Knowledge of LED heat dissipation problems

- Oct 02, 2018-

Knowledge of LED heat dissipation problems

When it comes to cooling systems, many people think of fans and heat sinks. In fact, they neglected a medium that is not eye-catching but plays an important role - the heat transfer medium. Computer CPU is a typical power device that needs good heat dissipation. Let's talk about thermal conductive materials. I hope you can discuss it and express your own experience and opinions on the heat dissipation of various power devices. Why do you need thermal media? Some people may think that the CPU surface or the bottom of the heat sink is very smooth, and no heat transfer medium is needed between them. This view is wrong! Since machining is not possible to create an ideal flat surface, there are many gullies or voids between the CPU and the heat sink, all of which are air. 

We know that the thermal resistance of air is very high, so other materials must be used to reduce the thermal resistance, otherwise the performance of the heat sink will be greatly reduced or even impossible to function. Then the heat transfer medium came into being. Its function is to fill the gap between the processor and the heat sink, and increase the contact area between the heat source and the heat sink. Therefore, heat conduction is only a function of the heat transfer medium, and increasing the effective contact area of the CPU and the heat sink is its most important function.

What are the thermal media?

 1. Thermal grease Silicone grease is the most widely used heat transfer medium. It is a kind of ester formed by using silicone oil as raw material and adding thickener and other fillers after heating, decompression, grinding and other processes. The substance has a certain consistency and no obvious graininess. Thermal grease has a working temperature of -50 ° C to 180 ° C. It has good thermal conductivity, high temperature resistance, aging resistance and water resistance. During the heat dissipation process of the device, after heating to a certain state, the thermal grease exhibits a semi-liquid state, fully filling the gap between the CPU and the heat sink, so that the two are more closely coupled, thereby enhancing heat conduction. Under normal circumstances, thermal grease is insoluble in water, is not easily oxidized, and has certain lubricity and electrical insulation.

2, thermal silica gel and thermal grease similar, thermal silica gel is also added to the silicone oil a certain chemical raw materials, and chemical processing. However, unlike thermal grease, there is a certain viscosity in the chemical raw materials it adds, so the finished thermal silica gel has a certain adhesive force. The most important feature of thermal silica gel is that it has a hard texture after solidification and its thermal conductivity is slightly lower than that of thermal grease. At present, there are two kinds of thermal silica gel on the market: one is a white solid after solidification, and the other is a solid black pigment after solidification. The average manufacturer is accustomed to using the first type of silica gel as a bonding agent between the heat sink and the heat generating object. The advantage is that the viscosity is very strong, which is precisely its disadvantage. When we need to repair, often after a lot of effort to separate the bonded device and the heat sink, we will find a large amount of solid white silica gel on the contact surface of the two. These silica gels are quite difficult to clean. In contrast, the second silica gel advantage is more obvious: first, its heat dissipation efficiency is higher than the first one, and secondly, the black solid formed after solidification is brittle, and the residue is easily removed. In any case, the thermal conductivity of the thermal silica gel is not strong, and it is easy to "stick" the device and the heat sink, so it is recommended to use it unless otherwise specified.

3, soft silicone thermal pad soft silicone thermal insulation pad has good thermal conductivity and high-grade pressure insulation, thermal conductivity of 1.75W / mK, resistance voltage breakdown of more than 4000 volts, is a substitute for thermal grease The product itself has a certain flexibility, which is well matched between the power device and the heat-dissipating aluminum sheet or the machine casing, so as to achieve the best heat conduction and heat dissipation purposes, and meet the requirements of the current electronic industry for the heat-conducting material, which is an alternative. The best product for the thermal cooling system of thermal grease and mica sheet. These products can be cut at will, which is convenient for automated production and product maintenance.

The thickness of the silicone thermal insulation insulating mat varies from 0.5mm to 5mm, 0.5mm per mm, ie 0.5mm 1mm 1.5mm 2mm~5mm, and the special requirement can be increased to 15mm. It is specially designed for the transmission of heat through the gap. Filling the gap, completing the heat transfer between the heat-generating part and the heat-dissipating part, and also functioning as a shock-absorbing and insulating seal, which can meet the design requirements of miniaturization and ultra-thinness of the social equipment, and is a new material with great processability and usability. Fire performance meets UL 94V-0 requirements and complies with EU SGS environmental certification