Welcome to Yiwu Leifeng Electronic Technology Co., Ltd. website
In accordance with the spirit of the "YiWu City High-Tech Enterprise Recognition and Management Measures" (YiZhengFa [2010] No. 112), and with the approval of the municipal government, YiWu LeiFeng Electronic Technology Co., Ltd., YiWu HengBang Intelligent Building Technology Co., Ltd., and Zhejiang XinDa Chemical Fiber Co., Ltd. are recognized as YiWu City high-tech enterprises.
13
2020/05
Heat dissipation of various circuit boards
Before connecting the LEDs to the heatsink, they must first be soldered into the circuit. This is because the LEDs must first be connected in series and parallel, and also connected to the constant current source in the circuit. The simplest method is to solder them directly to a standard printed circuit board (PCB). For some low-power LEDs, such as LED indicators, this is indeed feasible. However, for most high-brightness and high-power LEDs, the thermal conductivity of ordinary fiberglass PCBs is too poor, and it is necessary to switch to copper-clad boards, aluminum-clad boards, or even ceramic-clad boards. The performance of various substrates is as follows: Almost all LED luminaires in the past used aluminum substrates. The copper foil of the circuit on the aluminum substrate must have sufficient thickness and width for both electrical conductivity and thermal conductivity, with a thickness between 35µm and 280µm. Its width should ideally cover the entire substrate to facilitate heat dissipation. The underlying insulator requires good insulation and thermal conductivity. However, these two properties are contradictory; conductors generally have good thermal conductivity, while insulators have poor thermal conductivity. Achieving both good thermal conductivity and good insulation is difficult and remains a research topic. Currently, a modified epoxy resin or epoxy glass cloth adhesive sheet containing ceramic fillers is used. The copper foil, insulator, and aluminum plate are bonded together by hot pressing. Some LED luminaires, although the heatsink is carefully designed, fail quickly. The problem lies in the use of aluminum substrates with high thermal resistance or poor peel strength. After a period of use, the circuit film curls up, completely losing its ability to conduct heat, and quickly burning out the LEDs. For high-quality aluminum substrates, the thermal resistance is typically required to be less than 1°C/W. The following table shows the specifications for a certain type of aluminum substrate:
10
2017/08
How is the junction temperature of an LED chip generated?
LEDs generate heat because not all of the electrical energy input is converted into light energy; a portion is converted into heat energy. The luminous efficacy of LEDs is currently only 100 lm/W, and their electro-optical conversion efficiency is only about 20-30%. This means that approximately 70% of the electrical energy is converted into heat energy. Specifically, the LED junction temperature is generated due to two factors. 1. Low internal quantum efficiency; that is, when electrons and holes recombine, not 100% of them produce photons. This is usually referred to as "current leakage" causing carriers in the PN region
10
2017/08
LED integrated heat dissipation
Currently, many manufacturers integrate numerous LED chips to create high-power LEDs. These LEDs can achieve power outputs exceeding 5W, commonly appearing in power ratings of 10W, 25W, and 50W. To connect multiple LED chips (using either eutectic or flip-chip packaging), precise printed circuits are required due to the chips' minute size. Ceramic substrates are typically used for improved heat dissipation. These ceramic substrates are composed of aluminum oxide and aluminum nitride. The thermal conductivities of various materials are shown in the table below
10
2017/08