JP2014192177A - Wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wiring board capable of improving reliability by constructing the board to be suitable for connection with components.SOLUTION: This wiring board 10 comprises a pad 61 and a solder resist 81 having formed therein an opening 82 for causing the pad 61 to be exposed. A protruding conductor 71 is secured to part of a surface 62 of the pad 61. The protruding conductor 71 is connected to the surface 62 of the pad 61, and provided with a shank 72 whose outside diameter A3 is set to smaller than an outside diameter A1 of the pad 61 and a head 73 connected to the shank 72 and whose outside diameter A6 is set to larger than the outside diameter A3 of the shank 72. The head 73 is disposed in a state apart from a surface 83 of the solder resist 81.

Description

  The present invention relates to a wiring board including a pad and a solder resist in which an opening for exposing the pad is formed.

  Conventionally, a wiring substrate (so-called semiconductor package) on which components such as an IC chip are mounted is well known. Here, as a structure for achieving an electrical connection with the IC chip, a plurality of pads (so-called “so-called pads”) arranged on a plurality of terminals arranged on the bottom surface of the IC chip or on the main surface of the wiring board. There has been proposed a solder bump formed on a C4 pad (Controlled Collapsed Chip Connection pad).

  The solder bump is formed by, for example, a printing method. The printing method is a method of forming solder bumps by printing a solder paste on a plurality of pads formed on a main surface of a substrate using a metal mask and then reflowing. Further, in this type of wiring board, a solder resist is formed so as to cover the main surface of the board, and the solder resist is provided with a plurality of openings for exposing the pads.

  By the way, in order to improve the bondability between the wiring board and the IC chip, it is preferable that the individual solder bumps formed on the pads have the same height. However, since the solder bump is formed by changing the solder paste, which is heated and melted, into a spherical shape with the surface tension, the height of the solder bump is determined by the volume of the solder paste. That is, when the volume of the solder paste is small, it is difficult to form a high solder bump. In addition, the height of individual solder bumps may vary as the printed solder paste volume varies. Therefore, even if solder bumps are formed, connection failure may occur between individual pads and the IC chip. Therefore, since the manufactured wiring board becomes defective, the reliability of the wiring board may be reduced.

  Therefore, a technique has been proposed in which a copper post, which is a protruding conductor, is fixed to a part of the surface of the pad, and the surface of the pad and the surface of the copper post are covered with solder bumps (see, for example, Patent Document 1). In this way, even if solder is printed on the pad to form a solder bump, the solder bump can be formed high. As a result, the heights of the individual solder bumps can be made uniform, so that connection failure between the individual pads and the IC chip can be prevented. That is, since the structure is suitable for connection with the IC chip, the reliability of the wiring board can be improved.

JP2012-129368A (FIG. 1 etc.)

  However, the pad is formed to be small corresponding to the refinement of the C4 pad. Along with this, the copper post also tends to be reduced in diameter. However, in this case, since the contact area between the solder bump and the copper post (and pad) is reduced, the adhesion between the solder bump and the copper post (and pad) is reduced, so that the contact between the IC chip and the solder bump is reduced. Connection failure may occur.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a wiring board capable of improving reliability by adopting a structure suitable for connection with a component.

  Means for solving the above problems (means 1) include a plurality of pads arranged on the main surface of the substrate and a plurality of openings that cover the main surface of the substrate and expose the plurality of pads. A soldering resist, wherein a protruding conductor is fixed to a part of the surface of the pad, and the protruding conductor is connected to the surface of the pad and has an outer diameter outside the pad. A shaft portion set smaller than the diameter, and a head connected to the shaft portion and having an outer diameter set larger than the outer diameter of the shaft portion, and the head is made of the solder resist. There is a wiring board characterized in that it is arranged in a state of being separated from the surface.

  Therefore, according to the wiring board of the means 1, the protruding conductor has a head set larger than the outer diameter of the shaft portion in addition to the shaft portion. Therefore, since the head is formed large even when the shaft portion is formed small in association with the so-called C4 pad refinement, the projecting conductor, A contact area with a solder bump used for connection with a component can be secured. Furthermore, since the head is arranged in a state of being separated from the surface of the solder resist, by inserting solder between the head and the surface of the solder resist, a part of the solder bump is placed on the bottom surface of the head (solder resist Or the outer surface of the shaft portion. As a result, the contact area between the protruding conductor and the solder bump is further increased, and the adhesion between the protruding conductor and the solder bump is improved, so that connection failure between individual pads and components can be prevented. In addition, even if thermal stress acts on the protruding conductor during cooling of the solder after connecting the components, the stress is relieved by the bending of the shaft portion, thus preventing damage to the connection portion between the pad and the component. be able to. From the above, since the protruding conductor has a structure suitable for connection with a component, the reliability of the wiring board can be improved.

  The type of the wiring board is not particularly limited and is arbitrary. For example, a resin board or the like is used. Examples of the resin substrate include substrates made of EP resin (epoxy resin), PI resin (polyimide resin), BT resin (bismaleimide-triazine resin), PPE resin (polyphenylene ether resin), and the like. In addition, a substrate made of a composite material of these resins and glass fibers (glass woven fabric or glass nonwoven fabric) may be used. A substrate made of a composite material of these resins and organic fibers such as polyamide fibers may be used. Alternatively, a substrate made of a resin-resin composite material in which a thermosetting resin such as an epoxy resin is impregnated into a three-dimensional network fluorine-based resin base material such as continuous porous PTFE may be used. As other materials, for example, various ceramics can be selected. The structure of the wiring board is not particularly limited, and examples thereof include a build-up multilayer wiring board having a build-up layer on one or both sides of the core board, and a coreless wiring board having no core board.

  A plurality of pads constituting the wiring board are arranged on the main surface of the board. The pad can be formed of a conductive metal material or the like. Examples of the metal material constituting the pad include gold, silver, copper, iron, cobalt, nickel, and the like. In particular, the pad may be formed mainly of copper. In this case, the resistance of the pad can be reduced and the conductivity of the pad can be improved as compared with the case where the pad is mainly formed of other materials. The pad is preferably formed by plating. In this way, the pad can be formed with high accuracy and uniformity. If the pads are formed by reflowing a metal paste, it is difficult to form the pads with high accuracy and uniformity, which may cause variations in the height of individual pads.

  The solder resist constituting the wiring board is made of a resin having insulating properties and heat resistance, and functions as a protective film that protects the main surface of the substrate by covering the main surface of the substrate. Specific examples of the solder resist include a solder resist made of an epoxy resin or a polyimide resin. In addition, examples of the shape of the plurality of openings formed in the solder resist in a plan view include a circular shape in plan view, an elliptical shape in plan view, a triangular shape in plan view, a rectangular shape in plan view, and a square shape in plan view. .

  Further, the protruding conductors constituting the wiring board are fixed to a part of the surface of the pad. Examples of the material constituting the protruding conductor include copper, silver, iron, cobalt, nickel, and the like. In particular, it is preferable that the material be formed mainly of copper. In this way, since copper is a relatively soft material, the shaft portion is liable to bend (cracks are not easily generated even when stress is applied). Further, the resistance of the protruding conductor can be reduced and the conductivity of the protruding conductor can be improved as compared with the case where the protruding conductor is formed mainly of other materials. The protruding conductor may be formed mainly of the same conductive material as the pad. In this way, it is not necessary to prepare a material different from the pad when forming the protruding conductor. Therefore, since the material necessary for manufacturing the wiring board is reduced, the cost of the wiring board can be reduced.

  Examples of the method for forming the protruding conductor include a method of forming the protruding conductor by plating. In this case, if the protruding conductor has a columnar shape, the protruding conductor can be easily formed by plating. Further, when the protruding conductor is formed mainly of copper, for example, the protruding conductor may be formed by copper plating. In this way, the conductivity of the protruding conductor is improved as compared with the case where the protruding conductor is formed of, for example, a conductive paste. Other methods of forming the protruding conductor include a method of forming a protruding conductor by printing a conductive paste on the pad, or after attaching a conductive member to be a shaft portion on the pad, A method of forming a projecting conductor by pasting a conductive member to be a head on the surface, or a projecting conductor by pasting a plate material having conductivity larger than that of the projecting conductor on a pad and then etching the plate material The method of forming is mentioned.

  Further, the protruding conductor is connected to the surface of the pad, the shaft portion whose outer diameter is set smaller than the outer diameter of the pad, and the shaft portion is connected to the shaft portion, and the outer diameter is larger than the outer diameter of the shaft portion. With a larger head. Note that a constricted portion having an outer diameter smaller than that of the shaft portion and the head portion may be provided at a connection portion of the shaft portion with the head portion. In this way, the constricted portion of the shaft portion is particularly likely to be bent, so that the stress acting on the protruding conductor can be more reliably alleviated. Therefore, it is possible to more reliably prevent the connection portion between the pad and the component from being damaged. Moreover, it is preferable that the rounded part is provided in the outer peripheral part of the constriction part. If it does in this way, it will become still easier to make a shaft part.

  Furthermore, the surface of the protruding conductor may be covered with a plating layer made of a metal material different from the protruding conductor. In this way, for example, the solder easily adheres to the surface of the protruding conductor, so that the solder bump can be reliably formed.

  In addition, the head has an upper side surface having a curved cross section and a bottom surface disposed substantially parallel to the surface of the solder resist, and solder bumps used for connecting to components are in close contact with the upper side surface and the bottom surface. It may be. In this way, the contact area between the protruding conductor and the solder bump is more reliably increased, and the adhesion between the protruding conductor and the solder bump is further improved. It can prevent more reliably. Furthermore, a part of the solder bump may be filled in the gap between the bottom surface and the surface of the solder resist. In this way, the solder bump comes into contact with the bottom surface of the head, the outer surface of the shaft portion, and the surface of the solder resist. Therefore, the configuration of the solder bump and the wiring board side (protruding conductor and solder resist) The contact area is further increased. As a result, the adhesion between the solder bumps and the configuration on the wiring board side is improved, so that connection failure between individual pads and components can be prevented more reliably.

  Here, the solder material used for the solder bump is not particularly limited. For example, tin-lead eutectic solder (Sn / 37Pb: melting point 183 ° C.) is used. Sn / Pb solder other than tin-lead eutectic solder, for example, solder having a composition of Sn / 36Pb / 2Ag (melting point 190 ° C.) may be used. In addition to the above lead-containing solder, Sn-Ag solder, Sn-Ag-Cu solder, Sn-Ag-Bi solder, Sn-Ag-Bi-Cu solder, Sn-Zn solder It is also possible to select lead-free solder such as Sn—Zn—Bi solder.

  Suitable components connected by solder bumps include capacitors, resistors, semiconductor integrated circuit elements (IC chips), MEMS (Micro Electro Mechanical Systems) elements manufactured by a semiconductor manufacturing process, and the like. Further, examples of the IC chip include DRAM (Dynamic Random Access Memory), SRAM (Static Random Access Memory) and the like. Here, “semiconductor integrated circuit element” refers to an element mainly used as a microprocessor of a computer or the like.

1 is a schematic cross-sectional view showing a wiring board according to an embodiment of the present invention. The principal part sectional view showing a pad and a projection-like conductor. Explanatory drawing which shows the manufacturing method of a wiring board. Explanatory drawing which shows the manufacturing method of a wiring board. Explanatory drawing which shows the manufacturing method of a wiring board. Explanatory drawing which shows the manufacturing method of a wiring board. The principal part sectional view showing the wiring board in other embodiments. The principal part sectional drawing which shows the pad and protrusion-shaped conductor in other embodiment.

  Hereinafter, an embodiment embodying the present invention will be described in detail with reference to the drawings.

  As shown in FIG. 1, the wiring board 10 of this embodiment is a wiring board for mounting an IC chip. The wiring substrate 10 has a substantially rectangular plate shape having a substrate main surface 12 (upper surface in FIG. 1) and a substrate rear surface 13 (lower surface in FIG. 1). The wiring board 10 includes a substantially rectangular plate-shaped core substrate 21, a main surface side buildup layer 31 formed on the core main surface 22 of the core substrate 21, and a back surface formed on the core back surface 23 of the core substrate 21. And a side buildup layer 32.

  The core substrate 21 of the present embodiment has a substantially rectangular plate shape in plan view of 25 mm length × 25 mm width × 1.0 mm thickness. The core substrate 21 has a thermal expansion coefficient in the plane direction (XY direction) of 10 to 30 ppm / ° C. (specifically, 18 ppm / ° C.). The thermal expansion coefficient of the core substrate 21 is an average value of measured values between 0 ° C. and the glass transition temperature (Tg). Through-hole conductors 24 are formed at a plurality of locations on the core substrate 21. The through-hole conductor 24 connects and connects the core main surface 22 side and the core back surface 23 side of the core substrate 21. Note that the inside of the through-hole conductor 24 is filled with a closing body 25 such as an epoxy resin. A conductor layer 41 made of copper is patterned on the core main surface 22 and the core back surface 23 of the core substrate 21, and each conductor layer 41 is electrically connected to the through-hole conductor 24.

  As shown in FIG. 1, the back-side buildup layer 32 is formed by alternately laminating two resin insulating layers 34 and 36 (interlayer insulating layers) made of a thermosetting resin (epoxy resin) and a conductor layer 42. The resin insulating layers 34 and 36 have a thermal expansion coefficient of about 10 to 60 ppm / ° C. (specifically, about 30 ppm / ° C.). BGA pads 48 electrically connected to the conductor layer 42 through via conductors 43 are formed in an array at a plurality of locations on the lower surface of the second resin insulating layer 36. The lower surface of the resin insulating layer 36 is almost entirely covered with a solder resist 38. An opening 40 for exposing the BGA pad 48 is formed at a predetermined portion of the solder resist 38. On the surface of the BGA pad 48, a plurality of solder bumps 49 are provided for electrical connection with a mother board (not shown). The wiring board 10 shown in FIG. 1 is mounted on a mother board (not shown) by each solder bump 49.

  As shown in FIG. 1, the main surface side buildup layer 31 has substantially the same structure as the back surface side buildup layer 32 described above. That is, the main surface side buildup layer 31 has a structure in which two resin insulating layers 33 and 35 (interlayer insulating layer) made of thermosetting resin (epoxy resin) and a conductor layer 42 made of copper are alternately laminated. have. In this embodiment, the thermal expansion coefficients of the resin insulating layers 33 and 35 are about 10 to 60 ppm / ° C. (specifically, about 30 ppm / ° C.). In addition, the thermal expansion coefficient of the resin insulating layers 33 and 35 means an average value of measured values between 30 ° C. and the glass transition temperature (Tg).

  As shown in FIGS. 1 and 2, a pad 61 having a circular shape in a plan view is formed on the substrate main surface 12 of the wiring substrate 10 (on the upper surface of the second resin insulating layer 35). A plurality are arranged vertically and horizontally along the surface direction. Each pad 61 is electrically connected to the conductor layer 42 via the via conductor 43. As shown in FIG. 2, the outer diameter A1 of each pad 61 is larger than the outer diameter of the via conductor 43 (30 μm to 100 μm in this embodiment), and is set to 50 μm to 150 μm in this embodiment. ing. Further, the thickness A2 of each pad 61 in the present embodiment is set to 5 μm or more and 30 μm or less.

  Further, a protruding conductor 71 is fixed to the central portion of the upper surface 62 (front surface) of each pad 61. The protruding conductor 71 is formed separately from the pad 61. In addition, a plurality of protruding conductors 71 exist on the substrate main surface 12 side, and are arranged one by one with respect to one pad 61. Therefore, the number of protruding conductors 71 is equal to the number of pads 61. The protruding conductor 71 is a copper post formed mainly of copper, which is the same conductive material as the pad 61.

  As shown in FIG. 2, each protruding conductor 71 includes a substantially cylindrical shaft portion 72 connected to the upper surface 62 of the pad 61, and a substantially hemispherical head portion 73 connected to the shaft portion 72. ing. The outer diameter A3 of the shaft portion 72 is set smaller than the outer diameter A1 (50 μm or more and 150 μm or less) of the pad 61, and is set to 30 μm or more and 100 μm or less in the present embodiment. Further, in the shaft portion 72, the height A4 from the upper surface 62 of the pad 61 to the connection portion with the head portion 73 is set to be larger than the thickness A2 (5 μm or more and 30 μm or less) of the pad 61. Is set to 40 μm or more and 150 μm or less. Further, a constricted portion 74 having an outer diameter A5 (20 μm or more and 90 μm or less in the present embodiment) smaller than that of the shaft portion 72 and the head portion 73 is provided at a connection portion of the shaft portion 72 with the head portion 73. The central axis of the shaft portion 72 coincides with the central axis C 1 of the pad 61. The “center axis C1” refers to an axis that passes through the center of the pad 61 in plan view.

  As shown in FIG. 2, the head portion 73 has an upper side surface 75 that is a convex curved surface and a bottom surface 76 that is disposed substantially parallel to the upper surface 62 of the pad 61, and has a substantially semicircular cross section. ing. The outer diameter A6 of the head 73 is set larger than the outer diameter A3 (30 μm or more and 100 μm or less) of the shaft portion 72 and the outer diameter (30 μm or more and 100 μm or less) of the via conductor 43, and in this embodiment, 40 μm or more and 200 μm. It is set as follows. Further, the head 73 has a height A7 from the connecting portion with the shaft portion 72 to the highest point P1 of the upper side surface 75 larger than the thickness A2 of the pad 61 (5 μm or more and 30 μm or less), and the shaft portion 72. Is set to be slightly smaller than the height A4 (40 μm to 150 μm), and in the present embodiment, it is set to 20 μm or more and 140 μm or less. Further, the head portion 73 has a recess 77 at a boundary portion with the shaft portion 72 (neck portion 74). The recess 77 is open at the bottom surface 76 of the head 73, and the depth is set to 0 μm or more and 5 μm or less. The central axis of the head 73 passes through the highest point P1 and coincides with the central axis C1 of the pad 61.

  As shown in FIGS. 1 and 2, the substrate main surface 12 (the surface of the resin insulating layer 35) of the wiring substrate 10 is almost entirely covered with a solder resist 81. The solder resist 81 has a plurality of openings 82 that expose the plurality of pads 61 and the plurality of protruding conductors 71. Each opening 82 has a circular shape in plan view, and has an inner diameter of 30 μm or more and 100 μm or less. That is, the inner diameter of the opening portion 82 is set equal to the outer diameter A3 of the shaft portion 72, and the lower portion of the outer surface 78 of the shaft portion 72 is in close contact with the inner surface of the opening portion 82. In addition, the depth of each opening 82 (the height from the upper surface 62 of the pad 61 to the surface 83 of the solder resist 81) is set to be smaller than the height A4 (40 μm or more and 150 μm or less) of the shaft portion 72. In the form, it is set to 20 μm or more and 140 μm or less. Therefore, the head 73 is disposed in a state of being separated from the surface 83 of the solder resist 81, and the bottom surface 76 is disposed substantially parallel to the surface 83 of the solder resist 81. The size of the gap S1 between the bottom surface 76 of the head 73 and the surface 83 of the solder resist 81 is set to 20 μm or more and 80 μm or less.

  Further, the upper portion of the outer surface 78 of the shaft portion 72 and the surface (the upper side surface 75 and the bottom surface 76) of the head portion 73 are covered with a plating layer 79. The plating layer 79 is composed of a nickel layer, a palladium layer, and a gold layer. The nickel layer is a plating layer formed by coating the upper portion of the outer surface 78 of the shaft portion 72 and the surface of the head portion 73 with electroless nickel plating. The palladium layer is a plating layer formed by coating the surface of the nickel layer with electroless palladium plating. The gold layer is a plating layer formed by coating the surface of the palladium layer with electroless gold plating. Further, the pad 61 and the protruding conductor 71 are directly connected without intervening inclusions such as a plating layer. In addition, although the plating layer 79 of the present embodiment has a structure including a nickel layer, a palladium layer, and a gold layer, the layer structure can be changed as appropriate.

  As shown in FIGS. 1 and 2, solder bumps 84 used for connection to the IC chip 51 (component) are formed on the surface of the protruding conductor 71. More specifically, the solder bump 84 is in close contact with the upper side surface 75 and the bottom surface 76 of the head 73. Further, the solder bump 84 is in close contact with a region protruding from the surface 83 of the solder resist 81 on the outer surface 78 of the shaft portion 72. Furthermore, the solder bumps 84 are also in close contact with part of the surface 83 of the solder resist 81. A gap S 1 between the bottom surface 76 and the surface 83 of the solder resist 81 is filled with a part of the solder bump 84. Therefore, the protruding conductor 71 is covered with the solder bump 84 and cannot be seen. The height of the solder bump 84 is higher than the height of the protruding conductor 71 from the surface 83 of the solder resist 81 (50 μm or more and 200 μm or less), and is set to 100 μm or more and 200 μm or less in this embodiment. Note that the solder bumps 84 of the present embodiment are made of Sn-Ag solder that is lead-free solder.

  Each solder bump 84 is electrically connected to the surface connection terminal 52 of the IC chip 51 having a rectangular flat plate shape. In this state, since the upper side surface 75 of the head 73 and the surface of the surface connection terminal 52 are separated from each other, the protruding conductor 71 and the surface connection terminal 52 do not contact each other. Note that an area including the pads 61 and the solder bumps 84 is an IC chip mounting area 53 on which the IC chip 51 can be mounted. The IC chip mounting area 53 is set on the surface of the main surface side buildup layer 31. Further, via conductors 43 and 47 are provided in the resin insulation layers 33 and 35, respectively. These via conductors 43 and 47 electrically connect the conductor layer 42 and the pad 61 to each other.

  Next, a method for manufacturing the wiring board 10 will be described.

  First, a substrate preparation process for preparing the wiring substrate 10 is performed. Specifically, first, a copper clad laminate in which copper foil is pasted on both surfaces of a substrate made of glass epoxy is prepared. And drilling is performed using a drill machine, and the through-hole which penetrates the front and back of a copper clad laminated board is previously formed in the predetermined position. And the through-hole conductor 24 is formed in a through-hole by performing electroless copper plating and electrolytic copper plating with respect to the inner surface of a through-hole. Thereafter, the cavity of the through-hole conductor 24 is filled with an insulating resin material (epoxy resin) to form the closing body 25.

  Further, by performing electroless copper plating and electrolytic copper plating, a copper plating layer is formed on the surface of the copper clad laminate including the exposed portion of the closing body 25, and then the copper plating layer and the copper foil are subjected to, for example, a subtractive method. To pattern. As a result, an intermediate product of the core substrate 21 on which the conductor layer 41 and the through-hole conductor 24 are formed is obtained. The intermediate product of the core substrate 21 is a multi-piece core substrate in which a plurality of regions to be the core substrate 21 are arranged vertically and horizontally along the plane direction.

  Next, the main surface side buildup layer 31 is formed on the core main surface 22 of the core substrate 21, and the back surface side buildup layer 32 is formed on the core back surface 23 of the core substrate 21. Specifically, first, a resin insulating layer 33 is formed by applying (sticking) a thermosetting epoxy resin on the core main surface 22. Further, a resin insulating layer 34 is formed by depositing (attaching) a thermosetting epoxy resin on the core back surface 23. Instead of depositing a thermosetting epoxy resin, a photosensitive epoxy resin, an insulating resin, or a liquid crystal polymer (LCP) may be deposited.

  Further, laser drilling is performed using a YAG laser or a carbon dioxide laser to form via holes at positions where via conductors 47 are to be formed. Specifically, a via hole penetrating the resin insulating layer 33 is formed, and the surface of the conductor layer 41 is exposed. In addition, a via hole penetrating the resin insulating layer 34 is formed to expose the surface of the conductor layer 41. Next, electrolytic copper plating is performed according to a conventionally known method to form a via conductor 47 inside the via hole, and to form a conductor layer 42 on the resin insulating layers 33 and 34.

  Next, a thermosetting epoxy resin is deposited on the resin insulation layers 33 and 34 to form resin insulation layers 35 and 36. Instead of depositing the thermosetting epoxy resin, a photosensitive epoxy resin, an insulating resin, or a liquid crystal polymer may be deposited. In this case, via holes are formed in the resin insulating layer 36 at positions where the via conductors 43 are to be formed by a laser processing machine or the like. Next, electrolytic copper plating is performed according to a conventionally known method to form a via conductor 43 in the via hole of the resin insulating layer 36 and to form a BGA pad 48 on the resin insulating layer 36.

  In the subsequent pad forming step, a plurality of pads 61 are formed on the substrate main surface 12 by plating on the outermost resin insulating layer 35 having the substrate main surface 12 (see FIG. 3). In the present embodiment, the pad 61 is patterned on the resin insulating layer 35 by performing a semi-additive method. Specifically, first, via processing is performed to form via holes at predetermined positions of the resin insulating layer 35, and then desmear processing is performed to process smear in each via hole. Next, after electroless copper plating is performed on the surface of the resin insulating layer 35, a dry film is laminated on the resin insulating layer 35 to form a first plating resist (not shown). Further, laser processing is performed on the first plating resist using a laser processing machine. As a result, an opening having an inner diameter larger than the outer diameter of the via hole is formed at a position where the resin insulating layer 35 communicates with the via hole. Then, electrolytic copper plating is performed to form a via conductor 43 in each via hole, and the upper surface (substrate main surface 12) of the resin insulating layer 35 exposed through the opening and exposed through the opening. A pad 61 mainly composed of copper (copper layer) is formed on the upper surface of the via conductor 43. Thereafter, the first plating resist is peeled off and an unnecessary electroless copper plating layer is removed. In addition, the thickness of the copper layer in this embodiment is set to 5 μm or more and 30 μm or less. The copper layer of the present embodiment is formed by plating, but can be formed by other methods such as sputtering and CVD. However, in order to obtain a required height (5 μm or more and 30 μm or less) particularly in the copper layer, it is preferably formed by plating.

  In the subsequent protruding conductor forming step, the plurality of protruding conductors 71 are formed on the upper surface 62 of each pad 61 by plating each pad 61. Specifically, first, a dry film is laminated on the surface of the resin insulating layer 35 to form the second plating resist 91 (see FIG. 4). Next, laser processing using a laser processing machine is performed on the second plating resist 91. As a result, an opening 92 that exposes the central portion of the upper surface 62 of the pad 61 is formed. Then, electrolytic copper plating is performed on the central portion of the upper surface 62 exposed through the opening 92. At this time, the protruding conductor 71 mainly composed of copper is formed (see FIG. 5). At this time, the bottom surface 76 of the head 73 comes into contact with the surface of the second plating resist 91. Thereafter, the second plating resist 91 is peeled off.

In the electrolytic copper plating of the present embodiment, plating conditions are set such that the head 73 is reliably formed in addition to the shaft portion 72. Specifically, using a copper pyrophosphate plating bath, a temperature of about 50 ° C. to 60 ° C., a current density of about 1.0 A / dm ^{2 to} 3.0 A / dm ² , and a deposition time of about 20 minutes to 25 minutes. Electrolytic copper plating is performed under such conditions.

  In the subsequent solder resist formation step, a solder resist 81 is formed so as to cover the substrate main surface 12 by applying and curing a liquid epoxy resin on the resin insulating layer 35 on which the pads 61 are formed (see FIG. 6). ). At this time, the inner surface of the opening 82 of the solder resist 81 comes into contact with the outer surface 78 of the shaft portion 72. Further, the head 73 is separated from the surface 83 of the solder resist 81.

  Thereafter, soft etching is performed. As a result, a constricted portion 74 is formed in the entire portion of the shaft portion 72 protruding from the surface 83 of the solder resist 81, and a concave portion 77 is formed in a boundary portion of the head portion 73 with the shaft portion 72 (constricted portion 74). (See FIG. 6). The constricted portion 74 and the recessed portion 77 may be formed by roughening the surface of the protruding conductor 71.

  Further, electroless nickel plating is performed to form a nickel layer on the upper portion of the outer surface 78 of the shaft portion 72 and the surface of the head portion 73 (upper side surface 75 and bottom surface 76). Next, electroless palladium plating is performed to form a palladium layer on the nickel layer. Then, electroless gold plating is performed to form a gold layer on the palladium layer. At this point, the upper portion of the outer surface 78 of the shaft portion 72 and the surface of the head portion 73 are covered with the plating layer 79 (see FIG. 6). Here, the thickness of the nickel layer, the palladium layer, and the gold layer is set to 0.01 μm or more and 15 μm or less. In addition, although the nickel layer, palladium layer, and gold | metal layer of this embodiment are formed by plating, it is also possible to form by other methods, such as CVD.

  In the subsequent solder bump forming step, solder is printed on the plurality of protruding conductors 71 exposed through the openings 82 of the solder resist 81. More specifically, a solder paste is printed on the protruding conductor 71 exposed through the opening 82. Next, by heating and melting (reflowing) the solder paste by heating to a temperature 10 to 40 ° C. higher than the solder melting point, the solder bumps 84 for mounting the IC chip 51 in a hemispherical shape form the protruding conductors 71. It is formed to cover. At this point, the intermediate product of the wiring board 10 is completed.

  Thereafter, the intermediate product of the wiring board 10 is divided using a conventionally known cutting device or the like. As a result, the product parts are divided, and a large number of wiring boards 10 which are individual products are obtained simultaneously (see FIG. 1).

  Further, an IC chip mounting process is performed. Specifically, first, the IC chip 51 is placed on the substrate main surface 12 side of the wiring substrate 10. At this time, the surface connection terminals 52 arranged on the bottom surface side of the IC chip 51 are placed on the solder bumps 84 arranged on the wiring board 10 side. Then, the solder bumps 84 are heated and melted (reflowed) by heating to a temperature of about 230 ° C. to 260 ° C., whereby the pads 61 are flip-chip connected to the surface connection terminals 52, and the IC chip 51 is connected to the wiring substrate 10. Is mounted (see FIG. 1).

  Therefore, according to the present embodiment, the following effects can be obtained.

  (1) In the wiring board 10 of the present embodiment, the protruding conductor 71 includes a head portion 73 that is set larger than the outer diameter A3 of the shaft portion 72 in addition to the shaft portion 72. Therefore, as the pad 61 is formed smaller corresponding to the so-called fineness of the C4 pad, the head 73 is formed larger even if the shaft portion 72 is formed smaller. A contact area between the conductor 71 and the solder bump 84 can be ensured. Further, since the head portion 73 is disposed in a state of being separated from the surface 83 of the solder resist 81, a part of the solder bump 84 is formed by inserting solder between the head portion 73 and the surface 83 of the solder resist 81. The bottom surface 76 of the head 73 and the outer surface 78 of the shaft portion 72 can also be brought into contact with each other. As a result, the contact area between the protruding conductor 71 and the solder bump 84 is further increased, and the adhesion between the protruding conductor 71 and the solder bump 84 is improved, so that the connection between the individual pads 61 and the IC chip 51 is poor. Can be prevented. Further, even when a thermal stress acts on the protruding conductor 71 during the cooling of the solder after the IC chip 51 is connected, the stress is relieved by the bending of the shaft portion 72, so that the pad 61 and the IC chip 51 Damage to the connecting portion can be prevented. From the above, since the protruding conductor 71 has a structure suitable for connection with the IC chip 51, the reliability of the wiring board 10 can be improved.

  (2) In the present embodiment, a constricted portion 74 is provided at a connection portion between the shaft portion 72 and the outer surface 73, and a concave portion 77 is provided at a boundary portion between the head portion 73 and the shaft portion 72. As a result, the contact area between the protruding conductor 71 and the solder bump 84 is further increased, and the adhesion between the protruding conductor 71 and the solder bump 84 is further improved. Connection failure can be prevented more reliably.

  (3) In the present embodiment, the protruding conductor 71 is fixed to a part of the upper surface 62 of the pad 61, and the protruding conductor 71 has a substantially cylindrical shaft portion 72 and a substantially larger outer diameter than the shaft portion 72. It consists of a hemispherical head 73. Therefore, if the solder bump 84 covering the surface of the projecting conductor 71 is formed, the projecting conductor 71 is fitted in the solder bump 84, so that the adhesion strength between the projecting conductor 71 and the solder bump 84 is increased. It is possible to increase the height, and as a result, connection failure between the individual pads 61 and the IC chip 51 can be prevented. That is, by providing the pads 61 and the protruding conductors 71 suitable for connection with the IC chip 51, the reliability of the wiring board 10 can be further improved.

  In addition, you may change this embodiment as follows.

  In the wiring substrate 10 of the above embodiment, the inner diameter of the opening portion 82 of the solder resist 81 is set equal to the outer diameter A3 of the shaft portion 72 of the protruding conductor 71, and the outer surface 78 of the shaft portion 72 is the opening portion 82. It was in close contact with the inner surface. However, like the wiring board 110 shown in FIG. 7, the inner diameter of the opening 112 of the solder resist 111 is set larger than the outer diameter of the shaft 114 of the protruding conductor 113, and the outer surface 115 of the shaft 114 is formed. You may make it space apart from the inner surface of the opening part 112. FIG. In this case, the pad 116, the protruding conductor 113, and the substrate main surface 117 are exposed in the opening 112.

  In the above embodiment, after the constricted portion 74 and the concave portion 77 are formed on the surface of the protruding conductor 71, the upper portion of the outer surface 78 of the shaft portion 72 and the surface of the head portion 73 (upper side surface 75 and bottom surface 76). A plating layer 79 was formed on the substrate. However, after the plating layer is formed, the constricted portion and the concave portion may be formed. In this case, since the constricted portion 121 and the concave portion 122 are formed by performing soft etching or the like, the plating layer 125 remains on the entire upper side surface 123 or only on the outer peripheral portion of the bottom surface 124 (see FIG. 8).

  In the above embodiment, the solder resist forming step is performed after the protruding conductor forming step, but the protruding conductor forming step may be performed after the solder resist forming step.

  The protruding conductor 71 of the above embodiment is a conductor (copper post) formed by copper plating, but may be a conductor formed by printing a copper paste.

  In the above embodiment, one protruding conductor 71 is formed for one pad 61. However, the present invention is not limited to this, and two or more protruding conductors may be formed.

  The protruding conductor 71 of the above embodiment has been applied to the one used for joining the wiring substrate 10 and the IC chip 51. For example, the projecting conductor 71 is applied to one used for joining the wiring substrate 10 and the mother board. Also good.

  In the above embodiment, the package form of the wiring board 10 is BGA (ball grid array). However, the package form is not limited to BGA. For example, PGA (pin grid array) or LGA (land grid array) may be used. Good.

  Next, the technical ideas grasped by the embodiment described above are listed below.

  (1) In the above means 1, the inner diameter of the opening is set equal to the outer diameter of the shaft, and the outer surface of the shaft is in close contact with the inner surface of the opening. .

  (2) In the above means 1, the wiring board is characterized in that a concave portion is provided in a boundary portion between the head portion and the shaft portion.

DESCRIPTION OF SYMBOLS 10,110 ... Wiring board | substrate 12,117 ... Board | substrate main surface 51 ... IC chip 61, 116 as a component ... Pad 62 ... Upper surface 71, 113 ... Projection-like conductor 72,114 ... Shaft part 73 ... Head part as a pad surface 74, 121 ... Constriction part 75, 123 ... Upper side surface 76, 124 of head part Bottom face 81, 111 ... Solder resist 82, 112 ... Opening part 83 ... Surface of solder resist 84 ... Solder bump A1 ... Outside of pad Diameter A3 ... Shaft outer diameter A6 ... Head outer diameter S1 ... Clearance between bottom surface and solder resist surface

Claims (4)

A plurality of pads arranged on the main surface of the substrate;
A wiring board comprising a solder resist that covers the main surface of the substrate and is formed with a plurality of openings for exposing the plurality of pads.
A protruding conductor is fixed to a part of the surface of the pad,
The protruding conductor is
A shaft portion connected to the surface of the pad and having an outer diameter set smaller than the outer diameter of the pad;
A head portion connected to the shaft portion and having an outer diameter set larger than the outer diameter of the shaft portion;
The wiring board, wherein the head is disposed in a state of being separated from the surface of the solder resist.   2. The wiring board according to claim 1, wherein a constriction portion having an outer diameter smaller than that of the shaft portion and the head portion is provided at a connection portion of the shaft portion with the head portion. The head portion has an upper side surface having a curved cross section and a bottom surface disposed substantially parallel to the surface of the solder resist,
The wiring board according to claim 1, wherein solder bumps used for connection to a component are in close contact with the upper side surface and the bottom surface.   The wiring board according to claim 3, wherein a part of the solder bump is filled in a gap between the bottom surface and the surface of the solder resist.

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