无铅焊接中Lift-off现象产生的原因及抑制对策

本文首次提出三要素法来解释Lift-off的形成机理。相比传统的“Bi-Segregation”失效机理,“三要素法”可以解释含Bi和不含Bi的所有无铅钎料产生或不产生Lift-off的原因,并由此找出了Lift-off的抑制对策。

低温砷化镓的外延lift-off和范德华贴附研究

研究了低温砷化镓的外延lift-off和基于范德华力在石英新衬底上贴附的实验方法：腐蚀掉100nm厚的AlAs牺牲层，将外延生长的500nm厚的低温砷化镓（LT-GaAs）从生长衬底上揭下（lift-off），借助于范德华力将LT-GaAs外延膜贴附在新衬底上。Lift—off之前在LT-GaAs表面上滴附黑蜡，以增强在lift-off过程中对LT-GaAs的保护，和加快反应气体扩散离开反应区的过程。针对500nm厚的LT-GaAs外延薄膜的揭起和贴附，给出了低温砷化镓的最佳lift-off尺寸和提高范德华力贴附质量的实验技术。此外还给出了利用所得到的lift-off后的LT-GaAs制备的共平面条形结构光导开关的时间特性：上升时间小于1．5ps，FWHM小于2ps。

LASER LIFT-OFF OF GaN THIN FILMS FROM SAPPHIRE SUBSTRATES

Gallium Nitride film was successfully separated from sapphire substrate by laser radiation. The absorption of the 248nm radiation by the GaN at the interface results in rapid thermal decomposition of the interfacial layer, yielding metallic Ga and N2 gas. The substrate can be easily removed by heating above the Ga melting point (29℃). X-ray diffraction, atomic force microscopy and Photoluminescence of CaN before and after lift-off process have been performed, which demonstrated that the separation and transfer process do not alter the structural quality of the GaN films. And further discussions on the threshold energy and crack-free strategies of laser lift-off process have also been presented.

国产Lift-Off光刻胶在空间用太阳电池中的应用

选用两种较为典型的国产Lift-Off光刻胶(A和B)进行了实验优化,并进行了电极蒸镀后的牢固度测试、电致发光测试和电性能测试。在牢固度测试中发现,A电池样品有掉栅现象,B电池样品没有出现掉栅现象。通过EL测试和电性能测试分析证明,A电池的电极与太阳电池基体存在局部的接触不良现象。通过实验筛选出了一种应用前景较好的B型号国产Lift-Off负性光刻胶,有望经过进一步验证和优化后逐步应用在空间用太阳电池生产中。

萘酚基酚醛树脂的合成及其在lift-off光刻胶中的应用

首先以α-萘酚、间甲酚、甲醛为单体,通过缩聚反应合成了萘酚基酚醛树脂NAPR,随后与二碳酸二叔丁酯(DBDC)反应制备了一系列t-BOC改性的萘酚基酚醛树脂NAPR-BOC。用红外(FT-IR)、核磁(1 H NMR)、凝胶色谱(GPC)、热失重分析(TGA)对其结构及性能进行了表征。以NAPR-BOC-2为基体树脂配制成lift-off光刻胶,测试了光刻胶的分辨率、形貌和耐热性,得到的光刻胶分辨率最大为0.6μm,耐热可达130℃。

Epitaxial Lift-Off of Flexible GaN‑Based HEMT Arrays with Performances Optimization by the Piezotronic Effect

High-electron-mobility transistors(HEMTs)are a promising device in the field of radio frequency and wireless communication.However,to unlock the full potential of HEMTs,the fabrication of large-size flexible HEMTs is required.Herein,a large-sized(>2 cm^(2))of AlGaN/AlN/GaN heterostructure-based HEMTs were successfully stripped from sapphire substrate to a flexible polyethylene terephthalate substrate by an electrochemical lift-off technique.The piezotronic effect was then induced to optimize the electron transport performance by modulating/tuning the physical properties of two-dimensional electron gas(2DEG)and phonons.The saturation current of the flexible HEMT is enhanced by 3.15%under the 0.547%tensile condition,and the thermal degradation of the HEMT was also obviously suppressed under compressive straining.The corresponding electrical performance changes and energy diagrams systematically illustrate the intrinsic mechanism.This work not only provides in-depth understanding of the piezotronic effect in tuning 2DEG and phonon properties in GaN HEMTs,but also demonstrates a low-cost method to optimize its electronic and thermal properties.

Experimental analysis of sand particles' lift-off and incident velocities in wind-blown sand flux

The probability distributions of sand particles' lift-off and incident velocities in a wind-blown sand flux play very important roles in the simulation of the wind-blown sand movement. In this paper, the vertical and the horizontal speeds of sand particles located at 1.0 mm above a sand-bed in a wind-blown sand flux are observed with the aid of Phase Doppler Anemometry (PDA) in a wind tunnel. Based on the experimental data, the probability distributions of not only the vertical lift-off speed but also the lift-off velocity as well as its horizontal component and the incident velocity as well as its vertical and horizontal components can be obtained by the equal distance histogram method. It is found, according to the results of the χ2-test for these probability distributions, that the probability density functions (pdf's) of the sand particles' lift-off and incident velocities as well as their vertical components are described by the Gamma density function with different peak values and shapes and the downwind incident and lift-off horizontal speeds, respectively, can be described by the lognormal and the Gamma density functions. These pdf's depend on not only the sand particle diameter but also the wind speed.

Sand particle lift-off velocity measurements and numerical simulation of mass flux distributions in a wind tunnel

Lift-off velocity of saltating sand particles in wind-blown sand located at 1.0 mm above the sand bed surface was measured using a phase Doppler particle analyzer in a wind tunnel. The results show that the probability distribution of lift-off velocity can be expressed as a lognormal function, while that of lift-off angle follows an exponential function. The probability distribution of lift-off angle conditioned for each lift-off velocity also follows an exponential function, with a slope that becomes steeper with increasing lift-off velocity. This implies that the probability distribution of lift-off velocity is strongly dependent on the lift-off angle. However, these lift-off parameters are generally treated as an independent joint probability distribution in the literature. Numerical simulations were carried out to investigate the effects of conditional versus independent joint probability distributions on the vertical sand mass flux distribution. The simulation results derived from the conditional joint probability distribution agree much better with experimental data than those from the independent ones. Thus, it is better to describe the lift-off velocity of saltating sand particles using the conditional joint probability distribution. These results improve our understanding of saltation processes in wind-blown sand.

Fabrication of THz Dipole Antenna Using Lift-off Method

The microfabrication technique for THz dipole antenna,"lift-off" was studied in this paper.Its procedure has been examined in detail,and discreetly tweaked.Particularly,Chlorobenzene is suggested to assist the formation of undercut indispensible for fulfilling "lift-off".The experimental results of fabricated antennas confirm the effectiveness of this method.

Twisted Integration of Complex Oxide Magnetoelectric Heterostructures via Water‑Etching and Transfer Process

Manipulating strain mode and degree that can be applied to epitaxial complex oxide thin films have been a cornerstone of strain engineering.In recent years,lift-off and transfer technology of the epitaxial oxide thin films have been developed that enabled the integration of heterostructures without the limitation of material types and crystal orientations.Moreover,twisted integration would provide a more interesting strategy in artificial magnetoelectric heterostructures.A specific twist angle between the ferroelectric and ferromagnetic oxide layers corresponds to the distinct strain regulation modes in the magnetoelectric coupling process,which could provide some insight in to the physical phenomena.In this work,the La_(0.67)Sr_(0.33)MnO_(3)(001)/0.7Pb(Mg_(1/3)Nb_(2/3))O_(3)-0.3PbTiO_(3)(011)(LSMO/PMN-PT)heterostructures with 45.and 0.twist angles were assembled via water-etching and transfer process.The transferred LSMO films exhibit a fourfold magnetic anisotropy with easy axis along LSMO<110>.A coexistence of uniaxial and fourfold magnetic anisotropy with LSMO[110]easy axis is observed for the 45°Sample by applying a 7.2 kV cm^(−1)electrical field,significantly different from a uniaxial anisotropy with LSMO[100]easy axis for the 0°Sample.The fitting of the ferromagnetic resonance field reveals that the strain coupling generated by the 45°twist angle causes different lattice distortion of LSMO,thereby enhancing both the fourfold and uniaxial anisotropy.This work confirms the twisting degrees of freedom for magnetoelectric coupling and opens opportunities for fabricating artificial magnetoelectric heterostructures.

基于神经网络的高原机场飞机离地速度计算方法

针对现有飞行理论中对民航飞机在高原机场起飞离地速度计算研究不足,且计算方法单一、复杂的问题,利用MATLAB仿真平台构建在高原机场飞机起飞滑跑阶段模型,通过计算不同飞行条件下的飞机离地速度,得到大量训练样本,建立BP神经网络模型,将机场海拔、飞机质量、安全起飞速度、温度和可用起飞距离作为输入量,飞机离地速度作为输出量,对神经网络进行训练和测试,直至均方差达到要求。将神经网络所求估算值与仿真数据进行对比并进行分析。均方误差为4.1289,均方根误差为5.6121。使用神经网络计算方法效率高,误差小,可应用于不同高原机型在不同影响因素下的离地速度计算,对高原机场运行和机场跑道长度设计有一定参考价值。

反转胶lift-Off工艺制备堆栈电感

本文采用反转胶lift-off工艺,对比分析了金属淀积方式、光刻胶的选择及光刻胶烘干时间对金属剥离效果的影响,制备出最小线宽4μm,最小间距4μm,厚度为1μm,线宽误差小于0.5μm的金属线条,并最终实现具有三层金属的堆栈电感,经光学显微镜和台阶仪观测表明,器件外观良好成品率高。

Experimental study of laser lift-off of ultra-thin polyimide film for flexible electronics

It is increasingly crucial for flexible electronics to efficiently and reliably peel large-area, ultra-thin flexible films off from rigid substrate serving as substrates of flexible electronics device, especially in industrial production. This paper experimentally investigated the mechanism and technologic characteristics of laser lift-off(LLO) process of ultra-thin(～ 2 μm) polyimide(PI)film. It was found increasingly difficult to obtain desirable ultra-thin PI film by LLO with the decrease of the film thickness. The optimal process parameters were achieved considering laser fluence and accumulated irradiation times(AIT), which were found to be strongly correlative to the thickness of PI film. The process mechanism of LLO of PI film was disclosed that laser ablation of interfacial PI will result in the formation of gas products between the PI and glass substrate, enabling the change of interface microstructures to reduce the interface bond strength. The amount of gas products mainly determines the result of LLO process for ultra-thin PI film, from residual adhesion to wrinkles or cracking. The strategy of multi-scanning based on multiple irradiations of low-energy laser pulses was presented to effectively achieve a reliable LLO process of ultra-thin PI film. This study provides an attractive route to optimize the LLO process for large-scale production of ultra-thin flexible electronics.

脉冲涡流检测频域提离交叉点的测厚研究

针对时域LOI在铁磁性和非铁磁性材料的脉冲涡流检测信号中的获取方法不统一问题,并致使时域LOI信号特征的提取标准统一性受到限制.文章通过分析铁磁性和非铁磁性材料的脉冲涡流差分信号,研究探头提离变化对脉冲涡流差分信号幅值谱、相位谱、实部谱的影响规律,获取脉冲涡流差分信号频谱中的频域LOI,并进一步分析频域LOI的厚度测量的可行性,为统一和扩展LOI的获取方法及改善LOI的测量范围提供方法指导.

用于镀锌铁皮保护层下检测的脉冲涡流技术研究

在实际应用中,脉冲涡流检测技术会受到保温层外的保护层的影响,其中镀锌铁皮保护层对脉冲涡流信号影响较大。研究了不同保护层对脉冲涡流信号的影响,重点分析了镀锌铁皮厚度、提离高度和镀锌铁皮振动对脉冲涡流信号的影响,并提出了解决方案:当提离高度相同时,带镀锌铁皮保护层的脉冲涡流信号幅值较不带保护层时的信号幅值大幅减小,此时需选择穿透能力更强的检测探头并提高发射电流强度;当以晚期信号斜率作为表征壁厚的特征值时,提离高度对计算壁厚的影响较小;考虑到磁致伸缩引起的探头振动,检测过程中应避免检测探头与镀锌铁皮直接接触。

AZ~ 15nXT Photoresist for Lift-off Applications

AZ15nXT is a chemically-amplified negative-tone thick film photoresist.The resist has vertical profile and is widely used for redistribution layer(RDL)and through silicon vias(TSV)applications.For lift-off applications,however,the inverted profile is needed.In this paper,we report the effects of process conditions on the resist profile and process window for lift off applications.

碳钢件焊缝缺陷检测用正交涡流探头研究

由于传统涡流探头具有明显的提离效应,难以检测表面不平整的焊缝。为此,基于均匀涡流检测原理,设计一种用于焊缝缺陷检测的正交涡流探头。采用理论计算方法,研究正交探头检测原理,设计探头有限元仿真模型,分析探头结构和线圈尺寸对检测灵敏度的影响。利用设计的正交涡流探头对碳钢件焊缝开展探伤检测试验。当提离量不大于2 mm时,有效检测出宽度为0.25 mm、深度为1 mm的碳钢板焊缝表面人工开口裂纹。试验结果表明,正交涡流探头能有效抑制检测过程中提离效应的影响,验证了探头用于焊缝表面缺陷检测的可行性。

采煤机叶片提升角对截割滚筒的影响作用分析

采煤机是煤矿自动化综采的重要设备,滚筒的结构中叶片提升角是重要的设计参数,对滚筒截齿的数量及方向具有重要的影响,从而影响采煤机的开采效率及块煤率。针对采煤机滚筒受到的载荷作用进行分析,在不同的叶片提升角作用下,建立滚筒截割的数值分析模型,对滚筒受到的平均阻力、最大阻力、载荷波动系数及截割比能耗进行计算分析,从而为采煤机滚筒的设计使用提供参考。

基于两种波浪数据的施工船舶可作业预报对比

通过对基于全球海浪预报数据和全球海浪再分析数据的施工船舶可作业预报对比,探讨基于全球海浪预报数据的施工船舶可作业预报的可靠性。针对我国未来海上风电场规划,对2种波浪数据的波浪要素以及采用两种波浪数据的起重船大直径单桩可作业性进行对比,选择具有代表性的17个波浪数据点,在船舶可作业性计算中采用基于时-频域联合计算的方法。结果表明,两种波浪数据中对海上风电施工船舶作业影响较大的波高和波周期的均值和方差误差均较小,总体在10%以内。采用两种波浪数据的可作业性的预报误差不超过15%,大部分可控制在5%以内。表明,海浪预报数据进行施工船舶可作业性的预报依然具有较高的可靠性,可以作为海上风电场整体施工难度评价的依据。

Roughening surface morphology on free-standing GaN membrane with laser lift-off technique

An ultraviolet (UV) laser lift-off (LLO) technique was presented to form a roughened surface morphol-ogy on GaN membrane grown by metalorganic chemical vapor deposition (MOCVD). The etched sur-face showed cone-like structures on a free-standing GaN membrane. Based on the scanning electron microscopy (SEM) and atom force microscopy (AFM) measurements, the etching mechanism was proposed, which was related to the different decomposition depth caused by the dislocations in the GaN membrane. The etching efficiency and morphology of GaN by the LLO technique and the photo-electrochemical (PEC) wet etching technique was compared and analyzed. This roughed cone-like surface morphology by LLO can enhance the external efficiency of vertical structure n-side-up GaN-based light-emitting diodes (LEDs) simultaneously while being released of the performance con-strains impeded by sapphire.