Ultrasonic Wire Bonding Tapered Conductor Strand Integrity
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Solution Overview
Problem
Conventional ultrasonic bonding methods for electric wires often result in strand breakage due to tensile stress generated in the middle portions of the wire, as the strands are compressed between the anvil and horn during bonding.
Innovation Solution
A bonding method where the strands of an electric wire, exposed from the sheath, are bonded ultrasonically with an anvil and horn, with a bonded portion having a smaller outer diameter than the sheathed portion, and a maximum intersection angle calculated to prevent strand breakage, ensuring the distance between the anvil/horn and sheath is shorter than the strand's primary vibration length, and the intersection angle is below a critical threshold to avoid fatigue fracture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If strands are compressed between anvil and horn during ultrasonic bonding, then bonding strength is improved, but tensile stress in middle portions causes strand breakage
Solution Approach 1:
The patent applies preliminary action by forming a tapered middle portion in advance before ultrasonic bonding. This pre-formed geometry reduces tensile stress concentration during the bonding process, preventing strand breakage while maintaining bonding strength. The tapered structure is created prior to the bonding operation to mitigate the harmful tensile stresses that will occur during compression bonding.
2Reliability
If strands are bonded ultrasonically with compression, then bonding effectiveness is improved, but intersection angle exceeds critical value causing fatigue fracture
Solution Approach 1:
The patent applies parameter changes by controlling the intersection angle θ between strands and the wire axis to be less than a critical value θa. This angular parameter is carefully selected and maintained within safe limits during the bonding process to prevent fatigue fracture while ensuring effective bonding. The critical angle θa is determined based on material properties and bonding conditions.
3Speed
If distance between anvil/horn and sheath is increased, then strand vibration amplitude is improved for bonding, but tensile stress increases causing breakage
Solution Approach 1:
The patent applies local quality by creating a tapered middle portion with varying cross-sectional area along the wire length. This localized geometric modification ensures that the distance x between the anvil/horn and sheath remains shorter than the primary vibration length L of the strands in specific critical regions. The tapered structure provides different local characteristics: a smaller cross-section in the middle portion to control vibration amplitude and reduce tensile stress, while maintaining bonding effectiveness in the bonded portion.
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 effectively prevents strand breakage during bonding by reducing tensile stress and intersection angles, ensuring the strands are not subjected to excessive stress, thereby enhancing the reliability and durability of the bonded electric wire.
Implementation Method 1
a plurality of strands constituting the conductor are bonded to each other by ultrasonic vibrating the horn in a longitudinal direction of the electric wire
Implementation Method 2
each of the strands is compressed in a bonded portion in which the strands are ultrasonically bonded to each other
Implementation Method 3
the strands positioned in a middle portion existing between the sheath and the bonded portion in the longitudinal direction are pulled (tensile stress is generated in each strand)
Data Source
Figure 1~2
Figure 3A~3C
Figure 4~6
AI summary
A bonding method for a conductor of an electric wire includes a conductor formed of a plurality of strands and a sheath covering the conductor such that the conductor is exposed to a predetermined length, the bonding method bonding the plurality of strands of the electric wire to each other. The method includes bonding the strands of the conductor exposed from the sheath to each other, the strands being spaced apart from the sheath by a predetermined length. An outer diameter of a middle portion of the conductor between a bonded portion formed by bonding the strands of the conductor to each other and a portion covered with the sheath gradually decreases toward the bonded portion from the portion of the conductor covered with the sheath. A maximum value of an intersection angle between an upper surface of the bonded portion or a longitudinal direction of the electric wire and the strands of the middle portion of the conductor is smaller than a predetermined angle. The predetermined angle is an angle at which breakage of the strands is prevented when the bonding is performed.