Abstract:
A waveguide, printed circuit board and a method of fabricating a waveguide that includes: providing a ceramic powder and polymer binder slurry, and forming the waveguide from the slurry. The waveguide and a printed circuit that includes the waveguide are also described.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a waveguide, printed circuit board, and method. 
     BACKGROUND 
     Research on thin interconnect structures has been directed to reducing cost and reducing complexity in manufacturing, to attempt compete with printed circuitry. Development of thin interconnect structures for high data transfer is particularly tough due to problems with high frequency signals. Stability of Electro-Magnetic (EM) propagation, as well as consistent signal strength may be desirable for establishing effective data communication inside electronics devices. 
     SUMMARY 
     Here, a composite material is proposed to enable the production of waveguides having good EM wave confinement with low dissipation loss. 
     The invention relates to an architecture and method for directing travelling Electro-Magnetic (EM) waves by means of connecting a thin stripe between electronic integrated circuit (IC) chips on, particularly printed-circuit assembly. This invention aims to achieve high dielectric constant and low dielectric loss that are essential for high frequency interconnectivity. 
     In this method, a polymer-ceramic composite having controllable dielectric constant and low loss tangent is proposed. This material comprises fine powder of metal oxide, mixed with dispersion solution of PolyTetraFuoroEthylene particles suspended in water. By thorough mixing, a slurry mixture can be generated at room condition. 
     Particularly, a formation of thin dielectric sheet is proposed using coating method to dispense viscous paste containing organic binder and ceramic powder. Its dielectric characteristics are adjusted by the mixing ratio of ceramic content to attain high dielectric constant. This composite can be easily pressed or rolled to give uniform and consistent thin layer which may be sliced into desired patterns. 
     Such architecture of thin layer allows conformal surface contact on flat Printed Circuit Board (PCB). In this regard, the EM waves can be fed into thin layers and propagate between IC components at different locations with minimum EM radiation and absorption in electronics devices. 
     The present invention aims to provide a method for focusing and confinement of EM communication signal in thin waveguides by tuning their dielectric behaviours at high frequency range. 
     In general terms, the invention proposes a uniformly developed thin sheet that can be cut or machined into specific patterns for attaching on PCB to improve the interconnectivity between IC components. 
     A second aspect, the invention provides a method to enable a low cost processing method for making narrow stripes with multiple bends which fit between IC components, without modifying the production of PCB. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       One or more example embodiments of the invention will now be described, with reference to the following figures, in which: 
         FIG. 1  shows the proposed mixing of ceramic powder and polymeric binder. 
         FIG. 2  shows the proposed dispensing of composite slurry to form thin sheet. 
         FIG. 3  shows the schematic of composite sheet after polymerization. 
         FIG. 4  shows the proposed cutter assembly for composite sheet. 
         FIG. 5  shows the proposed cutting process of waveguide. 
         FIG. 6  shows the schematic of interconnect on PCB using waveguides. 
     
    
    
     DETAILED DESCRIPTION 
     In a high data transfer rate system, the material for interconnects plays an important role in achieving stable and robust Electro-Magnetic (EM) propagation. When the electronics assembly becomes smaller and more compact, the design of thin and narrow interconnects between integrated circuit (IC) components may become more difficult for high data volume. 
     Polymers are usually low in dielectric constant. A low dielectric constant may not desirable in waveguides as it makes the focusing and confinement of EM wave propagation less effective. However in liquid form, polymers may offer easier and cheaper production using coating and printing processes. 
     Ceramic particles may be processed in a complex heat sintering process to form a high dielectric constant medium. However, the process may be expensive. 
     In one embodiment, liquid polymer is used as a binder for ceramic particles. The fine ceramic particles are glued to form a thin sheet by curing the polymer, which avoids a complex heat sintering processes. 
     The liquid polymer-ceramic may comprises Metal Oxide powder  101 , for example, Strontium Titanate (SrTiO3), or Titanium Dioxide (TiO2), is stirred into liquid polymer  102 , for example, Poly-Tetra-Fluoro-Ethylene (PTFE), Poly-Styrene (PS) or Poly-Propylene (PP). The composite  103  is a viscous slurry with smooth texture, similar to paint, and carrying uniformly dispersed particles, which can be dispensed or coated to a desired mould. 
     The electrical behaviours of the mentioned ingredients are as follows: 
     
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
                   
               
               
                   
                   
                 Dielectric 
                 Loss 
               
               
                   
                 Chemical 
                 Constant 
                 Tangent 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Strontium Titanate 
                 300 
                 0.0050 
               
               
                   
                 Titanium Dioxide 
                 100 
                 0.0050 
               
               
                   
                 Poly-Tetra-Fluoro-Ethylene 
                 2.5 
                 0.0002 
               
               
                   
                   
               
               
                   
                 * Published at 1~10 GHz 
               
             
          
         
       
     
     Next, as illustrated in  FIG. 2 , the mixture is dispensed onto a flat tray  201  with a containing depth of about 0.5 mm˜1.0 mm. The depth of the tray determines the thickness of the dielectric sheet. Likewise, the surface area of the desired sheet may be adjusted by the size of tray  201 . Any excess from pouring the mixture  103  will overflow outside of the tray  201 . 
     Then dispensed liquid mixture  103  in the tray  201  is transferred into a low-pressure chamber for degassing. For degassing purpose, the painted composite layer may be placed in a low pressure desiccator at the range 50˜80 kPa, for at least 5 hours. This helps to remove the air bubbles in the dispensed layer generated from the mixing process. 
     Thermal curing of the liquid mixture  103  is used to dry and polymerize the organic content in the binder. This is carried out at about 300-350° C. for about 1 hour. Subsequently, the dried layer can be lifted off from the tray  201  as soon as it is cooled. As in  FIG. 3 , this sheet  301  made of the composite material should inherited to some extent, the high dielectric constant of ceramic with low loss tangent. 
     Depending on the desired interconnect shape, a mechanical cutting assembly  400  can be customised. As shown in  FIG. 4 , in the case which ‘Z’-shape is desired, the tailored cutting knife  401 , together with steel slotted dies  402 , 403  are designed, according to the dimensions and shape of the desired waveguide. The composite sheet  301  is clamped between two steel blocks  402 , 403 , positioned where the through patterned slots  404  in each block  403  were aligned. Following that, as in  FIG. 5 , the cutter knife  401  is pressed down through the slots  404  in the two steel blocks  402 , 403  sandwiching the composite sheet  301 , and a waveguide interconnect  501  is ejected from the slot  404  at the base of the cutter assembly  400 . 
     The waveguide interconnect  501  can be glued on PCB, as shown in  FIG. 6 , with both ends placed in contact with the IC chips or any other electronics components. The material properties of the composite should help to focus and retain the EM wave during the data transmission operations. The waveguide can be placed touching the IC chips, without any additional interface. Ideally, there should be minimum gap between the ends of waveguide and IC components. 
     While example embodiments of the invention have been described in detail, many variations are possible within the scope of the invention as will be clear to a skilled reader.