WIRING CIRCUIT BOARD AND METHOD OF PRODUCING THE WIRING CIRCUIT BOARD

A wiring circuit board includes a metal supporting layer, a first metal thin film, an insulating layer including a through hole, a second metal thin film disposed on the first metal thin film in the through hole, and a conductive pattern electrically connected to the metal supporting layer through the first metal thin film and the second metal thin film in the through hole. The first metal thin film includes an oxide coating at least on a contact surface in contact with the insulating layer. In the central part of the through hole, the oxide coating has a thickness of 0 or a thickness smaller than a thickness of the oxide coating on the contact surface.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priorities from Japanese Patent Application No. 2022-096919 filed on Jun. 15, 2022 and Japanese Patent Application No. 2022-168719 filed on Oct. 20, 2022, both of which are hereby incorporated by reference into this application.

TECHNICAL FIELD

The present invention relates to a wiring circuit board and a method of producing the wiring circuit board.

BACKGROUND ART

There has conventionally been a known wiring circuit board including a metal supporting board, a first metal layer disposed on the metal supporting board, an insulating layer disposed on the first metal layer, a second metal layer disposed on the insulating layer, and a conductive layer disposed on the second metal layer, wherein the conductive layer and the metal supporting board are electrically connected to each other through a via (for example, see Patent document 1 below).

CITATION LIST

SUMMARY OF THE INVENTION

Problem to be Solved by the Invention

To achieve the electrical connection with low resistance between the conductive layer and the metal supporting board, the first metal layer is removed from the part in which the via is to be formed by etching, and the via formed of the second metal layer and the conductive layer is in direct contact with the metal supporting board in the wiring circuit board described in Patent Document 1.

Thus, not only the first metal layer but also the metal layer (metal supporting board) under the first metal layer may be etched.

The present invention provides a wiring circuit board in which the metal layer under the first metal thin film is protected and the electrical resistance between the conductive pattern and the metal layer under the first metal thin film can be reduced, and a method of producing the wiring circuit board.

Means for Solving the Problem

The present invention [1] includes a wiring circuit board including: a metal supporting layer; a first metal thin film disposed on the metal supporting layer; an insulating layer disposed on the first metal thin film and including a through hole; a second metal thin film disposed on the insulating layer and also disposed on the first metal thin film in the through hole; and a conductive pattern disposed on the second metal thin film and electrically connected to the metal supporting layer through the first metal thin film and the second metal thin film in the through hole, wherein the first metal thin film includes an oxide coating at least on a contact surface in contact with the insulating layer, and wherein in a central part of the through hole, the oxide coating has a thickness of 0 or a thickness smaller than a thickness of the oxide coating on the contact surface.

In the structure described above, at least only a part of the oxide coating of the first metal thin film is removed in the through hole, and this structure allows the conductive pattern and the metal supporting layer to be electrically connected to each other while the first metal thin film remains.

Thus, the first metal thin film protects the metal supporting layer (the metal layer under the first metal thin film), and the electrical resistance between the conductive pattern and the metal supporting layer can be reduced by the removal of the oxide coating.

The present invention [2] includes a wiring circuit board comprising: a metal supporting layer; a first metal thin film disposed on the metal supporting layer; an insulating layer disposed on the first metal thin film and including a through hole; a second metal thin film disposed on the insulating layer and also disposed on the first metal thin film in the through hole; and a conductive pattern disposed on the second metal thin film and electrically connected to the metal supporting layer through the first metal thin film and the second metal thin film in the through hole, wherein in a central part of the through hole, the first metal thin film has a thickness smaller than a thickness of the first metal thin film between the metal supporting layer and the insulating layer.

In the structure described above, a part of the first metal thin film is removed in the through hole, and this structure allows the conductive pattern and the metal supporting layer to be electrically connected to each other while the first metal thin film remains.

Thus, the first metal thin film protects the metal supporting layer (the metal layer under the first metal thin film), and the electrical resistance between the conductive pattern and the metal supporting layer can be reduced by the thinning of the first metal thin film.

The present invention [3] includes a wiring circuit board comprising: a metal supporting layer; a first metal thin film disposed on the metal supporting layer; an insulating layer disposed on the first metal thin film and including a through hole; a second metal thin film disposed on the insulating layer; a third metal thin film disposed on the metal supporting layer in the through hole; and a conductive pattern disposed on the second metal thin film, also disposed on the third metal thin film in the through hole, and electrically connected to the metal supporting layer through the third metal thin film, wherein in a central part of the through hole, the third metal thin film has a thickness smaller than a total of a thickness of the first metal thin film between the metal supporting layer and the insulating layer and a thickness of the second metal thin film between the insulating layer and the conductive pattern and larger than the thickness of the first metal thin film between the metal supporting layer and the insulating layer or the thickness of the second metal thin film between the insulating layer and the conductive pattern.

In the structure described above, a part of the first metal thin film is removed in the through hole while the first metal thin film remains, and the second metal thin film is formed on the first metal thin film. This structure allows the conductive pattern and the metal supporting layer to be electrically connected to each other through the third metal thin film formed of the first metal thin film and the second metal thin film while the first metal thin film remains.

Thus, the first metal thin film protects the metal supporting layer (the metal layer under the first metal thin film), and the electrical resistance between the conductive pattern and the metal supporting layer can be reduced by the thinning of the first metal thin film.

The present invention [4] includes the wiring circuit board described in any one of the above-described [1] to [3], further comprising: an intermediate metal layer disposed between the metal supporting layer and the first metal thin film and having higher electrical conductivity than electrical conductivity of the metal supporting layer.

The structure described above enables the first metal thin film to protect the intermediate metal layer (the metal layer under the first metal thin film) and allows for the reduction in the electrical resistance between the conductive pattern and the intermediate metal layer even when the intermediate metal layer exists between the metal supporting layer and the first metal thin film.

The present invention [5] includes the wiring circuit board described in any one of the above-described [1] to [4], wherein the first metal thin film contains at least one of chromium, nickel, copper, titanium, tungsten, and molybdenum.

The present invention [6] includes the wiring circuit board described in any one of the above-described [1] to [4], wherein the first metal thin film is made of chromium.

The present invention [7] includes a method of producing the wiring circuit board described in any one of the above-described [1] to [6], the method comprising: a first step of preparing the metal supporting layer; a second step of forming the first metal thin film after the first step; a third step of forming the insulating layer after the second step; a fourth step of etching a surface of the first metal thin film in the through hole after the third step; a fifth step of forming the second metal thin film after the fourth step; and a sixth step of forming the conductive pattern after the fifth step.

The present invention [8] includes the method described in the above-described [7], wherein in the fourth step, a surface of the first metal thin film in the through hole is etched by plasma etching using at least one selected from helium, neon, argon, krypton, and xenon.

Effects of the Invention

The wiring circuit board of the present invention allows for the protection of the metal layer (the metal supporting layer or the intermediate metal layer) under the first metal thin film and the reduction in the electrical resistance between the conductive pattern and the metal layer under the first metal thin film.

The method of producing the wiring circuit board of the present invention allows for the production of the wiring circuit board described above.

DESCRIPTION OF THE EMBODIMENT

1. Wiring Circuit Board

As illustrated inFIG.1, the wiring circuit board1extends in a first direction and a second direction. In the present embodiment, the wiring circuit board1has an approximately rectangular shape. The shape of the wiring circuit board1is not limited.

As illustrated inFIG.2, the wiring circuit board1includes a metal supporting layer11, a first metal thin film12, an insulating layer13, a second metal thin film14, a conductive pattern and a cover layer16.

(1) Metal Supporting Layer

The metal supporting layer11supports the first metal thin film12, the insulating layer13, the second metal thin film14, the conductive pattern15, and the cover layer16. In the present embodiment, examples of the material of the metal supporting layer11include the stainless-steels and copper alloys.

(2) First Metal Thin Film

The first metal thin film12is disposed on the metal supporting layer11in a thickness direction of the wiring circuit board1. The thickness direction is orthogonal to the first direction and the second direction. The first metal thin film12is disposed between the metal supporting layer11and the insulating layer13. The first metal thin film12protects the metal supporting layer11. Examples of the material of the first metal thin film12include chromium, nickel, copper, titanium, tungsten, molybdenum, and alloys thereof. That is to say, the first metal thin film12contains at least one of chromium, nickel, copper, titanium, tungsten, and molybdenum. Preferably, the first metal thin film12is made of chromium.

The first metal thin film12includes an oxide coating121on a contact surface S1in contact with the insulating layer13and on a contact surface S2in contact with the second metal thin film14. The contact surface S2in contact with the second metal thin film14is disposed at an inside of a through hole131of the insulating layer13. The through hole131is described below.

The thickness of the oxide coating121on the contact surface S2is smaller than that of the oxide coating121on the contact surface S1. In detail, at least in a central part of the through hole131, a thickness T1of the oxide coating121on the contact surface S2is smaller than a thickness T2of the oxide coating121on the contact surface S1. In this manner, the electrical resistance between the first metal thin film12and the second metal thin film14can be reduced. In this manner, while the first metal thin film12protects the metal supporting layer11, the electrical resistance between the conductive pattern15and the metal supporting layer11can be reduced.

The thickness T1of the oxide coating121on the contact surface S2is, for example, 5 nm or less, preferably 3 nm or less.

The thickness T2of the oxide coating121on the contact surface S1is, for example, 1 nm or more, and, for example, 10 nm or less.

Provided that the thickness T2of the oxide coating121on the contact surface S1is 100%, the thickness T1of the oxide coating121on the contact surface S2is, for example, 85% or less, preferably 70% or less.

Not only the oxide coating121on the contact surface S2is thin but also, at least in the central part of the through hole131, a thickness T3of the first metal thin film12is smaller than a thickness T4of the first metal thin film12between the metal supporting layer11and the insulating layer13. Thus, while the first metal thin film12protects the metal supporting layer11, the electrical resistance between the conductive pattern15and the metal supporting layer11can be reduced.

The thickness T3of the first metal thin film12in the central part of the through hole131is, for example, 100 nm or less, preferably 75 nm or less, and, for example, 5 nm or more.

The thickness T4of the first metal thin film12between the metal supporting layer11and the insulating layer13is, for example, 100 nm or less, preferably 50 nm or less, and, for example, 5 nm or more.

Provided that the thickness T4of the first metal thin film12between the metal supporting layer11and the insulating layer13is 100%, the thickness T3of the first metal thin film12in the central part of the through hole131is, for example, 96% or less, preferably 92% or less, and, for example, 50% or more.

The insulating layer13is disposed on the first metal thin film12in the thickness direction. In other words, the insulating layer13is disposed on the metal supporting layer11through the first metal thin film12in the thickness direction. The insulating layer13is disposed between the metal supporting layer11and the conductive pattern15. The insulating layer13insulates the metal supporting layer11from the conductive pattern15. The insulating layer13is made of resin. Examples of the resin include polyimide, maleimide, epoxy resin, polybenzoxazole, and polyester. The insulating layer13has the through hole131. The through hole131is a via hole.

(4) Second Metal Thin Film

The second metal thin film14is disposed on the insulating layer13in the thickness direction. The second metal thin film14is disposed between the insulating layer13and the conductive pattern15. The second metal thin film14protects the conductive pattern15. Examples of the material of the second metal thin film14include chromium, nickel, copper, titanium, tungsten, molybdenum, and alloys thereof. The second metal thin film14preferably is made of chromium. The second metal thin film14is disposed on the first metal thin film12in the through hole131. In this manner, a third metal thin film17formed of the first metal thin film12and the second metal thin film14is formed in the through hole131. That is to say, the wiring circuit board1includes the third metal thin film17in the through hole131. The third metal thin film17is disposed on the metal supporting layer11in the thickness direction. The third metal thin film17is disposed between the metal supporting layer11and the conductive pattern15in the thickness direction.

At least in the central part of the through hole131, a thickness T5of the third metal thin film17is smaller than the total of the thickness T4of the first metal thin film12between the metal supporting layer11and the insulating layer13and a thickness T6of the second metal thin film14between the insulating layer13and the conductive pattern15. Furthermore, at least in the central part of the through hole131, the thickness T5of the third metal thin film17is larger than the thickness T4of the first metal thin film12between the metal supporting layer11and the insulating layer13or the thickness T6of the second metal thin film14between the insulating layer13and the conductive pattern15. Thus, while the first metal thin film12protects the metal supporting layer11, the electrical resistance between the conductive pattern15and the metal supporting layer11can be reduced.

The thickness T5of the third metal thin film17in the central part of the through hole131is, for example, 200 nm or less, preferably 150 nm or less, and, for example, 10 nm or more.

The thickness T6of the second metal thin film14between the insulating layer13and the conductive pattern15is, for example, 200 nm or less, preferably 100 nm or less, and, for example, 10 nm or more.

The conductive pattern15is disposed on the second metal thin film14in the thickness direction. In other words, the conductive pattern15is disposed on the insulating layer13through the second metal thin film14in the thickness direction. The conductive pattern15is disposed at an opposite side to the metal supporting layer11relative to the insulating layer13in the thickness direction. The conductive pattern15is made of metal. Examples of the metal include, for example, copper, silver, gold, iron, aluminum, chromium, and alloys thereof. In view of obtaining excellent electric properties, copper is preferably used. The shape of the conductive pattern15is not limited.

In the present embodiment, as illustrated inFIG.1, the conductive pattern15includes a plurality of wiring patterns15A,15B, and15C, and a ground pattern15D. The wiring patterns15B, and15C, and the ground pattern15D are arranged at intervals in the second direction.

The wiring pattern15A includes a terminal151A, a terminal152A, and a wire153A. The wiring pattern15A electrically connects an electronic component connected with the terminal151A to an electronic component connected with the terminal152A.

The terminal151A is disposed on one end portion of the wiring circuit board1in the first direction. The terminal151A has a square land shape.

The terminal152A is disposed on the other end portion of the wiring circuit board1in the first direction. The terminal152A has a square land shape.

One end of the wire153A is connected to the terminal151A. The other end of the wire153A is connected to the terminal152A. The wire153A electrically connects the terminal151A to the terminal152A.

Each of the wiring patterns15B and15C are described in the same manner as the wiring pattern15A is. Thus, the description of each of the wiring patterns15B and15C is omitted.

(5-2) Ground Pattern

The ground pattern15D has a ground terminal151D and a ground wire152D. The ground pattern15D connects an electronic component connected to the ground terminal151D with ground through the metal supporting layer11.

The ground terminal151D is disposed at the one end portion of the wiring circuit board1in the first direction. The ground terminal151D has a square land shape. The terminals151A,151B, and151C and the ground terminal151D are arranged at intervals in the second direction.

One end of the ground wire152D is connected to the ground terminal151D. The other end of the ground wire152D is connected to the metal supporting layer11through the through hole131of the insulating layer13(seeFIG.2).

In detail, as illustrated inFIG.2, in the through hole131, the other end of the ground wire152D is disposed on the second metal thin film14. In other words, the conductive pattern is disposed on the third metal thin film17in the through hole131. The other end of the ground wire152D is in contact with the second metal thin film14. In this manner, the ground wire152D is electrically connected to the metal supporting layer11through the first metal thin film12and the second metal thin film14. In other words, the conductive pattern15is electrically connected to the metal supporting layer11through the first metal thin film12and the second metal thin film14(i.e., the third metal thin film17) in the through hole131.

(6) Cover Layer

As illustrated inFIG.1, the cover layer16covers all the wires153A,153B, and153C, and the ground wire152D. In other words, the cover layer16covers the conductive pattern15. The cover layer16is disposed on the insulating layer13in the thickness direction. The cover layer16does not cover the terminals151A,151B, and151C, the ground terminal151D, and the terminals152A,152B, and152C. The cover layer16is made of insulating resin. Examples of the resin include polyimide, maleimide, epoxy resin, polybenzoxazole, and polyester.

2. Method of Producing Wiring Circuit Board

Next, a method of producing the wiring circuit board1is described.

In the present embodiment, the wiring circuit board1is produced in an additive method.

To produce the wiring circuit board1, a first step (seeFIG.3A), a second step (seeFIG.3B), a third step (seeFIG.3C), a fourth step (seeFIG.4A), a fifth step (seeFIG.4B), and a sixth step (seeFIG.4C) are carried out in this order. That is to say, the method of producing the wiring circuit board1includes the first step (seeFIG.3A), the second step (seeFIG.3B), the third step (seeFIG.3C), the fourth step (seeFIG.4A), the fifth step (seeFIG.4B), and the sixth step (seeFIG.4C).

(1) First Step

As illustrated inFIG.3A, in the first step, the metal supporting layer11is prepared. In the present embodiment, the metal supporting layer11is metal foil pulled out of a roll of metal foil.

(2) Second Step

Next, as illustrated inFIG.3B, in the second step after the first step, the first metal thin film12is formed on the metal supporting layer11. The first metal thin film12is formed, for example, by sputtering.

After the second step, the surface of the first metal thin film12is oxidized by the contact with the air during the transfer to the next step. In this manner, the oxide coating121is formed on the surface of the first metal thin film12.

(3) Third Step

Next, as illustrated inFIG.3C, in the third step after the second step, the insulating layer13is formed on the first metal thin film12.

To form the insulating layer13, first, a solution (varnish) of photosensitive resin is applied and dried on the first metal thin film12to form a film of the photosensitive resin. Next, the photosensitive resin film is exposed and developed. In this manner, the insulating layer13is formed on the first metal thin film12. A part of the first metal thin film12is exposed through the through hole131of the insulating layer13.

(4) Fourth Step

Next, as illustrated inFIG.4A, in the fourth step after the third step, the surface of the first metal thin film12in the through hole131is etched. In this manner, a part of the oxide coating121of the first metal thin film12is removed in the through hole131. In this manner, at least in the central part of the through hole131, the thickness T1of the oxide coating121on the contact surface S2becomes smaller than the thickness T2of the oxide coating121on the contact surface S1.

Examples of the method of etching the surface of the first metal thin film12include plasma etching and wet etching.

Examples of the method of discharging in plasma etching include a capacitively coupled plasma, an inductively coupled plasma, an electron cyclotron resonance plasma, a magnetic neutral line discharge plasma, and a DC plasma. Examples of the structure of the plasma etching device include a parallel plate type, a barrel type, a remote plasma type, and an ion beam type.

Further, the plasma electrode surface may be inclined relative to the surface of the first metal thin film12. The inclination angle formed between a direction perpendicular to the plasma electrode and a direction perpendicular to the surface of the first metal thin film12is, for example, 10° or more and 65° or less. When the inclination angle falls within the above-described range, the efficiencies in etching can be improved.

Preferably, plasma etching using at least one selected from a noble gas, a reactive gas, and another gas is carried out in the fourth step to etch the surface of the first metal thin film12in the through hole131. Examples of the noble gas include helium, neon, argon, krypton, and xenon. Examples of the reactive gas include a halogen gas. Examples of the halogen gas include tetrafluoromethane (CF4), trifluoromethane (CHF3), and chlorine. Examples of another gas include oxygen, nitrogen, and hydrogen.

If the etching of the whole of the first metal thin film12in the through hole131is carried out, not only the first metal thin film12in the through hole131but also even the metal supporting layer11under the first metal thin film12may be etched. Especially, when wet etching is employed as the method of etching the first metal thin film12, the etching solution may etch the metal supporting layer11under the first metal thin film12and may further etch the first metal thin film12between the metal supporting layer11and the insulating layer13.

In light of the foregoing, etching the surface of the first metal thin film12in the through hole131allows the first metal thin film12to remain in the through hole131. Thus, the etching of the metal supporting layer11under the first metal thin film12and the further etching of the first metal thin film12between the metal supporting layer11and the insulating layer13can be suppressed.

Especially, by carrying out plasma etching to etch the surface of the first metal thin film12, the surface of the first metal thin film12in the through hole131can be etched without etching the first metal thin film12between the metal supporting layer11and the insulating layer13.

(5) Fifth Step

Next, as illustrated inFIG.4B, in the fifth step after the fourth step, the second metal thin film14is formed on the insulating layer13. The second metal thin film14is formed, for example, by sputtering. The second metal thin film14is formed on the first metal thin film12in the through hole131. In this manner, in the through hole131, the third metal thin film17formed of the first metal thin film12and the second metal thin film14is formed on the metal supporting layer11.

(6) Sixth Step

Next, as illustrated inFIG.4C, in the sixth step after the fifth step, the conductive pattern15is formed on the second metal thin film14.

In detail, a plating resist is laminated on the second protective layer14. The plating resist is exposed while the part on which the conductive pattern15is to be formed is shielded from the light.

Next, the exposed plating resist is developed. This development removes the plating resist from the shielded parts. The second protective layer14is exposed at the part on which the conductive pattern15is to be formed. The plating resist at the exposed parts, i.e., the parts on which the conductive pattern15is not to be formed remains.

Next, the conductive pattern15is formed on the exposed second metal thin film14by electrolytic plating. This forms the other end of the ground wire152D on the second metal thin film14in the through hole131. In this manner, the ground wire152D is electrically connected to the metal supporting layer11through the first metal thin film12and the second metal thin film14(i.e., the third metal thin film17).

After the completion of the electrolytic plating, the plating resist is removed. Thereafter, the second metal thin film14covered with the plating resist is removed by etching.

Thereafter, in the same manner as the formation of the insulating layer13, the cover layer16is formed on the insulating layer13and the conductive pattern15(seeFIG.1andFIG.2).

3. Operations and Effects

(1) In the wiring circuit board1, as illustrated inFIG.2, at least only a part of the oxide coating121of the first metal thin film12is removed in the through hole131, and the conductive pattern15and the metal supporting layer11are electrically connected to each other while the first metal thin film12remains.

At least in the central part of the through hole131, the thickness T1of the oxide coating121on the contact surface S2is smaller than the thickness T2of the oxide coating121on the contact surface S1.

Thus, the first metal thin film12protects the metal supporting layer11(the metal layer under the first metal thin film12), and the oxide coating121is removed. This can reduce the electrical resistance between the conductive pattern15and the metal supporting layer11.

(2) In the wiring circuit board1, as illustrated inFIG.2, a part of the first metal thin film12is removed in the through hole131, and the conductive pattern15and the metal supporting layer11can electrically be connected to each other while the first metal thin film12remains.

At least in the central part of the through hole131, the thickness T3of the first metal thin film12is smaller than the thickness T4of the first metal thin film12between the metal supporting layer11and the insulating layer13.

Thus, the first metal thin film12protects the metal supporting layer11(the metal layer under the first metal thin film12) while the first metal thin film12is thinned. This can reduce the electrical resistance between the conductive pattern15and the metal supporting layer11.

(3) In the wiring circuit board1, a part of the first metal thin film12is removed in the through hole131as illustrated inFIG.3CandFIG.4A, and the second metal thin film14is formed on the first metal thin film12while the first metal thin film12remains as illustrated inFIG.4B.

Thus, as illustrated inFIG.2, while the first metal thin film12remains, the conductive pattern15and the metal supporting layer11can electrically be connected to each other through the third metal thin film17formed of the first metal thin film12and the second metal thin film14.

Thus, the first metal thin film12protects the metal supporting layer11(the metal layer under the first metal thin film12), and the first metal thin film12is thinned. This can reduce the electrical resistance between the conductive pattern15and the metal supporting layer11.

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 illustrated inFIG.5, in the central part of the through hole131, the oxide coating121may completely be removed. In other words, in the central part of the through hole131, the thickness of the oxide coating121may be 0. In the first metal thin film12, the part other than the oxide coating121remains. When the thickness of the oxide coating121is 0, the electrical resistance between the conductive pattern15and the metal supporting layer11can further be reduced.

(2) As illustrated inFIG.6, the wiring circuit board1may further include an intermediate metal layer100. The intermediate metal layer100is disposed between the metal supporting layer11and the first metal thin film12.

The intermediate metal layer100has higher electrical conductivity than the metal supporting layer11does. Examples of the intermediate metal layer100include at least one selected from the group consisting of gold, silver, and copper. The intermediate metal layer100preferably is made of at least one selected from the group consisting of gold, silver, and copper. When the metal supporting layer11is a copper alloy, the intermediate metal layer100preferably is made of copper.

The intermediate metal layer100is formed on the metal supporting layer11, for example, by sputtering, plating, or vacuum deposition.

(3) In the variation (1) or (2), the same operations and effects as the embodiment described above can be achieved.

INDUSTRIAL APPLICABILITY

The wiring circuit board of the present invention is used for the connection with an electronic component. The method of producing the wiring circuit board of the present invention is used for the production of wiring circuit boards.

DESCRIPTION OF REFERENCE NUMERALS