Demonstration of electrical connectivity between self-assembled structures

Abstract

A novel way of three dimensional (3D) chip stacking has been designed in a view to improve heat dissipation across the layers. Solder-based self assembled (SBSA) structures have been designed as 3D posts on simulated through silicon vias to demonstrate the concept. The fabrication of SBSA structures using a low temperature solder alloy and dip soldering method is described. Previously, two types of soldering—face soldering and edge soldering—were studied to fabricate SBSA structures. Face soldering refers to deposition of solder on the complete metal face whereas edge soldering refers to selective deposition of solder on only the edges of the metal face. Mechanical grinding of the 3D structures shows that face soldered SBSA structures were void free and robust enough to be used as a connection post for chip stacking. Edge soldered SBSA structures collapsed when grinding was performed. This suggests the edge soldered 3D structure may only be partially filled. Face soldered SBSA structures provide a solder bump that serves as a connection path in the integration of dissimilar electronic technologies. Cylindrical copper posts, developed in a previous project, can be an effective approach to integrated circuit stacking. However, the SBSA post provides more variety in size and shape and can serve as a reservoir for solder to aid in chip bonding. The solder bumps are heat resistant, and uniform thicknesses were obtained across a large array of SBSA structures. The electrical durability of SBSA posts were determined by completing I-V measurements after thermal treatment. SBSA posts were subjected to thermal cycling with temperatures ranging from room temperature to 300 °C. The interconnected SBSA posts are shown to be stable until 165 °C with little variation in measured resistance.