Light emitting diode (LED) is a semiconductor device which converts electrical energy into light energy. LED has taken an increasingly important place in the lighting area due to its advantages of high luminous efficacy, low power consumption, low radiation, etc. compared with traditional light sources. However, a LED light source generates a large mount of heat while generating light, and the accumulation of heat may significantly affect the service life of the LED light source. For example, when a LED chip is powered and glows, only about 30% of electric energy is converted into light which is radiated out, and most of electric energy is converted into heat energy and make the LED chip working in a high temperature environment. The optimal operating temperature of a LED chip is around 80 degree C. The operating life of the LED chip and the electric to light conversion efficiency will be reduced significantly when working in high temperature, e.g. 100 degree C. or higher temperature. As such, more electric energy is converted into the residual heat energy, resulting in a deteriorated cycle of the unceasing reduction of the electric to light conversion efficiency.
The current practice of conducting the heat, which is generated by the LED, away from the LED chip is fixing the chip on a substrate using conductive adhesive or non-conductive adhesive materials, and then connect the LED terminals by gold wire bonding to the electrical circuit wiring on the substrates. The heat generated by the chip is dissipated through the heat conductive substrate and it is acted as a heat transfer medium. Since copper is a good heat conductor. Cooper is a heat transfer material that is most commonly used for making the lead frames for high power LED chips. The China utility model patent CN201985093U disclosed a LED copper support with a number of LED chips mounted on its upper portion, the Chinese utility model patent CN202839739 disclosed a high power LED packaging structure comprising a copper substrate for fixing, conducting heat and reflecting light for a LED chip, and the Chinese utility model patent CN203150615U disclosed a LED light source module with high cooling efficiency comprising columnar LED heat sink copper columns.
All of above prior arts relate to achieving the heat radiation of LED chips using copper materials. However, the coefficient of thermal expansion (CTE) of copper is about 19, and the CTE of sapphire substrate frequently used by LED chips is about 5, the difference between which is large. When a high current applies to a LED chip and temperature raise occurs, the heat which is generated by the LED chip transfers onto the copper lead frame, leading to a rapid expansion of the copper, and the sapphire substrate on the chip may be easily broken due to the different expansion of the LED chip and the copper substrate.
Therefore, it is desirable for a novel structure designed for cooling LED chips to avoid the phenomenon of break of a chip substrate.
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