JP4435293B2 - Method for manufacturing printed wiring board - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a process for producing a printed wiring board having a through-hole.
[0002]
[Prior art]
In recent years, with the era of highly information-oriented society, downsizing, high density, high-speed signal processing, etc. of electronic devices and printed wiring boards used for them have become important issues.
In order to manufacture a small and high density printed wiring board, formation of a circuit pattern by a build-up method is often employed. Specific manufacturing procedures include, for example, the following.
[0003]
First, a through hole is formed in a required portion of the substrate, and a conductor layer is formed on the inner peripheral surface of the through hole and the substrate surface by chemical plating and electrolytic plating. Next, filling printing is performed in the through holes to fill the resin material, and after the resin material is cured, the resin portion protruding from the substrate surface is polished to obtain a smooth substrate. Then, chemical plating and electrolytic plating are again performed on the substrate surface to form a conductor layer, and unnecessary portions thereof are removed by an etching method to form a predetermined circuit pattern.
[0004]
By the way, since the signal propagation speed in the circuit pattern formed on the printed wiring board is proportional to the reciprocal of the square root of the effective dielectric constant of the board material, the base material, filler, resin, etc. constituting the printed wiring board The dielectric constant is preferably as low as possible. Accordingly, conventionally, a resin material having a low dielectric constant is also used as a resin material for filling a through hole formed in a base material of a printed wiring board from such a viewpoint.
[0005]
[Problems to be solved by the invention]
However, it is difficult to say that the resin material having a low dielectric constant conventionally used has sufficient adhesion to the circuit pattern. As described above, with the recent trend toward miniaturization and higher density of wiring boards, the number of circuit patterns has been increasing. However, as the number of circuit patterns stacked increases, The force applied to increases. For this reason, if the adhesion between the resin material filled in the through-hole and the lowermost circuit pattern formed on the resin material is poor, peeling easily occurs at those contact portions, and the reliability of the substrate The problem of the decline of sex occurs.
[0006]
In order to solve such problems, the metal material is mixed in the resin material to be filled in the through hole, or the metal paste is embedded in place of the resin so that the filling material in the through hole and the circuit pattern are mixed. Attempts were made to increase adhesion. However, the use of such a material is not preferable because the dielectric constant of the entire substrate material is increased and the signal propagation speed is greatly reduced.
[0007]
The present invention has been made in view of the above circumstances, and is a method for producing a printed wiring board that maintains the dielectric constant of a resin material in a through hole as low as before and is excellent in adhesion to a circuit pattern. Is intended to provide .
[0009]
[Means, actions and effects for solving the problems]
According to the printed wiring board manufactured by the present invention , since the resin layer located in the deep layer portion in the through hole has a low dielectric constant, the signal propagation speed of the printed wiring board can be maintained at a high speed comparable to the conventional one. it can. In addition, since the resin layer of the surface layer portion in contact with the circuit pattern is composed of a resin having excellent adhesion, the circuit pattern and the resin layer are difficult to peel off, and the reliability of the printed wiring board can be improved. There is an effect.
[0010]
As the resin material constituting the low dielectric constant layer, an acrylate-epoxy resin that has been conventionally used as a resin for filling holes in printed wiring boards is preferable, but other materials having a low dielectric constant of 40 or less can be used. Any material may be used as long as it satisfies various conditions such as a high glass transition temperature and a low water absorption rate, which has a thermal expansion coefficient close to that of the base material. Moreover, as a resin material which comprises a highly adhesive layer, what has favorable interface adhesiveness with a metal surface and a dissimilar resin material is preferable, for example, an epoxy resin etc. are mentioned. Further, the plating adhesion strength with copper is preferably 1.0 kg / cm or more.
[0011]
According to a first aspect of the present invention, there is provided a printed wiring board manufacturing method comprising: a hole filling step of filling a through hole formed in a printed wiring board with a low dielectric constant resin material having a dielectric constant of 40 or less; and after the resin material is cured A recess forming step for removing the surface portion of the low dielectric constant layer to form a recess, and a recess embedding step for filling the recess with a highly adhesive resin material having better adhesion to the circuit pattern than the low dielectric constant layer, A polishing process for smoothing the substrate by polishing the highly adhesive layer after curing of the resin material, a surface roughening process for roughening the surface of the highly adhesive layer, and then forming a circuit pattern on the surface of the substrate The circuit pattern forming process is performed.
[0012]
According to the above manufacturing method, since the inside of the through hole is first filled with the same low dielectric constant resin material as before, the through hole of the printed wiring board can be filled under the same conditions using a conventional apparatus. Possible (hole filling process). Next, after curing this low dielectric constant resin material, only the surface portion of the resin material is dissolved and removed to form a recess (recess formation process), and this recess is filled with a highly adhesive resin material (recess embedding) Process). When the resin material is cured and the surface of the substrate is smoothed (polishing process), the resin layer in the through-hole is mostly made of a resin layer having a low dielectric constant similar to the conventional one, while only the surface layer portion is increased. The structure is replaced with an adhesive resin material. Furthermore, the resin surface is roughened by, for example, a buffing machine (surface roughening step), thereby providing an excellent effect that adhesion with a circuit pattern formed thereon can be remarkably improved.
[0013]
According to a second aspect of the present invention, there is provided a printed wiring board manufacturing method according to the first aspect, wherein the low dielectric constant resin material is a two-stage curable resin capable of ultraviolet curing and thermosetting, and the high adhesion resin material is thermosetting. A low-dielectric-constant resin material that is primarily cured by irradiating ultraviolet rays after the hole-filling step, and heated after the recess-filling step. Characterized by heat curing.
[0014]
According to the above manufacturing method, since the low dielectric constant resin material previously filled in the through hole is a two-stage curable resin, the resin material is half-filled by first irradiating with ultraviolet rays after filling the hole. It becomes a cured state. And since the removal of a surface layer part is performed in that state, there exists an effect that a recessed part formation can be performed rapidly and easily.
In addition, since the thermosetting of the low dielectric constant resin material is performed simultaneously with the thermosetting of the high adhesion resin material filled in the recess, it is not necessary to increase the number of curing steps.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to FIGS.
In this embodiment, the copper clad laminated board 10 which affixes the copper foil 12 on both surfaces of the glass epoxy board | substrate 11 with a thickness of 100-3000 micrometers is used as a base material (refer FIG. 1). A through hole 13 is drilled in a required portion of the copper-clad laminate 10 using a known drill or the like (see FIG. 2), and chemical plating and electrolytic plating are performed to include the inner peripheral surface of the through hole 13. Then, a copper plating layer 14 is formed over the entire area so that the thickness of the conductor layer on the substrate surface is about 20 μm (see FIG. 3). The following steps are sequentially performed on this wiring board.
[0016]
<Hole filling process>
First, the two-stage curing type low dielectric constant resin material 15 of ultraviolet and heat curing is printed from one side of the wiring board, and the through hole 13 is filled with the low dielectric constant resin material 15. Then, this low dielectric constant resin material 15 is exposed by a well-known exposure apparatus, is primarily cured, and is polished by, for example, a buffing machine or a belt sander so that the surface becomes flat (see FIG. 4).
[0017]
<Recess formation process>
Next, only the surface portion of the low dielectric constant resin material 15 is dissolved and removed by a strong alkaline aqueous solution by about 20 to 50 μm. Then, as shown in FIG. 5, a recess 16 is formed in the portion where the through hole 13 is located.
[0018]
<Recess filling process>
Next, the recesses 16 are filled with a high adhesion resin material 17 having better adhesion than the low dielectric constant resin material 15 on both sides of the wiring board by, for example, screen printing. When heating is performed, the semi-cured low dielectric constant resin material 15 located in the deep layer portion is completely cured by heat, and the high adhesion resin material 17 in the surface layer portion is also cured.
[0019]
<Polishing process>
Then, the cured highly adhesive resin material 17 rising from the through hole 13 to the substrate surface is, for example, buffed to obtain a smooth substrate (see FIG. 6). The highly adhesive resin material 17 is exposed at the position of the through hole on the substrate surface.
[0020]
<Surface roughening process>
Further, the surface of the polished resin portion of the smooth substrate is roughened by, for example, permanganic acid etching (see FIG. 7). This further improves the adhesion with the copper circuit pattern formed on the resin.
[0021]
<Circuit pattern formation process>
Then, a copper plating layer 18 is formed again on the surface of the wiring board thus obtained by chemical plating and electrolytic plating, and unnecessary portions are removed together with the lower plating layer 14 by a known photoetching method. A circuit pattern is formed. Specifically, for example, a photosensitive etching resist is first printed on a wiring substrate, and after drying, a circuit pattern film is overlaid and exposed. When this is developed, a wiring board is obtained in which a cured etching resist is superimposed on a portion to be left as a circuit pattern.
Therefore, this wiring board is immersed in an etching resist solution, and unnecessary portions of the plating layers 14 and 18 are dissolved and removed. Then, if the etching resist is removed, the required portions of the plating layers 14 and 18 remain, and the circuit pattern is completed (see FIG. 8).
[0022]
<Effect of this embodiment>
As described above, according to the printed wiring board and the manufacturing method thereof of the present embodiment, the surface layer portion of the resin layer in the through hole is made of a highly adhesive resin material. Accordingly, the adhesiveness between the resin layer and the circuit pattern formed thereon is increased, and separation between the two is less likely to occur, so that the reliability of the substrate can be greatly improved.
[0023]
Specifically, when the peel strength of the circuit pattern of the printed wiring board produced by the manufacturing method as in the above embodiment was measured based on the JIS standard, only the conventional low dielectric constant resin material was embedded in the through hole. However, while the conventional one was 0.3 kg / cm, the one obtained by replacing the surface layer portion with a highly adhesive resin material as in the present embodiment was greatly improved to 1.2 kg / cm.
[0024]
Further, since the deep layer portion is made of a low dielectric constant resin material, the dielectric constant of the entire substrate can be kept low, and the signal propagation speed can be maintained at a high speed comparable to that of the prior art.
Further, in this embodiment, since the low dielectric constant resin material in the deep layer portion that is previously filled in the hole is a two-stage curable resin, the surface portion of the resin layer can be removed in a semi-cured state, thereby forming a recess. There is an effect that it can be performed quickly and easily. In addition, since the resin layer in the deep layer portion is completely cured simultaneously with the thermosetting of the highly adhesive resin material in the surface layer portion, the number of curing steps does not increase.
[0025]
In the above embodiment, a preferable result was obtained when the depth of the recess 16 was 20 to 50 μm. This is because, when the thickness is 20 μm or less, the high adhesion layer of the surface layer portion is too thin, and the etching liquid enters the resin interface between the surface layer portion and the deep layer portion during permanganic acid etching, and peeling at the resin interface is likely to occur. it is conceivable that. On the other hand, when the thickness is 50 μm or more, it is considered that the concave portion 16 becomes too deep, and printing defects easily occur in the concave portion embedding process. However, the appropriate range of the recess depth varies depending on the thickness of the conductor layer on the surface of the base material, the hole diameter, and the like, and is not limited to the numerical values in the above embodiment.
[0026]
<Other embodiments>
The present invention is not limited to the embodiments described with reference to the above description and drawings. For example, the following embodiments are also included in the technical scope of the present invention, and further, within the scope not departing from the gist of the invention other than the following. Various modifications can be made.
(1) In the above embodiment, the circuit pattern is formed by the subtractive method. However, the present invention is not limited to this, and the circuit pattern may be formed by another method such as an additive method.
(2) In the above embodiment, the low dielectric constant resin material is filled into the through hole from one side surface, but may be filled from both side surfaces.
(3) In the above-described embodiment, the two-stage curable low dielectric constant resin material is used. However, the present invention is not limited to this, and a thermosetting or ultraviolet curable resin may be used.
(4) In the above embodiment, only a single layer of the circuit pattern is formed on the resin layer. However, the present invention is not limited to this, and it goes without saying that a plurality of layers may be laminated.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a substrate of a wiring board according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of the wiring board that also shows a drilling process. 4 is a cross-sectional view of the wiring board that also shows the hole filling process. FIG. 5 is a cross-sectional view of the wiring board that also shows the recessed portion forming process. FIG. Cross-sectional view of the wiring board showing the roughening process. [FIG. 8] Cross-sectional view of the wiring board showing the circuit pattern forming process.
DESCRIPTION OF SYMBOLS 10 ... Copper-clad laminate 13 ... Through-hole 14, 18 ... Plating layer 15 ... Low dielectric constant resin material 16 ... Concave part 17 ... High adhesion resin material

Claims (2)

A hole filling step for filling a through hole formed in the printed wiring board with a low dielectric constant resin material having a dielectric constant of 40 or less, and removing a surface portion of the low dielectric constant layer after curing of the resin material to form a recess. Polishing the recessed portion forming step, filling the recessed portion with a highly adhesive resin material having better adhesion to the circuit pattern than the low dielectric constant layer, and polishing the highly adhesive layer after curing of the resin material A polishing step for smoothing the substrate, a surface roughening step for roughening the surface of the highly adhesive layer, and a circuit pattern forming step for forming a circuit pattern on the surface of the substrate. A method for manufacturing a printed wiring board. The low dielectric constant resin material is a two-stage curable resin capable of ultraviolet curing and thermosetting, and the high adhesion resin material is a thermosetting resin, and is irradiated with ultraviolet rays after the hole filling step. 2. The low dielectric constant resin material is first cured, and the low dielectric constant resin material and the high adhesion resin material are thermally cured by heating after the recess embedding step. A method for manufacturing a printed wiring board.

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