Effective Transmission of High Frequency Ultrasound into a Silicon Chip through a Polymer Layer

Abstract

In this paper, we describe an effective transmission method of high frequency ultrasound into a silicon chip via the polymer layers. The layer is inserted between water and the chip, and the pressure of about 0.1 MPa is applied to the contact interface between the layer and the chip. The polyvinylidene chloride and polyvinyl chloride layers of 9 µm thick bring the ultrasonic resonance between water and silicon, and the ultrasound in the frequency range of 20 to 80 MHz is transmitted into the chip more effectively than the usual water immersion case. In practice, we carry out the acoustic imaging of the flip chip package via the layer, and clearly visualize the defective solder bumps beneath the chip under the dry-contact condition. Besides, the quality of the dry-contact image is equivalent to the water immersion image.

Theory and applications of high frequency broadband ultrasound via a thin layer in contact with a solid

“…Figure 4 shows that the joints between the package substrate and the solder balls are clearly imaged in both cases. Figures 5(a) and (b) show the echoes obtained using the dry-contact ultrasonic technique with a 9 m thick polyvinylidene chloride (PVDC) film and that obtained using the conventional water immersion technique, respectively (Tohmyoh and Saka, 2004b). The sample is a flip chip package with a bare silicon chip.…”

“…This matching phenomenon is treated in the next section. (Tohmyoh and Saka, 2004b) with the permission of The Japan Society of Mechanical Engineers.…”

“…An example of g E for a 100 MHz focused ultrasonic transducer with 2a of 6.35 mm and z 0 of 12.7 mm is shown in Fig. 14 (Tohmyoh and Saka, 2004b). Here  is obtained from the silicon/acrylic resin interface using a PVDC film.…”

Polymer acoustic matching layer for broadband ultrasonic applications

“…14 Furthermore, it has been discovered experimentally that the signal intensity of ultrasound transmitted via a solid layer sometimes exceeds that achieved by water immersion due to the ultrasonic resonance that occurs between water, the layer, and the sample. 4, 15 Desilets et al have reported a design method for producing acoustic thindisk transducers, which is based on the use of quarter-wave matching layers between a piezoelectric material and the acoustic load, and the validity of their method has been verified by the experiments using ultrasound of up to several MHz in frequency. 16 Today, this method is widely used to design piezoelectric transducers for medical imaging.…”