LED development is the key to heat

With the continuous evolution of LED materials and packaging technology, to promote the brightness of LED products continue to improve, the application of LED more and more widely, and to provide a stable growth of the LED industry market territory. LED as a backlight of the display, it is a hot topic recently, the small size of the display backlight source gradually developed to the large size LCD TV backlight, quite gradually replace the CCFL backlight posture. LED is mainly in color, brightness, life, power consumption and environmental requirements are more advantages than the traditional cold cathode tube (CCFL), thus attracting the industry to actively invest. Early single chip LED power is not high, calorific value is limited, the problem of heat is not large, so its packaging is relatively simple. But in recent years, with the constant breakthroughs in LED material technology, packaging technology of LED also changed, from the early development of shell type package single chip multi chip package module becomes flat, large area; the working current of the early low power LED about 20mA, high power LED to the current 1/3 to about 1A. The input power of a single LED more than 1W, even to 3W, 5W. Package more evolved due to thermal problem of high brightness high power LED system will affect the product function quality key, LED components will heat quickly discharged to the surrounding environment, we must first from the package level (L1& L2) on the thermal management; the current practice is to solder or conductive LED grain then in a paste heat spreaders, through heat spreaders reduce the package thermal impedance module, the LED module which is currently on the market the most common and main sources of Lumileds, OSRAM, CREE and Nicha LED and other international well-known manufacturers. These LED modules can be assembled in a row of a line source in the actual application, or to be arranged in array or round, then bonding as the surface light source in a radiating substrate. But for many applications such as terminal, mini projector, vehicle and lighting light source, lumen volume required in specific area of more than thousands or tens of thousands of lumens lumens, rely on single grain packaging module is clearly not enough to cope with, to multi chip LED and chip package, direct adhesion is the substrate the future development trend. LED in actual product application, whether for display backlight LEDs or general lighting, usually need to be considered a number of LED assembled on a circuit substrate. A circuit substrate plays bearing LED module structure, on the other hand, with the output power of LED is more and more high, also must play the role of heat dissipation substrate, to transfer heat from the LED chip out, in the choice of materials, so it must take into account the structural strength and heat demand. Worry about the material cost of traditional LED cooling power is small, the problem is not serious, as long as the foil printed circuit board with the use of general electronic is enough to cope with, but with the high power LED is more and more popular, this board is no longer sufficient to meet the cooling demand, therefore need to printed circuit board attached to a metal plate, which is called Metal Core PCB, in order to improve the heat transfer path. There is also a direct approach on aluminum substrate directly as an insulating layer or a dielectric layer on the surface of dielectric layer, and a circuit layer, so the LED module can be directly to the wire bonding in the circuit layer. At the same time, in order to avoid the dielectric layer due to poor thermal conductivity and increase the heating impedance, and sometimes take the way of perforation, so that the bottom of the LED module of the heat sink is directly exposed to the metal substrate, that is, the so-called chip direct adhesion. In addition to the metal substrate, due to the development of high power LED packaging and chip direct adhesion substrate, the substrate material in addition to considering the heat dissipation, and the chip must also consider the coefficient of thermal expansion matching, in order to avoid thermal deformation and reliability problems caused by thermal stress, so at home and abroad are the development of ceramic and metal composite substrate. These newly developed substrate materials not only have good heat dissipation, while the thermal expansion coefficient (4~8ppm / K) and LED chips are matched, the only drawback is that the price is more expensive than the general metal substrate. In fact, the focus of non fan cooling, LED heat sink and CPU heat dissipation are similar to the heat sink, heat pipes, fans and thermal interface material consisting of the main gas cooling module, of course, is one of the hot water cooling strategy. The large size LED TV backlight module is the most popular, 40 inch and 46 inch LED backlight input power were 470W and 550W, with 80% of them turn into heat, heat the required amount of about 360W and 440W. How will these heat away, useful water for cooling, but the high price and reliability concerns; also useful with heat pipe heat sink and fan for cooling (such as SONY 46 LED TV), but the fan power consumption and noise problems. Therefore, how to design the cooling mode of the non fan is the key to determine who can win in the future.

Source: HC