Metallic Ink

United States Patent Application	20080286488
Kind Code	A1
Li; Yunjun ; et al.	November 20, 2008

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METALLIC INK

Abstract

Forming a conductive film comprising depositing a non-conductive film on a surface of a substrate, wherein the film contains a plurality of copper nanoparticles and exposing at least a portion of the film to light to make the exposed portion conductive. Exposing of the film to light photosinters or fuses the copper nanoparticles.

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Inventors:	Li; Yunjun; (Austin, TX) ; Roundhill; David Max; (Austin, TX) ; Yang; Mohshi; (Austin, TX) ; Pavlovsky; Igor; (Cedar Park, TX) ; Fink; Richard Lee; (Austin, TX) ; Yaniv; Zvi; (Austin, TX)
Correspondence Name and Address:	FISH & RICHARDSON P.C. P.O BOX 1022 Minneapolis MN 55440-1022 US
Assignee Name and Adress:	Nano-Proprietary, Inc. Austin TX
Serial No.:	121260
Series Code:	12
Filed:	May 15, 2008

U.S. Current Class:	427/541; 427/554; 427/555; 427/557; 427/559
U.S. Class at Publication:	427/541; 427/557; 427/559; 427/554; 427/555
Intern'l Class:	B05D 3/00 20060101 B05D003/00; B05D 3/06 20060101 B05D003/06

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Claims

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1. A method of forming a conductive film comprising: depositing a film containing a plurality of copper nanoparticles on a surface of a substrate; and exposing at least a portion of the film to light to make the exposed portion conductive.

2. The method of claim 1, wherein the exposing at least a portion of the film to light causes at least a portion of the copper nanoparticles to fuse together.

3. The method of claim 1, wherein the exposing at least a portion of the film photosinters at least a portion of the copper nanoparticles.

4. The method of claim 3, wherein the photosintering of copper nanoparticles comprises a first transformation of CuO and Cu.sub.2O to Cu.sub.2O and a second transformation of the Cu.sub.2O to Cu.

5. The method of claim 4, wherein during the photosintering process, the copper oxide migrates away from an area where the nanoparticles are fusing.

6. The method of claim 1, wherein exposing at least a portion of the film comprises directing a laser at the film.

7. The method of claim 1, wherein exposing at least a portion of the film comprises exposing the film to a flash lamp.

8. The method of claim 1, wherein exposing at least a portion of the film comprises exposing the film to a focused beam of light.

9. The method of claim 1, wherein the intensity of the light and a time of exposure is sufficient to make the exposed portion conductive.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001]This application claims the benefit under 35 U.S.C. .sctn.119(e) of U.S. provisional application 60/938,975, filed on May 18, 2007, which is incorporated by reference herein in its entirety.

BACKGROUND

[0002]The present disclosure is directed towards metallic ink such as copper. Metal conductors on printed circuit boards (PCB) and flex tape connectors are generally copper (Cu) lines that are either laminated onto the PCBs or are deposited by electroplating techniques. Patterning the copper material to form conducting lines, wire and connecting leads between components requires photolithography and acid etching of blanket copper films. Alternatively, such methods can be used to define copper line patterns during the plating process. In either case, the chemicals used to etch the copper and the resultant chemical waste generated from the processes add significant cost to the products that are made. The cost is further increased due to the time and labor necessary for the etching and photopatterning process steps.

[0003]An alternative technique to lamination and electroplating for forming metal conductors on PCB includes printing the metal lines. Silver metal based inks and pastes exist for inkjet printing, screen printing and other printing techniques. Although silver is highly conductive and can be processed at low temperatures, it is an expensive metal, making it cost prohibitive for many applications.

SUMMARY

[0004]In contrast to silver, copper metal is a standard in the electronics industry and is about one tenth the cost. Accordingly, copper is a suitable alternative to silver for use in applications such as electronic interconnects, radio-frequency ID tags and display manufacturing process, among others.

Source

Graphene-stabilized copper nanoparticles as an air-stable substitute for silver and gold in low-cost ink-jet printable electronics

CLICK pic to ENLARGE

Figure 4. Printed copper patterns. (a) Line patterns for electrical
conductivity measurements. The inset shows a homogeneous and
crack-free print surface. (b) Manually cracked pattern for
investigation of the film thickness after five overprints, revealing a
print thickness of 500 nm per print cycle. The magnification inset of
the fracture surface shows the inner structure of the composite film.
(c) Graph showing the decrease of resistance with larger line width
of the pattern (error bars obtained from five samples at each line
width). The mean electrical conductivity was 1.56 ± 0.48 S cm−1.
(d) Light-emitting diodes directly glued onto printed copper lines.
Norman A Luechinger 2008 Nanotechnology doi: 10.1088/0957-4484/19/44/445201

	PDF (611 KB) | References

Norman A Luechinger, Evagelos K Athanassiou and Wendelin J Stark¹
Institute for Chemical and Bioengineering, Department of Chemistry and Applied Biosciences, ETH Zurich, CH-8093 Zurich, Switzerland
¹ Author to whom any correspondence should be addressed
E-mail: wendelin.stark@chem.ethz.ch

Abstract. Metallic copper nanoparticles were synthesized by a bottom-up approach, and in situ coated with protective shells of graphene in order to get a metal nanopowder of high air stability and chemical inertness. Using an amphiphilic surfactant, a water-based copper nanocolloid could be prepared and successfully printed onto a polymer substrate by conventional ink-jet printing using household printers. The dried printed patterns exhibited strong metallic gloss and an electrical conductivity of >1 S cm^-1 without the need for a sintering or densification step. This conductivity currently limits use in electronics to low current application or shielding and decorative effects. The high stability of graphene-coated copper nanoparticles makes them economically a most attractive alternative to silver or gold nanocolloids, and will strongly facilitate the industrial use of metal nanocolloids in consumer goods.

Print publication: Issue 44 (5 November 2008)
Received 11 July 2008, in final form 19 August 2008
Published 26 September 2008

Source