激光对金属铜微孔加工的热力学过程研究

采用纳秒激光脉冲对铜金属进行了打孔实验,对微孔形貌进行了观察并对其热力学过程进行了相应的分析。研究表明,微孔的形貌是由凹坑和周围隆起组成,坑深随着脉冲能量的增加而增加。热力学分析表明,激光辐照金属打孔需要两个基本条件：一是激光脉冲能量的沉积,使金属材料发生熔化、汽化以及电离等相变,使得材料更容易去除;激光等离子体作为二次热源会更有效把激光脉冲能量耦合到金属表面;二是激光等离子体的冲击波效应,这种效应会把发生相变的材料有效及时排出,从而有效形成微孔。     

单脉冲纳秒激光诱导硅表面微结构

利用Nd:YAG纳秒脉冲激光(波长532nm)在空气中对单晶硅表面进行单脉冲辐照,研究了激光能量密度和光斑面积变化对微结构的影响。通过场发射扫描电子显微镜和原子力显微镜(AFM)对样品表征,并对纳秒激光辐照硅的热力学过程进行分析。结果显示:当脉冲激光的能量密度接近硅的熔融阈值且光斑直径小于8μm时,形成尖峰微结构;随着能量密度或光斑面积增大,尖峰结构消失,形成边缘隆起和弹坑微结构。通过流体动力学模型得到微结构形貌的解析解,模拟得到的微结构形貌与实验测得的AFM数据一致。研究表明微结构的形成主要是由于表面张力引起的熔融硅流动。表面张力与表面温度和表面活性剂的质量浓度有关。温度梯度引起的热毛细流作用和表面活性剂浓度引起的毛细作用共同影响下形成尖峰、边缘隆起和弹坑微结构。     

超短激光打孔中快速相变的格子玻尔兹曼模拟

采用双重分布函数的格子玻尔兹曼模型，对单脉冲激光金属打孔过程中的快速相变传热进行研究.模型考虑了金属材料熔化后熔体的流动换热，并采用浸没移动边界方案对过程中的固液界面进行追踪.采用纯导热模型和考虑对流的换热模型计算，将结果和试验进行对比，结果表明：在激光打孔过程中熔体的流动对相变传热产生较大影响，采用考虑流动换热模型的结果与实验更接近.进而对熔化速度、熔化深度以及温度场的变化进行分析，并探讨不同激光工艺参数对相变过程的影响.模拟发现一个脉冲结束后，激光的脉宽越大，孔深越小，孔径越大，且最高温度较短脉冲激光越低.     

不同脉冲激光波形在打孔实验上的比较与分析

为了获得高质量小孔,克服单脉冲激光打孔的不足,设计了一种能够产生多脉冲激光波形的激光器电源.并在1mm厚的薄钢片上得到直径小于1mm的小孔.多脉冲打孔理论分析表明,多脉冲激光打孔不但减少了熔融物和等离子体的产生,而且降低了激光打孔对高能量的要求,获得的小孔质量优于单脉冲激光打孔.另外脉冲宽度和脉冲间距的选择对激光小孔加工质量起决定性作用,在加工高质量孔的时候,应该选用较短的激光脉冲宽度.实验表明,利用三脉冲激光输出波形打孔所获得的小孔质量要优于单脉冲激光打孔效果,有效脉冲平均能量为350mJ,宽度为100μs,脉冲间距为100μs.     

窄脉宽激光诱导背向选择性去除金属薄膜制备微电路(特邀)EI北大核心CSCD

为了在透明基板上制备出导电性能良好的微电路,研究了窄脉宽激光正向和背向选择性去除金属薄膜制备的微结构形貌特征,开展了纳秒激光选择性去除Cu薄膜(厚度为150 nm)的实验和温度场仿真研究,揭示了正、背面去除的烧蚀机理和材料的喷射机制。实验结果表明,当激光脉冲能量为0.270~0.542μJ,扫描速度为2 mm/s时,激光诱导背向去除金属薄膜在加工质量方面优于正向加工,其去除几何精度高,轮廓边缘平整,几乎没有溅射。采用优化后的纳秒激光加工工艺参数,激光脉冲能量为0.403μJ,扫描速度2 mm/s,扫描线间距为3μm,制备出均匀分布的铜阵列图案。在相同参数下对玻璃基板上的铜薄膜背向选择性去除,得到具有良好导电性和粘附性的微电路。     

0.05mm薄塑料片小孔群光纤激光精密加工技术

利用光纤激光加工系统对厚度为0.05mm的薄塑料片进行了打孔试验,分析了激光功率、脉冲宽度、辅助气体压强及种类等工艺参数对薄塑料片小孔群加工质量的影响情况。实验结果表明:小孔孔径随激光功率、激光脉冲宽度、辅助气体压强的增大而增大。相比氮气作为辅助气体,采用氧气作为辅助气体,由于氧气有助燃的作用,孔径明显增大,孔质量变差,热影响区增大。采用优化后的激光加工工艺参数,加工出的小孔群孔径为40±2μm,孔壁光滑,加工质量满足设计要求。     

0.12mm不锈钢薄板光纤激光回转法打孔工艺优化分析

利用光纤激光加工系统对厚度为0.12mm的SUS304材料进行回转法打孔。通过正交实验方法分析了激光功率比、占空比、切割速度、重复频率、辅助气压等参数对打孔质量的影响。实验结果表明,激光打孔工艺最优参数组合是:切割速度为12mm/s,占空比为8%,重复频率为1.5kHz,功率比为85%,辅助气压为0.8MPa。在此优化参数下得到的最小打孔锥度为0.05°,且微小孔边缘热影响区较小,孔真圆度较好,可以保证较高的打孔质量。     

激光烧结石墨烯铜复合材料温度场有限元模拟

在激光烧结石墨烯增强铜基复合材料的过程中,了解瞬时温度场分布对优化工艺参数、控制烧结质量有重要作用。建立了激光烧结预涂在42CrMo基板上的石墨烯铜的混合粉末的有限元模型。研究了激光烧结过程温度场分布,熔池的几何参数以及烧结层与基体的冶金结合宽度。为了验证模拟结果,使用与模拟相同的参数进行了单道激光烧结的实验。研究表明,热传导、热辐射和相变潜热在激光烧结过程的温度场分布中起重要作用。实验结果与模拟结果较为一致。所以可以依据模拟结果预测实验的温度场分布和熔池几何参数,同时也可以据此优化激光烧结参数。     

飞秒纳秒脉冲激光微构造和掺杂单晶硅（英文）

在SF6气氛下,分别利用钛宝石飞秒脉冲激光与掺钕钇铝石榴石纳秒脉冲激光对单晶硅表面进行了微构造和重掺杂,以用于光伏材料。对制备的单晶硅表面微结构的形貌、结晶性和硫元素杂质含量与分布进行了研究。实验结果表明纳秒脉冲激光制备的单晶硅表面微结构的薄层电阻较小,缺陷密度较低(结晶性高),硫元素杂质含量较高且在表面分布的范围较广,深度较大(约1μm)。此外,材料的可见-近红外波段吸收率可接近80%。基于纳秒脉冲激光微构造的单晶硅的优异性能,在样品表面制备了有效光照面积达8cm2的太阳能电池。其中,最佳太阳能电池的串联电阻、开路电压、短路电流密度分别为0.5Ω,503mV,35mA/cm2,转换效率约12%。上述太阳能电池性能还可通过优化制备工艺进一步提高。     

飞秒激光多脉冲烧蚀镍钛合金的数值模拟

为了研究飞秒激光多脉冲累积效应对镍钛合金材料的影响,通过考虑多脉冲之间的时间间隔改写激光光源项,利用改进的双温模型,采用有限差分法,对飞秒激光三脉冲烧蚀镍钛合金的温度场分布进行数值模拟,得到了电子和晶格温度随时间和烧蚀深度的演化规律.分析了多脉冲累积效应的内在机理;讨论了三脉冲条件下不同参量对电子和晶格温度的影响.结果表明:镍钛合金在飞秒激光三脉冲的作用下,电子有3个递增的峰值温度,相比单脉冲的作用,三脉冲使电子和晶格温度明显升高;多脉冲的时间间隔直接影响多脉冲的累积效应;脉冲宽度影响电子的峰值温度和达到峰值温度所用的时间;激光能量密度影响电子和晶格的温度;电声耦合常量对电子与晶格的耦合时间和电子晶格的平衡温度也有重要影响.     

激光相干合成中单元的相位和振幅波动对合成光束远场分布的影响

运用傅里叶光学分析法推导出系统抖动造成单个光源的相位和振幅发生波动时的远场光强表达式,以1维阵列为例分析了系统抖动对远场的影响。研究表明:随着参与合束的发光单元数目的增加,尖峰变锐,能量更集中;系统抖动引起了远场峰值光强的减少,出现了本底现象,破坏了远场的对称性和光束质量;激光阵列单个光源的相位随机抖动应该控制在3/8范围内;相干合束发光单元数目越多,系统抖动对远场的影响越小。     

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.     

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.     

Numerical simulation of process dynamics during laser beam drilling with short pulses

In the last years, laser beam drilling became increasingly important for many technical applications as it allows the contactless production of high quality drill holes. So far, mainly short laser pulses are of industrial relevance, as they offer a good compromise between precision and efficiency and combine high ablation efficiency with low thermal damage of the workpiece. Laser beam drilling in this pulse length range is still a highly thermal process. There are two ablation mechanisms: evaporation and melt expulsion. In order to achieve high quality processing results, a basic process understanding is absolutely necessary. Yet, process observations in laser beam drilling suffer from both the short time scales and the restricted accessibility of the interaction zone. Numerical simulations offer the possibility to acquire additional knowledge of the process as they allow a direct look into the drill hole during the ablation process. In this contribution, a numerical finite volume multi-phase simulation model for laser beam drilling with short laser pulses shall be presented. The model is applied for a basic study of the ablation process with μs and ns laser pulses. The obtained results show good qualitative correspondence with experimental data.     

Femtosecond laser drilling of alumina ceramic substrates

In the paper, the result on femtosecond laser drilling of alumina ceramic substrate was reported. The effects of various laser parameters such as different focus position, traverse speed, drilling pattern, pausing time, etc. on the drilled hole quality in terms of surface finish, heat affected zone (HAZ), hole circularity, debris, microcracks were studied. The quality of laser-drilled holes on alumina ceramic substrates was evaluated with optical microscope, SEM/EDX, and X-ray μ-CT analysis. The optimum drilling conditions were identified. High-quality laser-drilled holes on alumina ceramic substrates were demonstrated. The developed process has potential application in manufacturing of alumina substrate based electronic devices.     

Numerical and experimental investigation of seam welding with a pulsed laser

The present work develops two numerical models to compute thermal phenomena during pulsed laser welding. The first one which is based on finite difference model calculates the welding width and its penetration by utilizing heat transfer equations. Parametric design capabilities of the finite element code ANSYS were also employed for the simulation of the second model. The transient temperature profiles, the fusion dimensions and the heat affected zones (HAZ) have been calculated here. The thermo-physical properties are dependent on temperature and so a nonlinear solution is employed. It is found that the temperature profile and penetration depth are strongly dependent on the pulse parameters of laser beam. Finally, the results of the two models and the experimental outcomes are compared.     

ANSYS仿真激光切割氧化锌纳米线

 以脉冲高斯激光为光源,直径在500 nm～1 000 nm、长度10 μm的一维氧化锌材料为对象,采用有限元分析软件ANSYS建立了激光切割氧化锌纳米线的热力学仿真模型,并采用生死单元技术对超过熔点的单元进行处理,得到不同激光工作参数和氧化锌纳米线直径下的温度分布场和切割形貌。讨论了纳米线直径和聚焦光斑相对纳米线的位移对切割的影响,纳米线直径越大允许的激光离焦量越小;当无离焦或负离焦较小时,切割纳米线产生的形貌较为理想。     

Optodynamic study of multiple pulses micro drilling

This paper describes an analysis of pulsed lasers micro-drilling of different metals. Study focuses to an optodynamic phenomenon which appears as thermal effects induced by laser light pulses and leads to dynamic process manifested as ultrasonic shock waves propagating into the sample material. The shock waves are detected by a non-contact optical method by using arm compensated Michelson. Monitoring of the main parameters of the micro drilling such as material ablation rate and efficiency was realized by analysis of the optodynamic signals. The process is characterized by decreasing ablation rate that leads to the finite hole depth. The experimental part of study comprehends a comparison between various metals. In order to describe decreasing ablation rate a theoretical model based on the energy balance is proposed. It considers the energy/heat transfer from the laser beam to the material and predicts a decreasing drilling rate with an increasing number of successive laser pulses. According to the proposed model, the finite depth of the hole appears as a consequence of the increasing surface area through which the energy of the laser beam is conducted away to the material around the processed area. Decreasing ablation rate and the finite hole depth predicted by model were in good agreement with the experimental results.     

A statistical approach to determine process parameter impact in Nd:YAG laser drilling of IN718 and Ti-6Al-4V sheets

The numerous unique advantages afforded by pulsed Nd:YAG laser systems have led to their increasing utility for producing high aspect ratio holes in a wide range of materials. Notwithstanding the growing industrial acceptance of the technique, the increasingly tighter geometrical tolerances and more stringent hole quality requirements of modern industrial components demand that “defects” such as taper, recast, spatter etc., in laser-drilled holes are minimized. Process parameters like pulse energy, pulse repetition rate, pulse duration, focal position, nozzle standoff, type of gas and gas pressure of the assist gas are known to significantly influence hole quality during laser drilling. The present study reports the use of Taguchi design of experiments technique to study the effects of the above process variables on the quality of the drilled holes and ascertain optimum processing conditions. Minimum taper in the drilled hole was considered as the desired target response. The entire study was conducted in three phases:(a) screening experiments, to identify process variables that critically influence taper in laser drilled holes, (b) Optimization experiments, to ascertain the set of parameters that would yield minimum taper and (c) validation trials, to assess the validity of the experimental procedures and results. Results indicate that laser drilling with focal position on the surface of the material being drilled and employing low level values of pulse duration and pulse energy represents the ideal conditions to achieve minimum taper in laser-drilled holes. Thorough assessment of results also reveals that the laser-drilling process, optimized considering taper in the drilled hole as the target response, leads to very significant improvements in respect of other hole quality attributes of interest such as spatter and recast as well.