Laser cutting silicon-glass double layer wafer with laser induced thermal-crack propagation

This study was aimed at introducing the laser induced thermal-crack propagation (LITP) technology to solve the silicon-glass double layer wafer dicing problems in the packaging procedure of silicon-glass device packaged by WLCSP technology, investigating the feasibility of this idea, and studying the crack propagation process of LITP cutting double layer wafer. In this paper, the physical process of the 1064 nm laser beam interact with the double layer wafer during the cutting process was studied theoretically. A mathematical model consists the volumetric heating source and the surface heating source has been established. The temperature and stress distribution was simulated by using finite element method (FEM) analysis software ABAQUS. The extended finite element method (XFEM) was added to the simulation as the supplementary features to simulate the crack propagation process and the crack propagation profile. The silicon-glass double layer wafer cutting verification experiment under typical parameters was conducted by using the 1064 nm semiconductor laser. The crack propagation profile on the fracture surface was examined by optical microscope and explained from the stress distribution and XFEM status. It was concluded that the quality of the finished fracture surface has been greatly improved, and the experiment results were well supported by the numerical simulation results.     

Double pulse UV laser induced breakdown spectroscopy of stainless steel

Results of experimental investigations of 304 austenitic stainless steel (ASS) ultraviolet spectral range by single and double pulse laser induced breakdown spectroscopy (LIBS) at atmospheric pressure are reported. Various parameters, such as laser energy, placement of the laser beam focus with respect to the surface of illumi-nation, and collinear double laser pulse delay were used as variables. This study contributes to a better under-standing of the LIBS plasma dynamics by observing the temporal evolution of various emission lines. Temperature measurements were made by the Boltzmann diagram method using singly ionized Fe lines, and electron densities were found from Stark broadening. The temporal behaviors of these parameters were also estimated. It was found that the electron temperature for double pulses is higher than that for single pulse of the same total energy. For double pulse LIBS, the iron line emission intensities are enhanced and the analytical performance is improved. For instance, the intensity of iron line Fe I 275.01 nm was a factor of about 300 times higher if a double pulse of 2 × 20 mJ was used instead of a single pulse of 40 mJ when focusing the beam 4.7 mm behind the target surface. Published in Zhurnal Prikladnoi Spektroskopii, Vol. 79, No. 5, pp. 654–660, 2006.     

超薄Fe(4(A))膜磁特性极化中子反射研究

利用分子束外延薄膜生长技术,制备了200 (A)V/4 (A) Fe/900 V/MgO(100)薄膜样品,通过X射线反射和极化中子反射两种测量手段获得了薄膜的表面、界面及各层膜厚的相关结构信息.中子反射结果表明,Fe原子磁矩在室温下约为1.0±0.1μB,随着温度的降低,Fe原子磁矩增加,在10 K时达到1.5±0.1μB.利用指数定律拟合磁矩随温度的变化情况,外推得出4(A)铁薄膜样品的居里温度约为310±30 K.

Abstract：

Uhrathin Fe film 200 (A)V/4 (A)Fe/900 (A)V/MgO(100) has been prepared by molecular beam epitaxy (MBE). The structure parameters, such as the surface and interface roughness and the thickness of each layer, were obtained by X-ray and neutron reflectivity measurement. The magnetic properties of the thin Fe layer were investigated by polarized neutron reflectometry at different temperature. The result shows that the magnetic moment of an Fe atom is about 1.0 ± 0.1 μB at room temperature and increases to 1.5 ±0.1 μBat 10 K. The Curie temperature of the thin Fe film is estimated to be 310 ± 30 K.     

飞秒激光烧蚀金属靶的冲击温度

在明确飞秒激光与物质相互作用过程冲击温度概念的基础上, 讨论了飞秒激光烧蚀铝靶和铜靶过程中的冲击温度与其他物理量的关系, 利用飞秒激光烧蚀金属的双温模型提取了冲击温度的绝对值, 基于非傅里叶热传导模型计算了冲击温度的分布. 此项研究结果对飞秒激光安全加工含能材料有借鉴意义. 关键词： 飞秒激光 含能材料 烧蚀 冲击温度     

Radiation transfer in metallic powder beds used in laser processing

Two-dimensional radiation transfer in a powder layer backed with a substrate of the same material and normally irradiated with a narrow axially symmetric bell-like or the flat-top laser beam is numerically calculated. This corresponds to physical experiments with the powder layer of 50 μm thickness and the laser beam diameters 60–120 μm. The powder bed is treated as an equivalent homogeneous absorbing scattering medium, the radiative properties of which are estimated from the optical properties of the solid phase and the morphological parameters of the powder bed. The theoretical analysis shows that the absorptance of a semi-infinite powder bed of opaque particles is a universal function of the absorptivity of the solid phase being independent of the specific surface and the porosity. This is confirmed by literature experimental data. The radial transport of the radiative energy due to scattering of the incident laser beam in the powder layer can considerably reduce the deposited energy at the centre of the beam but the widening of the radial profile of the deposited energy is not pronounced. The fraction of laser energy deposited within the projection of the incident laser beam is evaluated. The efficiencies of laser heating the whole powder/substrate system and the substrate decrease with increasing the reflectivity of the material. More uniform heating of the powder layer can be attained at higher reflectivity.     

激光辐照转动充压圆柱壳体热力学效应

 采用有限元计算方法对激光辐照下转动充压壳体的热力学问题进行了较为全面的数值计算，获得了激光辐照下转动内压圆柱壳壁上的温升、应力、应变、位移分布等物理图像，为进一步分析转动充压圆柱壳体在激光辐照下的破坏与失效奠定了基础。提出的解决数值计算中移动热流载荷问题的双时间步长法，可以有效提高计算效率，同时提高计算精度。研究结果表明：对于给定的壳体结构，其损伤阈值时间主要取决于靶面激光强度与壳体旋转频率；在辐照过程中，损伤最先出现在最初受激光辐照的区域。     

Theoretical analysis and experimental verification of AZO/i-ZnO/CdS/CIGS multilayer stack isolation using 1064 nm and 355 nm laser wavelengths

This study analyzed the thermal field effect and experimental verification of laser scribing of stainless foil based copper indium gallium selenide solar cells of the AZO/i-ZnO/CdS/CIGS multilayer stack films (P3 layer) using Nd:YAG (1064 nm) and ultraviolet (355 nm) lasers. To prevent breakdown of molybdenum films of the solar cell, the laser processing temperature must be lower than the ablation temperature (2896 °C) of the Mo layer, but higher than the ablation temperature (2248 °C) of aluminum doped zinc oxide layer. Therefore, the scribing depth of the P3 layer is limited to the range 1.5–1.7 μm. First, the ANSYS Parameter Design Language program in the ANSYS finite element software is used to establish the simulation mathematical thermal model of the laser scribing process. To simulate the actual laser scribing process, a three-dimensional FE model for laser scribing process with a moving laser beam was constructed. Comparison the theoretical analysis and experimental results indicated that two sets of simulation parameters could not completely remove the P3 layer when the Nd:YAG laser was used. However, when the UV laser was used, the theoretical and experimental results were in favorable agreement. The findings of this study indicate that simulation analysis results can be helpful as reference data for experimental parameters during the actual scribing process.     

超薄Fe(4?)膜磁特性极化中子反射研究

Ultrathin Fe film 200  V/4  Fe/900  V/MgO（100） has been prepared by molecular beam epitaxy （MBE）. The structure parameters, such as the surface and interface roughness and the thickness of each layer, were obtained by X-ray and neutron reflectivity mea 关键词： 超薄Fe膜 磁特性 极化中子反射 分子束外延     

Simulated Effects of Physical Parameters on Heat Transfer of Intumescent Fire-Retardant Polypropylene during Burning

Physical properties of intumescent materials are important parameters as input data in modeling the combustion behavior of intumescent materials in a fire. In this paper, effects of important physical properties on heat transfer of intumescent materials during burning are simulated based on a combustion model of intumescent fire-retardant polypropylene (IFR-PP) materials. Physical properties selected are thermal conductivity of virgin material and char layer, specific heat capacity of virgin material, density of virgin material, surface emissivity of virgin material and char layer, and intumescent temperature. Predicted temperature curves at a location 9 mm from the bottom of the IFR-PP material at an incident heat flux of 50 kW/m² are shown for the varied physical parameters values. The results show that these varied parameter values can affect the heat transfer of materials remarkably.     

Analysis of oxide formation induced by UV laser coloration of stainless steel

Laser-induced coloration on metal surfaces has important applications in product identification, enhancing styles and aesthetics. The color generation is the result of controlled surface oxidation during laser beam interaction with the metal surfaces. In this study, we aim to obtain in-depth understanding of the oxide formation process when an UV laser beam interacts with stainless steel in air. The oxide layer is analysed by means of optical microscopy, scanning electron microscopy (SEM) and time-of-flight secondary ion mass spectrometer (TOF-SIMS). TOF-SIMS results clearly show the formation of duplex oxide structures. The duplex structure includes an inner layer of Cr oxide solution and an outer layer of Fe oxide solution. The oxide layer thickness increased as the results of Fe diffusion to surface during multiple laser scanning passes.     

Diode laser welding of ABS: Experiments and process modeling

The laser beam weldability of acrylonitrile/butadiene/styrene (ABS) plates is determined by combining both experimental and theoretical aspects. In modeling the process, an optical model is used to determine how the laser beam is attenuated by the first material and to obtain the laser beam profile at the interface. Using this information as the input data to a thermal model, the evolution of the temperature field within the two components can be estimated. The thermal model is based on the first principles of heat transfer and utilizes the temperature variation laws of material properties. Corroborating the numerical results with the experimental results, some important insights concerning the fundamental phenomena that govern the process could be extracted. This approach proved to be an efficient tool in determining the weldability of polimeric materials and assures a significant reduction of time and costs with the experimental exploration.     

Influence of laser beam profile on the generation of ultrasonic waves

The different ultrasonic fields generated in metallic materials by a laser beam with flat and Gaussian profile are investigated experimentally and using the finite element method (FEM). A high power laser beam irradiating a solid surface produces elastic waves with a mechanics that depends on many parameters, including the profile of the laser beam. The influence of the beam profile is investigated with the FEM analysis, considering the temperature dependence of material properties.     

激光切割脆性材料的温度场模拟

激光切割脆性材料是一个复杂的光致热过程。在综合考虑材料的热物性参数、初始条件及边界条件的情况下,运用Ansys软件建立了激光切割脆性材料温度场的三维有限元模型。采用APDL语言实现了对热流密度的高斯分布和强制对流换热及移动激光热源的模拟。通过设置不同的激光切割参数,对温度场的变化进行了模拟分析。所建立的温度场模拟系统可以对实际激光切割脆性材料的热过程进行前期预测,并能对激光切割参数的选择进行一定的优化,以减少实际切割的盲目性。     

百太瓦飞秒激光驱动复合靶产生质子的特性研究

在SILEX-I激光装置上实验研究了超强超短激光与Au/CH复合靶相互作用中在靶背法线方向发射的质子束的空间分布特征。 保持复合靶前表面的Au厚度不变,质子束流随着后表面的C8H8层厚度的增加而减小, 同时质子空间分布呈现环状、成丝和圆盘状分布。 实验没有发现高于2.75 MeV的高能质子产生。实验进一步完善了超短超强激光等离子体相互作用的物理模型。Proton beam behavior at the normal direction of the rear surface of the target produced from ultra intense short pulse laser irradiated Au/CH double layers targets was explored on SILEX I laser facility. With the same thickness of Au layer,the proton beam flux decreases with the increasing of CH layer thickness,and the corresponding spatial profile of proton beam shows ring, filament,and disc like distribution. The energy of proton beam was not beyond 2.75 MeV in our experiment.     

等电子谱线法测量Mg/Al等离子体电子温度空间分布

 在“星光Ⅱ”激光装置上对Mg/Al混合材料埋点靶进行三倍频激光打靶实验,用空间分辨晶体谱仪测量靶材料发射的X光光谱,获取了示踪离子谱线实验数据。采用多组态Dirac-Fock方法计算所需原子参数,并在局域热动平衡条件下建立了双示踪离子谱线强度比随电子温度的变化关系。在此基础上由双示踪元素等电子谱线法确定了Mg/Al混合材料埋点靶激光等离子体电子温度空间分布。     

超薄Fe层在反铁磁NiO(001)面上沉积的研究

通过分子束外延(MBE)和脉冲激光沉积(PLD)方法，将1—10个Fe原子层(ML)以楔形方式沉积到反铁磁单晶NiO(001)基片上.表面磁光克尔效应的原位测试结果表明：通过MBE沉积的Fe原子层在Fe/NiO界面处产生了约2ML的磁死层；而通过PLD沉积的Fe原子层在Fe/NiO界面处产生了约3ML的磁死层.X射线光电子能谱对Fe/NiO界面进行研究的结果表明，在Fe原子与单晶NiO间发生了界面化学反应. 关键词： 磁性薄膜 表面磁性 X射线光电子能谱     

热图法测量激光强度时空分布的重构理论研究

为了把量热法应用于远场激光强度时空分布测量,研究了基于热像仪靶面温度测量反演入射激光强度时空分布的重构理论。针对背光面两种不同边界条件(对流-辐射热流边界和恒定温度边界)推导出了由靶面温度分布反演激光束时空分布的重构表达式。获得的分析表达式对广泛的材料具有适用性。通过引入广义参量F0=α/L2,分别就F0》1和F0《1情况给出了重构近似表达式,并对满足F0》1条件的回推算法进行了数值模拟验证。数值结果表明,两种背光面边界条件下回推得到的激光束时空分布与原始激光束达到了很好的一致,但存在一与靶材傅里叶数相关的最小起始回推时间τ0。成果可用于强激光远场参量测量设备的研制。     

Optimisation of direct laser structuring of printed circuit boards

A model-based optimisation of the process of printed circuit board laser structuring is presented. For this purpose, a comprehensive theoretical model of the interaction between the travelling pulsed laser beam and conductive layer, as well as between the laser beam and the induced plasma plume is employed. The model is used to calculate process speed. Based on the process speed determined, the influence of pulse power, duration, and frequency on process speed is analysed. In addition, an optimal range of process parameters with respect to process speed and quality is defined.     

强激光与双锥靶作用加速准单能质子束

提出了一种新型的双锥靶结构用于准单能质子束加速。利用二维PIC粒子模拟程序研究了强激光与双锥靶作用加速产生质子束的物理过程以及质子束品质。双锥靶产生的质子束在峰值能量和发散角度等方面都明显优于相同激光条件下单锥靶和平面靶的结果。尤其与平面靶相比,双锥靶质子束的峰值能量提高了5倍以上,而且很好地保持准单能性。一方面双锥靶的内锥部分是临界密度材料,提高了激光的吸收效率;另一方面双锥靶内形成了更强的准静态磁场,可以约束引导更多的超热电子传输过锥尖,进而增强加速质子束的鞘层电场。     

Applications of the matrix-assisted pulsed laser evaporation method for the deposition of organic,biological and nanoparticle thin films: a review

The matrix-assisted pulsed laser evaporation (MAPLE) technique offers an efficient mechanism to transfer soft materials from the condensed to the vapor phase, preserving the versatility, ease of use and high deposition rates of the pulsed laser deposition (PLD) technique. The materials of interest (polymers, biological cells, proteins, …) are diluted in a volatile solvent. Then the solution is frozen and irradiated with a pulsed laser beam. Here, important results of MAPLE deposition of polymer, biomaterials and nanoparticle films are summarized. Finally, the MAPLE mechanism is discussed. A review of experimental and theoretical works points out that the simple model of individual molecule evaporation must be abandoned. Solute concentration, solubility, evaporation temperature of solvents, laser pulse power density and laser penetration depth emerge as important parameters to explain the morphology of the MAPLE-deposited films.