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Ceramic material of the heat in the LED lighting applications

Hangzhou JWG Technology Co.Ltd | Updated: Aug 26, 2014

With the help of aluminum metal density, high thermal conductivity, surface-handling skills mature advantages of LED lighting has been the backbone of the material separatist market. Followed the crowd to mobilize the required safety function, the conductivity of aluminum become a deadly scar, in order to mobilize the LED lamps use mine safety, electrical insulating materials (hereinafter simply called LED lamps) generated the attention of the crowd.
Has emerged of an electrically insulating material and high thermal conductivity ceramic material plastic. Human ceramic materials have been used for thousands of years, the preparation of the ceramic material has a contemporary skills insulation, high thermal conductivity, an orange-red radiation rate is high, the low expansion characteristic parameters, can be a completely new material of LED lighting. Now, the important ceramic materials for heat sink material LED packaged chip, circuit board materials and fixtures radiator materials. With the help of its high thermal conductivity, high-quality plastic electrical insulation and low density value, high-profile heat sink material is inserted market, because the price is high, the application rate is not at this stage. In this paper, an important discussion of ceramic materials in the LED lighting application skills.
Heat transfer mechanism of a ceramic material
Ceramic subordinate non-metallic materials, the crystal structure does not have a free electron, with a classic insulation performance. It is dependent phonon thermal heat transfer mechanism, when the lattice complete without shortcomings, per capita free path of the phonons bigger, higher thermal conductivity. Theoretical explanation, the largest thermal parameters ceramic crystal materials can be up to 320W / mK.
Ordinary think, in the thermal conductivity of the ceramic material impact Nagisa many conditions, the structure is the main drawback of the impact conditions. In the sintering process, the oxygen impurities in the crystal lattice of the ceramic insert, along with vacancies, dislocations, and other structural shortcomings APB significantly decreased the average free path of the phonons, resulting in thermal conductivity decreases. After generating the second ceramic contemporary skills relative to the oxygen in the grain boundary is fixed, decreasing the possibility of insertion of lattice oxygen impurity, the oxygen purity at the grain boundaries along with greatly decreased, the spontaneous diffusion of oxygen to the inside of the crystal grains at the grain boundaries, inside the grain matrix oxygen content decreased, the number and variety of shortcomings decreasing, thereby reducing the probability of phonon scattering, increase per capita free path of the phonons. Is not the same as the preparation of skill, the thermal conductivity of the ceramic material are not the same, the thermal parameters of the conventional ceramic materials shown in Table 1.
Thermal conductivity of ceramic materials and additive content also has a close relationship. 粱广川 Hebei university relations, who Y2O3 content of rare earth compounds with density and thermal conductivity also done a test discussion. An aluminum nitride (AlN) ceramic powder are referenced as follows: average particle size of 3m, the oxygen impurity content 0.97wt%, a purity of 99.95% of the additive Y2O3.
Atmospheric nitrogen by sintering, polished (finish 0.25m) deal, Y2O3 content of powders and thermal parameters of the relationship as shown in picture 1. From Picture 1, adding the right amount of rare earth compounds Y2O3 can make aluminum nitride ceramic thermal parameters reach around 160W / mK, has gone beyond the thermal parameters of die-cast aluminum ADC12 (thermal parameters ADC12 is 96.2W / mK), can completely producer as a heat sink material.
Aluminum nitride ceramics lower parameter expansion, high thermal parameters, often used as a heat sink chip package. A major bottleneck in the thermal parameters for cooling LED circuit board, the conventional aluminum substrate is only 1.0 ~ 2.5W / mK, is less than the ceramic substrate (such as a picture 2) 20% of the ceramic substrate may refer to a large degree of convergence of the PN junction LED drops temperature (under lu Jane called junction temperature).
Ceramic circuit board can be subjected to casting or eutectic sintering, but the price is high, large-scale application of modern touch early; ceramics used as a heat sink device chip package, due to simple geometry, some LED packaging manufacturers have already adopted . Important is the use of the above-described two functional thermally conductive material transferring heat to the heat sink, the heat almost no weigh how Phi to oxygen, it is designed to focus on thermal parameters.
LED lamps for heat sink Phi space to four weeks, often cited compound aluminum radiator (Al2O3) ceramic materials (like lamp as picture 3). Ceramic compound aluminum price cheap, skills mature, cited sintering casting skills, design flexibility, lower price, at this stage must get regulatory touch applications, this conduct thorough dissection under lu.
Thermal radiation mechanism two ceramic materials
We know that the fundamental method of heat exchange is: conduction, convection and radiation. In order to effectively heat, the crowd often through decreasing the thermal resistance of the heat flow method and parameters to achieve the consolidation of convection, heat radiation often overlooked. LED lamps for general reference, of course transfer heat, heat sink LED happen quickly drive to the radiator surface, because of the lower convection parameter, the heat can not be promptly sent to the oxygen around Phi, the resulting surface temperatures, LED's work Og of environment. Emissivity can effectively mobilize the heat sink via the surface of the heat radiation situation away ordinary anodized aluminum compound to mobilize the radiator surface emissivity ceramic material itself may have a high radiation characteristic is not necessary to carry out the subsequent processing of complex .
Radiation mechanism of ceramic materials are non-resonant utility by PAA of sensational two-phonon and multi-phonon occur. High radiation ceramic materials such as silicon carbide, metal compounds, boron etc. exist strong orange outer activation polarity sensation, these polar sensation because they have a very strong non-harmonic utility, which draw parameters dual-band and frequency region, the ordinary has a number of 100 ~ 100cm-1 level, a considerable area in the lower medium intensity reflectivity absorb residual reflection band in this region, therefore, is conducive to constitute a relatively flat slip intense radiation belt.
General terms, with heat radiation efficiency of radiation belt extends roughly from strong resonance wavelength phonons to shortwave Quintana two regional engagement and frequency, including part of the multi-phonon bonding area, which is characteristic of the majority with a ceramic material with high radiation radiation belts It can be said with strong radiation from the band's two important phonon engagement radiation. Except for a few exceptions, the general radiation ceramic accumulate in the radiation belts of two phonons than 5m, three-phonon region. Therefore, in view of an orange-red radiation ceramic terms, 1 ~ 5m important band radiation from the free-carrier band transitions or electronic straightforward transition from the impurity level to the conduction band, band radiation than 5m importance attributed to two-phonon engagement radiation.
Weiliang, Luosu Ming thermostat ceramic orange radiation were discussed, quizzes ceramic goods like orange radiation rate of about 0.82 to 0.94, on the surface quality is not the same as far orange outer ceramic glazed also carried out tests, radiation rate of about 0.6 to 0.88, SEM photo from ceramic starvation draw away orange outer ceramic powder dosage radiation function when 10wt% in the glaze, glazed quality, color and cost better, the radiation rate reached 0.83, the other functions have reached the national day porcelain scale requirements. Cuiwan Qiu, Wu Chunyun low temperature outer ceramic blocks away orange sample goods carried out tests, orange radiation rate of 0.78 to 0.94. Lee orange Tao, Liu Studies Forum found that the thermostat is far outside the ceramic orange radiance up to 0.85 ordinary foreign Enecoat glaze coating the maximum radiation rate of 0.93 to 0.94. Diverse discussions are described, or glazed ceramic material itself has a very, very high rate of orange-red radiation, which replace the traditional aluminum radiator is a big key factor.
3 ceramic material of aluminum compound LED lamps discussed mine
3.1 Ceramic LED lighting laboratory tests
Ingredients ceramic thermal parameters of aluminum compounds and compounds of aluminum (pure) has a very great relationship (Table 2). Usual Nom.95% compound aluminum ceramics (Jane called 95 ceramic) thermal parameters about 22.4W / mK, withstand 10kV / mm, goods made therefrom kind of LED lamps as shown in picture 4.
Lighting specifications for GU10, shape proportion 49.5mm50mm, fin heat sink and lamp holders are referenced 95 ceramic material, and after rib joints.
Lighting installation three Handson (Henderson) LED light source, built-in constant current drive power, the total power consumption of about 3.55W, cited lens with light, the total luminous flux of about 150lm.
Because the LED junction temperature can not be measured straightforward, often indirect reference test method, and now there are two kinds of important:
① Power coefficient method: LED junction temperature rise along both ends of a linear voltage drop ratio parameter K is typically 4mV / ℃, the junction temperature according to equation (1) to carry out the measurement; ② thermocouple indirect test method: After the test LED temperature welding foot sp indirectly junction temperature values, then the junction temperature according to equation (2) to carry out the measurement.
Where: is the junction temperature, primary air temperature is 0, K is the ratio of the parameter, △ F of positive voltage change value.
Where: The junction temperature, sp feet for LED solder temperature, th for the PN junction to solder heat resistance feet per capita, as the chip power.
The way to carry out tests for thermocouple temperature test method. LED test point two solder feet, the lamp body radiator three point test, the ambient air temperature thermocouple two reference tests, the test results shown in Table 3.
Computer Simulation 3.2 ceramics and aluminum die-casting LED lamps LED lamps
In order to discuss and design of ceramic LED lamps, we use computer software to carry out simulation anatomy. The reference flow field dissection software for Flo-EFD (referred to as the EFD, EngineeringFluidDynamics), EFD NIKA flagship commodity, it is important for the automotive, aerospace, aerospace, machinery, sea ship, electronics through flood, treatment equipment, resources, chemicals, warm pass, fluid manipulation facilities, LED semiconductor industries. Software can carry out all sorts of LED packaging goods, aerospace aerospace heat lamps, all kinds of energy saving lamps, LED reflective tube, automotive lighting, display and other anatomy.
For purposes of comparison with laboratory tests carried out, the computer simulation anatomy, the ambient air temperature to 15 ℃, the resulting temperature distribution as shown in picture 5 (for ease of observation with, concealed a lens and a fixed part). To compare the 95 ceramic lamps and aluminum die-casting lamps thermal performance, through computer simulation resulting temperature distribution as shown in picture 6 (lamps radiator material is aluminum ADC12, PBT plastic holder for the remaining coefficients unchanged.)
3.3 Results anatomy
Ceramic lamp holder for 95 wear-resistant ceramic material (aluminum die-cast lamp holder for PBT plastic), each device has been fully utilized. When laboratory tests, 1.0h simply reach thermal flat, mathematical average value of the environment temperature is about 14.4 ℃, will carry out laboratory tests and computer simulation of the temperature distribution of the value of comparative anatomy, the results shown in Table 4.
Computer dissection showed that, of course, convection conditions, 95 ceramic lamp aluminum die-casting thermal performance as much as lamps, ceramic lamps can take advantage of their geometrical characteristics of the zero of the device, thus lighting groups temperatures dropped to a lower level.
Future four ceramic materials for LED mine lamp
Ceramics has a long history of making high thermal conductivity ceramic materials prepared contemporary craft, oxygen of course shed, completely mine LED lamps can act as heat sink material. Aluminum nitride ceramic package crystal frame can be as straightforward or circuit layer; compound cheap price of aluminum ceramics, sintering skills mature, you can glaze a different color, because of its excellent electrical insulation performance, and acid and alkali resistance, by many, many users of all ages . However, the ceramic material is not flawless, ceramic radiator fins can not be too thin (thick degree 1.5mm), higher density (about 1.5 times aluminum), cracks occur in high-stress, pollution and other unglazed surface is easy .
In general, the future of ceramic materials for the LED is good, especially suitable for compact mine lamps.

Hangzhou JWG Technology Co.Ltd