Microwire Connection via Indium Cap and Spring Strain Relief
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Solution Overview
Problem
Existing methods for making connections to microwires, particularly those with a low melting point metal core and a higher melting point polymer sheath, face challenges such as damage to the polymer sheath and inferior conductivity, which are critical issues for flexible electronic devices like wearable fabrics, where reliability and durability are essential without introducing 'hard points' that can cause wire failure.
Innovation Solution
A method involving dipping the microwire tip into a bath of molten indium to form a cap that encapsulates the conductor while preserving the polymer sheath, combined with using a varying-pitch coil spring for strain relief and secure connections, ensuring flexibility and durability by avoiding 'hard points' during bending.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the polymer sheath is removed to make connection to the metal core, then electrical connection can be established, but the wire strength is reduced because the polymer sheath is the principal strength-providing component
Solution Approach 1:
A varying-pitch coil spring is introduced as an intermediary component between the microwire and external connections. The spring makes contact with the metal core through the intact polymer sheath, eliminating the need to remove the sheath for electrical connection while maintaining wire strength. The spring acts as a mediator that enables electrical connectivity without compromising the structural integrity provided by the polymer sheath.
2Reliability
If a rigid connection method is used to establish electrical connection, then connection reliability is improved, but flexibility is reduced creating 'hard points' that can cause wire failure during bending
Solution Approach 1:
The connection system is made dynamic by introducing a varying-pitch coil spring instead of a rigid connector. The spring can compress and extend, allowing the connection to adapt to bending and flexing movements. This dynamic structure eliminates hard points while maintaining reliable electrical connection, enabling the microwire to be used in flexible electronic devices that require repeated bending without failure.
3Ease of manufacture
If the polymer sheath is removed using heat or mechanical methods, then access to the metal core is achieved, but the metal core is damaged because the polymer melts at a higher temperature than the metal
Solution Approach 1:
The varying-pitch coil spring serves as an intermediary that enables electrical connection without requiring removal of the polymer sheath. By making contact through the sheath, the spring eliminates the need for heat or mechanical removal methods that would damage the low-melting-point metal core, thus preserving the integrity of both the polymer sheath and metal core.
4Reliability
If a micro-pin system is used to puncture through the polymer coating, then connection to the metal core is achieved, but the polymer sheath is damaged reducing wire strength
Solution Approach 1:
The varying-pitch coil spring acts as an intermediary component that establishes electrical connection without puncturing or damaging the polymer sheath. The spring's flexible structure allows it to make contact with the metal core through the intact sheath, eliminating the need for micro-pins that would compromise the sheath's strength-providing structure.
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 creates a reliable, durable, and highly conductive connection that maintains the microwire's strength and flexibility, preventing premature failure due to bending and ensuring effective electrical conductivity.
Implementation Method 1
dipping the microwire tip into a bath of molten indium to form a cap that encapsulates the conductor while preserving the polymer sheath
Implementation Method 2
dipping the micrawire tip into a bath of molten indium, such that the metal at the end of the conductor is remelted by contact with the indium in the bath
Data Source
AI summary
Connections can be made to microwires comprising a conductor of a lower melting point metal (e.g., indium 290) in a sheath of higher melting point polymer (e.g., PETG) by placing a small diameter spring, slightly larger in inside diameter than the outer diameter of the microwire, and of a readily solderable material over the distal end of the microwire. The conductor of the microwire is then soldered to the distal end of the spring in any of several ways that result in a solid member at the distal end of the microwire. The flexible spring provides a flexible support for the microwire, so that as the microwire flexes in use, the spring provides a strain relief; that is, the proximal portion of the spring flexes along with the microwire, so that the microwire bends over some distance rather than at a single point.