Multilayer Coil Component Surface Grain Control
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Solution Overview
Problem
Multilayer coil components face issues with ferrite crystal grains falling off due to low sinterability, leading to deteriorated magnetic characteristics and residual stress, which can be exacerbated by the presence of insulating materials on the surface.
Innovation Solution
A multilayer coil component with a ferrite sintered body and internal conductors, where the surface is covered with an insulating layer made of glass, ensuring the insulating material is not present among the crystal grains, thereby preventing stress and ferrite grain loss, and maintaining higher sinterability and density between conductors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the sinterability of the ferrite crystal grains is decreased to relax residual stress, then the magnetic characteristics are improved, but the ferrite crystal grains are likely to fall off from the element body
Solution Approach 1:
The patent applies different sinterability characteristics to different regions of the element body. The surface region has lower sinterability to prevent crystal grain fall-off, while the internal region maintains higher sinterability for overall structural integrity. This is achieved by controlling the green sheet composition and sintering conditions to create a gradient in crystal grain growth characteristics between the surface and internal regions.
2Strength
If the average crystal grain size in the surface region is made small to prevent crystal grain fall-off, then the adhesiveness is improved, but the sintered density may be reduced
Solution Approach 1:
The patent creates a local quality difference in crystal grain size between surface and internal regions. The surface region maintains smaller crystal grain sizes (0.5-2.0 μm) to prevent fall-off, while the internal region allows larger crystal grain growth for density. This is achieved through controlled sintering conditions and green sheet composition that favor different grain growth rates at different depths.
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 solution effectively suppresses the deterioration of magnetic characteristics and secures the strength of the element body by maintaining a smaller average crystal grain size on the surface and higher density between conductors, while the insulating layer's through holes absorb stress, preventing damage.
Implementation Method 1
A surface of the element body is covered with a layer made of an insulating material. The insulating material is not present among the crystal grains in the surface region of the element body.
Implementation Method 2
In the layer made of an insulating material, there may be formed through holes. In which case, the through holes in the layer made of an insulating material absorb stress acting on the layer made of an insulating material.
Implementation Method 3
The green sheets in which the conductor patterns are formed and the green sheets in which no conductor patterns are formed are laminated in an intended order. Through these processes, a laminated body of green sheets is obtained. After that, the obtained laminated body of green sheets is cut into a plurality of chips of a predetermined size. The obtained chips are fired to obtain element bodies.
Data Source
AI summary
A multilayer coil component includes an element body made of a ferrite sintered body and a coil. The coil is configured with a plurality of internal conductors juxtaposed in the element body and electrically connected to one another. An average crystal grain size in a surface region of the element body is smaller than an average crystal grain size in a region between the internal conductors in the element body. A surface of the element body is covered with a layer made of an insulating material. The insulating material is not present among the crystal grains in the surface region of the element body.