Bump bonding hybridization techniques use arrays of indium bumps to electrically and mechanically join two chips together. Surface-tension issues limit bump sizes to roughly as wide as they are high. Pitches are limited to 50 microns with bumps only 8–14 microns high on each wafer. A new process uses oriented carbon nanotubes (CNTs) with a metal (indium) in a wicking process using capillary actions to increase the aspect ratio and pitch density of the connections for bump bonding hybridizations. It merges the properties of the CNTs and the metal bumps, providing enhanced material performance parameters.
By merging the bumps with narrow and long CNTs oriented in the vertical direction, higher aspect ratios can be obtained if the metal can be made to wick. Possible aspect ratios increase from 1:1 to 20:1 for most applications, and to 100:1 for some applications. Possible pitch density increases of a factor of 10 are possible.
Standard capillary theory would not normally allow indium or most other metals to be drawn into the oriented CNTs, because they are non-wetting. However, capillary action can be induced through the ability to fabricate oriented CNT bundles to desired spacings, and the use of deposition techniques and temperature to control the size and mobility of the liquid metal streams and associated reservoirs.
This hybridization of two technologies (indium bumps and CNTs) may also provide for some additional benefits such as improved thermal management and possible current density increases.
This work was done by James L. Lamb, Matthew R. Dickie, Robert S. Kowalczyk, and Anna Liao of Caltech; and Michael J. Bronikowski of Atomate Corporation for NASA’s Jet Propulsion Laboratory. NPO-46592
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Bump Bonding Using Metal-Coated Carbon Nanotubes
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Overview
The document titled "Bump Bonding Using Metal-Coated Carbon Nanotubes" from NASA's Jet Propulsion Laboratory outlines significant advancements in hybrid bonding techniques utilizing carbon nanotubes (CNTs) and metal coatings, specifically Indium. The research focuses on improving bump bonding methods, which are crucial for electrically and mechanically joining semiconductor chips.
The document details a series of experiments aimed at enhancing the growth and application of CNTs in bump bonding. The initial experiments involved varying pitch densities and the use of Indium in vapor phase to achieve microscopic particles. While some experiments faced challenges, such as insufficient adatom mobility, subsequent attempts led to successful results. Notably, a fourth experiment achieved effective coating of CNT bundles with Indium, demonstrating the potential of a metal "wicking" process that allows for better integration of CNTs in hybrid devices.
The significance of these results lies in the ability to increase the aspect ratio of bumps, which can address limitations in current bump bonding technologies. Traditional methods face challenges with surface tension and alignment, restricting bump sizes and pitches. The use of CNTs, which can be grown to considerable lengths, offers a solution to these issues, enabling higher density contacts and improved thermal management. This advancement is particularly relevant as the size of chip applications continues to shrink, necessitating more efficient bonding techniques.
The document also highlights the potential benefits of combining CNTs with Indium, including enhanced bond strength and improved interface bonding for CNT field emitters. The research indicates that this hybridization could lead to better performance in various applications, including optical interfaces for analog electronic neural networks.
Two new technology reports were filed as a result of this research, focusing on the enhancement of bump bonding through the use of oriented CNTs and the metal wicking process. The document acknowledges contributions from key individuals involved in the research and emphasizes the broader implications of these findings for aerospace and other technological fields.
In summary, this document presents a promising approach to improving bump bonding techniques through the innovative use of carbon nanotubes and metal coatings, paving the way for advancements in semiconductor technology and related applications.
