Abstract:
A flexible substrate embedded with wires includes a flexible substrate constituted by a polymer material, and a continuous wire pattern containing a plurality of pores embedded in the flexible substrate, wherein the polymer material fills the pores. A method for fabricating a flexible substrate embedded with wires providing a carrier; forming a continuous wire pattern on the carrier, the continuous wire pattern containing a plurality of pores; covering a polymer material over the continuous wire pattern and the carrier and to fill into the pores; and separating the polymer material and the carrier to form a flexible substrate embedded with the continuous wire pattern” where the only change is the addition of wires.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This Application claims the benefit of U.S. Provisional Application No. 61/944,279, filed on Feb. 25, 2014, and priority of Taiwan Patent Application No. 103145994, filed on Dec. 29, 2014, the entireties of which are incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     The technical field relates to a flexible substrate embedded with wires and a method for fabricating the same. 
     BACKGROUND 
     Currently, flexible printed circuit boards mainly rely on flexible copper clad laminates (FCCL) which are classified into non-adhesive flexible copper clad laminates (2-layer FCCL) and adhesive flexible copper clad laminates (3-layer FCCL) by the number of layers, and the greatest difference between those two is whether there is an adhesive between a copper foil and a polyimide thin film. 2L FCCL has the advantages of high heat-durability, high warp resistance, and improved dimension stability. However its cost is comparatively higher. Therefore, most flexible substrates mainly use 3L FCCL, only higher level flexible substrates adopt 2L FCCL. 
     3L FCCL requires using epoxy resin as an adhesive between a flexible substrate and wires. However, the heat-durability of a general epoxy resin adhesive is worse than that of polyimide. Therefore, there is a temperature restriction on the use of an epoxy resin adhesive. Additionally, the reliability thereof is unsatisfactory. However, in order to meet the requirements of wire patterning, 2L FCCL also requires the steps of surface treatment, film deposition and etching whose manufacturing procedure is complicated and time-consuming. 
     SUMMARY 
     In accordance with one embodiment of the disclosure, a flexible substrate embedded with wires is provided. The flexible substrate embedded with wires comprises a flexible substrate constituted by a polymer material and a continuous wire pattern containing a plurality of pores embedded in the flexible substrate, wherein the polymer material fills the pores. 
     In accordance with another embodiment of the disclosure, a method for fabricating a flexible substrate embedded with wires is provided. The fabrication method comprises providing a carrier, forming a continuous wire pattern on the carrier, wherein the continuous wire pattern contains a plurality of pores, covering a polymer material over the continuous wire pattern and the carrier and to fill into the pores, and separating the polymer material and the carrier to form a flexible substrate embedded with the continuous wire pattern. 
     A detailed description is given in the following embodiments with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
         FIG. 1  is a cross-sectional view of a flexible substrate embedded with wires in accordance with one embodiment of the disclosure; 
         FIG. 2  is a cross-sectional view of a flexible substrate embedded with wires in accordance with one embodiment of the disclosure; 
         FIGS. 3A-3C  are cross-sectional views of a method for fabricating a flexible substrate embedded with wires in accordance with one embodiment of the disclosure; and 
         FIGS. 4A-4D  are cross-sectional views of a method for fabricating a flexible substrate embedded with wires in accordance with one embodiment of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the disclosed embodiments. It will be apparent, however, that one or more embodiments may be practiced without these specific details. In other instances, well-known structures and devices are shown schematically in order to simplify the drawing. 
     Referring to  FIG. 1 , in accordance with one embodiment of the disclosure, a flexible substrate embedded with wires is provided. The flexible substrate  10  embedded with wires comprises a flexible substrate  12  and a continuous wire pattern  14 . The flexible substrate  12  is constituted by a polymer material  12 ′. The continuous wire pattern  14  contains a plurality of pores  16  embedded in the flexible substrate  12 . The polymer material  12 ′ fills the pores  16 . 
     The polymer material  12 ′ may comprise polyimide (PI) or polyvinylidene fluoride (PVDF). 
     The wire pattern  14  may comprise, for example, silver, copper, nickel or an alloy thereof. The wire pattern  14  has a resistivity ranging from about 1.6×10 −6  Ω·cm to about 10×10 −6  Ω·cm. 
     The pore  16  contained in the continuous wire pattern  14  has a size ranging from about 10 nm to about 100 μm. 
     In this embodiment, the continuous wire pattern  14  is embedded in an area inside the flexible substrate  12 , as shown in  FIG. 1 . 
     Referring to  FIG. 2 , in accordance with another embodiment of the disclosure, a flexible substrate embedded with wires is provided. The flexible substrate  100  embedded with wires comprises a flexible substrate  120  and a continuous wire pattern  140 . The flexible substrate  120  is constituted by a polymer material  120 ′. The continuous wire pattern  140  contains a plurality of pores  160  embedded in the flexible substrate  120 . The polymer material  120 ′ fills the pores  160 . 
     The polymer material  120 ′ may comprise polyimide (PI) or polyvinylidene fluoride (PVDF). 
     The wire pattern  140  may comprise, for example, silver, copper, nickel or an alloy thereof. The wire pattern  140  has a resistivity ranging from about 1.6×10 −6  Ω·cm to about 10×10 −6  Ω·cm. 
     The pore  160  contained in the continuous wire pattern  140  has a size ranging from about 10 nm to about 100 μm. 
     In this embodiment, the continuous wire pattern  140  is embedded in an area near a surface of the flexible substrate  120 , as shown in  FIG. 2 . 
     Referring to  FIGS. 3A-3C , in accordance with one embodiment of the disclosure, a method for fabricating a flexible substrate embedded with wires is provided. First, as shown in  FIG. 3A , a carrier  18  is provided. The carrier  18  may comprise glass or metal. 
     Next, a continuous wire pattern  14  is formed on the carrier  18 . The continuous wire pattern  14  contains a plurality of pores (not shown). In this embodiment, the step of forming the continuous wire pattern  14  containing a plurality of pores on the carrier  18  may comprise forming the continuous wire pattern  14  on the carrier  18  using, for example, a screen printing process, and then performing a sintering process with a sintering temperature ranging from about 250° C. to about 300° C. on the continuous wire pattern  14  to form the continuous wire pattern  14  containing a plurality of pores. The wire pattern  14  may comprise, for example, silver, copper, nickel or an alloy thereof. The wire pattern  14  has a resistivity ranging from about 1.6×10 −6  Ω·cm to about 10×10 −6  Ω·cm. Additionally, the pore contained in the continuous wire pattern  14  has a size ranging from about 10 nm to about 100 μm. 
     In one embodiment, the step of forming a continuous wire pattern  14  on the carrier  18  comprises providing a metal glue (not shown) with a solid content ranging from about 80% to about 85%, forming a continuous pattern  14  of the metal glue on the carrier  18 , and performing a sintering process on the carrier  18 . The sintering process has a sintering temperature ranging from about 300° C. to about 350° C. and a sintering time ranging from about 30 min to about 40 min. 
     Next, a polymer material  12 ′ is covered the continuous wire pattern  14  and the carrier  18  using, for example, a coating process, and the polymer material  12 ′ is filled into the pores (not shown). The polymer material  12 ′ may comprise polyimide (PI) or polyvinylidene fluoride (PVDF). 
     In one embodiment, the step of covering a polymer material  12 ′ over the continuous wire pattern  14  and the carrier  18  comprises providing a polyvinylidene fluoride (PVDF) (not shown) with a solid content ranging from about 5% to about 30%, forming a polyvinylidene fluoride (PVDF) layer  12 ′ on the continuous wire pattern  14  and the carrier  18 , and performing a baking process on the carrier  18 . The baking process has a baking temperature ranging from about 50° C. to about 180° C. and a baking time ranging from about 10 min to about 30 min. 
     In another embodiment, the step of covering a polymer material  12 ′ over the continuous wire pattern  14  and the carrier  18  comprises providing a polyimide (PI) (not shown) with a solid content ranging from about 5% to about 40%, forming a polyimide (PI) layer  12 ′ on the continuous wire pattern  14  and the carrier  18 , and performing a baking process on the carrier  18 . Specifically, the baking process has a baking temperature ranging from about 50° C. to about 210° C. and a baking time ranging from about 30 min to about 60 min. 
     Next, the polymer material  12 ′ and the carrier  18  are separated using, for example, a cutting process, to form a flexible substrate  12  embedded with the continuous wire pattern  14 . 
     In this embodiment, the continuous wire pattern  14  is embedded in an area inside the flexible substrate  12 , as shown in  FIG. 3C . 
     Referring to  FIGS. 4A-4D , in accordance with one embodiment of the disclosure, a method for fabricating a flexible substrate embedded with wires is provided. First, as shown in  FIG. 4A , a carrier  180  is provided. The carrier  180  may comprise glass or metal. 
     Next, a continuous wire pattern  140  is formed on the carrier  180 . The continuous wire pattern  140  contains a plurality of pores (not shown). In this embodiment, the step of forming the continuous wire pattern  140  containing a plurality of pores on the carrier  180  may comprise forming the continuous wire pattern  140  on the carrier  180  using, for example, a screen printing process, and then performing a sintering process with a sintering temperature ranging from about 250° C. to about 300° C. on the continuous wire pattern  140  to form the continuous wire pattern  140  containing a plurality of pores. The wire pattern  140  may comprise, for example, silver, copper, nickel or an alloy thereof. The wire pattern  140  has a resistivity ranging from about 1.6×10 −6  Ω·cm to about 10×10 −6  Ω·cm. The pore contained in the continuous wire pattern  140  has a size ranging from about 10 nm to about 100 μm. 
     Next, a polymer material  120 ′ covers the continuous wire pattern  140  and the carrier  180  using, for example, a coating process, and the polymer material  120 ′ is filled into the pores (not shown). The polymer material  120 ′ may comprise polyimide (PI) or polyvinylidene fluoride (PVDF). 
     Next, the polymer material  120 ′ and the carrier  180  are separated using, for example, a cutting process, to form a flexible substrate  120  embedded with the continuous wire pattern  140 . 
     Next, a surface treatment process  200 , for example, a plasma process, is performed on the flexible substrate  120  embedded with the continuous wire pattern  140  to expose the continuous wire pattern  140 . 
     In this embodiment, the continuous wire pattern  140  is embedded in an area near a surface of the flexible substrate  120 , as shown in  FIG. 4D . 
     In the disclosure, a full-printing substrate structure design which is capable of embedding metal wires in a flexible substrate is developed which resolves the current problems of poor reliability and poor adhesion force between the substrate and wires, and the simplicity of its manufacturing procedure provides optimal benefits. As such it has been widely applied to flexible electronics, flexible printed circuits, LEDs, and related industries. In the disclosure, the flexible substrate structure embedded with metal wires exhibits poor adhesion force between the metal wires and the carrier, and after the used polymer material is coated and shaped, the polymer material and the metal wires are capable of easily being taken down from the carrier to form the polymer material embedded with metal wires which possess high warp resistance in structure and high adhesion force between the substrate and the wires, such that it is not easy to peel the wires off the substrate. 
     In the disclosed flexible substrate structure, the polymer material fills and penetrates the pores of the wires such that the metal wires are effectively coated by the polymer material, resulting in the metal wires being buried inside the polymer substrate or embedded near a surface of the polymer substrate which gives the metal wires the characteristics of heat-durability, soldering resistance, warp resistance, reduced thickness and rapid electronic conduction, etc. In addition, the novel flexible substrate conductor circuit structure developed by the disclosure is capable of being applied in the formation of ultra-thin polymer substrate and circuits, achieving a reduced thickness of the overall integration, also effectively being applied to flexible displays such as flexible LED package substrates, touch panels, displays, etc. Additionally, this structure can also be applied to the adhesion of high-power electronic chips and reduce the thickness of packaging and electronic circuits. 
     EXAMPLES 
     Example 1 
     Preparation of the Flexible Substrate Embedded with Wires ( 1 ) and Analysis of the Characteristics Thereof 
     Referring to  FIGS. 3A-3C , first, as shown in  FIG. 3A , a carrier  18  was provided. The carrier  18  comprised glass. 
     Next, a continuous wire pattern  14  was formed on the carrier  18 . The continuous wire pattern  14  contained a plurality of pores (not shown). In this example, the step of forming the continuous wire pattern  14  containing a plurality of pores on the carrier  18  comprised dissolving C 11 H 23 OOAg (8 g) in xylene (16 ml) to form a solution, blending the solution with spherical metallic silver powder with a size ranging from 100 nm to 300 nm (40 g) to prepare a conductive silver glue (with a viscosity of 100,000 cp.) with a solid content of 85%, forming the continuous wire pattern  14  on the carrier  18  using a screen printing process (mesh: 325), and performing a sintering process with a sintering temperature of about 300° C. on the continuous wire pattern  14  for about 30 min to form the continuous wire pattern  14  containing a plurality of pores. The pore contained in the continuous wire pattern  14  had a size ranging from 10 nm to 100 μm. 
     Next, a polymer material  12 ′ covered the continuous wire pattern  14  and the carrier  18  using a coating process, and the polymer material  12 ′ was filled into the pores (not shown). In this example, the step of covering the polymer material  12 ′ over the continuous wire pattern  14  and the carrier  18  comprised coating a polyimide (PI) solution with a solid content of about 20% (dissolving 6 g of PI in 24 ml of dimethylacetamide to form a solution) on the continuous wire pattern  14  and the carrier  18  using a 300-μm scraper to form a polyimide (PI) film and performing a baking process on the polyimide (PI) film to obtain a transparent polyimide (PI) thin film. In the baking process, the polyimide (PI) film was baked at 50° C. for 30 min, at 140° C. for 30 min, and at 210° C. for 60 min. 
     Next, the polymer material  12 ′ and the carrier  18  were separated using a cutting process to form a flexible substrate  12  embedded with the continuous wire pattern  14 . The cutting process was a simple mechanical cutting process. 
     In this example, the continuous wire pattern  14  was embedded in an area inside the flexible substrate  12 , as shown in  FIG. 3C . 
     Next, the characteristics (adhesion force between the flexible substrate and the wire, resistivity of the wire) of the flexible substrate embedded with wires prepared by this example were analyzed, and deflection and solder tests thereof were also performed. The results are shown in Table 1. 
     Example 2 
     Preparation of the Flexible Substrate Embedded with Wires ( 2 ) and Analysis of the Characteristics Thereof 
     Referring to  FIGS. 3A-3C , first, as shown in  FIG. 3A , a carrier  18  was provided. The carrier  18  comprised stainless steel. 
     Next, a continuous wire pattern  14  was formed on the carrier  18 . The continuous wire pattern  14  contained a plurality of pores (not shown). In this example, the step of forming the continuous wire pattern  14  containing a plurality of pores on the carrier  18  comprised dissolving C 11 H 23 OOAg (8 g) in xylene (16 ml) to form a solution, blending the solution with spherical metallic silver powder with a size ranging from 100 nm to 300 nm (40 g) to prepare a conductive silver glue (with a viscosity of 100,000 cp.) with a solid content of 85%, forming the continuous wire pattern  14  on the carrier  18  using a screen printing process (mesh: 325), and performing a sintering process with a sintering temperature about 300° C. on the continuous wire pattern  14  for about 30 min to form the continuous wire pattern  14  containing a plurality of pores. The pore contained in the continuous wire pattern  14  had a size ranging from 10 nm to 100 μm. 
     Next, a polymer material  12 ′ covered the continuous wire pattern  14  and the carrier  18  using a coating process, and the polymer material  12 ′ was filled into the pores (not shown). In this example, the step of covering the polymer material  12 ′ over the continuous wire pattern  14  and the carrier  18  comprised coating a polyvinylidene fluoride (PVDF) solution with a solid content of about 15% (dissolving 6 g of PVDF in 34 ml of dimethylacetamide to form a solution) on the continuous wire pattern  14  and the carrier  18  using a 500-μm scraper to form a polyvinylidene fluoride (PVDF) film and performing a baking process on the polyvinylidene fluoride (PVDF) film to obtain a transparent polyvinylidene fluoride (PVDF) thin film. In the baking process, the polyvinylidene fluoride (PVDF) film was baked at 80° C. for 10 min and at 180° C. for 30 min. 
     Next, the polymer material  12 ′ and the carrier  18  were separated using a cutting process to form a flexible substrate  12  embedded with the continuous wire pattern  14 . The cutting process was a simple mechanical cutting process. 
     In this example, the continuous wire pattern  14  was embedded in an area inside the flexible substrate  12 , as shown in  FIG. 3C . 
     Next, the characteristics (adhesion force between the flexible substrate and the wire, resistivity of the wire) of the flexible substrate embedded with wires prepared by this example were analyzed, and deflection and solder tests thereof were also performed. The results are shown in Table 1. 
     Example 3 
     Preparation of the Flexible Substrate Embedded with Wires ( 3 ) and Analysis of the Characteristics Thereof 
     Referring to  FIGS. 4A-4D , first, as shown in  FIG. 4A , a carrier  180  was provided. The carrier  180  comprised glass. 
     Next, a continuous wire pattern  140  was formed on the carrier  180 . The continuous wire pattern  140  contained a plurality of pores (not shown). In this example, the step of forming the continuous wire pattern  140  containing a plurality of pores on the carrier  180  comprised dissolving C 11 H 23 OOAg (8 g) in xylene (16 ml) to form a solution, blending the solution with spherical metallic silver powder with a size ranging from 100 nm to 300 nm (40 g) to prepare a conductive silver glue (with a viscosity of 100,000 cp.) with a solid content of 85%, forming the continuous wire pattern  140  on the carrier  180  using a screen printing process (mesh: 325), and performing a sintering process with a sintering temperature of 300° C. on the continuous wire pattern  140  for about 30 min to form the continuous wire pattern  140  containing a plurality of pores. The pore contained in the continuous wire pattern  140  had a size ranging from 10 nm to 100 μm. 
     Next, a polymer material  120 ′ covered the continuous wire pattern  140  and the carrier  180  using a coating process, and the polymer material  120 ′ was filled into the pores (not shown). In this example, the step of covering the polymer material  120 ′ over the continuous wire pattern  140  and the carrier  180  comprised coating a polyimide (PI) solution with a solid content of about 20% (dissolving 6 g of PI in 24 ml of dimethylacetamide to form a solution) on the continuous wire pattern  140  and the carrier  180  using a 300-μm scraper to form a polyimide (PI) film and performing a baking process on the polyimide (PI) film to obtain a transparent polyimide (PI) thin film. In the baking process, the polyimide (PI) film was baked at 50° C. for 30 min, at 140° C. for 30 min, and at 210° C. for 60 min. 
     Next, the polymer material  120 ′ and the carrier  180  were separated using a cutting process to form a flexible substrate  120  embedded with the continuous wire pattern  140 . The cutting process was a simple mechanical cutting process. 
     Next, a surface treatment process  200  was performed on the flexible substrate  120  embedded with the continuous wire pattern  140  to expose the continuous wire pattern  140 . The surface treatment process  200  was a plasma process. 
     In this example, the continuous wire pattern  140  was embedded in an area near a surface of the flexible substrate  120 , as shown in  FIG. 4D . 
     Next, the characteristics (adhesion force between the flexible substrate and the wire, resistivity of the wire) of the flexible substrate embedded with wires prepared by this example were analyzed, and deflection and solder tests thereof were also performed. The results are shown in Table 1. 
     Comparative Example 1 
     Preparation of a Conventional Flexible Substrate with Wires Formed Thereon and Analysis of the Characteristics Thereof 
     First, a substrate was provided. The substrate comprised polyimide (PI). 
     Next, a wire pattern was formed on the substrate. In this example, the step of forming the wire pattern on the substrate comprised dissolving C 11 H 23 OOAg in xylene to form a solution, blending the solution with spherical metallic silver powder with a size ranging from 100 nm to 300 nm to prepare a conductive silver glue with a solid content of 85%, and then forming the wire pattern on the substrate using a screen printing process (mesh: 325). 
     Next, the characteristics (adhesion force between the flexible substrate and the wire, resistivity of the wire) of the flexible substrate with wires formed thereon prepared by this example were analyzed, and deflection and solder tests thereof were also performed. The results are shown in Table 1. 
     
       
         
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Adhesion 
                   
                   
                   
               
               
                   
                 force  
                   
                   
                   
               
               
                   
                 between 
                   
                 Deflection 
                   
               
               
                   
                 flexible 
                   
                 test 
                 Solder  
               
               
                   
                 substrate  
                   
                 (R = 0.38 cm/ 
                 test 
               
               
                 Example/ 
                 and wire 
                 Resistivity 
                 1,000 
                 (&gt;280°  
               
               
                 Com. Example 
                 (B) 
                 (Ω · cm) 
                 times) 
                 C.) 
               
               
                   
               
             
             
               
                 Example 1 
                 5 
                 6 × 10 −6   
                 Pass 
                 Pass 
               
               
                 Example 2 
                 5 
                 6 × 10 −6   
                 Pass 
                 Pass 
               
               
                 Example 3 
                 5 
                 6 × 10 −6   
                 Pass 
                 Pass 
               
               
                 Com. Example 1 
                 1 
                 6 × 10 −5   
                 No Pass 
                 No Pass 
               
               
                   
               
             
          
         
       
     
     It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed embodiments. It is intended that the specification and examples be considered as exemplary only, with the true scope of the disclosure being indicated by the following claims and their equivalents.