1. Field of the Invention
The invention relates to a surface-mount light-emitting diode (LED). More particularly, the invention relates to a surface-mounted LED including an LED chip mounted in a recess provided in a substrate, in which a sealant resin is applied to seal the LED chip.
2. Description of the Related Art
A conventional surface-mounted LED may have the structure shown in FIGS. 8 and 9. FIG. 8 is a top view and FIG. 9 is a cross-sectional view taken along line A-A in FIG. 8. It includes a pair of circuit patterns 51a, 51b formed in the upper surface of an insulator 50 at both opposite ends. The circuit patterns 51a, 51b extend from edges of the insulator 50 to the lower surface around sides of the insulator 50. A recess 52 is provided almost at the center in the upper surface of the insulator 50. A circuit pattern is formed over the entire bottom 53 and the entire inner circumferential surface 54 in the recess 52. This circuit pattern is connected as an extension from the one circuit pattern 51a of the pair of circuit patterns 51a, 51b formed in the upper surface of the insulator 50. The other circuit pattern 51b extends toward the center of the insulator 50.
An LED chip 56 is mounted on the bottom 53 in the recess 52 via a conductive adhesive 55. In this case, the lower electrode of the LED chip 56 is connected to the circuit pattern 51a formed on the bottom 53 in the recess 52 for achievement of the electrical conduction therebetween. The upper electrode of the LED chip 56 is connected via a bonding wire 57 to the circuit pattern 51b that extends substantially toward the center of the substrate for achievement of the electrical conduction therebetween.
A light transmissive resin 58 is applied to cover the LED chip 56 and the bonding wire 57 for sealing and protecting the LED chip 56 from the external environmental elements such as humidity, dirt, and gases. In addition, it protects the bonding wire 57 from mechanical stresses such as vibrations and impacts (see, for example, Patent Publication 1: JP-A 7/202271 along with its associated English Abstract, machine translation, and drawings, which are submitted herewith in an Information Disclosure Statement and are hereby incorporated in their entireties by reference).
Surface-mounted LEDs are often employed together with other surface-mounted electronic components and are generally surface-mounted on a component-mounting board in an electronic instrument through a solder reflow furnace. In this case, the surface-mounted LED is extremely small and, accordingly, the temperature of the whole LED may elevate almost up to the heating temperature of the solder reflow furnace.
At the elevated temperature, the light transmissive resin for use in sealing the LED chip and the bonding wire have a difference in thermal expansion coefficient as compared to the circuit pattern formed on the bottom in the recess. This difference and other factors may cause a stress that results in peel at a contact interface between the circuit pattern and the resin. Then, the light transmissive resin exerts a force on the conductive adhesive and the LED chip to lift them above the circuit pattern. In this case, the light transmissive resin may peel off the circuit pattern, possibly resulting in an electrical property failure.
Even after the surface-mounted LED is mounted on the component-mounting board, the repetition of switching the LED on/off can cause repeated thermal expansion and contraction of the light transmissive resin. In addition, the stress at that time may exert the same action as described above and possibly result in an electrical property failure.