JP3785223B2 - Manufacturing method of multilayer printed wiring board - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
Relates to a manufacturing method of the present invention is a multilayer printed wiring board, and more particularly, to a method for manufacturing a multilayer printed circuit board comprising interstitial via holes.
[0002]
[Prior art]
Among the multilayer printed wiring boards, a representative example of a four-layer printed wiring board will be explained. The four-layer printed wiring board has a prepreg on both sides of an inner layer circuit base material in which an inner layer electric circuit is formed using a copper-clad laminate. Used as an outer layer circuit base material, laminated and fixed copper foil for outer layer electric circuit, formed through hole or non-through hole, applied copper plating, etched copper foil for outer layer circuit and copper plating layer, etc. Thus, an outer layer electric circuit is formed. The inner layer electric circuit and the outer layer electric circuit are electrically connected by an interstitial via hole (hereinafter referred to as “IVH”).
[0003]
Next, FIG. 1 shows a sectional view of a typical four-layer printed wiring board. The four-layer printed wiring board 1 includes an inner layer circuit substrate 2 and outer layer circuit substrates 3 and 4 laminated on both surfaces thereof. The four-layer printed wiring board 1 has three types of IVH, that is, IVH1, IVH2, and IVH3.
[0004]
In these IVHs, since IVH3 is not directly related to the present invention, the description thereof will be omitted, and IVH1 and IVH2 will be described.
[0005]
The IVH 1 is provided with a non-through hole in the outer layer circuit base material 3, and electrically connects the outer layer electric circuit 31 of the outer layer circuit base material 3 and the first electric circuit 21 of the inner layer circuit base material 2 with the copper plating layer 5. It is what you do. The electric circuit 31 includes a copper foil 31 a and a copper plating layer 5. The electric circuit 21 includes a copper foil 21a and a copper plating layer 21b formed on the surface thereof. However, the electric circuit 21 may be only the copper foil 21a without forming the copper plating layer 21b.
[0006]
The IVH 2 is provided with non-through holes in the outer layer circuit base 3 and the inner layer circuit base 2, the electric circuit 31 of the outer layer circuit base 3, the first electric circuit 21 of the inner layer circuit base 2, and the inner layer circuit base. The second electric circuit 22 of the material 2 is configured to be electrically connected by the copper plating layer 5. In this case, the first electric circuit 21 may not be electrically connected together by the copper plating layer 5. Similarly to the electric circuit 21, the electric circuit 22 includes a copper foil 22a and a copper plating layer 22b formed on the surface thereof. However, the electric circuit 22 may be only the copper foil 22a without forming the copper plating layer 22b.
[0007]
In the four-layer printed wiring board 1 having the above structure, the non-through holes of IVH1 and the non-through holes of IVH2 are often formed by irradiating laser light. As the laser light source, it is common to use a laser light source such as a carbonic acid laser or an excimer laser, which has a characteristic that the laser light dissolves only the inner layer circuit substrate 2 and the outer layer circuit substrates 3 and 4 without melting copper. Is. The laser beam is applied to a position where the copper foil 31a has been previously removed with a predetermined aperture.
[0008]
Next, a conventional method for manufacturing IVH1 using laser light that does not dissolve copper will be described with reference to FIG. Since IVH2 is a modification of IVH1, description of the conventional method for manufacturing IVH2 is omitted.
[0009]
The IVH1 manufacturing method will be described. In forming a non-through hole with laser light, conventionally, as shown in FIG. 4 (a), the width of laser light irradiation (hereinafter referred to as the opening diameter T1 of the copper foil 31a). Written as “laser beam width.” W2 was larger. For this reason, for example, when a non-through hole with a diameter of 150 μm is to be formed, a laser beam having a width of, for example, 500 μm and a width W2 larger than the opening diameter T1 of 150 μm has to be irradiated. The laser light reaches the outer layer circuit base 3 under the irradiation width regulated by the opening diameter T1 of the copper foil 31a, evaporates the outer layer circuit base 3, and finally the first of the inner layer circuit base 2 1 to the surface of the electric circuit 21. As a result, the opening diameter T2 of the non-through hole formed in the outer layer circuit substrate 3 is also 150 μm, and as a result, the opening diameter of the non-through hole 6 is T1 = T2 = 150 μm as shown in FIG. Will be formed.
[0010]
The inner wall surface 3a of the non-through hole 6 formed as described above is rough (irregularities, scratches, etc.), and the remaining residue of the outer layer circuit substrate 3 remains in the non-through hole 6. Yes. If the inner wall surface 3a is rough or the outer layer circuit substrate 3 remains, good copper plating cannot be applied to the non-through holes 6 in a later step. Therefore, as a pretreatment, the inside of the non-through hole 6 is washed with an organic solvent to chemically dissolve and remove the roughness of the inner wall surface 3a and the residue of the outer layer circuit substrate 3. Then, IVH1 provided with the copper plating layer 5 as shown in FIG.4 (b) was formed by performing copper plating.
[0011]
[Problems to be solved by the invention]
However, according to the conventional manufacturing method, the opening diameter T2 of the non-through hole 6 is regulated to the width of the opening diameter T1 of the copper foil 31a. The air that stays when the organic solvent was poured in was poorly removed. Therefore, there is a problem that it is difficult to flow an organic solvent sufficient for cleaning into the non-through hole 6.
[0012]
Further, in the pretreatment, the inner wall surface 3a itself is also dissolved, so that the opening diameter T2 of the non-through hole 6 where T1 = T2 becomes the opening diameter T21, and T1 <T21. Further, in the shape of the non-through hole 6 described above, it was difficult to smoothly discharge the organic solvent, and the organic solvent was likely to remain in the non-through hole 6. As a result, the inner wall surface 3a itself was greatly dissolved. Finally, the non-through hole 6 obtained before copper plating has an overhang shape (see FIG. 4B) in which the copper foil 31a projects from the outer layer circuit base material 3 in a bowl shape. It was.
[0013]
Since the non-through hole 6 has the above-described shape, the plating solution did not flow smoothly, and a thin portion or a non-existing portion was formed in the copper plating layer 5 in the non-through hole 6. Furthermore, the copper plating layer 5 was easily peeled off or peeled off from the inner wall surface 3a. As described above, since the satisfactory copper plating layer 5 could not be formed in the non-through hole 6, the electrical reliability of the IVH was impaired.
[0014]
The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for manufacturing a multilayer printed wiring board having an electrically reliable IVH.
[0015]
[Means for Solving the Problems]
The method of manufacturing the onset Ming, when forming a non-through-hole, the opening of the copper foil, and irradiated the smaller irradiation width than the opening diameter, and the laser beam does not dissolve the copper, dissolved the irradiated surface Then, an electric circuit is exposed on the bottom surface to form a non-through hole having a diameter smaller than the opening diameter of the copper foil, and then an organic solvent that does not dissolve copper is dissolved in the non-through hole. It was characterized in that the IVH was formed by providing a copper plating layer after forming the non-through hole into a substantially V-shaped cross-sectional shape with its opening edge cut off by pouring while being most promoted and chemically washed. Is.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
A representative example of the IVH manufacturing method according to the present invention will be described with reference to FIGS. 2 (a) and 2 (b) are enlarged views showing the steps for forming IVH1 in FIG.
[0017]
FIG. 2A shows a state in which the non-through hole 6 of IVH1 according to the present invention is formed. For example, when the non-through hole 6 is formed by irradiating the laser beam with a light width W1 of 150 μm, FIG. The opening diameter T11 of the foil 31a is formed with a diameter larger than the laser beam width W1, for example, 250 μm, and when the laser beam is irradiated, the laser beam reaches the outer layer circuit substrate 3 and the outer layer circuit substrate 3 It evaporates and finally reaches the surface of the first electric circuit 21 of the inner layer circuit substrate 2. As a result, the opening diameter T22 of the non-through hole 6 formed in the outer layer circuit base 3 is also 150 μm, which is the same as the laser beam width W1. Therefore, the opening diameter of the non-through hole 6 is T22 (150 μm) <T11 (250 μm), and the non-through hole 6 having a stepped shape is obtained. As the laser light source used in the present invention, any laser light source that can dissolve only the circuit substrate without dissolving copper conventionally used can be used.
[0018]
Next, in order to remove the roughness of the inner wall surface 3a of the outer layer circuit base material 3 and the residue of the outer layer circuit base material 3, as in the conventional manufacturing method, the organic material that does not dissolve copper in the non-through holes 6 Chemically wash with solvent. Examples of the organic solvent include concentrated sulfuric acid and potassium permanganate. In this case, since the organic solvent is poured into the step-shaped non-through hole 6 having an opening diameter T22 smaller than the opening diameter T11, dissolution of the opening edge of the outer layer circuit base 3 is most accelerated. Is done. Therefore, the opening edge of the outer layer circuit base material 3 is scraped to form a non-through hole 6 having a substantially V-shaped cross section as shown in FIG. Accordingly, the organic solvent or the like can be smoothly discharged from the non-through hole 6.
[0019]
After finishing the above-described cleaning treatment, IVH1 (see FIG. 2B) in which the copper plating layer 5 is formed as in the conventional case and the first electric circuit 21 and the copper foil 31a are electrically connected to each other is obtained. Form.
[0020]
On the other hand, FIGS. 3A and 3B show I in FIG. 1 formed by the manufacturing method according to the present invention.
The process of VH2 is expanded and shown. IVH2 is a modification of IVH1, and laser light irradiation is performed under the same conditions as those of IVH1 according to the present invention shown in FIG. The IVH2 shown in FIG. 3 is applied when forming an IVH in which three or more layers of electric circuits of a multilayer printed wiring board in which four or more layers of electric circuits are laminated are electrically connected by one non-through hole. The
[0021]
FIG. 3A shows a state in which the non-through hole 7 of IVH2 according to the present invention is formed. For example, when the non-through hole 7 is formed by irradiating the laser beam with a light width W1 of 150 μm, FIG. The opening diameter T11 of the foil 31a is formed with a diameter larger than the laser light width W1, for example, 250 μm, and the first electric circuit 21 of the inner layer circuit substrate 2 also has a diameter larger than the laser light width W1, In addition, when the opening diameter T3 is formed with a diameter equal to or smaller than the opening diameter T11 of the copper foil 31a, for example, 200 μm, and the laser light is irradiated, the laser light causes the outer layer circuit base 3 and the inner layer circuit base 2 to pass through. It evaporates and reaches the surface of the second electric circuit 22 of the inner layer circuit substrate 2. As a result, the opening diameters T22 and T4 of the non-through holes 7 formed in the outer layer circuit substrate 3 and the inner layer circuit substrate 2 are also 150 μm, which is the same as the laser beam width W1. Therefore, the opening diameter of the non-through hole 7 is T11 (250 μm)> T3 (200 μm)> T22 (150 μm) = T4 (150 μm), and the copper foil 31a and the first electric circuit 21 in the cross-sectional shape are the outer layer circuit base. A non-through hole 7 having a step which is recessed from the material 3 and the inner layer circuit substrate 2 is obtained.
[0022]
Next, in order to remove the roughness of the inner wall surface 3a of the outer layer circuit substrate 3 and the residue of the outer layer circuit substrate 3, and the roughness of the inner wall surface 2a of the inner layer circuit substrate 2 and the residue of the inner layer circuit substrate 2, The inside of the hole 7 is chemically cleaned with an organic solvent that does not dissolve copper. In this case, the organic solvent is poured into the step-shaped non-through hole 6 having an opening diameter T22 smaller than the opening diameter T11, like the IVH1 according to the present invention. The dissolution of both the opening edges of the inner layer and the opening edge of the inner layer circuit base 2 is most promoted. Therefore, both the opening edge of the outer-layer circuit base material 3 and the opening edge of the inner-layer circuit base material 2 are shaved, and the non-penetration provided with a substantially V-shaped cross section as shown in FIG. A hole 7 is formed.
[0023]
After finishing the above-described cleaning process, the copper plating layer 5 is formed in the same manner as in the prior art, and the IVH2 (which connects the copper foil 31a, the first electric circuit 21, and the second electric circuit 22 to each other) ( 3B) is formed. In this case, the first electric circuit 21 may not be electrically connected together by the copper plating layer 5 like the conventional IVH 2.
[0024]
【The invention's effect】
As described above, in the manufacturing method according to the present invention, when forming the IVH non-through hole, a laser beam having a diameter smaller than the opening diameter of the copper foil located on the outer layer side is set to the opening diameter of the copper foil. Irradiated to form IVH non-through holes having the same diameter as the irradiated surface .
[0025]
In the non-through hole according to the present invention, when the edge of the opening of the circuit substrate is most easily dissolved when washed with an organic solvent that does not dissolve copper, the cross-sectional shape of the non-through hole also has an opening edge. The shape is substantially V-shaped so that the organic solvent can be smoothly supplied into the non-through hole. Moreover, since the organic solvent in the non-through holes and the residue of the circuit base material can be smoothly discharged, the cleaning effect can be enhanced.
[0026]
Furthermore, since the non-through hole is substantially V-shaped in cross-sectional shape, the plating solution can be poured smoothly, and not only a thin portion of the copper plating layer or a portion where the copper plating layer does not exist can be uniformly formed. A copper plating layer having an appropriate thickness can be formed. Furthermore, the copper plating layer is not peeled off or peeled off from the inner wall surface of the non-through hole, and a multilayer printed wiring board with high electrical reliability can be provided.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a main part structure of a standard four-layer printed wiring board provided with IVH.
FIGS. 2A and 2B are explanatory views showing enlarged steps (a) and (b) of an example of the manufacturing method according to the present invention in correspondence with FIG.
FIGS. 3A and 3B are explanatory views showing, as enlarged (a) and (b), steps of another example of the manufacturing method according to the present invention in correspondence with FIG.
FIG. 4 is an explanatory diagram showing enlarged steps (a) and (b) of a conventional method corresponding to FIG. 2;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 4 layer printed wiring board 2, 3, 4 Circuit base material 2a, 3a Inner wall surface 6,7 Non-through-hole 21, 22, 31 Electrical circuit 21a, 22a, 31a Copper foil 21b, 22b, 5 Copper plating layer

Claims (1)

The opening of the copper foil for the outer layer electric circuit is irradiated with a laser beam having a diameter smaller than the opening diameter to form a non-through hole whose inner diameter is substantially the same as the irradiation width in the circuit substrate, and copper is placed in the non-through hole. An organic solvent that does not dissolve is poured into the opening edge while promoting the dissolution of the opening edge and is chemically washed to form a non-through hole in a substantially V-shaped cross-sectional shape with the opening edge cut away. A method of manufacturing a multilayer printed wiring board , comprising: forming an interstitial via hole in which a copper plating layer is formed in a through-hole and electrically connecting an outer layer electric circuit and an inner layer electric circuit .

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