FIG. 11 is a cross-sectional view illustrating a conventional light-emitting apparatus in which an LTCC (low temperature co-fired ceramic) substrate is used (see Patent Literature 1). The light-emitting apparatus includes an LTCC substrate 50, silver epoxy 52, reflecting barriers 51, transparent epoxy 53, and LED dies 54. In this conventional example, light emitted by an LED die 54 is reflected by a reflecting barrier 51, whereby a reduction in loss of the emitted light is achieved. Further, heat from the LED die 54 is dissipated by the reflecting barrier 51 into a related thermal diffusion section (not shown) and the LTCC substrate 50. LTCC packaging of a light-emitting apparatus in which an LTCC substrate is used is suitable in particular to diffusing heat generated by closely-packed LED dies or LED arrays.
FIG. 12 is a cross-sectional view illustrating an LTCC chip carrier having wire bonding (see Patent Literature 2). This LTCC chip carrier has a heat spreader 67, a second LTCC layer 61, and a top LTCC layer 60 stacked in this order on a motherboard 65. The top LTCC layer 60 has a cavity in the center thereof. In the cavity, a single LED chip 4 is fixed with an adhesive or the like on a thermal via 62 formed so as to pass through the second LTCC layer 61. The LED chip 4 is connected by wire bonding via a wire 90 to a second layer terminal 64 formed on the second LTCC layer 61. The second layer terminal 64 is connected via a via 68 to a top terminal 63 formed on the top LTCC layer 60. Furthermore, the top terminal 63 is connected by wire bonding via a wire 91 to an external terminal 66 formed on the motherboard 65. The top terminal 63, the second layer terminal 64, the external terminal 66, and the heat spreader 67 are made of conductors that can be co-fired. The cavity inside the top LTCC layer 60 that contains the LED chip is sealed with epoxy resin 69 or another type of organic material. Furthermore, for a thermal runaway, a heat sink 70 is placed below the motherboard 65 by a variety of methods.
LTCC intrinsically has higher thermal conductivity than organic material. Further, the provision of the thermal via 62 and a metalized conductor surface causes a further increase in thermal conductivity, thus enabling an improvement in heat radiation properties of the light-emitting apparatus.
Further, as a technique for improving the luminous efficiency of an LED, a technique of providing a metal reflecting layer between a light-emitting layer of the LED and a supporting substrate has been proposed (Non Patent Literature 1). This means that the reflection by the metal reflecting layer of light radiated from the LED toward the supporting substrate enables an increase in the amount of light that is emitted by the LED.