Patent Publication Number: US-2021195748-A1

Title: Inductor built-in substrate

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is based upon and claims the benefit of priority to Japanese Patent Application No. 2019-228099, filed Dec. 18, 2019, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to an inductor built-in substrate that has an inductor built therein. 
     Description of Background Art 
     Japanese Patent Application Laid-Open Publication No. 2016-197624 describes a method for manufacturing an inductor component built in a wiring substrate. The entire contents of this publication are incorporated herein by reference. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, an inductor built-in substrate includes a core substrate having openings and first through holes formed therein, a magnetic resin filling the openings and having second through holes formed therein, first through-hole conductors formed in the first through holes respectively such that each of the first through-hole conductors includes an electroless plating film and an electrolytic plating film, and second through-hole conductors formed in the second through holes respectively such that each of the second through-hole conductors includes an electroless plating film and an electrolytic plating film. The first through-hole conductors and the second through-hole conductors are formed such that a thickness of the electroless plating film in the first through-hole conductors is larger than a thickness of the electroless plating film in the second through-hole conductors. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
         FIG. 1A  is a cross-sectional view of an inductor built-in substrate according to an embodiment of the present invention; 
         FIG. 1B  is an enlarged view of a core substrate of the inductor built-in substrate; 
         FIGS. 2A-2E  are process diagrams illustrating a method for manufacturing an inductor built-in substrate according to an embodiment of the present invention; 
         FIGS. 3A-3D  are process diagrams illustrating the method for manufacturing an inductor built-in substrate according to the embodiment; 
         FIGS. 4A-4C  are process diagrams illustrating the method for manufacturing an inductor built-in substrate according to the embodiment; and 
         FIG. 5  is a plan view of a core substrate of an inductor built-in substrate according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Embodiments will now be described with reference to the accompanying drawings, wherein like reference numerals designate corresponding or identical elements throughout the various drawings. 
       FIG. 1A  illustrates a cross-sectional view of an inductor built-in substrate  10  of an embodiment that has an inductor built therein. The inductor built-in substrate  10  has a core substrate  30  that is formed to include: an insulating base material  20  that has a first surface (F) and a second surface (S) on an opposite side with respect to the first surface (F); a first conductor layer (conductor circuit) ( 58 F) on the first surface (F) of the insulating base material; a second conductor layer ( 58 S) on the second surface (S) of the insulating base material; and through-hole conductors  36  that connect the first conductor layer ( 58 F) and the second conductor layer ( 58 S) to each other. The core substrate  30  has a first surface (F) and a second surface (S) on an opposite side with respect to the first surface (F). The first surface (F) of the core substrate  30  and the first surface (F) of the insulating base material  20  are the same surface, and the second surface (S) of the core substrate  30  and the second surface (S) of the insulating base material  20  are the same surface. The insulating base material  20  is formed of a resin such as an epoxy resin and a core material  14  such as a glass cloth for reinforcement. The insulating base material  20  may further contain inorganic particles such as silica particles. 
     The inductor built-in substrate  10  further has an upper side build-up layer ( 450 F) formed on the first surface (F) of the core substrate  30 . The upper side build-up layer ( 450 F) includes: an insulating layer ( 450 A) formed on the first surface (F) of the core substrate  30 ; a conductor layer ( 458 A) formed on the insulating layer ( 450 A); and via conductors ( 460 A) penetrating the insulating layer ( 450 A) and connecting the first conductor layer ( 58 F) and the conductor layer ( 458 A) to each other. The upper side build-up layer ( 450 F) further includes: an insulating layer ( 450 C) formed on the insulating layer ( 450 A) and the conductor layer ( 458 A); a conductor layer ( 458 C) formed on the insulating layer ( 450 C); and via conductors ( 460 C) penetrating the insulating layer ( 450 C) and connecting the conductor layer ( 458 A) and the via conductors ( 460 A) to the conductor layer ( 458 C). 
     The inductor built-in substrate  10  further has a lower side build-up layer ( 450 S) formed on the second surface (S) of the core substrate  30 . The lower side build-up layer ( 450 S) includes: an insulating layer ( 450 B) formed on the second surface (S) of the core substrate  30 ; a conductor layer ( 458 B) formed on the insulating layer ( 450 B); and via conductors ( 460 B) penetrating the insulating layer ( 450 B) and connecting the second conductor layer ( 58 S) and the conductor layer ( 458 B) to each other. The lower side build-up layer ( 450 S) further includes: an insulating layer ( 450 D) formed on the insulating layer ( 450 B) and the conductor layer ( 458 B); a conductor layer ( 458 D) formed on the insulating layer ( 450 D); and via conductors ( 460 D) penetrating the insulating layer ( 450 D) and connecting the conductor layer ( 458 B) and the via conductors ( 460 B) to the conductor layer ( 458 D). 
     The inductor built-in substrate of the embodiment further includes a solder resist layer ( 470 F) having openings ( 471 F) formed on the upper side build-up layer ( 450 F) and a solder resist layer ( 470 S) having openings ( 471 S) formed on the lower side build-up layer ( 450 S). 
     Upper surfaces of the conductor layers ( 458 C,  458 D) or the via conductors ( 460 C,  460 D) exposed from the openings ( 471 F,  471 S) of the solder resist layers ( 470 F,  470 S) function as pads. A protective film  472  formed of Ni/Au, Ni/Pd/Au, Pd/Au, or OSP is formed on each of the pads. Solder bumps ( 476 F,  476 S) are respectively formed on the protective films. An IC chip (not illustrated in the drawings) is mounted on the inductor built-in substrate  10  via the solder bumps ( 476 F) formed on the upper side build-up layer ( 450 F). The inductor built-in substrate  10  is mounted on a motherboard (not illustrated in the drawings) via the solder bumps ( 476 S) that are formed on the lower side build-up layer ( 450 S). 
       FIG. 1B  illustrates an enlarged view of a portion of the core substrate  30  in  FIG. 1A . In the core substrate  30 , the through-hole conductors  36  connecting the first conductor layer ( 58 F) and the second conductor layer ( 58 S) to each other include first through-hole conductors ( 36 A) that are respectively formed in first through holes ( 20   a ) penetrating the core substrate  30  and second through-hole conductors ( 36 B) that are respectively formed in second through holes ( 18   b ) of a magnetic resin  18  filled in openings ( 20   b ) of the core substrate  30 . A diameter (da) of each of the first through holes ( 20   a ) and a diameter (db) of each of the second through holes ( 18   b ) are substantially equal to each other. A resin filler  16  is filled inside the first through-hole conductors ( 36 A) and the second through-hole conductors ( 36 B), and through-hole lands ( 58 FR) are formed of cover plating. The through-hole lands ( 58 FR) include first through-hole lands ( 58 FRA) respectively formed on the first through-hole conductors ( 36 A) and second through-hole lands ( 58 FRB) respectively formed on the second through-hole conductors ( 36 B). 
     The magnetic resin  18  contains iron oxide filler (magnetic particles) and a resin such as an epoxy resin. Examples of the magnetic particles include iron oxide fillers such as iron (III) oxide particles. A content of the iron oxide filler in the magnetic resin is preferably 60-90% by weight. From a point of view that the content of the iron oxide filler can be increased and magnetic permeability and heat conductivity can be increased, particle sizes of the iron oxide filler are desirably non-uniform. 
     As illustrated in  FIG. 1B , the first through-hole conductors ( 36 A) that are respectively formed in the first through holes ( 20   a ) penetrating the core substrate  30  are respectively in contact with the first through holes ( 20   a ). The first through-hole conductors ( 36 A) are formed of a second electroless plating film  32  on the first through holes ( 20   a ), and a second electrolytic plating film  34  on the second electroless plating film  32 . The second through-hole conductors ( 36 B) that are respectively formed in the second through holes ( 18   b ) penetrating the magnetic resin  18  are respectively in contact with the second through holes ( 18   b ). The second through-hole conductors ( 36 B) are formed of a second electroless plating film  32  on the second through holes ( 18   b ), and a second electrolytic plating film  34  on the second electroless plating film  32 . 
     In the inductor built-in substrate  10  of the embodiment, a thickness (ta 1 ) of the second electroless plating film  32  of the first through-hole conductors ( 36 A) is larger than a thickness (tb 1 ) of the second electroless plating film  32  of the second through-hole conductors ( 36 B). By increasing the thickness of the second electroless plating film  32  the first through-hole conductors ( 36 A) which are mainly used for signal transmission, a thickness (ta 2 ) of the second electrolytic plating film  34  on the second electroless plating film  32  of the first through-hole conductors ( 36 A) can also be larger than a thickness (tb 2 ) of the second electrolytic plating film  34  of the second through-hole conductors ( 36 B). By increasing the thickness (ta) of the first through-hole conductors ( 36 A) formed of the second electroless plating film  32  and the second electrolytic plating film  34 , variation in thickness of the first through-hole conductors ( 36 A) can be reduced, signal transmission characteristics of the first through-hole conductors ( 36 A) can be uniformized, and deterioration in signal transmission characteristics can be suppressed. For example, the thickness (ta 1 ) of the second electroless plating film  32  of the first through-hole conductors ( 36 A) is 0.35 micron or more and 0.55 micron or less, and the thickness (tb 1 ) of the second electroless plating film  32  of the second through-hole conductors ( 36 B) is 0.2 micron or more and 0.4 micron or less. 
     A thickness (ta) of the second electroless plating film  32  and the second electrolytic plating film  34  that form the first through-hole conductors ( 36 A) is larger than a thickness (tb) of the second electroless plating film  32  and the second electrolytic plating film  34  that form the second through-hole conductors ( 36 B). When the thickness (ta) of the first through-hole conductors ( 36 A) that are respectively formed in the first through holes ( 20   a ) of the insulating base material  20  having a low heat conductivity is larger than the thickness (tb) of the second through-hole conductors ( 36 B) that are respectively formed in the second through holes ( 18   b ) of the magnetic resin  18  having a high heat conductivity, a balance in heat dissipation between the first through-hole conductors ( 36 A) and the second through-hole conductors ( 36 B) is adjusted. 
     The first through-hole lands ( 58 FRA) and the first conductor layer ( 58 F) on the insulating base material  20  are each formed of the copper foil  22  as a lowermost layer, the first electroless plating film ( 24   m ) on the copper foil  22 , the first electrolytic plating film ( 24   d ) on the first electroless plating film ( 24   m ), the second electroless plating film  32  on the first electrolytic plating film ( 24   d ), the second electrolytic plating film  34  on the second electroless plating film  32 , the third electroless plating film  35  on the second electrolytic plating film  34 , and the third electrolytic plating film  37  on the third electroless plating film  35 . The second through-hole lands ( 58 FRB) and the first conductor layer ( 58 F) on the magnetic resin  18  are each formed of the first electroless plating film ( 24   m ) as a lowermost layer, the first electrolytic plating film ( 24   d ) on the first electroless plating film ( 24   m ), the second electroless plating film  32  on the first electrolytic plating film ( 24   d ), the second electrolytic plating film  34  on the second electroless plating film  32 , the third electroless plating film  35  on the second electrolytic plating film  34 , and the third electrolytic plating film  37  on the third electroless plating film  35 . The first electroless plating film ( 24   m ) and the first electrolytic plating film ( 24   d ) form a shield layer  24 . 
     In the core substrate  30  of the embodiment, the first conductor layer ( 58 F) (connection pattern ( 58 FL)) and the second conductor layer ( 58 S) (connection pattern ( 58 SL)) which are connected to each other via the second through-hole conductors ( 36 B) formed in the magnetic resin  18  illustrated in  FIG. 1A  are formed in a helical shape (a spiral shape along an axis in a direction parallel to the front and back surfaces of the core substrate), and together with the second through-hole conductors ( 36 B) form an inductor  59 . 
     In the inductor built-in substrate  10  of the embodiment, the first conductor layer ( 58 F) and the second conductor layer ( 58 S) are formed on the surfaces of the core substrate  30 , and the second through-hole conductors ( 36 B) connecting the first conductor layer ( 58 F) and the second conductor layer ( 58 S) to each other are directly formed in the second through holes ( 18   b ) penetrating the magnetic resin  18 . Therefore, a ratio of a magnetic material in the inductor built-in substrate  10  is increased and an inductance can be increased. 
     Method for Manufacturing Inductor Built-In Substrate 
     A method for manufacturing an inductor built-in substrate according an embodiment of the present invention is illustrated in  FIGS. 2A-4C . 
     A substrate ( 20   z ) is prepared which is formed of a copper-clad laminated plate which is formed by laminating a copper foil  22  on both sides of the insulating base material  20  ( FIG. 2A ). The openings ( 20   b ) for filling the magnetic resin therein are formed in the insulating base material  20  ( FIG. 2B ). A resin paste containing an iron oxide filler (magnetic particles) in an amount of 90% by weight and an epoxy resin is vacuum-printed in the openings ( 20   b ). The resin paste is temporarily cured (semi-cured) at a temperature at which a viscosity of the resin paste is 2 or less times that at a normal temperature, and a temporarily cured magnetic resin ( 18 β) is formed ( FIG. 2C ). 
     On a surface of the insulating base material  20  and a surface of the temporarily cured magnetic resin ( 18 β) exposed from the openings ( 20   b ), a first electroless plating film ( 24   m ) is formed by an electroless plating treatment, and a first electrolytic plating film ( 24   d ) is formed by an electrolytic plating treatment ( FIG. 2D ). The first electroless plating film ( 24   m ) and the first electrolytic plating film ( 24   d ) form a shield layer  24 . 
     The first through holes ( 20   a ) are formed in the insulating base material  20  by mechanical drilling, laser processing, or the like ( FIG. 2E ). Thereafter, the first through holes ( 20   a ) are subjected to a desmear treatment using a chemical solution. During the desmear treatment, the temporarily cured magnetic resin ( 18 β) covered by the shield layer  24  formed by the first electroless plating film ( 24   m ) and the first electrolytic plating film ( 24   d ) is not affected by the chemical solution. 
     The second through holes ( 18   b ) are formed in the temporarily cured magnetic resin ( 18 β) by mechanical drilling, laser processing, or the like. In this embodiment, since the iron oxide filler is contained in an amount of 90% by weight, through hole formation after fully curing is not easy. However, since the through holes are formed before fully curing, the through holes can be easily formed. The magnetic material layer in a temporarily cured state is heated to cause the resin contained therein to crosslink, and thereby, the magnetic material layer is fully cured to form the magnetic resin  18  ( FIG. 3A ). Here, the heating is performed at 150° C.-190° C. for 1 hour. By high pressure washing, processing smear occurred at the time of the through hole formation is removed. Desmearing may be performed using an alkaline agent. However, there is a risk that an alkaline agent may cause the iron oxide filler contained in the magnetic resin  18  to fall off during a process in which the resin is swelled and peeled off. Therefore, here, high-pressure water washing is performed. 
     The second electroless plating film  32  is formed by an electroless plating treatment on the shield layer  24  on the surfaces of the insulating base material  20  and the magnetic resin  18 , and on side walls of the first through holes ( 20   a ) and the second through holes ( 18   b ) ( FIG. 3B ). By adjusting electroless plating conditions so that elution of the iron oxide filler occurs first on the surfaces of the second through holes ( 18   b ) and copper deposition on the surfaces of the second through holes ( 18   b ) is delayed, the thickness (ta 1 ) of the second electroless plating film  32  that is in the first through holes ( 20   a ) of the resin insulating base material and forms the first through-hole conductors is made larger than the thickness (tb 1 ) of the second electroless plating film  32  that is in the second through holes ( 18   b ) of the magnetic resin and forms the second through-hole conductors. 
     The second electrolytic plating film  34  is formed on the second electroless plating film  32  by an electrolytic plating treatment. By the second electroless plating film  32  and the second electrolytic plating film  34 , the first through-hole conductors ( 36 A) are formed in the first through holes ( 20   a ) and the second through-hole conductors ( 36 B) are formed in the second through holes ( 18   b ) ( FIG. 3C ). By increasing the thickness (ta 1 ) of the second electroless plating film  32  of the first through-hole conductors ( 36 A), the deposition of the second electrolytic plating film  34  on the second electroless plating film  32  of the first through-hole conductors ( 36 A) is promoted, and the thickness (ta 2 ) of the second electroless plating film  34  of the first through-hole conductors ( 36 A) is larger than the thickness (tb 2 ) of the second electrolytic plating film  34  of the second through-hole conductors ( 36 B). 
     The resin filler  16  is filled inside the first through-hole conductors ( 36 A) formed in the first through holes ( 20   a ) and inside the second through-hole conductors ( 36 B) formed in the second through holes ( 18   b ), and the surfaces of the insulating base material  20  are polished ( FIG. 3D ). A third electroless plating film  35  is formed by electroless plating on the second electrolytic plating film  34  and on exposed surfaces of the resin filler  16 , and a third electrolytic plating film  37  is formed on the third electroless plating film  35  ( FIG. 4A ). An etching resist  54  of a predetermined pattern is formed on the third electrolytic plating film  37  ( FIG. 4B ). 
     The third electrolytic plating film  37 , the third electroless plating film  35 , the second electrolytic plating film  34 , the second electroless plating film  32 , the first electrolytic plating film ( 24   d ), the first electroless plating film ( 24   m ), and the copper foil  22  exposed from the etching resist  54  are removed, and thereafter, the etching resist is removed, and the first conductor layer ( 58 F), the second conductor layer ( 58 S) are formed and the core substrate  30  is completed ( FIG. 4C ). 
     The upper side build-up layer ( 450 F), the lower side build-up layer ( 450 S), the solder resist layers ( 470 F,  470 S), and the solder bumps ( 476 F,  476 S) may be formed on the core substrate  30  using known manufacturing methods ( FIG. 1A ). 
       FIG. 5  is a schematic plan view of the core substrate of the inductor built-in substrate according to the embodiment. 
     The first through-hole conductors ( 36 A) are provided in the insulating base material  20 , and the second through-hole conductors ( 36 B) are provided in the magnetic resin  18  filled in the openings ( 20   b ) formed in the insulating base material  20 . The first through-hole conductors ( 36 A) are mainly used for signal transmission, and the second through-hole conductors ( 36 B) are used for power supply and grounding. The first through-hole conductors ( 36 A) are provided in a number larger than that of the second through-hole conductors ( 36 B). A pitch (P 1 ) of the first through-hole conductors ( 36 A) is smaller than a pitch (P 2 ) of the second through-hole conductors ( 36 B). For example, in the inductor built-in substrate of the embodiment, the pitch (P 1 ) of the first through-hole conductors ( 36 A) is 300-450 microns, and the pitch (P 2 ) of the second through-hole conductors ( 36 B) is 400-600 microns. 
     In Japanese Patent Application Laid-Open Publication No. 2016-197624, a magnetic material is accommodated inside a resin layer, through-hole conductors are provided in the resin layer, and the through-hole conductors are prevented from being in contact with the magnetic material. 
     In Japanese Patent Application Laid-Open Publication No. 2016-197624, since the through-hole conductors are formed in the resin layer, it is thought that a ratio of the magnetic material with respect to a size of the inductor component is low and it is difficult to increase an inductance. 
     An inductor built-in substrate according to an embodiment of the present invention is small in size, has a large inductance, and has good signal transmission characteristics. 
     An inductor built-in substrate according to an embodiment of the present invention includes: a core substrate in which openings and first through holes are formed; a magnetic resin that is filled in the openings and has second through holes; first through-hole conductors that are formed of an electroless plating film and an electrolytic plating film formed in the first through holes; and second through-hole conductors that are formed of an electroless plating film and an electrolytic plating film formed in the second through holes. A thickness of the electroless plating film of the first through-hole conductors is larger than a thickness of the electroless plating film of the second through-hole conductors. 
     In the inductor built-in substrate according to an embodiment of the present invention, the second through-hole conductors that are formed of the electroless plating film and the electrolytic plating film are directly formed in the second through holes of the magnetic resin. Therefore, a volume of the magnetic resin of an inductor component can be increased, and an inductance can be increased. By increasing the thickness of the electroless plating film of the first through-hole conductors which are mainly used for signal transmission, the thickness of the electrolytic plating film on the electroless plating film can also be increased. By increasing the thickness of the first through-hole conductors that are formed of the electroless plating film and the electrolytic plating film, variation in thickness of the first through-hole conductors can be reduced, signal transmission characteristics of the first through-hole conductors can be uniformized, and deterioration in signal transmission characteristics can be suppressed. 
     Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.