Effect of randomness of Cu-Sn intermetallic compound layerthickness on reliability of surface mount solder joints

A statistical reliability analysis on thermal fatigue lifetime of surface mount solder joints, considering randomness of Cu-Sn intermetallic compound (IMC) layer thickness, is presented. Based on published thermal fatigue life test data, the two-parameter Weibull distribution of the thermal fatigue lifetime for a fixed IMC layer thickness is found, and a K-S goodness-of-fit test is conducted to examine the goodness of fit of the assumed Weibull distribution. Then, the Weibull parameters as functions of IMC layer thickness are obtained. Considering the randomness of IMC layer thickness, the MTTF and reliability of surface mount solder joints on thermal cycles are analyzed. For surface mount solder joints formed under the same conditions and loaded during the same thermal cycling as stated in the publication, numerical results of the MTTF and reliability are presented. The results show that when the mean value of MC layer thickness is low (e.g., smaller than 1.5 μm), the effect of randomness of IMC layer thickness is significant; i.e., the MTTF has strong dependence on IMC layer thickness distribution; and the reliability is significantly different at high thermal cycles. When the mean value of IMC layer thickness is high (e.g., greater than 2.0 μm), the effect of randomness of IMC layer thickness is negligible. Therefore, the presented results are important to the reliability study of surface mount solder joints. Even though the validity of the presented results based on the test data remains to be verified from other sources of data, the proposed statistical method is generally applicable for thermal fatigue reliability analysis of surface mount solder joints. By combining the proposed method with the forming mechanism of IMC layer under varying manufacturing and loading conditions, a comprehensive reliability analysis on thermal fatigue lifetime of surface mount solder joints can be expected     

Evaluation of reliability of μBGA solder joints through twisting and bending

The paper describes a study on the solder joint mechanical reliability evaluation of two grid array packages: a micro land grid array (μLGA) and a micro ball grid array (μBGA) for mobile phones. The μGA packages considered in this paper are at early development stages and significant changes are expected in the future. The study was carried out to evaluate whether solder joints can stand mechanical stresses induced on PCBs during normal use. Stresses induced in normal use can include: thermal changes and stresses during indoor and outdoor use, in keypad pressing, carrying phones in (tight) jeans pockets, in accidentally dropping phones, etc. The above was studied by subjecting PCBs to two types of mechanical stresses. These were cyclic twisting and bending PCBs with μBGAs to failure, while continuously monitoring the electrical continuity. Cyclic twisting and bending tests were carried at two levels.Time to failure test data was analyzed using the Weibull model. Results indicate that it is most unlikely to anticipate μBGA solder joint failures in normal use. Solder joint failures were analysed by micro sectioning and X-raying. Failure analysis revealed as expected that solder joint failure occurs primarily due to fatigue. It is recommended to continue tests with more representative, updated packages and to carry out comparative tests with current technology PCBs.     

Pt-based metallization of PMOS devices for a compatible monolithic integration of semiconducting/Yba2Cu3O7−δ superconducting devices on silicon

Mo, Pt, Pt/Mo and Pt/Ti thin films have been deposited onto Si and SiO₂ substrates by RF sputtering and annealed in the YBa₂Cu₃O_7−δ (YBCO) growth conditions. The effect of annealing on the sheet resistance of unpatterned layers was measured. A Pt-based multilayered metallization for the PMOS devices was proposed and tested for a compatible monolithic integration of semiconducting devices and YBCO sensors on the same silicon substrate. The best results were obtained with a Pt/Ti/Mo-silicide structure showing 0.472 Ω_□ interconnect sheet resistivity and 2×10⁻⁴ Ω cm² specific contact resistivity after annealing for 60 min at 700 °C in 0.5 mbar O₂ pressure.     

Nanoscale analysis of YBa2Cu3O7−x/La0.67Ca0.33MnO3 interfaces

The structure of interfaces in superconducting/ferromagnetic YBa₂Cu₃O_7−x/La_0.67Ca_0.33MnO₃ superlattices has been analyzed by scanning transmission electron microscopy and high spatial resolution electron energy loss spectroscopy. Individual layers are flat over long lateral distances. The interfaces are coherent, free of defects, exhibiting no roughness, and are located at the BaO plane of the superconductor. Concerning chemical disorder, EELS measurements show the absence of measurable chemical interdiffusion within experimental error bars.     

Dielectric tunable properties of (Ba1−xSrx)TiO3 thin films on LaAlO3 substrate

(Ba_1−xSr_x)TiO₃ (1−x=0.8, 0.7, 0.6 and 0.5) thin films were prepared on (0 0 1) LaAlO₃ substrates by sol–gel method. The films were found to be crystallized in preferential (0 0 1) orientation after post-deposition annealing at 750°C for 1.5 h and 1100°C for 2 h in air, respectively. We investigated the dependence of tunability and dissipation factor on annealing temperature and different Ba/Sr ratios. It was found that the tunability increased dramatically and dissipation factor decreased obviously with increasing annealing temperature, and Ba_0.6Sr_0.4TiO₃ thin films annealed at 1100°C for 2 h have a tunability of 46.9% at 80 kV/cm bias filed and a dissipation factor of 0.008 at 1 MHz.     

一种基于退化数据的元器件可靠性定量检验方法研究

针对高可靠元器件可靠性鉴定中缺乏可靠性级别定量评价的问题,基于失效物理,分析了键合强度参数退化及失效判据,并给出了退化模型的数学表达和参数估计方法,研究基于退化量分布的可靠性定量检验方法,并采用AD厂家的AD524SD作为试验器件,进行了相应的试验分析和验证。结果表明,提出的高可靠性级别器件鉴定检验方法具有很好的工程适用性和应用价值。     

Microwave properties of epitaxial large-area Ca-doped YBa2Cu3O7−δ thin films on r-plane sapphire

Ca doping of YBa₂Cu₃O_7−δ (YBCO) is well known to enhance the critical current density in large-angle grain boundaries for example of bicrystals. However, up to now no data are available on microwave properties of epitaxial Ca-doped YBa₂Cu₃O_7−δ thin films on r-plane sapphire with CeO₂ buffer layer.Therefore, first results are presented for large-area pulsed laser deposition (PLD) grown Ca_xY_1−xBa₂Cu₃O_7−δ films on 3-in. diameter sapphire wafers. The PLD process is optimised for undoped YBCO thin films and shows high reproducibility for YBCO. The microwave surface resistance R_s at 8.5 GHz of Ca-doped YBCO (x=0.1) thin films shows clear reduction (up to 20%) with respect to that of YBCO for temperatures from about 20–50 K. In addition, microwave surface resistance R_s of Ca-doped YBCO is lower than that of YBCO even for enhanced microwave surface magnetic field up to about 20 mT for temperatures 20 and 40 K.     

Thin films of CoSi2 on Si1−yCy substrate layers

The reaction of Co with epitaxial Si_1−yC_y(001) films is investigated with regard to dependence on annealing temperature and C concentration y. Resistance measurements and RBS analysis reveal a small increase in the disilicide formation temperature. The electrical properties are very similar for thin CoSi₂ films grown at 650°C on Si_0.999C_0.001 and on Si. Whereas the CoSi₂ is fully polycrystalline on Si(001), partially oriented CoSi₂ has been observed on C-containing substrate layers. An increase of the number of epitaxially grown CoSi₂ crystallites has been observed with increasing C concentration.     

A methylammonium iodide healing method for CH3NH3PbI3 perovskite solar cells with high fill factor over 80%

Repressing the thermal decomposition during the process of heat treatment plays an indispensable part in the preparation of perovskite films. Here, a methylammonium iodide healing method was applied to prevent the volatilization of the organic component inside the perovskite structure during the heat treatment. High-quality CH₃NH₃PbI₃ film with a much larger grain size over 800 nm was successfully fabricated via this healing method. Besides, the absorption and photoluminescence intensity were also both improved. Finally, the best power conversion efficiency of 18.89% with a fill factor over 80% was realized in an n–i–p configuration while possessing outstanding stability. This work suggests that methylammonium iodide healing method is a reliable way to promote crystal growth and improve the photovoltaic performance and humidity stability of the CH₃NH₃PbI₃ solar cells.     

Effects of Ag addition and Ag3Sn formation on the mechanical reliability of Ni/Sn solder joints

Formation of intermetallic compounds (IMCs) in solder joints is closely associated with the mechanical reliability of the system. Though internal voids formed in Ni/Sn solder joints are known to be related to the formation of Ni₃Sn₄ IMC, a detailed study on the mechanical reliability has not yet been reported. In this study, the mechanical reliability of Ni/Sn joints was investigated using two different soldering systems: Ni/Ag-Ag/Sn/Ni bilayers and Ni/Sn/Ag-Ag/Sn/Ni sandwich structures. The failure mode was found to be closely related to the formation and growth of an Ag₃Sn phase. Filling of the voids with Ag₃Sn IMC resulted in maximum shear strength, with a failure locus through Ni₃Sn₄ and Ag₃Sn. However, formation of a large amount of Ag₃Sn decreased the shear strength once again.     

(Pb0.97La0.02) (Zr0.75Sn0.25-xTix) O3 反铁电陶瓷温度诱导相变效应

Pb0：97La0：02（Zr0：75Sn0：25x Ti x/O3（x D0.10, 0.105, 0.11）（PLZST） antiferroelectric ceramics with highly preferred-（110） orientation were successfully fabricated via the conventional solid-state reaction method.The antiferroelectric nature of PLZST ceramics induced by electric field was demonstrated by the dielectric constant-temperature（D-T） and the polarization-electric field（P-E） measurement. Typical phase transition from ferroelectric（FE） to antiferroelectric（AFE）, and then to paraelectric（PE） is obtained. The results indicate that the phase transition behavior is suppressed with increasing of x, and T c is remarkably shifted to higher temperature of168 ℃, 170 ℃ and 174 ℃, respectively. Besides, high phase transition current（110 6A, 810 7A and 610 7A, respectively） is obtained with temperature induced. Consequently, the excellent electric properties and the restraint between temperature and electric field would provide basis on the application of PLZST antiferroelectric ceramics in microelectronic integrated systems and sophisticated weapons systems.     

Effects of TMF heating rates on damage accumulation and resultant mechanical behavior of Sn–Ag based solder joints

Solder joint reliability depends on several service parameters such as temperature extremes encountered, dwell times at these temperatures, and the ramp-rates representing the rate at which the temperature changes are imposed. TMF of Sn–Ag based solder alloy joints of realistic dimensions were carried out with dwell of 115 min and 20 min at 150 °C and −15 °C, respectively. Different heating rates were obtained by controlling the power input during heating part of TMF cycles. Surface damage and residual mechanical strength of these solder joints were characterized after 0, 250, 500, and 1000 TMF cycles to evaluate the role of TMF heating rate on the solder joint integrity.     

Submicrometric SrTiO3-δ based devices realized by an atomic force microscope

SrTiO₃ (STO) is one of the key compounds in the emerging field of oxide electronics. Because of the low carrier concentration needed to turn it into the conducting state (10¹⁸ e/cm³) and to its high bulk mobility (10⁴ cm²/Vs @ 4.2 K), we consider STO suitable as functional conducting element in future oxide based devices.In this work we show how by applying a negative voltage to the conducting tip of an atomic force microscope it is possible to modify on sub-micron scale structural and electrical properties of conducting SrTiO_3-δ thin films grown on insulating LaAlO₃ substrates, thus realizing sub-micrometric STO electrical circuits. After discussing the mechanisms of the process, we present the fabrication of a SrTiO_3-δ based side gate field effect transistor.     

Electrical characterisation and reliability of HfO2 and Al2O3–HfO2 MIM capacitors

Current leakage and breakdown of MIM capacitors using HfO₂ and Al₂O₃–HfO₂ stacked layers were studied. Conduction in devices based upon HfO₂ layers thinner than 8 nm is probably dominated by tunnelling. Al₂O₃–HfO₂ stacked layers provide a limited benefit only in term of breakdown field. Constant-voltage wear-out of samples using insulating layer thicker than 6 nm is dominated by a very fast increase of the leakage current. A two step mechanism involving the generation of a conduction path followed by a destructive thermal effect is proposed to explain breakdown mechanism.     

激光合成Si3N4吸收系数值的实时测量方法和修正因子

吸收系数α是反应激光合成时,光能转换效率与喷咀截面关系的重要参数.本文论述α值的实时测量方法和修正因子,这在实时测量中是颇有实用价值的.     

Critical current characteristics of YBa2Cu3O7 thin films on (110) SrTiO3

The material and electrical characteristics of YBa₂Cu ₃O₇ (YBCO) thin films deposited by inverted cylindrical magnetron sputtering on (110) SrTiO₃ (STO) were investigated. X-ray diffractometry shows the grain orientations to be predominantly the YBCO (110) and (103) with no evidence of c-axis grains, Electron micrographs show the film surface to consist of coupled elongated grains parallel to the (110) STO edge. The films were patterned into small 2.5 mm squares parallel to the substrate edges for electrical characterization. Transport currents parallel and perpendicular to the (110) substrate edge showed a 945:1 anisotropy in film resistance and a factor of two in critical current density for temperatures below 60% of the transition temperature (T_c). The temperature dependence of the critical current near T_c was quadratic-like and strongly dependent on the value of T_c used in the analysis. For the two orientations, there was nearly a 6 K difference in T_c as determined by the point at which the critical current became zero. The response of the critical current to small magnetic fields was greater for transport current along the c-axis direction and was observable over a temperature interval nearly four times greater than for current along the basal plain. These YBCO thin films have good response to small magnetic fields and are suitable for vortex flow device development     

N型表面钝化晶体硅太阳电池Al2O3/SiNx减反射叠层的优化研究

减反射特性是进一步提高N型太阳电池能量转换效率的重要因素之一。研究采用Al2O3/SiNx叠层优化了N型太阳电池的减反射特性,并通过理论模拟和实验测量系统地探讨了叠层中SiNx厚度对表面反射性能的影响。研究证实在Al2O3层上增加一层SiNx,可以有效地优化表面减反射性质,从而提高N型太阳电池的光伏性质。     

Possibility ofNd1.9Ba1.1Cu3O7+δ andPr1.14Ba1.86Cu3O7-δsingle crystals for insulator in high-speed superconductingcircuits

Dielectric properties of both Nd_1.9Ba_1.1Cu ₃O_7+δ (NBCO-213) and Pr_1.14Ba_1.86Cu₃O_7-δ (Pr-rich PBCO) single crystals have been examined at low temperature. These materials have good lattice matching to high-T_c superconductors (HTS), but they are conductive at room temperature. Below 80 K, they are insulators with low dielectric constants, ε _τ below 25, and low dielectric loss tan δ below 0.1 at 100 kHz. The value of ε_τ is suitable for insulators in integrated circuits using strip line widths of 10 μm order, providing short delay time, no excitation of surface wave, and low radiation loss. The value of tan δ is comparable to loss of superconducting surface resistance above 100 GHz. These results indicate the applicability for the insulator layers in multilayer superconducting electronic devices such as Single Flux Quantum (SFQ) circuits operated at high speed     

A 5-μm-wide 18-cm-long low-loss YBa2Cu3O7-δ coplanar line for future multichip moduletechnology

Narrow and low-loss YBa₂Cu₃O_7-δ (YBCO) coplanar lines, which can be used in multichip module technology for future high-density and high-speed digital circuits, have been developed. Etch-back planarization and a patterning process combining Ar-ion milling and wet-etching enabled us to form an 18-cm-long 5-μm-wide YBCO coplanar line without electrical shorts, even for the narrow spacing of 2.5 μm. The surface resistance of this line was kept at a level comparable to that of 10- or 25-μm-wide YBCO coplanar lines and also comparable to that of unpatterned films. This indicates successful fabrication of the 5-μm-wide YBCO coplanar line without notable loss increase resulting from process damage. The 5-μm-wide line showed a low-transmission loss of 0.49 dB at 10 GHz and 55 K. This level of loss is similar to that in Cu coaxial cables. No significant increase in transmission loss was observed up to an input power level of 16 mW at 10 GHz and 55 K. This input power is comparable to the power-handling capability required for transmitting high-speed digital signals through the lines with characteristic impedance of 50 Ω. These results show that the narrow 5-μm-wide YBCO coplanar line has great potential for high-density and high-speed digital circuits     

Sn掺杂对(In0.95-xSnxFe0.05)2O3薄膜的结构、电学及磁特性的影响

我们利用脉冲激光沉积的方法制备了一系列(In0.95-xSnxFe0.05)2O3 (x=0~0.09)薄膜,并在其中发现了室温铁磁性。X射线衍射结果表明锡与铁离子已掺入氧化铟晶格。随着锡的掺入,样品内的载流子浓度得到了很大的提高,但相应的铁磁性却几乎没有变化。我们认为氧空位相关的束缚磁极化子模型能够跟好的解释我们的铁掺杂氧化铟薄膜中的铁磁耦合的机制,而载流子传导的RKKY相互作用则不适用于这一系统。