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Optical microscopy is ubiquitous in diverse fields within academic research and commercial industries. It is an affordable, rapid analytical imaging technique used to visualize samples. While optical microscopes may be common, many instruments fall far short on performance when compared with the cutting-edge digital microscope systems available at Covalent. Advanced optical microscopes generate images in the same way modern digital cameras do, by capturing the light reflected back from (or transmitted through) a sample under set illumination. However, unlike a simple camera, modern optical microscopes also include intrinsic lens systems and sophisticated illumination systems that facilitate high magnification and dynamic range images with micron-scale resolution. Our systems additionally incorporate extended depth-of-field optics, with automated compositing and image-stitching technologies to process and integrate images captured across different focal planes and oversized lateral domains. This enables fully focused, high-resolution imaging across the entirety of the desired field of view, even spanning large height differences in the features of interest. Distinct illumination modes (including: bright-field, dark-field, and mixed lighting, polarized lighting, and directional lighting) can be acutely controlled within a high-precision automation system to enable thorough characterization of critical surface features which may not otherwise be observable. In addition, this system has the unique ability to tilt the microscope with respect to the sample for enhanced edge definition images.
Atomic Force Microscopy (AFM) measures surface topography of materials with sub-nm vertical resolution. The technique delivers fast data, with simple scans requiring only a few minutes to complete. An AFM cantilever with a protruding ultra-sharp tip is raster scanned over the sample, which makes either intermittent or constant contact with the surface. The tip interacts with the sample, experiencing repulsive or attractive inter-atomic forces. A laser beam is reflected off the back of the cantilever onto a detector. As the cantilever scans, the detector monitors changes in the beam deflection. The z position of the cantilever shifts up or down to maintain a constant beam deflection and determine the vertical height of the surface. Alternative advanced imaging modes allow for visualization and measurement of other material properties, such as: adhesion, modulus, charge distribution, work function, and magnetic domains (among others).
Attenuated-total-reflectance (ATR) is a sampling mode which enhances the Fourier Transformed Infrared Spectroscopy (FTIR) signal obtained from sample surfaces, increasing sensitivity and allowing efficient measurements with minimal sample preparation. Like standard FTIR measurements, ATR-FTIR is used for chemical qualification of a sample from raw optical spectra and is often used to determine organic composition. For ATR-FTIR, a specialized accessory is incorporated into an FTIR system. This accessory includes an internal crystal which promotes multiple internal reflections of the incident IR beam. The crystal is oriented to be in direct contact with the sample surface, allowing it to absorb photons of characteristic energies, based on its chemical composition. When incoming beams lose photons through absorption in the sample, the reflected light wave will have an attenuated intensity. A spectrometer parses the extent of this attenuation over the entirety of the sampled Infrared (IR) domain. Peaks and unique conformations of the resulting ATR spectrum are then interpreted to yield chemical information about the functional groups and elements present in the sample.
Auger electron spectroscopy (AES) is a surface-sensitive analytical technique used to quantify and map the elemental composition of the outermost 2-10 nm of a material. This technique utilizes high-energy electron beam as an excitation source resulting in the emission of Auger electrons, whose kinetic energies are characteristic of the elements and chemical states present in the surface of a sample. The emitted auger electrons are picked up by a specialized detector, which scans over an energy range and analyzes the amount of auger electrons at each kinetic energy value. The resulting spectrum allows analysts to quantitatively determine the elemental composition of the surface. The source electron beam can also be finely focused to diameters as small as ~5 nm to create secondary electron and Auger images which are used not only for compositional and topographic analysis but also to locate features of interests. In conjunction with ion beam sputtering, depth profiling can also be done on samples to provide composition as a function of depth as well as layer thicknesses.
Chromatic dispersion profilometry is a non-contact, nondestructive analytical technique used to measure surface topography. It is particularly well suited for large area characterization (e.g. full wafers) requiring high vertical accuracy. Chromatic dispersion profilometers employ a confocal optical configuration in which a broadband white-light beam is focused downward onto a point area of the sample using a lens with intentionally large optical dispersion. The lens causes focal length to vary with wavelength, such that different wavelengths will be in focus at different distances from the detector. Only the narrow band of wavelengths which are in focus at the sample surface are reflected back to the detector, allowing the system to measure surface height at the illuminated point with nm-scale vertical accuracy. Additionally, the large-area sample stage can also translate (move) laterally to allow the measurement lens to analyze surface height at a series of points. This enables 2D or 3D modeling and mapping of surface topography across a full scanned region on the sample.
Differential scanning calorimetry (DSC) is a thermal analysis technique used to characterize a variety of temperature-dependent physical and chemical changes in a material. DSC instruments measure the amount heat transferred (exothermic (heat produced) and endothermic (heat required) between a sample and its environment as the overall temperature of the system is modulated / ramped. The sample is placed in a small pan and sealed. To increase the precision of the measurement, the system simultaneously measures heat flux in both the sample of interest, and an adjacent reference (a “blank,” or empty) pan. After the energy transfer in the reference is subtracted from the specimen signal, one is left with a DSC curve that quantitatively reflects the temperature dependence of numerous thermal events. Characteristic features in a DSC curve correspond to certain thermodynamic processes, as well as exothermic and endothermic chemical and physical transitions. These transitions can include include: recrystallization, softening and phase changes. By identifying these, it is possible to quantify the temperatures at which they occur, often allowing identification of the material (s) and to calculate additional, correlated thermal properties.
Dye and Pry testing is a destructive, IPC-prescribed failure-analysis and quality-control technique performed on solder joints on printed circuit board assemblies (PCBA) to identify certain defects unique to solder joints, such as: cracks, “head-in-pillow” defects, and other joint separations. Even when compared against X-ray analytical techniques, 'Dye and Pry' remains the most widely accepted technique for characterizing solder-ball die-attach quality defects. Dye an Pry procedures begin by submerging a target board in a specialized red, blue or green fluorescent dye, using vacuum-pressure impregnation. The marker fluid penetrates any cracks or other openings in the exposed solder joints. As part of this process, a final bake-out is done to set the dye. After bake-out, a pulling jig (which can sometimes be as simple as a hex bolt) is bonded to the top surface of the attached component using epoxy. Once the epoxy is set, the components are manually pulled from the board to allow visual assessment of the solder joints. Any pre-existing cracks will be stained red. Each joint is then inspected at a minimum 40X magnification using Advanced Optical Microscopy. Covalent provides a complete report of this analysis, which includes a selection of images captured of the total board and representative solder joints from planar (top-down) and lateral (side) orientations. Our technical experts have over 20 years of experience executing Dye & Pry analysis in accordance with IPC standards.
Dynamic light scattering (DLS) provides a nondestructive, indirect measurement of the average size and size distribution of particles and colloids in solutions. Particles suspended in a liquid are constantly undergoing random Brownian motion, and their size directly affects their speed: smaller particles move faster than larger ones. When a laser light source is applied to an aqueous sample of particles in solution, it scatters around them as it passes. The scattered light is detected and recorded at some pre-defined angles and the time-dependence of changes in the scattered intensity profiles can be correlated to the particles’ speed, and therefore to their average size and distribution throughout the system. Plots of the relative frequency of distinct particle sizes and speeds can then be generated for subsequent analysis.
Dynamic mechanical analysis (DMA) is used to study changes in the mechanical properties of a material under periodic stress as the temperature is varied. DMA results are used to assess: glass transitions, melting points, elastic modulus, strain-to-break, toughness, creep, and numerous other thermal and mechanical properties. In a DMA measurement, an oscillating force is applied with a set frequency to a sample suspended in a near-frictionless environment. This force can be set to bend, stretch and compress, torque, or maintain tension directionally within the sample. While the dynamic stress is applied to the sample, the whole system is simultaneously subjected to set temperature change: either constant or iterated heating / cooling at fixed or variable rates. The material’s stress response over time is measured both through its dimensional changes and its damping of the oscillating force. DMA systems detect dimensional changes with hypersensitive optical sensors, and track damping through the applied force probe. These two metrics, recorded as a function of time and temperature, are used to produce DMA curves which provide robust, quantitative analysis of the sample’s thermomechanical characteristics.
Electron probe microanlysis (EPMA) is a non-destructive technique used for high-sensitivity, quantitative determination of the elemental composition of a material. This technique focuses an energetic beam of electrons onto the sample surface, thereby stimulating x-ray fluorescence. The wavelength of the x-ray is characteristic of the fluorescing element. The strength of that x-ray signal relates then to the abundance of its element within the excited volume, the depth the element is within the sample, and the effects of other elements in the sample. Similarly, to Wavelength Dispersive X-ray Fluorescence Spectroscopy (WDXRF), EPMA systems use wavelength-dispersive spectroscopy (WDS) detectors – which act like diffraction gratings – calibrated to detect various x-ray wavelengths.. By using wavelength-analyzers, EPMA achieves high resolution separation of emission lines, with low background, allowing for quantitative sensitivity to 10 ppm with appropriate use of reference standards. Additionally, because EPMA systems like Scanning Electron Microscopes , can be used to generate 2D element maps by measuring fluorescence at multiple points in a raster-scan. The EPMA system utilized at Covalent also contains an energy dispersive x-ray spectroscopy (EDS) detector that can quickly obtain entire XRF spectra from points on the sample, albeit with much lower spectral resolution and sensitivity. This allows for rapid identification of the elements present to expedite quantitative analysis of their respective concentrations.
Like other high-resolution scanning electron microscopes, Focused-ion-beam scanning electron microscopes (FIB-SEMs) are used to produce 2D and 3D images of surface topography, and are able to resolve nm-scale features on a sample surface. On a FIB-SEM, the added focused-ion-beam allows for in situ sample manipulation. Normally the FIB beam is used to cross-section the sample at a precise location. The FIB allows advanced analytical workflows such as: cross-section, tomography, lithography, lamella prep, and many others. The imaging capabilities of the scanning-electron-beam in a FIB-SEM work as they do in any other SEM: the system generates an image by detecting electrons scattered by a highly-focused, high-energy applied electron beam as it is raster-scanned over the surface of a sample. The secondary focused-ion-beam is comprised of high-energy, charged atoms (most commonly Ga+). When applied to the sample, the FIB can be tuned to either ablate material from the surface, or deposit atoms of an accompanying neutral gas. Additionally, both in-house FIB-SEM instruments at Covalent also incorporate energy dispersive spectroscopy (EDS) detectors that enable measurement and mapping of elemental composition alongside all other FIB-SEM operations.
Fourier-transformed infrared spectroscopy (FTIR) is a nondestructive, optical technique used to analyze chemical composition and the optical properties of a material. In an FTIR measurement, an initially wide range of infrared wavelengths are simultaneously shone upon an area of the sample. Using an interferometer, the FTIR system then extracts a specific wavelength band at a time and measures its light intensity: selectively detecting either reflected or transmitted beams. The operator will determine whether to target transmittance or reflectance intensity based on the sample's composition and topography. After this initial measurement, the extracted wavelength band is subsequently scanned over the entirety of the wavelength range, capturing an intensity measurement at each band. The resulting values are then fourier-transformed to produce the initial sample spectrum. To isolate the real sample spectrum, a reference - or 'blank' - trial is conducted without any material inserted in the beam path. This spectrum is used to normalize the sample spectrum and to isolate the relevant specimen information from the total signal. In the wavelength range of interest, different types of chemical bonds absorb at different wavelengths: providing a spectral signature which is material dependent. The resulting background-subtracted spectrum can then be used to qualitatively identify chemical functional groups and trace chemicals present in the specimen. ATR-FTIR is a variant FTIR measurement mode which uses a specialized crystal to generate multiple internal reflections along the lateral dimension of the sample, increasing signal-to-noise and surface sensitivity.
EDXRF is a fast, nondestructive spectroscopy technique used to determine the elemental composition of a near-surface volume, and...
EDXRF is a fast, nondestructive spectroscopy technique used to determine the elemental composition of a near-surface volume, and...