Patent Publication Number: US-2023141402-A1

Title: Wiring circuit board

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority from Japanese Patent Application No. 2021-183757 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 
     There is a need for the reduction in the content of heavy metals having a large environmental impact, such as chromium, in the circuit board as described in Patent Document 1. 
     The present invention provides a wiring circuit board that allows the reduction in the content of heavy metals having a large environmental impact therein. 
     Means for Solving the Problem 
     The present invention [1] includes a wiring circuit board comprising: a first insulating layer; a conductive pattern disposed on the first insulating layer; and a protective layer disposed between the first insulating layer and the conductive pattern 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], further comprising: a second insulating layer disposed on the first insulating layer and covering the conductive pattern, 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], further comprising: a metal supporting layer disposed at an opposite side to the conductive pattern with respect to the first insulating layer and supporting the first insulating layer and the conductive pattern; and a second protective layer disposed between the first insulating layer and the metal supporting layer and protecting the metal supporting layer. 
     The present invention [4] includes the wiring circuit board described in any one of [1] to [3], wherein the protective layer contains aluminum. 
     The present invention [5] includes the wiring circuit board described in any one of [1] to [4], 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 first insulating layer and the conductive pattern consists of a metal oxide. 
     Thus, as compared to a case in which the protective layer consists of a heavy metal such as chromium, the content of heavy metals having a large environmental impact can be reduced. 
     Not only the heavy metal content in the wiring circuit board but also the heavy metal effluent discharged in the production process of the wiring circuit board 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 F  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 and then a second protective layer on the first insulating layer.  FIG.  3 D  illustrates a step of removing the second protective layer in the via by etching.  FIG.  3 E  illustrates a step of forming a conductive pattern on the second protective layer.  FIG.  3 F  illustrates a step of forming a third protective layer on the conductive pattern. 
         FIG.  4    is an explanatory view for explaining a first variation. 
         FIG.  5    is an explanatory view for explaining a second variation. 
         FIG.  6    is an explanatory view for explaining a third variation. 
         FIG.  7    is an explanatory view for explaining a fourth variation. 
     
    
    
     DESCRIPTION OF THE EMBODIMENT 
     1. Wiring Circuit Board 
     As shown in  FIG.  1   , a wiring circuit board  1  extends in a first direction and a second direction. In the present embodiment, the 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  as an example of the protective layer, a conductive pattern  15 , a third protective layer  16 , 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, and  15 C, and the ground pattern  15 D are described below. In the present embodiment, the second protective layer  14  is an insulator. When the second protective layer  14  is an insulator, the second protective layer  14  may be disposed between the first insulating layer  13  and the second insulating layer  17 . 
     The second protective layer  14  consists of a metal oxide. The second protective layer  14  does not have magnetism. Examples of the metal oxide of the second protective layer  14  include aluminum oxide, zinc oxide, aluminum silicate, silicon dioxide, and magnesium oxide. 
     Further, the 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 second protective layer  14  preferably contains aluminum. The second protective layer  14  more preferably contains aluminum oxide. As the metal oxide, aluminum oxide and aluminum silicate are preferable. 
     The ratio of the aluminum in the second protective layer  14  is, for example, 0.5% by mass or more, preferably 0.9% by mass or more. When the ratio of the aluminum in the second protective layer  14  is the above-described lower limit or more, the second protective layer  14  is easily etched in the method of producing the wiring circuit board  1  as described below. The upper limit of the ratio of the aluminum in the second protective layer  14  is not limited. The ratio of the aluminum in the second protective layer  14  is, for example, 60% by mass or less. 
     Further, the ratio of the aluminum oxide in the second protective layer  14  is, for example, 1% by mass or more, preferably 2% by mass or more. When the ratio of the aluminum oxide in the second protective layer  14  is the above-described lower limit or more, the second protective layer  14  is easily etched in the method of producing the wiring circuit board  1  as described below. The upper limit of the ratio of the aluminum oxide in the second protective layer  14  is not limited. The ratio of the aluminum oxide in the second protective layer  14  is, for example, 100% by mass or less. 
     The second protective layer  14  has a thickness of, for example, 1 nm or more, preferably 3 nm or more. When the thickness of the second protective layer  14  is the above-described lower limit or more, wires  153 A,  153 B,  153 C, and a ground wire  152 D is surely protected. The thickness of the second protective layer  14  is, for example, 100 nm or less, preferably 20 nm or less, more preferably 10 nm or less. When the thickness of the second protective layer  14  is the above-described upper limit or less, the second protective layer  14  is easily etched in the method of producing the wiring circuit board  1  as described below. 
     (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 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 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 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 first protective layer  12  through the via hole  13 A (see  FIG.  2 A ) of the insulating base layer  13 . 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  and  FIG.  2 B , the third protective layer  16  covers the whole of 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 . The third protective layer  16  consists of a metal. Examples of the metal include nickel and nickel phosphorus alloys. 
     (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 a 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. The plating layer  18  consists of a metal. Examples of the metal of the plating layer  18  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  is 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, 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 D , the second protective layer  14  in the via hole  13 A is removed by etching with an acid aqueous solution or an alkaline aqueous solution. Preferably, the second protective layer  14  is removed by etching with an acid aqueous solution. 
     In detail, an etching resist is laminated on the second protective layer  14 . The etching resist is exposed while the part on the via hole  13 A is shielded from the light. 
     Next, the exposed etching resist is developed. This development removes the etching resist on the via hole  13 A. The second protective layer  14  in the via hole  13 A is exposed. The etching resist at the exposed part, i.e., the part that is not etched remains. 
     Next, the second protective layer  14  in the via hole  13 A is etched with an acid aqueous solution or an alkaline aqueous solution. In this manner, the second protective layer  14  in the via hole  13 A is removed. After the completion of the etching, the etching resist is released. 
     The second protective layer  14  in the via hole  13 A may be removed by laser etching. 
     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 of 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 third protective layer  16  is formed on a surface of the conductive pattern  15  by electroless plating. 
     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, the ground terminal  151 D, and the terminals  152 A,  152 B, and  152 C. 
     Next, as shown in  FIG.  2 B , the plating layer  18  is formed on a surface of each of the terminals  151 A,  151 B, and  151 C, the ground terminal  151 D, and the terminals  152 A,  152 B, and  152 C by electroless plating. 
     3. Operations and Effects 
     (1) In the wiring circuit board  1 , as shown in  FIG.  2 A , the second protective layer  14  disposed between the first insulating layer  13  and the conductive pattern  15  consists of a metal oxide. 
     Thus, as compared to a case in which the second protective layer  14  consists of a heavy metal such as chromium, the content of heavy metals having a large environmental impact can be reduced. 
     Not only the heavy metal content in the wiring circuit board, but also the heavy metal effluent discharged in the production process of the wiring circuit board  1  can be reduced. 
     (2) In the wiring circuit board  1 , as shown in  FIG.  2 A , the second protective layer  14  is an insulator and disposed also between the first insulating layer  13  and the second insulating layer  17 . 
     When the second protective layer  14  is a semiconductor or conductor, it is necessary to remove the second protective layer  14  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 second protective layer  14  between the first insulating layer  13  and the second insulating layer  17 , the step of removing the second protective layer  14  between the first insulating layer  13  and the second insulating layer  17  is required at the time after the formation of the conductive pattern  15  and before the formation of the second insulating layer  17 . 
     In view of this point, when the second protective layer  14  is an insulator, the removal of the second protective layer  14  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 third protective layer  16  may also be formed from a metal oxide. In this case, the third protective layer  16  is formed on the conductive pattern  15  and the second protective layer  14  by, for example, sputtering. After the formation of the second insulating layer  17 , 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. 
     (2) As shown in  FIG.  5   , the first protective layer  12  may also be formed from a metal oxide. In this case, at the etching of the second protective layer  14  in the via hole  13 A, the first protective layer  12  in the via hole  13 A is also removed by the etching. 
     (3) As shown in  FIG.  6   , among the first protective layer  12 , the second protective layer  14 , and the third protective layer  16 , only the first protective layer  12  may be formed from a metal oxide. In this case, the first protective layer  12  in the via hole  13 A is removed by etching after the formation of the first insulating layer  13 . After the formation of the conductive pattern  15  on the second protective layer  14 , the second protective layer  14  covered with the plating resist is etched with an acid aqueous solution or an alkaline aqueous solution. 
     (4) As shown in  FIG.  7   , all of the first protective layer  12 , the second protective layer  14 , and the third protective layer  16  may be formed from a metal oxide. 
     (5) 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 conductor include alumina-doped zinc oxide. 
     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. 
     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 
           14  second protective layer 
           15  conductive pattern 
           17  second insulating layer