Synthesis of tungsten disulphide nanoparticles by the chemical vapor condensation method

Crystalline tungsten disulphide nanoparticles were successfully synthesized by the chemical vapor condensation (CVC) method. The process performed as decomposition of tungsten hexacarbonyl over sulphur vapor in inert gas flow, where WS₂ nanoparticles were synthesized by direct reaction between as formed pure tungsten nanoclusters and sulphur vapor. Influence of experimental parameters on shape, size distribution, structure and phase composition of nanoparticles were evaluated by transmission and scanning electron microscopy and X-ray diffraction analysis. The produced nanoparticles have closely spherical shape with the mean size in the range 20–70 nm in diameter dependently of process parameters. Nested “onion-like” structure of nanoparticles was observed. The mean value of interlayer distance in the {0 0 0 1} direction, is about 0.6358±0.031 nm. Due to nanodimensional size, physical properties and layered structure tungsten disulphide nanoparticles have great potential as a solid lubricant material.     

用低熔点玻璃封接氦-氖激光管的一种方法

一、引言 氦-氖激光器是比较成熟的气体激光器件。我国现在有许多厂家生产这种激光管,普遍的问题是激光管的寿命(不论存放寿命或使用寿命,下同)很不稳定,这是一个急待解决的问题。 影响激光管寿命的因素很多,国内已经有许多单位研究和注意到了这个问题。普遍认为环氧树脂粘结剂是影响激光管寿命的一个主要因素。其它影响寿命的因素,一般均能通过严格的工艺处理,选择合适的材料和     

Superplastic creep of low melting point solder joints

In prior work, we showed that eutectic Sn-Pb solder joints exhibit superplastic behavior after rapid solidification. Further examples of superplasticity in nominally air-cooled solder joints are reported in this study of three low-melting point alloys: 40In-40Sn-20Pb (wt. %), eutectic 52In-48Sn, and 43Sn-43Pb-14Bi, which were creep-tested in shear at 20°, 65°, and 90° C. The test results indicate that above 65° C, the indium-containing solders have stress exponents between 2.4 to 2.9, a possible overall shear strains of 500%, and an absence of primary creep; at 90° C, 43Sn-43Pb-14Bi solder has a stress exponent close to 2.3. Optical microstructures of the three solders are presented; they help to explain the superplastic behavior.     

低熔点高Δn值双环向列相液晶的合成研究

为了获得低熔点、折射率各向异性(Δn)大的快速响应向列相液晶材料,高Δn值的液晶混合体系中需要加入熔点在50℃以下、Δn大于0.35的双环类液晶组分,以使快速响应向列相液晶材料满足室温工作的要求。本文合成了异硫氰基含氟二苯乙炔类液晶化合物;一方面由于在分子苯环侧位引入F原子,减小分子间作用力,使化合物的熔点下降;另一方面在两个苯环间引入三键、分子末端接入异硫氰基极性基团,增加了分子的共轭性,提高了目标化合物的Δn值。获得了熔点分别为31℃和50℃、Δn为0.39和0.40,这两种低熔点化合物与目前已具有的毫秒级快速响应向列相液晶化合物混合,可使其熔点低至10℃以下。     

New, creep-resistant, low melting point solders with ultrafine oxide dispersions

Nano-sized, nonreacting, noncoarsening oxide dispersoids have been incorporated into solder alloys to create a new, improved solder structure with an ultrafine grain size of ∼200–500 nm. The new solders exhibit significantly enhanced creep resistance combined with increased strength. The well-known thermal instability problem with ultrafine-grained structure appears to have been overcome in these solder alloys and the microstructure was seen to be quite stable upon high temperature exposure (e.g. 120°C). This is attributed to the presence of very fine dispersoid particles which impede grain boundary sliding and dislocation movement. The dispersions are seen to have a profound effect on the mechanical deformation characteristics of the solders with respect to creep. As much as three orders of magnitude reduction in the steady state creep rate has been achieved. The new solders also exhibit improved ductility under high strain rate deformation and improved strength (4–5 times higher tensile strength) at low strain rates. It is demonstrated that with a dispersion of TiO₂ particles, the Pb-Sn eutectic solder with a melting point of 183°C can be made more creep-resistant than the 80Au-20Sn eutectic solder with a much higher melting point of 278°C. The new creep-resistant solders can be useful for optical and optoelectronic packaging in which dimensional stability of the assembled structure is essential.     

一种低熔点玻璃保护浆料

研制了一种厚膜片电阻用低熔点玻璃保护浆料。这种浆料由玻璃粉、颜料及有机载体按一定比例混合而成。烧结温度约６００℃，黏度１８０～２４０Ｐａ·ｓ，颗粒度不大于３μｍ，被封电阻烧成后，平均阻值变化率为０．６５％。     

SnAgCu无铅焊点的电迁移行为研究

电迁移引发的焊点失效已经成为当今高集成度电子封装中的最严重的可靠性问题之一。应用SnAgCu无铅焊膏焊接微米级铜线,进行电迁移实验。结果表明:焊点形貌从原来的光滑平整变得凹凸不平,阴极处出现了裂纹和孔洞,并且在铜基板和Cu6Sn5金属间化合物(IMC)之间出现薄薄的一层Cu3Sn金属间化合物,由ImageJ软件测量其平均厚度约为2.11μm;而在阳极附近没有明显的Cu3Sn金属间化合物形成。     

Electrical and mechanical characterization of an anisotropic conductive adhesive with a low melting point solder

For the highly reliable interconnection in a micro-packaging technology requiring an excellent electrical and mechanical performance, the new anisotropic conductive adhesive (ACA) system with a low melting point solder was designed and characterized. An optimum flip-chip bonding cycle considering the chemo-rheological properties of a polymer matrix and solder was proposed. The bonding mechanism of the new ACA system was experimentally observed by the optical microscope. The electrical properties such as electrical resistance of about 5.6 mΩ and current density of 10,000 A/cm² were measured by the 4-point probe test. The measured shear strength was 304 MPa after bonding process.Electrical and mechanical performances were measured and compared before and after a pressure cooker test (PCT). In order to get a more stable ACA system during processing, the polymer matrix mixed with a reductant and a low melting point solder powder will be continuously developed in the near future.     

Synthesis of CuInSe2 nanoparticles by phase transformation of In2Se3 via wet chemical process in low temperature

Chalcopyrite-type CulnSe2 nanoparticles are successfully prepared by using In2Se3 nanoparticles as a precursor reacted with copper chloride （CuCl） solution via a phase transformation process in low temperature. The reaction time is a key parameter. After the reaction time increasing from 0.5 h to 8 h, In2Se3 and CuCl react with each other gradually via phase transformation into CuInSe2 without any intermediate phase. The crystalline structure and morphology of the CuInSe2 nanoparticles are characterized by X-ray diffraction （XRD） and field emission scanning electron microscopy （FESEM）. The diameter of CuInSe2 nanoparticles with good dispersibility ranges from 10 nm to 20 nm. The band gap of the CulnSe2 nanoparticles is 1.04 eV calculated from the ultraviolet-visible （UV-VIS） spectrum.     

Characterization of polymer matrix and low melting point solder for anisotropic conductive film

The chemo-rheological mechanisms of a polymer matrix and a low melting point solder for an anisotropic conductive film (ACF) have been characterized. For the material characterization of the polymer matrix and solder, a differential scanning calorimetry (DSC) and a dynamic mechanical analyzer (DMA) experiments were conducted. The conversion and viscosity of the polymer matrix was observed by DSC and DMA, respectively. In order to control the curing conditions such as the reaction temperature and time of polymer matrix, the adequate amount of catalyst was used. The compatibility between the viscosity of a polymer matrix and a melting temperature of solder was characterized to optimize the processing cycle. The reductant was also added to remove the oxide layer performed on the surface of solder in the air environment. Based on these chemo-rheological phenomena of the polymer matrix and solder, the optimum polymer system and its processing cycle were designed for the high performance and reliability in the electrical interconnection system.     

Revealing the nucleation and growth mechanism of a novel solder developed from Sn-3.5Ag-0.5Cu nanoparticles by a chemical reduction method

Sn-3.5Ag-0.5Cu nanoparticles were synthesized by chemical precipitation with NaBH₄. By using x-ray diffraction and transmission and scanning electron microscopy, the microstructural characteristics of particle growth were evaluated. The results indicated that the primary particles after precipitation were (Ag,Cu)₄Sn, with a size of 4.9 nm. (Ag,Cu)₄Sn was transformed into (Ag,Cu)₃Sn, when the total amount of Sn contributed from both (Ag,Cu)₄Sn and Sn covering the (Ag,Cu)₄Sn overtook that of (Ag,Cu)₃Sn. The final particle size of polycrystalline particles was 42.1 nm owing to the depletion of Sn atoms in the solution. Nucleation and growth mechanisms of Sn-3.5Ag-0.5Cu nanoparticles are also discussed and proposed.     

Improved stability of contact resistance of low melting point alloy incorporated isotropically conductive adhesives

With the driving force of "green" revolution in the electronics industry, tremendous efforts have been made in pursuing lead-free alternatives. Although lately lead-free alloys have drawn a lot of attention, their technical weaknesses, such as high processing temperature, poor wetting and high surface tension, limit their applications on the thermally sensitive, flexible, nonsolderable substrates and the ultra-fine pitch size flip chip interconnection. Conventional isotropically conductive adhesives (ICAs) have been used widely in surface mount and die-attach technologies for electrical interconnection and heat dissipation. The low temperature processing of ICAs is one of the major advantages over lead-free solders, which brings a low system stress, simple manufacture process and the like. In order to enhance the contact resistance of ICAs, the low melting point alloy (LMA) incorporating technology has been developed by our group. In this paper, LMA fusing methods were studied, since nonfused LMA in ICAs after a curing process can adversely affect the physical property and contact resistance stability. A differential scanning calorimeter (DSC) was used for the basic examination of depleting rate of LMAs in the typical ICAs. The cross-sectional morphology, LMA distribution and intermetallic compound were investigated by a scanning electron microscope (SEM). In addition, contact resistance for the ICA formulation incorporated with LMAs under elevated temperature and humidity was evaluated.     

低熔点SnBi合金对导电银胶性能的影响

以银粉为主要导电填料,选定环氧树脂体系,添加不同量低熔点共晶SnBi合金制得导电胶,利用四点探针法和万能材料试验机考察了SnBi合金添加量对导电胶导电性能和力学性能的影响.发现当SnBi合金添加量占填料质量分数的15%时,导电胶的体积电阻率可以达到3.4×10<,-4>Ω·cm,剪切强度为12.56 MPa.SnBi合...     

Operation time control of a high density packaging using a low melting point alloy

This paper describes a concept of controlling operation time of a high-density packaging using a phase change material (PCM). A low cost alloy, which is composed of Bi/Pb/Sn/In and having melting point less than 343 K, was used as the PCM. Thermal experiments using the alloy were carried out and it was confirmed that the substrate back surface temperature could be kept constant at the melting temperature of the PCM for several minutes by thermal absorption, while the PCM phase changed from its original solid state into the liquid state. Also, in the present work, it was confirmed that thermal network method is practically useful for the thermal design of a package with a PCM.     

低信噪比时混沌信号降噪的微扰方法

该文提出一种新的混沌信号降噪方法微扰法,并且给出了微扰法的一个具体实例算法梯度微扰法。该文还对用梯度微扰法进行混沌信号降噪的效果进行了实验研究。实验结果表明,梯度微扰法能够在低信噪比时得到很好的降噪效果。文中还对梯度微扰法的参数选择问题进行了实验研究。     

Effects of novel carboxylic acid-based reductants on the wetting characteristics of anisotropic conductive adhesive with low melting point alloy filler

A low viscosity epoxy resin with carboxylic acid-based novel reductants was introduced to improve the process ability and reliability of an anisotropic conductive adhesive (ACA) resin with a low melting point alloy (LMPA) filler system. The curing degree of the ACA resin and the melting of the LMPA filler were investigated using differential scanning calorimetry (DSC) conducted in the dynamic mode in order to control the curing conditions such as the reaction temperature and a melting temperature of solder. The temperature-dependent viscosity characteristics of the ACA resin were investigated using a rheometer. The compatibility between the viscosity of a polymer matrix and a melting temperature of solder was characterized to optimize the processing cycle. Three different types of carboxyl acid-based reductants were added to remove the oxide layer on the surfaces of the filler particles and the conductive pad. Good wetting properties were achieved between the LMPA filler and the Cu pad in the epoxy resin using these carboxylic acid-based reductants.     

Wave soldering with a low melting point Bi-Sn Alloy: Effects of soldering temperatures and circuit board finishes

Wave soldering with low solid fluxes at temperatures as low as 175°C on test boards with a Cu/Imidazole surface finish has been shown to be feasible using a Pb-free, Bi-45%Sn-0.33%Ag solder that melts at temperatures of ∼140∼145°C. Other surface finishes such as Pd/Ni, Au/Ni, and Bi exhibit unacceptable soldering at temperatures below 210°C. Intermediate in performance are Sn surface finishes, which exhibit acceptable soldering at 190°C, but not at 175°C. Acceptable joints wave soldered on Cu/Im finishes passed class I/II inspection criterion and exhibited pull strengths in excess of the ultimate strength of the component leads.     

Electrical properties of CdTe near the melting point

A new experimental setup for the investigation of electrical conductivity (σ) in liquid and solid CdTe was built for a better understanding of the properties near the melting point (MP). The temperature dependence of σ was studied, within the interval 1,050–1,130°C, at defined Cd-partial pressures 1.3–1.6 atm, with special attention to the liquid-solid phase transition. We found that the degree of supercooling decreases with increasing Cd overpressure and reaches the lowest value at 1.6 atm without change of the melting temperature during heating.     

Fe_3Si纳米颗粒低温固相制备及磁学性能研究

以乙酰丙酮铁(C_(15)H_(21)FeO_6)和二氧化硅纳米颗粒(SiO_2)分别作为铁和硅的前驱体,280℃低温固相法合成Fe_3Si纳米颗粒,同时加入钠盐(NaCl)调控颗粒的尺寸。利用扫描电子显微镜、原子力显微镜、X射线衍射和超导量子磁强计对所制备的Fe_3Si纳米颗粒进行表征分析。研究发现该法可以高效制备稳定的DO_3型Fe_3Si纳米颗粒,加入的NaCl能有效调控颗粒粒径。随着Fe_3Si纳米颗粒尺寸的减小,Fe_3Si纳米颗粒的居里温度、截止温度均有明显降低,饱和磁化强度也有所减小。