Drilling, bonding, and forming conductive path in the hole by laser percussion drilling

Abstract

Several studies have focused on the electrical connections between the front and rear surfaces of stacked substrates in order to improve device performance. The fabrication and mounting process of the substrates involves three steps: (1) through-hole drilling, (2) formation of a conductive path inside the hole, and (3) physical bonding and electrical wiring connection of the substrates. In this paper, we demonstrate a technique for performing the process above simultaneously by laser percussion drilling. A borosilicate glass sample was used as the substrate, while copper was used as the wiring material. The substrate was drilled to a diameter of ~30 μm by laser radiation, while the copper was evaporated and deposited in a ~12-μm-thick layer on the inner surface of a glass-copper hole. Hence, a conductive path was formed inside the glass hole, facilitating bonding and conduction between the glass substrate and the copper sheet. The conductivity and bonding strength per 100 points between the glass surface and the copper sheet were ~5 Ω and ~1 N respectively. Furthermore, gaps were observed between the glass substrate and the copper sheet by energy dispersive X-ray analysis using a scanning electron microscope. However, the glass substrate and the copper sheet were bonded by the formation of a redeposited layer on the inner surface of the hole and in the gap between the glass and copper surfaces.