Printed wiring board and manufacturing method thereof

Abstract

To provide a printed wiring board that does not break by thickening a portion of the part that contacts a land through hole filling plating.SOLUTION: A printed wiring board in which electrical continuity between the front and back surfaces is achieved by electrical continuity between lands provided on the front and back surfaces, a circular through hole contained in the land partially has a protruding shape toward the outer periphery of the land, and the through hole is filled with copper inside, thereby providing electrical continuity between the lands provided on the front and back surfaces.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a printed wiring board in which through holes are filled with copper plating and lands are connected to the filling plating. [Background technology]

[0002] 2. Description of the Related Art Conventionally, there are printed wiring boards in which holes penetrating from the front surface side to the back surface side of the printed wiring board are filled with copper plating. Typically, through holes are drilled to form circular through holes from the front side to the back side. Wiring called lands is formed around the through hole on the front side or back side. Furthermore, a metal layer is formed on the inner wall of the through hole by electroless plating to connect with the land, enabling electrical continuity between the front and back sides. Electrical continuity between the front and back sides can also be achieved by filling the through hole with copper plating to form hole filling plating. After the lands on the front and back are electrically connected, the printed wiring board is completed through various processes. If through holes are formed by blasting from both sides, the through holes will be narrower near the center.

[0003] Filling plating for such through holes starts on the inner wall near the center of the through hole. The plating continues to adhere to both surfaces and comes into contact with the lands on the front and back. If the filling plating in the area that comes into contact with the lands is thin (shallow), it may cause a break in the connection. Patent Document 1 discloses that when copper plating is formed on the inner wall of a through hole by electroless plating, the surface layer portion of the through hole is made into a funnel-shaped opening. Patent Document 2 discloses a filling method that reduces defects in plugging plating. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 10-126025 [Patent Document 2] Patent Publication No. 2019-214795 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a printed wiring board in which a portion of the portion in contact with the land is thickened by the filling plating, thereby preventing discontinuity in electrical continuity between the land and the filling plating. [Means for solving the problem]

[0006] A first aspect of the present invention is a printed wiring board in which electrical conductivity between the front and back surfaces is achieved by electrical conductivity between lands provided on the front and back surfaces, characterized in that a circular through hole contained in the land has a protruding shape that partially points toward the outer periphery of the land, and the through hole has a copper filling inside the through hole, thereby providing electrical conductivity between the lands provided on the front and back surfaces.

[0007] A second aspect of the present invention is a printed wiring board according to the first aspect, characterized in that the projection shape in the first aspect is narrow on the side close to the outer periphery of the land and wide on the side in contact with the through hole.

[0008] A third aspect of the present invention is a printed wiring board, characterized in that the protrusion shape in the first and second aspects is formed in the direction of wiring connected to the land.

[0009] A fourth aspect of the present invention is a method for manufacturing a printed wiring board, comprising the steps of: forming a resist mask having an opening with a pattern of through holes, the through holes having a protruding shape, which is narrow on a side close to the outer periphery of the land and wide on a side contacting the through hole, in a direction of wiring connected to a land, on the copper layers on the front and back of the insulating layer of a substrate material; using the resist mask formed on the front and back of the substrate material as a resist mask for etching, and removing the copper layer exposed from the openings by etching; using the resist mask used for the resist mask for etching as a resist mask for blasting, and removing the insulating layer exposed from the openings from the front and back sides by blasting to form through holes; and filling the through holes with copper plating. [Brief description of the drawings]

[0010] [Figure 1] Fig. 1a is a schematic diagram of a printed wiring board according to the present invention, showing the shape of a through hole formed in a land of the printed wiring board, (a0) is a plan view explaining the shape of a through hole having a protrusion shape according to the present invention, (a1) is a cross-sectional view taken along line "a-a'" in the plan view (a0). Fig. 1b is a schematic diagram of a printed wiring board according to a conventional example, (b0) is a plan view explaining the shape of a circular through hole, and (b1) is a cross-sectional view taken along line "b-b'" in the plan view (b0). [Diagram 2] FIG. 1 is a flow chart of a manufacturing process for a printed wiring board according to the present invention, in which (a0) is a cross-sectional view of a resist mask having protruding openings, (a1) is a plan view of a resist mask having protruding openings, (b) is a cross-sectional view after etching of the copper layer having protruding openings, (c0) is a cross-sectional view after blasting processing having protruding openings, (c1) is a plan view after blasting processing having protruding openings, (d0) is a cross-sectional view after peeling off the resist mask for blasting processing having protruding openings, (d1) is a plan view after peeling off the resist mask for blasting processing having protruding openings, (e) is a cross-sectional view after filling plating with protruding openings, and (f) is a cross-sectional view after forming a circuit pattern with protruding openings. [Diagram 3] FIG. 2 is an enlarged view of the vicinity of a land of a printed wiring board according to the present invention. [Figure 4] This is a manufacturing process flow diagram of a conventional printed wiring board, where (a0) is a cross-sectional view of a conventional resist mask, (a1) is a plan view of a conventional resist mask, (b) is a cross-sectional view after conventional copper layer etching, (c) is a cross-sectional view of an insulating layer by conventional blast processing, (d0) is a cross-sectional view after the conventional resist mask for blast processing has been peeled off, (d1) is a plan view after the conventional resist mask for blast processing has been peeled off, (e) is a cross-sectional view after conventional hole-filling plating, and (f) is a cross-sectional view after conventional circuit pattern formation. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] In hole filling plating using copper plating, the copper sulfate plating bath generally contains a suppressor that suppresses plating growth and an accelerator that promotes plating growth. The deposition theory of hole filling plating is that first, the accelerator is uniformly adsorbed to the inner wall of the through hole and the surface of the substrate. Then, as the plating grows, the surface area of ​​the inner wall of the through hole decreases, so the accelerator on the inner wall of the through hole becomes denser. As a result, the plating growth rate inside the through hole becomes faster than the plating growth rate on the surface of the substrate, and the through hole is filled with plating. Therefore, by creating a portion where the surface area of ​​the inner wall of the through hole decreases faster than the inner wall of other portions, the plating speed of that portion is further increased, promoting the filling plating of that portion and making the plating thicker. In other words, by making the part of the through hole where it connects to the land convex and the land side concave, the plating growth speed of the convex part of the through hole is increased and a thick filling plating is formed in the part where it connects to the land, which makes it possible to prevent disconnection.

[0012] A method for manufacturing a printed wiring board embodying the features of the above-described filling plating for through holes of the present invention will be described below with reference to the manufacturing process flow diagram of FIG. 2 and the plan view of the printed wiring board of the present invention in FIG. 1(a0). First, a board material is prepared having copper layers 2 on both sides of an insulating layer 3. This board material is not shown in FIG. 2, which shows the manufacturing process flow, but the reference numerals used in FIG. 1 and FIG. 2 are the same. A specific form of the board material is generally a copper-clad laminate having a total thickness of 34 to 370 μm, with a copper layer of 2 to 35 μm formed on an insulating layer. Next, as shown in Figures 2(a0) and (a1), a resist mask 1 is formed on the copper layers 2 on both the front and back sides of the copper-clad laminate of the prepared substrate material, the resist mask 1 having through-hole openings 5 ​​which are substantially circular (usually circular) through-hole patterns protruding in the direction of wiring 9 connecting to lands 8 (see Figure 1(a1)) and having protruding openings 4 which are narrow on the side close to the outer periphery of the lands 8 and wide on the side in contact with the through-hole openings 5. Next, the resist masks 1 formed on both the front and back surfaces of the substrate material are used as resist masks for etching, and the copper layer 2 exposed from the through-hole openings 5 ​​is removed by etching (see FIG. 2(b)).

[0013] Next, the same resist mask 1 is used as a blasting resist mask, and blasting is performed from the front and back sides of the substrate material to remove the insulating layer 3 exposed from the through-hole opening 5, thereby forming a through-hole 6 (see Figures 2(c0) and (c1)). The through hole 6 formed by this blasting process has a protruding through portion 14 that is generally triangular, trapezoidal, arc-shaped, or the like, narrow on the side closer to the outer periphery of the land 8 and wide on the side in contact with the through hole 6, toward the wiring 9 (see FIG. 1(a0)) that connects to the land 8 (see FIG. 1(a0) and (a1)) (see FIG. 2(c1)). The corners of the generally triangular or trapezoidal shape are rounded. Next, a power supply metal film 10 is formed on the inner wall of the through hole 6 by electroless plating (see FIGS. 2(d0) and (d1)).

[0014] Next, the through-hole 6 having the power supply metal film 10 thereon is filled with a copper plating layer 7 by hole filling plating. The copper plating layer 7 formed by filling plating is formed in a commonly used copper sulfate plating bath, which contains additives such as a brightener component, a leveller component, a polymer component, and a chlorine component. This hole-filling plating causes the plating growth rate to be faster in the protrusion penetration portion 14 of the through hole 6 than in the circular portion of the through hole 6, and a protrusion copper plating layer 7a is reliably formed in the portion connected to the land (see FIG. 2(e)). The printed wiring board has a plurality of through holes to be filled with filler plating, and even if there are through holes with poor filling properties due to variation, the phenomenon in which the plating thickness at the connection portion with the land becomes thin can be prevented, thereby ensuring a reliable connection with the land. Next, resist masks for forming wiring circuits are provided on the front and back surfaces of the substrate, and then the desired wiring circuits are formed by etching to complete the printed wiring board (see FIG. 2(f)). EXAMPLES

[0015] The present invention will be described in detail below with reference to examples. EXAMPLES

[0016] A test printed wiring board according to an embodiment as shown in Fig. 3 was produced in accordance with the manufacturing process flow of the present invention as shown in Fig. 2. It has a shape having a copper plating layer 7 of φ60 μm by hole-filling plating in the center of a land 8 of outer diameter φ80 μm, a through-hole shape in which a wiring 9 of 10 μm width is connected to the land, and a hole-filling plating protrusion 7a according to the present invention.

[0017] <Manufacturing of printed wiring boards> A printed wiring board having a through-hole shape according to the present invention shown in Fig. 3 was produced according to the manufacturing process flow of Fig. 2. The following mainly describes the production of the through-hole shape according to the present invention. First, a copper-clad laminate was prepared as a substrate material, in which a 12 μm-thick copper layer was formed on both sides of a 0.2 mm-thick insulating layer made of glass epoxy resin. Next, in order to obtain the through-hole shape of Figure 3, a resist layer with a thickness of 25 μm was formed on both sides of the substrate material, and a resist mask 1 was formed having an opening pattern such that a through-hole shape would be formed in the φ60 μm through-hole in the direction of the wiring (see Figure 3, number 9, wiring width: 10 μm) connecting to the φ80 μm land (see Figure 3, number 8), with a protrusion length (see Figure 3, number 12) to the side near the outer periphery of the land of 30 μm, and a protrusion width (see Figure 3, number 11) of 26 μm on the side contacting the through-hole (see Figures 2(a0) and 2(a1)).

[0018] The resist mask thus formed was used as a resist mask for etching, and etching was carried out to remove the copper layer exposed through the openings of the resist mask (see FIG. 2(b)). Next, using the same resist mask as a resist mask for blasting, blasting was performed from one surface side of the substrate material to a depth approximately to the center of the insulating layer 3, and then blasting was performed from the other surface side to form through holes 6 (see Figures 2(c0) and 2(c1)). After that, the resist mask 1 was removed (see Figures 2(d0) and (d1)).

[0019] Next, a metal film (copper plating film) 10 having a thickness of several μm was formed on the inner wall of the through hole 6 by electroless plating (see FIG. 2(d0) and FIG. 2(d1)). In the process of making the through hole, in the conventional example, an opening is made in the resist mask so that the through hole pattern is circular (see Figures 4(a0) and 4(a1)), but in the present invention, a through hole opening 5 is made by adding a protrusion shape to only one side of the part where the circle connects with the circuit wiring pattern (see Figures 2(a0) and 2(a1)).

[0020] Next, the through-hole 6 having the power supply metal film 10 is filled with a copper plating layer 7 by hole filling plating (see FIG. 2(e)). The copper plating layer 7 formed by this hole-filling plating is performed in a commonly used copper sulfate plating bath, and additives (nonionic surfactants, gloss agents, levelers, etc.) such as brightener components, leveler components, polymer components, and chlorine components are added.

[0021] This hole-filling plating causes the plating growth rate to be faster at the protrusion opening 4 of the through-hole 6 than at the circular portion of the through-hole 6, and a protrusion copper plating layer 7a is reliably formed at the portion connected to the land 8 (see FIG. 2(e)). The printed wiring board has a plurality of through holes to be filled with filler plating, and even if there are through holes with poor filling properties due to variation, the phenomenon in which the plating thickness at the connection portion with the land becomes thin can be prevented, thereby ensuring a reliable connection with the land.

[0022] Next, resist masks for forming wiring circuits are provided on the front and back surfaces of the substrate, and then the desired wiring circuits are formed by etching to complete the printed wiring board (see FIG. 2(f)). In the printed wiring boards produced by the manufacturing method of the present invention, the rate of defective wire breaks in the plugging plating is extremely low as compared with the printed wiring boards produced by the conventional method, and defective wire breaks are suppressed very well.

[0023] (Conventional example) A conventional printed wiring board was produced under the same conditions as in Example 1 according to the manufacturing process flow shown in FIG. 4, and the plugging plating was evaluated for disconnection defects by measuring electrical resistance using a four-terminal method. The incidence rate of breaks in the filling plating was about 0.1% per month. [Explanation of symbols]

[0024] 1. Resist mask 2 Copper Layer 3. Insulation layer 4 protrusion opening 5 Through hole opening 6 Through holes 7 Filling plating area (copper plating layer) 7a Hole-filling plating protrusion (protrusion copper plating layer) 8 Land 9 Wiring 10 (Power supply) Metal film 11 Width of filling plating protrusion 12 Length of filling plating protrusion 14 protrusion penetration part

Claims

1. A printed wiring board in which electrical continuity between the front and back surfaces is achieved by electrical continuity between lands provided on the front and back surfaces, A printed wiring board characterized in that a circular through hole contained in the land has a protruding shape partially extending toward the outer periphery of the land, and the through hole has a copper filling inside the through hole, thereby providing electrical conductivity between the lands provided on the front and back surfaces.

2. 2. The printed wiring board according to claim 1, wherein the projection has a shape narrower on a side closer to an outer periphery of the land and wider on a side in contact with the through hole.

3. 3. The printed wiring board according to claim 1, wherein the protrusion is formed in a direction of a wiring connected to the land.

4. forming a resist mask on the copper layers on the front and back of an insulating layer of a substrate material having copper layers on the front and back of the insulating layer, the resist mask having an opening with a pattern of the through hole having a protruding shape narrow on a side close to the outer periphery of the land and wide on a side contacting the through hole in a direction of wiring connecting to the land; a step of removing the copper layer exposed from the opening by etching using the resist masks formed on the front and back surfaces of the substrate material as an etching resist mask; a step of using the resist mask used as the etching resist mask as a blast resist mask, and removing the insulating layer exposed from the opening from the front side and the back side by blast processing to form a through hole; a hole filling plating step of filling the through hole with copper plating; A method for producing a printed wiring board, comprising:

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