Multilayer wiring board

Abstract

To provide a multilayer wiring board with high connection reliability.SOLUTION: The present invention relates to a multilayer wiring board 010 comprising: a conductor layer formed on a first insulation resin layer 001; a second insulation resin layer 003 formed on the first insulation resin layer and the conductor layer and including an opening 004 in which a part of the conductor layer is exposed as a conductor pad 002; a conductor post 006 formed on the conductor pad 002 and protruding from the second insulation resin layer 003; and a solder layer formed on the conductor post 006. In a root portion 6A positioned inside of the opening 004 in the conductor post 006, a diameter becomes larger as the same is closer to the conductor pad 002 in a direction from an axially middle position of the root portion 6A to the conductor pad 002 in a case where an area of a cross section of the root portion 6A is converted into an area of a circle.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a multilayer wiring board having high connection reliability. [Background technology]

[0002] In recent years, with the increasing integration and functionality of electronic devices, there has been a demand for finer pitch wiring and connection terminals in multilayer wiring boards. As finer pitches become more common, multilayer wiring boards have been proposed that incorporate conductor posts (pillar-shaped connection terminals) such as those disclosed in Patent Document 1 in order to ensure standoff between the multilayer wiring board and the semiconductor element when mounting the semiconductor element on the multilayer wiring board. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5011329 Summary of the Invention [Problem to be solved by the invention]

[0004] However, as described in Patent Document 1, conventionally, the conductor post has a shape that is narrowest at the bottom of the opening in the insulating resin (solder resist) on the connection pad, and therefore the joint between the connection pad and the lower end of the conductor post (conductor pad) becomes the stress concentration area where the most stress is concentrated after the semiconductor element is mounted. This stress concentration area is the boundary between the connection pad (conductor pad) and the electrolytic copper plating of the conductor post, and there is also electroless copper plating, which acts as a plating seed layer, between them, making them discontinuous. As stress concentrates in areas with relatively weak connection reliability, cracks and breaks are more likely to occur at the joint (see part marked X in Figure 12). The present invention has been made in view of the above points, and has as its object to provide a multilayer wiring board having high connection reliability. [Means for solving the problem]

[0005] In order to solve the problem, one aspect of the present invention is a multilayer wiring board comprising: a conductor layer formed on a first insulating resin layer; a second insulating resin layer formed on the first insulating resin layer and the conductor layer, the second insulating resin layer having an opening that exposes a portion of the conductor layer as a conductor pad; a conductor post formed on the conductor pad and protruding from the second insulating resin layer; and a solder layer formed on the conductor post, wherein, when the cross-sectional area of ​​the root portion is converted into the area of ​​a circle, the root portion of the conductor post located within the opening has an outwardly expanding shape such that the diameter increases as it approaches the conductor pad from an axial midpoint of the root portion toward the conductor pad. [Effects of the Invention]

[0006] According to this aspect of the present invention, the lower portion of the conductor post, where stress is greatest, has a shape that expands outward toward the conductor pad, thereby alleviating local stress concentration at the boundary between the conductor pad and the conductor post. As a result, this aspect of the present invention makes it possible to suppress the occurrence of cracks and breaks in the conductor post and provide a multilayer wiring board with high connection reliability. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is an enlarged cross-sectional view showing a multilayer wiring board according to an embodiment of the present invention. [Figure 2] FIG. 4 is an enlarged cross-sectional view showing the shape of an opening. [Figure 3] FIG. 10 is an enlarged cross-sectional view showing a modified example of the opening portion. [Figure 4] FIG. 10 is an enlarged cross-sectional view showing a modified example of the opening portion. [Figure 5] FIG. 10 is an enlarged cross-sectional view showing a modified example of the opening portion. [Figure 6] FIG. 10 is an enlarged cross-sectional view showing a modified example of the opening portion. [Figure 7] 1A to 1C are diagrams illustrating a manufacturing process of a multilayer wiring board according to the present invention. [Figure 8] 1A to 1C are diagrams illustrating a manufacturing process of a multilayer wiring board according to the present invention. [Figure 9] 1A to 1C are diagrams illustrating a manufacturing process of a multilayer wiring board according to the present invention. [Figure 10] FIG. 4 is an enlarged cross-sectional view showing exposure light during exposure of a second insulating resin according to the present invention. [Figure 11] FIG. [Figure 12] FIG. 1 is a cross-sectional view showing a conventional multilayer wiring board. DETAILED DESCRIPTION OF THE INVENTION

[0008] Next, an embodiment based on the present invention will be described with reference to the drawings. The drawings are schematic, and the relationship between the thickness and planar dimensions of each component, the ratio of each component, etc., differ from the actual ones. Furthermore, the embodiments shown below are merely examples of configurations for embodying the technical idea of ​​the present disclosure, and the shape, structure, etc., of the components are not limited to those described below. Various modifications can be made to the technical idea of ​​the present disclosure within the technical scope defined by the claims. Furthermore, the same reference numerals are used to designate the same components.

[0009] (composition) FIG. 1 is an enlarged view of a portion of a multilayer wiring substrate 010 according to an embodiment, and is a cross-sectional view showing the structure around a conductor post 006. As shown in FIG. The multilayer wiring board 010 of this embodiment is a cored board formed by alternately laminating one or more conductor layers having a predetermined circuit pattern and resin insulating layers on one or both sides of a core board (not shown). Alternatively, the multilayer wiring board 010 of this embodiment is a coreless board that does not have a core board.

[0010] As shown in Fig. 1, the multilayer wiring board 010 of this embodiment has a first insulating resin layer 001, which is the outermost resin insulating layer, and a conductor layer 002 formed in a predetermined circuit pattern on the first insulating resin layer 001. Furthermore, a second insulating resin layer 003 is formed on the first insulating resin layer 001 and the conductor layer 002. The second insulating resin layer 003 has an opening 004 that exposes a portion of the conductor layer. The portion of the conductor layer exposed by the opening 004 constitutes a conductor pad 002.

[0011] The lower end of a conductor post 006 is electrically connected to the conductor pad 002. The conductor post 006 is erected with its axis pointing away from the conductor pad 002. Here, although a plurality of other conductor layers and resin insulating layers are often provided alternately below the first insulating resin layer 001, these are omitted from the drawings. Also, although the conductor layer 002 often includes various patterns such as wiring, shielding, ground, and dummy patterns, these are omitted from the drawings.

[0012] A solder layer 008 is formed on the tip surface of the conductor post 006 . In this embodiment, as shown in FIG. 1, a surface treatment layer 007 is formed between the conductor post 006 and the solder layer 008, but the surface treatment layer 007 does not have to be formed. The material constituting the surface treatment layer 007 is, for example, a metal such as tin, nickel, palladium, or gold, or may be an organic coating. The material constituting the first insulating resin layer 001 is, for example, a thermosetting resin or a photosensitive insulating resin, such as an epoxy resin, a phenol resin, or a polyimide resin composition, etc. These may also contain inorganic fillers such as silica or alumina.

[0013] The material constituting the second insulating resin layer 003 is, for example, a negative photosensitive insulating resin such as solder resist, for example, a resin composition containing an epoxy resin, a phenol resin, or a polyimide resin and an inorganic filler such as silica or alumina, etc. Note that the second insulating resin layer 003 does not necessarily need to contain an inorganic filler. The material that constitutes the conductor layer 002 and the conductor posts 006 is a conductive metal, such as copper or a metal containing copper as a main component. The conductive posts 006 and the openings 004 will be further described.

[0014] <Conductor post 006 and opening 004> In this embodiment, the description will be made assuming that the cross sections of the conductor post 006 and the opening 004 are circular. The opening of the opening 004 is generally circular, but does not have to be circular. The cross section is a cross section in a direction perpendicular to the thickness direction of the layer (the axial direction of the conductor post 006). The conductor post 006 has a root portion 6A formed within the opening 004 and an exposed portion 6B that is continuous with the root portion 6A and protrudes from the opening 004. The root portion 6A and the exposed portion are integral. In general, the cross-sectional area of ​​the exposed portion 6B is larger than the minimum cross-sectional area of ​​the root portion 6A. The shape of the outer surface of the base portion 6A follows the shape of the wall surface of the opening 004. That is, the shape of the outer surface of the base portion 6A is the same as the shape of the wall surface of the opening 004. 1, the reference numeral 005 denotes a seed layer. The seed layer 005 is formed on the wall surface of the opening 004 and between the second insulating layer and the conductor post 006.

[0015] <Opening 004> 2, when the cross-sectional area of ​​the opening 004 in this embodiment is converted into the area of ​​a circle, the opening shape (wall surface shape) expands outward, with the diameter increasing from a midpoint in the axial direction (position of smallest diameter) toward the conductor pad 002 (bottom side) as it approaches the conductor pad 002. The midpoint in the axial direction is preferably at least 20% of the thickness of the second insulating resin layer 003 and away from the opening end on the conductor pad 002 side (bottom side).

[0016] Furthermore, when the cross-sectional area of ​​the opening 004 in the embodiment is converted into the area of ​​a circle, the diameter of the opening 004 preferably increases from a midpoint in the axial direction (the position of smallest diameter) toward the opening end (opening end on the exposed side) on the side away from the conductive pad 002 (top side) of the opening 004. The midpoint in the axial direction is preferably 20% or more of the thickness of the second insulating resin layer 003 and away from the opening end on the side away from the conductive pad 002 (opening end on the top side).

[0017] In particular, as shown in Fig. 2, it is preferable that the wall shape of the opening 004 has a contour shape along the axial direction that is a continuous curved shape in the axial direction. A continuous curved shape refers to a shape that has no sharp curvatures (corners) along the axial direction. However, the wall shape of the opening 004 may have a predetermined unevenness (roughness) due to a filler or the like contained in the second insulating resin. By forming the conductive post 006 in a continuous curved shape, it is possible to avoid the formation of localized areas where stress is likely to concentrate, and therefore the conductive post 006 is shaped in a way that makes it less susceptible to cracking and breaking.

[0018] Furthermore, when the cross-sectional area of ​​the opening 004 is converted to the area of ​​a circle, the diameter at the smallest axial position (minimum opening diameter R2) is preferably 50% to 90% of the diameter at the largest axial position (maximum opening diameter R1 or R3). The diameter difference is preferably 60% to 70%. The reason why it is set to 50% or more is that if the difference between the maximum and minimum diameters is too large, the diameter of the minimum diameter part becomes too small, which may weaken the strength of that part.The reason why it is set to 90% or less is that if the bottom side of the base part 6A is expanded outward to increase its strength, the effect of suppressing buckling will be weakened.

[0019] Here, the outer surface shape of the base portion 6A of the conductive post 006 is determined by the wall surface shape of the opening 004, and has the same shape as the opening 004. In other words, by determining the shape of the opening 004, the outer surface shape of the base portion 6A of the conductive post 006 is determined. The present inventors have found that the opening shapes described above can be achieved by adjusting the inorganic filler contained in the resin that constitutes the second insulating resin layer 003, as will be described later.

[0020] 1 and 2 illustrate an example in which the opening shape of the opening 004 has the smallest diameter at the axial center. The position at which the smallest diameter occurs does not have to be the axial center, and may be a position shifted from the thickness center (axial center) to the bottom side or the top side, as shown in FIGS. 5, only the bottom side of the opening 004 may have a shape that widens outward toward the opening end. In other words, the top side does not have to widen outward toward the opening end.

[0021] 6, a recess 011 larger than the opening end of the opening 004 on the conductor pad side may be formed in the conductor pad 002. The opening end on the bottom side of the opening 004 is shaped so that it fits completely within the recess 011 in plan view. In this case, it is possible to form the bottom side of the base portion 6A into a shape that further expands outward toward the conductor pad 002 without increasing the diameter of the opening 004.

[0022] (Operation etc.) With the above-described configuration, in the multilayer wiring board 010 of this embodiment, the strength of the boundary between the conductor pad 002 and the conductor post 006 (the joint portion corresponding to the portion marked with X in FIG. 12), which was previously prone to stress concentration, is significantly increased. As a result, the conductor post 006 is less likely to crack or break, making it possible to provide a multilayer wiring board 010 with high connection reliability. Furthermore, by forming the base portion 6A of the conductor post 006 into a continuous curved shape along the axial direction, even if the base portion 6A has a minimum diameter at a midpoint in the axial direction, stress is prevented from concentrating locally at the minimum diameter position. As a result, it is possible to provide a multilayer wiring substrate 010 that is highly reliable and less susceptible to cracks and breaks.

[0023] (Manufacturing method) The method for manufacturing the multilayer wiring substrate 010 of this embodiment includes, for example, the following steps a to i. a: Step of forming a second insulating resin layer 003 on a first insulating resin layer 001 and a conductor layer 002 b: Step of forming opening 004 c: Step of forming a plating seed layer 005 on the second insulating resin layer 003 d: Step of forming a resist on the seed layer 005 for forming conductor posts 006 using plated copper. e: A process of forming conductor posts 006 using plated copper f: Step of forming a surface treatment layer on the conductor post 006 g: A process for forming a solder layer on the surface treatment layer h: A step of removing the resist i: Step of removing the seed layer 005 that is not covered by the conductor posts 006

[0024] An example of a method for manufacturing the multilayer wiring substrate 010 in this embodiment will be specifically described below with reference to FIGS. A conductor layer is formed in a predetermined pattern on the first insulating resin layer 001 (see FIG. 7(a)). Next, a resin for forming the second insulating resin layer 003 is applied or laminated on the first insulating resin layer 001 and the conductor layer 002 to form the second insulating resin layer 003. After that, a part of the second insulating resin layer 003 is exposed and developed to expose a part of the conductor layer 002 as a conductor pad 002, thereby forming an opening 004 in the second insulating resin layer 003 (see FIG. 7(b)).

[0025] Here, the inventors have found that when forming the opening 004, the second insulating resin layer 003 contains more inorganic filler than conventional ones, the photoinitiator is adjusted, the transmittance of the resin is reduced, and the scattering intensity is increased, so that the exposure light 012 scatters and spreads in the thickness direction of the second insulating resin layer 003 from the top (surface) toward the inside, as shown in Figure 10, and becomes more difficult to reach as it approaches the bottom (bottom), thereby improving the curing range in the direction perpendicular to the thickness between the top and bottom, and making the diameter other than the top and bottom the narrowest after development (the shape of Figure 2).

[0026] Furthermore, we found that it is possible to adjust the thinnest position in the thickness direction by adjusting the exposure dose or by changing the wavelength ratio when exposing with a composite wavelength of g-line, h-line, i-line, etc. This is thought to be because the transmittance or absorptance up to the bottom of the second insulating resin differs depending on the wavelength. Based on these findings, by forming the opening 004 as described above, the opening 004 is formed so that the diameter of the opening becomes wider from the midpoint in the axial direction toward the bottom side, and further, by forming the lower end of the conductor post 006 in the opening 004, the base portion 6A of the conductor post 006 can be formed into an outward-spreading shape.

[0027] Next, although not shown in the manufacturing process, the conductive pad 002 exposed from the opening 004 in the second insulating resin layer may be etched to form a recess 011 larger than the bottom opening diameter R1 of the opening 004 in the second insulating resin layer (see FIG. 6). In this case, the boundary between the conductive pad 002 and the conductive post 006 is located outside the bottom opening diameter R1 of the opening 004, further reducing the risk of stress concentration at the boundary portion, which has low reliability. In addition, the bottom of the conductive post 006 is shaped to sink under the opening 004 in the second insulating resin layer, thereby improving reliability through an anchor effect.

[0028] Next, a plating seed layer 005 is formed on the surface of the conductive pad 002, the side surface of the opening 004 in the second insulating resin layer, and the surface of the second insulating resin layer 003 (see FIG. 7(c)). The plating seed layer 005 is formed by electroless plating or sputtering. When forming it by sputtering, it is preferable to process while tilting and rotating the substrate so that the plating seed layer 005 is also formed on the wall surface near the bottom of the opening 004. Next, a plating resist 009 is applied or laminated on the seed layer 005, and is exposed and developed to form a resist pattern corresponding to the conductor posts 006 (see FIG. 7(d)).

[0029] Next, the conductive posts 006 are formed by electrolytic plating on the seed layer 005 exposed by the resist 009 (see FIG. 8(e)). For example, by using filled plating for the electrolytic copper plating, the top of the conductor post 006 can be made flat or convex without any depression due to the opening 004 in the second insulating resin layer. Also, by using conformal plating for example for the electrolytic copper plating, the top of the conductor post 006 can be intentionally made depressed, thereby suppressing the subsequent spreading of the solder to the side surface of the conductor post 006 during reflow.

[0030] Next, a surface treatment layer 007 is formed on the conductor post 006 (see FIG. 8(f)). The surface treatment layer 007 may be formed of a metal such as tin, nickel, palladium, or gold by electroless plating, or may be formed of an organic coating by spray processing or the like. The surface treatment layer 007 does not necessarily have to be formed. Next, a solder layer 008 is formed on the surface treatment layer 007 (see FIG. 8(g)). The solder layer 008 may be formed, for example, from a solder paste by screen printing, or from tin by electroless plating. Furthermore, if the surface treatment layer 007 is not formed, it can be formed directly on the conductor post 006.

[0031] Next, the solder layer 008 is reflowed to be shaped into a substantially hemispherical shape (see FIG. 9(h)). Note that this step may be carried out after removing the resist 009 (not shown). Next, the resist 009 is removed (see FIG. 9(i)). Next, the seed layer 005 that is not covered by the conductor posts 006 is removed by etching (see FIG. 9(j)).

[0032] (others) The present disclosure may also have the following configuration. (1) A multilayer wiring board comprising: a conductor layer formed on a first insulating resin layer; a second insulating resin layer formed on the first insulating resin layer and the conductor layer, the second insulating resin layer having an opening that exposes a portion of the conductor layer as a conductor pad; a conductor post formed on the conductor pad and protruding from the second insulating resin layer; and a solder layer formed on the conductor post, wherein a root portion of the conductor post located within the opening has an outwardly expanding shape such that, when the cross-sectional area of ​​the root portion is converted into the area of ​​a circle, the diameter increases as it approaches the conductor pad from an axial midpoint of the root portion toward the conductor pad.

[0033] (2) When the cross-sectional area of ​​the root portion is converted to the area of ​​a circle, the root portion has an outwardly expanding shape in which the diameter increases as it approaches the opening end away from the conductor pad from a midpoint in the axial direction of the root portion toward the opening end away from the conductor pad of the opening. (3) The contour shape of the outer surface of the base portion along the axial direction is a curved surface shape that is continuous in the axial direction. (4) When the cross-sectional area of ​​the root portion is converted to the area of ​​a circle, the diameter at the point where the diameter in the axial direction is smallest is 50% or more and 90% or less of the diameter at the point where the diameter in the axial direction is largest. (5) A surface treatment layer is provided between the conductor post and the solder layer. (6) A seed layer is included between the conductor post and the second insulating resin layer and between the conductor pad and the second insulating resin layer. (7) The conductive pad has a recess that is larger than the opening end of the opening on the conductive pad side. [Example]

[0034] Example 1 An example in which the opening 004 is formed by the manufacturing method described in the embodiment will be described. First, the anti-rust film on a copper-clad laminate (manufactured by Showa Denko Materials Co., Ltd.) was removed, and the copper surface was roughened with a roughening solution (manufactured by MEC Co., Ltd.). A dry film solder resist (manufactured by Taiyo Ink Mfg. Co., Ltd.) was then vacuum laminated on top of the copper surface. The main light sources were h-rays and i-rays, and the illuminance ratio was approximately h:i = 70%:100%, resulting in an illumination of approximately 130 mJ / cm. 2 The solder resist was exposed to light at 1000 W and developed by spraying, thereby forming openings 004 in the solder resist. A cross-sectional SEM image of the opening 004 of the solder resist formed by the above-mentioned method is shown in Fig. 11. As shown in Fig. 11, it was found that the opening 004 of the solder resist has a constricted portion with the smallest diameter at a position other than the bottom opening on the conductor side and the top opening on the surface side of the solder resist according to the present invention. [Explanation of symbols]

[0035] 002 Conductor layer (conductor pad) 004 Opening 005 seed layer 006 Conductor post 6A Base part 6B Exposed part 007 Surface treatment layer 008 Solder layer 009 Resist 010 Multilayer wiring board 011 recess 012 Exposure light

Claims

1. A multilayer wiring board comprising: a conductor layer formed on a first insulating resin layer; a second insulating resin layer formed on the first insulating resin layer and the conductor layer, the second insulating resin layer having an opening that exposes a part of the conductor layer as a conductor pad; a conductor post formed on the conductor pad and protruding from the second insulating resin layer; and a solder layer formed on the conductor post, a root portion of the conductive post located within the opening has an outwardly expanding shape in which, when the cross-sectional area of ​​the root portion is converted into the area of ​​a circle, the diameter increases as the root portion approaches the conductive pad from an axial midpoint of the root portion toward the conductive pad, a surface treatment layer is provided between the conductor post and the solder layer; the surface treatment layer is formed of tin, The contour shape of the outer surface of the base portion along the axial direction is a curved surface shape that is continuous in the axial direction, the conductor post has the base portion formed within the opening and an exposed portion that is continuous with the base portion and protrudes from the opening, a cross-sectional area of ​​the base portion at a position closest to the contact pad is smaller than a cross-sectional area of ​​the exposed portion at a position closest to the solder layer; the conductor pad is a portion where a part of the conductor layer is exposed from the opening, and the exposed portion has a recess having an opening diameter larger than an opening diameter of the opening on the conductor pad side, an opening end of the opening on the side of the conductor pad in a plan view is completely within the recess; A multilayer wiring board characterized by:

2. the root portion has an outwardly expanding shape such that, when the cross-sectional area of ​​the root portion is converted into the area of ​​a circle, the diameter increases from an axial midpoint of the root portion toward the opening end of the opening away from the conductive pad, as it approaches the opening end away from the conductive pad.

2. The multilayer wiring board according to claim 1.

3. when the cross-sectional area of ​​the base portion is converted into the area of ​​a circle, the position where the diameter in the axial direction is smallest is located at a position shifted from the axial center portion toward the conductor pad.

3. The multilayer wiring board according to claim 1 or 2.

4. When the cross-sectional area of ​​the base portion is converted into the area of ​​a circle, the position of the base portion having the smallest diameter in the axial direction is shifted from the axial center portion toward the solder layer.

3. The multilayer wiring board according to claim 1 or 2.

5. When the cross-sectional area of ​​the base portion is converted into the area of ​​a circle, the diameter at the position where the diameter is smallest in the axial direction is 50% or more and 90% or less of the diameter at the position where the diameter is largest in the axial direction.

5. The multilayer wiring board according to claim 1, wherein the first and second wiring layers are made of a metal.

6. a seed layer is included between the conductive post and the second insulating resin layer and between the conductive post and the second insulating resin layer and the conductive pad; 6. The multilayer wiring board according to claim 1, wherein the first and second wiring layers are made of a polyimide.

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