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Laser Flash Thermal Conductivity 
Thermal conductivity of constituent materials plays a critical role in many applications requiring component cooling or heat insulation. These applications include electronic packaging, design of new heat sink materials, advanced structural ceramics used in propulsion, and many other high thermal demand situations. Over the past few decades, the laser flash method has developed into one of the most accurate and flexible techniques for the measurement of the thermal conductivity of various kinds of solids, powders and liquids.  

Engineers at CMC Laboratories were some of the original developers of laser flash thermal conductivity testing.  With over 30 years in TC measurement analysis coupled with CMC's extensive background in materials science, we are able to provide extremely precise measurement results as well as a strong understanding of the specific material properties or defects that influence thermal conduction.
Thermal Conductivity & Diffusivity
Measurement Range
CMC's Laser Flash system covers the widest measuring range of all techniques, 0.1 up to 2000W/m*K for Thermal Conductivity and 0.01 up to 1000 mm2/s for Thermal Diffusivity.  

(Values may vary for special applications)
Accuracy & Repeatability
Highest Accuracy and Repeatability, +/- 1.5-3% depending on material and specimen construction.  

(Values may vary for special applications)
Materials Analyzed
    - Ceramics (AlN, Alumina, BeO, etc)
    - Ceramic composites
    - Metals
    - Metal matrix composites
    - Semiconductors
    - Building materials (Concrete, etc)
    - Glasses and other dielectrics
    - Sapphire and diamond
    - Plastics (with and without fillers)
    - Polymers (with and without fillers)
    - TIMs
    - Layered structures
Acceptable Sample Size
CMC's Laser Flash system was designed to accept a wide range of sample sizes in order to test realistic components without size reductions.  (This avoids limitations common in many other laser flash systems of 10-25mm in diameter).  CMC can test thermal conductivity on the following samples ranges.

        Sample Diameter: 3mm - 150mm
        Sample Thickness: 0.1mm - 6mm
The Laser Flash Measurement

Laser Flash Thermal Diffusivity (TD) measurements consists of pulse heating the front side of a sample surface with a short laser pulse, and then measuring the time evolution of the back surface temperature using an infrared detector.  The resulting temperature profile curve is tailored using a one dimensiontal heat flow model (1D Model). The sample's TD is then extracted from the model and thermal conductivity (TC) can be calculated using the TD, density, and specific heat.  Sample thickness and sample size can affect the 1D model and may effect the accuracy of the TD results.  CMC Laboratories has developed a 1D model that allows for proper curve fitting evaluation to insure the 1D heat flow condition has been met. CMC can adjust apertures in the system to optimize the 1D condition.
Temperature and Enviromental Options
 Samples can be tested at temperatures from RT to 350°C 
Standard Compliance​​
CMC's Laser Flash system complies with national and international standards ASTM E-1461, DIN 30905, and DIN EN 821.
Thermal Diffusivity (m2/s) = α = 0.1388 L2/ t1/2 
Thermal Conductivity (W/m*K) = k = Cp p α
Cp = Heat Capacity        p = Density
Application Examples: Aluminum, Copper, and Graphite

Aluminum, Copper, and Graphite are perfect materials to show the performance of CMC's Laser Flash Thermal Conductivity measurement capability as a function of temperature.  Measured values are within 2% of published literature values.  CMC's system has been commonly used to certify standards for NIST as well as routineprocess monitoring coupons for the ceramics, telecommunications, aerospace, and semiconductor industries. 
Thermal Conductivity of Layered Structures
Utilizing CMC's Laser Flash technique and applying advanced heat flow models, CMC Laboratories has the capability of measuring the thermal conductivity of layered structures. Typically this technique is used to find the thermal conductivity of an interlayer between two materials with known thermal conductivity. The interlayer thermal conductivity includes both the bulk thermal conductivity of the interlayer and the thermal impedance of the interfaces.  

Some specific examples of how this technique is used:
  • Used to determine the "actual" thermal conductivity of:
                   - Thermal Interface Materials (TIMs)
                   - Thermal Conductive Epoxies
                   - Thermal greases, pastes, pads, etc
                   - Solders

This technique is perfect for measuring a material stack-up as it is used in real life.  This is especially important in understanding the thermal interface impedance of a die attach or TIM where segregation at the interfaces can have large impacts on the thermal conductivity.

Heat Spreader

Silver Conductive Epoxy

Aluminum Housing

In Plane and Out of Plane Thermal Conductivity Measurements
CMC utilizes its laser flash measurement technique to measure both in-plane thermal conductivity (X-Y plane) and out-of-plane thermal conductivity (Z direction). These can both can often be done on the same sample without any elaborate sample preparation.

The out-of-plane measurement utilizes the laser pulse to heat the top side of the sample while an IR detection system monitors the backside temperature. This is the standard geometry described above.

For in-plane thermal conductivity measurements, a topside patterned mask is applied to the sample.  The mask causes a ring shaped laser heating pattern on sample surface. Temperature on the backside is montored at a point in the center of this illuminated ring. In this geometry, heat originates in the ring pattern and is detected as it travels along the XY plane toward the center. This methodology is ideal for measuring samples with anisotropic thermal conductivity (higher XY thermal conductivity vs. Z direction) and very thin, high thermal conducting samples where heat transit times in the z direction may be too short to measure accurately. 

Certain composits are generally good examples of an anisotropic thermal conducting material.  For example a copper graphite composite, where the thermal conductivity on graphite is different along the fireber direction than across the fiber.  Example of a high thermal conductivity thin film would be CVD Diamond.
CMC's Laser Flash Thermal Conductivity Measuring Equipment
CMC has built a custom laser flash thermal conductivity measurement system with the goal of over coming many of the short-comings of commercial systems.

This system features:

- Very high power CO2 pulsed laser with a wavelength of 10.6 microns. This high laser power increases signal to noise for low thermal conductivity samples
- High sensitivity, liquid nitrogen cooled HgCdTe infra-red detector
- Beam and detection geometry allow a wide range of sample dimensions
- The system is controlled by National Labview Software which also provides curve fitting and data analysis capability
- The system accuracy has been verified utilizing standards from NIST
- The sample mount includes a heating system which can increase sample temperature up to 350C, allowing high temperature thermal conductivity measurements
- CMC is now working on the second generation of this system which will further improve measurement sensitivity
Small Dimension Samples
CMC's Laser Flash system has the capability of measuring thermal conductivity of very small dimension samples. Utilizing some specialized design features, CMC routines measures samples with XY dimension below 1mm. This can be done for a conventional single layer sample or a multilayer structure such as a small semconductor device with a die attach layer and a flange. Since many high frequency devices and components are very small, this capability allows quantitative evaluation of die attach thermal performance utilizing actual devices assembled with production assembly processes.