PROCESS FOR LAMINATING GRAPHENE-COATED PRINTED CIRCUIT BOARDS

Abstract

Processes for laminating a graphene-coated printed circuit board (PCB) are disclosed. An example laminated PCB may include a lamination stack that may include an inner core, an adhesive layer, and at least one graphene-metal structure. Pressure and heat—which may be applied under vacuum or controlled gas atmosphere—may be applied to the lamination stack, after all materials have been placed. The graphene of the graphene-metal structure is designed to promote high frequency performance and heat management within the PCB.

Claims

1. A method of forming a lamination stack comprising: providing a core; applying an adhesive layer to a top surface of the core; and attaching a graphene-metal structure to a top surface of the core via the adhesive layer, wherein the graphene-metal structure comprises a metal layer and a graphene layer on at least one of a top surface of the metal layer or a bottom surface of the metal layer.

2. The method according to claim 1, further comprising applying a cool down period to the lamination stack, wherein the cool down period comprises a steady decrease in temperature over a duration of the cool down period.

3. The method according to claim 1, further comprising heating the lamination stack from a base of the lamination stack.

4. The method according to claim 1, wherein the graphene-metal structure is a first graphene-metal structure, the method further comprising attaching a second graphene-metal structure to a top surface of the first graphene-metal structure, wherein the second graphene-metal structure comprises a second metal layer and a second graphene layer on at least one of a top surface of the second metal layer or a bottom surface of the second metal layer.

5. The method according to claim 4, further comprising defining one or more holes through the metal layer of the first graphene-metal structure, the second metal layer of the second graphene-metal structure, and intervening layers.

6. The method according to claim 5, further comprising filling the one or more holes with conductive material.

7. The method according to claim 1, further comprising applying a second adhesive layer to a bottom surface of the core.

8. The method according to claim 7, further comprising applying a third graphene-metal structure to a bottom surface of the second adhesive layer, wherein the third graphene-metal structure comprises a third metal layer and a third graphene layer on at least one of a top surface of the third metal layer or a bottom surface of the third metal layer.

9. The method according to claim 8, further comprising attaching a fourth graphene-metal structure to a bottom surface of the third graphene-metal structure, wherein the fourth graphene-metal structure comprises a fourth metal layer and a fourth graphene layer on at least one of a top surface of the fourth metal layer or a bottom surface of the fourth metal layer.

10. A lamination stack comprising: a core; an adhesive layer applied to a top surface of the core; and a graphene-metal structure attached to a top surface of the core via the adhesive layer, wherein the graphene-metal structure comprises a metal layer and a graphene layer on at least one of a top surface of the metal layer or a bottom surface of the metal layer.

11. The lamination stack of claim 10, wherein the graphene-metal structure is a first graphene-metal structure, the lamination stack further comprising a second graphene-metal structure attached to a top surface of the first graphene-metal structure, wherein the second graphene-metal structure comprises a second metal layer and a second graphene layer on at least one of a top surface of the second metal layer or a bottom surface of the second metal layer.

12. The lamination stack of claim 11, further comprising a second adhesive layer applied to a bottom surface of the core.

13. The lamination stack of claim 12, further comprising a third graphene-metal structure attached to a bottom surface of the second core via the second adhesive layer, wherein the third graphene-metal structure comprises a third metal layer and a third graphene layer on at least one of a top surface of the third metal layer or a bottom surface of the third metal layer.

14. The lamination stack of claim 13, further comprising a fourth graphene-metal structure attached to a bottom surface of the third graphene-metal structure, wherein the fourth graphene-metal structure comprises a fourth metal layer and a fourth graphene layer on at least one of a top surface of the fourth metal layer or a bottom surface of the fourth metal layer.

15. The lamination stack of claim 11, further comprising one or more holes, wherein each hole is defined by the metal layer of the first graphene-metal structure, the second metal layer of the second graphene-metal structure, and intervening layers.

16. The lamination stack of claim 15, wherein the one or more holes are filled with conductive material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Having thus described the disclosure in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:

[0016] FIG. 1A illustrates a side-view of a lamination stack associated with a PCB comprising at least a graphene-metal structure, in accordance with one or more embodiments of the present invention;

[0017] FIG. 1B illustrates another side-view of a lamination stack associated with a PCB comprising at least a graphene-metal structure, in accordance with other embodiments of the present invention;

[0018] FIG. 2 illustrates a side-view of a lamination stack prior to the lamination process, in accordance with one or more embodiments of the present invention;

[0019] FIG. 3 illustrates an example PCB, post-lamination process, rotated at a 45-degree angle, in accordance with one or more embodiments of the present invention; and

[0020] FIG. 4 provides an example flowchart of the lamination process, in accordance with one or more embodiments of the present invention.

DETAILED DESCRIPTION

[0021] Example embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all, embodiments are shown. Indeed, the embodiments may take many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like reference numerals refer to like elements throughout. The terms “exemplary” and “example” as may be used herein are not provided to convey any qualitative assessment, but instead merely to convey an illustration of an example. As used herein, terms such as “front,” “rear,” “top,” “inside,” “outside,” “inner,” “outer,” etc. are used for explanatory purposes in the examples provided below to describe the relative position of certain components or portions of components. Furthermore, as would be evident to one of ordinary skill in the art in light of the present disclosure, the terms “substantially” and “approximately” indicate that the referenced element or associated description is accurate to within applicable engineering tolerances. Thus, use of any such terms should not be taken to limit the spirit and scope of embodiments of the present invention.

[0022] A lamination stack, generally, may be understood to be the stack, or layers, of materials used to create a PCB. For example, such materials may include a non-conductive material (e.g., the core) which may further comprise dielectric properties, an adhesive layer, and a conductive metal such as copper. The lamination stack may then be laminated (i.e., heated and/or pressurized under vacuum or controlled gas atmosphere) to solidify a bond between the materials to create the structure of the PCB. In some aspects of the present invention, heat may be applied to the base of the lamination stack (e.g., from below the lamination stack), applied to the top of the lamination stack (e.g., from a heat-source placed above the lamination stack), or applied to surround the lamination stack (e.g., similar to an oven chamber heating the lamination stack from multiple sides). The metal material (e.g., copper) may then be etched to create the conductive trace of the PCB.

[0023] In the present invention, a lamination stack comprising a graphene-metal structure, rather than just a metal layer (e.g., copper), is described, where the graphene-metal structure allows the PCB to have improved high frequency performance and improved heat management. The graphene-metal structure is arranged on or around the core of the PCB. An adhesive layer may be used to attach the graphene-metal structure to the core of the lamination stack at the pre-processing stage of the PCB. By adding a graphene-metal structure to a lamination stack, where traditionally only a metal structure is placed on the lamination stack, the PCB has improved properties over the prior art. For instance, graphene improves heat management because of its high heat conductivity properties, promotes higher electrical conductivity, and allows higher electron mobility, without having to make allowances for thickness on a PCB (i.e., graphene is extremely thin as a monolayer).

[0024] With reference to FIG. 1A, a core 101 is provided as the non-conductive material of the lamination stack of the PCB. The adhesive layer(s) 102, 112 of the lamination stack may be applied directly to a surface of the core 101. The adhesive layer(s) 102, 112 may be applied to the bottom or top surface of the core 101, or both surfaces of the core 101 within the lamination stack. A graphene-metal structure 103, 104, 105 may be attached to a top surface of the core 101 using the adhesive layer 102. Another graphene-metal structure 113, 114, 115 may be attached to a bottom surface of the core 101 using the adhesive layer 112.

[0025] In some embodiments, the graphene-metal structure 103, 104, 105 may comprise only one graphene layer and one metal structure when it is attached to a surface of the core (e.g., 103, 104 for a bottom/inner graphene layer or 104, 105 for a top/outer graphene layer). The graphene-metal structure, in those noted embodiments, may comprise a graphene layer on the bottom/inner surface of the metal structure (e.g., 103 and 104 of FIG. 1A) on the top surface of the core 101; a graphene layer on the top surface of the metal structure (e.g., 104 and 105 of FIG. 1A) on the top/outer surface of the core 101; a graphene layer on the bottom/outer surface of the metal structure (e.g., 114 and 115 of FIG. 1A) on the bottom surface of the core 101; a graphene layer on the top/inner surface of the metal structure (e.g., 113 and 114 of FIG. 1A) on the bottom surface of the core; or any combination thereof.

[0026] In yet other embodiment, the graphene metal structure of FIG. 1A may comprise a metal structure having a graphene layer on both a top surface and a bottom surface attached to the core 101. An example of such embodiment may be seen in FIG. 1A comprising a core 101, an adhesive layer 102, a bottom/inner surface of graphene 103 attached to a metal layer 104 on the top surface of the core 101, and a top/outer surface of graphene 105 attached to a metal layer 104 on the top surface of the core 101.

[0027] Once the structure of the lamination stack is in place, as described above in connection with FIG. 1A, the lamination process may be performed. In particular, frictionless substrates 106, 108, 116, and 118 may be placed between the lamination stack (comprising the core 101, at least one adhesive layer 102 and/or 112, and at least one graphene-metal structure 103, 104, 105 and/or 113, 114, 115) and pressure pads 107 and 117 of a lamination apparatus. The pressure pads 107 and 117 may be used to apply pressure to the lamination stack at a steady rate or at varying rates so as to apply optimal pressure without creating breakage or separation of layers of the lamination stack or its components. The frictionless substrates 106, 108, 116, and 118 allow for easier removal of the lamination stack from the pressure pads 107 and 117, thereby reducing the chance for breakage by minimizing the risk of the lamination stack sticking to the pressure pads 107 and 117. Lastly, carrier plates 109 and 119 may be used to carry the lamination stack through the lamination process (e.g., through a lamination apparatus, such as the CVD System of the applications incorporated by reference herein), which may apply the pressure with the pressure pads 107 and 117.

[0028] In all of the listed embodiments herein described, and as will be understood by one skilled in the art in light of this disclosure, the graphene layer may comprise a monolayer of graphene (e.g., a single atom of thickness) or a multi-layer of graphene (e.g., comprising multiple monolayers of graphene stacked, or grown, on top of each other).

[0029] In some embodiments, a lamination stack is formed that includes both top and bottom graphene-metal structures with respect to the core. With reference to FIG. 1B, a core 151 is provided. The adhesive layer(s) 152, 172 of the lamination stack may be applied directly to the surface of the core 151 as described above with respect to FIG. 1. The adhesive layer(s) 152, 172 may be applied to the bottom or top surface of the core 151, or both surfaces of the core 151 within the lamination stack.

[0030] In some cases, more than one graphene-metal structures 153, 154, 155; 156, 157, 158 may be attached to a top surface of the core 151 using the adhesive layer 152. Moreover, in some embodiments, multiple graphene-metal structures 173, 174, 175; 176, 177, 178 may be attached to a bottom surface of the core 151 using the adhesive layer 172. In some embodiments, the lamination stack of FIG. 1B may only comprise one graphene-metal structure (e.g., 153, 154, 155; 156, 157, 158; 173, 174, 175; or 176, 177, 178), may comprise two graphene metal structures of any combination of the graphene-metal structures herein listed (e.g., graphene-metal structure 153, 154, 155 may be coupled with the graphene-metal structure 156, 157, 158; or the graphene-metal structure 173, 174, 175 may be coupled with the graphene-metal structure 176, 177, 178 within the lamination stack, graphene-metal structure 153, 154, 155 may be coupled with the graphene-metal structure 173, 174, 175, and all other combinations of graphene-metal structures herein listed).

[0031] The top-most or bottom-most graphene metal structures—156, 157, 158 and 176, 177, 178, respectively—may be used as a frictionless material between the graphene layers. For instance, graphene layer placed adjacent to another graphene layer can form a frictionless interface between the two graphene layers such that the layers may easily be removed from each other. Thus, even after the lamination process described herein has taken place to form the PCB, if the top-most or bottom-most graphene-metal structures need to be removed, the top-most and bottom-most graphene-metal structures may be removed without any structural damage to the PCB (post-process lamination stack) (e.g., the 156 graphene layer, including the rest of the top-most graphene-metal structure of 156, 157, 158, may be removed from the 155 graphene layer).

[0032] In other embodiments, one or more graphene-metal structures may be added such that a third graphene-metal structure may be placed adjacent to the top-most and/or bottom-most graphene metal structures shown in FIG. 1B, 156, 157, 158 and/or 176, 177, 178, respectively. Such embodiments would then have three graphene-metal structures (not pictured) on either, or both, the top surface of the core 151 and the bottom surface of the core 151. Further, additional graphene-metal structures beyond the three layers described herein may be used, especially for the purpose of increasing trace surface area without increasing the length and width of the PCB to an unusable size for the purposes of small electronics. In such embodiments, a conductive material may be placed between the metal structures for each PCB comprising multiple graphene-metal structures to connect the multiple graphene-metal structures after they have been traced to create a conductive pathway. Such conductive materials may include copper (Cu) rods to connect the traces formed from each metal layer. In some embodiments, a prepreg material may be comprised between the graphene-metal structures to act as a glue between the graphene-metal structures when heat and pressure under vacuum or controlled gas atmosphere are applied.

[0033] In some embodiments, the multiple graphene-metal structures added around the core 151, such that the top-most graphene-metal structure 156, 157, 158 and bottom-most graphene-metal structure 176, 177, 178, may not be removed post-lamination process. Instead, holes may be drilled through the one or more graphene-metal structures attached to the top surface of the core (e.g., graphene-metal structures 153, 154, 155 and 156, 157, 158) and conductive material (e.g., copper or nickel) may be placed in the holes to connect the metal layers of each graphene-metal structure (e.g., connect the metal layers 154 and 157). By connecting the metal layers, the surface area of the trace may be enlarged without further enlarging the PCBs surface area in a horizontal direction and (only minimally) increasing the PCB thickness in a vertical direction as the graphene monolayers are very thin (e.g., the graphene monolayers ranging from 0.335 nm-1000 nm in thickness for multiple graphene layers). Additionally, the process of drilling holes and placing conductive materials to connect layers of conductive materials (e.g., connecting the metal layers of the graphene-metal structures) may be repeated for the graphene-metal structures attached to the bottom surface of the core (e.g., 173, 174, 175 and 176, 177, 178) and any additional graphene-metal structures that may be added to the present invention.

[0034] With reference to FIG. 2, a core 201 is provided as the non-conductive material of the lamination stack of the PCB. The adhesive layer(s) 202, 212 of the lamination stack may thus be applied directly to a surface of the core 201. The adhesive layer(s) 202, 212 may be applied to the bottom (212) or top surface (202) of the core 201, or both the bottom and top surfaces within the lamination stack. A graphene-metal structure 203-205 may be attached to a surface of the core using the adhesive layer(s) 202, 212. In some embodiments, the graphene-metal structure may comprise only one graphene layer and one metal layer when it is attached to a surface of the core 201. The graphene-metal structure, in those noted embodiments, may comprise a graphene layer on the bottom/inner surface of the metal layer (e.g., 203) on the top surface of the core 201; a graphene layer on the top/inner surface of the metal layer (e.g., 213) on the bottom surface of the core 201; a graphene layer on the top/outer surface of the metal layer (e.g., 205) on the top surface of the core 201; a graphene layer on the bottom/outer surface of the metal layer (e.g., 215) on the bottom surface of the core 201; or any combination thereof.

[0035] In some embodiments, the graphene metal structure of FIG. 2 may comprise a metal layer having a graphene layer on both a top surface and a bottom surface attached to the core 201. An example of such embodiment may be seen in FIG. 2 comprising a core 201, an adhesive layer 202, a bottom/inner surface of graphene 203 attached to a metal layer 204, and a top/outer surface of graphene 205 attached to the metal layer 204. In addition, a second graphene-metal structure may be attached to the bottom surface of the core 201 similar to that shown in FIG. 2. For instance, the second graphene-metal structure (e.g., 213, 214, 215) may be attached to the bottom surface of the core 201 using the adhesive layer 212, such that there is a graphene layer 213 on the top/inner surface of the metal layer; a graphene layer on the bottom/outer surface of the metal layer 215 on the bottom surface of the core 201; or any combination thereof.

[0036] In still other embodiments, the graphene-metal structure of the lamination stack may only comprise one layer of graphene on a surface of the metal structure. For instance, in FIG. 2, only a graphene-metal structure comprising the metal structure 204 and graphene layer 205 or 203 may be grown on the metal structure 204. Additionally, the bottom graphene-metal structure 213-215 attached the bottom surface of the core 201 may also only comprise a metal structure 214 and graphene layer 213 or 215, which can be grown on the metal structure 204. Any combinations of the structure described herein may also be understood by someone of skill in the art.

[0037] With reference to FIG. 3, a PCB (post lamination process of the lamination stack) is shown. The PCB comprises the core 301; the bottom/inner layer of graphene 303 of the graphene-metal structure attached to the top surface of the core 301; the metal structure 304 of the graphene-metal structure; the top/outer layer of graphene 305 of the graphene-metal structure attached to the top surface of the core 301; and the top/inner layer of graphene 313 attached to the bottom surface of the core 301.

[0038] After the lamination process described herein has been used to form the PCB, the graphene-metal structure of the PCB may undergo a lithography process to outline the conductive path(s) (i.e., trace) of the PCB, then the PCB may undergo a laser ablation or chemical etching process to create the trace on the surface of the PCB.

[0039] In some embodiments, the outline of the trace of the PCB may be made through a lithography process or laser ablation. The pre-designed trace (or conductive path) of the PCB may be outlined on a photomask, which may then be placed on a photo-sensitive (e.g., light-sensitive) chemical photoresist, where the photoresist was previously applied to the surface of the PCB.

[0040] In some embodiments, after the outline of the trace of the PCB is created, a laser ablation process may be used to remove unwanted material(s) from the PCB (e.g., excess copper and graphene not protected by the lithography trace outline) to form the trace of the PCB. In some embodiments, the laser ablation process starts by irradiating the surface of the PCB in specific localized areas, which in turn heats the material and causes the unwanted material to evaporate in the chosen localized areas. Such materials that may be removed to create the trace of the PCB include the surrounding graphene-metal structures outside the specific outline of the trace created by the lithography process. The laser of the laser ablation process may remove the graphene-metal structures on the surface of the PCB such that only the core is left underneath.

[0041] In some embodiments, and after the outline of the trace of the PCB is created through lithography, a chemical etching process may be used to remove unwanted material(s) from the PCB (e.g., excess copper and graphene not protected by the lithography trace outline), to form the trace of the PCB. The chemical etching process of the PCB may comprise plasma etching of the graphene of the graphene-metal structure(s) using such material as argon or oxygen plasma. The chemical etching process may continue by etching the metal structure using a metal etchant (e.g., for a copper metal structure a copper etchant may be used). An example PCB after the traces have been made, either via laser ablation, chemical etching, or another known process, may be seen in FIG. 3 as the post-etched PCB.

[0042] FIG. 4 is a flowchart providing an example method 400 for facilitating the lamination stack in accordance with one or more embodiments of the present invention. It will be understood that each block of the flowcharts, and combinations of blocks in the flowcharts, may be implemented by various means. In some example embodiments, certain ones of the operations herein may be modified or further amplified as described below. Moreover, in some embodiments additional optional operations may also be included. It should be appreciated that each of the modifications, optional additions, or amplifications described herein may be included with the operations herein either alone or in combination with any others among the features described herein. The operations illustrated in FIG. 4 may, for example, be performed by an example apparatus (not pictured) to add each material or layer (e.g., core, adhesive layer, graphene-metal structure, etc.) to form the PCB.

[0043] The method (e.g., method 400) may include the steps of providing a core to form the lamination stack at block 401.

[0044] Embodiments of the method may further include applying an adhesive layer to the top surface of the core at step 402. At step 403, a graphene-metal structure (e.g., a graphene-metal-graphene structure) may be attached to the top or bottom surface of the core via the adhesive layer before the lamination process of step 404 (heating and pressurizing of the lamination stack under vacuum or controlled gas atmosphere) takes place. The graphene-metal structure (pre-lamination process) may have one or more layers of graphene grown on the metal layer of the graphene-metal structure before the lamination process is conducted or as part of the lamination process.

[0045] Many modifications and other embodiments of the present inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the present inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Moreover, although the foregoing descriptions and the associated drawings describe example embodiments in the context of certain example combinations of elements and/or functions, it should be appreciated that different combinations of elements and/or functions may be provided by alternative embodiments without departing from the scope of the appended claims. In this regard, for example, different combinations of elements and/or functions than those explicitly described above are also contemplated as may be set forth in some of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.