FIG. 16 is a perspective view of conventional coil device 1. FIGS. 17 and 18 are sectional views of coil device 1. Coil device 1 includes winding 3, package 2A for sealing winding 3, and external terminals 4A electrically connected to winding 3. Respective portions of external terminals 4A are exposed to the outside of package 2A.
In coil device 1, upon having a current supplied, winding 3 generates magnetic flux 5, which may leak outside package 2A, i.e., coil device 1 while being emitted from winding 3. In the case that coil device 1 is mounted with other devices highly-densely, effects of coil device 1 on the devices are considered. Patent Documents 1 and 2 disclose conventional coil devices preventing the leakage of magnetic flux.
Package 2A may be made of magnetic material to reduce the effects. In order to increase the reduction of the leakage of the magnetic flux with the magnetic material, package 2A is generally made of magnetic material having a high magnetic permeability, has a large size, or includes shields 6A having a magnetic shielding effect.
These approaches, however, have the following problems. Package 2A made of the magnetic material having the high magnetic permeability can hardly be molded, thus having its cost increase. More specifically, package 2A can hardly be molded with a high-pressure pressing machine, which increases the density of the magnetic material of package 2A. In addition, the magnetic material having the high magnetic permeability containing amorphous magnetic powder or Ni is expensive. Package 2A having a large size increases the size of coil device 1, and accordingly causes other devices to be arranged less densely. Further, shields 6A attached to package 2A causes energy loss due to eddy currents generated in shields 6A and increases material cost.
Patent Document 1: JP 2003-168610A
Patent Document 2: JP 2004-266120A