Printed wiring board and method for manufacturing printed wiring board

A printed wiring board includes resin insulating layers including an outermost resin insulating layer, conductor layers laminated on the resin insulating layers, a copper layer formed in the outermost insulating layer, and metal bumps formed on the copper layer such that the bumps have upper surfaces protruding from the outermost insulating layer and that each metal bump includes Ni film, Pd film and Au film. The copper layer is reduced in diameter toward upper surface side such that the copper layer has upper and bottom surfaces and each upper surface has diameter that is smaller than diameter of each bottom surface, the outermost insulating layer has cylindrical sidewalls formed such that at least part of the copper layer is not in contact with the sidewalls, and the bumps are formed such that the Ni film is filling spaces between the copper layer and the sidewalls of the outermost insulating layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is based upon and claims the benefit of priority to Japanese Patent Application No. 2020-025489, filed Feb. 18, 2020, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a printed wiring board having metal bumps.

Description of Background Art

Japanese Patent Application Laid-Open Publication No. 2015-115335 describes a method for manufacturing a printed wiring board in which a conductor layer and a resin insulating layer are laminated on a support plate and which does not have a core substrate that separates the support plate. In Japanese Patent Application Laid-Open Publication No. 2015-115335, it is thought that pads are formed of a single metal on the support plate. The entire contents of this publication are incorporated herein by reference.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a printed wiring board includes resin insulating layers including an outermost resin insulating layer, conductor layers laminated on the resin insulating layers, respectively, a copper layer formed in the outermost resin insulating layer of the resin insulating layers, and metal bumps formed on the copper layer such that the metal bumps have upper surfaces protruding from the outermost resin insulating layer and that each of the metal bumps includes a Ni film, a Pd film and an Au film. The copper layer is reduced in diameter toward an upper surface side thereof such that the copper layer has upper surfaces and bottom surfaces and that each of the upper surfaces has a diameter that is smaller than a diameter of each of the bottom surfaces, the outermost resin insulating layer has cylindrical sidewalls formed such that at least part of the copper layer is not in contact with the cylindrical sidewalls, and the metal bumps are formed such that the Ni film is filling spaces between the copper layer and the cylindrical sidewalls of the outermost resin insulating layer.

According to another aspect of the present invention, a method for manufacturing a printed wiring board includes preparing a support plate having a copper foil, forming a metal layer including a copper film, a Ni film and a copper layer on the copper foil of the support plate, forming a build-up layer including resin insulating layers and conductor layer on the copper foil, separating a structure including the copper foil, the metal layer of the copper film, Ni film and copper layer, and the build-up layer from the support plate, etching the copper foil of the support plate and the copper film of the metal layer such that the copper foil of the support plate and the copper film of the metal layer are removed from the build-up layer, applying plasma etching to partially remove the outermost resin insulating layer such that the Ni film and an upper surface side of the copper layer are exposed, applying selective etching to remove the Ni film of the metal layer and soft etching to remove a portion of the copper layer such that cylindrical sidewalls are formed in the outermost resin insulating layer, and forming metal bumps including a Ni film, a Pd film and an Au film on the copper layer such that the Ni film fills spaces between the copper layer and the cylindrical sidewalls of the outermost resin insulating layer.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1Aillustrates a printed wiring board10according to an embodiment of the present invention.

The printed wiring board10has a first surface (F) and a second surface (S) on an opposite side with respect to the first surface, and includes three resin insulating layers including an outermost resin insulating layer (50C), a second resin insulating layer (50B) and a first resin insulating layer (50A). The outermost resin insulating layer (50C), the second resin insulating layer (50B) and the first resin insulating layer (50A) are formed by buildup-laminating resin films. A first conductor layer (58A) forming pads is formed on the second surface (S) side of the first resin insulating layer (50A). A solder resist layer78having openings79is provided on the first resin insulating layer (50A) and the first conductor layer (58A). A second conductor layer (58B) is formed on the second surface (S) side of the second resin insulating layer (50B). The first conductor layer (58A) and the second conductor layer (58B) are connected to each other via via conductors (60A) penetrating the first resin insulating layer (50A). A third conductor layer (58C) is formed on the second surface (S) side of the outermost resin insulating layer (50C). The second conductor layer (58B) and the third conductor layer (58C) are connected to each other via via conductors (60B) penetrating the second resin insulating layer (50B). An outermost conductor layer34is formed on the first surface (F) side of the outermost resin insulating layer (50C). The third conductor layer (58C) and the outermost conductor layer34are connected to each other via via conductors (60C) penetrating the outermost resin insulating layer (50C).

FIG. 1Cis an enlarged cross-sectional view of one of metal bumps40.

In the uppermost conductor layer34, a portion (upper half) of a side surface (34S) and an upper surface (34T) protrude from the outermost resin insulating layer (50C), and a portion (lower half) of the side surface (34S) and a bottom surface (34B) remain inside the outermost resin insulating layer (50C). The metal bumps40are each formed by providing a Ni film42, a Pd film44, and an Au film46on the uppermost conductor layer (copper layer)34.

FIG. 4Cis an enlarged cross-sectional view of the uppermost conductor layer (copper layer)34before the formation of the Ni film, the Pd film and the Au film.

Around the uppermost conductor layer (copper layer)34, a cylindrical sidewall (51C) of the outermost resin insulating layer (50C) is formed. The sidewall (51C) is formed by being in contact with a sidewall of the copper layer before an etching process. The copper layer34is reduced in diameter toward the upper surface (34T) side such that a diameter (d2) of the upper surface (34T) is smaller than a diameter (d1) of the bottom surface (34B). A portion of or the entire side surface (34S) of the copper layer34is not in contact with the cylindrical sidewall (51C) of the outermost resin insulating layer (50C) around the side surface.

As illustrated inFIG. 1C, the Ni film42fills between the side surface (34S) of the copper layer34and the cylindrical sidewall (51C) of the outermost resin insulating layer (50C). Since the copper layer34tightly adheres to the outermost resin insulating layer (50C) via the Ni film42, connection reliability of the metal bumps40can be increased. The Ni film42extends laterally to an upper surface (50CT) of the outermost resin insulating layer (50C) on an outer side of the sidewall (51C). An outer diameter (maximum diameter) (d3) of the Ni film42is larger than the diameter (d1) of the bottom surface (34B) of the copper layer34. The bottom surface (34B) of the copper layer34and the side surface (34S) that is in contact with the outermost resin insulating layer (50C) are larger in roughness than the upper surface (34T) and the side surface (34S) that is not in contact with the outermost resin insulating layer (50C). The diameter (d1) of the bottom surface (34B) of the copper layer34forming the metal bump is 50 μm or less. A pitch of the metal bumps40is 90 μm or less, and a spacing between the metal bumps is 50 μm or less.

FIG. 1Billustrates an application example in which an electronic component90is mounted on the printed wiring board10of the embodiment.

The electronic component90is mounted on the printed wiring board10by connecting pads92of the electronic component90via a metal layer73on the metal bumps40.

The resin insulating layers (50A,50B,50C) are each formed of a resin that does not contain a core material but contains about 50 w % of an inorganic filler. The solder resist layer78is formed of a resin that does not contain inorganic fibers but contains about 20 w % of an inorganic filler.

Manufacturing Method

FIGS. 2A-4Cillustrate a method for manufacturing a printed wiring board according to an embodiment of the present invention.

A support plate (20z) in which a copper foil22is laminated on a support substrate20is prepared (FIG. 2A). A plating resist32is formed on the copper foil22of the support plate (20z) (FIG. 2B). On the copper foil22exposed from the plating resist32, a relatively thin copper film38, a Ni film36, and a relatively thick copper layer34are formed by electrolytic plating (FIG. 2C). The plating resist is peeled off, and side surfaces of the copper film38, the Ni film36and the copper layer34are exposed (FIG. 2D). The outermost resin insulating layer (50C) is laminated on the copper foil22and the copper layer (outermost conductor layer)34(FIG. 2E). Openings (51D) reaching the outermost conductor layer34are formed in the outermost resin insulating layer (50C) (FIG. 3A). By electroless plating and electroplating, the via conductors (60C) are formed in the openings (51D), and the third conductor layer (58C) is formed on the outermost resin insulating layer (50C) (FIG. 3B). The processes ofFIGS. 2E-3Bare repeated, and the second resin insulating layer (50B), the via conductors (60B) and the conductor layer (58B) are formed, the first resin insulating layer (50A), the via conductors (60A) and the first conductor layer (58A) are formed, the solder resist layer78is formed on the first resin insulating layer (50A) and the first conductor layer (58A), and an intermediate110is completed (FIG. 3C).

The support substrate20is separated from the intermediate110, and the copper foil22and the copper film38are removed (FIG. 3D). When the copper foil is removed by etching, the outermost copper film38is also etched. Therefore, the Ni film36is recessed relative to the upper surface (50CT) of the outermost resin insulating layer (50C). By plasma etching of a CF4+O2 plasma gas, the surface of the outermost resin insulating layer (50C) is removed by 3-8 μm, and the Ni film36and the upper surface (34T) side of the copper layer34are exposed from the outermost resin insulating layer (50C) (FIG.4A). The inorganic filler exposed from the outermost resin insulating layer (50C) by the plasma etching is removed by wet blasting. As a result, when an underfill material is filled on the outermost resin insulating layer (50C), adhesion with the underfill material is increased.

The Ni film36is removed by etching. A portion of the copper layer is also etched when the Ni film is removed. Further, the surface of the copper layer is etched by soft etching. As illustrated inFIG. 4C, the side surface (34S) of the copper layer34is inclined (FIG. 4B). Around the uppermost conductor layer (copper layer)34, the cylindrical sidewall (51C) of the outermost resin insulating layer (50C) is formed. The sidewall (51C) is formed by being in contact with the sidewall of the copper layer before the etching process. The copper layer34is reduced in diameter toward the upper surface (34T) side such that the diameter (d2) of the upper surface (34T) is smaller than the diameter (d1) of the bottom surface (34B). The unetched bottom surface (34B) of the copper layer34and the unetched side surface (34S) that is in contact with the outermost resin insulating layer (50C) are larger in roughness than the etched upper surface (34T) and the etched side surface (34S) that is not in contact with the outermost resin insulating layer (50C). A portion of or the entire side surface (34S) of the copper layer34is not in contact with the cylindrical sidewall (51C) of the outermost resin insulating layer (50C) around the side surface.

As illustrated inFIGS. 1A and 1C, the Ni film42, the Pd film44and the Au film46are provided on the copper layer34to form the metal bumps40, and the printed wiring board10is completed. The Ni film42fills between the side surface (34S) of the copper layer34and the cylindrical sidewall (51C) of the outermost resin insulating layer (50C). Since the copper layer34tightly adheres to the outermost resin insulating layer (50C) via the Ni film42, connection reliability of the metal bumps40can be increased.

The electronic component90is mounted on the printed wiring board10by connecting the pads92of the electronic component90via the metal layer73on the metal bumps40(FIG. 1B).

According to the method for manufacturing a printed wiring board according to the embodiment, the metal bumps40are formed to each include the copper film38, the Ni film36and the copper layer34formed on the copper foil22. Then, by completely removing, by etching, the copper film38and the Ni film36and keeping the copper layer34, the metal bumps are formed. Since the Ni film is completely removed by etching and the copper layer34is kept, the copper layer34does not vary in height, and the metal bumps40can have uniform heights even when being formed with small diameters. The connection reliability of the metal bumps40can be increased.

In Japanese Patent Application Laid-Open Publication No. 2015-115335, the pads are formed of a single metal, and when metal bumps are formed by exposing the pads, it is thought that it is difficult for the metal bumps to have uniform heights.

A printed wiring board according to an embodiment of the present invention is formed by alternately laminating conductor layers and resin insulating layers. In the printed wiring board, upper surfaces of metal bumps of an outermost resin insulating layer protrude from outermost resin insulating layer; the metal bumps are each formed by forming a Ni film, a Pd film and an Au film on a copper layer; the copper layer is reduced in diameter toward an upper surface side thereof such that a diameter of an upper surface thereof is smaller than a diameter of a bottom surface thereof; a portion or entire side surface of the copper layer is not in contact with a cylindrical sidewall of the outermost resin insulating layer around the side surface; and the Ni film fills between the side surface of the copper layer and the cylindrical sidewall of the outermost resin insulating layer.

A method for manufacturing a printed wiring board according to another embodiment of the present invention has metal bumps and includes alternately laminating conductor layers and resin insulating layers. The method includes: preparing a support plate having a copper foil; forming a copper film, a Ni film and a copper layer on the copper foil; forming a build-up layer including a resin insulating layer and a conductor layer on the copper foil; separating the copper foil and the build-up layer from the support plate; removing the copper foil and the copper film by etching; exposing the Ni film and an upper surface side of the copper layer by partially removing the outermost resin insulating layer by plasma etching; exposing a cylindrical sidewall of the outermost resin insulating layer by removing the Ni film by selective etching and then removing a portion of the copper layer by soft etching, the cylindrical sidewall being formed by being in contact with a side surface of the copper layer before an etching process; and forming the metal bumps by forming a Ni film, a Pd film and an Au film on the copper layer. The Ni film fills between the side surface of the copper layer and the cylindrical sidewall of the outermost resin insulating layer.

In a printed wiring board according to an embodiment of the present invention, the Ni film forming the metal bumps fills between the side surface of the copper layer and the cylindrical sidewall of the outermost resin insulating layer. Since the copper layer tightly adheres to the outermost resin insulating layer via the Ni film, connection reliability of the metal bumps can be increased.

According to a method for manufacturing a printed wiring board according to an embodiment of the present invention, the metal bumps are formed to each include the copper film, the Ni film and the copper layer formed on copper foil. Then, by completely removing, by etching, the copper film and the Ni film and keeping the copper layer, the metal bumps are formed. Since the Ni film is completely removed by etching and the copper layer is kept, the copper layer does not vary in height, and the metal bumps can have uniform heights even when being formed with small diameters. The connection reliability of the metal bumps can be increased.