Thermal Interface Material Analysis Thermal Interface Material Analysis

I. What is a thermal interface material
II. Why thermal interface materials are needed
III. What is the ideal thermal interface material?
IV. Introduction of several common thermal interface materials.

1. Thermal grease
2. Thermally conductive silicone sheet
3. Thermally conductive phase change materials
4. Thermally conductive double-sided stickers 5. Thermally conductive graphite sheets

V. Selection of thermal interface materials for LED lamps.
VI. Initiatives

I. What is a thermal interface material

• Thermal interface materials [Thermal Interface Materials], also known as thermal interface materials or interface heat conduction materials, are materials commonly used in IC packaging and electronic heat dissipation, mainly used to fill the micro-gap and The uneven holes on the surface reduce the heat transfer contact resistance and improve the heat dissipation performance of the device.

• Thermal Interface Materials (TIM) play a key role in thermal management and are an important branch of discussion in this discipline.

II. Why thermal interface materials are needed

• There are extremely fine uneven gaps between the surface of the microelectronic material and the heat sink. If they are directly installed together, the actual contact area between them is only 10% of the base area of the heat sink, and the rest are air gaps. Because the thermal conductivity of air is only 0.024W/(m·K), it is a poor conductor of heat, which will lead to an extremely large contact thermal resistance between the electronic components and the heat sink, which seriously hinders the conduction of heat, and finally causes the performance of the heat sink to be low. .

• Use thermal interface materials with high thermal conductivity to fill these gaps, remove the air in them, and build effective heat conduction channels between electronic components and heat sinks, which can greatly reduce contact thermal resistance and make the heat sink fully play its role .

III. What is the ideal thermal interface material?

The properties that an ideal thermal interface material should have are:
(1) High thermal conductivity;
(2) High flexibility, to ensure that the thermal interface material can fully fill the gap between the contact surface under low installation pressure conditions, and ensure that the contact thermal resistance between the thermal interface material and the contact surface is small; (3) Insulation;
(4) Easy to install and detachable;
(5) Wide applicability, it can be used to fill both small gaps and large gaps.

IV. Introduction of several common thermal interface materials
• 1. Thermal grease
〔1〕. Thermally conductive silicone grease is commonly known as heat dissipation paste. Thermally conductive silicone grease is a thermally conductive silicone grease compound made of organic silicone as the main raw material and adding materials with excellent heat resistance and thermal conductivity.
〔2〕 Advantages: high cost performance, the most frequent heat conduction material in electronic heat dissipation.
Points to note: It is inconvenient to operate. Ordinary thermal paste will have silicone oil, which will dry out after a long time. It is not recommended to use thermal paste for products with a long service life.

2. Thermally conductive silicone sheet
   A. Thermally conductive silica gel sheet is a thermally conductive medium material synthesized by a special process with silica gel as the base material, adding various auxiliary materials such as metal oxides.
   B. In the industry, it is also known as heat-conducting silicone pad, heat-conducting silicon film, soft heat-conducting pad, etc., which are specially produced for the design scheme of using gaps to transfer heat, which can fill the gaps and complete the heat transfer between the heating part and the cooling part. .
   C. At the same time, it also plays the role of insulation, shock absorption, sealing, etc., which can meet the design requirements of miniaturization and ultra-thin equipment. It is extremely manufacturable and usable, and has a wide range of thickness. Filler.
   Advantages of thermally conductive silicone sheets
   • 1) The range and stability of the thermal conductivity of the thermal silica film
   • 2) Bridging the technological gap in the structure of the heat-conducting silicone sheet, reducing the technological tolerance requirements of the radiator and heat dissipation structural parts
   • 3 〕The heat-conducting silicone sheet has the property of insulation.
   • 4) The heat-conducting silicone sheet has the effect of shock absorption and sound absorption.
   • 5 〕Heat-conducting silicone sheet has the convenience of installation, testing and reusability.

Thermally Conductive Phase Change Materials
• Phase Change Material (PCM – Phase Change Material) refers to a substance that changes shape with temperature and can provide latent heat. The process of phase change material changing from solid to liquid or from liquid to solid is called phase change process. At this time, the phase change material will absorb or release a large amount of latent heat.
• Advantages: Phase change materials are mainly solid-solid phase change now. In the case of thermal shock, they can absorb a certain amount of heat through phase change and slow down the impact of large heat flux. It is like adding a water storage to the heat conduction channel Chi. The phase change temperature of phase change materials on the market today may be around 45 °C to 50 °C. Phase change materials are mainly used on heat sources with instantaneous high heat flux such as CPUs, which can play a very good role in protection, especially At the moment of starting up or restarting. Points to note: There is a certain heat capacity and thermal resistance, which is less than the thickness of the heat-conducting silica gel sheet, and the thickness can be as thin as 0.125mm. It is not easy to save and install, and there is silicone oil precipitation, which will affect the light effect of the lighting equipment and change the heat-conducting medium. It is more suitable for consumer electronics and other products, especially notebook computers, game consoles, etc. However, its reliability is not good, and its performance will decrease under high temperature for a long time. Generally, the performance will decrease by 40% to 70% after 2 years of use.

Thermally conductive double-sided adhesive
• Thermally conductive double-sided adhesive, also known as thermally conductive tape, is composed of acrylic polymer filled with thermally conductive ceramic powder and compounded with silicone adhesive. It has the characteristics of high thermal conductivity and insulation, and has softness, compression, conformity and strong viscosity. Adapt to a wide temperature range, can fill the uneven surface, can closely and firmly fit the heat source device and heat sink, and conduct heat quickly.
• Advantages: It is very convenient to bond other heat sinks and heating equipment. Put the heat-conducting double-sided sticker between the heat sink and the heat sink, press it firmly, and the heat sink is firmly fixed on the heat sink. It is easy to use Convenient and conducive to improving production efficiency. Its heat dissipation effect is more obvious than that of ordinary heat dissipation stickers, which greatly improves the life of components, and is the first choice for some high-end electronic products that need heat conduction.
• Points to note: high requirements on the bonding surface, printing and electroplating surfaces are not suitable for use.

Thermal graphite sheet
• Thermally conductive graphite sheet is a brand-new heat-conducting and heat-dissipating material, which conducts heat evenly in two directions, shields heat sources and components, and improves the performance of consumer electronics products. High heat dissipation efficiency, small footprint, light weight, uniform heat conduction in two directions, eliminating “hot spot” areas, shielding heat sources and components while improving the performance of consumer electronics products.
• Advantages: high thermal conductivity, relatively thin material, high cost performance, super longitudinal thermal conductivity, and can quickly eliminate hot spots.
• Points to note: no insulation, relatively brittle material, large loss during punching.

V. Selection of thermal interface materials for LED lamps.

1. led street light:
   Different manufacturers have different designs. I have seen that some manufacturers do not use it, but it is not integrated lamp beads. Aluminum baseplates and housings are required to be extra flat. Some manufacturers use thermal paste, and also use thermal silica gel sheets. In the past two years, some manufacturers have used thermal conductive graphite sheets and solder paste.
   Suggestion: Use graphite sheet and thermal silica gel sheet.
2. led fluorescent lamp and panel lamp:
   It is best to use thermally conductive double-sided tape
3. Led spotlights and downlights: heat-conducting insulating sheet [0.23mm, withstand voltage 5kv], heat-conducting graphite sheet
   The above is just my contact with the selection of thermal interface materials by customers. Each manufacturer has different market positioning and selection is not the same. Heat dissipation affects the entire structure of the product, and the ultimate heat dissipation effect is determined not only by these thermal interface materials, but as a whole. Only when all materials and processes are in place can the best heat dissipation effect be produced. VI initiative
4. Don’t just superstitiously believe in one parameter of thermal conductivity. For example, the hardness of the thermal silica gel sheet is too high, and no matter how high the thermal conductivity is, it will have no effect, because the compression modulus is too small
5. Don’t be obsessed with low prices.
6. The most important thing is to actually install the product to test the final performance.
7. Finally, welcome everyone to research and study together. Our information is in the picture.