Development of In-Process Ultrasonic Measurement For Quality Assurance of Microjoints in Electronic Devices

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In the assembly process of electronic devices, many bonding techniques are applied to the small area or thin layr, in which poor bonding may result in electrical failures. Therefore, in-line or in-process testing of micro bonded area are demanded for the quality assurance of electronic devices. However, there are few techniques applicable to the micro bonded area. In this study, two methods are proposed for the non-destructive evaluation of small or thin bonded area in the microcircuit. First method is the ultrasonic testing of wire bonded area with a delay line. Another one is the ultrasonic testing of die bonding with a focused probe. The results obtained are as follows.1.Ultrasonic testing of wire bonding with a delay lineAn ultrasonic testing with delay line is proposed, in which a bonding tool or capillary is used for the delay line and is connected to the probe. In this method, the reflected wave through the capillary indicates proportional amplitude change to the fracture load i … More n the push test. Since the fracture load corresponds to the wire bonding state, this method enables the non-destructive evaluation of wire bonding. Although the reflected wave depends upon the measuring pressure, contact of capillary with probe and couplant, the same condition of measuring pressure to bonding process suggests that this method is applicable to the in-process measurement of wire bonding.2.Ultrasonic testing of die bonding with a focused probeA newly developed ultrasonic testing with a focused probe is applied to the die bonded area, where the paste is supplied in the thin layr between 0.15 mm thick substrate and 0.29 mm thick microcircuit. Under the measuring condition of shorter water path than the focal length of ultrasonic beam, the interface echo reflected from the interface between the substrate and paste is detected with an observable time delay behind surface echo. The interface echo in the scanning indicates the corresponding amplitude change to the lack of paste as well as the debonding. The measurement in the volatile liquid prevents the microcircuit from the corrosion and absorption of water, and shows the same results in the water. The ultrasonic testing in the volatile liquid is available to the in-line measurement of micro devices. Less