Liquid-Assisted Contactless Adhesive Bonding: Experimental validation and 2D Multiphysics simulation

Abstract

Handling ultra-thin semiconductor dies during assembly remains challenging due to their mechanical fragility and sensitivity to placement forces. Contactless die transfer methods reduce mechanical loading and have potential to enable higher placement speeds and improved throughput but introduce challenges such as uncontrolled impact dynamics, die rebound, and misalignment during landing. This work investigates a liquid-assisted contactless adhesive bonding approach in which droplets deposited on stencil-printed conductive adhesive act as transient damping and alignment media during die landing. Dummy silicon dies with a gold (Au) surface finish were released from a short distance onto the adhesive. Four liquids with different physical and chemical properties—deionized (DI) water, isopropyl alcohol (IPA), acetone, and liquid flux—were investigated to evaluate the influence of key fluid parameters, including surface tension, viscosity, and density, on die impact dynamics, stabilization, and subsequent bonding quality. The results demonstrate that droplet material properties significantly influence die landing dynamics in liquid-assisted contactless assembly. Among the investigated liquids, deionized water enabled reliable die entrapment and damping. In contrast, for the lower-surface-tension solvents isopropyl alcohol (IPA) and acetone, the droplets were not sufficiently confined under the experimental conditions, and therefore no direct die entrapment was observed, although impact damping was still achieved. Die entrapment and stabilization behavior were analyzed using high-speed camera recordings and complementary two-dimensional simulations performed in COMSOL Multiphysics. Furthermore, the impact of the droplets on the resulting bond interface and joint quality was evaluated through post-bond characterization. The study provides insight into droplet-mediated die landing and offers guidelines for selecting liquids for reliable contactless micro-assembly.