Thermal Interface Material(TIM) Application Notes. Technical Document. Reference layout, design tips, guides, and cautions for GlobalTop GPS modules.

Transcription

1 Technical Document Ver. A01 GlobalTop Technology Inc. Thermal Interface Material(TIM) Application Notes Revision: A00 Reference layout, design tips, guides, and cautions for GlobalTop GPS modules. prior permission of GlobalTop Tech Inc. Specifications subject to change without prior notice. Copyright 2011 GlobalTop Technology Inc. TCPA Applied Materials Business Unit. All Rights Reserved. No.16 Nan-ke 9 th Rd, Science-Based Industrial Park, Tainan, 741, Taiwan, R.O.C. Tel: / Fax: / sales@gtop-tech-materials.com / Web:

2 2 Version History Title: Subtitle: Doc Type: GlobalTop GPS Module Application Notes Thermal Interface Material Technical Document Revision Date Editor Description A Liv First Release

3 3 Table of Contents 1. Introduction Heat Transfer Conduction Thermal Conductivity Thermal Resistance & Impedance Thermal Diffusivity Thermal Interface Material (TIM) Aluminum Nitride (AlN) Aluminum nitride applications... 11

4 4 1. Introduction The rapid development of today's electronics industry, the trend toward short, light with the the latest process R & D and innovation, the trend of electronic products. Since the volume of the electronic products are getting smaller and smaller, but the increase of the function so that the power required to also followed improved and therefore often will cause the temperature of the electronic component is too high due to the heat generated by the unit volume is too large, or even make a component failure, In order to make the operating temperature of the electronic components can meet the requirements, the design of the electronic cooling performance of precision electronic products will have a very significant impact. Between the various cooling module and electronic products, often due to problems on the production gap can not completely seal, resulting in increased contact resistance between the interface (contact resistance), resulting in the temperature of electronic components and thus improve. In order to reduce this contact thermal resistance between the heat source and heat sink module often required by a good thermal conductivity properties of thermal interface material (thermal interface material TIM), to reduce the thermal resistance, and improve the efficiency of the cooling module. 2. Heat Transfer Thermal energy is related to the temperature of matter. For a given material and mass, the higher the temperature, the greater its thermal energy. Heat transfer is a study of the exchange of thermal energy through a body or between bodies which occurs when there is a temperature difference. When two bodies are at different temperatures, thermal energy transfers from the one with higher temperature to the one with lower temperature. Heat always transfers from hot to cold. There are three modes of heat transfer: conduction, convection, and radiation. Any energy exchange between bodies occurs through one of these modes or a combination of them. Conduction is the transfer of heat through solids or stationery fluids. Convection uses the movement of fluids to transfer heat. Radiation does not require a medium for transferring heat; this mode uses the electromagnetic radiation emitted by an object for exchanging heat. 2.1 Conduction Conduction is at transfer through solids or stationery fluids. When you touch a hot object, the heat you feel is transferred through your skin by conduction. Two mechanisms explain how heat is transferred by conduction: lattice vibration and particle collision. Conduction through solids occurs by a combination of the two mechanisms; heat is conducted through stationery fluids primarily by molecular collisions.

5 5 In solids, atoms are bound to each other by a series of bonds, analogous to springs as shown in Figure 1.1. When there is a temperature difference in the solid, the hot side of the solid experiences more vigorous atomic movements. The vibrations are transmitted through the springs to the cooler side of the solid. Eventually, they reach an equilibrium, where all the atoms are vibrating with the same energy. 圖 1.1 Conduction by lattice vibration Solids, especially metals, have free electrons, which are not bound to any particular atom and can freely move about the solid. The electrons in the hot side of the solid move faster than those on the cooler side. This scenario is shown in Figure 1.2. As the electrons undergo a series of collisions, the faster electrons give off some of their energy to the slower electrons. Eventually, through a series of random collisions, an equilibrium is reached, where the electrons are moving at the same average velocity. Conduction through electron collision is more effective than through lattice vibration; this is why metals generally are better heat conductors than ceramic materials, which do not have many free electrons. 圖 1.2 Conduction by particle collision 2.2 Thermal Conductivity The effectiveness by which heat is transferred through a material is measured by the thermal conductivity, k. A good conductor, such as copper, has a high conductivity; a poor conductor, or an insulator, has a low conductivity. Conductivity is measured in watts per meter per Kelvin (W/mK). The rate of heat transfer by conduction is given by:

6 6 where A is the cross-sectional area through which the heat is conducting, Δ T is the temperature difference between the two surfaces separated by a distance Δ x (see Figure 1.3). In heat transfer, a positive q means that heat is flowing into the body, and a negative q represents heat leaving the body. 2.3 Thermal Resistance & Impedance Thermal resistance(r) is a measurement of a material's ability to resist heat transfer. For conduction, the thermal resistance is expressed as: where L is the thickness, k is the thermal conductivity, and A is the cross-sectional area. Thermal Impedance(I) is defined as the temperature gradient per unit of heat flux, (q/a), passing through the interface. It is calculated by simply multiplying thermal resistance by the component area: I = R x A = A/(K.L) 2.4 Thermal Diffusivity A high conductivity material tends to have a more even temperature distribution than one with a low thermal conductivity. A material with low specific heat requires less thermal energy to heat; therefore, it heats faster than one with a high specific heat. Thermal diffusivity(α ) is the combination of the three properties: where k is the thermal conductivity, ρ is the density, and cp is the specific heat. Thermal diffusivity measures the effectiveness by which a material conducts thermal energy with respect to its ability to store thermal energy. A material with high a is characterized by a quick response to the changes in surrounding temperatures. A material with low a takes longer to reach a steady state condition, but is excellent at retaining heat once heated.

7 7 3. Thermal Interface Material (TIM) Electronic equipment or electronic components, heat, heat source and heat sink module is often required by a good thermal conductivity properties of thermal interface material (thermal interface material, TIM), in order to reduce the thermal resistance between the heat source and heat sink moduleimprove the efficiency of the cooling module and can further reduce the temperature of the heat generating element. AIR In general, thermal interface material (TIM), the thinner the better, the thermal conductivity as high as possible, the thermal paste (liquid) to fill the gap better than thermal pads (solid). The thermal interface material consists essentially of a thermally conductive filler material (thermal filler) and the base material (matrix), the thermally conductive filler material is divided into: the ceramic (ZnO, SiO2, Al2O3, BN, AlN, SiC, BeO...), a metal (Al, Ag...) and other (Graphite, the Diamond...), the substrate due to the application of the finished product varies main substrate shown

8 8 3.1 Aluminum Nitride (AlN) AlN was first synthesized in 1877, but it was not until the middle of the 1980s that its potential for application in microelectronics was realized due to its relative high thermal conductivity for an electrical insulating ceramic ( W/mK for polycrystalline material, and as high as 285 W/mK for single crystals). Aluminum nitride is a ceramic insulator, ceramics, usually thermal conductivity, relatively low, but was very excellent heat retaining capacity, aluminum nitride is a substance covalently linked, for the hexagonal crystal structure, it is different with the beryllium oxide is aluminum nitridenon-toxic. Its main characteristics are as follows: (1) Aluminum nitride production and inspection processes are as follows: (2) The aluminum nitride divided into BF, AF, SF three categories, AF metal impurities treatment, SF after the processing of the metal impurities, and then the silane surface treatment.

9 9 (3) Aluminum nitride according to the diameter (D50) the divided ALN020 ALN050, ALN100, ALN200 four specifications, D50 represents the average of the powder particle size, commonly refers to the cumulative particle size distribution of a sample of the percentage reaches 50% corresponding toparticle size. And the particle diameter the larger the specific surface area (SSA) smaller. (4) Effect of particle size Large particle diameter (10,20 um) aluminum nitride powder is suitable when the heat-conductive filler material, the particle diameter the larger the specific surface area, the lower the viscosity of the resin after adding a powder relative filling amount may be higher, and the large particle diameter powder specific surface areathe small contact area between the small, and the base material (resin), the thermal resistance decreases. Small particle size (2,5 um) aluminum nitride powder suitable substrate sintering, the particle diameter is smaller than the large surface area, adding a powder resin after adding a powder resin after the relatively high viscosity and therefore the filling volume is low, the small particle diameter ratio The large surface area in contact with the base material (resin), the area is large, adverse heat through conduction, the thermal resistance increases. (5) The effect of particle size hybrid

10 10 Order to maximize filler loadings, it is possible to use several different particle diameter mixed, the particle size distribution of the impact on the viscosity is large, dispersed same volume, the viscosity of the two different particle size after mixing, will be much smaller than a, the use of three or moreparticle size, the maximum filling amount can be as high as 90% or more. If the filling of a single particle size powders, it is recommended to use 20 um, if filling two kinds of particle size mixed powder, it is recommended to use a ratio of 5 um: 30um = 3: 7, if filled three particle size mixed powder, the recommended ratio for 2um: 5 um: 30um = 9: 24: 67. (6) The effect of Purity AlN powder for the filling level is less the required purity, for MCPCB AlN powder due to impact on the electrical properties required purity AlN powder sintering stage of the substrate due to the impact of sintering, it is also required purity. (7) Oil absorption The amount of oil that is required to "wet out" 100 grams of pigment and to make paint with a pigment is called oil absorption. Oil Absorption is expressed in number of grams of oil per 100 grams of pigment (or volume relationship from weight). This value varies depending upon the pigments physical nature and particle size. (8) surface treatment Coupling agent (coupling agent) silane commonly used to improve liquidity, resistance to hydrolysis, enhanced with organic bonding capacity. Because aluminum nitride is sensitive to moisture, surface treatment may be resistant to hydrolysis, without the surface treatment of aluminum nitride, preferably vacuum or irrigation nitrogen and to seal completely avoid hydrolysis. Hydrolysis-resistant surface treatment Organic bonding capacity enhancement SF aluminum nitride is silane (3-glycidoxypropyltrimethoxysilane, KBM-403) to do the surface treatment of a variety of silane (silane), subject to the mixed resin required to make the appropriate choice.

11 11 <remark> E: Most effective or most common P :Effective / Popular (9) AlN Content v.s. Thermal conductivity( k) Particle size Content Thermal conductivity K (um) (wt%) (W/m*k) Remark Epoxy Epoxy Epoxy Epoxy Epoxy Epoxy TCPA TCPA TCPA 3.2 Aluminum nitride applications Application of the aluminum nitride may be unsintered and high temperature sintered two categories, the non-sintered aluminum nitride powder can be made of the thermal paste (Thermal Grease), the thermally conductive adhesive tape (Thermal Tape), thermal pads (Thermal pad), a phase changematerial (Phase Change Material, PCM), thermal plastic (Thermal plastic), a metal core substrate (Metal core Printed Circuit Board, MCPCB), soft copper foil substrate (Flexible Copper Clad Laminate, FCCL), etc., of the ceramic substrate must be sintered at high temperatures.

12 12 (1) Thermal grease Thermal grease is a viscous fluid substance, originally with properties akin to grease, which increases the thermal conductivity of a thermal interface by filling microscopic air-gaps present due to the imperfectly flat and smooth surfaces of the components; the compound has far greater thermal conductivity than air (but far less than metal). The main ingredients of the thermal grease for silicone oil and hydroxide compounds containing silicon can be divided into substandard silicon and can mount three. Thermal paste is applied in a variety of electronic, electrical appliances, motor crystal cooling, the first thermal paste applied to the crystal, and then lock in the heat sink (aluminum), because of the power transistor will generate heat at work, fast heat conduction to heat through thermal grease aluminum plate heat, on the one hand, the growth of crystals of life, on the one hand, the crystal will not be distorted, because of its power crystal larger area of natural coating, used to sound up, in addition to the power supply, computer, regulator the use of anti-theft devices, etc. are the most common.

13 13 Screen Printing (2) Thermal Tape No-reforced tape:acrylic polymer composition, covered by the PET film, thickness 0.05~0.40 mm Two-sided tape:glass fiber coating pressure-sensitive adhesive, thickness 0.05~0.50 mm No-reforced tape Two-sided tape (3) Thermal pad

14 14 The thermal pads is added to the silicone within the thermally conductive filler (aluminum nitride) powder, generally used for the adhesion between the heat sink and crystal, the fins and the CPU take gum thermal effect without resulting in the IC, the CPU and other partstemperature to burn. Silicone need hardening molding (two-parts), with a low surface tension, wetting covering the surface of the vast majority of high, soft, easy to shape, the characteristics of high insulation and high temperature (> 200 ). (4) Phase Change Material (PCM) The phase change material in the solid to liquid phase change (solidification or melting) process can effectively save or the release of a lot of the latent heat, the biggest feature in that transfer of latent heat of the process, the temperature of the system was almost maintained on the fixed phase change temperature. The phase change material may be divided into the phase change material and wax (Paraffin Wax) hydration (Hydrated) a phase change material, this material at room temperature material is a solid and easy to install, used between the heat sink and the device. When achieve product phase transition temperature, the material becomes soft and flows, filling the the minute irregularities contact surface to the device, the ability to completely fill the voids between the interface air gap and the device and heat sink, so that the phase change pad is superior to noncurrent elastomer or graphite-based thermal pad, and having a thermally conductive silicone performance. (5) Thermal Plastic Thermoplastic engineering plastics and AlN via twin screw extrusion machines, extrusion granulation uniform mixing via injection molding machine injection molding required shape.

15 15 (6) Metal Core Printed Circuit Board (MCPCB) As the primary thermal path the MCPCB substrate to the metal (Al), but the board itself conductive metal, so the metal plate surface to be coated or bonded polymer dielectric layer dielectric (Epoxy + AlN). High power LED (> 1W), MCPCB mainstream market. MCPCB Process (7) Flexible Copper Clad Laminate (FCCL)

16 16 FCCL was one of the main raw material of soft board upstream. According to the number of layers can be divided into non-gel FCCL (2 Layer FCCL) and glue FCCL (3 Layer FCCL), the biggest difference is between the copper foil and polyimide film with or without adhesive (Epoxy + AlN). 2L FCCL, scratch off good heat resistance, good dimensional stability, but the cost is relatively high, so a large part of the soft board 3L FCCL the higher order FPC will be used 2L FCCL. Its major suppliers in notebook computers, mobile phones, LCD monitors, CD-ROM drive, digital camera. (8) Thermal Substrate The aluminum nitride ceramic substrate as compared with alumina, about seven times more than the high thermal conductivity, thermal expansion coefficient close to silicon, for loading large silicon and high reliability of the thermal loop, high electrical insulating properties, and a small dielectric constant, there arebetter than alumina and mechanical strength, has good corrosion resistance to the molten metal, and impurity content is extremely low, no toxicity, high purity. Sintered aluminum nitride powder requirements, small particle size, large surface area, high purity, normally takes to join the sintering sintering aids (Yttria, Y2O3) and Binder eight hours after sintering temperatures above The purity of the aluminum nitride powder has a considerable impact coefficient (k) of the thermal conductivity of the substrate after sintering. The various ceramic substrates comparison table below. Thermal Substrate process Substrate Comparison Characteristics AlN Al2O3 BeO SiC Typical property Purity wt% >99.6 > Density g/cm

17 17 Thermal property Electrical property Mechanical property Thermal conductivity CTE (RT~400 ) RT W/mK x10-4 / insulativity Ω.cm >10 14 >10 15 >10 15 >10 14 >10 13 dielectric constant (RT) 1MHz Tan δ x10-4 (1MHz) 5~ Hardness Kg/mm Flexural strength Kg/mm 2 30~40 30~ fracture Toughness MN.m -2/