title: The penetration of acoustic cavitation bubbles into micrometer-scale cavities.
abstract: The penetration of acoustically induced cavitation bubbles in micrometer-scale cavities is investigated experimentally by means of high-speed photography and acoustic measurements. Micrometer-scale cavities of different dimensions (width=40 μm, 80 μm, 10 mm and depth=50 μm) are designed to replicate the cross section of microvias in a PCB. The aim here is to present a method for enhancing mass transfer due to the penetration of bubbles in such narrow geometries under the action of ultrasound. The micrometer-scale cavities are placed in a test-cell filled with water and subjected to an ultrasound excitation at 75 kHz. A cavitation bubble cluster is generated at the mouth of the cavity which acts as a continuous source of bubbles that penetrate into the cavity. The radial oscillation characteristics and translation of these bubbles are investigated in detail here. It is observed that the bubbles arrange themselves into streamer-like structures inside the cavity. Parameters such as bubble population and size distribution and their correlation with the phase of the incident ultrasound radiation are investigated in detail here. This provides a valuable insight into the dynamics of bubbles in narrow confined spaces. Mass transfer investigations show that fresh liquid can be continuously introduced in the cavities under the action of ultrasound. Our findings may have important consequences in optimizing the filling processes for microvias with high aspect ratios.
authors.affiliation: Institute of Fluid Mechanics, University of Erlangen-Nuremberg, D-91058 Erlangen, Germany; Erlangen Graduate School of Advanced Optical Technologies (SAOT), University of Erlangen-Nuremberg, D-91052 Erlangen, Germany. Electronic address: haresh.vaidya@fau.de.
authors.forename: Haresh Anant
authors.initials: HA
authors.lastname: Vaidya
authors.affiliation: Department of Mechanical Engineering, Ozyegin University, 34662 Istanbul, Turkey.
authors.forename: Özgür
authors.initials: Ö
authors.lastname: Ertunç
authors.affiliation: Institute of Fluid Mechanics, University of Erlangen-Nuremberg, D-91058 Erlangen, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Lichtenegger
authors.affiliation: Institute of Fluid Mechanics, University of Erlangen-Nuremberg, D-91058 Erlangen, Germany; Erlangen Graduate School of Advanced Optical Technologies (SAOT), University of Erlangen-Nuremberg, D-91052 Erlangen, Germany.
authors.forename: Antonio
authors.initials: A
authors.lastname: Delgado
authors.affiliation: Atotech Deutschland GmbH, D-90537 Feucht, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Skupin
keywords: Acoustic cavitation; Bubble dynamics; Mass transfer; Microvias; Ultrasound