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Making your materials more thermally conductive

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Tailoring the thermal conductivity of plastic materials with 3M™ Boron Nitride Cooling Fillers

  • 3M™ Boron Nitride Cooling Fillers are a family of advanced ceramic materials used to improve thermal conductivity in polymers while maintaining or improving electrical insulation. Their unique properties make these additives suitable for a wide variety of electrical and electronic applications. Using 3M Boron Nitride Cooling Fillers, thermal conductivity can be tailored to meet the thermal requirements in your system – harmonized with performance criteria such as target electric insulation, flame retardancy, mechanical properties and compound/system cost requirements.

    Our experienced global team of materials scientists, product specialists and application engineers will work closely with you to develop formulations and processes that can help you achieve optimal thermal conductivity and performance levels.

    Our mission is to help you be successful in the implementation of new product ideas or in the optimization of existing designs using 3M Boron Nitride Cooling Fillers. By taking advantage of their expertise and insights, you can realize the full potential of these amazing materials.

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Comparing thermal conductivity of various thermal fillers

  • Chart comparing thermal conductivity of thermal fillers
  • There are many good reasons why plastics are favorite materials of modern designers, including their relatively low cost; suitability for high volume production; and the exceptional design freedom which they allow.

    In the area of electronics, however, the usefulness of many plastics is limited. That’s because electronic components require materials that can effectively dissipate heat in a small space. Although conventional plastics are not thermally conductive, adding boron nitride as a filler material easily resolves this shortcoming.

    In general, the intrinsic thermal conductivity of a filler material is determined by its chemical composition and morphology.

    The best example is carbon:
     

    • Hexagonal modification -> up to 165 W/m•K
    • Cubic modification -> up to 2,300 W/m•K
    • Graphene -> up to 6,000 W/m•K
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  • Thermal conduction path of low aspect ratio fillers
  • Low Aspect Ratio Fillers

    Most thermal fillers are isotropic and/or close to spherical. Graphite and hexagonal boron nitride, in contrast, are anisotropic in structure. When properly applied, this structure can be used to significantly enhance thermal conductivity. The thermal conduction path of round or low aspect ratio fillers, such as alumina, alumina silicate and others, is hindered by these characteristics:
     

    • No contact between the particles
    • Polymer behaves like a thermal resistance between the particles
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  • Thermal conduction path of high aspect ratio fillers
  • High Aspect Ratio Fillers

    The thermal conduction path of anisotropic fillers, such as graphite and hexagonal boron nitride, takes a more efficient route:
     

    • More contact points at the same filler loading
    • Bridging is reached with lower loading, leading to higher thermal conductivity
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  • Chart showing in-plane conductivity of PA 6 compounds containing boron nitride and other fillers
    • Laser Flash Measurement: ASTM E 1461/DIN EN 821
    • Martoxid is registered trademark of Huber Martinswerk Silatherm is a registered trademark of Quarzwerke GmbH
  • Improving thermal performance with boron nitride

    The benefit of this anistropy is demonstrated in this graph, which shows the in-plane conductivity of PA6 compounds formulated with boron nitride and two other filler materials.

    While conventional thermal fillers are limited to < 4 W/m•K in-plane thermal conductivity, 3M™ Boron Nitride Cooling Fillers can achieve > 10 W/m•K in-plane and up to 4 W/m•K throughplane thermal conductivity.

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  • Chart showing different densities of thermal fillers, including 3M boron nitride cooling fillers

    For 2 W/mK in-plane thermal conductivity:
     

    • 70 wt.% of Alumina Silicate is needed
    • 70 wt.% of Alumina is needed
    • 30 wt.% of Boron Nitride Cooling Filler is needed
  • Density of Thermally Conductive Filler

    Also note that 3M™ Boron Nitride Cooling Fillers have a much lower density than other thermal fillers.
     

    • A lower wt-% is needed to achieve the same thermal conductivities as alternative thermal fillers
    • Less filler content means less impact on the mechanical properties of the compound
    • Less filler means less weight is added
    • Comparisons with other thermal filler should always be considered on the basis of volume percent

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Boosting the thermal conductivity of existing compounds with 3M™ Boron Nitride Cooling Filler Flakes

Today’s plastic compounds often contain a variety of additives to adjust factors such as mechanical properties, flame retardancy and cost. The thermal conductivity of these existing compounds can be drastically increased by introducing 3M Boron Nitride Cooling Filler Flakes into the compound.

  • Microscopic image of aluminum hydroxide

    Aluminum Hydroxide

  • Microscopic image of aluminum talcum

    Talcum

  • Microscopic image of alumina silicate

    Alumina Silicate

  • Microscopic image of wollastonite

    Wollastonite

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  • Illustration of different shapes, size of fillers

    Size, shape and intrinsic thermal conductivity of secondary fillers have a strong influence on the thermal conductivity of compounds.

  • Illustration showing effect different geometries have on thermal conductivity path

    Using a combination of particles having differing geometries creates a complex network in the polymer. This allows for better percolation, enhanced thermal conductivity path in the z-direction and less interfaces between the filler and the polymer.

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  • chart showing increase in thermal conductivity with boron nitride

    Thermal conductivity in W/m•K, for epoxy filled with boron nitride flakes

    This first example shows how the thermal conductivity of an epoxy potting resin containing aluminosilicate can be increased by the addition of 3M™ Boron Nitride Cooling Filler CFF 500-3.

    In potting resins, the anisotropic boron nitride is generally not oriented but is evenly distributed in the polymer matrix. Therefore, in-plane and through-plane thermal conductivities are similar.

  • chart showing increase in thermal conductivity of an injection molded PA 6 compound with boron nitride

    Thermal conductivity in W/m•K, in-plane (x/y-direction), PA 6 filled with boron nitride flakes

    This second example shows how the thermal conductivity of an injection molded PA 6 compound can be boosted with the addition of boron nitride flakes.

    PA 6, like most thermoplastic materials, is traditionally injection molded, which causes an orientation / alignment of the anisotropic boron nitride in the polymer matrix. Therefore, in-plane and through-plane thermal conductivities are different, and the effect of boosting in injection molded PA 6 is higher on in-plane thermal conductivity.


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How modifying injection molding parameters influences thermal conductivity

  • parallel orientation of boron nitride flakes during injection molding

    Boron Nitride Flakes commonly orient parallel to the injection direction due to the friction towards the mold.

  • influences on orientation during injection molding

    Orientation in the middle zone of the injection molded part can, however, be influenced by the injection molded parameter.

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  • Variables that impact through-plane thermal conductivity

    Laser Flash Measurement: ASTM E 1461/DIN EN 821

  • Through-plane thermal conductivity can be further increased by:
     

    • Lowering melt temperature
    • Decreasing injection speed
    • Decreasing mold temperature

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How modifying compounding parameters influences thermal conductivity

  • Influences on thermal conductivity during twin screw extrusion

    Laser Flash Measurement: ASTM E 1461/DIN EN 821

  • Thermal conductivity can also be influenced during compounding in a twin screw extruder.

    Decreased screw speed as well as soft mixing conditions can minimize break-down of the agglomerate and increase the thermal conductivity.


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Comparing thermal conductivity of various Boron Nitride Fillers

  • car cutaway from BMBF project
  • The following is a summary of the BMBF Project, funded by the German government. The project is designed to evaluate innovative materials for process and system simplification in lithium ion batteries.

    The technical requirements of the study are as follows:
     

    • Polymer matrix: PA 6
    • Electrical insolation: el. resistance (IEC 60093) 1,00E+14 Ohm•m
    • Thermal conductivity (DIN 52612-1) of thin injection molded parts: x / y / z = 4 / 4 / >2W/m•K
    • Filled PA6 compounds with:
      -Failure stress (ISO 527-1/-2): 100 MPa
      - Elongation at break (ISO 527-1/-2): 2-2.3%
      - Charpy (DIN EN ISO 179−1): 40 KJ/m²
    • Economical compound costs
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  • Chart comparing thermal conductivity of boron nitride platelets and flakes
  • The study compared the thermal conductivity of 3M™ Boron Nitride Platelets and Flakes. As shown in this graph, the boron nitride flakes increased through-plane thermal conductivity by a factor of 2.5.

    Why the difference? First, it’s important to understand that thermal conduction takes place through the boron nitride particles. Any contact points are a thermal resistor. Increasing particle size reduces the number of contact points.

    As the illustration below demonstrates, a 500 μm flake has much fewer interruption points than 3 μm platelets at the same filler loadings – giving heat a more direct path to escape (indicated by the red lines). As a result, thermal conductivity is higher with larger particles.

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  • Image of platelets in side by side comparison of platelets and flakes

    Small Particle Size (Platelets)

  • Image of flakes in side by side comparison of platelets and flakes

    Bigger Particle Size (Flakes)


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Using 3M™ Boron Nitride Cooling Fillers to save costs all along the value chain

  • example showing how TIMs, heat sinks, reflectors work together
  • Recent initiatives in the electrical and electronics industry have demonstrated that plastics incorporating boron nitride cooling fillers can help save costs, improve product performance and expand design opportunities.

    The following example shows a solution for a new LED flashlight that brings together TIMs, secondary heat sinks – and even the reflector – while simplifying the overall construction.

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Project participants

  • Lehmann & Voss & Co. logo

    Developer and manufacturer of “made-to-measure” compound

  • RFPLAST logo

    Provided thermal modeling, tool design and injection molding service

  • Häusermann logo

    Manufacturer of printed circuit board

  • OSRAM logo

    Supplier of LED

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Because it is electrically insulating, the boron nitride filled compound can be directly injection-molded around the printed circuit board, functioning as both heat sink and reflector.

By decreasing the number of components and enabling one-step manufacturing, total system costs were reduced by 30%, compared with previous solutions that use metal housings.

At the same time, excellent heat management extends the lifetime of the LED.

  • Image of conventional unfilled polymer in comparison of conventional-unfilled polymer and thermally conductive polymer

    Conventional Unfilled Polymer

  • Image of thermall conductive polymer in comparison of conventional-unfilled polymer and thermally conductive polymer

    Thermally Conductive Polymer


Support

Contact us if you need product, technical or application advice or want to collaborate with a 3M Technical Specialist.


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