Currently, various illumination devices using light emitting diodes (hereinafter, called LEDs) are being in practical use. In particular, LED devices that are mainly practically used today typically have the following structures. A configuration has a structure, in which three-color light emitting elements that emit light of colors being close to the three primary colors of light are installed on a single light-emitting-element mount substrate, and a front surface is covered with protection light-transmissive sealing resin. Also, another configuration has a structure, in which a blue or near-ultraviolet light emitting element is installed on a light-emitting-element mount substrate, and the light emitting element is covered with sealing resin containing a fluorescent substance or a phosphorescent substance.
With each of the structures, the light emitting element being an LED element is mounted on the light-emitting-element mount substrate and the light emitting element is covered with the resin. A configuration generally has one of structures shown in FIG. 1. FIGS. 1(A), 1(B), and 1(C) are side sectional views showing representative structure examples of conventional LED devices.
An LED device 10PA in FIG. 1(A) includes a light emitting element 900 and a light-emitting-element mount substrate 100PA. The light-emitting-element mount substrate 100PA includes a box-shaped substrate body 101PA having a recess formed of a bottom plate and side walls extending along the outer circumference of the bottom plate. The substrate body 101PA is made of insulating ceramic. Mounting electrodes 102P for mounting the light emitting element 900 are formed on a surface at a recess side of the bottom plate of the substrate body 101PA. External-connection electrodes 103P are formed on a surface at a side opposite to the recess side of the bottom plate of the substrate body 101PA. Via electrodes 104P are formed in the bottom plate of the substrate body 101PA. The via electrodes 104P electrically connect the mounting electrodes 102P with the external-connection electrodes 103P. The substrate body 101PA, the mounting electrodes 102P, the external-connection electrodes 103P, and the via electrodes 104P form the light-emitting-element mount substrate 100PA. The light emitting element 900 is arranged inside the recess of the substrate body 101PA and is mounted on the mounting electrodes 102P. The recess is filled with sealing resin 901. Hence, the light emitting element 900 is covered with the sealing resin 901.
An LED device 10PB in FIG. 1(B) includes a light emitting element 900 and a light-emitting-element mount substrate 100PB. The light-emitting-element mount substrate 100PB includes a flat-plate-shaped substrate body 101PB. Mounting electrodes 102P for mounting the light emitting element 900 are formed on a front surface of the substrate body 101PB. External-connection electrodes 103P are formed on a back surface of the substrate body 101PB. Via electrodes 104P are formed in the substrate body 101PB. The via electrodes 104P electrically connect the mounting electrodes 102P with the external-connection electrodes 103P. The substrate body 101PB, the mounting electrodes 102P, the external-connection electrodes 103P, and the via electrodes 104P form the light-emitting-element mount substrate 100PB. The light emitting element 900 is arranged on the front surface of the substrate body 101PB and is mounted on the mounting electrodes 102P. Sealing resin 901 is provided on a front surface of the light-emitting-element mount substrate 100PB so that the light emitting element 900 is covered with the sealing resin 901.
An LED device 10PC in FIG. 1(C) includes a light emitting element 900 and a light-emitting-element mount substrate 100PC. The light-emitting-element mount substrate 100PC includes a box-shaped substrate body 101PC having a recess formed of a bottom plate and side walls extending along the outer circumference of the bottom plate. The substrate body 101PC is made of heat-resisting resin. Mounting electrodes 102PC for mounting the light emitting element 900 are arranged on the bottom plate of the substrate body 101PC. The mounting electrodes 102PC are exposed from a surface at a recess side and a surface at a side opposite to the recess side. The substrate body 101PC and the mounting electrodes 102PC form the light-emitting-element mount substrate 100PC. The light emitting element 900 is arranged inside the recess of the substrate body 101PC and is mounted on the mounting electrodes 102PC. The recess is filled with sealing resin 901. Hence, the light emitting element 900 is covered with the sealing resin 901.
With each of the LED devices, heat generated by the light emitting element has to be efficiently released to an external circuit board. To attain this, in Japanese Unexamined Patent Application Publication No. 2003-197972 (Patent Document 1), a silicon semiconductor substrate or a metal substrate having a good heat release property is used for a substrate body of a light-emitting-diode mount substrate.
Also, to prevent electrostatic destruction of a light emitting element, there is an LED device including an ESD protection element. For example, in Japanese Unexamined Patent Application Publication No. 2001-15815 (Patent Document 2), a substrate body of a light-emitting-element mount substrate is formed of a semiconductor substrate, and an ESD protection element is formed in the semiconductor substrate. In the LED device descried in Patent Document 1, if a low-resistance silicon substrate is used for the substrate body of the light-emitting-element mount substrate, mounting electrodes, with which two terminals of a light emitting element are connected, have to be insulated. Hence, the low-resistance silicon substrate has to be electrically isolated in two regions. Hence, in Patent Document 1, an insulating layer for insulating and isolation is formed in a straight-line shape near a center portion of the low-resistance silicon substrate. To be more specific, for example, an insulating layer made of a silicon oxide layer is formed at the low-resistance silicon substrate.