Ansys Icepak高级培训教材

1、Advanced Thermal Modeling,Advanced Thermal Modeling,Icepak高级建模,Fluent.inc,Course Outline,1. Introduction 简介 2. Printed Circuit Boards (PCB板) 3. IC Packages (IC 封装) 4. Heat Sinks 散热器 5. Interface Resistance 接触热阻 6. Fans, Impellers and Blowers 风扇，叶轮，离心风机 7. Altitude Effects 高度的影响 8. Flow Resistances 气

2、流阻尼 9. Radiation 幅射 10. Heat Pipes 热管 11. Joule Heating 电阻发热 12. Thermoelectric Coolers 热电冷却,Course Outline,13. Cold Plates 冷板 14. Transformers 变压器 15. Flow Baffles 气流挡板 16. Wall Effects 壁的效果 17. External Coolers/Heaters 外部冷却器/加热器 Exercises: 练习： 1. PBGA Model PBGA 模型 2. Selecting a Heat Sink 选择散热器 3

3、. Modeling TEC 热电冷却器模型 4. Selecting a Baffle 选择挡板 5. Modeling External Coolers 外部冷却器建模,Introduction,Introduction,简介,The Case for Thermal Management,The heat generated in an electronic circuit is inversely proportional to the efficiency of the circuit 电子线路板产生的热与它的效率成反比 The power that is not converted

4、 to perform useful electromagnetic work is lost in the form of heat to the surroundings 没有转换成电磁功率的热耗散到了周围的环境 The power wasted as heat includes: 热耗包括 Joule heating (I2R) loss 电阻损失 Power supply 电能提供 The reliability of a semiconductor device is directly affected by its operating temperature 工作环境的温度直接影响

5、到半导体设备的可靠性,The Case for Thermal Management,Virtually all electronic failure mechanisms are enhanced by the increase in package temperature: 实际上，所有电子失效的机理都是由于封装温度升高引起的 Stresses due to TCE (=Total Composite Error 总综合误差）mismatch 不匹配 Corrosion 腐蚀 Electro-migration 电子移动 Oxide breakdown 氧化物崩溃 Current leak

6、age (which doubles with every 10 c in active devices) 电流泄漏 Degradation in electrical performance (due to change in device parameters) 电性能下降,The Case for Thermal Management,The rate of failure of electronic packages is directly proportional to heat and increases exponentially with the maximum tempera

7、ture of the package 电子封装失效的比例直接与热成正比，而且与封装的最高温度成指数增长 The rate of failure can be expressed as: 失效的比例可描述为： F = Ae-E/KT where, F = failure rate, 失效率 A=constant 常数 E = activation energy in electron volts (eV) 激活的电能 K = Boltzmanns constant (8.63e-5eV/K), and T = junction temperature in K,The Case for The

8、rmal Management,The Case for Thermal Management,The Effect of Package Temperature on Failure (Number of failures after 1000 hr of operation per million units) 每百万个元件工作1000hr失效的数目,The Case for Thermal Management,Major Causes of Electronic Failure 电子失效的主要原因,Source: U.S. Airforce Avionics Integrity Pro

9、gram (Reynell, M., 1990),IC Package Trends,Packages are getting thinner 封装变薄 Number of leads is getting larger leads数目增多 Package footprint decreasing to approach chip size 为满足chip的尺寸，封装的footprint降低 Package pin pitch is decreasing 封装的pin pitch减少 Clock speed is increasing 时钟速度提高 IC chips are performin

10、g more complex tasks IC chips功能更复杂 Moving towards system-on-chip technology Packages are dissipating more power 功耗增加 Operating junction temperature remains fixed 工作的温度保持不变 55 C for commodity and handheld devices 生活用品55C 125 C for automotive systems 汽车系统125C Budget per watt of heat removal is decreas

11、ing 每watt的预算减少,Packaging Trends,Package Power Projection Trends (Watts) 封装功耗的发展趋势,Commodity: Low cost ($300) consumer products Hand-Held: Battery powered ($1000) products such as cellular, etc. Cost/Performance: Maximum performance with cost limit ($300) (Notebooks, etc.) High Performance: Performan

12、ce is the primary driver (Servers, Avionics, etc.) Harsh Environment: Automotive, Military, etc.,Cooling Methods,Types of cooling methods: 散热方法种类： Natural convection air cooling 自然对流 Forced air cooling 强迫对流 Immersion liquid cooling 浸润冷却 Boiling 蒸发冷却 Heat pipes 热管 Cold plates 冷板 Thermoelectric cooler

13、s 热电冷却 Microchannel cooling 微通道冷却 Microjet 微喷射冷却 Natural convection air cooling is used for low power applications 自然对流散热主要用于低功耗 It is the simplest and cheapest cooling method available,Cooling Methods,Forced air cooling（强迫对流）is used for relatively large loads of heat 主要用于相对大的热耗 It requires a fan, b

14、lower, etc. to move the air Immersion cooling is used to remove large loads of heat by immersing the components inside inert dielectric fluid such as fluorocarbon or Freon 浸润主要用于大热耗，通过将元件浸润到惰性非导热流体中，如碳氟化合物或氟利昂 Typical applications include mainframe computers, supercomputers, high-power transmitters,

15、 etc. Boiling heat transfer （蒸发换热）is the absorption of heat by a boiling fluid and is used for high power applications A cold plate（冷板） is a block of metal, liquid-cooled by forced convection, on which circuit cards or components are mounted They are used in military and high-power electronic applic

16、ations 主要是军用和高功耗电子设备,Cooling Methods,Microchannel Cooling （微通道冷却） is a technology dealing with very small fins that are placed extremely close to the heat dissipating element the coolant can be liquid or gas Thermoelctric coolers （热电冷却） are solid state heat pumps that do not have any moving parts no

17、r any working fluid They move heat from one location to another through the Peltier effect Heat pipes （热管）are devices that provide a passive method of transferring heat from one area to another Heat is absorbed at one end through evaporation and is rejected by condensation at the opposite end,Coolin

18、g Roadmap,Natural Convection,Moderate Forced Air,Advanced Forced Air,Liquid Cooling,Cooling Roadmap,Air Natural Convection + Radiation,Forced Air Convection,Immersion Natural Convection Fluorocarbons,Immersion-Boiling Florocarbons,Water Forced Convection,Modes of Heat Transfer,Three models of heat t

19、ransfer:三种传热方式： Conduction 传导 Convection 对流 Radiation 幅射 Conduction is a process in which heat flows between two media (solid, liquid or gas) that are in direct contact with one another 传导是发生在两种直接接触的介质（固体，液体，气体） In conduction, energy is transferred through: 传导过程中，能量通过以下方式传递 Movement of free electron

20、 自由电子运动 lattice vibration 点阵振动 Convection is the transfer of thermal energy between a surface and a moving fluid having some temperature difference对流发生在有温差的表面和运动流体间的传热,Modes of Heat Transfer,Convection can be: 对流有如下两种方式： Free (natural) convection Forced convection Radiation is the transfer of heat b

21、etween two surfaces that have no direct contact: 幅射发生在两种没有直接接触的表面 Energy is emitted through electromagnetic waves 能量通过电磁波传递 All object at temperatures above 0 K emit thermal radiation 所有物体大于0 K均发生热幅射 Most of the thermal radiation takes place in the infrared (红外）wavelength (0.1 to 100 micron)几乎所有热幅射发

22、生在红外波长范围 The rate of energy transfer depends on surface conditions and the view between the participating bodies 能量传递率与表面条件及相关物体间的视角有关,Conduction,Fouriers Law of Conduction: (1D conduction) 1D传导,Conduction,Where, Q = heat transfer T = temperature A = cross-sectional area k = thermal conductivity of

23、the slab DX = slab thickness R = DX/(kA) = Conduction resistance The slab is assumed to conduct in one direction,Fouriers Law of Conduction: (1D conduction),Conduction,Fouriers Law of Conduction: (1D conduction),Conduction,Fouriers Law of Conduction: (1D conduction),Convection,Convection may be free

24、 or forced.对流可以是自然和强迫 In free convection the flow is induced by density differences caused by temperature variations within the fluid. 自然对流是由于温度变化引起的流体内部密度不同产生的 In forced convection the flow is generated by external means such as fan, blower, pump, wind, etc. 强迫对流则是由于外部方式造成的气流 Flows may also be clas

25、sified as internal flows and external flows.气流也可以分为内流和外流 An internal flow is flow through confined domain such as ducts or channels.内流是发生在一定的空间内，如管道等 An external flow is flow over surfaces which can be fully or partially unconfined. 外流是全部或部分不在空间内的气流,Convection,Flows may also be classified as气流可以被分为：

26、 laminar, or 层流或 Turbulent 湍流 A laminar flow is a highly ordered flow where fluid particles move along identifiable paths层流是很规则的气流，气流的流线轨迹比较一致 In turbulent flows fluid motion is highly irregular and is characterized by random, three-dimensional motion 湍流很不规则，比较任意，三维运动 It involves strong mixing and m

27、ore vigorous heat transfer flow is inherently time-dependent Most real life flows are turbulent flows 大多数流动是湍流 Flows very near surfaces (of objects) are usually laminar flows离开物体表面很近气流通常是层流 This region is well within the boundary layer It is called the laminar sub-layer,Convection,External Flow 外流,I

28、nternal Flow 内流,Convection,Laminar Flow 层流,Turbulent Flow湍流,Convection: Newtons Law of Cooling,Convection: Typical h values,Representative h and R values典型的h和R值,Convection: Factors Affecting h,The heat transfer coefficient, h, depends on many factors: 传热系数取决于很多因素 Turbulent flows have larger heat tra

29、nsfer coefficient than laminar flows 湍流比层流 h值大 In general, forced convection flows have higher heat transfer coefficient than natural convection flows 强迫对流比自然对流h值大 Liquid flows have larger heat transfer coefficient than gas flows 液体比气体h值大 Rough surfaces have larger heat transfer coefficient than smo

30、oth surfaces (due to flow turbulence) 粗糙表面比光滑表面h值大 Entry (undeveloped) flows have larger heat transfer coefficient than fully developed flows 未展开气流比完全展开气流h值大 Unsteady flows tend to have higher heat transfer coefficient than steady ones 非稳态比稳态h值大,Printed Circuit Boards,PCBs,Printed Circuit Boards,Com

31、ponent-side (top) view,Source: Pixeldirect,Printed Circuit Boards,Solder-side (bottom) view,Source: Pixeldirect,Printed Circuit Boards,A printed circuit board (PCB) is generally a multi-layered board made of a dielectric material (glass-reinforced polymer or FR4) and several layers of copper planes

32、PCB是由FR4和几层铜板构成 It serves to wire mounted IC chips that would otherwise need thousands of point-to-point wire connections A single-layer board has components mounted on one side and copper (conductor) pattern on the other 一层板的元件安装在一边，铜线（导热器）在另一边 The copper pattern is established by photo-etching a c

33、opper foil pasted over FR4 A double-layer board has copper (conductor) pattern as well as components on both sides 两层板有铜，两边都有元件 A multi-layer board is made of several double-sided boards with insulating layers in between 多层板由几个两层板组成，在层与层之间有绝缘层,Printed Circuit Boards,Heat and pressure is applied to l

34、aminate the layers into a rigid structure called the PCB加热和加压而制成一种坚硬的结构叫PCB Multi-layer PCBs generally have 4-10 layers of copper 多层PCBs通常有4-10层铜线 To establish electrical connection between the different components and the copper layers, vias (small holes lined with metal plates) are drilled through

35、 the thickness of the PCB 为了使不同元件和铜线层建立连接，通过在PCB厚度上打孔 （vias） The vias may cut through the entire thickness of the PCB or connect a few layers only Vias 可能穿透整个板或只连接几层 In a multi-layer board, some of the copper layers are used to provide ground and power supply voltages, while the remaining layers are

36、 used to interconnect the IC chips 多层板中，有些铜线层会用来提供基础和电流电压，而其它的层用来提供IC chips 间的连接,Printed Circuit Boards,Laminates in a multi-layer PCB,Printed Circuit Boards,The area coverage of the copper layers can vary between 10% to 90% 铜线层的含量通常在10%到90% The thickness of one layer of copper is about 35 micron or

37、, as is commonly reported in the industry, it contains 1 oz of copper per square foot 一层铜的厚度约在35微米或每平方英尺含1 oz的铜 Components may be mounted on a PCB using 元件可以通过以下方式安装到 PCB上 Though-Hole Technology (THT), or穿孔型 Surface-Mount Technology (SMT)表面安装型 In THT, the legs (pins) of the components pass through h

38、oles and are soldered at the opposite side of the PCB THT 方法，pins通过孔到PCB另一面焊接 In SMT, the chips are soldered to the PCB and connected to the conductor layer on the same side of the PCB SMT方法，chips被焊接到PCB同一侧,Printed Circuit Boards,The conductivity of pure FR4 is 0.25 W/mK 纯FR4的导热率为0.25 The conductivi

39、ty of pure copper is 388 W/mK 铜的导热率为388 From thermal modeling point of view, a PCB be treated as a homogeneous material with non-isotropic (direction-dependent) conductivity从热模型的角度来看，PCB应作为一种非正交导热率的材料 The PCB model may will contain in-plane and normal-to-plane conductivity values PCB应有面内和法向导热值 The i

40、n-plane conductivity is much larger than the normal-to-plane conductivity面内值要比法向大得多 The in-plane conductivity increases with the number of copper layers of the PCB 面内导热率随着铜线层的增加而增加 The normal conductivity a PCB is nearly constant at about 0.3 W/mK 法向导热率通常在0.3,Printed Circuit Boards,The in-plane and

41、normal-to-plane conductivity values may be calculated as follows: 面内导热率可采用下面公式计算： kin-plane = S(kiti) /( Sti) knormal = Sti / S(ti/ki) ki = fi*kcu where, fi = fractional coverage of copper k = conductivity of a layer (W/mK) t = thickness of a layer (m) When higher accuracy is desired, a PCB may be m

42、odeled using multiple plates: 如果还希望得到更准确的数值，PCB应采用多层板来建模 A conducting thick plate for the FR4, and several conducting thin plates for the copper layers,Printed Circuit Boards,Example 例如： Number of cu layers = 8 Thickness of 1 layer of copper = 1 oz = 3.5e-5 m Thickness of 1 layer of FR4 = 1.453e-4 m

43、 Conductivity of copper = 388 W/mK Conductivity of FR4 = 0.25 W/mK In-plane conductivity: Kp = (8*388*3.5e-5) + (9*0.25*1.453e-4)/1.588e-3 = 68.6 W/mK Normal conductivity: Kn = 1.588e-3/(8*3.5e-5/388) + (9*1.453e-4/0.25) = 0.303 W/mK,Printed Circuit Boards,PCB Modeling,A PCB may be modeled using one

44、 of two ways: PCB可以采用如下的两种方法建模： Detailed model Compact model The Detailed PCB Model includes: 详细PCB包括： An FR4 plate or block, and Copper layers modeled as conducting thin plates The Compact PCB Model includes: 简化PCB模型包括： A Non-isotropic plate In-plane conductivity is much higher than the normal cond

45、uctivity The copper layers are not modeled separately,PCB Modeling,Icepak menu for PCB creation,PCB Modeling,Compact PCB Model,Detailed PCB Model,K (in-plane) = 27 W/mK K (normal) = 0.34 W/mK,FR4 (K=0.3 W/mK),Copper layers,Non-Isotropic material,IC Packages,IC Packages,IC封装,IC Packages,IC Packages,A

46、n IC package is the housing that protects the chip from: IC封装是为了保护的空间 Environmental stress such as humidity and pollution环境压力如湿度，污染 Mechanical stress such as cracking and overheating机械压力如破裂，过热 Electrical discharge during handling 操作过程中的放电 The IC package must also provide: IC封装必须提供： Interface for tes

47、ting 用于测试的接触面 Electrical interconnection to the next level of packaging 与PCB连接的电子连接面 An IC package must satisfy the above requirements while meeting other objects such as cost, quality and reliability IC封装还应满足其它要求如成本，质量和可靠性 It is the first level of electronic packaging 它是电子封装的第一级 The second level be

48、ing Package-PCB assembly 第二级是封装-PCB装配 The third level is PCB assembly to the Backplane 第三级是PCB与底板装配,Levels of Packaging,System-level Assembly,Backplane Assembly,IC Package,PCB Assembly,Chips,IC Packages,Packages may be classified (by mounting method) as: 封装可以分为（按安装方法）： Through-hole type (THT) 穿孔型 Su

49、rface mount type (SMT) 表面安装型 Special packages 特殊类型 THT packages have pins that are inserted into holes drilled across the thickness of the PCB THT封装的pins穿过PCB上的孔 They are used in package where board space is not premium Examples are DIP, PGA, etc. SMT packages have flat structure with the lead pins

50、soldered directly into the conductor pattern on the surface of the PCB SMT封装的pins直接焊接在PCB的表面 They are used in high pin density packages Examples are QFP, QFJ, etc.,THT Package Examples,ZIP (Zigzag In-line Package),DIP (Dual In-line Package),SMT Package Examples,QFP (Quad Flat Package),SSOP (Shrink S

51、mall Outline Package),IC Packages,IC Packages,Special packages are packages such as: 特殊类型封装如： Chip-on-board (COP) packages where the chip is mounted and sealed on the PCB COP封装被安装并密封在PCB上 Tape Carrier Packages (TCP) 带载封装 Memory modules 记忆模块 Power dissipation per chip is a function of: 每种芯片耗散功率是下列参数的

52、函数： Frequency, f 频率 Capacitance, C 电容 Voltage, V 电压 Gate count (I/O count) 门数 More specifically: 即： Power = F(f, C, V2, Gate count),IC Packages,Logic (ASIC) chips have more gates (and hence produce more power) than memory chips 逻辑芯片比记忆芯片有更多的门 Thus, from cooling perspective, logic chips are more diff

53、icult to cool than memory chips 因此，从散热的观点来看，逻辑芯片比记忆芯片要难,Examples of IC Packages,Plastic Ball Grid Array (PBGA) Low Conducting top ( 1 W/m/K) 顶部的导热率低(1 W/m/K) PCB type Material Substrate PCB 材料型底部 Small die (1/3 of package size) 小尺寸die Interconnect is at the die top, and so is the power die顶部与热源内部相连,

54、Examples of IC Packages,Tape Ball Grid Array (TBGA) High Conducting Top (copper)顶部的导热率高 Tape Substrate (thinner than PBGA) Substrate 比PBGA薄 Die is 1/3 of Package Interconnect is at the die bottom, and so is the power,Examples of IC Packages,Fine Pitch Ball Grid Array (FPBGA) Low Conducting top ( 1 W

55、/m/K)顶部的导热率低(1W/m/K) PCB type Material Substrate Chip Scale Package (CSP) (die is about 70% of package size) Interconnect is at the die top, and so is the power Model is exactly the same as PBGA 模型与PBGA相似,Examples of IC Packages,Flip Chip Ceramic Ball Grid Array (Flip chip-CBGA) Exposed die, optiona

56、l heat spreader, No wire Bonds 外露的die,可选的散热板，无线 Ceramic Substrate (K15 W/m/K) 陶瓷Substrate Interconnect at die bottom; Interconnect junctions is attached to solder bumps, which in turn connects signal traces Model is exactly the same as PBGA 模型与PBGA相似,Examples of IC Packages,Plastic Quad Flat Pack (P

57、QFP) Low Conducting overmolding ( 1 W/m/K)顶部的导热率低 Die is about 1/3 of package; No substrate Interconnect is at the die top, and so is the power Connects peripherally to PCB circuitry via gold wire leads,Examples of IC Packages,ABGA (Advanced BGA),Package with Ceramic Substrate (CBGA),Conduction Path

58、s,Types of Package Models,Detailed Models详细的模型 Details of the package are included in the model, such as solder balls, leads, die, encapsulation, substrate, etc. Used for Package Level Modeling and measurement validation Compact (Semi-Detailed) Models 简化的模型(半详细) The main components are modeled using

59、 Thick or Thin conducting plates, components such as the die, solder balls, substrate, etc. This model is used to reduce the mesh count There is some drop in accuracy as a result Good for Board and Sub-system Level Modeling,Types of Package Models,Network (Resistance) Models 网络模型 Package modeled using resistance network The network can be two-resistor network, Star network, Shunt network, etc. The user must supply the resistance Values for the network The resistance values may be obtained from manufacturers,