Surface-Mount Inductor Terminal Plating for Thermal Shock Bonding
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Solution Overview
Problem
Conventional surface-mount inductors face issues with high initial resistance and unstable bonding between the conductive wire and external terminals due to weak bonding strength, leading to peeling off under thermal shock, and high manufacturing costs due to the use of expensive metal fine particles.
Innovation Solution
A surface-mount inductor design with external terminals comprising a first plating layer over metal magnetic powder exposed portions and a conductive paste layer formed on the plating layer, ensuring strong bonding and improved connection reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conductive paste containing metal fine particles with particle diameter smaller than 100 nm is used, then initial resistance of bonding portion is improved, but bonding strength between molded body and external terminal becomes weak causing peeling off under thermal shock
Solution Approach 1:
The patent changes the particle size parameter of metal particles in conductive paste from fine particles (diameter < 100 nm) to granular particles (diameter 1 µm to 10 µm). This parameter change resolves the contradiction by providing sufficient bonding strength while maintaining acceptable initial resistance, as the larger granular particles create stronger mechanical bonding between the molded body and external terminal.
Solution Approach 2:
The patent uses a composite material approach by combining granular metal particles (1 µm to 10 µm) with resin to form conductive paste. This composite structure provides both the bonding strength from the granular particles and the conductive properties, resolving the contradiction between initial resistance and bonding strength.
2Manufacturing precision
If a conductive paste containing metal fine particles with particle diameter smaller than 100 nm is used, then initial resistance of bonding portion is improved, but manufacturing cost increases
Solution Approach 1:
The patent replaces expensive metal fine particles (diameter < 100 nm) with cheaper granular metal particles (diameter 1 µm to 10 µm). This substitution significantly reduces manufacturing cost while still achieving acceptable initial resistance through the sintering process, thus resolving the cost contradiction.
Solution Approach 2:
The patent changes the particle size parameter from fine particles to granular particles, which not only reduces material cost but also simplifies the manufacturing process. The larger granular particles are easier to handle, disperse, and sinter, thereby reducing overall manufacturing costs while maintaining functional performance.
3Ease of manufacture
If conventional conductive paste with thermosetting resin is used, then manufacturing process is simple, but bonding strength between conductive wire and external terminal is weak
Solution Approach 1:
The patent changes the particle size parameter of metal particles in the conductive paste from fine to granular (1 µm to 10 µm). This parameter change enhances bonding strength through better mechanical interlocking and sintering characteristics, while the thermosetting resin component maintains the simple manufacturing process, thus resolving the contradiction between ease of manufacture and bonding strength.
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 design provides enhanced bonding strength and connection reliability, preventing peeling off under thermal stress while reducing manufacturing costs by optimizing the use of conductive paste.
Implementation Method 1
an external terminal formed over an exposed surface of each of the lead-out end parts and a metal magnetic powder exposed portion formed at least around the exposed surface. The external terminal at least includes a first plating layer formed over the metal magnetic powder exposed portion and the exposed surface of the lead-out end part
Implementation Method 2
a conductive paste layer formed on the first plating layer and made of a solidified conductive paste
Implementation Method 3
The conductive paste is made conductive by bringing metal particles dispersed in the resin into contact with each other, or with a conductive wire, by utilizing a contraction stress due to curing of the thermosetting resin.
Data Source
AI summary
A surface-mount inductor comprises a molded body containing a metal magnetic powder; at least one coil buried in the molded body such that lead-out end parts at both ends of the coil are at least partially exposed on a surface of the molded body; and an external terminal formed over an exposed surface of each of the lead-out end parts. A metal magnetic powder exposed portion is formed at least around the exposed surface. The external terminal at least includes a first plating layer formed over the metal magnetic powder exposed portion and the exposed surface of the lead-out end part, and a conductive paste layer formed on the first plating layer and made of a solidified conductive paste. Consequently, the surface mount inductor comprises an external terminal having high connection reliability.