Undercooled Core-Shell Metal Particles for Low-Temperature Microscale Joining
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Solution Overview
Problem
Current joining and repair techniques for metallic components, especially at the microscale, face challenges such as high costs, inefficiencies, and the need for specialized conditions, making them unsuitable for large-scale manufacturing and miniaturization, and there is a need for energy-efficient methods that can operate at low temperatures to accommodate temperature-sensitive components.
Innovation Solution
The use of undercooled metallic core-shell particles with a stable liquid metallic core encapsulated in an oxide or organic shell, which can be ruptured to form a metallurgical bond at ambient conditions without heating, using mechanical stress or chemical etching to initiate alloying and solidification, allowing for joining or repairing of non-particulate components like metallic films and wires.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If conventional joining techniques like soldering and welding are used, then bulk materials can be joined, but they cannot be adopted to smaller sizes at the microscale and smaller
Solution Approach 1:
The invention divides the joining process into discrete microscale particles that can be individually positioned and applied to small components. The core-shell particle structure allows each particle to function as an independent joining unit, enabling microscale and nanoscale assembly operations.
Solution Approach 2:
The invention changes the physical state parameter of the metal from solid to liquid by using undercooled liquid metal cores within the particles. This parameter change enables the metal to flow and bond at lower temperatures, making it suitable for microscale joining where heat input must be minimized.
2Object-affected harmful factors
If lead-free solders are used to address environmental concerns, then health and environmental issues are resolved, but higher processing temperatures (>450 K) are required which limits use and increases cost
Solution Approach 1:
The invention changes the temperature parameter by using undercooled liquid metal particles that remain liquid below their melting point. This allows lead-free soldering to occur at lower temperatures than conventional lead-free solders, reducing thermal stress on components and expanding application possibilities.
Solution Approach 2:
The invention uses composite core-shell particles where the core contains the lead-free metal alloy and the shell provides protective and functional properties. This composite structure enables the lead-free metal to be handled and applied at lower temperatures while maintaining its beneficial environmental properties.
3Strength
If conventional joining methods are used for temperature sensitive components, then joining can be achieved, but high processing temperatures damage components like LEDs and polymer substrates
Solution Approach 1:
The invention changes the temperature parameter by utilizing undercooled liquid metal particles that enable bonding at ambient or near-ambient temperatures. This parameter change preserves the integrity of temperature-sensitive components while achieving strong metallurgical bonds.
Solution Approach 2:
The invention replaces thermal energy input with mechanical energy for shell rupture and bonding initiation. By using mechanical stress to rupture the shell and initiate metal flow, the process eliminates the need for high temperature heating, making it suitable for temperature-sensitive components.
4Temperature
If undercooled liquid metal particles are used for joining, then low temperature joining is enabled, but the particles must be stabilized against solidification at ambient conditions
Solution Approach 1:
The invention uses composite core-shell particles where the shell material is specifically selected to be immiscible with the liquid metal core and to provide stabilizing effects. This composite structure allows the undercooled liquid metal to remain stable at ambient conditions without solidifying, enabling storage and handling of the particles before use.
Solution Approach 2:
The shell acts as an intermediary layer between the undercooled liquid metal core and the ambient environment. This intermediary shell prevents nucleation and solidification of the core metal at ambient temperatures, while still allowing controlled rupture and metal release when needed for joining.
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 method enables efficient, low-cost joining and repair of metallic components at ambient temperatures without the need for heating or specialized equipment, facilitating the use of lead-free solders and reducing energy consumption, while maintaining the stability of undercooled particles for high-yield production.
Implementation Method 1
undercooled of a liquid metal or alloy below its freezing point without it becoming solid
Implementation Method 2
encapsulated inside an outer shell, which can comprise an oxide or other stabilizer shell
Implementation Method 3
the outer shells of the undercooled core-shell particles is ruptured to release the undercooled liquid metallic material of the cores
Implementation Method 4
initiates a cascade of metallic liquid flow from the particle cores with concomitant deformation, combination/alloying, shaping, and, solidification
Implementation Method 5
release the undercooled liquid metallic material of the cores to contact the components and solidify to produce a metallurgical joint
Implementation Method 6
produce a metallurgical joint between the components
Data Source
Figure 1A~1B
Figure 1C~1D
Figure 2A~2B
AI summary
Undercooled liquid metallic core-shell particles, whose core is stable against solidification at ambient conditions, i.e. under near ambient temperature and pressure conditions, are used to join or repair metallic non-particulate components. The undercooled-shell particles in the form of nano-size or micro-size particles comprise an undercooled stable liquid metallic core encapsulated inside an outer shell, which can comprise an oxide or other stabilizer shell typically formed in-situ on the undercooled liquid metallic core. The shell is ruptured to release the liquid phase core material to join or repair a component(s).