JPH0513954A - How to fill conductor in green sheet - Google Patents

Abstract

(57) [Abstract] [Purpose] It is an object of the present invention to provide a method for filling a green sheet with a conductor, which can reduce the occurrence rate of defective filling. In a method of filling a conductor into a green sheet in which a via hole 2 of a perforated green sheet 1 is filled with a conductor powder 4 by using a squeegee 3, after filling a conductor powder 4a having a small grain size, particles smaller than that are filled. The conductor powder 4b having a large diameter is supplementarily filled, and the conductor powder 4
The static electricity of the green sheet 1 is removed prior to the filling of a and 4b.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for filling a green sheet with a conductor.

[0002]

2. Description of the Related Art Generally, a multilayer ceramic printed wiring board is formed by forming a green sheet, forming a via hole in the green sheet, filling the via hole with a conductor such as copper powder, printing a conductor pattern on the surface, and laminating the conductor pattern. It is made according to the procedure of sintering (green sheet method).

As a method for filling the via hole with copper powder, as shown in FIG.
Alternatively, a procedure of placing a copper paste and rubbing the via hole 2 with a squeegee 3 is generally adopted.

As a conductor to be filled in the via hole 2 (via conductor), a copper paste in which a copper powder 4 is dispersed in an organic solvent was once the mainstream. However, when the copper paste is used, the filling efficiency into the via hole 2 is low, the organic component is gasified during the subsequent sintering, and air bubbles remain in the via hole to cause conduction failure. There is a problem that the conductor pattern is damaged or deteriorated due to the ejection of the organic component.

Therefore, in recent years, a technique for filling the copper powder 4 itself as a via conductor has been developed. The particle size of the copper powder 4 with which the via hole 2 is filled is often set to about several percent or less of the hole diameter of the via hole 2 in order to reduce the occurrence rate of voids and lower the electric resistance. In a multilayer ceramic printed wiring board with a high circuit density, the diameter of the via hole 2 is reduced to about 90 μm, and correspondingly, the diameter of the copper powder used is also reduced to about several μm. Has been done.

[0006]

However, in this conventional method for filling the conductors into the green sheet, it is necessary to sufficiently fill the copper powder 4 in all the via holes 2 in which tens of thousands of holes can be opened per one green sheet. However, there is a problem that defective filling occurs at a rate of about 30 holes per 100,000 holes.

As a form of defective filling, a hole 5 is formed in the middle portion of the via hole 2 as shown in FIG.
As shown in FIG. 3 (B), the copper powder 4 itself aggregates to form a gap 6 in the filling, and as shown in FIG. 3 (C), the copper powder 4
And the like, in which the space 7 of insufficient filling occurs due to a local decrease in the distribution.

The main causes of these defective fillings are
The copper powder 4 easily aggregates due to static electricity accumulated on the green sheet, such as static electricity generated when the surface of the green sheet 1 is rubbed by the squeegee 3, and the finer copper powder 4 reduces the weight of the copper powder 4. It seems that they are easily aggregated.

Therefore, an attempt was made to supplementarily fill the copper powder 4 having the same particle size at the location where such a defective filling occurs. However, since the copper powder 4 has a high fluidity, a large amount of stress is generated during the supplemental filling. It was found that the holes 5 and the gaps 6 were dispersed in the direction and could not be efficiently crushed.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a conductor filling method for a green sheet, which can reduce the occurrence rate of defective filling.

[0011]

According to the present invention, for example, as shown in FIG. 1, a method of filling a green sheet with a conductor powder 4 by using a squeegee 3 to fill a via hole 2 of a perforated green sheet 1 with a conductor powder 4. In order to achieve the above-mentioned object, in order to achieve the above-mentioned object, after filling the conductor powder 4a having a small particle diameter, the conductor powder 4b having a larger particle diameter is supplementarily filled. If the above method is carried out after the static electricity of the green sheet 1 is removed in advance, the effect can be further enhanced.

[0012]

In the present invention, the conductor powder 4a having a small particle size is first filled, so that the conductor powder 4a is densely filled in most of the via holes 2. In addition, when the conductor powder 4a having a small particle size is filled, the conductor powder 4 in the via hole 2 is filled.
When a hole or a gap is formed between a and the conductor powder 4b having a larger particle size than that, a large internal stress is generated in the conductor powder 4b, and the internal stress is generated by the internal stress. The holes and gaps can be efficiently crushed. Furthermore, by removing the static electricity of the green sheet 1 in advance, the green sheet 1 and the conductor powder 4a,
The charge amount of 4b can be reduced, and the agglomeration due to the charge of the conductor powders 4a and 4b hardly occurs.

[0013]

Embodiments of the present invention will be specifically described below with reference to the drawings. As shown in FIG. 1A, tens of thousands of via holes 2 each having a diameter of about 90 μm are formed in the green sheet 1 that has been perforated. The surface of this green sheet 1 is electrically conductive and is grounded
0 is contacted to remove the static electricity of the green sheet 1.

Next, as shown in FIG. 1 (b), a copper powder 4a as a conductor powder is placed on the green sheet 1,
Rub into the via hole 2 using the squeegee 3. Copper powder 4
The particle diameter of a is several μ which is about several percent of the diameter of the via hole 2 in order to reduce the occurrence rate of voids and lower the electric resistance and to enhance the fluidity of the copper powder 4a at the time of filling.
It is about m. Although most of the via holes 2 are filled with the copper powder 4 due to the filling of the copper powder 4a, a filling failure of about 30 holes per 100,000 holes, for example, a filling failure due to the formation of the holes 5 or the gaps 6 occurs. Is being experienced.

Thereafter, as shown in FIG. 1C, a copper powder 4b having a particle size larger than that of the previous copper powder 4a is placed on the green sheet 1 and rubbed into the via hole 2 using a squeegee 3. The via hole 2 which is already sufficiently filled with the copper powder 4a is not rubbed with the copper powder 4b having a large grain size, but the via hole 2 in which the holes 5 and the gaps 6 are formed is formed.
Alternatively, the insufficiently filled via hole 2 is supplementarily filled with copper powder 4b having a large grain size. That is, since the copper powder 4b having a large particle size has low fluidity, the squeegee 3
A large internal stress is generated when rubbing with, and this crushes the array of the copper powder 4a having a small grain size inside the via hole 2 to effectively eliminate the voids and gaps, and
The space above the via hole 2 created by the collapse of the gap is filled. Further, the space above the via hole 2 caused by insufficient filling is also filled.

As a result, the occurrence of defective filling could be reduced to about 10 holes per 100,000 holes. In this embodiment, the particle size of the copper powder 4b having a large particle size is about 10 μm, but this particle size may be larger than the particle size of the previously filled copper powder 4a. However, if the particle size is made too large, the gap formed between the particles of the copper powder 5b becomes too large, and the electrical resistance of the via conductor may become too large.

[0017]

As described above, according to the present invention, the unfilled portions such as voids and voids formed by the conductor powder having the fine particle diameter that is initially filled are filled with the conductor powder having the fine particle diameter. By supplementarily filling the conductor powder having a large diameter, the conductor powder is effectively crushed and the shortage is supplemented by the conductor powder having a large particle diameter, so that the occurrence of conductor defects can be reduced. Further, by pre-charging the green sheet, the charge amount of the conductor powder filled in the via hole of the green sheet can be reduced, and the conductor powder is less likely to be aggregated due to electrification. Can be reduced.

[Brief description of drawings]

FIG. 1 is a procedure explanatory diagram of an embodiment of the present invention.

FIG. 2 is a procedure explanatory diagram of a conventional example.

FIG. 3 is a schematic cross-sectional view showing a form of defective filling.

[Explanation of symbols]

1 green sheet 2 Beer holes 3 squeegee 4a Small diameter copper powder (conductor powder) 4b Large diameter copper powder (conductor powder)

Claims (2)

[Claims] 1. A method for filling a green sheet with a conductor, wherein a via hole (2) of a perforated green sheet (1) is filled with a conductor powder (4) using a squeegee (3). A method for filling a conductor in a green sheet, which comprises filling (4a) and then filling conductor powder (4b) having a larger particle size than that supplementarily. 2. A step before filling the conductor powder (4),
The method for filling a conductor in a green sheet according to claim 1, wherein static electricity on the green sheet (1) is removed in advance.