ADVANCED PACKAGE PROTOTYPING USING NANO-PARTICLE SILVER PRINTED INTERCONNECTS
Authors: Sungchul Joo and Daniel F. Baldwin, Ph.D. Company: The George W. Woodruff School of Mechanical Engine Date Published: 11/1/2006
IWLPC (Wafer-Level Packaging)
Abstract: To reduce manufacturing cost, lead time, process complexity, and enhance electrical and mechanical reliability performance, an embedded-active approach that targets rapid prototyping and low-volume production in micro-system packaging is being developed. The approach involves a rapid prototyping of micro-system packaging by a data-driven chip-first packaging process using direct printing of nano-particle metals. In the chip-first process, bare dice are first embedded into a copper or stainless steel carrier substrate, fixed by filling up the gap between the chips and the substrate with thermoplastic adhesives, and planarized to a common planar surface. On the coplanar substrate, polyimide or liquid crystal polymer (LCP) film is laminated to form a dielectric layer. Through the dielectric layer to the chip metal pads, micro vias are drilled by laser ablation. The vias are filled with nano-particle silver (NPS), which has high conductivity and good adhesion to copper, polyimide, and LCP. The NPS is deposited by screen printing and a three dimensional electrical circuit is formed. This packaging approach is data-driven, so requires no masks and reduces packaging turn-around time from months to days. It is also less limited by substrate composition and morphology, eliminates the need for special chip processing such as the need required for flip chip solder bumps, and permits using any chip technology and any chip supplier allowing mixed devices. The embedded-active process with nano-particle metals avoids the extreme processing conditions required for standard IC fabrication such as wet chemistry processing and vacuum sputtering. The nano-particle conductors typically measure around 5nm in diameter and can be sintered at plasticcompatible temperatures as low as 220C to form material nearly indistinguishable from the bulk metal. The embedded-active packaging shows an excellent reliability performance in terms of thermal shock, which is performed in the range of -45 and 125 degree Celsius. These results represent an important step to a system packaging characterized by high density, low cost, and data-driven fabrication for rapid package prototyping. This paper presents an electrical performance characterization of the nano-particle conductors, details of the rapid prototyping process sequence, an initial reliability characterization of the package architecture, and a failure mode analysis of the packages.