One example of a LED module is shown in FIG. 10. The LED module X shown in FIG. 10 includes a substrate 91, metal electrodes 92 and 93 arranged in the substrate 91, a LED chip 94 electrically connected to the metal electrodes 92 and 93, a wire 95 and an encapsulating resin 96 covering these components. The substrate 91 is made of, e.g., a glass epoxy resin. The metal electrodes 92 and 93 are spaced apart from each other at the opposite marginal edges of the substrate 91. Each of the metal electrodes 92 and 93 covers a region extending from the front surface of the substrate 91 to the rear surface across the side surface. The LED chip 94 is mounted on the portion of the metal electrode 92 covering the front surface of the substrate 91. One end of the wire 95 is fixed to the portion of the metal electrode 93 covering the front surface of the substrate 91. The other end of the wire 95 is connected to the LED chip 94. The LED module X, when in use, is embedded to, e.g., a circuit board 97 built in an illuminating device. As shown in FIG. 10, the portions of the metal electrodes 92 and 93 covering the rear surface of the substrate 91 are connected to wiring lines 98 provided in the circuit board 97. When installing the LED module X on the circuit board 97, a process is performed in which the LED module X and the circuit board 97 are heated in a reflow furnace with solder materials inserted between the metal electrodes 92 and 93 and the wiring lines 98.
The encapsulating resin 96 is provided to protect the LED chip 94 and the wire 95 and is formed of an epoxy resin transparent to the light emitted from the LED chip 94. The encapsulating resin 96 is formed to cover the portions of the metal electrodes 92 and 93 positioned on the front surface of the substrate 91. Gold-plated layers are often formed on the surfaces of the metal electrodes 92 and 93 in order to increase the conductivity. However, the epoxy resin and the gold are not easily bonded to each other, possibly posing a problem set forth below. As stated above, a heating process is performed when installing the LED module X on the circuit board 97. At this time, the encapsulating resin 96 is thermally deformed. However, the encapsulating resin 96 and the metal electrodes 92 and 93 may be exfoliated, since the epoxy resin and the gold-plated layer are not strongly bonded together. If such situation occurs, there is a possibility that the LED chips 94 are not turned on.