JP7567182B2 - Circuit board manufacturing method - Google Patents

Description

The present invention relates to a circuit board and a method for manufacturing a circuit board.

Large Scale Integration (LSI) devices such as CPUs (Central Processing Units) and FPGAs (Field Programmable Gate Arrays) used in computers are increasing in number of pins as transmission speeds increase, while at the same time there is a demand for smaller board sizes and higher density mounting. This has resulted in a trend towards an increase in the number of wires connecting between components, and it has become necessary to provide a large number of through-hole vias in multi-layer circuit boards to connect and pull out the power supply layers of LSIs and components, and these through-hole vias can take up a lot of space on the circuit board. Furthermore, if you try to avoid connections using these through-hole vias, it becomes difficult to secure the wiring area on the circuit board where the circuit patterns should be located.

The multi-layer circuit board manufactured by the method described in Patent Document 1 has a structure in which a conductor layer that becomes a via is formed on the inner circumference of a small-diameter first through hole, then a second through hole that is larger in diameter than the first through hole is formed, and a conductor that becomes a via is formed on the inner circumference of this second through hole, thereby providing independent vias in the first and second through holes.

The multi-layer circuit board described in Patent Document 2 is configured such that through holes are formed by machining using drills of two different diameters, one large and one small, and a conductor layer that will become a via is formed in each through hole, and then a larger diameter drill is used to partially remove the conductor layer that will become the via, thereby forming multiple vias that are separated from each other.

The multilayer circuit board described in Patent Document 3 is configured as a manufacturing method in which a conductor layer that becomes a via formed on the inner surface of a through hole is cut using a drill with a smaller diameter than the through hole.

JP 2015-185735 A JP 2005-235963 A Japanese Patent Application Publication No. 8-330735

However, the circuit board described in Patent Document 1 requires repeated machining steps to form through holes and chemical processing steps such as plating to form a conductor layer on the inner circumference of the through holes, which complicates the manufacturing process.

The circuit board described in Patent Document 2 requires a machining process to form through holes, a chemical processing process such as plating to form a conductor layer on the inner circumference of the through holes, and a machining process to remove part of the conductor layer that has been formed. Since it is necessary to remove all of the unnecessary conductor layer in the subsequent machining process, there is an issue that the conductor layer that is removed is wasted.

In addition, the circuit board described in Patent Document 3 discloses a cutting process in which a drill is moved inside the through hole, but does not clearly indicate how the cutting edge at the tip of the drill, which has a smaller diameter than the through hole, acts to cut the via on the inner circumference of the through hole at the desired location.

The purpose of this invention is to facilitate the manufacture of circuit boards with vias for connecting layers.

In order to solve the above problems, the present invention proposes the following means.
A circuit board according to a first aspect of the present invention comprises a laminated board constructed by repeatedly stacking conductor layers, core layers, and prepreg layers in multiple layers, a through hole penetrating the laminated board in the thickness direction and having an inner diameter gradually increasing from one side of the laminated board to the other side, and a plurality of conductor vias provided on the inner periphery of the through hole in a plurality of regions separated from each other in the thickness direction of the laminated board, and electrically connected to conductor layers of the laminated board corresponding to each region.

The method for manufacturing a circuit board according to the second aspect of the present invention includes the steps of forming a laminated board by stacking multiple conductor layers, core layers, and prepreg layers, forming a through hole that penetrates the laminated board in the thickness direction, forming a conductor via connected to the conductor layer on the inner surface of the through hole, and cutting the conductor via by rotating the cutting tool within the conductor via with the thickness direction of the laminated board as the center of rotation, thereby dividing the conductor via into multiple pieces.

The present invention makes it easy to manufacture circuit boards in which each conductor layer is connected by multiple split vias.

FIG. 2 is a cross-sectional view showing an example of a minimum configuration of the first embodiment of the present invention. FIG. 11 is a cross-sectional view of a circuit board according to a minimum configuration example of the second aspect of the present invention. 2 is a cross-sectional view of the substrate according to the first embodiment of the present invention before a through hole is provided therein. FIG. 3 is a cross-sectional view of the substrate according to the first embodiment of the present invention after a through hole is provided therein. FIG. 5 is a cross-sectional view of the through hole of FIG. 4 after conductor plating has been applied thereto. FIG. 5 is a cross-sectional view of the via of FIG. 4 with a cutting tool inserted therein; 7 is a cross-sectional view showing a circuit in a circuit board in which a via is divided by the process of FIG. 6. FIG. 8 is a cross-sectional view showing a current flow in the modified example of FIG. 7 . FIG. 11 is a cross-sectional view of a circuit board according to a second embodiment of the present invention after a through hole is provided therein. 10 is a cross-sectional view of the through hole of FIG. 9 in a state where conductor plating has been applied thereto. FIG. 11 is a cross-sectional view of the via of FIG. 10 with a cutting tool inserted therein; 12 is a cross-sectional view showing a circuit in a circuit board in which a via is divided by the process of FIG. 11 . 12 is an explanatory diagram of the relationship between the cutting tool shown in FIG. 11 and the inner diameter of a through hole. FIG. FIG. 11 is a cross-sectional view of a substrate according to a third embodiment of the present invention after a through hole is provided therein. 15 is a cross-sectional view of the through hole of FIG. 14 after conductor plating has been applied thereto. FIG. 16 is a cross-sectional view of the via of FIG. 15 with a cutting tool inserted therein. 17 is a cross-sectional view showing a circuit in a circuit board in which a via is divided by the process of FIG. 16.

The minimum configuration of a circuit board according to a first aspect of the present invention will be described with reference to FIG.
Reference numeral 1 denotes a laminated substrate, which is constructed by repeatedly stacking a conductor layer 2, a core layer 3, and a prepreg layer 4 in a plurality of layers. The laminated substrate 1 has a through hole 5 penetrating the substrate in the thickness direction and gradually expanding in inner diameter from one surface (upper surface in FIG. 1) of the laminated substrate 1 to the other surface (lower surface in FIG. 1), and a plurality of conductor vias 6 provided on the inner periphery of the through hole 5 in a plurality of regions separated from each other in the thickness direction of the laminated substrate 1 and electrically connected to the conductor layers 2 of the laminated substrate 1 corresponding to each region.

In the illustrated example, if the inner diameter of the through hole 5 on one surface side is d1 and the inner diameter of the other surface side is d2, then:
The relationship is d1<d2. The conductive via 6 is formed, for example, by plating the inner surface of the through hole 5 with a metal or by inserting a tapered cylindrical conductor having a similar shape, and is divided into two parts, an upper part and a lower part.

When forming the conductor vias 6 on the inner surface of the through hole 5, which has different inner diameters at the top and bottom, the inner surface of the through hole 5 is coated with plating of a conductor such as metal, and the multiple conductor vias 6 can be separated by cutting with a cutting tool such as a drill having an outer diameter intermediate between d1 and d2. Therefore, by optimally setting the outer diameter of the cutting tool, a circuit board with multiple conductor vias separated at required locations can be manufactured by the simple process of moving the cutting tool in the axial direction.

In the circuit board of the above configuration, as shown by arrow A in Figure 1, current can flow from the top conductor layer 2 through the upper conductor via 6 to the second conductor layer 2A from the top. That is, the conductor circuit formed by the top conductor layer 2 and the conductor circuit formed by the second conductor layer 2A can be electrically connected by the upper conductor via 6. Also, as shown by arrow B, current can flow from the bottom conductor layer 2 through the lower conductor via 6 to the second conductor layer 2B from the bottom.

The minimum configuration of the method for manufacturing a circuit board according to the second aspect of the present invention will be described with reference to FIG.
In the second aspect, a circuit board is manufactured by the steps of: laminating multiple conductor layers 2, core layers 3, and prepreg layers 4 to form a laminated substrate 1; forming a through hole 5 penetrating the laminated substrate 1 in the thickness direction; forming a conductor via 6 connected to the conductor layer 2 on the inner surface of the through hole 5; and cutting the conductor via 6 by rotating a shank 8 of a cutting tool 7 within the conductor via 6 with the thickness direction of the laminated substrate 1 as the center of rotation, thereby forming a plurality of conductor vias 6 divided in the vertical direction.

In the manufacturing method of the above configuration, the cutting tool 7 is rotated and moved in the direction of the rotation center axis and in the direction intersecting the rotation center, thereby dividing the conductor via 6 covering the inner surface of the through hole 5 in the thickness direction of the laminated substrate 1. For example, by cutting and removing the conductor via 6 between the second conductor layer 2A and the conductor layer 2B below it, the conductor via 6 is divided into upper and lower parts, and a current can flow from the uppermost conductor layer 2 to the second conductor layer 2A. Also, a current can flow from the lower conductor via 6 to the lowermost conductor layer 2 to the lower conductor via 6 to the second conductor layer 2B from below.

First Embodiment
A method for manufacturing a circuit board according to a first embodiment of the present invention, which is realized by embodying Figures 1 and 2, will be described with reference to Figures 3 to 8. Note that in the figures, the same reference numerals are used for the same components as those in Figures 1 and 2, and the description will be simplified.
As shown in FIG. 3, a conductor layer 2 and a core layer 3 are laminated to form a laminated substrate 1A.
4, a through hole 5 is formed penetrating the laminated substrate 1 in the thickness direction. In the illustrated example, the through hole 5 has a constant inner diameter.
5, the inner periphery of the through hole 5 is plated with a conductor such as a metal to form an integral conductor via 16. The conductor via 16 is formed so as to cover the surface of each conductor layer 2 and is electrically connected.

As shown in FIG. 6, a cutting tool 7 with a turning radius smaller than the inner diameter of the inner surface of the through hole 5 (specifically, the plating layer that constitutes the conductor via 16 on the inner circumference of the through hole 5), for example a milling cutter that performs rotary cutting on the circumference and end face defined in JIS B0172, is inserted into the through hole 5, and the shank 8, which serves as the center of rotation, is moved in the axial direction and in a direction perpendicular to the shank 8 using a milling machine or the like, thereby cutting the conductor via 16 in the vertical direction in FIG. 6 and dividing it into multiple conductor vias 6.

By cutting and removing the conductor via 16 between the second conductor layer 2A and the conductor layer 2B below it by machining with a cutting tool 7 shown in FIG. 6, the conductor via 16 can be divided into upper and lower parts as shown in FIG. 7. As a result, as shown by arrow A, a current can flow from the uppermost conductor layer 2 to the second conductor layer 2A via the upper conductor via 6. Also, as shown by arrow B, a current can flow from the lowermost conductor layer 2 to the lower conductor via 6 via the lower conductor via 6 to the second conductor layer 2B from below. Therefore, by designing the wiring pattern in advance assuming that the conductor via 6 will be cut, it becomes possible to use the conductor via 16, which was originally a single cylinder provided in the same through hole 5, in multiple circuits (circuit patterns). In other words, since it is now possible to use a single conductor via in multiple circuits, the number of conductor vias used to transfer between wiring across different layers of the laminated substrate 1 is reduced, and the reduction in wiring ability due to conductor vias (the reduction in the degree of freedom in wiring due to the reduction in the area on the surface of the laminated substrate that can actually be wired) is mitigated, improving wiring ability and enabling higher density component mounting.

Figure 8 shows a modified example in which the conductor via 16 is divided into three. As shown in Figure 8, by continuously cutting and removing a portion of the conductor via 16 between the second conductor layer 2A and the conductor layer 2C below it in the circumferential direction, the conductor via 16, which was an integral cylinder, is divided into an upper conductor via 6 and a lower conductor via 6, so that a current can flow from the uppermost conductor layer 2 to the second conductor layer 2A as shown by the arrow A. Furthermore, by continuously cutting and removing a portion of the conductor via 16 between the conductor layer 2D and the conductor layer 2B below it in the circumferential direction, a current can flow from one conductor layer 2C in the middle part to the other conductor layer 2D via the conductor via 6 in the middle part as shown by the arrow C. Furthermore, by cutting the conductor via 16, a current can flow from the lowermost conductor layer 2 to the conductor layer 2B as shown by the arrow B.

That is, by dividing the conductor via 16 into two or three parts on the same axis using cutting processing and electrically insulating them from each other, it is possible to provide a number of circuits in the laminated substrate 1A that corresponds to the number of divided conductor vias 6. Therefore, compared to providing conductor vias at multiple locations along the surface direction of the laminated substrate 1A, in other words providing multiple conductor vias, the area on the substrate that can be used to form the circuit pattern is less taken up by the conductor vias, and the area of the laminated substrate 1A can be used effectively.

Second Embodiment
A second embodiment of the present invention which embodies the embodiment shown in Fig. 1 will be described with reference to Fig. 9 to Fig. 13. Note that in the figures, components common to Fig. 1 to Fig. 8 are given the same reference numerals and the description will be simplified.
The laminated substrate 1B of the second embodiment has a tapered through hole 5A whose inner diameter gradually increases from one surface on the upper side in FIG. 9 to the other surface on the lower side in FIG.
9 shows the shape after the tapered through hole 5A is formed in the laminated substrate 1B having the conductor layer 2, the core layer 3, and the prepreg layer 4. The through hole 5A is formed, for example, by forming a through hole as a pilot hole with a drill having an outer diameter corresponding to the minimum diameter, and then mechanically enlarging the inner diameter with a cutting tool such as a reamer having a shape corresponding to the taper to be formed, or by mechanically processing using a milling cutter.

Figure 10 shows the state where a conductor via 16A electrically connected to the conductor 2 is formed on the inner surface of the through hole 5A formed in Figure 9. That is, in the process of Figure 10, the inner circumference of the through hole 5A is plated with a conductor such as metal to form an integral conductor via 16A. This conductor via 16A is formed with a constant thickness on the inner circumference surface of the through hole 5A, so it has a tapered shape with the same inclination as the through hole 5A.

A cutting tool 7A (in the illustrated example, a tool such as a drill with a cutting edge at the tip defined in JIS B0171) is inserted into the conductor via 16A from below (the side with the larger inner diameter) and rotated around the axis of the shank 8, cutting and removing the conductor via 16A until the inner diameter becomes equivalent to the outer diameter of the tip of the cutting tool 7A.

Specifically, as shown in FIG. 13, the cutting tool 7A has an outer diameter Dx, and this outer diameter Dx satisfies the relationship d1<Dx<d2 with respect to the minimum diameter d1 and maximum diameter d2 of the through hole 5A.
That is, when the cutting tool 7A is inserted into the conductor via 16A while being rotated, the cutting edge at the tip of the cutting tool 7A starts cutting and removing the conductor via 16A from a point where the inner diameter of the conductor via 16A coincides with the outer diameter Dx of the cutting tool 7A. Then, when the cutting tool 7A is inserted until the outer diameter Dx of the cutting tool 7A coincides with the inner diameter dx of the through hole 5A, a predetermined range of the conductor via 16A, more specifically, the conductor layer formed by plating, is removed, and the conductor via 16A is divided into a plurality of conductor vias 6. This drill processing can be performed by simply moving the cutting tool in the axial direction, and can therefore be performed by a relatively simple machine tool such as a drill press.

FIG. 11 shows the state in the middle of cutting the conductor via 16A with the cutting tool 7A. When the cutting tool 7A is inserted to a predetermined depth, conductor vias 6 that are electrically insulated from each other are formed at two locations, upper and lower, as shown in FIG. 12.
That is, as shown by arrow A, a current can flow through a path passing through the upper conductor layer 2, the upper conductor via 6, and the conductor layer 2A. Also, as shown by arrow B, a current can flow through a path passing through the lower conductor layer 2, the lower conductor via 6, and the conductor layer 2B.

Note that by performing cutting using a cutting tool with a smaller diameter than the cutting tool 7A shown in FIG. 11, the conductive vias 16A can be cut and removed further up than in FIG. 12, thereby dividing the conductive vias 16A at even more locations and increasing the number of conductive vias 6. Note that before cutting with the cutting tool 7A shown in FIG. 11, cutting may be performed using a cutting tool with a larger diameter to cut and remove the conductive vias 16A further down than in FIG. 12.

In other words, by performing cutting while changing the diameter of the cutting tool (drill) from large to small diameter, the conductor via 16A can be divided into two in the axial direction (thickness direction of the board), or even into three depending on the design requirements of the circuit board, and multiple conductor vias can be formed that are electrically insulated from each other.
Therefore, compared to the case where conductor vias are provided in multiple locations along the surface direction of the laminated substrate, the area on the substrate that can be used to form a circuit pattern is less occupied by conductor vias, and the area of the laminated substrate 1A can be used effectively.
Furthermore, if a milling cutter is used as the cutting tool, the conductor via 16A can be divided at a predetermined location by moving the cutting tool in the axial direction and in a direction intersecting the axis, without having to change to a drill of a different diameter as in the case of using the drill described above.

By cutting and removing the conductor via 6 between the second conductor layer 2A and the conductor layer 2B below it by machining with the above cutting tool, the conductor via 16A can be divided into upper and lower parts as shown in FIG. 7. As a result, as shown by arrow A, current can flow from the top conductor layer 2 to the second conductor layer 2A via the upper conductor via 16A. Also, as shown by arrow B, current can flow from the bottom conductor layer 2 to the second conductor layer 2B from below via the lower conductor via 16A.

Third Embodiment
A third embodiment of the present invention which embodies the embodiment shown in Fig. 1 will be described with reference to Figs. 14 and 15. In the drawings, components common to those shown in Figs. 1 to 13 are given the same reference numerals and their description will be simplified.
The laminated substrate 1C in Fig. 14 has a through hole 5 whose inner diameter is larger on the side of the other surface on the lower side of Fig. 14 than on the side of the one surface on the upper side of Fig. 14. In detail, a cutting tool such as a drill having an outer diameter equivalent to the inner diameter of the through hole 5A is inserted from one surface to the other surface shown in Fig. 14 to form a small-diameter through hole 5A that penetrates at least halfway through the thickness direction of the laminated substrate 1C, and then a cutting tool such as a drill having an outer diameter equivalent to a through hole 5B having a larger diameter than the through hole 5A is inserted from the other surface to the one surface to form a large-diameter through hole 5B that penetrates halfway through the thickness direction of the laminated substrate 1C.

By repeating such cutting processing using a drill, a through hole 5 having a stepped shape with different inner diameters as shown in FIG. 14 is formed.
Fig. 15 shows a state in which a conductor via 16A electrically connected to the conductor 2 is formed on the inner surface of the through holes 5A and 5B shown in Fig. 14. That is, in the process of Fig. 15, a process such as plating is performed on the inner circumference of the through hole 5A with a conductor such as a metal to form an integral conductor via 16B. This conductor via 16B is formed with a constant thickness on the inner circumference surface of the through holes 5A and 5B.

15, a drill having an outer diameter slightly smaller than the inner diameter of conductor via 16B covering the inner periphery of lower through hole 5B and larger than the inner diameter of upper through hole 5A is inserted from the other surface (lower side) of laminated substrate 1C to cut and remove conductor via 16B in the portion between through holes 5A and 5B, dividing conductor via 16B into the inner periphery portion of through hole 5A and the inner periphery portion of through hole 5B. In other words, two conductor vias 6 divided vertically are formed, and each conductor via 6 is connected to conductor layers 2A, 2B.
Instead of the examples shown in FIGS. 14 and 15, the through holes 5 having different inner diameters may be formed in multiple stages to divide the conductor vias 16B into even more sections.

By cutting and removing the conductor via 16B between the second conductor layer 2A and the conductor layer 2B below it by machining with the above cutting tool, the conductor via 16B can be divided into upper and lower parts as shown in FIG. 16. As a result, as shown by arrow A, current can flow from the top conductor layer 2 to the second conductor layer 2A via the upper conductor via 6. Also, as shown by arrow B, current can flow from the bottom conductor layer 2 to the second conductor layer 2B below via the lower conductor via 6.

The above describes an embodiment of the present invention in detail with reference to the drawings, but the specific configuration is not limited to this embodiment, and design changes and the like that do not deviate from the gist of the present invention are also included.

The present invention can be used in circuit boards and their manufacturing methods.

REFERENCE SIGNS LIST 1 laminated substrate 2, 2A, 2B conductor layer 3 core layer 4 prepreg layer 5, 5A, 5B through hole 6 conductor via 7, 7A cutting tool 8 shank 16, 16A, 16B conductor via

Claims (1)

A step of laminating a plurality of conductor layers, core layers, and prepreg layers to form a laminated substrate;
forming a through hole penetrating the laminated substrate in a thickness direction;
forming a conductor via connected to the conductor layer on an inner peripheral surface of the through hole;
a step of rotating a cutting tool around an axis along a thickness direction of the laminated substrate within the conductor via to cut the conductor via and divide it into a plurality of pieces in the thickness direction;
having
the through hole has an inner diameter larger on one surface side of the laminated substrate than on the other surface side, and the inner diameter gradually increases from one surface to the other surface of the laminated substrate;
a first through hole on the one surface side, a second through hole on the other surface side, and an intermediate through hole having the same inner diameter and disposed between the first through hole and the second through hole,
the cutting tool is a drill, and the drill is moved in an axial direction of the conductor via to divide the conductor via into a plurality of parts and separate them from each other above and below the intermediate through hole;
The drill is selected from a plurality of types having an outer diameter between the maximum diameter portion and the minimum diameter portion of the through hole depending on the division location of the conductor via .
A method for manufacturing a circuit board.

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