Reliable Microjoints Formed by Solid-Liquid Interdiffusion (SLID) Bonding Within a Chip-Stacking Architecture
Resource
IEEE Transactions on Components, Packaging and Manufacturing Technology, 2(6), 979-984
Journal
IEEE Transactions on Components, Packaging and Manufacturing Technology
Journal Volume
2
Journal Issue
6
Pages
979-984
Date Issued
2012
Date
2012
Author(s)
Abstract
In this research, thousands of 20-μm pitch microbumps with a diameter of 10 μm and a structure of a pure Sn cap on a Cu pillar were electroplated on 8-inch wafers, and those wafers were then respectively singularized as a top chip and bottom Si interposer for stacking. Two methods, namely conventional reflow and solid-liquid interdiffusion (SLID) bonding, were adopted to interconnect the microbumps. In the former case, the as-plated Sn caps were fluxed, and the chip was then placed on the Si interposer. Afterward, the Sn caps on the chip and on the Si interposer were melted and interconnected at a peak temperature of 250 ° C. The flux residues were cleaned after reflow, and the microgap between the chip and the Si interposer was fully sealed by a capillary underfill. In the SLID bonding process, the oxides on the as-plated Sn caps were removed by a plasma etcher first, and then the chip was placed on the interposer with a bonder as well, subsequently, the Sn caps were heated to 260°C to react with the Cu pillar to form Cu 6 Sn 5 . In the final step, the intermetallic microjoints were protected by the same capillary underfill. After assembly, the Joint Electron Devices Engineering Council preconditioning test was used to screen the test vehicles for reliability assessment, and then a temperature cycling test was performed to predict the lifespan of the microjoints. The test results showed that the microjoints formed by SLID bonding provided a superior reliability performance to those assembled by reflow. The fracture of the microjoints was caused by the volume contraction induced by the growth of Cu 6 Sn 5 , but the failure mechanisms of those two microjoints were quite different.
Type
journal article
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