JP2000349442A - Method for forming pad over through hole - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for forming over a through hole a pad which has superior flatness and comes into excellent contact with the substrate. SOLUTION: This method includes a process for hardening paste 4 after filling the through hole with the paste by applying the paste to a multi-layered circuit board having the through hole made electrically conductive by a plating layer 3 on the surface, a process for leveling the surface of the paste with the surface of the multi-layered circuit substrate by polishing the surface of at least the paste, a process for forming a plating layer 5 by plating the entire polished surface with a conductor, and a process for forming the pad 6A closing the through hole by patterning the plating layer. Here, the paste is no-solvent type metal-powder containing paste.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a pad on a through-hole, and more particularly, to a method for forming a pad having good adhesion to a paste filled in a through-hole formed on a multilayer circuit board and having a flat surface. The present invention relates to a method for forming a pad having excellent properties on a through hole.

[0002]

2. Description of the Related Art There are two types of through holes formed in a multilayer circuit board: a through hole penetrating the upper and lower surfaces of the board, and a via hole for establishing conduction between inner layers.
In each case, a plating layer is formed on the wall surface of the hole to impart conductivity.

In the case of these through holes, for example, a land is provided on the surface of the uppermost layer of the multilayer circuit board, or a pad is provided in a state where the through hole is closed, and a predetermined component such as a chip component is provided here. It is mounted or connected to a predetermined circuit pattern. Here, a description will be given of a conventional typical example of a method of forming a pad in a case where the through-hole is a through-hole formed in a multilayer circuit board.

First, after a through-hole 2 having a predetermined hole diameter is formed at a predetermined position of the substrate 1, the entire surface is subjected to, for example, electroless copper plating to form an electrode on the surface 1 a of the substrate 1 and the inner wall 2 a of the through-hole 2. A thin chemical copper plating layer 3A is formed (FIG. 1). Next, for example, electrolytic copper plating is performed on the whole.
As a result, as shown in FIG. 2, the inner wall of the through-hole 2 and the entire surface of the substrate 1 are covered, and the copper plating layer 3 having a predetermined thickness of the electrolytic copper plating layer 3B and the chemical copper plating layer 3A is formed. It is formed.

The paste is filled into the through-hole 2 by a printing method through a screen having an opening slightly larger than the through-hole 2, for example, and then the paste is cured. As a result, as shown in FIG. 3, the surface of the plating layer 3 in the vicinity of the through-hole is covered with the cured paste, and at the same time, the cured paste 4 is filled in the through-hole 2.

Next, the surface of the substrate 1 is buffed, for example, to remove the hardened paste on the surface of the plating layer 3 so that the surface 3a of the plating layer 3 of the substrate 1 and the surface 4a of the filling paste 4 are flush. As a result, as shown in FIG. 4, the surface 3a of the plating layer 3 is out table, intermediate material A ₁ is obtained paste 4 is filled in the through-hole 2. And
For example, electroless copper plating and electrolytic copper plating are sequentially performed on the surface of the substrate 1 to form a copper plating layer 5 having a predetermined thickness on the surface of the paste 4 filled in the through-hole and the surface of the plating layer 3 to form an intermediate layer. producing material a ₂ (Fig. 5).

Then, patterning is performed on the plating layer 5 by, for example, a combination of photolithography and etching, and portions of the plating layer other than the portion of the pad to be formed and the portion of the conductor circuit are etched off to the surface of the substrate 1. . As a result, as shown in FIG. 6, on the substrate 1, a conductor circuit 6B of a predetermined pattern including the plating layer 3 and the plating layer 5, the paste 4 filling the through hole, and the pad covering the upper surface 4a are provided. 6A is formed.

In the above process, a paste containing a solvent is generally used as a paste for filling the through holes 2. For example, a non-conductive paste made of a two-pack type epoxy resin and cured by heat or ultraviolet light is often used.

[0009]

By the way, in the above process, when a paste of the type described above is printed on a substrate and the through holes are filled with the paste, air is entrained in the paste, and the defoaming is performed. It will be very difficult. Further, in the case of a paste containing a solvent, the following problems occur when the paste is cured.

That is, at the time of curing, the solvent escapes, and in the process, the shrinkage of the paste proceeds, and as shown in FIG. 7, the portion of the paste located on the through hole is slightly recessed. When the surface is polished in this state, as shown in FIG. 8, the edge portion 3b of the plating layer 3 is also polished, and eventually, the plating layer 5 formed thereon is also shown by a virtual line in the figure. As a result, the shape becomes concave.

When such a situation occurs, the flatness of the pad formed thereafter deteriorates, and, for example, the reliability of mounting chip components thereon decreases. SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for forming a pad on a through-hole, which solves the above-mentioned problem when forming a conventional pad, has excellent flatness, and has a large adhesive force with a lower layer paste.

[0012]

In order to achieve the above-mentioned object, according to the present invention, a paste is applied to a multilayer circuit board having a through hole having a surface provided with conductivity, and the paste is applied to the through hole. A step of filling and curing after filling the paste; a step of polishing at least the surface of the paste to make the surface of the paste and the surface of the multilayer circuit board flush; plating a conductor on the entire polished surface to form a plating layer And a step of patterning the plating layer to form a pad for closing the through hole, wherein the paste contains solvent-free metal powder. A method for forming a pad in a through hole, which is a paste, is provided.

In particular, there is provided a method of forming a pad on a through-hole, wherein the through-hole is a through-hole and / or a via-hole, and chemical copper plating and electroplating are formed on the inner wall of the through-hole. Is done.

[0014]

DETAILED DESCRIPTION OF THE INVENTION In the present invention, except that the paste to be filled in the through holes is a solventless paste containing metal powder, there is no difference from the forming method shown in FIGS. Absent. As a paste as described above,
Either a non-conductive paste or a conductive paste can be used.

Specific examples of the non-conductive paste include a non-solvent type thermosetting epoxy resin containing copper powder, and examples of the conductive paste include a non-solvent type thermosetting epoxy resin containing silver-coated copper powder. Epoxy resin and the like. Since all of these pastes are solventless types, the amount of dimensional shrinkage during curing is extremely small and practically zero. Therefore, paste 4 is
As shown in FIG. 9, the through holes are filled without being recessed. In addition, since the resin is a resin containing a metal powder having a high specific gravity, air trapped when filling the through-hole is completely defoamed.

Then, even if this is polished, unlike the case where the concave portion 4A is formed as shown in FIG.
As shown in the above, the surface 4a of the paste 4 and the surface 3a of the plating layer 3 are flat and flush, and the edge 3b of the plating layer 3 is not polished. Therefore,
When a plating layer 5 is formed on this surface, and further patterning is performed to form a pad and a conductor circuit, the formed pad is flat and is a paste containing metal powder.
The adhesion to the paste also increases.

Although the above description has been made on the case of through through holes penetrating the upper and lower surfaces of the substrate, the method of the present invention is not limited to this. For example, a multilayer circuit substrate may be formed by a build-up method. The present invention can also be applied to the case of via holes formed in each inner layer during manufacturing.

[0018]

EXAMPLE An FR-4 grade epoxy double-sided copper-clad laminate 1 (copper foil thickness: 18 μm, overall thickness: 1.6 mm) was prepared and treated with a sulfuric acid-hydrogen peroxide soft etching solution. The thickness of the copper foil was set to about 5 μm. Next, a through-hole 2 having a diameter of 0.3 μm was formed in the laminated board, and then electroless copper plating was performed.
A was formed (FIG. 1). Subsequently, the entire surface was subjected to electrolytic copper plating to form an electrolytic copper plating layer 3B having a thickness of about 20 μm. As a result, as shown in FIG. 2, the plating layer 3 covering the inner wall of the through-hole and the entire surface of the copper-clad laminate was formed.

Next, a non-conductive paste of a non-solvent type thermosetting epoxy resin containing copper powder is filled into the through-hole 2 by a printing method through a tetron screen plate having an opening having a diameter of 0.4 mm, and program control is performed. Using a hot air circulating dryer of the formula BOX type, heat from room temperature to 80 ° C. over 15 minutes, hold at 80 ° C. for 30 minutes, and heat from 80 ° C. to 160 ° C.
Heating was performed to 15 ° C. for 15 minutes, and the filled non-conductive paste 4 was cured by holding at 160 ° C. for 60 minutes (FIG. 3).

Then, the entire surface is covered with a belt sander.
Times, polished twice with buff, the entire surface to smooth surface, and the intermediate material A ₁ shown in FIG. At this time, the cured paste 4
The surface 4a had a smoothness of 4 μm or less. After roughening the surface 4a of the hardened paste with permanganic acid, the entire surface is subjected to chemical copper plating, and further to electrolytic copper plating,
And the intermediate material A ₂ by forming a plating layer 5 having a thickness of about 15 [mu] m (FIG. 5).

Then, an etching process is performed by a tenting method to form a copper foil 1a having a thickness of about 5 μm as shown in FIG.
Then, a conductor circuit 6B having a predetermined pattern composed of a plating layer 3 having a thickness of about 20 μm and a plating layer 5 having a thickness of about 15 μm, and pads 6A were formed. The peel strength of the pad 6A formed on the cured paste 4 was measured as follows.

That is, all the copper foil of the used double-sided copper-clad laminate was removed by etching, the used non-conductive paste was solid printed on the surface of the laminate via a screen plate, and then hardened. To form a plating layer thereon to obtain peel strength (conditions: tensile speed 200 mm / min,
180 ° peel). The measurement result is 0.8 to 0.8.
It was 9 kgf / cm. This value is 30 to 40% higher than that of a conventionally used non-conductive paste of thermosetting epoxy resin containing no copper powder.

As described above, according to the present invention, the adhesion strength of the pad formed on the filling paste is greatly improved as compared with the related art.

[0024]

As is clear from the above description, according to the present invention, a pad having excellent flatness and a large adhesion can be formed on a through hole. This is an effect obtained by filling the through-hole with a solventless paste containing metal powder.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a state in which a through hole is formed in a substrate, and further, electroless plating is performed on the entire surface.

FIG. 2 is a cross-sectional view showing a state where a plating layer is formed on the substrate of FIG.

FIG. 3 is a cross-sectional view showing a state where a paste is applied and cured on a substrate.

4 is a sectional view showing the intermediate material A ₁ of the paste surface is polished and removed.

5 is a cross-sectional view showing the intermediate material A ₂ forming a plating layer on the surface of the intermediate material A ₁ in FIG. 4.

6 is a sectional view showing a state in which the intermediate material A ₂ to form a pad and conductor circuit.

FIG. 7 is a cross-sectional view showing a recessed portion formed in an opening of a through hole when a conventional paste is used.

FIG. 8 is a cross-sectional view showing a state when the surface paste of FIG. 7 is polished.

FIG. 9 is a cross-sectional view showing a projection formed in an opening of a through hole when the paste of the present invention is used.

FIG. 10 is a cross-sectional view showing a state when the surface paste of FIG. 9 is polished.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 1a Surface (copper foil) of substrate 1 2 Through hole 2a Inner wall of through hole 2 3 Plating layer 4 Paste 4a Surface of paste filled in through hole 2 5 Plating layer 6A Pad 6B Conductor circuit

Continued on front page F term (reference) 5E319 AA03 AA06 AC02 AC11 CC11 GG03 5E346 AA06 AA12 AA15 AA42 AA43 BB01 BB16 CC31 DD22 DD32 FF04 FF18 GG01 GG17 GG19 GG22 HH11

Claims (2)

[Claims] 1. A step of applying a paste to a multilayer circuit board having a through hole having a surface provided with conductivity, filling the through hole with the paste, and then curing the paste; at least polishing the surface of the paste. Making the surface of the paste flush with the surface of the multilayer circuit board; plating a conductor over the entire polished surface to form a plating layer; and patterning the plating layer to block the through hole A method of forming a pad on a through-hole, the method comprising: forming a pad on the through-hole, the method comprising: forming a pad on the through-hole; 2. The method for forming a pad on a through hole according to claim 1, wherein the through hole is a through hole and / or a via hole.