JP2010177533A - Wiring board and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wiring board in which the connection strength of a through-hole plating is secured even if not thickening the through-hole plating like before, the thin line processing of the circuit pattern of a substrate surface is possible, moreover, there are few swellings and tapers of a through-hole inner wall in the whole depth direction of the through-hole, and the reduced diameter of the through-hole formed by laser can be attained, and to provide a method of manufacturing the same. <P>SOLUTION: The wiring board includes a base which is prepared with a through-hole, wherein the area of the sidewall of the through-hole is larger than the area of the sidewall at the time of presupposing that the through-hole is a cylinder, and the method of manufacturing the same is disclosed. Moreover, the perimeter shape of the through-hole is a variant shape in a plan view, and is an identical-shape in the whole depth direction of the through-hole in the wiring board and the method of manufacturing the same. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a wiring board and a method for manufacturing the wiring board, and more particularly to a wiring board having a high density and excellent through hole connection reliability and a method for manufacturing the wiring board.

  With the demand for higher density of wiring boards, it is easier to process through holes with a small diameter than drilling, so laser processing is often used for drilling through holes.

  In FIG. 3, a through hole 3 serving as a mask for laser processing is provided in advance on the copper foil 1 on the front surface 15 and the rear surface 16 of the base 2 by providing the through-hole 3. This is an example in which the laser beam is irradiated toward the back side 16 from the side. In this case, the through-hole 3 tends to have a hole diameter that decreases in the through-hole depth direction.

  In FIG. 4, the non-penetrating through hole 3 is preliminarily provided with a window hole 13 serving as a mask for laser processing by etching only on the copper foil 1 on the surface side 15 of the base material 2. This is an example in which the laser beam is irradiated toward the back side 16 from the side. While the opening of the non-penetrating through hole 3 is formed on the front surface side 15 of the base material 2, the back surface side 16 is provided with a portion (bottom surface) 10 that is not penetrating by the copper foil 1. This is a so-called pad-on-via structure, and the copper foil 1 in the non-penetrating portion (bottom surface) 10 can be used as a processed component mounting portion or a free wiring, which meets the demand for higher density. The non-through-hole 3 in this case tends to have a hole diameter that decreases in the depth direction of the through-hole, as in the case of the through-through hole 3.

  In this way, the through hole formed by laser processing has a shape in which the cross-sectional shape of the through hole has a taper in the depth direction of the through hole in both cases of the through through hole and the non-through through hole. There is a tendency that the hole diameter on the back surface side or the bottom surface becomes smaller than the hole diameter. If the hole diameter on the back side or the bottom surface is small, the area around the through-hole plating in this portion is reduced, the plating thickness is reduced, and the connection strength is likely to be reduced. For this reason, when the reliability is evaluated, the through-hole plating around the back surface or the bottom surface often cracks first, and the through-hole is often broken. This is because the through-hole strength on the back side or bottom is low.

  In recent years, due to miniaturization of devices, higher density of wiring boards has been demanded, and accordingly, there has been a demand for smaller hole diameters regardless of whether they are through-holes or non-through-holes. As the diameter of the through hole is reduced, as described above, the through hole formed by laser processing has a taper, so that the hole diameter on the back side or the bottom surface becomes increasingly smaller, resulting in a significant decrease in reliability. It is expected that.

  For higher density by reducing the diameter of the through hole, the base material with the highest heat shrinkage temperature is placed at the top to prevent the through hole diameter from expanding by controlling the bulge and taper formation of the inner wall of the through hole. Then, from the upper surface to the lower surface of the base material, a circuit forming substrate (Patent Document 1) in which the base materials are arranged in the order of high heat shrinkage temperature, and multiple shots while shifting the irradiation position so that the irradiation areas of the pulse laser overlap. A laser processing method to be performed (Patent Document 2) is known.

  Regarding the reliability of the through hole, a manufacturing method (Patent Document 3) in which the inner surface shape of the cross-section of the non-through hole is a concave shape in order to improve the plating coverage at the time of through hole plating, In order to make it easier to enter, there is known a wiring board (Patent Document 4) having a non-through-through hole having a long hole shape and a side surface shape having an inclination angle extending from the bottom to the surface.

JP 11-330649 A JP 2003-053560 A JP 2000-022337 A JP 2001-203456 A

  In order to cope with the higher density of the wiring board, it is necessary to reduce the diameter of the through hole, but at the same time, reliability must be ensured. At present, the diameter of the through hole is at a level that can be mass-produced at a minimum of about 100 μm to 150 μm, and it is difficult to stabilize and ensure the reliability of the through hole having a smaller hole diameter.

  In such a small-diameter through hole, in order to ensure reliability, a method of dealing with increasing the copper plating thickness of the through hole has been adopted, but at the same time the copper thickness of the substrate surface will increase, When producing a circuit pattern in a subsequent process, there are problems such as difficulty in thin wire processing.

  According to Patent Documents 1 and 2, since the hole diameter formed by the laser can be controlled so as not to expand in the thickness direction of the substrate, high density can be achieved, but the hole diameter of the through hole can be achieved over the entire thickness direction of the substrate. Since the plating solution is difficult to enter the through-hole because it is the same cylindrical shape, especially in the non-through-hole, there is a problem in reliability because the through-hole plating is poorly attached to the bottom of the through-hole and the connection strength is weak. .

  In Patent Documents 3 and 4, since the plating around the through hole is improved, the reliability can be improved, but the through hole formed by the laser has a relatively large inner wall bulge and taper. There is a problem that it is difficult to increase the density by reducing the diameter.

  The present invention has been made in view of the above problems, and it is possible to ensure the connection strength of the through-hole plating without increasing the thickness of the through-hole plating as in the prior art. Provided is a wiring board that can be processed and that has a small through-hole in the through-hole in the entire depth direction of the through-hole, and that can reduce the diameter of the through-hole formed by a laser, and a method for manufacturing the same. The purpose is to do.

The present invention relates to the following.
(1) A wiring board including a base material provided with a through hole, wherein a side wall area of the through hole is larger than a side wall area when the through hole is a cylinder.
(2) The wiring board according to (1), wherein an outer peripheral shape of the through hole is an irregular shape in a plan view and has the same shape over the entire depth direction of the through hole.
(3) The wiring board according to (2), wherein the through hole has an outer peripheral shape that is a wavy shape, a jagged shape, or a polygonal shape in plan view.
(4) The wiring board according to any one of (1) to (3), wherein unevenness or grooves or protrusions on the side wall formed by the shape of the outer periphery of the through hole are continuous in the depth direction of the through hole.
(5) The wiring board according to any one of the above (1) to (4), wherein the through hole is a non-through hole, and the non-penetrating portion is formed of a copper foil.
(6) The wiring board according to (5), wherein the outer periphery of the non-penetrating portion of the through hole has an irregular shape.
(7) After forming a window hole serving as a laser processing mask on the copper foil on the substrate, a laser is irradiated through the window hole to form a through hole in the substrate in the region corresponding to the window hole. In the method of manufacturing a board, the outer peripheral shape of the window hole is a wavy shape, a jagged shape or a polygonal shape in plan view, and the wiring board forms a through hole having the same shape over the entire depth direction of the through hole Manufacturing method.
(8) In a method of manufacturing a wiring board in which a laser beam is irradiated from above a copper foil on a base material to form a through hole in the base material together with the copper foil, the laser beam diameter is fixed, and the beam diameter of 5 Of the wiring board that forms a through hole that has the same shape throughout the depth direction of the through hole, while the outer peripheral shape of the through hole is an irregular shape in plan view while being moved at a pitch of 70% to 70%. Production method.

  According to the present invention, since the connection strength of the through-hole plating can be ensured without increasing the thickness of the through-hole plating as in the prior art, the fine patterning of the circuit pattern on the surface of the substrate becomes possible. Since there is little swelling or taper of the inner wall of the through hole over the entire depth direction of the hole, it is possible to provide a wiring board that can reduce the diameter of the through hole formed by the laser and a manufacturing method thereof.

It is sectional drawing in each process of the non-through-through hole of Example 1, 2 of this invention, and the through-hole outer peripheral shape of planar view. The side wall of the non-penetrating through hole of Example 2 of the present invention is observed by SEM obliquely from above (the side wall of the through hole formed with a UV laser). It is the cross-section of the through-hole of a conventional example, and the through-hole outer periphery shape of planar view. It is sectional drawing after through-hole plating of the non-through-hole of a comparative example (conventional example), and the through-hole outer periphery shape of planar view.

  As an example of the wiring board of the present invention, as shown in FIGS. 1 and 2, a wiring board 5 including a base material 2 provided with a through hole 3 can be cited.

  As a base material, what is generally used as a wiring board or a substrate for semiconductor mounting can be used. As such, for example, in addition to glass cloth epoxy resin-impregnated copper-clad laminates, glass non-woven cloth epoxy resin-impregnated copper-clad laminates and polyimides with copper foil bonded on both sides are used for flexible wiring boards. Resin copper clad laminate and the like. As a layer structure of the wiring board, it can be used for a multilayer board as well as a double-sided double-layer board.

  The through holes include all through holes that have a function as a through hole such as a through hole that penetrates the base material, a non-through hole, a stack via, a buried via, and an IVH (interstitial via hole). In the case of a non-penetrating through hole, for example, the non-penetrating portion (bottom surface) is made of copper foil, and the non-penetrating portion (bottom surface) of the copper foil can be used as a processed component mounting portion or free wiring. The so-called pad-on-via structure is also included.

  The through-hole can be formed by drilling, but it is more preferable to use a laser because it is easy to control the outer peripheral shape of the through-hole. As a laser used for processing, a carbon dioxide laser, a YAG laser, or the like used for manufacturing a wiring board or a semiconductor mounting substrate can be used.

  The processing of the side wall after the formation of the through hole can remove the resin residue by a desmear process using permanganic acid, which is used for manufacturing a wiring board or a semiconductor mounting board. For the through-hole plating, conventional techniques such as electrolytic copper plating and electroless copper plating, which are used for manufacturing a wiring board and a substrate for mounting a semiconductor, can be used as they are. Subsequent circuit pattern formation, solder resist formation, plating treatment, and the like can use processes, materials, and equipment that use conventional techniques as they are.

  The through hole is formed such that the area (surface area) of the side wall of the through hole is larger than the area of the side wall when the through hole is a cylinder. This is possible because the inner wall of the through hole is not flat as in the case where the through hole is a cylinder, but has irregularities, grooves, or protrusions. For this purpose, it is desirable that the outer peripheral shape of the through hole is an irregular shape in plan view, and is the same shape throughout the depth direction of the through hole. Here, the irregular shape means that the outer periphery of the through hole is not a simple circle. For example, the outer periphery of the through hole may be a wavy shape, a jagged shape or a polygonal shape in plan view. Further, the same shape over the entire depth direction of the through hole may not be a completely identical shape, and is a conventional level taper (the hole diameter of the through hole on the surface side of the substrate is 100 μm, This includes cases where the shape and size change due to the taper of the hole diameter on the back surface side of about 90 μm.

  As a result, the amount of through-hole plating formed on the through-hole side wall is greater than when the through-hole side wall is flat. It becomes easy to do. In addition, when the through-hole side wall is not flat, the length of the outer edge of the through-hole side wall in the depth direction (that is, the portion reaching the copper foil on the front and back of the substrate) Therefore, the through-hole plating is connected to the copper foil on the front and back of the substrate. For this reason, a through hole having excellent connection reliability can be formed.

  It is desirable that the irregularities or grooves or protrusions on the side wall formed by the shape of the outer periphery of the through hole be kept straight in the depth direction of the through hole while maintaining the shape. In this way, unevenness or grooves or protrusions on the side wall are continuously straight in the depth direction of the through hole, thereby forming unevenness or grooves or protrusions continuous in the depth direction of the through hole, Since the depth direction of the through hole is smooth, the penetration of the plating solution into the through hole becomes difficult to be prevented during the through hole plating, and the plating coverage is improved.

  It is desirable that the through hole is a non-penetrating through hole, the non-penetrating portion is made of copper foil, and the outer periphery of the non-penetrating portion of the through hole has an irregular shape. Thereby, since the length of the outer periphery of the end portion in the depth direction of the side wall of the through hole (that is, the portion reaching the copper foil of the non-penetrating portion) is longer than that of a simple cylindrical through hole, The portion where the through-hole plating is connected to the copper foil on the front and back of the substrate is enlarged. For this reason, a through hole having excellent connection reliability can be formed.

  For example, such an irregular shape on the outer periphery of the through hole corresponds to the window hole by forming a window hole serving as a mask for laser processing on the copper foil on the substrate and then irradiating the laser through the window hole. It can be formed by a wiring board manufacturing method (so-called conformal mask method) in which through holes are formed in the base material in the region. For example, in this case, the outer peripheral shape of the window hole is a wavy shape, a jagged shape or a polygonal shape in plan view, and the outer shape of the through hole is obtained by laser processing using the window hole of such a shape as a mask. Through-holes having substantially the same shape can be formed over the entire depth direction of the through-hole. The outer peripheral shape of the window hole can be freely formed by a method such as a so-called subtract method used when forming a circuit pattern of a wiring board.

  As another method of forming a deformed shape on the outer periphery of the through-hole, a method of manufacturing a wiring board (so-called direct) that directly irradiates a laser from a copper foil on a substrate and forms a through-hole in the substrate together with the copper foil. (Laser construction method). Trepan processing, spiral processing, circle processing, etc. can be used as a method of making the outer peripheral shape of the through hole into a wavy shape, a jagged shape or a polygonal shape in plan view. For example, by fixing the laser beam diameter to about 25 μm and moving it so as to draw a circle with a pitch of about 5% to 70% of the beam diameter, the outer shape of the through hole becomes a wavy shape and a jagged shape in plan view. Through holes having irregular shapes such as shapes or polygonal shapes and having substantially the same shape over the entire depth direction of the through holes can be formed. The pitch of the laser beam is more preferably about 10% to 50% in order to secure the through hole plating and the strength of the through hole.

  Examples of the present invention will be described below, but the present invention is not limited thereto.

Example 1
[Step (a)]
As shown in FIG. 1 (a), a polyimide resin copper-clad laminate in which a copper foil 1 having a thickness of 12 μm is bonded to both surfaces of a base material 2 (product name MB12-25-12CEG, manufactured by Nippon Steel Chemical Co., Ltd.) Prepared.
[Step (b)]
As shown in FIG. 1B, the window hole 13 was formed in the copper foil 1 by a subtracting method using a photolithograph. The outer peripheral shape 14 of the window hole 13 was a jagged shape with a protrusion-groove pitch of about 10 μm. Moreover, the diameter of the window hole 13 was 150 micrometers, 100 micrometers, 50 micrometers, and 30 micrometers in the diameter outside.
[Step (c)]
As shown in FIG. 1C, the through hole 3 penetrating through the 12 μm copper foil 1 and the 25 μm polyimide substrate 2 was opened by laser processing (carbon dioxide laser). The outer peripheral shape 11 of the through hole 3 is a jagged shape having a projection and groove pitch of about 10 μm in plan view, and the through hole 3 having substantially the same shape is formed over the entire depth direction of the through hole 3. . The diameter of the through hole 3 was 150 μm, 100 μm, 50 μm, and 30 μm on the outside of the jagged shape.
[Step (d)]
As shown in FIG. 1D, after performing desmearing using permanganic acid, a through-hole plating 4 was formed to a thickness of 4 μm by electrolytic copper plating.

(Example 2)
[Step (a)]
As shown in FIG. 1 (a), a polyimide resin copper-clad laminate in which a copper foil 1 having a thickness of 12 μm is bonded to both surfaces of a base material 2 (product name MB12-25-12CEG: product name) manufactured by Nippon Steel Chemical Co., Ltd. Prepared.
[Step (c)]
Unlike Example 1, without forming the window hole 13, as shown in FIG.1 (c), the through-hole 3 which penetrates to 12 micrometer copper foil 1 and 25 micrometer polyimide base material 2 is laser-processed ( (UV-YAG laser). As the processing method, circle processing was used, the laser beam diameter was set to about 25 μm, and the through hole 3 was formed by moving in a circle at a pitch (about 20 μm) of 40% of the beam diameter. The outer peripheral shape 11 of the through hole 3 is a jagged shape having a projection and groove pitch of about 10 μm in plan view, and the through hole 3 having substantially the same shape is formed over the entire depth direction of the through hole 3. . The diameter of the through hole 3 was 150 μm, 100 μm, 50 μm, and 30 μm on the outside of the jagged shape. In addition, the result of having observed the through hole 3 in the case of 100 micrometers in diameter by SEM is shown in FIG. 2 as an example.
[Step (d)]
As shown in FIG. 1D, after performing desmearing using permanganic acid, a through-hole plating 4 was formed to a thickness of 4 μm by electrolytic copper plating.

(Comparative example)
[Step (b)]
As shown in FIG. 4, the window hole 13 was formed in the copper foil 1 by the subtract method using the photolithograph similarly to Example 1, and the through-hole plating 4 was formed in thickness of 4 micrometers by the electrolytic copper plating. Unlike Example 1, the outer peripheral shape 14 of the window hole 13 was circular. Except this, it is the same as the first embodiment. As shown in FIG. 4, the outer peripheral shape 12 of the through hole 3 is circular in plan view, and the through hole 3 having substantially the same shape is formed over the entire depth direction of the through hole 3.

  About Examples 1, 2 and the comparative example, the hot oil test was done and the connection reliability of the through hole was tested. The hot oil test was performed by repeating the cycle of 260 ° C., 10 seconds to 25 ° C., 10 seconds, and measuring the resistance of through holes on the front and back of the substrate every predetermined number of cycles. The number of cycles until the resistance value increased by 10% from the initial value was counted. The results are shown in Table 1. It was found that the reliability of the through hole was significantly improved in the case of the jagged shape of the present invention as compared to the case of the conventional circular shape. Moreover, since reliability was ensured even if it became a hole with a smaller diameter than a comparative example, it turned out that a densification is possible.

DESCRIPTION OF SYMBOLS 1 ... Copper foil, 2 ... Base material, 3 ... Through-hole (through-through hole or non-through-through hole), 4 ... Through-hole plating, 5 ... Wiring board, 6 ... Outer periphery shape (before plating), 7 ... Peripheral shape of through hole (after plating), 8 ... side wall, 9 ... unevenness or groove or protrusion, 10 ... non-penetrating part (bottom surface), 11 ... outer shape of through hole (before plating), 12 ... through hole Peripheral shape (after plating), 13 ... Window hole, 14 ... Peripheral shape of window hole, 15 ... Front side, 16 ... Back side

Claims (8)

  A wiring board comprising a base material provided with a through hole, wherein a side wall area of the through hole is larger than a side wall area when the through hole is a cylinder.   The wiring board according to claim 1, wherein an outer peripheral shape of the through hole is an irregular shape in a plan view and has the same shape throughout the depth direction of the through hole.   3. The wiring board according to claim 1, wherein the through hole has an outer peripheral shape that is a wavy shape, a jagged shape, or a polygonal shape in plan view.   4. The wiring board according to claim 1, wherein unevenness or grooves or protrusions on the side wall formed by the shape of the outer periphery of the through hole are continuous in the depth direction of the through hole.   5. The wiring board according to claim 1, wherein the through hole is a non-through hole, and the non-penetrating portion is made of a copper foil.   6. The wiring board according to claim 5, wherein an outer periphery of a through hole in a non-penetrating portion has an irregular shape.   Manufacturing a wiring board that forms a through hole in a base material in a region corresponding to the window hole after forming a window hole as a mask for laser processing on a copper foil on the base material and then irradiating a laser through the window hole In the method, the outer peripheral shape of the window hole is a wavy shape, a jagged shape or a polygonal shape in a plan view, and a method of manufacturing a wiring board in which a through hole having the same shape is formed throughout the depth direction of the through hole .   In a method of manufacturing a wiring board in which a laser beam is irradiated from above a copper foil on a base material to form a through hole in the base material together with the copper foil, the laser beam diameter is fixed, and from 5% to 70% of the beam diameter. %, The through hole has an irregular shape in plan view, and forms a through hole having the same shape throughout the depth direction of the through hole.

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