This application relates to processes of forming a circuit pattern on an object, and more particularly to a process of forming a graphene circuit pattern on flexible substrates, such as Polyimide (PI), Liquid Crystal Polymer (LCP) and Cyclo-olefin polymers (COP).
Graphene applications on flexible substrates have advantages in photonics, optoelectronics and organic electronics such as in light-emitting diodes and touch screen technology due to their unique electrical, mechanical, optical and thermal properties. Excellent electrical conductivity, thermal conductivity, and chemical resistance make graphene a perfect material for replacing copper as circuits. Massive flexible graphene circuit manufacturing can be achieved by transferring graphene onto flexible substrates and performing plasma etching afterwards. Chemical Vapor Deposition (CVD) graphene can be transferred onto flexible substrates as good quality raw material for patterning circuits. It is proved that CVD graphene has good adhesion on commonly used base films PI and LCP, which allows the possibility of manufacturing graphene circuits by oxygen plasma etching.
A conventional transfer method includes the following steps of: grow CVD graphene on a metal foil, usually copper; covering a thermo-releasable material on the graphene film, followed by pressing and peeling off the thermo-releasable material on the graphene film so as to attach the graphene film thereon; and covering the thermo-releasable material together with the graphene film on the planar surface of the object, followed by heating so as to directly attach the graphene film onto the planar surface of the object; and modifying the graphene surface by plasma etching to form circuits is performed using reel to reel format afterwards.
Compared to conventional copper circuits, graphene circuits on PI, LCP and COP offer significantly improved electrical conductivity, thermal conductivity and chemical resistance. U.S. Pat. No. 8,241,992 (Clevenger et al), U.S. Pat. No. 9,012,882 (Duan et al), and U.S. Pat. No. 9,087,692 (Accardi et al) teach graphene patterning methods.
It is an object of the present disclosure to provide an improved graphene circuit board with improved electrical conductivity, thermal conductivity and chemical resistance.
Yet another object of the present disclosure is to provide an improved graphene circuit board that can be embedded within the substrate with an air gap to provide electrical connections.
A further object is to provide an improved graphene circuit board having a reduction in overall thickness.
In accordance with the objectives of the present disclosure, a process for forming a graphene circuit pattern on an object is achieved. A graphene layer is grown on a metal foil. A cover film is laminated onto the graphene layer. The metal foil is etched away and the graphene layer is transferred onto a first core dielectric substrate. Thereafter the graphene layer is etched using oxygen plasma etching to form graphene circuits on the first core dielectric substrate. The first core dielectric substrate having graphene circuits thereon is bonded together with a second core dielectric substrate wherein the graphene circuits are on a side facing the second core dielectric substrate wherein an air gap is left therebetween.
Also in accordance with the objective of the present disclosure, a graphene circuit board is achieved comprising two core dielectric substrates having graphene patterns thereon wherein the two substrates are bonded together wherein an air gap is formed therebetween.
In the accompanying drawings forming a material part of this description, there is shown:
The present disclosure aims to overcome the shortcomings of the existing flexible printed circuit board to provide a new graphene circuit board with improved electrical conductivity, thermal conductivity and chemical resistance. The graphene pattern or circuit can be embedded within the substrate with an air gap to provide electrical connections. It also offers excellent flexibility by reduction in overall thickness for use in the coming wearable electronics devices, fingerprint sensors, flexible displays, and touch screen panels.
Two preferred embodiments of the present disclosure are described with respect to
The target substrate 20, shown in
Also shown is a base layer 12 such as polyester (PET) on which is formed the bonding film 10. The bonding film 10 can be any kind of thermoset adhesive film reinforced with fibers, such as epoxy, cyanide ester, acrylic adhesive, etc. The fibers can be glassy fiber, or aramide paper, etc. The adhesive film will have a low coefficient of thermal expansion (CTE) of less than about 46 and a high glass transition temperature (Tg) of more than about 200 degrees C.
One of the bonding film candidates is ABF (Ajinomoto Bonding Film), an epoxy resin-based adhesive film consisting of:
Another bonding film candidate is Dupont FR0100 bonding film made of modified acrylic:
Phenol: >=0, 1−<0, 25%
Other possibilities are Katpon/Acrylic, LCP, or unreacted thermal cure resin.
As shown in
Now, as shown in
Also shown in
Next, the roughened bonding film 10 is laminated onto the graphene/metal surface by a hot press process, as shown in
Referring now to
Now, oxygen plasma etching is performed to form graphene circuits in the transferred graphene. Etching the graphene after it has been transferred to the substrate provides better fine line width definition and spacing than if the etching were performed prior to transfer; also better alignment accuracy can be achieved with the support of fiducial marks.
First, a dry film or photo-resist 25 is applied on the graphene surface to provide a protection for the desired graphene from plasma etching as shown in
Preferably, plasma etching is conducted by a reel to reel format oxygen plasma etching machine. When the graphene pattern is formed at high density on top of a bonding film of the target substrate in a reel to reel process, the pitch can be reduced to 15 μm with 7.5 μm line and 7.5 μm spacing. The patterned graphene 22 is shown in FIG. 1H. More preferably, after etching, the dry film or photo-resist is removed from the patterned graphene layer, as shown in
Referring now more particularly to
Now, as shown in
Also shown in
As shown in
The PET film 12 is peeled off, and then the substrate 20 and the bonding film 10 are laminated together, as shown in
Referring now to
Now, oxygen plasma etching is performed to form graphene circuits in the transferred graphene. Etching the graphene after it has been transferred to the substrate provides better fine line width definition and spacing than if the etching were performed prior to transfer; also better alignment accuracy can be achieved with the support of fiducial marks.
First, a dry film or photo-resist 25 is applied on the graphene surface to provide a protection for the desired graphene from plasma etching as shown in
Preferably, plasma etching is conducted by a reel to reel format oxygen plasma etching machine. The patterned graphene 22 is shown in
In
The core dielectric substrate 20 may further be laminated with one or more conductive metal layers 30 on a side of the substrate opposite to the graphene patterned side, as shown in
Now, the graphene substrate can be used in a variety of applications, such as for wearable electronic devices, fingerprint sensors, flexible displays, and touch screen panels. For example, two core dielectric substrates 20 and 21 with graphene patterns 22 and 24, respectively, can be bonded with the graphene sides facing each other, as shown in
The circuit board of the present disclosure provides improved electrical and thermal conductivity and chemical resistance. Graphene has excellent properties in many aspects including: better electrical conductivity than silver and improved thermal conductivity over copper. It has been found in one experiment that graphene's thermal conductivity goes to roughly 5300 watts/degree Kelvin, while copper's thermal conductivity is approximately 390 watts/degree Kelvin. Furthermore, graphene offers very good chemical resistance compared to materials commonly used in the flexible substrate field.
While an air gap cannot provide electrical connection, when a finger press is applied on an application of the graphene circuits with air gap, the air gap will be closed by the finger press and electrical connection will be realized through contact of surface 22 with surface 24 or 26. The graphene on a flexible substrate provides excellent flexibility and durability due to its thinner profile than the conventional circuit board. The thickness of this flexible circuit board can be thinner, down to 10 μm. It also can be bent easily and can conform well to its final shape without bounce back.
Although the preferred embodiment of the present disclosure has been illustrated, and that form has been described in detail, it will be readily understood by those skilled in the art that various modifications may be made therein without departing from the spirit of the disclosure or from the scope of the appended claims.
Number | Name | Date | Kind |
---|---|---|---|
7070923 | Loftus | Jul 2006 | B1 |
8241992 | Clevenger et al. | Aug 2012 | B2 |
9012882 | Duan et al. | Apr 2015 | B2 |
9087692 | Accandi et al. | Jul 2015 | B2 |
20070190296 | Yoshikawa | Aug 2007 | A1 |
20080252799 | Lee | Oct 2008 | A1 |
20100220074 | Irvin, Jr. | Sep 2010 | A1 |
20150033968 | Derichs | Feb 2015 | A1 |
20150228859 | Morreale | Aug 2015 | A1 |
Number | Date | Country | |
---|---|---|---|
20170290167 A1 | Oct 2017 | US |