[0001] Electronic devices require power to operate, some of which is given off as heat. Heat generated by electronic devices and circuitry disposed within the devices must be dissipated in order to improve reliability of the devices and prevent premature failure. Various techniques are known for heat dissipation, such as the use of heat sinks, which generally transfers heat from a heat source of an electronic device into the ambient atmosphere. As technology continues to shrink the size and increase the computational power of electronic devices, the area left for utilizing a heat sink within an electronic device continues to be minimized.

BRIEF DESCRIPTION OF THE DRAWINGS

[0002] Figures 1 (a)-(e} illustrate top views of the surface of a metal substrate at various stages in the coating process of a thermally conductive coating and a non- thermally conductive coating, according to an example;

[0003] Figures 2(a)-(e) illustrate side views of the surface of the metal substrate at various stages in the coating process of the thermally conductive coating and the non-thermaily conductive coating, according to an example;

[0004] Figures 3(a)-(d) illustrate variations in the shape of the patterns of a first patterned coating, according to an example; and

[0005] Figure 4 is a flow diagram in accordance with an example of the present disclosure.

DETAILED DESCRIPTION

[0006] Examples disclosed herein provide methods for applying a combination of a thermally conductive coating and a non-thermaily conductive coating to a surface of an electronic device. Electronic devices may be housed in metal housings, or housings having at least some metal surfaces. By applying at least the thermally conductive coating to the metal housing or metal surfaces of the electronic device, the thermally conductive coating may transfer heat from a heat source of the

. i - electronic device, which is in contact with the metal housing, into the ambient atmosphere,

[0007] In one exampie, a method of applying coatings to a surface of a metal substrate includes applying a first coating of one of a thermally conductive coating or a non-thermally conductive coating to the surface of the metal substrate. The first coating is applied in a pattern to partially cover the surface. Upon applying the first coating, the method includes applying a second coating of the other of the thermally conductive coating or the non-thermally conductive coating to the surface of the metal substrate. The second coating is repelled by the first coating and is to coat the surface of the metal substrate in areas uncoated by the first coating.

[0008] In another example, a method of applying coatings to a surface of a metal substrate includes applying a first coating of one of a thermally conductive coating or a non-thermally conductive coating to the surface of the metal substrate. The first coating is applied in a pattern to partially cover the surface, wherein one of the thermally conductive coating or the non-thermally conductive coating is a

hydrophobic coating, and the other of the thermally conductive coating or the non- thermally conductive coating is a hydrophilic coating. Upon applying the first coating, the method includes applying a second coating of the other of the thermally conductive coating or the non-thermally conductive coating to the surface of the metal substrate. The second coating is repelled by the first coating and is to coat the surface of the metal substrate in areas uncoated by the first coating.

[0009] Yet another example includes a housing having at least one metallic surface. The metallic surface includes a first patterned layer of one of a thermally conductive coating or a non-thermally conductive coating patterned to partially cover the metallic surface. The metallic surface includes a second patterned layer of the other of the thermally conductive coating or the non-thermally conductive coating, located over the metallic surface in areas uncoated by the first patterned layer.

[0010] As an example, the thermally conductive coating and the non-thermally conductive coating may be applied to the surface of an electronic device by using a two-step process that includes applying a coating of hydrophobic materials and a coating of hydrophilic materials or water-borne materials. As an example, a first patterned coating of one of the materials (e.g., hydrophobic materials or water-borne materials) may be applied to the surface of the electronic device. Subsequently, a second fill coating of the other material (e.g., the other of the hydrophobic materials or water-borne materials) may be applied to the surface of the electronic device.

[0011] Due to the nonpolar nature of hydrophobic material and the polar nature of water-borne materials (or hydrophiiic materials), the second fill coating may be repelled by the first coating. For example, the coating of hydrophobic materials may be incapable of forming hydrogen bonds with water, reducing the surface area of the hydrophobic coating exposed to water. As a result, the surface of the first coating may not be coated by the second coating. As will be further described, one of the thermally conductive coating or the non-thermally conductive coating may be the hydrophobic coating, and the other of the thermally conductive coating or the non- thermally conductive coating may be the water-borne coating.

[0012] With reference to the figures, Figures 1 (a)-(e) and Figures 2(a}-(e) provide top views and side views, respectively, of the surface of a metal substrate at various stages in the coating process of a thermally conductive coating and a non-thermally conductive coating, according to an example. As mentioned above, electronic devices may be housed in metal housings, or housings having at least some metal surfaces. Figure 1 (a) illustrates a portion of a metal substrate 101 or metal housing that may be used for an electronic device. Examples of the metal substrate 101 include, but are not limited to, a magnesium lithium (MgLi) alloy, aluminum, magnesium, titanium, lithium, zinc, niobium, or an alloy of one or more of these metals.

[0013] Prior to applying the thermally conductive coating and the non-thermally conductive coating, the surface of the metal substrate 101 may be degreased. As an example, the degreasing may be performed with an alkaline solution with or without surfactants. The degreased surface of the metal substrate 101 may then be chemically polished, for example, by sandblasting, buffing, or performing a chemical or chemical mechanical polishing (CMP) step.

[0014] Referring to Figure 1 (b), after chemically polishing the metal substrate 101 , the surface of the metal substrate 101 may be passivafed to form a surface passivation layer 102. As an example, the metal substrate 101 may be passivated by applying one or more thin layers of aluminum zinc phosphate, calcium zinc molybdate, zinc moiybdate phosphate, calcium borosiiicate or strontium

phosphosilicate, phosphates, manganese salts, manganese phosphate, calcium phosphate, zinc phosphate, vanadium, stannates, zirconates, etc.

[0015] Referring to Figure 1 (c), a patterned coating of hydrophobic material 103 may be coated onto the passivated surface 102. As an example, the hydrophobic coating 103 may be applied by Inkjet printing, screen printing, 3D printing, or spray drying. As mentioned above, the hydrophobic coating may be the first coating to be applied, in which case it may be patterned, and the water-borne coating may be used to fill the pattern, as will be further described. Alternatively, the water-borne coating may be patterned as the first coating and the hydrophobic coating may be used to fill the pattern.

[0016] The coating of hydrophobic material may be applied in a pattern to partially cover the surface. As an example, the coating may cover continuous areas of the surface, where the coating of hydrophobic material is an unbroken series or pattern. As an example, the coating may cover non-continuous areas of the surface, where the coating of hydrophobic material covers disparate areas of the surface. As illustrated in Figure 1 (c), the pattern may include spot shapes having circles.

Examples of other spot shapes are illustrated in Figures 3(a)-(d), but are not limited to those illustrated. Referring to Figures 3(a)-(d), the pattern may include spot shapes having triangles (Figure 3(a)}, squares, rectangles, or trapezoids, (Figure 3(b)), ovals (Figure 3(c)), crescents (Figure 3(d)), logos, or any other shape including random shapes or combinations of any or all of these. The shapes may be applied in regular patterns created by masking or controlling an output of a print head spatially, or may be more random if applied by methods such as unmasked spraying of droplets.

[0017] The hydrophobic coating 103 may be a transparent, translucent or opaque coating. As an example, the hydrophobic coating 103 may include a f!uoropolymer coating selected from fluoridated oiefin-based polymers, specialty fluoroacryiates, fluorosi!icone acryiates, fluorourethanes, perf!uoropolyethers/perfluoropolyoxetanes, fluorotelomers (C-6 or lower products), po!ytetrafluoroethy!ene (PTFE),

polyvinyiidenefluouride (PVDF), fiuorosiloxane, fiuoro UV polymers, and hydrophobic polymers (C-7 or longer). The thicknesses of the hydrophobic coating 103 may be in the range of 1 -100 urn and generally in the range of 5-30 urn. The spots in the pattern of the hydrophobic coating may be in the range of 3nm to 30μηι across and may cover up to 40% of the area of the metallic substrate surface 101 , as an example. Referring to Figure 2(c), a side view of the surface of the electronic device indicates the hydrophobic coating 103 may be applied in a pattern to partially cover non-continuous areas of the surface 101. However, the hydrophobic coating 103 may also cover continuous areas of the surface 101.

[0018] As mentioned above, one of the thermally conductive coating or the non- thermaily conductive coating may be the hydrophobic coating 103, and the other of the thermally conductive coating or the non-thermaily conductive coating may be the water-borne coating 104 (e.g., see Figures 1 (d) and 2(d)). As an example, materials of thermally conductive species may be added into either the hydrophobic coating 103 or the water-borne coating 104. Examples of the thermally conductive species include, but are not limited to, species selected from a group of nano/micro particles of graphene, carbon nanotube, natural graphite, synthetic graphite, aluminum, copper, silver, silicon, gold, diamond, synthetic thermally conductive materials, etc. Referring to the hydrophobic coating, nano/micro particles of the thermally conductive species may be added to the fiuoropolymer coating described above. After applying the hydrophobic coating 103, the coating 103 may be baked. As an example, the baking temperature of the first coating may be in the range of 60-120°C for 30-60 minutes.

[0019] Referring to Figure 1 (d), a water-borne coating material 104 may then be coated onto the passivated surface 102 of the metal substrate 101 , in order to cover areas not coated by the hydrophobic coating 103. As described above, due to the nonpoiar nature of the hydrophobic coating and the polar nature of the water-borne coating 104 (or hydrophilic coating), the second fill coating may be repelled by the first coating. For example, the hydrophobic coating 103 may be incapable of forming hydrogen bonds with water, reducing the surface area of the hydrophobic coating 103 exposed to water. As a result, the surface of the first coating (e.g., the hydrophobic coating 103) may not be coated by the second coating (e.g., the water- borne coating 104). Similar to the coating of hydrophobic material, the water-borne coating material 104 may cover continuous areas or non-continuous areas of the passivated surface 102.

[0020] The material used for the water-borne coating 104 may be applied by flow coating, spraying, screen printing, or Inkjet printing, as an example. The material used for the water-borne coating 104 may be selected from water-borne epoxy, acrylic-epoxy hybrids, acrylics, poiyurethane dispersions, and water-borne polymers (including water-borne UV polymers). As an example, rather than adding the thermally conductive species to the hydrophobic coating 103, the thermally conductive species may be added to the water-borne coating 104 instead.

[0021] The thicknesses of the water-borne coating 104 may also be in the range of 1- 100 μπΊ and generally in the range of 5-30 μηι and it will generally cover the surface of the metallic substrate 101 not covered by the hydrophobic coating 103, as illustrated in Figure 2(d). As an example, the thickness of non-thermally conductive coating may be thicker than the thermally conductive coating. For example, if the thermally conductive species is added to the hydrophobic coating 103, the water- borne coating 104 (e.g., the non-thermally conductive coating) may be thicker than the hydrophobic coating 103. By having a thicker non-thermally conductive coating, the surface of the electronic device may be pleasant for a user to touch, while the thinner thermally conductive coating may dissipate heat from a heat source of the electronic device to the ambient atmosphere. Dissipating heat away from the electronic device may improve reliability of the device and prevent premature failure.

[0022] After applying the hydrophobic and water-borne coatings 103, 104, the coatings may then be cured. As an example, the curing of the hydrophobic and water-borne coatings 103, 104 may be performed at a temperature in the range of 120-180°C for 30-120 minutes. For UV polymers, the curing may be performed under UV exposure for less than 3 minutes and preferably in the range of 15-30 seconds.

[0023] Referring to Figure 1 (e), a protective coating 105 or protective film may be applied over the cured hydrophobic and water-borne coatings 103, 104. As an example, the protective coating 105 may be applied using a process selected from coating or film transfer, and may include one of in-mould decoration, out-side mould decoration, in-mould film, in-mould label, release film, and nano-imprint lithography. The protective coating 105 may be a combination of poiyacrylic resin and a fluoropoiymer such as fluorosi!oxane applied, for example, by flow coating, spraying, screen printing or Inkjet printing. The protective coating 105 or film may be applied with a thickness in the range of 1 -50 μηι and preferably in the range of 5-30 μηι, according to an example. Upon applying the protective coating 105, the coating may then be cured, similar to the curing of the hydrophobic and water-borne coatings 103, 104.

[0024] While Figures 1 (a)~(e) illustrate a process in which application of a patterned hydrophobic coating 103 is followed by application of a water-borne coating 104 it will be appreciated that the first coating could be a water-borne coating followed by a hydrophobic coating. In addition, either the first coating or the second coating may be the thermally conductive coating, while the other coating is the non-thermally conductive coating.

[0025] Referring to Figure 4, a flow diagram is illustrated in accordance with various examples. The flow diagram illustrates the coating process of a thermally conductive coating and a non-thermally conductive coating to a surface of a metal substrate, according to an example. The order of the processes is not meant to limit the disclosure. Rather, it is expressly intended that one or more of the processes may occur in other orders or simultaneously. The disclosure is not to be limited to any particular example.

[0026] A method 400 may begin and progress to 402, where a first coating of one of a thermally conductive coating or a non-thermally conductive coating is applied to the surface of the metal substrate. As an example, the first coating may be applied in a pattern to partially cover the surface. One of the thermally conductive coating or the non-thermally conductive coating may be a hydrophobic coating, and the other of the thermally conductive coating or the non-thermally conductive coating may be a hydrophilic coating (or water-borne coating}. The thermally conductive coating may include nano-sized or micro-sized particles of thermally conductive materials added to one of the hydrophobic coating or the hydrophilic coating. Examples of the thermally conductive materials include, but are not limited to, species selected from a group of nano/micro particles of graphene, carbon nanotube, natural graphite, synthetic graphite, aluminum, copper, silver, silicon, gold, diamond, synthetic thermally conductive materials, etc. As described above, prior to applying the first coating, the metal substrate may be degreased, chemically polished, and

passivated.

[0027] The first coating may cover continuous areas or non-continuous areas of the surface of the metal substrate. As illustrated in Figure 1 (c), the pattern may include spot shapes having circles. Examples of other spot shapes are illustrated in Figures 3(a)-(d), but are not limited to those illustrated. Referring to Figures 3(a)-(d), the pattern may include spot shapes having triangles (Figure 3(a)), squares, rectangles, or trapezoids, (Figure 3(b)), ovals (Figure 3(c)), crescents (Figure 3(d)), logos, or any other shape including random shapes or combinations of any or all of these. The shapes may be applied in regular patterns created by masking or controlling an output of a print head spatially, or may be more random if applied by methods such as unmasked spraying of droplets.

[0028] Progressing to 404, upon applying the first coating, a second coating of the other of the thermally conductive coating or the non-therma!!y conductive coating is applied to the surface of the metal substrate, wherein the second coating is repelled by the first coating and is to coat the surface of the metal substrate in areas uncoated by the first coating. Due to the nonpolar nature of the hydrophobic coating and the polar nature of the water-borne coating (or hydrophilic coating), the second fill coating may be repelled by the first coating. For example, the hydrophobic coating may be incapable of forming hydrogen bonds with water, reducing the surface area of the hydrophobic coating exposed to water. As a result, the surface of the first coating (e.g., the hydrophobic coating) may not be coated by the second coating (e.g., the water-borne coating).

[0029] As an example, the non-thermally conductive coating may be thicker than the thermally conductive coating. As an example, after applying the first coating, and before applying the second coating, the metal substrate may be baked. After applying the second coating, both coatings may be cured, As an example, a protective coating or protective film may be applied over the cured hydrophobic and water-borne coatings. Upon applying the protective coating, the coating may then be cured.

[0030] It is appreciated that examples described herein below may include various components and features. It is also appreciated that, in the following description, numerous specific details are set forth to provide a thorough understanding of the examples. However, if is appreciated that the examples may be practiced without limitations to these specific details. In other instances, well known methods and structures may not be described in detail to avoid unnecessarily obscuring the description of the examples. Also, the examples may be used in combination with each other.

[0031] Reference in the specification to "an example" or similar language means that a particular feature, structure, or characteristic described in connection with the example is included in at least one example, but not necessarily in other examples. The various instances of the phrase "in one example" or similar phrases in various places in the specification are not necessarily all referring to the same example.

[0032] It is appreciated that the previous description of the disclosed examples is provided to enable any person skilled in the art to make or use the present disclosure. Various modifications to these examples will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other examples without departing from the spirit or scope of the disclosure. Thus, the present disclosure is not intended to be limited to the examples shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.