Nanowire Package Structure for Low-Temperature Cu-to-Cu Bonding
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Solution Overview
Problem
Existing Cu-to-Cu bonding processes using nanowires face issues such as delamination of thick aluminum foils, structural integrity loss due to strong acids, and reduced pillar diameter and pitch, leading to unreliable electrical connections and high bonding temperatures.
Innovation Solution
A package structure with conductive elements and nanowires formed on a temporary carrier, using a reflowable bonding layer to transfer nanowires onto conductive pillars, forming intermetallic compounds for improved bonding strength and allowing low-temperature metal-metal bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If thick aluminum foil is used as AAO template, then nanowire formation is enabled, but delamination from substrate occurs
Solution Approach 1:
The patent divides the bonding structure into multiple functional layers: a thin AAO template layer (50-200 nm) for nanowire formation, a separate conductive pillar structure for electrical connection, and a bonding layer for attachment. This segmentation allows each layer to be optimized independently - the thin template avoids delamination while still enabling nanowire growth through its porous structure.
Solution Approach 2:
The patent introduces a conductive pillar structure as an intermediary between the substrate and the nanowire bonding interface. These pillars serve as both mechanical support and electrical conductors, eliminating the need for thick aluminum foil that would otherwise be required for both structural and conductive functions, thereby preventing delamination.
2Manufacturing precision
If strong acid is used for AAO template fabrication, then porous structure is achieved, but structural integrity is compromised
Solution Approach 1:
The patent uses an ultra-thin AAO template (50-200 nm) as a flexible sacrificial layer that can be fully removed after nanowire formation. This thin-film approach allows strong acid to create the necessary porous structure without compromising the underlying substrate, as the template itself is thin enough to be completely etched away without leaving residual damage.
Solution Approach 2:
The AAO template is designed as a temporary sacrificial structure that is completely removed after serving its purpose of guiding nanowire formation. The strong acid etching process that creates the porous template also enables its complete removal, leaving no harmful residues and restoring the substrate to its original structural integrity.
3Manufacturing precision
If nanowires are directly formed on conductive pillars, then fine-pitch integration is achieved, but bonding temperature remains high
Solution Approach 1:
The patent introduces a bonding layer as an intermediary between the conductive pillars and the nanowires. This bonding layer (containing materials like Cu, Ag, or Sn) enables low-temperature bonding by forming intermetallic compounds with the nanowires at temperatures below 200°C, while the conductive pillars maintain their fine-pitch configuration for high-density integration.
Solution Approach 2:
The patent changes the material composition and thermal properties of the bonding interface by introducing a bonding layer with lower melting point materials. This parameter change allows the bonding process to occur at reduced temperatures (below 200°C) while maintaining the fine-pitch geometry established by the conductive pillars, thus decoupling pitch precision from bonding temperature requirements.
4Manufacturing precision
If photoresist and AAO template are removed after nanowire formation, then clean bonding surface is achieved, but electrical connection reliability decreases
Solution Approach 1:
The patent introduces a conductive bonding layer as a permanent intermediary that remains after photoresist and AAO template removal. This bonding layer serves dual functions: it provides a clean bonding surface for nanowire attachment and maintains electrical connection reliability by forming conductive intermetallic compounds, thus replacing the temporary protective role of the template with a permanently functional conductive layer.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution achieves reliable electrical connections with reduced voids and improved structural integrity, enabling small pitch and low-temperature bonding, enhancing the reliability and efficiency of the bonding process.
Implementation Method 1
a plurality of wires having a surface area through which heat of the conductive element can be dissipated, lowering a bonding temperature of the conductive element
Implementation Method 2
a conductive layer disposed between the conductive element of the substrate and the plurality of wires
Implementation Method 3
forming intermetallic compounds for improved bonding strength
Data Source
AI summary
A package structure is disclosed. The package structure includes a substrate including a conductive element and a plurality of wires having a surface area through which heat of the conductive element can be dissipated, lowering a bonding temperature of the conductive element. The package structure also includes a conductive layer disposed between the conductive element of the substrate and the plurality of wires. The conductive contact layer attaches the plurality of wires over the conductive element.