Room Temperature Interconnection Technology for Bonding Fine Pitch Bumps Using NanoWiring, KlettWelding, KlettSintering and KlettGlueing

Abstract

With further development in the fabrication technologies the density of electronic packages has increased. Ball grid arrays (BGA) and land grid array (LGA) with high density of connecting terminals have given rise to higher miniaturization of the integrated circuits (IC) and advancement in their performance. Fan-Out is one of the main solutions to fill the I/O gaps between the IC and PCB evolution. In this solution the chip is embedded in a mold compound like epoxy and the connecting terminals are fanned out using a redistribution layer (RDL). No PCB type layer is needed. The major challengers of this solution are fan-In solution like wafer level chip scale packaging (WL-CSP) and flip-chip CSP (FCCSP) or flip-chip BGA (FCBGA). Anyway, all surface mounting technologies depend primarily on the high temperature treated processes like soldering, sintering and reflow. Such processes raise the need of using new rare metals or toxic alloys. The environmental pollution caused by such metals and their recycling is a challenge. Furthermore, thermal processes have limited the technologies in terms of bumps and pitch sizes and placement accuracy. Also, the electrical conductivity, shear strength and the life cycle of the pads are affected by high temperature surface mounting processes. Especially Fan-out packaging on panel level (FOPLP) is not adopted yet due to technical challenges in assembly, die placement on large panels and fabrication and mounting connections/spaces below $10 \mu \mathrm{m}/ 10 \mu \mathrm{m}$. With KlettWelding technology, the die placement takes place immediately at room temperature by using standard pick and place machines, needing no inert gas or under fill. KlettWelding technology can enable bonding ultrahigh dense pads with $3 \mu \mathrm{m}$ edge length and $5 \mu \mathrm{m}$ pitches. The KlettWelding interconnections are from pure copper and free of any rare or toxic metals and no multi-layer structure as well. Also, in this technique the mismatch of the thermal expansions between the BGA and substrates by rapid temperature changes [1] vanishes.