.T. Sebastian, LTCC tapes based on Al2 O3 –BBSZ glass with improved thermal conductivity, Ceram. Int. 41 (10) (2015) 13572–13581. [25] L. Ren, X. Luo, L. Hu, Q. Sun, Y. Xia, Y. Hu, et al., Synthesis and characterization of LTCC compositions with middle permittivity based on CaO-B2 O3 -SiO2 glass/CaTiO3 system, J. Eur. Ceram. Soc. 37 (2) (2017) 619–623.
Please cite this article in press as: L. Ren, et al., Fabrication of a high-performance film based borosilicate glass/Al2 O3 ceramics for LTCC application, J Eur Ceram Soc (2017), http://dx.doi.org/10.1016/j.jeurceramsoc.2017.01.031
ARTICLE IN PRESS
JECS-11036; No. of Pages 7
Journal of the European Ceramic Society xxx (2017) xxx–xxx
Contents lists available at www.sciencedirect.com
Journal of the European Ceramic Society journal homepage: www.elsevier.com/locate/jeurceramsoc
Fabrication of a high-performance film based borosilicate glass/Al2 O3 ceramics for LTCC application Luchao Ren a,b , Xianfu Luo a,b , Yunsheng Xia a,b , Yongkang Hu a,b , Hongqing Zhou a,b,∗ a b
College of Materials Science and Engineering, Nanjing Tech University, Nanjing Jiangsu, 210009, China Jiangsu Collaborative Innovation Center for Advanced Inorganic Function Composites, Nanjing Tech University, Nanjing Jiangsu, 210009, China
a r t i c l e
i n f o
Article history: Received 27 November 2016 Received in revised form 20 January 2017 Accepted 21 January 2017 Available online xxx Keywords: High-performance film Polymeric dispersant Tape casting LTCC application
a b s t r a c t The present work was initiated aiming at developing a high-performance film for LTCC application using a kind of polymeric dispersant in tape casting process of borosilicate-based glass/Al2 O3 ceramics. The dispersion mechanism of the polymeric dispersant with the powders was analyzed in detail and the optimal amount of the dispersant addition was also determined through the sedimentation experiment. Its effects on the compactness, tensile strength and surface roughness of the films were analyzed. In addition, the sintering and microwave properties of the composite fired at 850 ◦ C were also determined. For the application of tape technology, the co-firing compatibility between the composite and Ag electrodes at 850 ◦ C was also verified. After testing and verification with different qualitative and quantitative instruments, a flexible film optimized by 1.5 wt% polymeric dispersant achieved the best overall performance. © 2017 Published by Elsevier Ltd.
1. Introduction The recent rapid developments in the microelectronic industry demand miniature microwave devices with high processing speed [1]. To meet this requirement, Low Temperature Co-fired Ceramic (LTCC) technology, which combines the use of low permittivity dielectrics with low loss glasses, has been developing rapidly [2]. Recently, glass/Al2 O3 composites have received much attention because they can meet a lot of requirements of physical, electrical and thermal properties [3,4]. Different glass systems are designed to cater to the specific purpose, such as B2 O3 -Bi2 O3 SiO2 -ZnO(BBSZ) [5], Li2 O-B2 O3 -SiO2 (LBS) [6], Li2 O–SiO2 –ZrO2 (LSZ) [7], CaO–B2 O3 –SiO2 -Al2 O3 (CABS) [8], etc. Among the different LTCC glass-ceramics systems, CABS glass/Al2 O3 has been reported as a promising material for using in microelectronic packaging because of its low firing temperature and low dielectric loss [9]. In our previous study [10], the CABS glass/Al2 O3 sintered at 850 ◦ C showed r = 7.87 and tan ␦ = 20 × 10−4 at 7 GHz. The composite is physically and chemically compatible with the common electrode material, silver. For practical applications, the ceramic should be in the form of thin sheets through tape casting. The development of such flexible LTCC films with smooth surface, high
∗ Corresponding author at: College of Materials Science and Engineering, Nanjing Tech University, Nanjing Jiangsu, 210009, China. E-mail address: [email protected] (H. Zhou).
density and high performance is the most important step in the fabrication of multilayer ceramic modules [11]. In this work, we introduced a kind of polymeric dispersant into slurry system instead of the common castor oil which dispersion mechanism was found to be steric hindrance [12–14]. This kind of polymeric dispersant belongs to the type of weakly cationic polymeric amine (WCPA). The physicochemical property of polymeric dispersant and castor oil are listed in Table 1. It is expected to disperse primary particles and to hold them in a homogeneous suspension by two methods, ionic repulsion and steric hindrance [15]. So the deflocculation of polymeric dispersant is better than that of castor oil in theory. We investigated the optimization results of the polymeric dispersant on the tape casting process of CABS glass/Al2 O3 composite, expecting to develop a smooth surface, high density and strong mechanical films for further tape processing of LTCC application.
2. Experimental procedures CABS glass with composition 15CaO:5Al2 O3 :16B2 O3 :64SiO2 was prepared by conventional glass quenching method. After being equally mixed, raw materials were melted in a platinum crucible at 1500 ◦ C for about 1 h. To prevent the occurrence of any crystallization, the melt was quenched into deionized water to form frits. Then, the glass frits were dried and milled in high speed agate mill, resulting in fine glass powders. The resulting glass powder (D50 = 3.8 m) was mixed with the Al2 O3 ceramic pow-
http://dx.doi.org/10.1016/j.jeurceramsoc.2017.01.031 0955-2219/© 2017 Published by Elsevier Ltd.
Please cite this article in press as: L. Ren, et al., Fabrication of a high-performance film based borosilicate glass/Al2 O3 ceramics for LTCC application, J Eur Ceram Soc (2017), http://dx.doi.org/10.1016/j.jeurceramsoc.2017.01.031
G Model JECS-11036; No. of Pages 7
ARTICLE IN PRESS L. Ren et al. / Journal of the European Ceramic Society xxx (2017) xxx–xxx
2
Table 1 Physicochemical property of polymeric dispersant and castor oil. Dispersant
Ingredient
Molecular weight
Decomposition temperature
Weakly cationic polymeric amine(WCPA) Castor oil
Substituted amino-terminal (-NR3 + ) group polycaprolactone Ricinoleic acid, glyceride
12000 933.26
500 ◦ C 265 ◦ C
der (D50 = 3.0 m) at the mass ratio [m(Al2 O3 ):m(glass) = 45:55] for about 20 h. According to our previous study[8], the melting point of CABS glass was 710.7 ◦ C with r = 5.99 and tan␦ = 1.4 × 10−3 at 7 GHz. Due to the solid state of the polymeric dispersant, it should, firstly, be dissolved in solvent. So the tape casting slurry was prepared in a three stage process. In the first stage, polymeric dispersant was ball-milled for 5 h in the solvent (isopropanol/xylene/ethanol) ensuring it was fully dissolved. In the second stage, CABS glass/Al2 O3 ceramic powder was added and ball-milled for 24 h. In the third stage, binder (polyvinyl butyral) and plasticizer (dibutyl phthalate) were introduced and ball-milled for another 24 h. The final slurry was then degassed in a vacuum desiccator for 10 min to remove air bubbles and cast using a tape casting machine (BHLY-011A). After that, the tapes were dried at room temperature. The thickness of the green tape was 160 ± 5 m and the green tape was cut into circular sheets with the diameter of 21.46 mm. For the microwave test, 60 layers of the green tape were stacked and laminated together to obtain the final cylindrical sample at 21 MPa for 10 min at 70 ◦ C. The thickness of the laminated sheets were about 6 mm. After binder burnout and sintering, dense LTCC composite could be obtained. Zeta potentials of CABS glass/Al2 O3 suspensions were calculated from the measured electrophoretic mobility using ZetaPALS (Brookhaven Instruments Corporation, USA). The chemical information of the powders and dispersant was measured by means of Fourier Transformation Infrared Spectrometer (Nexus-670, Nicolet, USA). Density of the film was the average of five sample datum through the density formula-mass divided by volume. Mechanical property of films was defined through electronic universal material testing machine (CSS-2205). Surface roughness of the film was measured using an Atomic Force Microscope (AFM) (Dimension Edge, Bruker, Germany). The microstructure was investigated by scanning electron microscopy (SEM) analysis (JSM-5900).The bulk densities of the sintered samples were evaluated by Archimedean immersion method using water as medium with the accuracy of
±0.001 g/cm3 . The microwave properties (dielectric constant r and quality factor value) were determined by the cavity method with a network analyzer (HP 8722ET, Agilent, U.S.A.) operating at 7 GHz at room temperature. The temperature dependence of dielectric constant was also measured by the same method by changing temperature from −5 ◦ C to 45 ◦ C. The coefficient of thermal expansion (CTE) measurements from 23 ◦ C to 300 ◦ C were carried out by dilatometer Netzsch 402E. The heating rates for dilatometric measurements were 5 K/min. 3. Results and discussion 3.1. Surface features and dispersion mechanism To identify the glass/Al2 O3 powder surface properties (surface electrical behavior and surface chemical groups), Zeta potentials of CABS glass/Al2 O3 suspensions with different pH values and infrared absorption spectrum of glass/Al2 O3 powder were measured. Fig. 1a showed the zeta potentials of the powder suspensions with different WCPA content at different pH values. The zeta potential was noticeably decreased with the higher content of polymeric dispersant. The isoelectric point (IEP) of the powder was also affected by addition of polymeric dispersant WCPA, but all within the pH range from 2 to 4. The used powder could be determined to carry negative charges on the surface. Moreover, distinct changes of surface charge in dispersed glass/Al2 O3 suspensions were due to adsorption of dispersant on the surface of the particles, inducing more negative charges to the particle double layer [16]. Infrared absorption spectrum of polymeric dispersant WCPA and CABS glass/Al2 O3 was depicted in Fig. 1b. After detailed analysis, the determination of functional group was as follows: for WCPA, a typical spectrum showed the NH group stretching vibration absorption bond at 2495.47 cm−1 . The −NH group bending vibration absorption occurred at 1552.27 cm−1 and 1648.80 cm−1 . The peak at 1724 cm−1 indicated the existence of carbonyl (i.e. C O) in amide groups (i.e. −CONH2 ). The peak at 3436.89 cm−1 indicated
Fig. 1. Powder surface properties. a. Zeta potential as a function of pH value (surface electrical behavior). b. Infrared absorption spectrum of the dispersant and powder (surface chemical groups).
Please cite this article in press as: L. Ren, et al., Fabrication of a high-performance film based borosilicate glass/Al2 O3 ceramics for LTCC application, J Eur Ceram Soc (2017), http://dx.doi.org/10.1016/j.jeurceramsoc.2017.01.031
G Model JECS-11036; No. of Pages 7
ARTICLE IN PRESS L. Ren et al. / Journal of the European Ceramic Society xxx (2017) xxx–xxx
3
Fig. 2. Dispersion mechanism of the polymeric dispersant with the powders in solvents.
the existence of OH group. The peak at 1397.85 cm−1 stands for the existence of C N. Considering a strong peak at 1190.48 cm−1 and a weak peak at 1046.59 cm−1 (corresponding to asymmetry and symmetry stretching vibration of C O-C- respectively), there was no doubt that the gender structures of WCPA were CONH2 group(anchoring group) and polycaprolactone (solvatable chain). For inorganic powder, besides the characteristic peak of glass and Al2 O3 , a stretching vibration peak at 3448.70 cm−1 was identified as the hydroxyl ( OH), which would react with WCPA [17]. A definite understanding about the powder surface properties and the gender structure of WCPA makes for the interpretation of the dispersion mechanism of polymeric dispersant WCPA. For the structure of WCPA, one part is anchoring group, which can be tightly adsorbed on the surface of powders through chemical bond, hydrogen bond or Van der Wals forces; while the other functional group is a solvatable chain, which can extend in the solvent medium and form an adsorption layer with certain thickness on the surface of the powders. The dispersion mechanism of the polymeric dispersant is illustrated in Fig. 2. As indicated in the Fig, the action process between dispersion and powders is divided into three stages. In the first stage (reaction stage), after dissolving in the solvent, the polymeric dispersant WCPA with cations is readily attached to the surface of powder by counter-ion attraction [18]. Furthermore, the strong polar group −CONH2 of WCPA, which can form hydrogen bonds with the OH on the surface of the powders, plays the anchor role In enhancing the adsorption force between the dispersant and powders [19]. In the second stage (formative stage), after the powders have been anchored with WCPA, the polycaprolactone side chain extends into the solvents system and forms the thick solvate layer. The solvate outer layer mainly plays a role of steric hindrance to prevent coagulation [20]. Meanwhile, the mutually exclusive cations also exist on the WCPA. In the last stage (stabiliza-
Fig. 3. Variation of relative sediment height as a function of time for different amounts of WCPA. The inset is an image of the process of sedimentation measurement.
tion stage), due to the combined effect of electrostatic repulsion and steric hindrance, the powders are well dispersed in the solvents. 3.2. Sedimentation analysis The amount of polymeric dispersant WCPA could be optimized by sedimentation analysis. A simplified model system was designed for the sedimentation test. These systems were composed of glass/Al2 O3 powder, different amounts of polymeric dispersant WCPA and organic solvent (the mass ratio of powder and solvent is 10:10). Fig. 3 showed the variation of relative sediment height (H/H0 , H is the powder height at time t, H0 is the initial powder
Please cite this article in press as: L. Ren, et al., Fabrication of a high-performance film based borosilicate glass/Al2 O3 ceramics for LTCC application, J Eur Ceram Soc (2017), http://dx.doi.org/10.1016/j.jeurceramsoc.2017.01.031
G Model
ARTICLE IN PRESS
JECS-11036; No. of Pages 7
L. Ren et al. / Journal of the European Ceramic Society xxx (2017) xxx–xxx
4
Table 2 Final organic formula of the tape casting slurry (wt% of powder). WCPA
Solvent
Polyvinyl Butyral
Dibutyl Phthalate
1 1.3 1.5 1.7 1.9
51 51 51 51 51
10 10 10 10 10
3 3 3 3 3
height) as a function of time for different amounts of polymeric dispersant WCPA. It could be seen that suspensions with 1 wt% and 1.3 wt% WCPA settled fastly and showed higher relative sediment height; whereas, suspensions with 1.5 wt%, 1.7 wt% and 1.9 wt% WCPA settled slowly and exhibited the same lowest relative sediment height. As described by Richard E. Mistler [21], the dual action of dispersion and deflocculation can be observed as the higher additive concentrations take longer to finish setting; the plateau is reached when the deflocculant concentration is adequate to fully deflocculate the powder. In addition, compared with the settlement result of cast oil dispersion, it was obvious that the final sediment height of suspension with WCPA was far below that of suspension with cast oil (for cast oil, 2 wt% is the best addition [22]). The lowest sediment height meant the highest package density. After detailed analysis, we could conclude that the dispersing ability of WCPA was much stronger than cast oil, suspension with 1.5 wt% WCPA was dispersed most uniformly and the superfluous WCPA like those with 1.7 wt% and 1.9 wt% did not contribute to the further promotion of the dispersion. 3.2.1. Characteristics of films and fired ceramic Table 2 showed the final organic formula of the tape casting slurry. The amount of each component was calculated as the mass fraction of glass/Al2 O3 powder. After tape casting, the crack free tapes were obtained. For further tape processing, investigating den-
Fig. 4. Bulk density and tensile strength of films with different WCPA content.
sity and tensile strength of films is very significant [22]. Green bulk density is vital to quality control of a cast, since it is directly related to the distance between ceramic particles in the tape. Changes in interparticle distance have a direct effect upon firing shrinkage and can also affect fired bulk density (FBD) in many cases. In addition, many tapes are further processed with automatic or semiautomatic handling equipment. Specifically, when the tape is processed separate from the carrier film, the tensile forces should be applied to the cast tape, which require the tape to have a certain level of tensile strength to avoid damages [21]. The bulk density and tensile strength of films with different WCPA content were illustrated in Fig. 4. It could be seen that the density and tensile strength of film exhibited the same variation trend. They both attained the maximum when the WCPA content was 1.5 wt%. Associating the result of the sedimentation in Fig. 3, we can summarize a rule that the most uniformly dispersed slurry was, the highest bulk density and
Fig. 5. Surface micro-topography of the film with 1.5 wt% WCPA. (a) Optical microscope image. (b), (c) the SEM images in different magnifications.
Please cite this article in press as: L. Ren, et al., Fabrication of a high-performance film based borosilicate glass/Al2 O3 ceramics for LTCC application, J Eur Ceram Soc (2017), http://dx.doi.org/10.1016/j.jeurceramsoc.2017.01.031
G Model JECS-11036; No. of Pages 7
ARTICLE IN PRESS L. Ren et al. / Journal of the European Ceramic Society xxx (2017) xxx–xxx
5
Fig. 6. 2D and 3D AFM images of the film with 1.5 wt% WCPA.
Fig. 7. Co-firing compatibility with Ag electrodes at 850 ◦ C of the film with 1.5 wt% WCPA. (a) Optical microscope image of the composite co-fired with Ag electrodes. (b) SEM image of the composites’ cross sections. (c) SEM image on the interface between glass/Al2 O3 composite and Ag electrodes. (d) XRD pattern of the composite co-fired with Ag electrodes.
tensile strength films possessed. It could be interpreted by the zipper bag theory [18] (if the powder is not first deflocculated and deagglomerated in the solvent vehicle, groups of agglomerates are encased in a polymer film (binder) along with entrapped air and act as a single unit for the remainder of the tape casting process after binder being added. It would be as if there were a number of these zipper bags full of agglomerated particles and entrapped air being mixed in a solvent-rich slip. This phenomenon will deteriorate the powder accumulation effect). It is a well-known fact that a welldispersed and deagglomerated slip settles to a denser packed bed than does a slip that is only partially flocced or agglomerated [23]. This could also explain why the density of the green tape prepared by cast oil was only 1.63 g/cm3 [22]. Surface micro-topography of the film with 1.5 wt% WCPA was measured to analyze the state of inorganic powder and verify the compactness of the film (in Fig. 5). Optical microscope image in Fig. 5 (a) showed that the inorganic powder was uniformly dispersed without any agglomerates. SEM images in Fig. 5 (b) and (c) demonstrated that the glass and ceramic powders were surrounded by latex binder particles (the glass, ceramic powders and latex binder were marked clearly in Fig. 5(c)), which were uniformly
distributed from the surface of the film. Moreover, the powders were accumulated closely with few pores, which meant that the film had a good compactness. The surface roughness of film has great impact while printing circuit patterns in LTCC devices. For better printing of patterns on LTCC tape roughness is necessary since it promotes adhesion. The AFM images of film were shown in Fig. 6. The average surface roughness was found to be 224 nm. Most of the commercial LTCC films offer a surface roughness <500 nm/square inch [24], and the present LTCC tape’s roughness was on a par with commercial requirements. To avoid the formation of cracks or warpages in laminated tapes during debinder period, the heating rate was controlled at 0.5 ◦ C/min from room temperature to 500 ◦ C and the temperatures were held for 1 h at 300 ◦ C, 350 ◦ C, 400 ◦ C and 450 ◦ C, respectively. The co-firing compatibility with Ag electrodes at 850 ◦ C (held for 15 min) of the film with 1.5 wt% WCPA was presented in Fig. 7. The film was compactly sintered with the Al2 O3 powder well packaged by glass phase and the air pores filled by liquid phase [25], which could be seen from Fig. 7 (b). The XRD patterns in Fig. 7 (d) showed that there was no other phase formation except ␣-Al2 O3 , anorthite and Ag. The optical microscopy and SEM results in Fig. 7 (a) and
Please cite this article in press as: L. Ren, et al., Fabrication of a high-performance film based borosilicate glass/Al2 O3 ceramics for LTCC application, J Eur Ceram Soc (2017), http://dx.doi.org/10.1016/j.jeurceramsoc.2017.01.031
G Model
ARTICLE IN PRESS
JECS-11036; No. of Pages 7
L. Ren et al. / Journal of the European Ceramic Society xxx (2017) xxx–xxx
6
tive instruments. Results showed that the film with 1.5 wt% WCPA possessed the best compactness and mechanical property with the density at 2.01 g/cm3 and the tensile strength at 2.1 MPa. In addition, the roughness of the film with 1.5 wt% WCPA was 224 nm. These properties were superior to that of the green tapes prepared by cast oil and very helpful to the further tape processing, including cutting, punching, printing and so on. Moreover, the sintered LTCC composite exhibited good properties with the density at 3.08 g/cm3 , r = 7.92, CTE = 5.6 and tan␦ = 1.6 × 10−3 at 7 GHz. Besides, after co-firing with Ag electrodes at 850 ◦ C, the glass/Al2 O3 composite could meet the shrinkage requirement of Ag electrodes and would not possibly react with Ag electrodes. Based on the above findings, we could therefore assert that this kind of polymeric dispersant WCPA acted the best promoting role in the tape casting process and the flexible borosilicate-based glass/Al2 O3 film we have studied could be suitable for LTCC application. Acknowledgments Fig. 8. Variation of dielectric constant with the increase of temperature. Table 3 Sintering and microwave properties of the composite LTCC-1 and LTCC-2 fired at 850 ◦ C.
LTCC-1 LTCC-2
Density(g/cm3 )
r (7 GHz)
tan␦ (7 GHz)
CTE (ppm/K)
3.08 3.06
7.92 7.90
1.6 × 10−3 1.9 × 10−3
5.6 5.4
(c) showed that the glass/Al2 O3 composites could match Ag electrodes well without any intervals or permeations on the interface between them. The composites and Ag electrodes were locked into each other, and the crystalline grains of Ag were assembled together to constitute the Ag line. The temperature variation of the electrical properties is very important for practical applications. The temperature coefficient of dielectric constant should be practically zero over the operational temperature range. Fig. 8 showed the dependence of dielectric constant with temperature ranging from −5 ◦ C to 45 ◦ C at 7 GHz. It was obvious that the dielectric constant increased slightly as the temperature rose within the limits of 7.82-8.0. And the temperature coefficient of the dielectric constant was found to be +106.4 ppm/K. Table 3 showed the sintering and microwave properties of the composite produced by 1.5 wt% WCPA (LTCC-1) and 2 wt% cast oil (LTCC-2) dispersion fired at 850 ◦ C. The result comparison showed that the sintering and microwave properties of LTCC-1 and LTCC-2 were similar. This mainly because that after the organic ingredients burning out, the subsequent performance of the composites relied largely on the flow of liquid glass phase and rearrangement of the particles. Due to LTCC-1 and LTCC-2 possessed the same glass and Al2 O3 powders, there was no wonder that they had the similar performance. The sintered LTCC composite exhibited good properties with the density at 3.08 g/cm3 , r = 7.92 and tan␦ = 1.6 × 10−3 at 7 GHz. 4. Conclusion We presented here a novel method to optimize the tape casting process of borosilicate-based glass/Al2 O3 ceramics using a kind of polymeric dispersant WCPA. The dispersion mechanism of the polymeric dispersant with the powders was analyzed in detail and the optimal amount of WCPA addition was also determined through the sedimentation experiment. To judge its effect on the properties of films and sintering ceramic, the characteristics of films, sintering and microwave properties of composite fired at 850 ◦ C were established by employing different qualitative and quantita-
This work was financed by the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD), the Program for Innovative Research Team in University of Ministry of Education of China (No. IRT 15R35) and Research and Innovation Program for College Graduates of Jiangsu Province (KYZZ16 0233). References [1] R.R. Tummala, Ceramic and glass-ceramic packaging in the 1990, J. Am. Ceram. Soc. 74 (5) (1991) 895–908. [2] K. Manu, M.T. Sebastian, Tape casting of low permittivity Wesselsite–Glass composite for LTCC based microwave applications, Ceram. Int. 42 (1) (2016) 1210–1216. [3] M.T. Sebastian, R. Ubic, H. Jantunen, Low-loss dielectric ceramic materials and their properties, Int. Mater. Rev. 60 (7) (2015) 392–412. [4] M.T. Sebastian, H. Wang, H. Jantunen, Low temperature co-fired ceramics with ultra-low sintering temperature: a review, Curr. Opin. Solid. St. M. 20 (3) (2016) 151–170. [5] C. Liu, H. Zhang, H. Su, T. Zhou, J. Li, X. Chen, et al., Low temperature sintering BBSZ glass modified Li2 MgTi3 O8 microwave dielectric ceramics, J. Alloy. Compd. 646 (2015) 1139–1142. [6] S. Duan, E. Li, H. Chen, B. Tang, Y. Yuan, S. Zhang, Influence of Li2 O–B2 O3 –SiO2 glass on the sintering behavior and microwave dielectric properties of BaO–0.15ZnO–4TiO2 ceramics, Ceram. Int. 42 (7) (2016) 7943–7949. [7] S. Arcaro, F.R. Cesconeto, F. Raupp-Pereira, A.P. Novaes de Oliveira, Synthesis and characterization of LZS/␣-Al2 O3 glass-ceramic composites for applications in the LTCC technology, Ceram. Int. 40 (4) (2014) 5269–5274. [8] M. Liu, H. Zhou, X. Xu, Z. Yue, M. Liu, H. Zhu, Sintering, densification and crystallization of Ca–Al–B–Si–O glass/Al2 O3 composites for LTCC application, J. Mater. Sci. Mater. El.24 (10) (2013) 3985–3994. [9] M.T. Sebastian, H. Jantunen, Low loss dielectric materials for LTCC applications: a review, Int. Mater. Rev. 53 (2) (2008) 57–90. [10] L. Ren, H. Zhou, X. Li, W. Xie, X. Luo, Synthesis and characteristics of borosilicate-based glass–ceramics with different SiO2 and Na2 O contents, J. Alloy. Compd. 646 (2015) 780–786. [11] S. Arcaro, M. Isabel Nieto, J.B. Rodrigues Neto, A.P. Novaes de Oliveira, R. Moreno, I. Reimanis, Al2 O3 nanoparticulate LZS glass-ceramic matrix composites for production of multilayered materials, J. Am. Ceram. Soc. 99 (11) (2016) 3573–3580. [12] Z. Jingxian, J. Dongliang, L. Weisensel, P. Greil, Deflocculants for tape casting of TiO2 slurries, J. Eur. Ceram. Soc. 24 (8) (2004) 2259–2265. [13] Y. Qiao, Y. Liu, A. Liu, Y. Wang, Boron carbide green sheet processed by environmental friendly non-aqueous tape casting, Ceram. Int. 38 (3) (2012) 2319–2324. [14] M. Yu, J. Zhang, X. Li, H. Liang, H. Zhong, Y. Li, et al., Optimization of the tape casting process for development of high performance alumina ceramics, Ceram. Int. 41 (10) (2015) 14845–14853. [15] G.C.R. Moreno, Oil-related deflocculants for tape casting slips, J. Eur. Ceram. Soc. 17 (1997) 351–357. [16] Q. Tan, Z. Zhang, Z. Tang, S. Luo, K. Fang, Rheological properties of nanometer tetragonal polycrystal zirconia slurries for aqueous gel tape casting process, Mater. Lett. 57 (16–17) (2003) 2375–2381. [17] Y. Zhou, J. Yu, X. Wang, Y. Wang, J. Zhu, Z. Hu, Preparation of KH570-SiO2 and their modification on the MF/PVA composite membrane, Fiber Polym. 16 (8) (2015) 1772–1780. [18] G.H. Hsiue, L.W. Chu, I.N. Lin, Optimized phosphate ester structure for the dispersion of nano-sized barium titanate in proper non-aqueous media, Colloid Surf. A 294 (1–3) (2007) 212–220.
Please cite this article in press as: L. Ren, et al., Fabrication of a high-performance film based borosilicate glass/Al2 O3 ceramics for LTCC application, J Eur Ceram Soc (2017), http://dx.doi.org/10.1016/j.jeurceramsoc.2017.01.031
G Model JECS-11036; No. of Pages 7
ARTICLE IN PRESS L. Ren et al. / Journal of the European Ceramic Society xxx (2017) xxx–xxx
[19] P. Barick, B. Prasad Saha, R. Mitra, S.V. Joshi, Effect of concentration and molecular weight of polyethylenimine on zeta potential, isoelectric point of nanocrystalline silicon carbide in aqueous and ethanol medium, Ceram. Int. 41 (3) (2015) 4289–4293. [20] J. Zhu, G. Zhang, G. Liu, Q. Qu, Y. Li, Investigation on the rheological and stability characteristics of coal–water slurry with long side-chain polycarboxylate dispersant, Fuel Process. Technol. 118 (2014) 187–191. [21] E.R.T. Richard, E. Mistler, Tape Casting Theory and Practice, Wiley, New York, 2000. [22] L. Ren, X. Luo, W. Xie, L. Qian, Y. Gu, H. Zhou, Optimization of tape casting process via surface modification of glass/Al2 O3 powder, J. Mater. Sci-Mater. E.27 (9) (2016) 9877–9884.
7
[23] James S. Reed, J.W. Laughner, Introduction to the Principles of Ceramic Processing, Wiley, New York, 1988. [24] I.J. Induja, P. Abhilash, S. Arun, K.P. Surendran, M.T. Sebastian, LTCC tapes based on Al2 O3 –BBSZ glass with improved thermal conductivity, Ceram. Int. 41 (10) (2015) 13572–13581. [25] L. Ren, X. Luo, L. Hu, Q. Sun, Y. Xia, Y. Hu, et al., Synthesis and characterization of LTCC compositions with middle permittivity based on CaO-B2 O3 -SiO2 glass/CaTiO3 system, J. Eur. Ceram. Soc. 37 (2) (2017) 619–623.
Please cite this article in press as: L. Ren, et al., Fabrication of a high-performance film based borosilicate glass/Al2 O3 ceramics for LTCC application, J Eur Ceram Soc (2017), http://dx.doi.org/10.1016/j.jeurceramsoc.2017.01.031