1、Designation:D547006 (Reapproved 2011) Designation: D5470 12An American National StandardStandard Test Method forThermal Transmission Properties of Thermally ConductiveElectrical Insulation Materials1This standard is issued under the fixed designation D5470; the number immediately following the desig
2、nation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.This standard has been approved for use by
3、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 thermalconductivity for thermally conductive electrical insulation materials ranging from liquid compounds to hard solid materials.1.2 The term “t
4、hermal conductivity” applies only to homogeneous materials. Thermally conductive electrical insulatingmaterials are usually heterogeneous and to avoid confusion this test method uses “apparent thermal conductivity” for determiningthermal transmission properties of both homogeneous and heterogeneous
5、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 responsibilityof the user of this standard to establish appropriate safety and health practices and determin
6、e the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D374 Test Methods for Thickness of Solid Electrical InsulationE691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test MethodE1225 Test Method for Thermal Conductivi
7、ty of Solids by Means of the Guarded-Comparative-Longitudinal Heat FlowTechnique3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 apparent thermal conductivity (l), nthe time rate of heat flow, under steady conditions, through unit area of aheterogeneous material, per unit tempe
8、rature gradient in the direction perpendicular to the area.3.1.2 average temperature (of a surface), nthe area-weighted mean temperature.3.1.3 composite, na material made up of distinct parts which contribute, either proportionally or synergistically, to theproperties of the combination.3.1.4 homoge
9、neous material, na material in which relevant properties are not a function of the position within the material.3.1.5 thermal impedance (u), nthe total opposition that an assembly (material, material interfaces) presents to the flow of heat.3.1.6 thermal interfacial resistance (contact resistance),
10、nthe temperature difference required to produce a unit of heat fluxat the contact planes between the specimen surfaces and the hot and cold surfaces in contact with the specimen under test. Thesymbol for contact resistance is RI.3.1.7 thermal resistivity, nthe reciprocal of thermal conductivity. Und
11、er steady-state conditions, the temperature gradient, inthe 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/mK.3.2.2 A = area of a specimen, m2.3.2.3 d = thickness of specimen, m.3.2.4 Q = time rate
12、of heat flow, W or J/s.1This test method is under the jurisdiction of ASTM Committee D09 on Electrical and Electronic Insulating Materials and is the direct responsibility of SubcommitteeD09.19 on Dielectric Sheet and Roll Products.Current edition approved AprilJan. 1, 2011.2012. Published April 201
13、1.February 2012. Originally approved in 1993. Last previous edition approved in 20062011 asD547006.D5470 11. DOI: 10.1520/D5470-06R11.10.1520/D5470-12.2For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at serviceastm.org. For Annual Book of ASTM St
14、andardsvolume information, refer to the standards Document Summary page on the ASTM website.1This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possi
15、ble to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.*A Summary of Changes section appears at the end of this standard.Cop
16、yright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.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, (Km2)/W.4. Summary of Test Method4.1 This stand
17、ard is based on idealized heat conduction between two parallel, isothermal surfaces separated by a test specimenof uniform thickness. The thermal gradient imposed on the specimen by the temperature difference between the two contactingsurfaces causes the heat flow through the specimen. This heat flo
18、w is perpendicular to the test surfaces and is uniform across thesurfaces with no lateral heat spreading.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 o
19、f the cold meter bar, K,T4= colder temperature of the cold meter bar, K,A = area of the test surfaces, m2, andd = 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
20、= 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 divided by the heat flux through them,Km2/W, andapparent thermal conductivity = calculated from a plo
21、t of specimen thermal impedance versus thickness, W/mK.4.4 Interfacial thermal resistance exists between the specimen and the test surfaces. These contact resistances are included inthe specimen thermal impedance computation. Contact resistance varies widely depending on the nature of the specimen s
22、urfaceand the mechanical pressure applied to the specimen by the test surfaces. The clamping pressure applied to the specimen shouldtherefore 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
23、 pressure is insignificant. The computation for thermal impedance is comprised of thesum 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
24、 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 specimencan change during the test.4.5.2 The test specimen thickness can be m
25、onitored under test with an in situ thickness measurement if the dimension of thespecimen 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 D374Test Method C if it exhibits negligible compression deflectio
26、n.5. Significance and Use5.1 This standard measures the steady state thermal impedance of electrical insulating materials used to enhance heat transferin electrical and electronic applications. This standard is especially useful for measuring thermal transmission properties ofspecimens that are eith
27、er too thin or have insufficient mechanical stability to allow placement of temperature sensors in thespecimen as in Test Method E1225.5.2 This standard imposes an idealized heat flow pattern and specifies an average specimen test temperature. The thermalimpedances thus measured cannot be directly a
28、pplied to most practical applications where these required uniform, parallel heatconduction conditions do not exist.5.3 This standard is useful for measuring the thermal impedance of the following material types.5.3.1 Type IViscous liquids that exhibit unlimited deformation when a stress is applied.
29、 These include liquid compounds suchas greases, pastes, and phase change materials. These materials exhibit no evidence of elastic behavior or the tendency to returnto initial shape after deflection stresses are removed.5.3.2 Type IIViscoelastic solids where stresses of deformation are ultimately ba
30、lanced by internal material stresses thuslimiting further deformation. Examples include gels, soft, and hard rubbers. These materials exhibit linear elastic properties withsignificant deflection relative to material thickness.5.3.3 Type IIIElastic solids which exhibit negligible deflection. Examples
31、 include ceramics, metals, and some types ofplastics.5.4 The apparent thermal conductivity of a specimen can be calculated from the measured thermal impedance and measuredspecimen thickness if the interfacial thermal resistance is insignificantly small (nominally less than 1 %) compared to the therm
32、alresistance of the specimen.5.4.1 The apparent thermal conductivity of a sample material can be accurately determined by excluding the interfacial thermalresistance. This is accomplished by measuring the thermal impedance of different thicknesses of the material under test and plottingD5470 122ther
33、mal impedance versus thickness. The inverse of the slope of the resulting straight line is the apparent thermal conductivity. Theintercept 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
34、test surfaces of rigid test specimens (TypeIII).TEST METHOD6. Apparatus6.1 The general features of an apparatus that meets the requirements of this method are shown in Figs. 1 and 2. This apparatusimposes the required test conditions and accomplishes the required measurements. It should be considere
35、d to be one possibleengineering 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
36、madeby embedding wire wound cartridge heaters in a highly conductive metal block. Circulated fluid heaters consist of a metal blockheat exchanger through which a controlled temperature fluid is circulated to provide the required heat flow as well as temperaturecontrol.6.4 Heat flow through the speci
37、men 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 heaterand high quality insulation to limit heat leakage away from the primary flow through the specimen.6.4
38、.2 Heat flow meter bars can be constructed from high conductivity materials with well documented thermal conductivitywithin the temperature range of interest. The temperature sensitivity of thermal conductivity must be considered for accurate heatflow measurement. The thermal conductivity of the bar
39、 material is recommended to be greater than 50 W/mK.FIG. 1 Test Stack Using the Meter Bars as CalorimetersD5470 1236.4.3 Guard heaters are comprised of heated shields around the primary heat source to eliminate heat leakage to theenvironment. Guard heaters are insulated from the heat source and main
40、tained at a temperature within 60.2 K of the heater. Thiseffectively 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 epo
41、xy 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 requiredand 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 temp
42、erature of the test surfaces by extrapolating the linear array of meter bartemperatures to the test surfaces. This can be done for both the hot side and cold side meter bars. Surface temperatures can alsobe measured with thermocouples that are located in extreme proximity to the surfaces although th
43、is can be mechanically difficultto achieve. Meter bars can be used for both heat flow and surface temperature measurement or for exclusively one of thesefunctions.6.6 The cooling unit is commonly implemented with a metal block cooled by temperature controlled circulating fluid with atemperature stab
44、ility 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, leadscrews, pneumatics, and hydraulics. The desired range of forces must be applied to the test fixture in a direction that isperpendicular to the test surfaces
45、 and maintains the parallelism and alignment of the surfaces.7. Preparation of Test Specimens7.1 The material type will dictate the method for controlling specimen thickness. In all cases, prepare specimens of the samearea as the contacting test surfaces. If the test surfaces are not of equal size,
46、prepare the specimen equal to the dimension of thesmaller test surface.7.1.1 Type IUse shims or mechanical stops to control the thickness of the specimen between the test surfaces. Spacer beadsof the desired diameter can also be used in approximately 2 % volumetric ratio and thoroughly mixed into th
47、e sample prior to beingapplied to the test surfaces.FIG. 2 Guarded Heater Test StackD5470 1247.1.2 Type IIUse an adjustable clamping pressure to deflect the test specimen by 5 % of its uncompressed thickness. Thisrepresents a trade-off between lower surface contact resistance and excessive sample de
48、flection.7.1.3 Type IIIMeasure 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 anycontamination and dirt particles. Do not use solvent that will react with or c
49、ontaminate the specimens.8. Procedure8.1 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 temperatureof 50C (average of T2and 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 thicknes
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