Contents of the fillers in the silicone-resin layer 4 may be obtained by the following method. In the first place, the silicone-resin layer 4 is cut, and then is polished by using a Cross section polisher (CP) to obtain a polished surface. Next, by using an Energy Dispersive x-ray Spectroscopy (EDS) attached to a Scanning Electron Microscope (SEM), contents of components composing the silicone-resin layer 4 are measured. Or, the silicone-resin layer 4 is scraped off, and contents of components composing the silicone-resin layer 4 are measured by using an Inductively Coupled Plasma spectrometer (ICP) or an X-ray fluorescence spectrometer (XRF). When a total content of a silicon dioxide, a potassium titanate, an aluminum oxide, a silicon dioxide, a barium oxide, a barium sulfate, a zinc oxide, a titanium dioxide, a barium titanate, and a zirconium oxide, which compose the above-mentioned filler, is computed, the computed content is a content of the filler.