Scanning Acoustic Microscopy (CSAM) is a quick, non-destructive analysis technique that uses ultrasound waves to detect changes in acoustic impedances in integrated circuits (ICs) and other similar materials. Pulses of different frequencies are used to penetrate various materials to examine sample interiors for voids, cracks or delamination.

It is used for evaluation of die attach integrity, heat spreader adhesion, and solder quality.

Purpose:

Acoustic microscopy provides non-destructive investigation of opaque devices. This includes, but is not limited to, plastic or ceramic integrated circuits, chip capacitors, chip resistors, circuit

board traces, and discrete

semiconductor devices.

Acoustic microscopy is complimentary to X-ray analysis.

Longitudinal waves: wave movement is parallel to particle movement.

Acoustic Velocity (v): n = ¦ ´ l where ¦ = frequency and l = wavelength in material. Focal length of the transducer is dependent on acoustic velocity of the particular material.

Frequency (f): ¦ = n ¸ l . Lower frequency provides deeper penetration, but higher frequency provides better resolution. Transducer frequency ranges from » 5 MHz to 150 MHz.

The minimum detectable defect: this should be greater than or equal to _ l .

Sound reflectance (P_r ): P_r = , where Z₁ is the acoustic impedance of the first material, and Z₂ is the acoustic impedance of the second material.

Peak Amplitude C-scan

Phase Inversion C-scan