In the flip-chip structure, the light is taken out from the sapphire substrate and does not have to be taken out from the current diffusion layer, and the opaque current diffusion layer can be thickened to increase the current density. The bottom of the crystal grain is made of an alloy such as tin (Sn) or gold-tin (Au-Sn) as a contact surface plating layer, and the crystal grains can be soldered on a substrate plated with gold or silver. When the substrate is heated to a suitable eutectic temperature, gold or silver elements penetrate into the gold-tin alloy layer, the eutectic layer solidifies and the LED is soldered to the substrate, breaking the thermal bottleneck in the heat dissipation system from the chip to the substrate, and improving the LED life. The flip-chip eutectic LED technology has improved the problems of gold wire soldering, insufficient current resistance, gold wire breakage caused by thermal expansion and contraction of the packaged silica gel, and the influence of the gold wire in the process.
The high-current drive's excellent heat dissipation characteristics can only show its advantages in high-power devices. With the existence of the Droop effect, as the current increases, the efficiency of LED light output decreases, and the drop is severe. High-power devices are mainly used in high-power fields such as street lamps, tunnel lights, and mining lamps. They have high requirements for light efficiency. For example, 1-3W devices can pass 1000mA. Actually, for the demand of light efficiency, most of the use range is 350mA. In addition, LED driving power sources tend to have small currents and high voltages based on conversion efficiency and cost considerations, which are opposite to the high current and low voltage driving modes represented by flip chip eutectic. At present, the flip-chip eutectic technology involves expensive production equipment and materials, so that its cost is high, and the cost performance advantage cannot be realized. Flip-chip technology has been around for a long time, but it has been delayed for many reasons.
At present, the products of flip-chip eutectic are mainly international majors, CREE XLamp XT-E, Philips Lumileds LUXEON-T series devices, and Taiwan New Century Optoelectronics has launched AT. Since 2010, Guoxing Optoelectronics has been engaged in the research of flip-chip eutectic technology. The mass-produced ceramic eutectic 3535 device has reached the level of 140lm/w, and it has become one of the few enterprises in China to master this technology. The market competition is becoming increasingly fierce, and flip-chip LEDs are gradually receiving attention from the lighting market. As more and more LED manufacturers invest in flip-chip LED technology, they will accelerate their development in semiconductor lighting applications in terms of technology and cost.
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