1. Fundamentals of Thermal Conductivity Measurement via ASTM 5470by
Dr. John W. Sofia
Analysis Tech Inc.
2016
Fundamentals

2. Definition of Apparent Thermal Conductivity
ASTM 5470 is Ohms law applied to one-dimensional heat flow.
Conductivity defined only for heat flow between parallel, isothermal surfaces (ASTM 5470)
Fundamentals

3. Apparent versus Actual Thermal Conductivity
Hot Test Surface Q
Contact Resistance = Rt
Sample L Q Q
Contact Resistance = Rb
Cold Test Surface
kactual = kapp If Rt & Rb = 0
Actual conductivity of sample equals apparent conductivity only if contact resistances are zero
Fundamentals

4. Best Method for Conductivity Measurement
- best-fit data line - RA
Intercept = (Rt + Rb)*A
Sample Thickness
Fundamentals

5. Best Method for Conductivity Measurement Requirements:
Sum of Contact resistances must be the same for all samples
(stacked samples have higher total contact resistance)
Fractional composition must be the same all samples
(supporting matrices or meshes cause problems here)
Variable thicknesses must have uniform bulk properties
(fabrication can yield thickness-dependent properties)
Fundamentals

6. Test Error: Failure to Use Constant Pressure (Type 2 Material)
Fundamentals

7. Contact Impedance Versus Pressure (Type 3 material, hard rubber, dry contact)
Fundamentals

8. Characteristics of Surface Contact Resistances
Fundamentals

9. Treating Surface Contact Resistances
Fundamentals

10. Type 1 Samples (ASTM 5470)
Fundamentals

11. Best Method for Conductivity Measurement (Type 1 Materials)
Fundamentals

12. Testing of Thin Type I Samples (“bond-line” testing)
Hot Test Surface Q
Top-Contact Rt
Sample L Q
For small L, uncertainty, ε, dominates Rsamp measurement.
For small L and large k, Rsamp is small: yields low delta T and poor measurement accuracy
Hidden information about the test surfaces dominates RA Q
BottomContact Rb
Cold Test Surface
Fundamentals

13. Difficulties with Thin Type I Sample Testing
Fundamentals

14. Type 2 Samples (ASTM 5470)
Fundamentals

15. Best Method for Conductivity Measurement (Type 2 Materials)
Fundamentals

16. Type 3 Samples (ASTM 5470)
Fundamentals

17. Best Method for Conductivity Measurement (Type 3 Materials)
Fundamentals

18. Accuracy of TIM Measurements
Dependencies
Δ-temperature across sample (low RA)
Heat flow measurement (high RA)
Environment temperature stability
Impedance variation with time
Sample area measurement & mounting
Thickness measurement accuracy
TIM Tester Training

19. Repeatability of TIM Measurements
Fundamentals

20. TIM Tester Pressure Range Options
Kit 1: 5 to 95 psi (60 to 650 kPa) +/- 3 psi
Kit 2: 10 to 170 psi ( kPa) +/- 5 psi
Kit 3: 10 to 380 psi ( kPa) +/- 10 psi
Kit 3: recommended for mostly type 3 materials
Kits 1 & 2: recommended for mostly type 1 & 2 materials
Pressure accuracy is +/-2.7% of maximum pressure
Kits can be changed by end-user and are available in complete set of 3 kits.
Fundamentals

21. Fundamentals www.analysistech.com