Below are the questions asked during the event, along with their respective answers.
Q: Can this material be laminated with plastics and adhesive tapes? If so what are the typical thicknesses of the laminate materials?
A: Yes, most commonly PET plastic films and adhesive tapes are used to protect the graphite and provide a dielectric coating. Typical thicknesses range from as little as 5 micron (0.005mm) up to 30 or more microns. Examples are provided on NeoGraf technical data sheet 322.
Q: What is the relationship between the thickness and flexibility of the material?
A: In general the thicker and higher performance a graphite foil is the stiffer it will be. NeoNxGen products are high performance and relatively thick but being single layer they do not suffer from the plywood layering effect seen with multilayer solutions built up with layers of graphite and adhesive. Static bend radii will be as little as ~0.5mm for NeoNxGen N-80 and increasing for thicknesses up to ~300mm. NeoNxGen has also demonstrated superior performance in repeated flexing with materials up to at least 150 microns thick flexing for >40,000 cycles of 180-degree bend on R=5mm bend radii.
Q: What devices is the material already being used in today?
A: NeoNxGen has already been adopted into laptop applications to reduce surface touch temperatures, into smartphone applications as an economical alternative to a vapor chamber, and as a thermal strap material for aerospace applications.
Q: How does this material affect RFI?
A: NeoNxGen has not specifically been characterized yet however in historical testing of flexible graphite materials it has been determined that the thicker and higher thermal conductivity the foil has the higher its attenuation will be. Typical attenuation values for graphite are 80 to 100+ dB over a wide range frequencies, especially high frequency. NeoNxGen being 80 to 300 microns thick and >1,000W/mK is expected to have attenuation values around 100dB. If NeoNxGen will be used near an antenna it is recommended a cutout to made in the graphite to ensure there is no interference.
Q: What is the Coefficient of Thermal Expansion of the SPREADERSHIELD and NeoNxGen products?
A: All flexible graphite products made by NeoGraf have similar Coefficients of Thermal Expansion (CTE) including SpreaderShield™ and NeoNxGen™. CTE is -0.4 ppm/°C in the X-Y in-plane direction and 27.0 ppm//°C in the Z thru-plane direction.
Q: What about electrical conductance of Hitherm compressible TIM, can I use them as dielectrics as well?
A: All HiTherm(TM) thermal interface materials (TIMs) including the HT-C3200 compressible version are 100% graphite. Graphite is classified as a semiconductor and will pass current if a voltage potential is applied to the material. HiTherm products are not recommended if an electrically insulated solution is required. SpreaderShield(TM) and NeoNxGen(TM) are also electrically conductive but are commonly coated with plastic films as a dielectric coating. This is not done on HiTherm products as it will add undesirable thermal impedance at the interface and degrade the conformability/compliance of the graphite surface.
Q: What is the CTE of NeoNxGen? Can it be attached directly to a PCB?
A: All flexible graphite products made by NeoGraf have similar Coefficients of Thermal Expansion (CTE) including SpreaderShield™ and NeoNxGen™. CTE is -0.4 ppm/°C in the X-Y in-plane direction and 27.0 ppm//°C in the Z thru-plane direction. NeoNxGen can be attached directly to a PCB using a pressure-sensitive acrylic adhesive tape. Examples of common tapes are provided on NeoGraf technical data sheet 322.
Q: Is the material electrically conductive. If so, what insulation laminations can be provided?
A: All NeoNxGen products are 100% graphite. Graphite is classified as a semiconductor and will pass current if a voltage potential is applied to the material. To overcome this NeonxGen products can be laminated with thin plastic films for electrical isolation. Examples of tapes and adhesive are provided on NeoGraf technical data sheet 322. NeoNxGen can also be provided with an envelope edge seal where the top plastic film and bottom tape extend beyond the footprint of the graphite part to seal and to ensure 100% encapsulation of the graphite part on all sides, including the edges.
Q: Do you need to apply pressure to this material in order to make good thermal contact. What is the range of pressure for such application?
A: For most applications, NeoNxGen parts can simply be adhered to a surface or heat source using double-coated PET adhesive tapes with acrylic pressure-sensitive adhesive. NeoNxGen parts are delivered as simple peel and stick parts similar to a sticker. For applications with higher heat flux (typically >10-5W/cm²) or with a heat source with a small surface area (<1cm²) it can be advantageous to apply 15psi (100kPa) or more of pressure to reduce thermal impedance through mechanical clamping. Alternatively, silicone gap pads can be utilized to reduce the thermal impedance at the interface.
Q: How to resolve the conductive surface issue while not affecting the contact resistance.
A: All NeoNxGen products are 100% graphite. Graphite is classified as a semiconductor and will pass current if a voltage potential is applied to the material. To overcome this NeoNxGen products can be laminated with thin plastic films for electrical isolation. Examples of tapes and adhesive are provided on NeoGraf technical data sheet 322. NeoNxGen can also be provided with an envelope edge seal where the top plastic film and bottom tape extend beyond the footprint of the graphite part to seal and to ensure 100% encapsulation of the graphite part on all sides, including the edges. NeoGraf uses the thinnest laminate materials possible to minimize any additional thermal impedance. Typically the additional plastic laminates do not significantly increase the thermal impedance for applications with relatively low heat fluxes (below 10-15 W/cm²).
Q: Do you put any TIM material between the hot component and your NeoNxGen? Or is it a dry contact?
A: For most applications, NeoNxGen parts can simply be adhered to a surface or heat source using double-coated PET adhesive tapes with acrylic pressure-sensitive adhesive. NeoNxGen parts are delivered as simple peel and stick parts similar to a sticker. For applications with higher heat flux (typically >10-5W/cm²) or with a heat source with a small surface area (<1cm²) it can be advantageous to apply 15psi (100kPa) or more of pressure to reduce thermal impedance through mechanical clamping. Alternatively, silicone gap pads can be utilized to reduce the thermal impedance at the interface.
Q: How do you make it electrically insulating to the environment? When laminating with plastic film, is there any decrease in heat spreading performance?
A: All NeoNxGen products are 100% graphite. Graphite is classified as a semiconductor and will pass current if a voltage potential is applied to the material. To overcome this NeoNxGen products can be laminated with thin plastic films for electrical isolation. Examples of tapes and adhesive are provided on NeoGraf technical data sheet 322. NeoNxGen can also be provided with an envelope edge seal where the top plastic film and bottom tape extend beyond the footprint of the graphite part to seal and to ensure 100% encapsulation of the graphite part on all sides, including the edges. NeoGraf uses the thinnest laminate materials possible to minimize any additional thermal impedance. Typically the additional plastic laminates do not significantly increase the thermal impedance for applications with relatively low heat fluxes (below 10-15 W/cm²).
Q: Can this be used in EV battery pack applications?
A: Yes, examples of how SpreaderShield™ or NeoNxGen™ can be used to thermally manage EV battery packs is shown here. Please contact NeoGraf directly to discuss your specific application.
Q: How can be NeoNXGen compared with the Graphene thermal and structural performance?
A: It’s difficult to compare graphene and NeoNxGen directly. Graphene is one to about 10 atomic layers thick so its total thickness is measured in Angstroms. In comparison, NeoNxGen is anywhere from about 80 microns thick up to 300 microns thick. Each micron of NeoNxGen contains about 13,000 layers of graphene. While graphene has many interesting properties they are on the nanoscale. Thermally, graphene easily becomes thermally saturated because of its lack of volume and thermal capacity. NeoNxGen, however, was specifically designed to be thick so it can manage thermal loads while still having the very high (>1,000W/mK) thermal conductivity similar to graphene.
Q: How is graphite perform on shock and vibration?
A: NeoNxGen as both bare graphite and as finished components laminated with tapes and adhesives and adhered to a stainless steel substrate have been tested in various reliability tests including a 85°C/95% relative humidity heat soak, thermal cycling (300 cycles 85°C to -40°C) and a storage test (temp./humidity cycling for 10 days) as well as shock and vibration simulating a truck shipment (0.73 Gmrs) in packaging and airplane shipment (1.49 Gmrs). In all tests, NeoNxGen had no damage and no cosmetic or performance changes.
Q: What’s the temperature range of the peel and stick NeoNXgen?
A: NeoNxGen material itself is 100% graphite so it will perform in temperature ranges of at least -40°C to 400°C in an oxygenated environment. In an inert environment, NeoNxGen can operate to up to 3000°C. When tapes are added to the graphite the temperature operating range is reduced. PET-based plastic films and pressure-sensitive acrylic adhesive are the most commonly used and the temperature operating range for those products is typical about -40°C to a maximum of 150°C. Information on common laminates and adhesives including their temperature range can be found here.
Q: Hi-Therm has a different thermal conductivity in-plane and through-plane, does NeoNxGen behave the same, and what values?
A: Yes, due to its graphite crystal structure NeoNxGen has a much higher thermal conductivity in its X-Y in-plane direction versus its Z thru-plane direction. In the X-Y in-plane direction graphite has the same C-C bonds send in graphene. In the Z thru-plane direction graphite is bonded by the relatively weaker van Der Waals forces. NeoNxGen has a 200:1 ratio with in-plane thermal conductivity of ~1,100W/mk while its thru-plane thermal conductivity is ~5W/mK. This characteristic gives NeoGraf’s SpreaderShield product line its name. Heat is spread out in the X-Y plane at a high rate before the heat passes thru the thickness more slowly creating a heat-shielding effect between the top side and bottom side of the graphite foil.
Q: How do you prevent delimitation in application where it’s in tension instead of compression?
A: Typical and wherever possible it is recommended to utilize graphite products for their thermal performance only and rely on other materials such as plastic and metals for their mechanical properties. Laminating the graphite with thin PET plastic films can greatly enhance its durability and mechanical properties including minimizing the risk of delamination in tension. Examples of common plastic laminate films can be found here.
Q: Can it be used in EV battery packs?
A: Yes, examples of how SpreaderShield™ or NeoNxGen™ can be used to thermally manage EV battery packs are shown here. Please contact NeoGraf directly to discuss your specific application.
Q: Can I use it as a replacement for traditional TIM?
A: NeoNxGen is typically used as a heat spreader to cool a hot component, spread heat to reduce surface touch temperature, or to shield heat from a temperature-sensitive component as described here: https://neograf.com/wp-content/uploads/NeoNxGen-Sell-Sheet_Web.pdf. NeoGraf would recommend its HiTherm™ product for traditional TIMs. HiTherm is typically chosen for its wide temperature operating range and long-term reliability in extreme environments. Customers also perform is simple to install pad format. HiTherm is specifically designed to orient the graphite crystal structure in the Z-direction thru-thickness to maximize thru-thickness thermal conductivity and minimize thermal impedance. The soft, conformable surface of graphite also works well to conform to the surface roughness of the mating surfaces. More information on HiTherm including data sheets can be found here.
Q: What kind of thickness tolerances do these sheets have?
A: Standard thickness tolerances of NeoNxGen are thickness dependent. Thinner grades such as N-80 (0.080mm nominal thickness) have a tolerance of ±0.010mm. N-150 (0.150mm nominal thickness) has a tolerance of ±0.015mm. The thicker grades of NeoNxGen such as N-270 (0.270mm nominal thickness) have a tolerance of ±0.025mm. A technical data sheet for NeoNxGen N-Series can be found here. NeoGraf may also be able to customize the nominal thickness of the solution or the tolerance range. Please contact NeoGraf directly to discuss your specific application.
Q: Many customers are afraid that graphite would escape at the edges of cut egraf and cause short circuits?
A: All NeoNxGen products are 100% graphite. Graphite is classified as a semiconductor and will pass current if a voltage potential is applied to the material. To overcome this NeoNxGen products can be laminated with plastic films for electrical isolation. Examples of tapes and adhesive are provided on NeoGraf technical data sheet 322. NeoNxGen can also be provided with an envelope edge seal where the top plastic film and bottom tape extend beyond the footprint of the graphite part to seal and to ensure 100% encapsulation of the graphite part on all sides, including the edges.