JPH06169144A - Manufacture of printed wiring board - Google Patents

Abstract

PURPOSE:To improve a copper etching operation in accuracy when a fine pattern smaller than a specific value is formed through a printed wiring board manufacturing method. CONSTITUTION:Applying properties of tin that electroless plating tin is substituted with copper nearly in the ratio of 1 to 1, a photosensitive resin resist layer 17 is selectively formed on the specific part of a copper plating layer 5 formed on both sides of a board 1, and the exposed copper plating layer 5 is replaced with an electroless tin plating layer 8 at a certain depth. The copper plating layer 5 thinned by separating off tin metal is removed by copper etching solution, whereby copper is lessened in amount of etching in a vertical direction and etching time, and thus a fine pattern can be formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a printed wiring board, and more particularly to a method for manufacturing a printed wiring board which improves the accuracy of a wiring pattern and is compatible with high density of the pattern.

[0002]

2. Description of the Related Art Due to recent advances in downsizing, weight reduction, and enhancement of functions of electronic equipment, the degree of integration of semiconductors to be mounted has increased, the number of mounted parts on a printed wiring board has increased, and the pattern of a printed wiring board has a higher height. Densification is becoming a problem.

As a conventional method for producing a high density pattern, there is a pattern forming method using an electrodeposition resist (ED resist) as shown in FIG.

In this manufacturing method, first, as shown in FIG. 5A, for example, a thickness of 12 is formed on the front and back surfaces of a substrate 1 having a thickness of 1.6 mm.
A copper foil 2 having a thickness of μm is attached to form a copper-clad laminate 3, and a through hole 4 is formed in the copper-clad laminate 3 with a drill having a diameter of 0.4 mm. Next, as shown in FIG. 5B, a copper plating layer 5 having a thickness of 25 μm is formed on the entire surface of the copper-clad laminate 3 including the through holes 4, and through holes 6 are formed.

Next, as shown in FIG. 5C, a resist is applied on the entire surface by electro-deposition on the copper plating layer 5 including the through holes 6, and the ED resist layer is subjected to ultraviolet exposure and development processes using a photo tool. 11 is formed to a thickness of 20 μm.

Next, as shown in FIG. 5 (d), the exposed copper layer consisting of the copper plating layer 5 and the copper foil 2 is removed by etching, and then the ED resist layer 11 is peeled off with 3% sodium hydroxide. As shown in FIG. 5 (e), for example, a photo solder resist is applied by screen printing, then exposed to ultraviolet rays using a photo tool, developed with 1% sodium carbonate, and cured by heating at 130 ° C. for 45 minutes. The solder resist layer 9 is formed.

[0007]

In the prior art, the ED is used.
After the resist layer 11 is formed, a pattern is formed in the step of etching the copper layer including the copper plating layer 5 and the copper foil 2. At this time, if the copper layer is thick and the gap between the wiring patterns is narrow, a short circuit occurs between the skirt portions of the wiring patterns. In addition, since the width of the wiring pattern is narrowed due to the lateral etching at the time of etching, the width of the wiring pattern covered with the ED resist cannot be narrowed.

Therefore, when etching the copper layer,
The pattern width and its gap must be designed in consideration of the ratio formed by the difference between the etching amount in the vertical direction of the copper layer and the etching amount in the horizontal direction, which is called an etching factor, and if the copper layer is thick, Inevitably, both the wiring pattern gap width and the wiring pattern width must be increased.
For example, when the sum of the thicknesses of the copper foil 2 and the copper plating layer 5 is 50 μm, the pattern width and the pattern gap width need to be 100 μm or more. Therefore, in order to further increase the pattern density, in order to form a fine pattern, a method of preventing a short circuit between pattern skirts in the gap between the fine patterns by thinning the thickness of the copper layer in the vertical direction Is generally known.

However, in order to reduce the thickness of the copper layer, a method of reducing the thickness of the copper foil 2 of the copper-clad laminate 3,
There is a method of thinning the copper plating layer 5 for forming the through hole 6. However, when the thickness of the copper foil 2 of the copper-clad laminate 3 is advanced, there is a problem in that the adhesive force between the resin base of the substrate 1 and the copper foil 2 is lost. There is a problem that the reliability of the hole 6 is lost.

An object of the present invention is to provide a method for producing a printed wiring board, which comprises forming a fine pattern by replacing electroless tin-based plating with copper, peeling it off, and etching the remaining thinned copper. To provide.

[0011]

In order to achieve the above object, a method of manufacturing a printed wiring board according to the present invention is a print including a resist coating step, a plating step, a plating stripping step, and a fine pattern forming step. In the method of manufacturing a wiring board, the resist coating step selectively coats the photosensitive resin resist on the surface of the copper layer on the substrate, and the plating step exposes the photosensitive resin resist without coating. The surface of the copper layer is subjected to electroless tin-based plating having a substitution and deposition property with copper, and the copper layer up to a certain depth is replaced with a tin-based metal. Is removed and the exposed copper layer is thinned. In the fine pattern forming step, the thinned copper layer is etched and removed to form a fine pattern.

The method for manufacturing a printed wiring board according to the present invention also includes a first resist coating step, a plating step, a second resist coating step, a plating stripping step, a fine pattern forming step, and a resist stripping step. A method of manufacturing a printed wiring board, the first resist coating step selectively coating a photosensitive resin resist on a copper layer surface on a substrate, and the plating step comprising a photosensitive resin. After forming an electroless solder plating layer on the exposed copper layer surface without resist coating, the copper layer up to a certain depth is replaced with electroless solder by immersion treatment in an electroless solder plating bath. In the second resist coating step, the photosensitive resin resist is selectively coated on the area replaced with the electroless solder to form the pattern of the surface mounting pad. Is to peel and remove the electroless solder exposed without being coated with the photosensitive resin resist, and to thin the copper layer not masked by the photosensitive resin resist. The thinned copper layer is etched and removed to form a fine pattern, and the resist stripping step is to strip and remove the remaining photosensitive resin resist.

[0013]

The method of manufacturing a printed wiring board according to the present invention applies the characteristic that electroless tin-based plating is replaced with copper at a ratio of about 1: 1 to form a fine pattern. That is, a photosensitive resist is selectively formed on a predetermined portion of the copper layer provided on the front and back surfaces of the insulating substrate, and the exposed copper layer is replaced with a tin-based metal at a constant depth by electroless tin-based plating, By removing the tin-based metal and removing the thinned copper layer portion by etching with a copper etching solution, the vertical etching amount of copper is reduced, and the time required for etching is shortened.
A fine pattern is formed, and then the photosensitive resist is peeled off.

[0014]

The present invention will be described below with reference to the drawings.

(Embodiment 1) FIGS. 1 and 2 are sectional views showing Embodiment 1 of the present invention in the order of steps.

As shown in FIG. 1 (a), a copper-clad laminate 3 in which a 12 μm-thick copper foil 2 is adhered to the front and back surfaces of a substrate 1
Then, a through hole 4 having a diameter of 0.4 mm is drilled.

Next, as shown in FIG. 1 (b), electrolytic copper plating is applied to the entire surface of the copper-clad laminate 3 including the through holes 4 to obtain a thickness of 25 μm.
A thick copper plating layer 5 is formed and a through hole 6 is formed. Next, as shown in FIG. 1 (c), a photosensitive resin resist (Laminar GA dry film manufactured by Dynachem Co., Ltd.) having a thickness of 25 μm is applied, and 6 through holes and a pattern width 75 are applied.
A mask is applied to the pattern portion so that the pattern gap is 75 μm and the pattern gap is 75 μm, and the photosensitive resin resist layer 7 is patterned through a UV exposure and development process using a photo tool. The photosensitive resin resist layer 7 is laminated at 100 to 120 ° C. and a pressure of 3 to 5 kg / cm ² , and the photo tool is vacuum degassed on both sides.
Exposure is carried out at 200 mJ / cm ^2, and a phenomenon is carried out with 1 to 3% sodium carbonate for about 30 to 90 seconds.

Next, as shown in FIG. 1D, an electroless tin plating layer 8 is formed on the exposed copper plating layer 5. Electroless tin plating layer _{8, Sn (BF 4) 2 -} (NH 2) 2 C
A tin plating bath containing S-HBF ₄ is used, and it is formed by a substitution reaction with copper to a depth of 15 μm by immersion at 65 ° C. for 3 hours.

Next, as shown in FIG. 2 (e), the copper-clad laminate 3 is immersed in an acid-based stripping solution (made by Ebara Densan Co., Ltd.) at a temperature of 25 ° C. for 1 minute to form an electroless tin-plated layer 8. The copper plating layer 5 is peeled off to reduce the thickness of the copper plating layer 5 to 10 μm. After that, Figure 2
As shown in (f), the exposed and thinned residual copper plating layer 5 is removed by etching with a ferric chloride solution for 90 seconds. At this time, the thickness of the remaining thin portion of the copper plating layer 5 is 10 μm, which is 15 μm less than the initial thickness of 25 μm, so the time required for vertical etching is 90 seconds or less. At the same time, 12μ of copper foil 2
m and 10 μm of the remaining copper plating layer 5
Since the etching is performed in a thickness of .mu.m, the etching amount in the lateral direction is 1 / thick as compared with the conventional etching of a copper layer thickness of 37 .mu.m.
2 only, pattern width 75μm, pattern gap width 75μ
A fine pattern of m is easily formed. Further, the resist layer 7 is removed.

Finally, as shown in FIG. 2 (g), a photo solder resist is applied on the entire surface by screen printing, exposed to ultraviolet rays using a photo tool, developed with 1% sodium carbonate, and heated at 130 ° C. for 45 minutes. The photo solder resist layer 9 is formed by curing.

(Embodiment 2) FIGS. 3 and 4 are sectional views showing Embodiment 2 of the present invention in the order of steps.

As shown in FIG. 3A, a copper-clad laminate 3 in which a copper foil 2 having a thickness of 12 μm is adhered to the front and back surfaces of a substrate 1
Then, a through hole 4 having a diameter of 0.4 mm is drilled.

Next, as shown in FIG. 3B, electrolytic copper plating is applied to the entire surface of the copper-clad laminate 3 including the through holes 4, and the thickness is 25 μm.
A thick copper plating layer 5 is formed and a through hole 6 is formed. Next, as shown in FIG. 3C, a photosensitive resist having a thickness of 25 μm (Laminar GA dry film manufactured by Dynachem).
And the through hole 6 part and pattern width 75μ
m, the pattern portion is masked to have a pattern gap of 75 μm, and the photosensitive resin resist layer 7 is patterned through a UV exposure and development process using a photo tool. The photosensitive resin resist layer 7 is laminated at 100 to 120 ° C. and a pressure of 3 to 5 kg / cm 2, and a photo tool is attached to both sides, vacuum deaeration is performed, and then ultraviolet rays of about 60 to
It is exposed at 200 mJ / cm 2 and developed with 1 to 3% sodium carbonate for about 30 to 90 seconds.

Next, as shown in FIG. 3D, an electroless solder plating layer 10 is formed on the exposed copper plating layer 5. The electroless solder plating layer 10 uses an electroless solder plating bath (beam solder PC manufactured by Uemura Kogyo) at 70 ° C.
It is formed by a substitution reaction with copper to a depth of 15 μm by immersion for 20 minutes.

Next, as shown in FIG. 4E, FIG.
Similarly, a photosensitive resin resist having a thickness of 25 μm is deposited, a mask is formed so as to form a surface mounting pad, and the photosensitive resin resist layer 7 is patterned through a UV exposure and development process using a photo tool. The photosensitive resin resist layer 7 is formed similarly to FIG.

After that, as shown in FIG. 4 (f), the copper-clad laminate 3 was heated at a temperature of 25 with an acid-based stripping solution (made by Ebara Densan Co., Ltd.).
The electroless solder plating layer 10 is peeled off by immersing at 1 ° C. for 1 minute to reduce the thickness of the copper plating layer 5 to 10 μm.

Thereafter, as shown in FIG. 4 (g), the exposed and thinned residual copper is removed by etching with a ferric chloride solution for 90 seconds, and the pattern width is 75 μm, as in FIG. 2 (f).
A fine pattern having a pattern gap width of 75 μm is formed. Further, the surface-mounting pad 10 on which the electroless solder plating layer having a thickness of 15 μm is adhered is formed.

Finally, as shown in FIG. 4 (h), the pad 1
Except for 0, apply the photo solder resist on the entire surface by screen printing, and use a photo tool to expose it to ultraviolet rays and then 1%
The photo solder resist layer 9 is formed by developing with sodium carbonate and heating and curing at 130 ° C. for 45 minutes.

[0029]

As described above, according to the present invention, the electroless tin-based plating is replaced with copper, the copper is peeled off, and the remaining thinned copper is etched.
It is possible to form a fine pattern having m and a pattern gap of 75 μm while maintaining the reliability of the through hole and without impairing the photosensitivity of the copper foil.

Further, according to the second embodiment, by selectively leaving the electroless solder on the pad by 5 to 20 μm, the solder required in the mounting process can be supplied from the fine pad, and the short-circuit defect in the mounting process can be reduced to 1 It can be / 10 or less.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a first embodiment of the present invention in process order.

FIG. 2 is a cross-sectional view showing the first embodiment of the present invention in the order of steps.

FIG. 3 is a cross-sectional view showing a second embodiment of the present invention in process order.

FIG. 4 is a cross-sectional view showing a second embodiment of the present invention in process order.

FIG. 5 is a cross-sectional view showing a method of manufacturing a high-density pattern according to a conventional example in the order of steps.

[Explanation of symbols]

 1 substrate 2 copper foil 3 copper-clad laminate 4 through hole 5 copper plating layer 6 through hole 7 photosensitive resist 8 electroless tin plating layer 9 photo solder resist 10 electroless solder plating layer 11 ED resist layer

Claims (2)

[Claims] 1. A method for manufacturing a printed wiring board, comprising: a resist coating step, a plating step, a plating stripping step, and a fine pattern forming step, wherein the resist coating step is a photosensitive layer on the surface of a copper layer on a substrate. A resin resist is selectively applied.In the plating process, the surface of the copper layer that is exposed without the photosensitive resin resist being applied is subjected to electroless tin-based plating that has the property of precipitating substitution with copper. , The copper layer up to a certain depth is replaced with tin-based metal, and the plating stripping process strips and removes the tin-based metal and thins the exposed copper layer to form a fine pattern. The method is a method for producing a printed wiring board, wherein the thinned copper layer is etched and removed to form a fine pattern. 2. A method of manufacturing a printed wiring board comprising a first resist coating step, a plating step, a second resist coating step, a plating stripping step, a fine pattern forming step, and a resist stripping step. The first resist coating step selectively coats the photosensitive resin resist on the surface of the copper layer on the substrate, and the plating step exposes the copper layer exposed without being coated with the photosensitive resin resist. After the electroless solder plating layer is formed on the surface, the copper layer up to a certain depth is replaced with the electroless solder by immersion treatment in the electroless solder plating bath. The surface of the pads for surface mounting is formed by selectively applying a photosensitive resin resist to the areas replaced with solder.In the plating peeling process, the photosensitive resin resist is not applied and exposed. The copper layer not masked by the photosensitive resin resist is thinned by removing and removing the electroless solder that is being used. In the fine pattern forming step, the thinned copper layer is removed by etching. A method for manufacturing a printed wiring board, wherein a fine pattern is formed, and the resist stripping step strips and removes the remaining photosensitive resin resist.