PCB for high power LED
At present, there are three types of PCBs for heat dissipation using high-power LEDs: ordinary double-sided copper-clad (FR4), aluminum-based copper-clad (MCPCB), and flexible thin-film PCBs bonded to aluminum alloy boards.
The structure of the MCPCB is shown in Figure 7. The thickness dimensions of each layer are shown in Table 3.
Figure 7 MCPCB structure diagram
The heat dissipation effect is related to the thickness of the copper layer and the metal layer, such as the size and the thermal conductivity of the insulating medium. Generally, a 35 μm copper layer and a 1.5 mm aluminum alloy MCPCB are used. The structure of the flexible PCB adhered to the aluminum alloy plate is as shown in FIG. The thickness of each layer generally used is shown in Table 4. 1 to 3W star LEDs use this structure. MCPCBs with high thermal conductivity media have the best thermal performance, but they are more expensive.
Figure 8 Heat dissipation layer structure
Calculation example:
Here, part of the data of the NICHIA company's measurement TC is taken as a calculation example. The known conditions are as follows:
LED: 3W white LED, model MCCW022, RJC=16°C/W. The K-type thermocouple point thermometer is welded to the cooling pad.
PCB test board: double-layer copper plate (40 × 40mm), t = 1.6mm, weld surface copper layer area 1180mm2 back copper layer area 1600mm2.
LED working status: IF=500mA, VF= 3.97V.
According to Figure 9, the TC was measured with a K-type thermocouple thermometer, TC = 71 °C. The ambient temperature during testing is TA = 25 °C.
1.TJ calculation
TJ=RJC×PD+TC=RJC(IF×VF)+TC
TJ=16°C/W (500mA×3.97V)
Edit: Sophy
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