IACS CO., LIMITED (Yiwu Fuwei e-commerce firm)

Many companies are optimistic about the development of this sunrise industry, especially the obvious energy-saving advantages of semiconductor outdoor lighting. In the past two years, many companies that have been rushing to the top, under the characteristics of semiconductor road lighting production, have simulated, counterfeit, and made a variety of "snake heads" in the shape of today's conventional lighting street lamps. At one time, "a hundred schools of thought contend, flowers bloom." The products have been introduced to the market. After two years of testing on the road, most of the products have different levels of problems.

     Specifically in:

     1. Due to the lack of understanding of the working conditions of the LED light source, the light attenuation is severe or even dead.

      I will discuss the solution with you on the above issues:

     The discussion of the working environment of LED light source needs to have the basic knowledge of LED; its current high-power LED luminous efficiency is about 30%, 70% will be thermal energy, and it needs to be heat-dissipated. The junction temperature TJ of high-power white LEDs shows the relationship between life and lifetime when the brightness is attenuated by 70%: when TJ=50°C, the life is 90,000 hours, when TJ=80°C, the life is reduced to 34,000 hours, when TJ=115°C Its life expectancy is only 13,300 hours. TJ should propose the maximum allowable junction temperature value TJmax in the heat dissipation design. The actual junction temperature value TJ should be less than or equal to the required TJmax, ie TJ≤TJmax.

     From the above test data, the ambient temperature at which the tested LEDs can work properly should be (<85 °C). Above this temperature range, the efficiency will be greatly reduced, even burning. It can be seen the importance of temperature directly affecting it. It is particularly worth mentioning that the heat balance speed of the heat dissipating material requires attention, and the heat of the light source is not effectively treated, resulting in serious light attenuation. Nowadays, many manufacturers' high-power LED heat sink heat-dissipating shell applications basically use different alloy aluminum materials, and their thermal conductivity is different. The heat dissipation rate of some materials is difficult to meet the LED working conditions. The non-negligible aluminum substrate and thermal silica gel, the thermal conduction of the silicone grease material, and the actual life quality of the material used will directly affect the working heat dissipation conditions of the LED. How to reduce the intermediate link, directly contact with the heat sink and heat the heat to quickly achieve a balanced heat dissipation, is the direction that needs to be considered in the development of high-quality LED lighting products.

First from material analysis:

     Metal heat transfer coefficient table:

     Silver 429 copper 401 gold 317 aluminum 237 iron 80 tin 67 lead 34.8

     Silver heat transfer coefficient is better, but the disadvantage is that the price is too high, the pure copper heat dissipation effect is second, but it is already very good. However, copper also has disadvantages: high cost, heavy weight, and resistance to corrosion. Therefore, most of the heat sinks are made of light and strong aluminum materials, among which aluminum alloys have the best heat transfer capability, and good air-cooled heat sinks are generally made of aluminum alloy. As for copper, there is also a pure copper radiator on the market. The thermal conductivity of copper is much faster than that of aluminum, but the heat of copper is not as fast as aluminum. Copper can quickly take away heat, but it cannot be in a short time. Dissipating its own heat, and the oxidizability of copper is the biggest drawback of copper itself. When copper is in an oxidized state, it will greatly decrease in terms of heat conduction and heat dissipation.

     In contrast, the best heat sink material is not aluminum. A new type of process, copper-aluminum combination, has been formed in the comparison of copper and aluminum. The so-called copper-aluminum combination is a perfect combination of copper and aluminum with a certain process, so that copper can quickly transfer heat to aluminum, and then the heat is dissipated by a large area of aluminum, which not only increases the heat conduction of aluminum. Copper also compensates for the fact that copper is not as heat-dissipating as aluminum, and organic combination achieves rapid heat transfer and rapid heat dissipation.

     As a solution,

     Its function is to transfer the heat radiated from the aluminum substrate to the heat sink, so that the temperature of the aluminum substrate is maintained at a level that can work stably, and the aluminum substrate is prevented from being damaged due to poor heat dissipation, and the service life is prolonged.

     Thermal Conductivity

     The unit of thermal conductivity is W/m?K (or W/m?°C), which indicates the heat conduction when the temperature difference of the column with a cross-sectional area of 1 m2 is 1 Kelvin (K=°C+273.15). power. The larger the value, the faster the heat transfer rate of the material and the better the thermal conductivity.

     At present, the thermal conductivity of the mainstream thermal grease is greater than 1W/m?K, and the excellent can reach 6W/m?K or more, which is more than 200 times that of air. However, compared with the metal materials such as copper and aluminum, the thermal conductivity of thermal grease is only about 1/100 of them. In other words, the silicone grease layer is actually the bottleneck of heat dissipation in the entire heat dissipation system. For a heat dissipation system, not only the heat sink, but also the heat transfer medium is an important part:

     Total thermal resistance of the heat dissipation system = heat sink resistance + thermal resistance of the heat transfer medium

     It is worth noting that ordinary thermal grease will appear "dry" or "harden" after being used for a period of time in a high temperature environment, which will greatly affect the heat dissipation effect. Therefore, the thermal conduction between the aluminum substrate and the heat sink needs to be taken seriously.

     The relevant person is studying the special ceramization treatment on the heat sink material to directly install the circuit. After such optimization, the heat conduction part of the heat dissipation will be fundamentally solved.

  LED ceiling lights, LED wall washers, LED flood lights, LED tunnel lights, etc., a set of various lighting.

      The heat-dissipating material, the heat-conducting link and the scientific shape structure design are worthy of everyone's understanding in the production of high-power LED street lamps. From the doubts and even rejection of the LED streetlight market, to the current trial and acceptance, we have seen the dawn of the future, but we still need some way to go. With the continuous improvement of high-power LED light efficiency and the rapid development of silicon-based LEDs, it will fundamentally solve the bottleneck of high price of semiconductor lighting sources. Let us join hands to explore and discuss. I believe that with everyone’s efforts, we will use the fourth. Generation of light source to make better LED street lighting, replacing the high-pressure sodium street lamp this road will not be very far!

In the final analysis, what is the scientific basis for the phrase "copper is faster than aluminum, copper is not as fast as aluminum?" There may be very few people who can clearly say it. Today, Xiaobian will tell you the fundamentals of this phenomenon.

The common definition of heat transfer coefficient is "the heat per unit area per unit time under unit temperature difference", the unit is J/m2ks, or W/m2k, where J is the heat unit joule, m2 is the area unit square meter, K is The temperature unit Kelvin can also be replaced by C in Celsius, and s is the time unit. From the figure, the heat transfer coefficient of copper is about 1.69 times that of aluminum. Therefore, copper and aluminum are used to manufacture the same cross-sectional area of the heat sink. Pure copper can take more heat from the CPU core per unit time. It is faster than aluminum, and the first half has been proved.

Material specific heat capacity J/kgK

Aluminum 0.9

Silver 0.24

Copper 0.39

Metal specific heat capacity comparison table

The latter part of the sentence "Bronze does not have aluminum heat dissipation", this is indeed the case. Proving this need to lead to another important thermodynamic parameter: specific heat. Anyone who has studied middle school physics knows that the definition of specific heat is "the amount of heat required to increase the temperature of a unit mass by 1 degree" in units of J/kgK. From the above table, we can see that the specific heat capacity of copper is smaller than that of aluminum. The temperature of copper is reduced by 1 degree. The heat emitted should be smaller than that of aluminum. In this way, copper should dissipate heat faster than aluminum. But you may not notice that the density of copper is 8.9kg/m3, while the aluminum is only 2.7kg/m3, which is close to 3.3 times of aluminum. Therefore, the same volume of heat sink can be made, and the quality of copper will be nearly 3.3 times larger than that of aluminum. The pure copper material is nearly half the heat capacity of pure aluminum. When the heat capacity is large, the heat dissipation becomes slow. Through the above theory, we have found the reason why "copper has no heat dissipation from aluminum".

In this way, we fundamentally understand that "copper is faster than aluminum, and copper does not have aluminum to dissipate heat quickly." In the future, when choosing a radiator, you can use this theory. If you choose a pure copper radiator, you should choose a fan with a higher speed and a larger air volume to avoid the heat of copper and the heat bottleneck.

Material Thermal Conductivity K (W/m2K)

Silver 429

Copper 401

Gold 317

Aluminum 237

Metal thermal conductivity comparison table

Silicon carbide thermal conductivity: 20 kcal / m · hour · degree (very small with temperature)

Other physical properties are as follows:

Density: 3.2 g / cm 3

Mohs hardness: 9.5

Specific heat: 0.17 kcal / kg · degrees

Linear expansion coefficient: 5 × 10-6 (m / ° C)

Chemical properties:

Has good chemical stability and strong acid resistance. The alkaline substance has an erosive effect under high temperature conditions.

Long-term use above 1000 °C can have the following effects with oxygen and water vapor:

1SiC+2O2→Sio2+CO2 2SiC+4H2O=Sio2+4H2+CO2

As a result, the SiO2 content in the element is gradually increased, and the electric resistance is gradually increased, thereby aging. If there is too much water vapor, it will promote the oxidation of SiC. The H2 produced by the 2-type reaction reacts with the O2 in the air to react with H2O to produce a vicious cycle and reduce the life. Hydrogen (H2) can reduce the mechanical strength of the component. Nitrogen (N2) at 1200 ° C or less can prevent SiC from oxidizing at 1350 ° C or higher and reacting with Si to decompose SiC. Chlorine (Cl2) can completely decompose Sic.

 2

 Aluminum substrates are not unfamiliar in the LED and PCB industry. Although everyone is emphasizing that the heat conduction of the board is large, it is better, and the thermal resistance is small. But I think many people are not very clear about what is the heat conduction of aluminum substrates and what is the specific definition of thermal resistance.

   The so-called thermal conductivity of aluminum substrates: thermal conductivity is also known as thermal conductivity, thermal conductivity, thermal conductivity. It represents the physical quantity of the thermal conductivity of the material. When the isothermal surface has a vertical distance of 1 m and the temperature difference is 1 ° C, it passes through 1 m 2 of heat (kcal) in 1 h due to heat conduction. Its unit of expression is: kilowatts / meter. hours. ° C [kw / (m.h. ° C)]

    If the substrate material is required to have a greater heat dissipation effect, the substrate material used is required to have a high thermal conductivity (thermal conductivity). If it is necessary to insulate heat through the substrate material, it is desirable that the thermal conductivity of the substrate material used is as low as possible.

     Thermal Resistance of Aluminum Substrate: Quantitatively describes the thermal conductivity of an object. It can be expressed by thermal conductivity or by another characteristic parameter. It is called “thermal resistance”. According to the monograph, the thermal conductivity is suitable for characterizing the thermal conductivity of a material with a uniform material, and as a substrate material for a plurality of materials, its thermal conductivity is more suitable for quantitative description by thermal resistance.

     In the way of heat conduction, the difference in surface temperature on both sides of the object (referred to as temperature difference) is the driving force of heat transfer. The thermal resistance (Rr) is equal to this temperature difference (T1-T2) divided by the heat flow rate (P). Therefore, the smaller the thermal resistance of the substrate material, the higher its thermal conductivity.

    High-efficiency thermal conductive ceramic substrate and gasket, high thermal conductivity, thermal conductivity: 24W/MK; high temperature/high pressure resistance, uniform heat, fast heat dissipation; simple and compact structure, small size, resistance to acid and alkali corrosion of heating elements, durable; ROHS environmental standards.

    The ceramic substrate DCB refers to a special process in which the copper foil is directly bonded to the surface of the alumina (AL2Q3) or aluminum nitride (ALN) ceramic substrate (single or double sided) at a high temperature. The ultra-thin composite substrate produced has excellent electrical insulation properties, high thermal conductivity, excellent solderability and high adhesion strength, and can etch various patterns like a PCB board, and has a large current carrying current. ability. Therefore, the DCB substrate has become the basic material for high-power power electronic circuit structure technology and interconnection technology, and is also the basis of the chip-on-board technology in the development direction of packaging technology in this century.

Yiwu Fuwei e-commerce firm (IACS Co., Limited) is a very professional Led manufacturer who produces high quality outdoor led light. Our popular products are solar led lights, UFO lights, underwater lights and so on. If you have any question about the led product, please feel free to contact us.