Abstract:
A method for forming a conductive pattern on a substrate ( 208 ) includes providing an image pattern for imaging on the substrate; imaging the image pattern on the substrate creating imaged areas; spraying functional material ( 232 ) on the substrate that diffuse molecules of the functional material into the imaged areas; and applying electro-less copper coating that build conductive material traces on the imaged areas on the substrate.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     Reference is made to commonly-assigned copending U.S. patent application Ser. No. 13/676,441, filed Nov. 14, 2012, entitled FUNCTIONAL PRINTING SYSTEM, by Schuster; the disclosure of which is enclosed herein. 
     FIELD OF THE INVENTION 
     The present invention relates to a method for functional printing using computer to plate imaging technology. 
     BACKGROUND OF THE INVENTION 
     Functional printing is a category of printing that uses commercial printing equipment to print circuits or electronic devices which have a function other than or in addition to visual display of information. An example of printed circuits can be printing radio frequency identification (RFID) on a package or a product. Another example may be printing an electronic circuit on a package which is capable to produce a musical clip when the package is opened. 
     There are several approaches for printing functional patterns on substrates including direct printing of functional inks Other techniques use photolithography to mask and remove a pre-deposited functional layer. 
     SUMMARY OF THE INVENTION 
     Briefly, according to one aspect of the present invention specific substrate characteristics are used to deposit patterns of functional materials on a surface, based on temperature differences. As the temperature of the substrate increases in a certain position, it allows faster diffusion of chemical elements or allows the attachment of chemical elements to its surface. One uses thermal writing devices (e.g. laser writing heads, thermal transfer writing heads) to form a thermal pattern on the substrate which, combined with the chemical environment, forms a pattern of functional chemical traces on the substrate. This pattern can be used as is for various applications such as forming hydrophilic/hydrophobic regions for printing processes. Another use is to form a pattern of a catalyst material that can be used for electro-less deposition of metal such as copper, and thus manufacture copper traces on the substrate. 
     There is a need for accurate deposition for functional material. The use of laser imaging or thermal transfer means on a substrate with a combination of sprayed material (such as gas) applied on the imaged areas. The gas molecules are diffused towards the laser heated substrate to create a chemical compound between the gas and the material deposited on the surface of the substrate. The gas is referred to as functional gas and creates a compound of traces on the substrate that is used to form conductive lines for example. 
     The invention and its objects and advantages will become more apparent in the detailed description of the preferred embodiment presented below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  represents in diagrammatic form a prior art digital front end driving an imaging device; 
         FIG. 2  represents in diagrammatic form the imaging system disclosed herein; and 
         FIG. 3  represents in a diagrammatic form an electro-less coating machinery applied on a patterned substrate according to this invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will be directed in particular to elements forming part of, or in cooperation more directly with the apparatus in accordance with the present invention. It is to be understood that elements not specifically shown or described may take various forms well known to those skilled in the art. 
     While the present invention is described in connection with one of the embodiments, it will be understood that it is not intended to limit the invention to this embodiment. On the contrary, it is intended to cover alternatives, modifications, and equivalents as covered by the appended claims. 
       FIG. 1  shows a plate imaging device  108 . The imaging device is driven by a digital front end (DFE)  104 . The DFE receives imaging data in a digital form from desktop publishing (DTP) systems (not shown), and renders the digital information for imaging. The rendered information and imaging device control data are communicated between DFE  104  and imaging device  108  over interface line  112 . 
       FIG. 2  shows an imaging system  200 . The imaging system  200  includes an imaging carriage  212  on which a material spray element  224  is mounted along with an thermal imaging head  220 . The sprayed material can be in a form of gas. The thermal imaging head  220  can be based on thermal transfer means or laser imaging components. The thermal imaging head  220  is designed to operate in a wavelength matching the substrate  208  characteristics. The imaging head  220  is configured to image on substrate  208  mounted on a rotating cylinder  204 . The carriage  212  is adapted to move substantially in parallel to cylinder  204  guided by an advancement screw  216 . Controller  228  controls patterning process of imaging head  220  and material emission from material spray element  224 . A computer-to-plate device capable to image on flat surfaces, known as capstan devices, can be used as well for same purpose (not shown). An internal drum CTP (not shown) configuration can be used in conjunction with this invention as well. 
     Substrate  208  such as glass, metal or various polymeric materials is mounted on cylinder  204 . Depending on the specific process being applied, a material spray element  224  deploys a material in proximity of substrate  208 . The material deployment may be applied prior, during or after laser exposure. Imaging head  220  will image a pattern according to data received from DFE  104  on substrate  208 . The CTP imaging head  220  will elevate the temperature of substrate  208 , or opto-chemically modify its surface in the imaged areas to enable an efficient diffusion/bonding process of the functional sprayed material  232  molecules into substrate  208 . Thus, the pattern created by imaging head  220  induces a doping pattern on substrate  208 . For example, near IR (NIR) imaging head can be used for imaging on a specialized NIR absorbing polyethylene terephthalate (PET) substrate, while applying catalyst gas, such as 3-mercaptopropyltrimethoxysilane (MPTS) or palladium fine powder, to create traces of catalyst doping on substrate  208 . 
     Followed the completion of the required patterning on substrate  208 , a standard electro-less coating process is performed to build material traces such as copper, silver or nickel traces on substrate  208  by using electro-less coating machinery such as depicted in  FIG. 3 . These copper traces will form the pattern made by the CTP imaging head  220 . [Yinxiang Lu, Qian Liang, Longlong Xue, Applied Surface Science, Volume 258, Issue 10, 1 March 2012, Pages 4782-4787.] 
     Assuming the substrate heat capacity and density are ˜1.2 Jg-1K-1 and 1.37 gcm-3 respectively and assuming a penetration depth of 10 μm is required, energy in the vicinity of 1.644 mJ/cm2 will be needed for increasing substrate  208  temperature by 1K. Thus, to achieve 100K temperature an increase of 164 mJ/cm2 will be required, which within the working range of current CTP devices. 
     Patterning resolution is determined by the resolution of the CTP imaging head  220  and by substrate  208  characteristics such as thermal conductivity. 
     The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the scope of the invention. 
     PARTS LIST 
       104  digital front end (DFE) 
       108  imaging device 
       112  interface line 
       200  imaging system 
       204  rotating cylinder 
       208  imaging substrate 
       212  carriage 
       216  screw 
       220  thermal imaging head 
       224  material spray element 
       228  controller 
       232  sprayed material