Introduction of Thermal

GGT/RE – Environment Test Team

Primary Mechanic of Heat Transfer

Thermal energy transport: cause by temperature difference, high T -> low T

ConductionHeat transferring by solid medium

ConvectionTransferring energy between solid surface and fluidMass transportNatural (free) convectionForced convection

RadiationHeat transferring by electromagnetic waves

Conduction

Fourier’s LawQ= -KA ΔT/ΔLQ: heat transfer rateA: cross-sectional area of heat flux

ΔT/ΔL: temperature gradient K: thermal conductivity (W/mk)

Ex. Al = 230 Cu = 380 Mylar = 1.8

Convection Newtonian cooling LawQc = hc As (Ts – Ta)

Qc: convection heat transfer rateAs: surface areaTs: surface temperature of solidTa: tmperature of ambient

hc: heat transfer coefficient, f(flow type, body geometry, physical property, temperature, velocity, viscosity…)

Natural convection & Forced convctionhc of air, natural convection: 0.0015~0.015 W/in2℃

forced convection: 0.015~0.15 W/in2℃

Radiation

Qa = εσAF1-2( Ts4 – Ta4)Qa: radiation heat transfer rateε: emissivity, 0 ≦ ε ≦ 1σ: Stefan-Boltzmann constantA: surface areaF1-2: view factorTs: temperature of body sTa: temperature of body a

Thermal Resistance

R = V / IV: voltage = ΔT: temperature differenceI: current = Q: heat

ConductionRk = ΔL/KAk

Convection Rs = 1 / hcAs

RadiationRa = (Ts – Ta) /εσAF1-2( Ts4 – Ta4)

Basic Concepts for NB Thermal Design

Thermal Design TargetThermal design must meet thermal spec. of CPU, all ke

y components (HDD, FDD, CD-ROM, PCMCIA…), and all IC chips (Chipset, VGA, RAM, PCMCIA…), and all IC chips (Chipset, VGA, RAM, Audio…) in each user conditions

Thermal ResistanceΘj-a = (Tj – Ta) / Pcpu

Θ j-a : CPU junction to ambient thermal resistanceTj: CPU junction temperatureTa: ambient temperaturePcpu: CPU power

Basic Concepts for NB Thermal Design

System Thermal Coupling effect Θj-a = (Tj – Ta – Tsys) / Pcpu

Tsys: system temperature = Psys *Θ

= ΣPi*θi, (i: DRAM, Chipset, HDD, FDD, CD-ROM…)R: thermal coupling factor between Pcpu and Psys

Tj: CPU spec. for Intel: 100℃Ta: OEM spec., 35℃Θj-a, Tsys: OEM design dependent, Tsys = 10~15℃

Basic Concepts for NB Thermal Design

Thermal Solutions Passive thermal solution Active thermal solution Hybrid thermal solution

RHE Remote Heat Exchanger

Basic Concepts for NB Thermal Design

Characteristic of a good passive components Spreader plate connected to CPU should be

as large as possible Temperature variation on spreader plate

should be minimal

Characteristic of a good active component Air inlet and outlet should be clearly defined Length of air passage through NB should be

small to keep pressure drop low, flow rate high Possible reduce noise level of the fan Design must be capable of venting a portion

of hot air from NB inside

Important Components For Thermal Design

Heat Sink

Heat Pipe Fan TIM ( Thermal Interface Material)

Combination of aforementioned components

Heat Sink

MaterialMaterial : A1050 A6063 ADC12 C1100K(W/mk) : 230 210 192 384Specific gravity: 2.71 2.69 2.70 8.92

ProductionDie-castingExtruded

Q = -KAΔT/ΔLFin, Q = hAΔTDie-casting, extrusion, folder, stack, soldering fins

Heat Pipe Basic configuration and characteristicBasic specification

Material: copperWorking fluid: pure waterStandard working temperature: 0~100℃Size: ψ3, ψ4, ψ5, ψ6, ψ8

Typical heat pipe wick structuresFiber, mesh, groove, powder

Typical modification of heat pipeFlatteningBending

Heat Plate

Fan Structure

Rotator: magnetic blade, shaft Stator: bearing, wire, stainless plate Control circuit

TheoryType

Axial fan Blower fan

Selection Total cooling requirement

Q = Cp * m * ΔT = ρ* Cp * CFM * ΔT Total system resistance / system characteristic curve System operating point

Fan

Parallel and series operationAcoustical noise level (dB)To achieve low noise should consider System impedance Flow disturbance Fan speed and size Temperature rise Vibration Voltage variation Design considerations

TIM Thermal Interface Material To reduce contact thermal resistance

between CPU die and thermal module

Important of TIMMaterial Various material: silicon-base, carbon… Non-phase change Phase change

Pressure effect Pressure spec. on CPU spec. 100psi

Thermal Design ProcedureClarifyClarify Thermal Specification Thermal Specification

Design Thermal SolutionDesign Thermal Solution

Analytic Approach

Evaluate Solution Performance

Numerical Approach Experiment Approach

Verify

Design Thermal SolutionDesign Thermal Solution

Evaluate heat generationAllowable thermal resistanceAllowable design space

Evaluate Chassis heat dissipationEvaluate heat exchange areaEvaluate fan flow rate

PassFail

Inspect Structure.Production method.Cost…

Recommend Thermal Solution

Thermal Test in Working Sample

Verify Overall SystemMeeting Thermal Specification

Thermal Design OK!

Examine and ModifyThermal Solution

Pass

Fail

Thermal Design Guides

Design guide for thermal (Ver. 0.2)

Thank You!

fiber

Mesh

細絲( 銅絲 ) 螺旋

彈片

銅网

groove

直接加工而成

Powder 類型 : 金屬粉末燒結在 Heat Pipe 內壁 , 形成毛細結構

N

N

N

N

S SS S

無刷馬達轉動原理

有 Hall IC 感應其磁鐵 N.S. 極 , 經由電路控制其線圈之導通產生內部激磁使轉子部旋轉

CFM(ft3/min)

Static pressure

System resistance

curve

Fan curve

System operating

point

1. Thermal Module

1) Reserve space for thermal module (Intel recommendation)

Coppermine: 70*50*11.5mmTualatin: 75*55*11.5mmNorthwood: 85*60*19mm

2) It should reserve a gap between thermal module and top cover (keyboard cover)

1. Thermal Module

3) The gap between thermal module exit and NB case vent should be sealed well so the hot air couldn’t flow back to system. If leave an open gap along air flow path, it will affect thermal efficiency and acoustic noise.

1. Thermal Module

4) The thermal module and CPU should contact well.

a) The max pressure of the thermal module on CPU is 100psi. Within SPEC, efficiency of thermal module increases with pressure.

b) It’s better to fix module on M/B by four screws (avoiding three screws) and spring design.

2. Fan

1) Fan inlet constraints: gap 3~5mm is needed.

3mm ~ 80% performance4mm ~ 90% performance5mm ~ 100% performance

2) Configuration of air inlet & outlet vents can make dramatically flow resistance; therefore high open rate is better.

2. Fan

3) Don’t place blocks (large ICs or connector) near or below the fan to affect airflow induced into fan.

4) It is better for fixing fan by rubber instead of metal screws to avoid vibration.

2. Fan

5) The fan space design has some restrictions.

a) For efficiency and acoustic, the gap between fins and fan blade should keep a distance of L= 5 ~ 10 mm.

b) The distance W is better to keep as large as possible for good efficiency.

c) Fan blade should close to fan tongue for better efficiency.

3. PCMCIA Card

1) Don’t place PCMCIA on lower side of M/B, near hotter ICs, and stacked up key components (HDD, CD-ROM, DVD, FDD…).

2) If it needs to place PCMCIA near heat source, it is necessary to induce airflow to cool it.(Ex. For J2I++, L1R, it is removed metal plate

on PCMCIA slot and makes holes above PCMCIA if there is an Al plate upon it. By this way, air can flow through this area to cool PCMCIA card.)

3. PCMCIA Card

3) Due to aforementioned solution, PCMCIA should place near fan in order to induce airflow to cool.

4. Key Components

1) Because HDD, CD-ROM, FDD thermal SPCE is low, these key components need to be placed in colder region.

(Avoid placing them in the middle of the system and upon M/B with hot ICs, and stacking up each other).

2) It’s better to place FDD alone, not to put on/beneath CD-ROM or HDD.

5. Palm-Rest and Glid Pad

1) It should avoid placing hot components and ICs below palm-rest and glid pad.

2) It should reserve a gap to make a thermal resistance between palm-rest and the hot components or to add a metal plate for spreading heat.

6. LCD Inverter

It should reserve a gap between Inverter and LCD cover to make a thermal resistance or to add a metal plate for spreading heat.

7. Bottom case and Dimm Door 1) It should reserve a gap between IC chip

s and bottom case(gap > 3mm is better).

2) It might have a large Al-plate on bottom case for spreading heat.

3) M/B has a hole below fan in order to induce airflow under M/B.

4) It’s better to place hotter chips on upper side of M/B.

5) It should reserve a gap between Memory chips and dimm door (gape > 1.5mm is better).

8. M/B Layout

1) If there’s thermal issue of ICs, it should reserve space for thermal solutions

(Ex. Don’t place higher components beside these ICs, so it could put metal plate on ICs in future)

2) Don’t place low temperature spec ICs and components near hotter region or high temperature spec ICs and components.

9. Others

1) It’s better to use the thinner or phase change TIM (thermal interface material)

Ex. 28W CPU(phase change) Powerstrate 0.08mm 75℃

(phase change) T-pcm 0.25mm 83℃ T-pcm 0.50mm 86℃ (phase change with Al) T-mate 0.50mm 83℃ (non-phase change) Tx 0.25mm 90℃ Tx 0.5mm 96℃

9. Others1) Heat pipes on thermal module have

some restrictions 2) The thickness shouldn’t be less tha

n 2mm when be made flat. 3) The curve radius should be larger tha

n triple diameter at least when be bended.

4) It might need some holes on bottom case and sidewall of NB in order to induce airflow to dissipate heat.

3~5mm Air flow

Fan

3mm ~ 80% performance

4mm ~ 90% performance

5mm ~ 100% performance

Fan

Blocks

Bad design

L

W

Tongue

該縫隙越小 Fan 效率越高 , 但 Noise 也會隨之上升

L: 太大 , Fan 效率下降 ;

太小 , 噪音上升 .

W: 作為風道 , 盡量大

Single fan

Double fan Parallel

CFM

Pressure

Pressure

CFM

Single fan

Double fan Series

TIM: thermal interface material考慮將散熱器固定於發熱器件的方法時 , 重要的是要使二者之間界面熱傳到處效率最大 .也應考慮其他要求 , 如介電特性 , 電導性 , 附著強度和再次安裝的可能性 .發熱組件和散熱器之間界面的熱傳輸效率取決於空氣殘留 , 填充物類型和黏合曾的厚度等參數 .

方 法 優 點 缺 點機械安裝 有助於散熱 ;

可即時安裝空氣間隙導致較差的傳導率 ;緊固件導致壓應力

帶矽樹脂的機械安裝 ( 有 / 無雲母墊片 )

好的導熱率 流程控制困難 ; 由移植和灰塵造成的污染會引起接觸不良

帶可壓縮墊片和墊料的機械安裝

較好的導熱率 ;無移植問題

嚴重的扭矩變化會導致難以防止緊固件鬆動

帶還氧樹脂黏合劑的黏合

良好的導熱率 ;壓力均衡 ( 可避免鬆動 ); 無移植問題

要求混合 ; 罐裝壽命有限 ;熱固性不允許在線安裝

相變化材料 良好的導熱率 重複性使用差