Adhesion Promoting Material-Coated Electrically Conductive Carrier With Thermally Conductive Layer

Abstract

A composite structure for use as a constituent of a mounting device, wherein the composite structure comprises an electrically conductive carrier, an intermediate layer comprising adhesion promoting material and being arranged on the electrically conductive carrier, and a thermally conductive and electrically insulating layer on the intermediate layer.

Claims

1. A composite structure for use as a constituent of a mounting device, wherein the composite structure comprises: an electrically conductive carrier; an intermediate layer comprising adhesion promoting material and being arranged on the electrically conductive carrier; and a thermally conductive and electrically insulating layer on the intermediate layer.

2. The composite structure according to claim 1, wherein the electrically conductive carrier comprises or consists of copper.

3. The composite structure according to claim 1, wherein the intermediate layer comprises resin.

4. The composite structure according to, wherein the thermally conductive and electrically insulating layer comprises at least one of the group consisting of diamond-like carbon, a nitride, an oxide, and a thermally conductive polymer.

5. The composite structure according to claim 1, wherein the thermally conductive and electrically insulating layer is made of a material having a value of the thermal conductivity of at least 2 W/m K.

6. The composite structure according to claim 1, wherein a thickness of the thermally conductive and electrically insulating layer is in a range between 150 nm and 50 μm.

7. The composite structure according to claim 1, wherein the electrically conductive carrier and the intermediate layer together have a thickness in a range between 4 μm and 100 μm.

8. The composite structure according to claim 1, further comprising: a cover layer covering the thermally conductive and electrically insulating layer.

9. The composite structure according to claim 1, further comprising: at least one via extending through at least part of the composite structure and being filled with a thermally conductive material to thereby thermally couple the thermally conductive and electrically insulating layer to the electrically conductive carrier by the at least one via through the intermediate layer.

10. The composite structure according to claim 1, configured as a layer sequence.

11. A mounting device for mounting electronic components, wherein the mounting device comprises: a base structure comprising an electrically conductive structure and an electrically insulating structure; at least one composite structure according to claim 1 which is attached at its thermally conductive and electrically insulating layer to at least one main surface of the base structure.

12. The mounting device according to claim 11, wherein the electrically conductive structure comprises or consists of copper.

13. The mounting device according to claim 11, wherein the electrically insulating structure comprises or consists of at least one of the group consisting of prepreg, resin, FR4, and resin soaked glass fibres.

14. The mounting device according to claim 11, wherein an exposed surface of the thermally conductive and electrically insulating layer is, partially or entirely, directly connected to the electrically insulating structure.

15. The mounting device according to claim 11, comprising a further composite structure, wherein the base structure is sandwiched between the composite structure and the further composite structure.

16. The mounting device according to claim 11, configured as one of the group consisting of a circuit board, a printed circuit board, an interposer, and a substrate.

17. A method of manufacturing a composite structure for use as a constituent of a mounting device, wherein the method comprises: providing an intermediate layer, which comprises adhesion promoting material, on an electrically conductive carrier; forming a thermally conductive and electrically insulating layer on the intermediate layer.

18. The method according to claim 17, wherein the electrically conductive carrier and the intermediate layer are configured as a Resin Coated Copper foil.

19. The method according to claim 17, wherein the thermally conductive and electrically insulating layer is formed on the intermediate layer by one of group consisting of physical vapour deposition, chemical vapour deposition, and plasma enhanced chemical vapour deposition.

20.-22. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Embodiments of the invention will be described in more detail hereinafter with reference to examples of embodiment but to which the invention is not limited.

[0047] FIG. 1 illustrates a cross sectional view of a composite structure for a mounting device according to an exemplary embodiment of the invention.

[0048] FIG. 2 illustrates a cross sectional view of composite structures for a mounting device according to exemplary embodiments of the invention.

[0049] FIG. 3 illustrates a cross sectional view of two composite structures and a base structure pressed together for forming a mounting device according to an exemplary embodiment of the invention.

[0050] FIG. 4 illustrates a phase diagram indicating contributions of sp.sup.2 hybridized carbon, sp.sup.3 hybridized carbon and hydrogen of a carbon comprising thermally conductive and electrically insulating structure of a mounting device according to an exemplary embodiment of the invention, wherein mechanical and thermal properties of the mounting device may be adjusted by configuring a manufacturing procedure in accordance with a desired section of the phase diagram.

[0051] FIG. 5 illustrates a cross sectional view of a mounting device according to another exemplary embodiment of the invention.

[0052] The illustrations in the drawings are schematical. In different drawings, similar or identical elements are provided with the same reference signs.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0053] Before exemplary embodiments will be described in further detail referring to the figures, some general considerations of the present inventors will be presented based on which exemplary embodiments have been developed.

[0054] As miniaturization of substrates or mounting devices is going further on, meaning higher density of interconnection, multilayer build ups, active and passive component embedding, the energy consumption is increasing and hot spots are occurring. Heat affects tremendously the life time of components. This is a reason why the lifetime can be doubled by decreasing the working temperature of components by 10° C. With the implementation of heat dissipating layers, hot spots can be avoided by spreading the heat over the full substrate area. Therefore the lifetime of components in (i.e. embedded within) and/or on the substrate can be extended. In contrast to current materials these heat dissipating layers exhibit good thermal conductivities by maintaining low Dk (relative dielectric constant) values.

[0055] Conventionally, heat caused problems are solved by using thick heat sinks or metal compounds to minimize hot spots. Furthermore normally heat spreading materials exhibit good thermal conductivity because they are electrically conductive. Therefore designs have to be adopted to avoid short circuits. Regarding dielectric materials they possess thermal conductivities around or below 5 W/m K which are very low compared to metal or metal compounds. These materials are blocking the heat to flow away from hot spots which leads to a reduced component lifetime. Generally there is a fundamental contradiction between high thermal conductivity and low loss: Increase of thermal conductivity always leads to a rise of the Dk value. These problems can be solved according to exemplary embodiments, as described below.

[0056] RCC (Resin Coated Copper) foils are a common base material for PCBs (printed circuit boards). In contrast to prepreg foils, RCC foils possess no glass cloth inside. To increase the thermal performance of such an RCC foil, it is coated with a thermally conductive material according to exemplary embodiments. Appropriate coating methods are PECVD or sputter processes (PVD, ARC, etc.) which deliver layers directly on the adhesion promoting material surface.

[0057] Due to the fact that DLC (diamond like carbon)—as a preferred material for the thermally conductive and electrically insulating layer—and copper—as a preferred material for the electrically conductive carrier—are not directly compatible and lead to delaminations, a resin foil—as intermediate layer—can be pressed on the DLC surface to avoid a direct contact to thereby improve adhesion according to an exemplary embodiment of the invention. This thermally conductive composite structure or build up can be used instead of commonly used RCC foils to improve thermal performance of a resulting mounting device.

[0058] In a preferred embodiment, heat spreading can be realized by forming one or more vias into the foil to connect heat sources with spreading layers. The vias can be filled or coated with a metal or metal based composites. A thermal path should be made available for this purpose.

[0059] Concerning the deposited thermally conductive and electrically insulating layer, various thicknesses can be adjusted to obtain desired thermal conductivities. Furthermore, the thermally conductive and electrically insulating layer can be a dielectric aluminum compound or any thermally conductive but electrically non-conductive material. Heat spreading in x- and y-axis can be tremendously increased (wherein the xy-plane is perpendicular to a z-direction defining the thickness of the composite structure or the mounting device). Coating of RCC foils with amorphous carbon materials, aluminum compounds or other thermally conductive but electrically non-conductive materials can therefore be implemented to enhance the thermal conductivity of dielectric materials in x- and y-axis.

[0060] Applications of exemplary embodiments are any mounting devices for mounting electronic components where heat is generated and may cause problems.

[0061] FIG. 1 illustrates a cross sectional view of a composite structure 100 for a mounting device 300 according to an exemplary embodiment of the invention.

[0062] The planar composite structure 100 comprises a layer-shaped electrically conductive carrier 102 which is embodied as a copper foil. An intermediate layer 104 consisting of pure epoxy resin is arranged directly on the electrically conductive carrier 102. The electrically conductive carrier 102 and the intermediate layer 104 are together embodied as a Resin Coated Copper (RCC) foil. A thermally conductive and electrically insulating layer 106, which is embodied as a diamond like carbon (DLC) layer, has been deposited directly on the intermediate layer 104, for instance by PVD.

[0063] The composite structure 100 furthermore comprises an optional cover layer 108, here made of pure epoxy-based resin as well, which can be attached onto the composite structure 100 for covering the surface of the thermally conductive and electrically insulating layer 106.

[0064] The composite structure 100 shown in FIG. 1 can be used as a substitute for any conventional metal layer used for mounting devices, for instance as a substitute for conventional copper foils. In contrast to such conventional copper foils, the composite structure 100 has the advantage of a significantly improved thermal conductivity in view of the high thermal conductivity of the thermally conductive and electrically insulating layer 106 of DLC. At the same time, the composite structure 100 is only minimal thicker than a conventional copper foil and can therefore be used for manufacturing compact mounting devices. Since the direct adhesion between copper and DLC is poor, the resin material of the intermediate layer 104 functions as an adhesion promoting layer, thereby resulting in a mechanically robust composite structure 100. Alternative adhesion promoting layers are possible, for instance in the form of a coating of silane.

[0065] FIG. 2 illustrates a cross sectional view of two composite structures 100 for a mounting device 300 according to other exemplary embodiments of the invention.

[0066] One of these composite structures 100 comprises a cover layer 108 as described referring to FIG. 1, whereas the other one of the composite structures 100 is free of such a cover layer 108 (i.e. is configured as a three composite structure).

[0067] As can be taken from FIG. 2, the combined thickness, D, of the electrically conductive carrier 102 and the intermediate layer 104, here embodied as RCC foil, can be in a range between 9 μm and 18 μm. A thickness, d, of the thermally conductive and electrically insulating layer 106 can be in a range between 1 μm and 3 μm. The thickness of the optional cover layer 108 can be selected appropriately for a certain application, for instance in a range between 1 μm and 10 μm.

[0068] The composite structures 100 shown in FIG. 2 further comprise a plurality of vias 200 (which may for instance be arranged in a matrix like pattern, i.e. in rows and columns) vertically extending through the composite structures 100 and being filled with copper as a thermally conductive material to thereby thermally couple the thermally conductive and electrically insulating layer 106 to the electrically conductive carrier 102 through the intermediate layer 104. This accomplishes efficient heat spreading over the entire mounting device and prevents hotspots.

[0069] FIG. 3 illustrates a cross sectional view of two composite structures 100 of the type as shown in FIG. 1 and FIG. 2 and a base structure 302 (which may also be denoted as a core structure) of a mounting device 300 according to yet another exemplary embodiment of the invention.

[0070] The mounting device 300 is configured for mounting one or more electronic components (not shown, for instance packaged semiconductor chips) thereon. The mounting device 300 comprises the base structure 302 which, in turn, comprises an electrically conductive structure 304 of copper and an electrically insulating structure 306 of prepreg or FR4. The electrically conductive structure 304 can be formed of copper structures, and can be constituted by one or more continuous and/or patterned layers of electrically conductive material. The electrically insulating structure 306 can be formed of prepreg or FR4 structures, and can be constituted by one or more continuous and/or patterned layers of electrically insulating material.

[0071] Furthermore, the mounting device 300 comprises two composite structures 100 as described above, each of which being attached at its respective thermally conductive and electrically insulating layer 106 to a respective main surface of the base structure 302. Thus, the base structure 302 and the composite structures 100 may be connected to one another by pressing, thereby forming an interference fit assembly constituting the mounting device 300.

[0072] FIG. 4 illustrates a phase diagram 400 indicating contributions of sp.sup.2 hybridized carbon, sp.sup.3 hybridized carbon and hydrogen of a carbon comprising thermally conductive and electrically insulating structure 106 of a mounting device 300 according to an exemplary embodiment of the invention, wherein mechanical and thermal properties of the mounting device 300 may be adjusted by configuring a manufacturing procedure in accordance with a desired section of the phase diagram 400.

[0073] According to the phase diagram 400, the thermally conductive and electrically insulating structure 106 of diamond like carbon (DLC) is a hydrogen (H) comprising amorphous carbon coating with a mixture of sp.sup.2 and sp.sup.3 hybridized carbon. Preferably, the portion of sp.sup.2 hybridized carbon is in a range between 40 and 60 weight percent of the thermally conductive and electrically insulating structure 106, the portion of sp.sup.3 hybridized carbon is in a range between 25 and 40 weight percent of the thermally conductive and electrically insulating structure 106, and the percentage of hydrogen is above 10 weight percent preferably not above 40 weight percent. When the thermally conductive and electrically insulating structure 106 is formed by sputtering/physical vapor deposition PVD, the percentage of sp.sup.2 hybridized carbon is high. When however plasma enhanced chemical vapor deposition PECVD is used for forming the thermally conductive and electrically insulating structure 106, a higher hydrogen percentage is obtained. With a high percentage of sp.sup.2 hybridized and sp.sup.3 hybridized carbon, a high thermal conductivity of the thermally conductive and electrically insulating structure 106 may be obtained. With a high hydrogen percentage, a mechanically stable thermally conductive and electrically insulating structure 106 is obtained. By a selection of the manufacturing procedure for instance also adjustment of the precise process parameters and/or, if desired, a combination of the above-mentioned manufacturing procedures, the mechanical and thermal properties of the thermally conductive and electrically insulating structure 106 may be precisely set. A particularly appropriate composition in terms of the mechanical and thermal properties is shown in FIG. 4 with an area denoted with reference numeral 402.

[0074] FIG. 5 illustrates a cross sectional view of a mounting device 300 according to another exemplary embodiment of the invention, embodied as a printed circuit board.

[0075] The mounting device 300 is embodied as a printed circuit board and comprises electrically insulating structure 306, for instance made of FR4 material. On two opposing main surfaces of the electrically insulating structure 304, patterned composite structures 100 (compare FIG. 1) are arranged, wherein exposed surface portions of the composite structures 100 serve for electrically mounting electronic components (not shown), and another portion of the composite structures 100 is in direct contact with the FR4 material of the electrically insulating structure 306 and promotes the heat dissipation properties of the mounting device 300. The exposed surfaces of the composite structures 100 are electrically conductive, whereas the surfaces of the composite structures 100 in an interior of the mounting device 300 in direct contact with the electrically insulating structure 306 are electrically insulating and thermally conductive, see detail 500.

[0076] FIG. 5 furthermore shows through holes through the electrically insulating structure 306 filled with vias 502, compare also detail 550. The vias 502 may comprise a post-shaped central portion embodied as electrically conductive carrier 102 (for instance made of copper) covered with a hollow cylindrical adhesion promoting structure in form of the tubular intermediate layer 104 (for instance a resin layer) which, in turn, is covered with a hollow cylindrical or tubular thermally conductive and electrically insulating layer 106 (for instance made of DLC).

[0077] FIG. 5 shows that each conventionally used copper foil of a PCB can be substituted by a sandwich composition of the type shown as composite structure 100 in FIG. 1. However, not only foils can be substituted by such a composition, but also cylindrical bodies such as vias 502, or other electrically conductive structures. The dimension of any of such structures is only increased in thickness by a minimum extent, for instance by 2 μm to 3 μm (i.e. a summed dimension of intermediate layer 104 and thermally conductive and electrically insulating layer 106).

[0078] It should be noted that the term “comprising” does not exclude other elements or steps and the “a” or “an” does not exclude a plurality. Also elements described in association with different embodiments may be combined.

[0079] It should also be noted that reference signs in the claims shall not be construed as limiting the scope of the claims.

[0080] Implementation of the invention is not limited to the preferred embodiments shown in the figures and described above. Instead, a multiplicity of variants are possible which use the solutions shown and the principle according to the invention even in the case of fundamentally different embodiments.