Below are the questions asked during the presentation, along with their respective answers.

Q: Could you expand on why there is a 10W/mK theoretical limit for TIM thermal conductivity?
A: Lawrence E. Nielsen published a paper titled “The Thermal and Electrical Conductivity of Two-Phase Systems” in Industrial & Engineering Chemistry Fundamentals, Vol. 13, No. 1, 1974. In the paper, he did a critical review of theoretical modeling work and experimental studies on the subject. Utilizing the model presented there, the maximum composite thermal performance of a polymer resin with filler systems is somewhere around 10 W/mK. Please note that this limit was primarily for traditional composite systems with randomly dispersed spherical fillers. Advanced materials with highly aligned/oriented fillers (i.e. carbon fibers, graphite platelets, carbon nano tubes) may offer much higher thermal conductivity along the alignment. For more information about the advanced concepts, please search Nano Thermal Interface (NTI) program funded by Micro Technology Office of DARPA.

Q: Why is the industry looking to Silicone-free technology?
A: Typical silicone resins contain some low molecule weight components (primarily refers to D4-D10) that are volatile. Although their concentration is very low, they may outgas and contaminate surfaces of some sensible parts in the same package/assembly. Certain applications (i.e. camera modules or optical sensors) that have very strict requirement on surface cleanness may want silicone free product.

Q: I came late…did not understand what CTQ is?
A: CTQ stands for Critical to Quality. CTQs are the key measurable characteristics of a TIM product

Q: What do you see as the biggest challenge with current TIMs meeting the environmental stressors?
A: There are many environment stressors from all aspects. For TIM products, the commonly encountered stressors are extreme temperatures and humidity. Higher temperatures and fast fluctuations between highs and lows may lead to thermal induced fatigues and aging and cause material premature failures. So our TIM products have typically been tested in environments of high temperatures (125C and 150 C), high temperature and high humidity (85 C and 85% relative humidity) and thermal shocks (-50C to 150 C) for 1000 hours, respectively. We also advise our customers to do dual-diligent tests in their practical application conditions.

Q: Do you see ‘putty-like’, none cure dispensable TIMs being used more in EV’s?
A: ‘“Putty-like’, none cure dispensable TIMs” can excellently conform to different surface topography and a wide range of gaps and find more and more applications in various industries. Also, the dispensable nature can significantly improve manufacturing throughput. We can see a lot of potential for this product to be used in broader applications including EV. Comparing with fully cured products, this product needs to be thoroughly tested especially on long-time reliability since automotive industries generally have higher standards

Q: You mention K max is about 10 W/mK.
A: Lawrence E. Nielsen published a paper titled “The Thermal and Electrical Conductivity of Two-Phase Systems” in Industrial & Engineering Chemistry Fundamentals, Vol. 13, No. 1, 1974. In the paper, he did a critical review of theoretical modeling work and experimental studies on the subject. Utilizing the model presented there, the maximum composite thermal performance of a polymer resin with filler systems is somewhere around 10 W/mK. Please note that this limit was primarily for traditional composite systems with randomly dispersed spherical fillers. Advanced materials with highly aligned/oriented fillers (i.e. carbon fibers, graphite platelets, carbon nano tubes) may offer much higher thermal conductivity. For more information about the advanced concepts, please search Nano Thermal Interface (NTI) program funded by Micro Technology Office of DARPA.

Q: What is driving the trend towards sil-free TIMs?
A: Typical silicone resins contain some low molecule weight components (primarily refers to D4-D10) that are volatile. Although their concentration is very low, they may outgas and contaminate surfaces of some sensible parts in the same package/assembly. Certain applications (i.e. camera modules or optical applications) that have very strict requirement on surface cleanness may want silicone free products.

Q: Some vendors claim 17, how?
A: Please see response above regarding the 10 W/mK limit. In addition, test method, equipment and test conditions may affect measured thermal conductivity (TC) values. There are several different test systems for TC, including ASTM D5470, laser flash, C-Therm, 3-Omega, etc. Some of these are based on steady state conditions while others based on transient process. Some of them need to determine other properties first and then back calculate the TC. All of these can affect the results. Even with the same equipment, different test conditions may result in different numbers. For example, higher compression pressures can lead to better thermal performance (especially for medium-to-high modulus gap pads). So, we suggest doing a competitive study in which different TIM products are tested by the same equipment and process.

Q: Do you see any major differences in TIMs needs for power storage vs power conversion applications?
A: Both gap pads and liquid TIMs can be found in these two applications. Some of the applications may need silicone-free products. We also noticed that some power storage applications might require better dielectric properties to minimize current leakage or risks of electrical short. However, selection of a right TIM product may require more detailed information such as device design and geometries, assembly processes, application conditions and other factors. Please contact Henkel sales or technical service team for technical support on any specific applications.

Q: What is the roadmap for >20W/m-K high perf TIMs at Henkel? How about low compression (<20%) materials? And low pressure, <20psi?
A: Developing cutting-edge technologies and staying on top of competition is always a priority for Henkel. We are closely collaborating with research communities and industrial partners to develop new products to meet different needs. We already have several products that are ultra-soft and would result in very low pressure (much less than 20 Psi) on surfaces of components. We also have some new products that are highly compliant and can withstand high strains (much higher than 30%) without compromising long time reliability. Please contact our sales team or technical service team for more information. For advanced concepts of high thermal conductivity TIM (>20 W/mK), please see a paper published by Avram Bar-Cohen “Nanothermal Interface Materials: Technology Review and Recent Results”, 2015, Journal of Electronic Packaging, DECEMBER 2015, Vol. 137.

Q: Is there any Min contact pressure [from screws] required for either gap pad or liq form?
A: For a TIM product, the minimum pressure would be dependent on the material modulus. So different TIM products may have different requirements on the minimum pressure. Typically, we require at least a 10% compress strain to ensure good contact between the TIM material and surfaces.