Assessment Methodology on Mold Void Defect by Scanning Acoustic Microscopy (SAM) Non-Destructive Technique

The effects of delamination at the mold component/die interface during reliability testing are investigated using scanning acoustic microscopy (SAM), and electrical and physical analyses. The SAM results are correlated with electrical end point (EEP) tests and destructive physical analysis. The spread of delamination during temperature cycling of units is examined. It is demonstrated that scanning acoustic microscopy provides a significant improvement over cross sectioning for the inspection of critical defects in IC packages. The impact of this result on a test method for package reliability evaluation based on inspection for package cracks is discussed. >

With the modern and advance IC packaging structures introduced to the market now-a-day, the limitation and complication of the signal interpretation of the other nondestructive techniques, such as the scanning acoustic microscope (SAM) method, diminished the capability to identify any micro-crack on the die surface. In addition, the destructive analysis could also introduce the excess forces, which possibly induce the artifact micro-crack after the die is exposed by decapsulation or polishing techniques. Hence, the new non-destructive analysis technique for detecting micro-cracks and crack patterns in the IC memory devices has been proposed. This technique can easily detect the micro-cracks and crack patterns by utilizing the memory tester bitmap feature. The shorter analysis time and higher success rate can be achieved comparing to the other non-destructive techniques.

Now we are attempting to apply non destructive analysis from evaluation tests or failure analysis to acceptance tests or production tests. Needless to say non destructive analysis has an advantage of conserving the state of samples and the reducing the time of analysis as compared to conventional methods with destructive physical analysis. Moreover, we are paying attention to the following reasons for nondestructive physical analysis. It is difficult to keep the reproducibility of the analysis because of the high skill level required for destructive physical analysis. On the other hand, high reproducibility can be easily achieved by fixing the condition or parameters of the device during nondestructive analysis when performed by tools like X-ray. Moreover, we expect that neither the analytical result nor the quality of the nondestructive analysis depends upon the worker's capability. In this paper we will discuss the following two items from the viewpoint of quality assurance. 1. The method of the screening for fake parts (1) The procedure flow for the production discontinued parts (2) The comparison and examination between the diagnostic using X-ray computed tomography (X-ray CT) images and various examinations (3) Other observation cases using X-ray CT images 2. Effectiveness and consideration in reliability evaluation test using X-ray CT image (1) Comparison of observation cases with a variety of jointing points in parts (2) Consideration of application of nondestructive observation technique in reliability test Use of X-ray CT images is effective in diagnosing the quality of the product or the process. Moreover, we find that use of X-ray CT images is effective for the improvement of the reproducibility of the evaluation examination. Then we find that use of X-ray CT images can reduce the time of evaluation examination too.

Investigation of optical properties of benzocyclobutene wafer bonding layer used for 3D interconnects via infrared spectroscopic ellipsometry

Examination of cracks and other defects in sodium β & β″-alumina using acoustic, optical and electron microscopy

Previous work on determining the minimal air gap detectable in scanning acoustic microscope (SAM) focused on the gap thickness detectable in an idealized Newton ring sample using a 75 MHz transducer. However, air gaps thinner than 0.130 microns have been detected by SAM. These findings have prompted a return to the question of what is the minimal air gap detectability of SAM. To answer this question, further, Newton Ring experiments using transducers across the SAM frequency range have been performed. This article discusses the processes involved in these experiments and provides the results of SAM from actual packages. The procedure involved in cross-sectioning and scanning electron microscopy (SEM) imaging for correlating samples is also provided. Based on the SAM-cross-sectioning-SEM analysis, a detection of 0.056 - 0.183 micron air gaps was concluded for the delamination areas detected by SAM using a 35 MHz 12 mm transducer.

Various methods can characterize microstructural properties of reservoir rocks with the ultimate goal of relating microstructure to seismic properties. Scanning electron microscopy, transmission electron microscopy, and optical microscopy have traditionally been used for such studies. They have identified lithology, pore space, interconnectivity of pores, grain size, and cementation as the most important factors controlling seismic wave velocity and attenuation. However, these techniques provide qualitative descriptions only. The acoustic techniques presented here, scanning acoustic microscopy (SAM) and acoustic sounding (AS), can map and, more importantly, quantify microstructure as variations in acoustic impedance. Ultrasonic stress waves are sensitive to local variations in elastic properties and are therefore particularly suited for characterizing microstructural properties of reservoir rocks. Reflections from impedance boundaries in grains and between interfaces in the sample are used to construct the microstructural image. This paper will show that acoustic microscopy can be a powerful tool for studying internal structure and pore geometry of reservoir rocks. Acoustic microscopy's basic principle is almost identical to that of reflection seismology. Images of surface and subsurface microstructures are prepared on the basis of reflected acoustic waves—that is, on the impedance changes in the sample. Acoustic waves on a sample are mode converted, partly transmitted into the sample, and partly reflected. The reflection coefficient and with it the signal intensity received by the transducer are determined by the elastic constants of the material. Changes in acoustic impedance in the sample that influence wave reflection characteristics can be studied by mapping the reflected waves. Because the working frequency of the acoustic waves can be varied, their penetration depth into the sample and the resolution of microstructural features can be controlled. I will present results from high-frequency SAM (0.1–2 GHz) and low-frequency AS (25–100 MHz). The resolution of SAM is about 1 μm at 1 GHz; AS …

A scanning acoustic microscope (SAM) has been used to investigate the structure of thermoplastic leather. This material is formed by pressing fibers of leather under high pressure and moderate temperature. The result is a matrix from transformed, melted fibers in which leftover fibers act as reinforcement. Unlike the scanning electron microscope (SEM), the SAM is able to distinguish between completely and incompletely transformed fibers and also to penetrate the material beneath the surface. The results show that the matrix is built as a domain structure. The advantages of the SAM over the SEM for organic materials are indicated.

The main aim of this paper is to provide the feasibility of non-destructive testing (NDT) method, such as scanning acoustic microscopy (SAM), for damage detection in ultrasound (US) probes for medical imaging during the manufacturing process. In a highly competitive and demanding electronics and biomedical market, reliable non-destructive methods for quality control and failure analysis of electronic components within multi-layered structures are strongly required. Any robust non-destructive method should be capable of dealing with the complexity of miniaturized assemblies, such as the acoustic stack of ultrasonic transducers. In this work, the application of SAM in an industrial scenario was studied for 24 samples of a phased array probe, in order to investigate potential internal integrity, to detect damages, and to assess the compliance of high-demanding quality requirements. Delamination, non-homogeneous layers with micron-thickness, and entrapped air bubbles (blisters) in the bulk of US probe acoustic stacks were detected and studied. Analysis of 2D images and defects visualization by means of ultrasound-based NDT method were compared with electroacoustic characterization (also following as pulse-echo test) of the US probe through an ad-hoc measurement system. SAM becomes very useful for defect detection in multilayered structures with a thickness of some microns by assuring low time-consuming (a limit for other NDT techniques) and quantitative analyses based on measurements. The study provides a tangible contribution and identifies an advantage for manufacturers of ultrasound probes that are oriented toward continuous improvement devoted to the process capability, product quality, and in-process inspection.

New semiconductor chip technologies and technologies for 3D integration require information’s of packaging and interface defects in 3 dimensions, that means the lateral dimension of the defect and the location inside the device or package must be defined. In this paper, new methodical approaches for non destructive failure analysis on 3D integrated TSV samples are introduced. The concepts combine improved scanning acoustic microscopy (SAM) imaging hardware with unique software solutions for defect identification and quantitative analysis of mechanical properties using scanning acoustic investigations. In case of MEMS 3D integration, e.g. based on direct bonding, related interface defects must be investigated by SAM. With respect to 3D integration applications, the potential of recent SAM improvements applying specifically adapted hardware and custom-made signal processing algorithms will be discussed. Examples of SAM-based failure detection techniques for the application in 3D integration are demonstrated. New technologies are shown to improve the through put of fully wafer scanning using scanning acoustic microscopy. To improve the defect resolution, a new transducer design was developed to increase defect resolution and signal to noise for interface characterisation.

In this paper, the reliability of RF power transistors’ solder attachments is characterized through experiments and simulations. Test cases consisted of power amplifier (PA) modules on AlSi10Mg substrates with either a low or high mutual thermal mismatch. The module’s flange interconnections were stressed by means of thermal cycling testing (TCT) in the 15 °C–95 °C range. Scanning acoustic microscopy (SAM) was used intermittently to inspect the interconnections of selected structures during cycling breaks. Optical cross-polarization microscopy and scanning electron microscopy were used in the failure analysis of the solder joints. Different materials and dimensional variations were tested in simulations to observe differences in thermal stress. The viscoplastic behavior of lead-free solder in the interconnection was modeled using Anand’s constitutive equations. The first cracks could be observed with SAM after 100 cycles. SAM imaging showed that in the worst case, 72% of the interconnection area had cracked at the end of the 1100-cycle TCT. Only a marginal amount of cracks could be observed in PA modules with a better coefficients of thermal expansion match to the substrate. Simulations indicated that it is possible to decrease creep energies significantly and thereby increase the lifetime expectancy of interconnections by selecting the correct materials and structures.

Hybrid bonding, with wafer level bonding to form oxide-oxide bonds and Cu-Cu bonds is a promising technology for 3D integrated circuits. In this paper, the impact of various process parameters on the wafer-level bond quality of fusion (direct) and hybrid bonding have been evaluated. Investigated process parameters include: TEOS based oxide (Tetra-Ethyl-Ortho-Silicate) process deposition temperature, oxide densification annealing conditions, plasma conditions for wafer surface activation, chemical mechanical polishing (CMP) process conditions and post-bonding annealing conditions. In addition to these process parameters, design parameter such as Cu pad density is also critical. For fusion/hybrid bonding, surface properties are very critical. This includes surface roughness, bow and warpage, flatness and edge roll-off. Thus, all these surface properties were continuously monitored during the wafers fabrication. Bond quality was characterized by scanning acoustic microscopy (SAM) images. Bonding energy was calculated using Maszara model, where the crack length is measured from the SAM micrographs. Target objective of this study is to determine optimum process conditions in order to achieve eventual bonding energy > 1J/m2, which is a pre-requisite for 3D multi-wafer stacking without any delamination.

Reconstruction of 3-dimensional objects in Scanning Acoustic Microscopy (SAM) is now of great interest. From the mathematical point of view, the simplest kind of 3- dimensional objects are spherical particles, Investigations of the image formation of spheres have revealed different phenomena, which are of current scientific concern. First theoretical treatments1 showed that the image formation of spheres in transmission configuration of SAM is easily to understand, and is close to the imaging in optical microscopy. In transmission acoustic microscopy, the dimension of the image is only slightly dependent on the scanning plane position. The strongest image contrast arises when the focal plane coincides with the center of the sphere. The diameter of the image in this position is nearly equal to the particle size. In contrary, in reflection acoustic microscopy, image formation of spherical particles has revealed extraordinary properties2,3. The purpose of this report is to present an interpretation of the images of spheres at different focal plane positions, using Fourier spectrum approach in reflection SAM.

In this paper the performance of multi-narrow-band spectral analysis was evaluated concerning defect detection in microelectronic components with flip-chip contacts. Today, flip-chip technology is widely applied for interconnecting silicon dies to a substrate within high-end semiconductor packaging technologies. The integrity of the bump solder interconnection is of major concern for the reliability in this technology. Non-destructive defect localization and analysis of the flip-chip interconnections operating in a semi-automated mode is strongly desired. Scanning acoustic microscopy (SAM) combined with subsequent signal analysis has high potential for non-destructive localization of defective flip-chip interconnects. Analyzing multiple narrow spectral bands of signals acquired by a scanning acoustic microscope enabled the identification and localization of defective flip-chip interconnects. In the current study a 180 MHz transducer with 8 mm focal length was employed for acoustic data acquisition by SAM. Those data were then analyzed off-line by discrete Fourier transformation, chirp z-transform and cosine transform using custom made MATLAB software. Through multi-narrow band spectral analysis, defective flip-chip interconnects that have not been revealed by standard acoustical imaging methods have been detected successfully. Acoustically found defects have been confirmed by subsequent FIB-cross sectioning and SEM imaging. The high resolution SEM imaging revealed complete and partial delamination at the interface between the die and the bump.

Scanning acoustic microscopy (SAM) is a useful observational tool in cellular study as non-invasive living observation is feasible, unlike in conventional optical microscopy. In a previous study, cell morphological changes were successfully visualized using acoustic impedance measurements. These acoustic impedance changes correspond to cell elasticity, mainly reflecting changes in the cytoskeleton. In this study, we evaluate the elastic changes in murine breast cancer cell C127I during mitosis. C127I cells were cultured to ∼75% confluency before measurement, using a transducer with a central frequency of 320 MHz. Dynamic changes during mitosis were successfully mapped using SAM and confirmed by laser confocal microscopy. Cells in prometaphase, anaphase, and telophase, which could previously only be confirmed through immunostaining, were successfully visualized using SAM. This suggests that SAM is capable of distinguishing cells in different mitotic phases based on the changes in acoustic impedance.