The present invention relates to a package structure for solid-state to lighting devices and a method of fabricating the same, and more particularly to a packaging and a fabricating method for a light emitting diode (LED) utilizing a silicon substrate.
LEDs are generally applied to the indication lamps of household appliances, lighting apparatuses, the back light modules of liquid crystal displays, browsers, third brake lights for vehicles, etc. Furthermore, linear light sources and planar light sources of LEDs are readily available these days.
Current, research and development in the field of LED focuses on the efficiency of light extraction and heat dissipation. To improve the extraction efficiency, the epitaxy process, wafer process and package process are the most important. The heat dissipation problem can be solved by improving the package structure. Hence, the improvement of the package structure has a great effect on both extraction efficiency and heat dissipation efficiency.
There are several packaging types for LEDs, such as lamp and reflective cup. The LED utilizes the reflective cup to enhance the extraction efficiency by increasing the light reflection. In addition, modified designs of the reflective cup can also improve the heat dissipation efficiency. U.S. Pat. No. 6,562,643 put forth such a modified design, and U.S. Pat. No. 6,268,660 and U.S. patent publication No. 2004/0218390 have the same objectives. Moreover, U.S. Pat. No. 6,531,328 discloses that a silicon substrate 10 substitutes for a package substrate. A reflective cup is formed on the silicon substrate 10 by MEMS (micro electromechanical system) processes, as shown in FIG. 1. An insulation layer 12 and a metal layer 20 sequentially enclose the silicon substrate 10, and electrodes 22 and 24 are formed adjacent to the metal layer 20. An LED die 30 is attached to the interior of a reflective cup 50, and is electrically connected to the reflective cup 50 by bonding wires. Afterward, epoxy resin 40 encapsulates the LED die 30 in the reflective cup 50.
FIG. 2 is a flow chart for manufacturing the devices in FIG. 1. As shown in Step 21, the silicon substrate 10 is first provided for these steps. Subsequently, a plurality of reflective cavities are formed on the first surface of the silicon substrate 10 by wet etching, as shown in Step 22. Referring to Step 23, electrode guiding holes are drilled on the second surface opposite to the first surface by dry etching. Insulation layers are deposited on the surfaces of the silicon substrate 10 by a thermal oxidation method or a thermal nitrogenization method according to the instruction in Step 24. The insulation layers can be made of SiO2 or Si3N4. Subsequently, conductive layers are deposited on the insulation layers by electroplating, as shown in Step 25. Finally, a reflective layer is formed on the reflective cavities, and the electrodes 22 and 24 are arranged on the opposite surface by laser treatment.
However, the aforesaid structure of the LEDs on the silicon substrate has several shortcomings. First, the reflective layer and the electrodes are made of the same material. There is no metal simultaneously well-suited for both reflection and solderability. Furthermore, while the various LEDs emit light with different wavelengths, the reflective efficiency of the metal is directly related to the emitting wavelengths. Hence, the optimal material for the electrodes also varies with the emitting wavelengths. Solder is preferable for the material of the electrodes, but is not suitable for the material capable of reflecting visual light. Au, Ag, Pd and Pt are better reflective materials, but are not suitable for the electrodes.
In addition, the lowermost guiding holes are formed by dry etching. The etched pattern has less adaptability in subsequent processes. The metal layer needs laser treatment to form reflective surfaces, resulting in higher manufacturing costs.
Consequently, the optoelectronic market urgently needs a high power LED that has a reliable larger light area with a simple structure. The aforesaid problems have to be resolved with such a high power LED.