Flip-Chip Bonding of 3-D Copper Compressible Microinterconnects for Cryogenic Electronic Packaging

Abstract

A free-standing copper compressible microinterconnect (CMI) for cryogenic applications was fabricated, flip-chip bonded, and its electrical and mechanical characteristics were analyzed in this letter. To address the increasing demand for reliable off-chip interconnects in cryogenic electronic packaging, we present a pressure-contact-based 3-D copper CMI that exhibits linear elastic behavior, requires a relatively low bonding force, and offers reworkability. Ex-situ resistance measurements at room temperature and in-situ measurements from 300 K down to 14 mK were performed on a flip-chip bonded CMI array, revealing up to a 39.6% reduction in resistance upon cool down. Furthermore, a mechanistic investigation of the flip-chip bonding process was conducted, including force–displacement measurements, along with force–stress analysis using finite element analysis (FEA), to verify robustness.