Coil Terminal Electrode Fillet for Strong Thermocompression Bonding
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Solution Overview
Problem
Existing thermocompression bonding techniques for connecting wire terminals to terminal electrodes in coil components often result in core damage, wire disconnection, peeling of terminal electrodes, and insufficient bonding, especially under high-load reliability test conditions.
Innovation Solution
The coil component incorporates a fillet surface on the outer surface of the terminal electrode, which rises from the main surface toward the top surface of the wire, forming a concave curved surface. This design ensures appropriate thermocompression bonding conditions without excess or deficiency, enhancing the bonding area and reducing stress concentration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the thermocompression bonding condition is tightened to improve bonding strength, then the bonding area between wire terminal and terminal electrode is increased, but the core, winding core portion, or wire terminal may be damaged and the solder wettable layer may scatter
Solution Approach 1:
The patent applies local quality by creating a fillet surface with different geometric properties at the terminal electrode. The fillet surface has a specific curvature radius (R1) that is larger than the curvature radius (R2) of the wire terminal, creating a localized stress distribution pattern that concentrates bonding pressure on the wire terminal while protecting the core and solder wettable layer from damage.
Solution Approach 2:
The patent employs curvature principles by designing the fillet surface with a specific curvature radius (R1) that is larger than the curvature radius (R2) of the wire terminal. This curvature difference creates a stress distribution pattern during thermocompression bonding that enhances bonding strength while preventing damage to surrounding components and scattering of the solder wettable layer.
2Object-affected harmful factors
If the thermocompression bonding condition is loosened to avoid damage, then core damage and layer scattering are prevented, but the bonding area and fixing force are insufficient
Solution Approach 1:
The fillet surface creates a localized stress concentration zone with specific geometric properties. The larger curvature radius (R1) of the fillet surface compared to the wire terminal curvature radius (R2) creates a stress distribution pattern that protects the core while maintaining sufficient bonding pressure on the wire terminal, thus preventing damage while ensuring adequate fixing force.
Solution Approach 2:
By designing the fillet surface with a curvature radius (R1) larger than the wire terminal curvature radius (R2), the patent creates a geometric configuration that naturally distributes stress during bonding. This curvature relationship allows the bonding process to proceed without excessive force that would cause damage, while still achieving sufficient bonding area and fixing force through the optimized stress distribution.
3Reliability
If the wire terminal is pressed to be substantially flush with the terminal electrode surface, then bonding reliability is improved, but the core or wire terminal cannot withstand the pressure and may be damaged
Solution Approach 1:
The fillet surface creates a localized stress distribution pattern where the larger curvature radius (R1) distributes bonding pressure over a broader area compared to the wire terminal curvature radius (R2). This local geometric difference allows the wire terminal to be pressed flush with the terminal electrode surface, achieving high bonding reliability, while the stress distribution prevents damage to the core and wire terminal.
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 fillet surface design improves the fixing force between the terminal electrode and the wire terminal, reduces the risk of core damage and wire disconnection, and prevents destabilization of the coil component's posture during mounting.
Implementation Method 1
the terminal 8 of the wire is pushed toward the terminal electrode 4 by a heater chip... the terminal 8 of the wire is crushed so as to have a flat section, and is embedded up to a position substantially flush with the surface of the solder wettable layer 7
Data Source
AI summary
A coil component includes a terminal electrode and a terminal of a wire connected by thermocompression bonding on a bottom surface of a flange portion, to achieve a strong fixing force without the terminal of the wire protruding from the terminal electrode. A terminal of a wire extends along a main surface of a terminal electrode while at least a part of the terminal is disposed in the terminal electrode, and has a top surface positioned on a side opposite to a bottom surface side of a flange portion with respect to the main surface. A fillet surface which rises from the main surface toward the top surface and forms a concave curved surface is on an outer surface of the terminal electrode. The main surface is configured by a solder wettable layer made of tin or a tin alloy as an outermost layer of the terminal electrode.