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Simplify the LED heat dissipation design innovation as ceramic method

Light-emitting diode (LED) due to restricted by hot problem and prevent it become a kind of ideal lighting is understandable. We have given us a lot of attention to the radiator, but between the LED and the cooling surface of each layer and barrier to consider. 
Ideas and the change of the material besides can simplify the system implementation, also can improve thermal management ability and reliability. Adopt ceramic as the carrier of the radiator, circuit and part of the product design requires not only a new train of thought, have overcome the traditional model of will. 
Based on computational fluid dynamics (CFD) simulation process support thermal optimization and product design process. This article explains the theory method, the proof of concept and how to implement these improvement by using ceramic radiator eventually. 
What is hot 
It is well known that the LED is energy efficient light source, and because the small size was deeply loved by designers. But only when does not involve thermal management, they can be really called "small". Although compared with incandescent light source as much as the working temperature of 2500 , the temperature of the LED light source is much lower. As a result, many designers eventually realized that heat is a problem that cannot be ignored. Although the LED will still be hot, but its temperature is relatively lower, so it won't be any big problem. However, based on semiconductor devices LED its working temperature should be lower than 100 . 
According to the law of conservation of energy, heat (can) must be sent to the area. Leds can only work in between 100 and 25 ambient temperature, the temperature range is 75 only. Therefore, need a larger cooling surface and a very effective thermal management. 
Two optimal block 
As shown in figure 1, Group 1 is the LED itself, in general is still can't touch. Center position is LED bare chip and a bare chip and LED to the link at the bottom of the cooling copper bar. From the hot point of view, the ideal solution is the bare chip LED directly and radiator are tied together. Because of mass production, the concept of work in business. We put the LED as "directory" of a standardized product, can't do change. It is a black box. 
Group 2, including radiator, radiator is the function of the heat from the heat source to the heat source. Usually, the ambient air is free flow or forced convection. Radiator material more awkward, more needs to be hidden. However, the deeper it hidden, the refrigeration efficiency will be lower. Of course, also can choose appropriate appearance and performance of materials. These materials can be directly exposed in the air and become the visible part of product design. 
Between Group 1 and Group 2 is Group 3, it provides the mechanical connection, electrical isolation and thermal conduction. This seems to be very contradictory, because most of the thermal conductivity of good material can also be conductive. On the other hand, almost every electrical insulating materials and heat insulation. 
LED welded to the best compromise is glued on the metal radiator on the printed circuit board (PCB). PCB circuit board as the original function can be preserved. Although the PCB with various thermal conductivity, but they are on heat conduction block. 
Effective system thermal resistance 
Can get LED from the manufacturer (bare chip to) of thermal conductivity and thermal resistance between the radiator. However, few people pay attention to Group3 and its impact on the overall thermal performance significantly. The exception of the LED (Group 1) itself all thermal resistance, put together, you can get the total thermal resistance (RTT) (figure 2). Through the RTT can be real hot. 
Ceramics: a material to achieve two functions 
Only common optimization approach of radiator. There are hundreds of radiator design, they all basically by the aluminum structure. But in order to further improve the performance, it is necessary to improve or even cancel the Group 3. Electrical isolation functions must be generated by other materials from the radiator itself. We think the material should be ceramic. Such as Rubalit (alumina) or Alunit (aluminum nitride ceramic materials such as the two key features: electric insulation and heat transfer together. 
Rubalit thermal conductivity is lower than aluminum and Alunit slightly higher than aluminium. On the other hand, Rubalit not as expensive as Alunit (figure 3). Their thermal expansion coefficient can meet the requirements of the semiconductor. In addition, they are hard, corrosion resistance, and meet the eu's limit of harmful substances (RoHS) directive. Ceramics are completely inert substance, they are a part of the whole system the most durable. 
The simplified structure (without adhesive, insulation, etc.) will be a high power LED with ceramic radiator directly and permanently bound together, create the ideal working conditions for the entire component. This creates excellent long-term stability, thermal management and high reliability of safety. We have applied for this method is called Ceram for Cool patent. 
The theory basis for 
Ceram Cool ceramic radiator is an effective integration of circuit boards and the radiator, the heat sensitive components and circuits can be reliably heat dissipation. It supports directly and permanent connection between components. In addition, ceramics is not conductive, it can provide the binding surface by using metal gasket. If you need, and even can provide for customer 3 d conductor track structure. 
Can be used for power electronics applications, copper binding directly. Radiator into a module base board, leds and other components can be populated put above. It can quickly evaporate produce heat and does not produce any thermal barrier. 
The validation of the concept of 
First the several simulation model for the ceramic this idea is used for cross validation. To predict the thermal performance of various design invented a method based on CFD. In addition, it has developed an optimized 4 wled ceramic radiator. Will produce the requirements into consideration when developing. 
Optimized geometry allows 4 wled working temperature is highest do not exceed 60 , this has already passed the physical test. The design is a square layout (38 * 38 * 24 mm), and contains a thin fin occupies a larger space. And with the same geometric layout of the aluminum substrate (LED) with installed on the PCB can withstand temperature is much higher. According to the thermal conductivity of PCB (from 4 to 1.5 W/mK W/mK), 6 to 28 k temperature can rise. 
To reduce the temperature of hot 6 k means can significantly reduce the stress on the LED. Same shape Rubalit components of 13% of the total thermal resistance at least better than aluminum. Using Alunit Ceram can be Cool performance improvement at least 31%. If consider the heat drop of 28 k, Rubalit and Alunit real advantage of these two kinds of ceramic material more is much more significant. 
Methods the flexibility of the 
This is a flexible way, can be used for different purposes. You can choose the LED work in the best temperature to make sure the LED long life and a higher number of lumens per watt; Can also choose to receive a higher working temperature of service life and lower efficiency. 50 to 110 is a common temperature range. If you need higher lumens, 5 or 6 wled are equipped with 4 w radiator. With a few wled apportion power is helpful to improve heat dissipation: 1 65 corresponds to 5 w; 70 corresponding 6 w (figure 4). 
As the permanent reliably and Ceram Cool electrical insulating materials are tied together by the ceramic radiator absorbs more heat, more hot. It eliminates the LED heat burdens, important parts for the cooling. Reduces the bare chip temperature also allowed the use of smaller surface, therefore, the radiator can be made smaller. 


----------Archled Technology Co.,Limited


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E-mail: mack@archled.net

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