High current-carrying and highly-reliable 30μm diameter Cu-Cu area-array interconnections without solder

Innovative packaging technologies have delivered a remarkable generation of mobile devices, enabling the transition from simple single-function systems to advanced multifunctional computing and communication systems in the span of only a decade. Of many technology advancements, high interconnection (I/O) density has been a major contributing factor in this transition. However, the constant push for high I/O density has resulted in smaller pitch and interconnection dimensions, thereby introducing the concerns for thermo-mechanical reliability and electromigration resistance due to higher current density. Georgia Tech Packaging Research Center (GT-PRC) has been developing an ultra-fine pitch, copper-to-copper interconnection technology to overcome the limitations of current solder bump technology. This paper emphasizes the robustness of this interconnection technology by demonstrating its performance under high current density and high I/O area-array configuration. Already demonstrated at 30μm pitch, low profile copper-to-copper interconnections, developed at GT-PRC using a low-cost, low-temperature direct copper-to-copper bonding approach, have been shown [1-2] to have high reliability under thermal cycling test (TCT), high temperature storage (HTS) test and highly accelerated stress test (HAST). Utilized in the pioneering chip-last approach, this interconnection method has also been proven [3] ready for commercialization through a two-step high throughput multi-chip embedding process and three-dimensional stacking capability. This research demonstrates, for the first time, the ability of the aforementioned adhesive-bonded copper-to-copper interconnections to - (1) withstand 2000 thermal cycles in a high pin-count area-array configuration and (2) survive ~800 hours of testing at 10⁴-10⁵ A/cm² current density, which, to the best of authors´ knowledge is the highest ever reported for adhesive based interconnections [4-6].