| 摘要 |
PROBLEM TO BE SOLVED: To prevent external light form being transmitted through a substrate and to raise the quality of a read image, which is obtained by an image sensor, by a method wherein light-receiving elements are mounted on the surface of the substrate and the whole rear or one part of the rear of the substrate is covered with a light- shielding layer consisting of black pigments. SOLUTION: A substrate 6 is a plate-shaped ceramic main body 60 and is fitted into a recessed part 49 provided on the bottom of a case 4. A light-shielding layer 61 under the substrate 6 is formed into an outer surface facing downward and at the same time, an LED light source 2 and a plurality of light-receiving elements 52 are respectively installed in the case 4. The original color of the main body 60 is white. The layer 61 is a black glass obtainable by a method wherein the mixture obtainable by making two kinds of black pigments mix in a glass paste is applied on the rear of the main body 60 to calcine the main body 60. The two kinds of the black pigments are an Fe-Cr-Co pigment and a Cu-Cr pigment, the compounding ratio of the Fe-Cr-Co pigment to the Cu-Cr pigment is about 5:4 in weight ratio and the thicknesses of the pigments are 8 to 20 μm or thereabouts. Such the layer 61 has characteristics to shield light of a wide wavelength range of an ultraviolet range, a visible range and an infrared range. |
