JP2007067276A - Printed wiring board and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a printed wiring board having a through-hole with a high aspect ratio in which the plating thickness of the inner wall of the through-hole is increased sufficiently, and having a fine circuit pattern in the outer layer. <P>SOLUTION: The board includes a fine circuit pattern 14 and a through-hole 12. The fine circuit pattern 14 is formed by a plating 62 on a copper foil 20 which is held on a temporary substrate 50 to allow delamination, and is exposed on the surface after being transferred to a main substrate 16 with the copper foil. In the through-hole 12, a pad 22 is formed on the copper foil 20. The pad 22 of the through-hole 12 is formed on the copper foil 20 that has been transferred to the main substrate 16 from the temporary substrate 50. The fine circuit pattern 14 is the one that has been formed on the copper foil 20 of the temporary substrate 50 by plating and transferred to the main substrate 16. Therefore, the fine circuit pattern 14 can be made sufficiently thin. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a printed wiring board having an outer fine circuit pattern and a through hole, and a method for manufacturing the same.

  In recent years, high-density mounting of electronic components is required, and miniaturization of circuit patterns formed on printed wiring boards and high aspect ratios of through holes are required. Here, the aspect ratio is the ratio 1 / d of the depth l to the inner diameter (the inner diameter of the through hole processed in the substrate) d of the through hole.

JP2003-273488

  Patent Document 1 discloses that a fine circuit pattern cannot be formed if the conductor layer on the surface of the substrate is thick, so that the fine circuit pattern is formed after the surface conductor layer is thinned by etching and polishing. That is, if the plating thickness of the inner wall of the through hole is set to a sufficient thickness (30 μm), the plating layer on the substrate surface also becomes thick (about twice the plating thickness of the inner wall of the through hole, which is 60 μm). After closing, the surface conductor layer (plating layer) is thinned by etching and polishing. For example, the conductor layer is made 36 μm by etching and is thinned to 28 μm by polishing. Thereafter, a fine circuit pattern is formed by a known pattern forming process.

  In the method disclosed in Patent Document 1, since the pad formed in the opening of the through hole is thinned by etching and polishing, the connecting portion between the plated layer on the inner wall of the through hole and the pad is also thinned. It becomes weak and it becomes easy to generate | occur | produce a crack (crack). For this reason, there exists a problem that the reliability and durability of a printed wiring board fall.

  On the other hand, in the case of a high aspect ratio through-hole, if the plating thickness of the inner wall of the through-hole is made sufficiently thick, the surface plating layer becomes excessively thick and it becomes difficult to make the outer layer circuit pattern finer.

  In addition, when copper plating the inner wall of a through hole, it is known that the plating layer on the surface of the substrate can be made substantially the same thickness as the plating layer of the inner wall of the through hole by performing electrolytic plating at a low current density (Patent Document 1). , Paragraph 0006). In this case, however, it is impossible to make the surface conductor layer (plating layer) thinner than the plating layer on the inner wall of the through hole. Since this plating layer is formed on the copper foil (12 μm) on the substrate surface, the total thickness is reduced. Was about (30 + 12 =) 42 μm and could not be made sufficiently thin.

The present invention has been made in view of such circumstances, and it is a first object of the present invention to provide a printed wiring board having a through hole having a high aspect ratio in which the plating thickness of the inner wall of the through hole is sufficiently thick and an outer fine circuit pattern. 1 purpose.
A second object is to provide a method for manufacturing the printed wiring board.

  According to the present invention, a first object is to form a fine circuit pattern which is formed by plating on a copper foil releasably held on a temporary substrate and exposed to the substrate after being transferred to the substrate together with the copper foil, and the copper It can be achieved by a printed wiring board comprising a through hole having a pad formed on a foil.

  A second object is to provide a method for manufacturing a printed wiring board having an outer layer fine circuit pattern and a through hole. Providing a temporary substrate having a copper foil peelable on its surface; b. Forming a resist on the copper foil on the surface of the temporary substrate and forming grooves corresponding to the fine circuit pattern by exposure and development; c. A groove corresponding to the fine circuit pattern formed in step b is plated with a metal conductor having at least a plating layer in contact with the copper foil of the temporary substrate as a copper etch resistance; d. Removing the resist formed in step b, e. Laminating the final substrate through the prepreg, f. Peel off the temporary substrate leaving the copper foil on the substrate side, g. Processing through-hole holes in the substrate, and applying thick copper plating to the surface and inner walls of the through-hole holes; h. This is achieved by a method for producing a printed wiring board comprising the above steps a to h, wherein at least a fine circuit pattern is exposed by etching.

  According to the invention of claim 1, since the pad of the through hole is formed on the copper foil transferred from the temporary substrate to the main substrate, the plating thickness of the connecting portion between the plating layer on the inner wall of the through hole and the pad is set. It can be thick enough. For this reason, the strength of the connection portion between the inner wall of the through hole and the pad can be increased, and the reliability and durability of the circuit can be improved. In addition, the fine circuit pattern on the surface is the one formed by plating the copper foil of the temporary board to the main board, so it can be made sufficiently thin, and the line width and line spacing can be made sufficiently small to increase the wiring density. Can do.

  According to invention of Claim 3, the manufacturing method of this printed wiring board is obtained. Moreover, since the surface of the fine circuit pattern is not polished by merely removing the copper foil and the thick copper plating layer by etching (step h), the line spacing of the circuit pattern can be reduced.

  On the surface (outer layer) of the substrate, an outer layer circuit pattern formed by thick copper plating together with through holes and pads on the copper foil and connected to a fine circuit pattern can be formed. In this case, the outer layer circuit pattern is formed by laminating the copper foil and the thick copper plating layer, so that the electric resistance can be sufficiently reduced. Therefore, by connecting the fine circuit pattern to the outer layer circuit pattern, it is possible to suppress an increase in the DC electric resistance due to the miniaturization of the line sectional area of the fine circuit pattern. That is, it is possible to sufficiently avoid the inconvenience due to the increase in electrical resistance of the fine circuit pattern.

  The temporary substrate used in step a in the invention of claim 3 is suitably a laminate of a copper foil laminate in which a copper foil and a copper foil carrier are detachably laminated via a release layer on an insulating plate (invention 4). . Here, the copper foil carrier is sufficiently thicker (about 70 μm) than the copper foil, and is handled as a copper foil laminate that is laminated on the thin copper foil in order to protect and support the thin copper foil (about 9 μm). Usually a thin copper foil is applied to the substrate and the thick carrier is then peeled off. In this case, the copper foil transferred to the substrate is a thick copper foil carrier, but this copper foil is removed together with the copper plating so as to expose at least a fine circuit pattern by etching in step h. It is desirable in terms of shortening the processing time. For this purpose, a copper foil laminate is preferably attached (laminated) to the temporary substrate so that the copper foil carrier is in close contact.

  When the copper foil and the copper plating are removed in the step h, the metal conductor plating layer that becomes the fine circuit pattern in the step c needs to remain without being removed together with the copper foil and the copper plating. For that purpose, at least the surface in contact with the copper foil is made of a metal that is not removed by copper etching (copper etching resistance), for example, gold plating. In this case, it is preferable that nickel and copper are stacked on the gold plating. This is because the amount of expensive gold plating used is reduced.

  In step h, if the copper foil and the copper plating are removed leaving the through-hole pad and the normal outer layer circuit pattern that does not require fine circuit formation, a normal (non-fine circuit) circuit pattern is formed on the outer layer. (Claim 7).

  1-6 is a figure which shows the manufacturing process from which this invention differs in order. 1 is a diagram showing a temporary substrate, FIG. 2 is a diagram showing a process of forming a metal conductor plating layer to be a fine circuit pattern on the temporary substrate, FIG. 3 is a diagram showing a lamination process of the substrate, and FIG. 4 is a temporary substrate. FIG. 5 is a view showing a through-hole plating step, and FIG. 6 is a step showing exposing a fine circuit pattern portion by removing copper plating and copper foil by etching. FIG. FIG. 7 is a plan view showing an example of the surface pattern of the substrate after completion of processing, FIG. 8 is a sectional view taken along line VIII-VIII, and FIG. 9 is a process flow chart.

  The printed wiring board according to the present invention has a structure shown in FIGS. That is, the printed wiring board 10 is formed with a through hole 12 having a high aspect ratio and a fine circuit pattern 14. Here, the through hole 12 is formed by forming a through hole 18 having a hole diameter of 0.3 mm on a substrate (main substrate) 16 having a plate thickness of 3.0 mm, for example. In this case, the aspect ratio of the through hole 18 is 10. Is preferably 5 or more, particularly 7 or more.

  When copper plating of 30 μm is performed on the inner wall surface of the through hole 18, a plating layer having a thickness approximately twice (60 μm) can be formed on the surface of the normal substrate 16. When the plating layer on the surface becomes thick, it becomes impossible to make a fine pattern when the plating layer is etched to form a circuit pattern. As described above, it is possible to make the plating layer on the surface approximately the same as the plating thickness of the inner wall of the through hole by performing electrolytic plating at a low current density. In this case as well, the plating thickness of the surface is about It is 30 μm, and it is difficult to miniaturize the circuit pattern.

  In the present invention, as will be described later, the fine circuit pattern 14 is transferred to the substrate (main substrate) 16 together with the copper foil 20 after the fine circuit pattern 14 formed by plating on the copper foil 20 which is releasably held on the temporary substrate is plated. The unnecessary copper foil 20 remaining on the surface is removed so as to be exposed on the surface of the substrate (main substrate) 16. The pad 22 of the through hole 12 is formed on the copper foil 20 transferred to the substrate 16.

  Next, a manufacturing method is demonstrated based on FIG. First, a temporary substrate 50 shown in FIG. 1 is prepared (step a in FIG. 9). The copper foil 20 is detachably held on the surface of the temporary substrate 50. As the temporary substrate 50, for example, a double-sided copper-clad laminate in which the copper foil carrier 52 is not peeled off can be used. That is, the copper-clad laminate is a copper foil laminate in which the copper foil 20 (thickness of about 9 μm) and a copper foil carrier 52 (thickness of about 70 μm) for protecting and supporting the copper foil 20 are peeled off by the release layer 53. After bonding 54, only the copper foil carrier 52 is peeled off. In this case, the temporary substrate 50 can be used without peeling off the copper foil carrier 52. Therefore, in this case, the copper foil carrier 52 becomes the copper foil 20 of the present invention.

  However, as will be described later, since the copper foil 20 is removed by etching, a thin one is desirable in order to shorten the processing time. Therefore, here, the copper foil laminate 54 is affixed to the temporary substrate 50 so that the thin copper foil 20 is exposed on the surface (lower surface). In addition, although the thin copper foil 56 is affixed on the other surface (upper surface) of this temporary board | substrate 50, this may be omitted.

  A resist 58 is formed on the copper foil 20 of the temporary substrate 50 thus prepared by applying a dry film or applying a resist solution, and the resist 58 is provided with a groove 60 corresponding to a fine circuit pattern by exposure and development. Form (step b in FIG. 9, FIG. 2).

  The groove 60 is plated in the order of gold, nickel, and copper (step c in FIG. 9). The metal conductor 62 formed by this plating is transferred to the main substrate 16 to become the fine circuit pattern 14 as described later (see step f). The surface of the metal conductor 62 that is in contact with the copper foil 20 (in this embodiment, a gold plating layer) preferably has a property (etching resistance) that is not etched when the copper foil 20 is removed by etching in the later-described step h. .

  Next, the resist 58 is removed (step d). For this reason, as shown in FIG. 3A, the metal conductor 62, which is a plating layer that becomes the fine circuit pattern 14, remains on the copper foil 20 of the temporary substrate 50.

  An inner layer material 66 is laminated on the surface of the copper foil 20 of the temporary substrate 50 via a prepreg 64 and thermocompression bonded (step e, (A) and (B) in FIG. 3). Here, appropriate inner layer circuit patterns 68 and 68 are formed on the inner layer material 66. The laminated body of the prepreg 64 and the inner layer material 66 becomes the substrate of the printed wiring board 10 that is the final product, that is, the main substrate 16.

  The temporary substrate 50 is peeled from the laminated body of the temporary substrate 50, the prepreg 64, and the inner layer plate 66, leaving the copper foil 20 on the main substrate 16 side (step f, see FIG. 4). Since the copper foil 20 is laminated on the copper foil carrier 52 through the release layer 53 so as to be peeled off, the copper foil 20 can be easily peeled off at the release layer 53 which is an adhesive surface between them.

  Thus, the through-hole 18 used as the through hole 12 is processed in this board | substrate 16 which peeled the temporary board | substrate 50 (FIG. 4). And thick copper plating 70 is formed in the inner wall surface of this through-hole 18, and the surface of this board | substrate 16 (process g, FIG. 5). By performing the copper plating 70 at a low current density, it is possible to alleviate unevenness between the plating thickness of the surface and the plating thickness of the inner wall of the through hole 18.

  Next, the unnecessary copper plating 70 and the underlying copper foil 20 are removed from the surface of the copper plating 70 by known photoetching. That is, the pad 22 of the through-hole 12 and other outer layer circuit patterns 72 (FIGS. 7 and 8) are covered with a resist, and the copper plating 70 and the copper foil 20 in other regions are removed by copper etching (step h, FIG. 6). .

  As a result, the metal conductor 62 is exposed while being embedded in the surface of the substrate 16. That is, a fine circuit pattern 14 is formed.

  The outer layer circuit pattern 72 left on the surface can be connected to the fine circuit pattern 14 as shown in FIGS. That is, the metal conductor 62 is connected to the outer layer circuit pattern 72 via the copper foil 20. Since the outer layer circuit pattern 72 is sufficiently thicker than the fine circuit pattern 14 and has a large cross-sectional area, the DC electric resistance is reduced. For this reason, the fine circuit pattern 14 is formed only in the region where the wiring density is increased, thereby avoiding inconvenience due to the increase in electric resistance.

Diagram showing the structure of the temporary substrate Diagram showing metal conductor formation process Diagram showing the lamination process of this substrate The figure which shows the processing process of the through hole of the through hole Diagram showing copper plating process Diagram showing the removal process of unnecessary copper plating and copper foil The figure which shows the example of the surface circuit pattern of the printed wiring board VIII-VIII sectional view in FIG. Flow chart of manufacturing process

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Printed wiring board 12 Through hole 14 Fine circuit pattern 16 This board 18 Through hole of through hole 20 Copper foil 22 Pad of through hole 50 Temporary substrate 52 Copper foil carrier 53 Peeling layer 54 Copper foil laminated body 58 Resist 60 Groove 62 Metal conductor 70 Copper plating (thick copper plating)
72 Outer layer circuit pattern

Claims (7)

A fine circuit pattern exposed on the surface after being formed by plating on the copper foil releasably held on the temporary substrate and transferred to the substrate together with the copper foil,
A through hole in which a pad is formed on the copper foil;
A printed wiring board comprising:   2. The printed wiring board according to claim 1, wherein an outer layer circuit pattern formed by thick copper plating together with through holes and pads and connected to a fine circuit pattern is formed on the copper foil on the outer layer. In the method of manufacturing a printed wiring board having an outer layer fine circuit pattern and a through hole,
a. Prepare a temporary substrate that holds the copper foil peelable on the surface,
b. Form a resist on the copper foil on the surface of this temporary substrate, form grooves corresponding to the fine circuit pattern by exposure and development,
c. In a groove corresponding to the fine circuit pattern formed in step b, a metal conductor having a copper layer etching resistance at least on a plating layer in contact with the copper foil of the temporary substrate is plated,
d. Removing the resist formed in step b;
e. Laminate this substrate as the final substrate through the prepreg,
f. Remove the temporary substrate, leaving the copper foil on the main substrate side,
g. Process through-hole holes in this board, apply thick copper plating to the surface and inner walls of the through-hole holes,
h. At least a fine circuit pattern is exposed by etching,
A manufacturing method of a printed wiring board provided with the above process ah.   4. The method of manufacturing a printed wiring board according to claim 3, wherein the temporary substrate in step a is obtained by laminating a copper foil laminate in which a copper foil and a copper foil carrier are releasably laminated on an insulating plate.   The method for producing a printed wiring board according to claim 4, wherein the copper foil laminate is laminated with a copper foil carrier adhered to an insulating plate.   The method of manufacturing a printed wiring board according to claim 3, wherein the metal conductor in step c is obtained by laminating gold, nickel, and copper plating in order from the copper foil side of the surface of the temporary substrate.   4. The method of manufacturing a printed wiring board according to claim 3, wherein in step h, the copper plating and the copper foil are removed while leaving the through-hole pad and the outer layer circuit pattern that does not require fine circuit formation.

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