01 Ultrasonic testing principle

Ultrasonic is a sound wave with a frequency of more than 20KHz, which is beyond the frequency that can be heard by the human ear (the sound frequency that can be heard by the human ear: 16Hz-20KHz). When the internal uniformity of the material changes, its acoustic impedance will change, and the amplitude and phase of the echo signal will change; The waveform data (such as peak value, time, etc.) are displayed in different colors or gray values, and the internal structure of the tested sample can be displayed in real time.

Comparison between X-ray scanning and ultrasonic scanning

X-Ray►

Difference based on material density

Not sensitive to internal delamination, small cracks and faulty welding

The scanning result is a composite image of the entire sample thickness

SAM►

Very sensitive to bonding layer

Can penetrate most materials

High resolution, high sensitivity

real-time detection 

No harm to human health

02 Key technologies

Scan mode

Reflection scanning mode:

Use a probe to transmit and receive ultrasonic waves at the same time.

According to different scanning methods, they are A-Scan, B-Scan, C-Scan, D-Scan, X-Scan, G-Scan, Z-Scan and other scanning methods.

The image is clear at a specific level.

Transmission scanning mode:

Similar to X-ray detection, the detection method using transmitted ultrasonic as signal.

The ultrasonic signal penetrates the whole tested sample, and the defects of all interfaces can be detected by one scan.

The image is not as clear as reflection.

Autofocus scanning technology

When the traditional surface tracking technology is faced with large warping samples (such as wafer bonded samples after thinning), the position with serious warping will not be detected due to defocus. The application of automatic focusing scanning technology can make the probe Z direction adjust up and down in real time with the fluctuation of the sample surface during the scanning process, and always focus on the specified interface inside the sample, so as to track the 2-5mm large warping of the sample surface.

Frequency division scanning technology

The frequency division scanning technology can divide a frequency probe into multiple frequency bands for simultaneous detection. Fourier transform is used to decompose the echo signal into different frequency bands, and the existing probe is set to any frequency band for scanning through frequency conversion function to select the frequency band with the clearest image. Using this technology can effectively use the existing probe, reduce the cumbersome process of replacing the probe, and improve the scanning speed.

Interpolation scanning technology

Using the characteristics of high-speed data acquisition of ultrasonic scanning, the ultrasonic scanning image with comparable definition can be obtained in half of the time by interlacing and then using classical image interpolation, which greatly improves the scanning efficiency in the case of low resolution requirements.