原ASTM D5470-2006薄的热导性固体电绝缘材料传热性能的测试标准先更新为ASTM D5470-2012

Designation: D5470 – 12 An American National Standard

Standard Test Method for

Thermal Transmission Properties of Thermally Conductive

Electrical Insulation Materials1

This standard is issued under the fixed designation D5470; the number immediately following the designation indicates the year of

original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A

superscript epsilon （´） indicates an editorial change since the last revision or reapproval.

This standard has been approved for use by agencies of the Department of Defense.

1. Scope*

1.1 This standard covers a test method for measurement of

thermal impedance and calculation of an apparent thermal

conductivity for thermally conductive electrical insulation

materials ranging from liquid compounds to hard solid materials.

1.2 The term “thermal conductivity” applies only to homogeneous

materials. Thermally conductive electrical insulating

materials are usually heterogeneous and to avoid confusion this

test method uses “apparent thermal conductivity” for determining

thermal transmission properties of both homogeneous and

heterogeneous materials.

1.3 The values stated in SI units are to be regarded as

standard.

1.4 This standard does not purport to address all of the

safety concerns, if any, associated with its use. It is the

responsibility of the user of this standard to establish appropriate

safety and health practices and determine the applicability

of regulatory limitations prior to use.

2. Referenced Documents

2.1 ASTM Standards:2

D374 Test Methods for Thickness of Solid Electrical Insulation

E691 Practice for Conducting an Interlaboratory Study to

Determine the Precision of a Test Method

E1225 Test Method for Thermal Conductivity of Solids by

Means of the Guarded-Comparative-Longitudinal Heat

Flow Technique

3. Terminology

3.1 Definitions of Terms Specific to This Standard:

3.1.1 apparent thermal conductivity （l）, n—the time rate of

heat flow, under steady conditions, through unit area of a

heterogeneous material, per unit temperature gradient in the

direction perpendicular to the area.

3.1.2 average temperature （of a surface）, n—the areaweighted

mean temperature.

3.1.3 composite, n—a material made up of distinct parts

which contribute, either proportionally or synergistically, to the

properties of the combination.

3.1.4 homogeneous material, n—a material in which relevant

properties are not a function of the position within the

material.

3.1.5 thermal impedance （u）, n—the total opposition that an

assembly （material, material interfaces） presents to the flow of

heat.

3.1.6 thermal interfacial resistance （contact resistance）,

n—the temperature difference required to produce a unit of

heat flux at the contact planes between the specimen surfaces

ａnd the hot and cold surfaces in contact with the specimen

under test. The symbol for contact resistance is RI.

3.1.7 thermal resistivity, n—the reciprocal of thermal conductivity.

Under steady-state conditions, the temperature gradient,

in the direction perpendicular to the isothermal surface

per unit of heat flux.

3.2 Symbols Used in This Standard:

3.2.1 l = apparent thermal conductivity, W/m·K.

3.2.2 A = area of a specimen, m2.

3.2.3 d = thickness of specimen, m.

3.2.4 Q = time rate of heat flow, W or J/s.

3.2.5 q = heat flux, or time rate of heat flow per unit area,

W/m2.

3.2.6 u = thermal impedance, temperature difference per

unit of heat flux, （K·m2）/W.

4. Summary of Test Method

4.1 This standard is based on idealized heat conduction

between two parallel, isothermal surfaces separated by a test

specimen of uniform thickness. The thermal gradient imposed

on the specimen by the temperature difference between the two

contacting surfaces causes the heat flow through the specimen.

This heat flow is perpendicular to the test surfaces and is

uniform across the surfaces with no lateral heat spreading.

1 This test method is under the jurisdiction of ASTM Committee D09 on

Electrical and Electronic Insulating Materials and is the direct responsibility of

Subcommittee D09.19 on Dielectric Sheet and Roll Products.

Current edition approved Jan. 1, 2012. Published February 2012. Originally

approved in 1993. Last previous edition approved in 2011 as D5470 – 11. DOI:

10.1520/D5470-12.

2 For referenced ASTM standards, visit the ASTM website, , or

contact ASTM Customer Service at service. For Annual Book of ASTM

Standards volume information, refer to the standard’s Document Summary page on

the ASTM website.

1

*A Summary of Changes section appears at the end of this standard.

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4.2 The measurements required by this standard when using

two meter bars are:

T1 = hotter temperature of the hot meter bar, K,

T2 = colder temperature of the hot meter bar, K,

T3 = hotter temperature of the cold meter bar, K,

T4 = colder temperature of the cold meter bar, K,

A = area of the test surfaces, m2, and

d = specimen thickness, m.

4.3 Based on the idealized test configuration, measurements

are taken to compute the following parameters:

TH = the temperature of the hotter isothermal surface, K,

TC = the temperature of the colder isothermal surface, K,

Q = the heat flow rate between the two isothermal surfaces,

W,

thermal impedance = the temperature difference between the

two isothermal surfaces pided by the heat flux through them,

K·m2/W, and

apparent thermal conductivity = calculated from a plot of

specimen thermal impedance versus thickness, W/m·K.

4.4 Interfacial thermal resistance exists between the specimen

ａnd the test surfaces. These contact resistances are

included in the specimen thermal impedance computation.

Contact resistance varies widely depending on the nature of the

specimen surface and the mechanical pressure applied to the

specimen by the test surfaces. The clamping pressure applied to

the specimen should therefore be measured and recorded as a

secondary measurement required for the method except in the

case of fluidic samples （Type I, see section 5.3.1） where the

applied pressure is insignificant. The computation for thermal

impedance is comprised of the sum of the specimen thermal

resistance plus the interfacial thermal resistance.

4.5 Calculation of apparent thermal conductivity requires an

accurate determination of the specimen thickness under test.

Different means can be used to control, monitor, and measure

the test specimen thickness depending on the material type.

4.5.1 The test specimen thickness under test can be controlled

with shims or mechanical stops if the dimension of the

specimen can change during the test.

4.5.2 The test specimen thickness can be monitored under

test with an in situ thickness measurement if the dimension of

the specimen can change during the test.

4.5.3 The test specimen thickness can be measured as

manufactured at room temperature in accordance with Test

Methods D374 Test Method C if it exhibits negligible compression

deflection.

5. Significance and Use

5.1 This standard measures the steady state thermal impedance

of electrical insulating materials used to enhance heat

transfer in electrical and electronic applications. This standard

is especially useful for measuring thermal transmission properties

of specimens that are either too thin or have insufficient

mechanical stability to allow placement of temperature sensors

in the specimen as in Test Method E1225.

5.2 This standard imposes an idealized heat flow pattern and

specifies an average specimen test temperature. The thermal

impedances thus measured cannot be directly applied to most

practical applications where these required uniform, parallel

heat conduction conditions do not exist.

5.3 This standard is useful for measuring the thermal

impedance of the following material types.

5.3.1 Type I—Viscous liquids that exhibit unlimited deformation

when a stress is applied. These include liquid compounds

such as greases, pastes, and phase change materials.

These materials exhibit no evidence of elastic behavior or the

tendency to return to initial shape after deflection stresses are

removed.

5.3.2 Type II—Viscoelastic solids where stresses of deformation

are ultimately balanced by internal material stresses

thus limiting further deformation. Examples include gels, soft,

ａnd hard rubbers. These materials exhibit linear elastic properties

with significant deflection relative to material thickness.

5.3.3 Type III—Elastic solids which exhibit negligible deflection.

Examples include ceramics, metals, and some types of

plastics.

5.4 The apparent thermal conductivity of a specimen can be

calculated from the measured thermal impedance and measured

specimen thickness if the interfacial thermal resistance is

insignificantly small （nominally less than 1 %） compared to the

thermal resistance of the specimen.

5.4.1 The apparent thermal conductivity of a sample material

can be accurately determined by excluding the interfacial

thermal resistance. This is accomplished by measuring the

thermal impedance of different thicknesses of the material

under test and plotting thermal impedance versus thickness.

The inverse of the slope of the resulting straight line is the

apparent thermal conductivity. The intercept at zero thickness

is the sum of the contact resistances at the two surfaces.

5.4.2 The contact resistance can be reduced by applying

thermal grease or oil to the test surfaces of rigid test specimens

（Type III）.

TEST METHOD

6. Apparatus

6.1 The general features of an apparatus that meets the

requirements of this method are shown in Figs. 1 and 2. This

apparatus imposes the required test conditions and accomplishes

the required measurements. It should be considered to

be one possible engineering solution, not a uniquely exclusive

implementation.

6.2 The test surfaces are to be smooth within 0.4 microns

ａnd parallel to within 5 microns.

6.3 The heat sources are either electrical heaters or temperature

controlled fluid circulators. Typical electrical heaters are

made by embedding wire wound cartridge heaters in a highly

conductive metal block. Circulated fluid heaters consist of a

metal block heat exchanger through which a controlled temperature

fluid is circulated to provide the required heat flow as

well as temperature control.

6.4 Heat flow through the specimen can be measured with

meter bars regardless of the type of heater used.

6.4.1 Electrical heaters offer convenient measurement of the

heating power generated but must be combined with a guard

heater and high quality insulation to limit heat leakage away

from the primary flow through the specimen.

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6.4.2 Heat flow meter bars can be constructed from high

conductivity materials with well documented thermal conductivity

within the temperature range of interest. The temperature

sensitivity of thermal conductivity must be considered for

accurate heat flow measurement. The thermal conductivity of

the bar material is recommended to be greater than 50 W/m·K.

6.4.3 Guard heaters are comprised of heated shields around

the primary heat source to eliminate heat leakage to the

environment. Guard heaters are insulated from the heat source

ａnd maintained at a temperature within 60.2 K of the heater.

This effectively reduces the heat leakage from the primary

heater by nullifying the temperature difference across the

insulation. Insulation between the guard heater and the heat

source should be at least the equivalent of one 5 mm layer of

FR-4 epoxy material.

6.4.4 If the heat flow meter bars are used on both the hot and

cold surfaces, guard heaters and thermal insulation is not

required and the heat flow through the test specimen is

computed as the average heat flow through both meter bars.

6.5 Meter bars can also be used to determine the temperature

of the test surfaces by extrapolating the linear array of

meter bar temperatures to the test surfaces. This can be done

for both the hot side and cold side meter bars. Surface

temperatures can also be measured with thermocouples that are

located in extreme proximity to the surfaces although this can

be mechanically difficult to achieve. Meter bars can be used for

both heat flow and surface temperature measurement or for

exclusively one of these functions.

6.6 The cooling unit is commonly implemented with a metal

block cooled by temperature controlled circulating fluid with a

temperature stability of 60.2 K.

6.7 The contact pressure on the specimen can be controlled

ａnd maintained in a variety of ways, including linear actuators,

lead screws, pneumatics, and hydraulics. The desired range of

forces must be applied to the test fixture in a direction that is

perpendicular to the test surfaces and maintains the parallelism

ａnd alignment of the surfaces.

7. Preparation of Test Specimens

7.1 The material type will dictate the method for controlling

specimen thickness. In all cases, prepare specimens of the same

area as the contacting test surfaces. If the test surfaces are not

of equal size, prepare the specimen equal to the dimension of

the smaller test surface.

FIG. 1 Test Stack Using the Meter Bars as Calorimeters

FIG. 2 Guarded Heater Test Stack

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7.1.1 Type I—Use shims or mechanical stops to control the

thickness of the specimen between the test surfaces. Spacer

beads of the desired diameter can also be used in approximately

2 % volumetric ratio and thoroughly mixed into the

sample prior to being applied to the test surfaces.

7.1.2 Type II—Use an adjustable clamping pressure to

deflect the test specimen by 5 % of its uncompressed thickness.

This represents a trade-off between lower surface contact

resistance and excessive sample deflection.

7.1.3 Type III—Measure the sample thickness in accordance

with Test Method C of Test Methods D374.

7.2 Prepare specimens from material that is in original,

as-manufactured condition or as noted otherwise. Remove any

contamination and dirt particles. Do not use solvent that will

react with or contaminate the specimens.

8. Procedure

8.1 Determination of test specimen thickness.

8.1.1 Machines with in situ thickness measurement apparatus.

8.1.1.1 Close the test stack and apply the clamping pressure

required for the specimen to be tested.

8.1.1.2 Turn on the heating and cooling units and let

stabilize at the specified set points to give an average sample

temperature of 50°C （average of T2 and T3）, unless otherwise

specified.

8.1.1.3 Zero the thickness measuring device （micrometer,

LVDT, laser detector, encoder, etc.）.

8.1.2 Machines without an in situ thickness measuring

apparatus.

8.1.2.1 At room temperature, measure the specimen thickness

in accordance with Test Method C of Test Methods D374.

8.2 Load the specimen on the lower test stack.

8.2.1 Dispense Type I grease and paste materials onto the

lower test stack surface. Melt phase change compounds to

dispense onto the stack.

8.2.2 Place Type II and III specimens onto the lower test

stack.

8.3 Close the test stack and apply clamping pressure.

8.3.1 Type I materials being tested with shims to control the

test thickness require only enough pressure to squeeze out

excess material and contact the shim but not too much pressure

that will result in the shim damaging the surfaces of the test

stacks.

8.3.1.1 For machines with screw stops, electromechanical,

or hydraulic actuators controlling the position of the upper test

stack, the magnitude of the clamping pressure is not critical.

8.3.1.2 Raise the temperature of the test stack above the

specimen melting point to enable phase change materials to

flow and permit closing of the test stacks. After the material has

flowed, return the heating and cooling units to the required set

points to maintain an average specimen temperature of 50°C

before beginning the test, unless otherwise specified.

8.3.2 Type II materials require enough pressure to coalesce

stacked specimens together and minimize interfacial thermal

resistances. Too much pressure can damage the specimens.

This can be as low as 0.069 MPa （10 psi） for softer specimens

or as high as 3.4 MPa （500 psi） for harder specimens.

Alternatively, screws or linear actuators can be used to control

the specimen thickness under test for easily deformable Type II

materials.

8.3.3 Type III materials require enough pressure to exclude

excess thermal grease from the interface and to flatten specimens

that are not flat. This can be as low as 0.69 MPa （100 psi）

for flat specimens with low viscosity thermal grease or as high

as 3.4 MPa （500 psi） for non-flat specimens or when using high

viscosity thermal grease.

8.4 Record the temperatures of the meter bars and the

voltage and current applied to electrical heaters at equilibrium.

Equilibrium is attained when, at constant power, 2 sets of

temperature readings taken at 5 minute intervals differ by less

than 60.1°C, or if the thermal impedance has changed by less

than 1 % of the current thermal impedance over a 5 minute

time span.

8.5 Calculate the mean specimen temperature and the thermal

impedance. Label the calculated thermal impedance for the

single-layer specimen as the “thermal impedance” of the

sample.

8.6 Determine the thermal impedance of at least 3 specimen

thicknesses. Maintain the mean temperature of the specimens

at 50 6 2°C （unless otherwise specified） by reducing the heat

flux as the specimen thickness is increased.

8.6.1 For specimens that need to be stacked to get different

thicknesses, first measure the thermal impedance of one layer

alone, then measure the thermal impedance of 2 layers stacked

together, and then measure the thermal impedance of 3 layers

stacked together.

8.6.2 For specimens of 3 different thicknesses A, B, and C,

first measure the thermal impedance of specimen A alone, then

measure the thermal impedance of specimen B alone, then

measure the thermal impedance of specimen C alone.

9. Calculation

9.1 Heat Flow:

9.1.1 Heat Flow When Using the Meter Bars For

Calorimeters—Calculate the heat flow from the meter bar

readings as follows:

Q12 5

l12 3 A

d 3 @T1 – T2# （1）

Q34 5

l34 3 A

d 3 @T3 – T4# （2）

Q 5

Q12 1 Q34

2 （3）

where:

Q12 = heat flow in hot meter bar, W,

Q34 = heat flow in cold meter bar, W,

Q = average heat flow through specimen, W,

l12 = thermal conductivity of the hot meter bar material,

W/（m·K）,

l34 = thermal conductivity of the cold meter bar material,

W/（m·K）,

A = area of the reference calorimeter, m2,

T1 – T2 = temperature difference between temperature sensors

of the hot meter bar, K,

T3 – T4 = temperature difference between temperature sensors

of the cold meter bar, K, and

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d = distance between temperature sensors in the

meter bars, m.

9.1.2 Heat Flow When Not Using the Meter Bars for

Calorimeters—Calculate the heat flow from the applied electrical

power as follows:

Q 5 V 3 I （4）

where:

Q = heat flow, W,

V = electrical potential applied to the heater, V, and

I = electrical current flow in the heater, A.

9.2 Derive the temperature of the hot meter bar surface in

contact with the specimen from the following:

TH 5 T2 –

dB

dA

3 @T1 – T2# （5）

where:

TH = temperature of the hot meter bar surface in contact

with the specimen, K,

T1 = warmer temperature of the hot meter bar, K,

T2 = cooler temperature of the hot meter bar, K,

dA = distance between T1 and T2, m, and

dB = distance from T2 to the surface of the hot meter bar in

contact with the specimen, m.

9.3 Derive the temperature of the cold meter bar surface in

contact with the specimen from the following:

TC 5 T3 1

dD

dC

3 @T3 – T4# （6）

where:

TC = temperature of the cold meter bar surface in contact

with the specimen, K,

T3 = warmer temperature of the cold meter bar, K,

T4 = cooler temperature of the cold meter bar, K,

dC = distance between T3 and T4, m, and

dD = distance from T3 to the surface of the cold meter bar

in contact with the specimen, m.

9.4 Calculate the thermal impedance from Eq 7 and express

it in units of （K·m2）/W:

u 5

A

Q 3 @TH – TC# （7）

9.5 Obtain apparent thermal conductivity from a plot of

thermal impedance for single and multiple layered specimens

against the respective specimen thickness. Plot values of the

specimen thickness on the x axis and specimen thermal

impedance on the y axis.

9.5.1 The curve is a straight line whose slope is the

reciprocal of the apparent thermal conductivity. The intercept

at zero thickness is the thermal interfacial resistance, RI,

specific to the sample, clamping force used, and the clamping

surfaces.

9.5.2 As a preferred alternative, compute the slope and the

intercept using least mean squares or linear regression analysis.

10. Report

10.1 Report the following information:

10.1.1 Specimen identification:

10.1.1.1 Name of the manufacturer,

10.1.1.2 Batch or lot number,

10.1.1.3 Grade designation,

10.1.1.4 Nominal thickness, and

10.1.1.5 Any other information pertinent to the identification

of the material.

10.1.2 Number of layers used in the test.

10.1.3 Average temperature of the specimen, if other than

323 K.

10.1.4 Pressure used during testing,

10.1.5 Thermal transmission properties:

10.1.5.1 Apparent thermal conductivity from 9.5, and

10.1.5.2 Thermal impedance from 9.4 （normalized to nominal

thickness for Type II materials）.

11. Precision and Bias

11.1 A round robin was conducted on five Type II materials

having different constructions and thicknesses. Six laboratories

tested specimens from all of the materials using either the

specified test method or additional Test Method B of this

standard, which is now deleted. Table 1, prepared in accordance

with Practice E691, summarizes the results of the round

robin. Data obtained during the round-robin testing are being

made available in a research report.

11.2 From the data used to generate Table 1 the following

conclusion is made:

11.2.1 Thermal conductivity values for the same material

measured in different laboratories are expected to be within

18 % of the mean of the values from all of the laboratories.

11.3 Bias for this test method is currently under investigation

subject to the availability of a suitable reference material.

12. Keywords

12.1 apparent thermal conductivity; guarded heater method;

thermal conductivity; thermal impedance; thermally conductive

electrical insulation

TABLE 1 Precision for Conductivity Measurement

NOTE 1—Values are in units of watt per meter Kelvin.

Material Identity Average Sr

A SR

B rC RD

Material B 0.923 0.0383 0.163 0.107 0.456

Material E 1.245 0.0834 0.175 0.234 0.491

Material C 1.311 0.0423 0.192 0.119 0.536

Material A 2.732 0.2010 0.311 0.563 0.872

Material D 5.445 0.5691 0.711 1.594 1.991

A Sr = within-laboratory standard deviation of the average.

B SR = between-laboratories standard deviation of the average.

C r = within-laboratory repeatability limit = 2.8 3 Sr.

D R = between-laboratories reproducibility limit = 2.8 3 SR.

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SUMMARY OF CHANGES

Committee D09 has identified the location of selected changes to this test method since the last issue,

D5470 – 01, that may impact the use of this test method. （Approved April 1, 2006）

（1） The test method was heavily revised throughout to remove

non-mandatory language and to clarify mandatory aspects in

the method, apparatus, specimens, and procedures.

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