Light emitting diodes (LEDs) are being spotlighted in various applications due to long life-cycle and low power consumption. Particularly, LEDs are full of promise for indoor and outdoor lightings.
In general, such an LED is manufactured in a surface mount device (SMD) structure so that the LED is directly mounted on a printed circuit board (PCB). In this structure, heat-dissipating technologies for improving life-cycle and illumination of the LED become a main issue. For example, in case of streetlamps, an LED package having a high-output power of about at least 50 W or more, preferably, about 100 W to about 150 W is required. In general, when a bonding temperature reaches a temperature of about 120° C. in a structure of the LED package, LED chips may be damaged. In case of the power package for applying high current, technologies for dissipating generated heat has become a core challenge.
FIGS. 1 and 2 illustrate heat-dissipating package structures as LED modules developed according to a related art. Particularly, FIG. 1 illustrates a heat-dissipating package structure using a metal PCB, and FIG. 2 illustrates a heat-dissipating package structure using a thermal via.
Referring to FIG. 1, an LED chip 9 is disposed on a heat slug 8 having superior thermal conductivity and then molded by a plastic package 10 including a transparent lens disposed thereon to constitute an LED package. Also, a lead 7 electrically connected to each of a cathode (not shown) and an anode (not shown) of the LED chip 9 is bonded to an array electrode 5 for operating the LED chip 9 by using a solder 6. Also, the LED package is attached to PCBs 3 and 4 constituted by a metal layer 3 for surface-mounting and an insulation layer 4 formed of an epoxy resin or ceramic. The PCB is attached to a heat sink 1 for dissipating heat. Also, the above-described attachments may be performed through a thermal interface material (TIM) 2 generally selected from the group consisting of a heat-dissipating sheet, a heat-dissipating bond, and a heat-dissipating paste.
The module structure may relatively easily dissipate heat through the heat slug 8 attached to a bottom surface of the LED chip 9. However, in case of the high-output power LED, thermal efficiency may be very low due to thermal resistance between the LED chip 9 and the heat slug 8 and thermal resistance of the TIM 2 itself. Particularly, the TIM 2 may have mere thermal conductivity of about 2 W/m·K, and maximum about 4 W/m·K in case of commercial products.
In view of this point, according to the heat-dissipating package of FIG. 2, a thermal via 11 is disposed to pass through the PCBs 3 and 4 disposed in a lower portion of the LED package to define a heat-dissipating passage between the TIM 2 disposed under the slug 8 and the TIM 2 disposed on the heat-dissipating plate 1, thereby improving a heat-dissipating effect when compared to that of the heat-dissipating package of FIG. 1.
However, in this case, a drilling process for forming an additional via hole, a via hole filling process, and a material to be filled are required to increase manufacturing costs. In addition, according to the above-described related art, heat transferred into the heat slug 8 should pass through the epoxy resin or the insulation layer 4 formed of the ceramic material, which has relatively low thermal conductivity, of the PCBs 3 and 4 so as to transfer the heat into the lower heat-dissipating plate 1. As a result, the insulation layer 3 may ultimately cause a thermal transfer bottleneck phenomenon to reduce heat-dissipating efficiency.