Appeal No. 1997-2046 Page 3
Application No. 08/059,350
The inventive planar inductor has a spiral coil,
insulating layers stacked on both surfaces of the spiral coil,
and ferromagnetic layers stacked on the insulating layers.
Each ferromagnetic layer has a saturation magnetization (4BM )
s
of at least 10 kG and a thickness no greater than 100 Fm. DC
superposition characteristics are improved such that the
inventive planar inductor can be effectively applied to a DC-
to-DC converter. Each ferromagnetic layer is two
dimensionally divided into a plurality of portions. Such
division decreases high-frequency, thereby improving the
efficiency of the applied DC-to-DC converter.
When the inventive planar inductor is used in practice, a
relaxation layer for contraction of a mold resin is formed on
a surface of each ferromagnetic layer. Such formation relaxes
contraction generated when the mold resin is hardened and
contracted. Such relaxation prevents transmission of the
contraction to each ferromagnetic layer, which prevents
reduction in inductance due to an inverse magnetostrictive
effect.
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