Papers by Keyword: Lead-Free

Abstract: Barium titanate (BaTiO3 or BT) has become one of the most studied functional materials due to its potential application as multilayer ceramic capacitors, PTC thermistors, electromechanical devices, piezoelectric transducers, actuators, dynamic RAM or logic circuitry as well as a great variety of electro-optical devices. In the present study, high energy ball milling has been used to produce nanocrystalline powders of BT. Two categories of powders having average particle size of 35 nm and 25 nm were prepared by setting the milling speed at 250 rpm and 300 rpm respectively, fixing the milling time at 30 hours. Four ceramic samples, BT35-1350, BT25-1350, BT35-1400 and BT25-1400, were formed by sintering the two types of powders at 1350oC and 1400oC for 3 hours. The ferroelectric and piezoelectric properties of the ceramic samples were studied and found to be dependent on the size of the starting nanopowders. The bulk density and piezoelectric constant (d33) of B25-1350 were found to be less than those of BT35-1350, while the reverse was true in case of BT25-1400 and BT35-1400. Well saturated P-E hysteresis loops were observed for all the ceramics with the size and shape of the loops appearing different for the four samples. For both the pairs of ceramics sintered at 1350oC and 1400oC, the remnant polarization (Pr) decreases with starting particle size, that is, as we go from BT35-1350 to BT25-1350 as well as from BT35-1400 to BT25-1400. However, with decreasing particle size of the starting powders, the coercive field (Ec) increases for the ceramics sintered at 1350oC and decreases for the ceramics sintered at 1400oC. The study reveals the importance of an optimized combination of the size of the starting nanopowders and sintering temperature for obtaining BT ceramics with the desired properties.

Abstract: From the concept of environmental protection, the necessity of using lead-free solder was introduced. The development of lead-free solder at home or overseas has been reviewed. Some key problems in developing lead-free solder were analyzed and some suggestions of solving the problems have been put forward.

Abstract: System-in-package (SiP) has become a mainstream technology in IC package industry as it provides the solutions to the growing needs of high speed functions, mobility/portability, energy efficiency, and miniaturization of electronic products. One special form of SiP is the multi-chip module (MCM) in which multiple integrated circuits (ICs), semiconductor dies or other discrete components are packaged onto a unifying substrate. Thus, the reliability of package integrity becomes one of the major reliability concerns. In the present paper, a robust design analysis on the thermo-mechanical reliability of an MCM package with flip-chip technology is demonstrated. Our results show that for the specific package, the CTE of the substrate is the most influential factor to the fatigue reliability of the package. The optimal combination of the parameters is recommended. The robust design analysis optimizes the fatigue life from 165 cycles to 1080 cycles which is a 554.5% gain on the fatigue life.

Abstract: Adopting an accurate micro-tensile method based on dynamic mechanical analyzer (DMA) instrument, the tensile strength of three kinds of copper-wire/solder/copper-wire sandwich structured microscale lead-free solder joints that underwent current stressing with a direct current density of 1.0×10⁴ A/cm² and loading time of 48 hours were investigated, and compared with those solder joints isothermal aged at 100 0C for 48 hours and as-reflowed condition. These three kinds of microscale columnar solder joints have different volumes, i.e., a same diameter of 300 μm but different heights of 100 μm, 200 μm and 300 μm. Experimental results show that both current stressing and isothermal aging degrades the tensile strength of microscale solder joints, and the solder joint with smaller volume obtains higher tensile strength under same test condition. In addition, current stressing induces obvious electromigration (EM) issue under high current density of 1.0×10⁴ A/cm², resulting in the decreasing of tensile strength and different fracture position, mode and surface morphology of microscale solder joints. The degree of strength degradation increases with the increasing of joint height when keep joint diameter constant, this is mainly due to that electromigration leads to voids form and grow at the interface of cathode, and solder joints with larger volume may contains more soldering defects as well.

Abstract: The structure stability、micro-structure and electrical properties of lithium doping on potassium sodium niobate ceramics (Na0.5K0.5)NbO3 (NKN) were investigated in this study. Solid oxide mixing method with post calcination and sintering was employed to fabricate(Na0.5K0.5)(1-x) LixNbO3 ceramic. Lithium oxide was adopted as the sintering aids. For Li doping x=6 mol% in (Na0.5K0.5)(1-x) LixNbO3 ceramic a optimal crystallization and electrical properties could be achieved after 650°C calcination and 1060°C sintering. Ferroelectric properties of the lead-free ceramic behaved a coercive field of 12.5kV/cm and remanent polarization as high as 30uC/cm2.

Abstract: The introduction of lithium ion into BNT-BKT-BT ceramics with sol-gel method allows the development of high-performance lead-free piezoelectric ceramics. Nanoscale precursor powders were synthesized through calcination of amorphous gels, and densified ceramics with single perovskite structure were prepared at a relatively low sintering temperature 1110 °C. Crystal grain growth was fully developed with the Li+ addition through scanning electron microscope observation. Enhanced electrical properties, piezoelectric constant d33~184 pC/N and planar electromechanical coupling factor kp~0.30, were obtained for the ceramics.

Abstract: Lead-free potassium sodium niobate ceramic thin films were synthesized using rf magnetron sputtering technology for MFIS structures. The optimal sputtering parameters of the as-deposited KNN thin films for depositing times of 1h were obtained. Regarding the measured physical properties, the micro-structure and thickness of as-deposited KNN thin films for different oxygen concentration were obtained and compared by XRD patterns and SEM images. The surface roughness of KNN thin film was also observed by AFM morphology. The average grain size and root mean square roughness were 250 and 7.04 nm, respectively. For KNN thin films in the MFIS structure, the capacitance and leakage current density were 280 pF and 10^-8A/cm², respectively. We investigated that the leakage current density and the memory window increased, the capacitance critically increased as the oxygen concentration increased from 0 to 40%. However, the excess oxygen concentration process was decreased the electrical and physical of as-deposited KNN thin film. The effect of oxygen concentration on the physical and electrical characteristics of KNN thin films was investigated and determined.

Abstract: The structure and electrical characteristics of the lead-free Li_x(K_0.5Na_0.5)_1-x(Nb_0.8Ta_0.2)O₃ (x=0~0.05) piezoelectric ceramics for the conventional solid-state reaction method and the B-side pre-calcined method were achieved and compared. For the B-side pre-calcined method, the lead-free ceramic material exhibited the excellent electrical and piezoelectric properties. The relative dielectric constant (ε_r) and loss (tan δ) of the Li_x(K_0.5Na_0.5)_1-x(Nb_0.8Ta_0.2)O₃ for x=0.03 using the B-side pre-calcined method were 1223 and 0.021, respectively. In addition, the electromechanical coupling factors (k_p) and Curie temperature (T_c) was 48.5 % and 315°C. Finally, the electrical properties of the lead-free Li_x(K_0.5Na_0.5)_1-x(Nb_0.8Ta_0.2)O₃(x=0~0.05) homogeneity ceramics improved by the B-side pre-calcined method were also investigated and discussed.

Abstract: (1-x)KNbO3-xBaGeO3 based PTCR ceramic materials are prepared using high purity K2CO3, Nb2O5, GeO2, Al2O3 and BaCO3 powders as starting materials, and the structural and electrical properties have been investigated. The results indicated that the samples doped with minute Ba as donor show excellent PTCR effect above the temperature of about 36°C. For the 0.40at% Ba-doped sample, the minimum resistance of 4.2×104Ω·cm, temperature coefficient (αk) of 24.37%/°C, PTCR anomaly lg(Rmax/Rmin) of 3.82 and transition temperature (Tmin) of 36°C are obtained.

Abstract: In this study, %7 Li modified and 0.67 % copper oxide added potassium sodium niobate (KNN) ceramics were investigated. Copper oxide was used as a sintering aid. The ceramics were prepared with conventional solid state calcination technique. All samples were crystallized in pure perovskite phase with no additional peak. The density of the samples increased with copper addition and lithium modification. The Curie temperature of KNN ceramics was found to shift to lower temperatures by CuO addition. The Curie temperature was measured as 414°C and 504°C for copper oxide added and lithium modified KNN samples, respectively. The maximum strain of copper oxide added sample was 0.12%, whereas Li modified KL ceramics yielded up to 0.10 %.