Patent Publication Number: US-2023147342-A1

Title: Wiring circuit board

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority from Japanese Patent Application No. 2021-183756 filed on Nov. 10, 2021, the contents of which are hereby incorporated by reference into this application. 
     BACKGROUND ART 
     The present invention relates to a wiring circuit board. 
     There have been proposed circuit boards each including an insulating layer, a conductive circuit disposed on the insulating layer, a cover layer covering the conductive circuit, a chromium thin film and a copper thin film both of which are disposed between the insulating layer and the conductive circuit, and a metal thin film disposed between the cover layer and the conductive circuit (for example, see Patent document 1 below). 
     CITATION LIST 
     Patent Document 
     Patent Document 1: Japanese Unexamined Patent Publication No. H11-233906 
     SUMMARY OF THE INVENTION 
     Problem to be Solved by the Invention 
     In the circuit board as described in Patent Document 1, a metal having magnetism, such as nickel, may be used as the metal thin film. Use of a magnetic metal around the conductive circuit may make it difficult to reduce the transmission loss. 
     The present invention provides a wiring circuit board that allows the reduction in transmission loss. 
     Means for Solving the Problem 
     The present invention [1] includes a wiring circuit board including: a first insulating layer; a conductive pattern disposed on the first insulating layer; a second insulating layer disposed on the first insulating layer and covering the conductive pattern; and a protective layer disposed between the conductive pattern and the second insulating layer and protecting the conductive pattern, wherein the protective layer consists of a metal oxide. 
     The present invention [2] includes the wiring circuit board described in [1], wherein the protective layer is an insulator and disposed also between the first insulating layer and the second insulating layer. 
     The present invention [3] includes the wiring circuit board described in [1] or [2], wherein the protective layer contains aluminum. 
     The present invention [4] includes the wiring circuit board described in any one of [1] to [3], wherein the protective layer contains aluminum oxide. 
     Effects of the Invention 
     In the wiring circuit board of the present invention, the protective layer disposed between the conductive pattern and the second insulating layer consists of a metal oxide. 
     Thus, as compared to a case in which the protective layer consists of a magnetic metal, the transmission loss of the conductive pattern can be reduced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a plan view of a wiring circuit board as one embodiment of the present invention. 
         FIG.  2 A  is a cross-sectional view of the wiring circuit board of  FIG.  1   , taken along line A-A.  FIG.  2 B  is a cross-sectional view of the wiring circuit board of  FIG.  1   , taken along line B-B. 
         FIG.  3 A  to  FIG.  3 G  are explanatory views for explaining a method of producing the wiring circuit board.  FIG.  3 A  illustrates a step of preparing a supporting layer.  FIG.  3 B  illustrates a step of forming a first protective layer on the supporting layer.  FIG.  3 C  illustrates a step of forming a first insulating layer on the first protective layer.  FIG.  3 D  illustrates a step of forming a second protective layer on the first insulating layer.  FIG.  3 E  illustrates a step of forming a conductive pattern on the second protective layer.  FIG.  3 F  illustrates a step of removing the second protective layer exposed from the plating resist by etching.  FIG.  3 G  illustrates a step of forming a third protective layer on the first insulating layer and the conductive pattern. 
         FIG.  4    is an explanatory view for explaining a variation. 
         FIG.  5    is a graph showing the transmission loss of the wiring circuit board of each of Example and Comparative Example. 
     
    
    
     DESCRIPTION OF THE EMBODIMENT 
     1. Wiring Circuit Board 
     As shown in  FIG.  1   , the wiring circuit board  1  extends in a first direction and a second direction. In the present embodiment, a wiring circuit board  1  has an approximately rectangular shape. The shape of the wiring circuit board  1  is not limited. 
     As shown in  FIG.  2 A  and  FIG.  2 B , the wiring circuit board  1  includes a supporting layer  11 , a first protective layer  12 , a first insulating layer  13 , a second protective layer  14 , a conductive pattern  15 , a third protective layer  16  as an example of the protective layer, a second insulating layer  17 , and a plating layer  18 . 
     (1) Supporting Layer 
     The supporting layer  11  supports the first protective layer  12 , the first insulating layer  13 , the second protective layer  14 , the conductive pattern  15 , the third protective layer  16 , and the second insulating layer  17 . In the present embodiment, the supporting layer  11  consists of a metal. Examples of the metal include stainless steel and copper alloys. 
     (2) The First Protective Layer 
     The first protective layer  12  is disposed on the supporting layer  11  in a thickness direction of the wiring circuit board  1 . The thickness direction is orthogonal to the first direction and the second direction. The first protective layer  12  is disposed between the supporting layer  11  and the first insulating layer  13 . The first protective layer  12  protects the supporting layer  11 . The first protective layer  12  consists of a metal. Examples of the metal include chromium, nickel, titanium, and alloys thereof. 
     (3) The First Insulating Layer 
     The first insulating layer  13  is disposed on the first protective layer  12  in the thickness direction. In other words, the first insulating layer  13  is disposed on the supporting layer  11  through the first protective layer  12  in the thickness direction. The first insulating layer  13  is disposed between the supporting layer  11  and the conductive pattern  15 . The first insulating layer  13  insulates the first protective layer  12  from the conductive pattern  15 . The first insulating layer  13  consists of resin. Examples of the resin include polyimide, maleimide, epoxy resin, polybenzoxazole, and polyester. In the present embodiment, the first insulating layer  13  has a via hole  13 A. 
     (4) The Second Protective Layer 
     The second protective layer  14  is disposed on the first insulating layer  13  in the thickness direction. The second protective layer  14  is disposed between the conductive pattern  15  and the first insulating layer  13 . The second protective layer  14  protects the conductive pattern  15 . In detail, the second protective layer  14  is disposed between a wiring pattern  15 A and the first insulating layer  13 , between a wiring pattern  15 B and the first insulating layer  13 , between a wiring pattern  15 C and the first insulating layer  13 , and between a ground pattern  15 D and the first insulating layer  13 . The wiring patterns  15 A,  15 B,  15 C, and the ground pattern  15 D are described below. The second protective layer  14  consists of a metal. Examples of the metal include chromium, nickel, titanium, and alloys thereof. 
     (5) Conductive Pattern 
     The conductive pattern  15  is disposed on the second protective layer  14  in the thickness direction. In other words, the conductive pattern  15  is disposed on the first insulating layer  13  through the second protective layer  14  in the thickness direction. The conductive pattern  15  is disposed on an opposite side to the supporting layer  11  with respect to the first insulating layer  13  in the thickness direction. The conductive pattern  15  consists of a metal. Examples of the metal include copper, silver, gold, iron, aluminum, chromium, and alloys thereof. In view of achieving good electrical properties, copper is preferably used. The shape of the conductive pattern  15  is not limited. 
     In the present embodiment, as shown in  FIG.  1   , the conductive pattern  15  has the wiring patterns  15 A,  15 B, and  15 C, and the ground pattern  15 D. The wiring patterns  15 A,  15 B, and  15 C, and the ground pattern  15 D are aligned in the second direction while being separated from each other by an interval therebetween. 
     (5-1) Wiring Pattern 
     The wiring pattern  15 A has a terminal  151 A, a terminal  152 A, and a wire  153 A. The wiring pattern  15 A electrically connects an electronic appliance connected to the terminal  151 A and an electronic appliance connected to the terminal  152 A. 
     The terminal  151 A is disposed at one end portion of the wiring circuit board  1  in the first direction. The terminal  151 A has a square land shape. 
     The terminal  152 A is disposed at the other end portion of the wiring circuit board  1  in the first direction. The terminal  152 A has a square land shape. 
     One end of the wire  153 A is connected to the terminal  151 A. The other end of the wire  153 A is connected to the terminal  152 A. The wire  153 A electrically connects the terminal  151 A and the terminal  152 A. 
     Each of the wiring patterns  15 B and  15 C is described in the same manner as the wiring pattern  15 A. Thus, the description of each of the wiring patterns  15 B and  15 C is omitted. 
     (5-2) Ground Pattern 
     The ground pattern  15 D has a ground terminal  151 D and a ground wire  152 D. The ground pattern  15 D connects an electronic appliance connected to the ground terminal  151 D with ground through the supporting layer  11 . 
     The ground terminal  151 D is disposed at one end portion of the wiring circuit board  1  in the first direction. The ground terminal  151 D has a square land shape. The terminals  151 A,  151 B, and  151 C and the ground terminal  151 D are aligned in the second direction while being separated from each other by an interval therebetween. 
     One end of the ground wire  152 D is connected to the ground terminal  151 D. The other end of the ground wire  152 D is connected to the supporting layer  11  through a via hole  13 A of the first insulating layer  13  (see  FIG.  2   ). In this manner, the ground wire  152 D is electrically connected with the supporting layer  11  through the first protective layer  12 . 
     (6) The Third Protective Layer 
     As shown in  FIG.  2 A , the third protective layer  16  covers the conductive pattern  15 . The third protective layer  16  is disposed between the conductive pattern  15  and the second insulating layer  17 . The third protective layer  16  protects the conductive pattern  15 . In detail, the third protective layer  16  covers all the wires  153 A,  153 B, and  153 C, and the ground wire  152 D. The third protective layer  16  is disposed between the wire  153 A and the second insulating layer  17 , between the wire  153 B and the second insulating layer  17 , between the wire  153 C and the second insulating layer  17 , and between the ground wire  152 D and the second insulating layer  17 . The third protective layer  16  protects all the wires  153 A,  153 B, and  153 C, and the ground wire  152 D. As shown in  FIG.  2 B , the third protective layer  16  does not cover the terminals  151 A,  151 B, and  151 C, and the ground terminal  151 D. Although not shown, the third protective layer  16  does not cover the terminals  152 A,  152 B, and  152 C, either. In the present embodiment, the third protective layer  16  is an insulator. When the third protective layer  16  is an insulator, the third protective layer  16  may be disposed also between the first insulating layer  13  and the second insulating layer  17 . 
     The third protective layer  16  consists of a metal oxide. The third protective layer  16  does not have magnetism. Examples of the metal oxide of the third protective layer  16  include aluminum oxide, zinc oxide, aluminum silicate, silicon dioxide, and magnesium oxide. 
     Further, examples of the metal oxide include a metal oxide containing aluminum, silicon, zinc, and inevitable impurities as the metal components, and a metal oxide containing aluminum, gallium, silicon, zinc, and inevitable impurities as the metal components. 
     The third protective layer  16  preferably contains aluminum. The third protective layer  16  more preferably contains aluminum oxide. As the metal oxide, aluminum oxide and aluminum silicate are preferable. 
     The ratio of the aluminum in the third protective layer  16  is, for example, 0.5% by mass or more, preferably 0.9% by mass or more. When the ratio of the aluminum in the third protective layer  16  is the lower limit or more, the third protective layer  16  can easily be etched in the method of producing the wiring circuit board  1  described below. The upper limit of the ratio of the aluminum in the third protective layer  16  is not limited. The ratio of the aluminum in the third protective layer  16  is, for example, 60% by mass or less. 
     The ratio of the aluminum oxide in the third protective layer  16  is, for example, 1% by mass or more, preferably 2% by mass or more. When the ratio of the aluminum oxide in the third protective layer  16  is the lower limit or more, the third protective layer  16  can easily be etched in the method of producing the wiring circuit board  1  described below. The upper limit of the ratio of the aluminum oxide in the third protective layer  16  is not limited. The ratio of the aluminum oxide in the third protective layer  16  is, for example, 100% by mass or less. 
     The third protective layer  16  has a thickness of, for example, 1 nm or more, preferably 3 nm or more. When the thickness of the third protective layer  16  is the lower limit or more, the wires  153 A,  153 B, and  153 C, and the ground wire  152 D are surely protected. The thickness of the third protective layer  16  is, for example, 100 nm or less, preferably 20 nm or less, more preferably 10 nm or less. When the thickness of the third protective layer  16  is the upper limit or less, the third protective layer  16  can easily be etched in the method of producing the wiring circuit board  1  described below. 
     (7) The Second Insulating Layer 
     As shown in  FIG.  1   , the second insulating layer  17  covers all the wires  153 A,  153 B, and  153 C, and the ground wire  152 D. In other words, the second insulating layer  17  covers the conductive pattern  15 . The second insulating layer  17  is disposed on the first insulating layer  13  in the thickness direction. The second insulating layer  17  does not cover the terminals  151 A,  151 B, and  151 C, and the ground terminal  151 D, and the terminals  152 A,  152 B, and  152 C. The second insulating layer  17  consists of resin. Examples of the resin include polyimide, maleimide, epoxy resin, polybenzoxazole, and polyester. 
     (8) Plating Layer 
     As shown in  FIG.  2 B , the plating layer  18  covers the terminals  151 A,  151 B, and  151 C, and the ground terminal  151 D. Although not shown, the plating layer  18  also covers the terminals  152 A,  152 B, and  152 C. The plating layer  18  may have a plurality of layers. In the present embodiment, the plating layer  18  includes a first plating layer  18 A and a second plating layer  18 B. 
     The first plating layer  18 A consists of a metal. Examples of the metal of the first plating layer  18 A include nickel and nickel-phosphorus alloys. 
     The second plating layer  18 B consists of a different metal from the first plating layer  18 A. Examples of the metal of the second plating layer  18 B include gold. 
     2. Method of Producing Wiring Circuit Board 
     Next, a method of producing the wiring circuit board  1  is described. 
     In the present embodiment, the wiring circuit board  1  may be produced by an additive method. 
     To produce the wiring circuit board  1 , as shown in  FIG.  3 A , the supporting layer  11  is prepared first. In the present embodiment, the supporting layer  11  is metal foil pulled out of a roll of metal foil. 
     Next, as shown in  FIG.  3 B , the first protective layer  12  is formed on the supporting layer  11 . The first protective layer  12  is formed, for example, by sputtering. 
     Next, as shown in  FIG.  3 C , the first insulating layer  13  is formed on the first protective layer  12 . To form the first insulating layer  13 , first, a solution (varnish) of photosensitive resin is applied and dried on the first protective layer  12  to form a film of the photosensitive resin. Next, the photosensitive resin film is exposed and developed. In this manner, the first insulating layer  13  is formed on the first protective layer  12 . 
     Next, as shown in  FIG.  3 D , the second protective layer  14  is formed on the first insulating layer  13 . The second protective layer  14  is formed, for example, by sputtering. The second protective layer  14  is formed also on an inner peripheral surface of the via hole  13 A. 
     Next, as shown in  FIG.  3 E , the conductive pattern  15  is formed on the second protective layer  14  by electrolytic plating. 
     In detail, a plating resist is laminated on the second protective layer  14 . The plating resist is exposed while the parts on which the conductive pattern  15  is formed are shielded from the light. 
     Next, the exposed plating resist is developed. This development removes the plating resist of the shielded parts. The second protective layer  14  is exposed at the parts on which the conductive pattern  15  is formed. The plating resist at the exposed parts, i.e., the parts on which the conductive pattern  15  is not formed remains. 
     Next, the conductive pattern  15  is formed on the exposed second protective layer  14  by electrolytic plating. The conductive pattern  15  fills the via hole  13 A. After the completion of the electrolytic plating, the plating resist is released. 
     Next, as shown in  FIG.  3 F , the second protective layer  14  that is exposed by the release of the plating resist is removed by etching with an acid aqueous solution or an alkaline aqueous solution. 
     Next, as shown in  FIG.  3 G , the third protective layer  16  is formed on the first insulating layer  13  and the conductive pattern  15 . The third protective layer  16  is formed, for example, by sputtering. 
     Next, as shown in  FIG.  2 A , in the same manner as the formation of the first insulating layer  13 , the second insulating layer  17  is formed on the first insulating layer  13  and the conductive pattern  15 . As described above, the second insulating layer  17  covers all the wires  153 A,  153 B, and  153 C, and the ground wire  152 D and does not cover the terminals  151 A,  151 B, and  151 C, and the ground terminal  151 D, and the terminals  152 A,  152 B, and  152 C. 
     Next, as shown in  FIG.  2 B , the third protective layer  16  that is not covered with the second insulating layer  17  is removed by etching with an acid aqueous solution or an alkaline aqueous solution. The third protective layer  16  is removed preferably by etching with an acid aqueous solution. In this manner, the third protective layer  16  covering the terminals  151 A,  151 B, and  151 C, and the ground terminal  151 D, and the terminals  152 A,  152 B, and  152 C is removed. 
     Next, the plating layer  18  is formed on the surface of each of the terminals  151 A,  151 B, and  151 C, and the ground terminal  151 D, and the terminals  152 A,  152 B, and  152 C by electroless plating or electrolytic plating. 
     3. Operations and Effects 
     (1) In the wiring circuit board  1 , as shown in  FIG.  2 A , the third protective layer  16  disposed between the conductive pattern  15  and the second insulating layer  17  consists of a metal oxide. 
     Thus, as compared to a case in which a third protective layer  16  consists of a magnetic metal, the transmission loss of the conductive pattern  15  can be reduced. 
     (2) In the wiring circuit board  1 , as shown in  FIG.  2 A , the third protective layer  16  is an insulator and disposed also between the first insulating layer  13  and the second insulating layer  17 . 
     When the third protective layer  16  is a semiconductor or conductor, it is necessary to remove the third protective layer  16  between the first insulating layer  13  and the second insulating layer  17  to prevent the electrical short circuit of each of the wiring patterns  15 A,  15 B, and  15 C, and the ground pattern  15 D. 
     To remove the third protective layer  16  between the first insulating layer  13  and the second insulating layer  17 , the step of removing the third protective layer  16  between the first insulating layer  13  and the second insulating layer  17  is required at the time after the formation of the third protective layer  16  and before the formation of the second insulating layer  17 . 
     In view of this point, when the third protective layer  16  is an insulator, the removal of the third protective layer  16  between the first insulating layer  13  and the second insulating layer  17  is not required, and thus the production process can be simplified. 
     4. Variations 
     Next, variations are described. In each of the variations, the same members as in the above-described embodiment are given the same reference numerals and the detailed descriptions thereof are omitted. 
     (1) As shown in  FIG.  4   , the second protective layer  14  may also be formed from a metal oxide. 
     (2) The third protective layer  16  may be a semiconductor or a conductor. When the third protective layer  16  is a semiconductor or a conductor, the third protective layer  16  is not disposed between the first insulating layer  13  and the second insulating layer  17 . Examples of the semiconductor or the conductor include alumina-doped zinc oxides. 
     The aluminum oxide content in the alumina-doped zinc oxide is, for example, 1% by mass or more, preferably 2% by mass or more, and, for example, 10% by mass or less, preferably 5% by mass or less. 
     The silicon dioxide content in the alumina-doped zinc oxide is, for example, 10% by mass or more, preferably 15% by mass or more, and, for example, 30% by mass or less, preferably 25% by mass or less. 
     The zinc oxide content in the alumina-doped zinc oxide is, for example, 40% by mass or more, preferably 60% by mass or more, and, for example, 90% by mass or less, preferably 80% by mass or less. 
     EXAMPLES 
     Next, the present invention is described with reference to Example and Comparative Example. The present invention is not limited to Examples. The specific numeral values used in the description below, such as physical property values and parameters, can be replaced with the corresponding physical property values and parameters in the above-described “DESCRIPTION OF THE EMBODIMENTS”, including the upper limit values (numeral values defined with “or less”) or the lower limit values (numeral values defined with “or more”). 
     (1) Production of Wiring Circuit Board 
     (1-1) Example 
     First, sputtering was carried out, thereby forming a first protective layer (a thickness of 20 nm) consisting of chromium on a supporting layer (a thickness of 100 μm) pulled out of a roll of copper foil (see  FIG.  3 B ). 
     Next, a solution (varnish) of photosensitive polyamic acid (photosensitive resin) was applied and dried on the first protective layer, thereby forming a film of the photosensitive polyamic acid. 
     Next, the applied photosensitive polyamic acid film was exposed and developed, thereby forming a first insulating layer (a thickness of 12 μm) consisting of polyimide on the first protective layer (see  FIG.  3 C ). 
     Next, sputtering was carried out, thereby forming a second protective layer (a thickness of 20 nm) consisting of chromium on the first insulating layer (see  FIG.  3 D ). 
     Next, a plating resist was laminated on the second protective layer. Then, the plating resist was exposed while the parts on which a conductive pattern was to be formed were shielded from the light. 
     Next, the exposed plating resist was developed. By that, the plating resist of the shielded parts was removed, and the second protective layer was exposed at the parts on which the conductive pattern was to be formed. The plating resist of the exposed parts, i.e., the parts on which the conductive pattern was not to be formed remained. 
     Next, the conductive pattern (12 μm) consisting of copper was formed on the exposed second protective layer by electrolytic plating. After the completion of the electrolytic plating, the plating resist was released (see  FIG.  3 E ). 
     Next, the second protective layer that was exposed by the release of the plating resist was removed by etching with an acid aqueous solution (see  FIG.  3 F ). 
     Next, a third protective layer (a thickness of 10 nm) consisting of aluminum oxide was formed on the first insulating layer and the conductive pattern by sputtering. 
     Next, in the same manner as the formation of the first insulating layer, a second insulating layer (a thickness of 5 μm) consisting of polyimide was formed on the first insulating layer and the conductive pattern to cover the wire and expose the terminals (see  FIG.  1    and  FIG.  2 A ). 
     Next, the third protective layer that was not covered with the second insulating layer was removed by etching with an acid aqueous solution. In this manner, the third protective layer covering the terminals was removed. 
     Next, a first plating layer (a thickness of 200 nm) consisting of nickel and a second plating layer (a thickness of 100 nm) consisting of gold were formed on the surfaces of the terminals by electroless plating (see  FIG.  2 B ). 
     By the steps as described above, a wiring circuit board was produced. 
     (1-2) Comparative Example 
     A wiring circuit board was produced in the same manner as Example except that a third protective layer (a thickness of 20 nm) consisting of nickel instead of the third protective layer consisting of aluminum oxide was formed by electroless plating, and the third protective layer between the wire and the terminal was removed by etching. 
     (2) Measurement of Transmission Loss 
     Of each of Example and Comparative Example, the transmission loss of the wiring circuit board was measured using a PNA network analyzer (manufactured by Agilent Technologies). The results are shown in  FIG.  5   . It is found that Example can reduce the transmission loss better than Comparative Example. 
     While the illustrative embodiments of the present invention are provided in the above description, such is for illustrative purpose only and it is not to be construed as limiting in any manner. Modification and variation of the present invention that will be obvious to those skilled in the art is to be covered by the following claims. 
     INDUSTRIAL APPLICABILITY 
     The wiring circuit board of the present invention is used, for example, for the electrical connection between electronic appliances. 
     DESCRIPTION OF REFERENCE NUMERALS 
     
         
           1  wiring circuit board 
           13  first insulating layer 
           15  conductive pattern 
           16  third protective layer 
           17  second insulating layer