Inductance element
An inductance element includes a magnetic core and a coil having a portion embedded in the magnetic core. This portion includes a wound portion formed by winging a wire-shaped coil material including a wire-shaped conductive material and an insulating coating. The insulating coating includes a thin-walled portion reduced in thickness. A biting ratio R is defined by formula: R=ds/B, which is from 0.4 to 0.85 inclusive, where B is the average thickness of inter-coil insulating coatings, and ds is an upper biting limit obtained by measuring a biting depth, approximating a frequency distribution of the results by a normal distribution, and computing, as the upper biting limit, the sum of the mean da of the normal distribution and the product of 3.99 and the standard deviation σ. The biting depth is obtained by subtracting, from the average thickness B, the thickness of the thin-walled portion.
1. An inductance element comprising:
a magnetic core that is a compact containing a magnetic powder; and
a coil having an embedded portion embedded in the magnetic core, the embedded portion including:
a wound portion formed by winding a coil wire which includes a wire-shaped conductor and an insulation coating covering a surface of the conductor
wherein the insulation coating of the wound portion has a contact region in which portion of the insulation coating is in contact with the magnetic powder, the insulation coating in the contact region including a thin-walled portion having a reduced thickness due to the contact with the magnetic powder, and
wherein the thin-walled portion has a biting ratio R from 0.4 to 0.85 inclusive, the biting ratio R being defined by the following formula (I):
R=ds/B (I)
where B is an average thickness (unit: μm) of inter-coil insulation coatings which are portions of the insulation coating located between two adjacent parts of the conductor in the wound portion, the average thickness being an arithmetic mean of measured thicknesses obtained by measuring the thickness of the inter-coil insulation coatings at at least 100 points, and ds is a maximum biting amount (unit: μm) expressed by (da+3.99σ),
wherein da is a mean of a normal distribution that approximates a frequency distribution of a biting depth d (unit: μm) measured at at least 15 points in the inductance element, the biting depth d being obtained by subtracting the thickness of the thin-walled portion smaller than the average thickness B from the average thickness B, and σ is a standard deviation of the normal distribution.
2. The inductance element according to claim 1 ,
wherein the average thickness B of the inter-coil insulation coatings is from 1 μm to 5 μm inclusive.
3. The inductance element according to claim 1 ,
wherein at least part of the magnetic powder is made of an amorphous alloy material.
4. The inductance element according to claim 1 ,
wherein the magnetic powder has a median diameter D50 of 1 μm to 15 μm inclusive.
5. The inductance element according to claim 1 ,
wherein the insulation coating contains a polyimide-based material.
6. The inductance element according to claim 1 ,
wherein the conductor has a rectangular cross-section, and the wound portion is formed by edgewise winding of the coil wire.
7. The inductance element according to claim 6 ,
wherein the thickness of the thin-walled portions is measured at an end of the wound portion in a direction along a winding center line.
8. The inductance element according to claim 1 ,
wherein the inductance element includes a portion having an embedded depth equal to or less than 0.25 mm, the embedded depth being an amount of the coil wire embedded into the magnetic core in a direction along a winding center line of the wound portion.