LED circuit design to better solve the problem of heat dissipation, LED and some high power IC need to use aluminum based printed circuit board. Aluminum PCB consists of circuit layer ( copper foil layer), thermal insulation layer and metal base. The circuit layer should have a large current carrying capacity, so it should use thick copper foil, the thickness of which is generally 35 μ m ~ 280 μ m; Thermal insulating layer is the core technology of PCB aluminum substrate. It is generally composed of special polymers filled with special ceramics, with small thermal resistance, good viscoelasticity, resistance to thermal aging and ability to withstand mechanical and thermal stress. IMS-H01, The thermal insulation layer of high performance PCB aluminum substrate, such as IMS-H02 and LED-0601, is precisely using this technology, which makes it have excellent thermal conductivity and high strength electrical insulation performance. The metal base is the supporting member of the aluminum based, which requires high thermal conductivity. Generally, it is aluminum PCB. It can also use copper (which can provide better thermal conductivity). It is suitable for conventional machining such as drilling, punching, shearing and cutting. Surface finished are: HAL, Immersion gold,OSP, gold plating, HAL lead-free.
Why the thermal design of high temperature on electronic products:
Insulation degradation, component damage, material thermal aging, low melting point weld cracking, solder joint fall off; The effect of temperature on components: generally speaking, the increase of temperature decreases the resistance, the high temperature will reduce the service life of capacitor, and the high temperature will reduce the performance of transformer choke insulation material; Generally, the allowable temperature of choke coil is lower than 95C, and the structure of solder joint will change when it is too high-IMC thickening, solder joint brittle and mechanical strength decreasing. The increase of junction temperature will make the current amplification of transistor increase rapidly, lead to the increase of collector current, further increase the junction temperature, and finally lead to the failure of the module.
The purpose of the aluminum heat dissipation design is to control the temperature of all electronic components within the product so that it does not exceed the maximum temperature specified in the standard and specification in the working environment. The calculation of the maximum allowable temperature should be based on the stress analysis of the components and be consistent with the reliability requirements of the product and the failure rate assigned to each component. The heat dissipation design of LED is generally based on the fluid dynamics software simulation and basic design. First, the resistance of the fluid flow: because of the influence of the viscosity of the fluid and the influence of the solid boundary, the fluid is subjected to the resistance in the flow process, this resistance is called the flow resistance, which can be divided into two kinds: along the flow resistance and the local resistance; Second, the resistance along the course: the friction resistance of the fluid along the whole flow in the region where the boundary is constant; Third, local resistance: in the area where the boundary changes sharply, such as the sudden expansion or suddenly shrinking of the section, the local position of the elbow, it is the flow resistance caused by the rapid change of the fluid state of the fluid.
Usually, LED adopts radiator natural heat dissipation. The design of radiator is divided into three steps: 1. According to the relevant constraints, the outline of the radiator is designed. 2: according to the relevant design criteria of radiator, the tooth thickness, tooth shape, tooth spacing and substrate thickness of radiator are optimized. The design method of radiator 1, considering that the temperature boundary layer is thicker during natural cooling, if the tooth spacing is too small, the heat boundary layer of the two teeth is easy to cross, which affects the convection of the tooth surface, so generally speaking, It is suggested that the tooth spacing of natural cooling radiator is more than 12mm. If the tooth height of radiator is less than 10mm, the tooth spacing of radiator can be determined by tooth spacing ≥ 1.2 times of tooth height. 2, the heat transfer ability of the surface of natural cooling radiator is weak, and the effect of natural convection will not be greatly affected by increasing corrugation on the surface of the radiator, so it is suggested that no ripple teeth should be added to the surface of the radiator. 3, the radiator surface of natural convection is usually blackened to increase the radiation coefficient of the radiator surface and strengthen the radiation heat transfer. 4. Because the natural convection reaches the heat balance for a long time, the base plate and tooth thickness of the natural convection radiator should be sufficient to resist the impact of the instantaneous heat load, and it is suggested that the thickness of the natural convection radiator should be larger than 5mm.
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