Job Ha

Wavelet analysis based deconvolution to improve the resolution of scanning acoustic microscope images for the inspection of thin die layer in semiconductor

Scanning acoustic microscopy (SAM) is used as an important non-destructive test tool in semiconductor reliability evaluation and failure analysis. However, inspection of thin die layer has proven difficult as the reflected signals from the die top and bottom are superimposed. Conventional deconvolution techniques have been used for the improvement of time resolution in A-scan signal, however, they are not effective for SAM signal because the waveform of the reflected echo is quite different from the incident waveform due to the frequency dependent attenuation and the focal effect. In this paper, in order to overcome this difficulty, a new signal processing method, wavelet analysis based deconvolution technique is proposed. Its validity is approved by computer simulations and practical performances are demonstrated by experiments for the fabricated semiconductor sample.

Reliability evaluation of semiconductor using ultrasound

The semiconductor packaging industry is spending a great deal of time and effort developing thinner and thinner packages. Ultrasound works by measuring the amount of signal reflected from material interfaces. Thin packages create a potential problem because the resultant reflected signal from the die top and die attach layers can be nearly superimposed in the ultrasonic waveform. This makes it difficult to inspect for delaminations at the die attach adhesive interfaces. Generally a preconditioning test is performed to evaluate reliability of semiconductor packages. This includes utilizing a Scanning Acoustic Microscope (SAM) at the beginning and end of the test to aid in the discovery of the existence of physical defects, such as like delaminations or package cracks. In particular and of primary concern are package cracks and delaminations caused by moisture being absorbed under ambient conditions. This paper discusses the kind of failure mechanism associated with moisture absorption in plastic encapsulated semiconductors and the methodology of using SAMs to find failures such as cracks or delaminations grown during the preconditioning test.

Ultrasonic Estimation of Clamping Force in High-Tension Bolts

High-tension bolts have been used widely for the clamping of many kinds of large structures. In these bolts, the estimation of clamping force has been regarded as the main issue in the evaluation of clamping condition. This paper proposes a method using ultrasonic wave, which is based on the dependency of sound speed on the stress. In order to verify the usefulness of the proposed method, two kinds of experiments are carried out. The first one involves the measurement of sound speed when the bolt is stressed by the tension tester, and here, the relationship between the exact axial force and sound speed is calibrated. The result shows good agreement with the expected linear relationship between sound speed and axial stress. The second experiment involves the measurement of axial stress by the proposed method when the bolt is stressed by the torque wrench. The results are coincident to the strain gage measurement. From these results, we can conclude that the proposed method is indeed useful in evaluating clamping force in high-tension bolts.

Detection of Micro-Delamination in Electronic Packaging by Using the Ultrasonic Nonlinearity

Since micro cracks or delamination in electronic packaging that are potential failure mechanisms can cause a failure within the designed life-time, it is very important to analyze these micro defects in the bud of the growth for reliability assurance. Conventionally, SAM(Scanning Acoustic Microscope) has been used for the detection of these defects. However, as the size of defect to be detected becomes smaller, the higher frequency transducer is needed, and then it limits the depth of sample to be tested. Also there is some ambiguity to define the echo from the micro defect, since such echo amplitude is low. In this paper, in order to overcome these difficulties when we use SAM for the inspection of micro-delamination in the thin electronic package, a new method using the ultrasonic nonlinear effect is proposed. The basic concept of the proposed method is that the harmonic frequencies are generated in the transmitted ultrasonic wave due to the partial contact at the interface of delamination. Our method uses spectral analysis to measure the harmonic frequencies. The validity of the proposed method is shown through experiments using a specimen that contains an artificial micro-delamination fabricated inside and using real electronic packages.

Nonlinear Ultrasonic Method to Detect Micro-Delamination in Electronic Packaging

The linear ultrasonic technique has been extensively used as a powerful, non-destructive test tool for reliability testing and failure analysis of electronic packaging. This is used most often in the inspection of defects such as delaminations, voids, or cracks through use of a SAM (Scanning Acoustic Microscope). Then, as the reliability level that is required of electronic packaging becomes higher and the thickness of package becomes thinner, the possible defect which needs to be detected becomes smaller. In the conventional SAM, however it is very difficult to detect small defects less than m µ 1 . 0 , such as micro-delaminations. In order to solve such a problem, this paper proposes a nonlinear ultrasonic method, where the nonlinearity caused by the effect of crack-face interactions is considered. The basic concept of this method involves harmonic frequencies that are generated in the transmitted ultrasonic wave due to the partial contact at the interface of micro-delamination. As an evaluation index, the nonlinear parameter dependent on the amplitude of the second order harmonic frequency component is obtained by spectral analysis of the transmitted signal. Experimental results show that the nonlinear parameter has good correlation with the micro-gap and the proposed method can detect the micro-delamination even less than nm 1 .

Advanced Technologies for Estimation of Nonlinear Ultrasonic Parameter

This paper proposes an advanced signal processing technique for the precise estimation of a nonlinear ultrasonic parameter, based on power spectral and bispectral analysis. The power spectrum and bispectrum estimation of the pulse-like ultrasonic signal used in the commercial SAM (scanning acoustic microscopy) equipment is especially considered in this study. The usefulness of the proposed estimation is confirmed by experiments for a Newton ring with a continuous air gap and a real semiconductor sample with local delaminations. The results show that the nonlinear parameter obtained by the proposed method had a good correlation with the delamination.

Detection and Image Processing of Interfacial Micro-Delamination in the Thin-Layered Structure by Using Nonlinear Ultrasonic Effect

The detection of interfacial micro-delamination in the thin-layered structure such as the electronic package becomes very important as the electronic device becomes smaller and thinner. The conventional method used to detect the delamination in an electronic package is to use a scanning acoustic microscope (SAM). However, despite its high performance qualities, SAM is often faced with a tricky decision when a delaminated gap is too small. In this paper, a novel method based on ultrasonic nonlinearity is proposed to overcome this limit. The proposed method is integrated into the conventional SAM equipment, and its effectiveness is verified by experiments for the Newton Ring and the real semiconductor package that have micro-delaminations. The results showed that the nonlinear parameter had good correlation with the gap size of delamination. A method of imaging the nonlinear parameter is also proposed to assure the feasibility of the proposed method in the field application.