Cold-Welded Flip Chip Interconnects for Heat-Sensitive Qubit Assembly
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Solution Overview
Problem
Current methods for quantum device assembly, such as flip chip assembly, face challenges including damage to Josephson Junctions from heating, oxidation of metal deposits, and performance degradation due to solder deformation and warpage, which affect the reliability and efficiency of electrical connections in quantum computing devices.
Innovation Solution
The use of Gold and Platinum protrusions for cold welding with Indium, Tin, Lead, and Bismuth bumps, forming conical or pyramid-shaped protrusions, which are ductile and resistant to oxidation, to create stable electrical connections without heating, thereby maintaining the integrity of quantum circuits and reducing deformation-induced performance issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional flip chip assembly with soldering is used, then electrical connections are formed, but Josephson Junctions are damaged from heating
Solution Approach 1:
The patent changes the temperature parameter from conventional soldering temperatures (typically 180-250°C) to cryogenic temperatures (below 0°C, specifically around -196°C using liquid nitrogen). This parameter change enables the use of cold welding instead of thermal soldering, thereby preventing damage to temperature-sensitive Josephson Junctions while still forming reliable electrical connections between superconducting components
Solution Approach 2:
The patent replaces the thermal-mechanical soldering process with a cryogenic mechanical cold welding process. Instead of using heat to melt solder and form joints, the invention uses cryogenic temperatures to enable direct metallic bonding through plastic deformation and diffusion at the interface, eliminating thermal damage while achieving equivalent or superior connection reliability
2Reliability
If conventional soldering is used, then electrical connections are formed, but metal deposits oxidize
Solution Approach 1:
The patent employs a cryogenic environment as an inert atmosphere that prevents oxidation of metal deposits. At cryogenic temperatures, chemical reactivity including oxidation is significantly reduced, and the cold welding process occurs rapidly enough that oxidation does not have time to degrade the metallic surfaces. This eliminates the need for complex inert gas protection systems required in conventional soldering
Solution Approach 2:
The patent performs surface preparation and alignment of mating surfaces before the cold welding process, ensuring that fresh, uncontaminated metallic surfaces are brought into contact. The rapid cooling and bonding process occurs before oxidation can significantly degrade the surfaces, effectively pre-preventing oxidation through timing and environmental control
3Reliability
If solder bumps are used for connection, then electrical connections are formed, but deformation and warpage cause performance degradation
Solution Approach 1:
The patent changes the material state parameter from room-temperature solder bumps to cryogenic-temperature cold-welded protrusions. This parameter change eliminates the melting and solidification cycle that causes deformation and warpage. The cold welding process maintains materials in a solid state throughout bonding, preventing thermal expansion, contraction, and phase-change-induced distortion that plague conventional soldering
Solution Approach 2:
The patent designs the cold welding process to be self-aligning and self-compensating. The plastic deformation of metallic protrusions at cryogenic temperatures naturally accommodates minor misalignments and substrate warpage without requiring precise pre-positioning or additional correction steps. The material's ductility at cold temperatures enables self-adjustment during bonding, eliminating performance degradation from deformation
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
This approach enables reliable and stable electrical connections in quantum devices by preventing damage to Josephson Junctions and maintaining desired capacitance values, enhancing the overall performance and reliability of quantum computing systems.
Implementation Method 1
The use of Gold and Platinum protrusions for cold welding with Indium, Tin, Lead, and Bismuth bumps
Implementation Method 2
forming conical or pyramid-shaped protrusions, which are ductile and resistant to oxidation
Implementation Method 3
Gold and Platinum protrusions for cold welding with Indium, Tin, Lead, and Bismuth bumps, forming conical or pyramid-shaped protrusions, which are ductile and resistant to oxidation
Data Source
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AI summary
A quantum device includes a first set of protrusions (304) formed on a substrate (302, 302A) and a second set of protrusions formed on a qubit chip (310). The quantum device also includes a set of bumps (308) formed on an interposer (306), the set of bumps formed of a material having above a threshold ductility at a room temperature range, wherein a first subset of the set of bumps is configured to cold weld to the first set of protrusions and a second subset of the set of bumps is configured to cold weld to the second set of protrusions.