Chemical imaging with a confocal scanning Fourier-transform-Raman microscope

Traditional approaches in confocal microscopy have focused on techniques to generate volumetric intensity or phase images of an object. In these different imaging modes the scattered optical-field properties depend on local refractive index and absorption, properties not unique to a given material. We report here on a confocal microscope that uses Raman scattered light to generate volumetric chemical images of a material. We designed and built a prototype instrument, called a confocal scanning laser Raman microscope, that combines a confocal scanning laser microscope with a Fourier-transform-Raman spectrometer. The high depth and lateral spatial resolution of the confocal optics design define a volume element from which the Raman scattered light is collected, and the spectrometer analyzes its spectral content. The sample is scanned through the microscope probe volume, and a chemical image isgenerated based on the content of the Raman spectrum extracted from each scan position in the sample. The results inclu e instrument characterization measurements and examples of confocal chemical imaging.     

Computed-Tomography-Based Analysis of Voids in SnBi57Ag1 Solder Joints and Their Influence on the Reliability

The first area of research in this article focuses on the characterization of solder joints that contain voids by means of computed tomography (CT). This non-destructive test method made it possible to detect both cracks and voids in solder joints, to define their precise positions, and to capture the void volume of each void. In addition to CT, we carried out metallographic examinations so that we could demonstrate the interaction of both methods. In the process, CT was used to localize the defect and metallography to display the defect in high resolution. The article goes on to discuss the question of whether voids have an effect on the thermo-mechanical reliability of SnBi57Ag1 solder joints. For this purpose, the solder joints were first classified by their void area ratio using radioscopy. In order to analyze the effect of the void area ratio on the reliability of the joint, the assembly underwent an accelerated aging process through thermal shock testing according to IPC 9701. Subsequently, the shocked assemblies were sheared. With the shear values after 1000 cycles, we were able to show that the voids affect the reliability of the SnBi57Ag1 solder joints only slightly and that the joints were hardly damaged. By means of CT examinations performed prior to the thermal shocks, cracks starting from the meniscus tip could be attributed to the temperature changes. These cracks may be crucial when they occur with cracks found on macrovoids inside the meniscus.     

Standardless semiquantitative analysis of metals using single-shot laser ablation inductively coupled plasma time-of-flight mass spectrometry

A method has been developed that allows the accurate, standardless measurement of the elemental composition of metal samples from single laser ablation (LA) pulses. This technique provides a fast, low-sample-consumption means for the characterization of samples having a range of matrixes. The method directly compares adjusted elemental signals with the total mass spectrometric signal to produce relative percent composition information. Three mathematical techniques were used to determine the accuracy and precision of single-shot LA measurement. Comparison of the techniques showed that a linear regression calculation, which plots individual elemental signals as a function of the summed signal for all elements in the sample on a point-by-point basis during a laser ablation transient proved superior. The simultaneous extraction capability of time-of-flight mass spectrometry permits the sampling of all analytes from any temporal position within the transient laser ablation pulse, thereby reducing quantitation error. A typical concentration dynamic range of 3 orders of magnitude, from 0.1 to 100%, was achieved. However, by measuring low-abundance isotopes for matrix elements, the dynamic range of the technique was extended to 4 orders of magnitude. The new technique is largely immune to sample matrix effects commonly experienced in laser ablation. By performing a complete elemental analysis from a single ablation pulse, high spatial resolution should be achieved.     

Characterization of Diffraction Gratings by use of a Tabletop Soft-X-Ray Laser

We have demonstrated the use of a high-repetition-rate 46.9-nm tabletop laser to characterize diffraction gratings designed for grazing-incidence operation in the soft-x-ray spectral region. The efficiencies for various diffraction orders were measured as a function of angle of incidence and compared with the results of model simulations. This measurement technique provides benchmarks with which to improve electromagnetic codes used in the design of soft-x-ray diffraction gratings. The results illustrate the potential of compact tabletop soft-x-ray lasers for use as a new tool for characterization of short-wavelength optics at the manufacturer's site.     

Manufacturing‐induced surface contaminations

In the course of classical optics manufacturing glass components are in permanent direct contact with aqueous operating materials. Such contact leads to a certain absorption of water and hydrogenous compounds that may induce severe glass defects. In this contribution, absorption of hydrogen and other contaminants during grinding of glass was observed and qualitatively detected via laser‐induced breakdown spectroscopy. It is shown that hydrogen, calcium, magnesium, and carbon are implanted into the glass surface where the contaminant concentration increases over grinding time or contact time of the glass surface with water and the grinding tool, respectively. The contaminants hydrogen, calcium, and magnesium can be attributed to the water used as lubricant. In contrast, carbon most likely originates from wear debris of the used silicon carbide grinding pads. Several possible mechanisms that lead to such surface contamination of glasses during grinding – diffusion, accumulation in micro cracks as well as the formation of hydrated silica – are finally introduced.     

Testing of the quality of solder joints through the analysis of their thermal behaviour with an interferometric laser probe

We present an optical contactless method for testing the quality of solder joints in surface mounted components by measuring their thermal dynamic behaviour. We detect surface normal displacements induced by Joule heating with a high resolution interferometnc laser probe. This probing method, based upon a homodyne Michelson interferometer, is an interesting tool for investigating the mechanisms of heat deposition and flow inside electronic devices. It allows the precise time evolution of the surface normal displacement to be measured (the laser probe has subnanometric resolution). This new approach of thermal behaviour laser testing is based upon the analysis of the diffusion of heat produced by the Joule effect in the structure (lead, solder and copper strip) from short current pulses and will influence heat diffusion. Solder joint failures (intermetallics, hidden voids, etc. ) behave as a thermal barrier. The optical test consists of measuring the dynamics of the solder joint expansion, and the variations from a standard response (good quality solder joints) will reveal defects. Important variations have been observed in solder joints that have undergone thermal cycling ageing tests. We have also investigated the thermal response of joints on IMS (insulated metallic substrate) and epoxy substrates. They show a very different time response.     

Complete spatial characterization of a pulsed doughnut-type beam by use of spherical optics and a cylindrical lens.

A complete spatial characterization (in second-order moments) of a doughnut-type beam from a pulsed transversely excited atmospheric CO2 laser is described. It includes the measurement of the orbital angular momentum carried by the beam. The key element in the characterization is the use of a cylindrical lens in addition to the usual spherical optics. Internal features of the beam that would have remained hidden if only spherical optics were employed were revealed by use of the cylindrical lens. The experimental results are compared and agree with a theoretical Laguerre-Gauss mode beam.     

Improving the reliability of ball grid arrays under random vibration by optimization of module design

Abstract

In this work, three different arrangements of circuit board in an electronic device were designed and the effects of random vibration frequencies on the reliability of ball grid arrays (BGA) in these arrangements were evaluated. The failure criterion in solder balls was the root mean square of peeling stress exerted during the dynamical loadings. According to the finite element method (FEM) results, the uttermost stress concentration was generated at the interface of printed circuit board (PCB) and the solder balls. It was also revealed that the increase of input power spectral density (PSD) decreased the fatigue life of solder joint in all the arrangements. Considering the arrangements of circuit boards, it was found that the maximum domain of peeling stress had a minimum effect on the solder balls when the heat sinks were away from the packages. The microstructural characterization of critical zone in solder balls indicated that with the increase of maximum peeling stress, the crack initiated and propagated along the interface.     

基于空耦换能器的碳纤维增强环氧树脂编织复合材料激光超声检测技术

激光超声技术具有无需耦合剂、快速及高分辨等特点,适用于各向异性碳纤维增强树脂编织复合材料的缺陷检测。运用有限元法分析了激励位置和编织结构对激光点源激发超声波信号的影响,获得了弹性波在材料内部的传播规律以及能量分布特征,并采用1 MHz空气耦合换能器搭建了一套小型化、低成本的非接触激光超声C扫描成像系统,开展了斜纹和缎纹碳纤维增强树脂编织复合材料的近表微结构和内部缺陷检测实验。结果表明,基于空气耦合换能器的激光超声成像可以高精度地再现碳纤维增强树脂编织复合材料的近表树脂囊、碳纤维束形状、取向、尺寸及其内部缺陷等空间分布特征,有望为航空复合材料提供一种原位的微结构表征和缺陷检测方法。      

Structural-defect formation in CeO<Subscript>2</Subscript> nanoparticles upon laser ablation

Cerium-dioxide nanoparticles are prepared by laser ablation, and their structure is studied by transmission electron microscopy and X-ray-diffraction analysis. The semiquantitative elemental composition is determined by electron energy-loss spectroscopy. Based on the spectral data obtained before and after annealing of particles, the significant oxygen-vacancy concentration in the structure of ablated CeO₂ nanoparticles is established.     

冲击环境下PBGA焊点动态特性分析

根据焊点成形理论和影响焊点可靠性因素对PCB和PBGA256组件进行有限元建模，并以此为基础对其进行模态分析及瞬态冲击动态响应分析，得出了最大应力应变在PGBA256上分布曲线；并根据实际情况简化得出焊点局部模型应变分布，从而找出焊点最易断裂失效的区域。最后，通过激光测振系统测得的实验模态和计算结果比较，表明所建立的有限元模型，可作为以后进行焊点疲劳寿命估计和焊点形态优化的基础。     

Design and experimental characterization of a high-resolution instrument for measuring the extreme-UV absorption of laser plasmas

The performances of a spectrometer for the observation of laser plasma absorption with high spectral and spatial resolution are described. Aspherical optics are used to correct the astigmatism in an extended spectral region. In this way only a small portion of the absorbing medium is probed, thus giving a good selection of the ionization stage acting as the absorption. Moreover, in the focal plane the plasma emission from the absorbing medium is spatially separated from the probe beam, with a consequent enhancement of the measurement sensitivity. The predicted optical performances from a ray tracing are compared with experimental observations for both spectral and spatial resolution.     

Combining laser ablation/liquid phase collection surface sampling and high-performance liquid chromatography-electrospray ionization-mass spectrometry

This letter describes the coupling of ambient pressure transmission geometry laser ablation with a liquid phase sample collection method for surface sampling and ionization with subsequent mass spectral analysis. A commercially available autosampler was adapted to produce a liquid droplet at the end of the syringe injection needle while in close proximity to the surface to collect the sample plume produced by laser ablation. The sample collection was followed by either flow injection or a high-performance liquid chromatography (HPLC) separation of the extracted components and detection with electrospray ionization mass spectrometry (ESI-MS). To illustrate the analytical utility of this coupling, thin films of a commercial ink sample containing rhodamine 6G and of mixed isobaric rhodamine B and 6G dyes on glass microscope slides were analyzed. The flow injection and HPLC-ESI-MS analysis revealed successful laser ablation, capture, and with HPLC, the separation of the two compounds. The ablated circular area was about 70 μm in diameter for these experiments. The spatial sampling resolution afforded by the laser ablation, as well as the ability to use sample processing methods like HPLC between the sample collection and ionization steps, makes this combined surface sampling/ionization technique a highly versatile analytical tool.     

Laser soldering with light-intensity patterns reconstructed from computer-generated holograms

We describe a laser soldering technology with diffractive optics. This technology provides efficient one-step laser illumination for components to be soldered. A phase-only computer-generated hologram set in a variable-focal-length optical configuration generates a diffraction pattern with the dimensions required for processing solder. We verified the effectiveness of the proposed scheme by sealing a ceramic package such that it could house a quartz device. The factors for successful soldering include alignment of the diffraction pattern to the work piece, the thermal properties of the materials involved, and the wavelength of the laser used to process the solder. The beam intensity across the diffraction pattern influences the process, and the 0th-order intensity should be minimized to prevent damage to the work piece.     

Determination of elemental compositions from mass peak profiles of the molecular ion (m) and the m + 1 and m + 2 ions

The relative abundances of M + 1 and M + 2 ions help to identify the elemental composition of the molecular ion (M). But scan speed, sensitivity, and resolution limitations of mass spectrometers have impeded determination of these abundances. Mass peak profiling from selected ion recording data (MPPSIRD) provided faster sampling and enhanced sensitivity, which permitted use of higher resolution. M + 2 profiles having only a few percent of the ion abundance of M were monitored at 20?000 resolution. The relative abundances, exact masses, and shapes of M, M + 1, and M + 2 mass peak profiles were determined. By applying five criteria based on these quantities, elemental compositions were determined even for ions too large (up to 766 Da) to be uniquely assigned from their exact mass and accuracy limits alone. A profile generation model (PGM) was written to predict these resolution-dependent quantities by considering all M + 1 and M + 2 ions for each candidate composition. The model also provided assurance that no other compositions were possible. Characterization of the M + 1 and M + 2 profiles by MPPSIRD and the PGM greatly expanded the practical ability of high-resolution mass spectrometry to determine elemental compositions.     

Capabilities of surface composition analysis using a long laser-induced breakdown spectroscopy spark

An apparatus has been investigated based on laser-induced breakdown spectroscopy (LIBS) for the rapid determination of the spatial distribution of elements on surfaces. Cylindrical optics are used to create a linear spark approximately 1 cm in length. Light emitted by atoms excited along the spark is collected and provides a spatial profile of elemental composition in the sample when analyzed with a spectrometer and gated charge-coupled device (ICCD) detector. Moving the spark across the sample surface as spectral data is recorded at regularly spaced intervals allows for the development of a three-dimensional elemental distribution map (emission intensity versus spatial distribution across an area). An analysis of the spatial resolution of this methodology is presented along with representative data from several sample types. Application of full-image analysis allowing for simultaneous investigations into the spatial distributions of multiple elements is also discussed and results are presented.     

Parametric light generation

Since its invention more than 40 years ago, the laser has become an indispensable optical tool, capable of transforming light from its naturally incoherent state to a highly coherent state in space and time. Yet, due to fundamental limitations, operation of the laser remains confined to restricted spectral and temporal regions. Nonlinear optics can overcome this limitation by allowing access to new spectral and temporal regimes through the exploitation of suitable dielectric materials in combination with the laser. In particular, optical parametric oscillators are versatile coherent light sources with unique flexibility that can provide optical radiation across an entire spectral range from the ultraviolet to the far-infrared and over all temporal scales from continuous wave to the ultrafast femtosecond domain.     

Microstructural evolution of tool steels after Nd-YAG laser repair welding

The present paper is aimed at investigating the microstructural behaviour of tool steels after repair welding or refurbishing by a pulsed Nd-YAG precision laser. The 1.2311 (40CrMnMo7), 1.2083 (X42Cr13) and 1.2343 (X38CrMoV5-1) steels were selected for experimental investigations to cover a wide range of steel grades, commonly used in tooling industry.Laser repair welding condition was simulated by preparing small deposits in one or more passes on steel samples having several reference geometries. Investigations on microstructural properties, microhardness evolution and on defect formation were carried out. The effects of different laser welding parameters were also considered.The study allowed to state several fundamental information on tool behaviour during repair welding in order to gain a deeper insight into this process, routinely considered in industrial practice but often neglected in scientific research works on welding metallurgy.     

Imaging and microanalysis of liquid phase sintered silicon-based ceramic microstructures

This review paper is focussed on the characterization of the microstructural development during liquid phase sintering and post-densification crystallisation heat treatment of ceramic materials based on the Si₃N₄ or SiC structures. Grain shape and size distributions, assessed by quantitative microscopy in combination with stereological methods, and fine scale microstructures, investigated by electron diffraction and high resolution imaging and microanalysis in the TEM, are discussed and related to the fabrication process and the overall composition of the ceramic material. It is demonstrated that combined high resolution analytical and spatial information from chemically and structurally distinct fine scale features, such as grain boundary films of residual glass, is obtained by electron spectroscopic imaging and subsequent computation of elemental distribution images. These images reveal that residual glassy grain boundary films are rich in oxygen and cations originating from the metal oxide/nitride additives, consistent with fine probe EDX analysis in the FEGTEM. Elemental analysis with high spatial resolution has also shown that grain growth into pockets of residual liquid/glass is associated with diffusion profiles in the glass in front of the growing grain. High resolution imaging in the TEM and elemental maps computed from electron energy filtered images show that the intergranular film thickness, in general, varies within a particular silicon nitride or sialon microstructure. Furthermore, grain boundaries, apparently free from residual glass may co-exist with glass-containing grain boundaries in some silicon nitride microstructures. In addition to the choice and weight fraction of sintering additives, factors such as the ionic radius of the cations originating from the additives, the local nano-scale chemistry and the relative grain orientation have an effect on the volume fraction and morphology of the intergranular microstructure.     

Microscopic Experimental Investigation on Shear Failure of Solder Joints

A microscopic investigation has been made on the shearing of one leaded and two lead-free solders by using an in situ SEM method. A shear lap joint specimen is designed and fabricated to accommodate a thin layer of solder alloy between copper strips. A non-contact method that measures strains in a very narrow area in the solder was applied. A laser grid was also used on the copper strip for measuring the back-face strain. Simultaneously micrographs at various stages were also taken. Where in situ measurements and micrographs are recorded they can reveal the continual development of damage and fracture mechanisms consistent with observations generated by low-cycle fatigue loading. This means that the shear test can be used as an alternative test to fatigue loading tests. By comparison, two lead-free solder specimens showed much smaller elongation to failure than the leaded solder, although all specimens showed similar sequence of events leading to final failure, including the boundary layer fracture phenomenon. The back-face strain indicator for the formation of a macro crack is due to the shifting of high stress concentration area from the joint-edge region to outside the joint region as revealed by a damage-coupled finite element procedure. The procedure also provides an estimate on the critical back-face strain.