JPH03211789A - Method of filling via hole in ceramic board with metal fine powder - Google Patents

Abstract

PURPOSE:To enhance the filling density of metal fine particles in a via hole by mixing three and more types of metal fine particles whose grain sizes are different from each other. CONSTITUTION:Metal fine particles 4 are mixed by three and more types of metal fine particles whose grain sizes are different from each other so as to produce mixed powder. The greatest grain size (a primary grain size) is first determined based on the size of void produced between the particles when they are the most densely but in hexahedron close-packed structure, and then a large grain size (a secondary grain size) is determined. Then, their mixing ratio is determined based on the capacity of a via hole 3 and the capacity of void between the particles produced when the metal fine particles 4 of the primary grain size are the most densely put in hexahedron close-packed structure. In addition, the size of the void between the particles remaining after the metal fine particles 4 of the primary and secondary sizes are put in, is determined, based on the aforesaid data, a three-dimensional grain size and the mixing ratio are determined. Other grains sizes are then determined so as to produce their minimum grain size which is over 0.5mum which does not produce any coagulation. This construction makes it possible to minimize the void formed between the metal powder 4 in the via hole 3.

Description

[Detailed Description of the Invention] [Summary] Regarding a method for filling fine metal powder into via holes of a ceramic substrate, the present invention aims to increase the packing density of fine metal powder filled in the via holes. In a method for filling a via hole with fine metal powder,
The above-mentioned fine metal powder was configured to be a mixed powder of three or more types having different particle sizes.

[Industrial application field]

The present invention relates to a method for filling a via hole with fine metal powder.

[Conventional technology]

The ceramic substrate used is a green sheet in which a slurry of ceramic raw material is thinly spread on a Mylar film and then cut into regular lengths. This green sheet is then aged for about two weeks to release the stress applied to the ceramic raw material during the laying and cutting of the raw material. After that, the via hole is opened, and as explained in detail below, the via hole is filled with fine metal powder. Furthermore, each layer with a printed conductor pattern is laminated and fired, and finally, a surface conductor pattern is formed. A ceramic substrate is obtained.

There are a dry method and a wet method for filling the metal fine powder, and FIG. 2 shows the dry method for filling the metal fine powder. First, Koumei processes the aged green sheet 1 shown in FIG. 2(a) to form via holes 3 of approximately 90 to 120 μm as shown in FIG. 2(b).
As shown in FIG. 2(c), the via hole 3 is filled with metal fine powder 4 for forming a conductor. In this step, the Mylar film 2 of the green sheet 1 is placed on the upper side,
Sprinkle fine metal powder 4 over the Mylar film 2, and rub the top surface of the Mylar film 2 with a squeegee 5 made of rubber, for example, to rub the fine metal powder 4 into the via hole 3, and remove metal from other parts. The fine powder 4 is scraped off from one side of the Mylar film 2. After this filling step, in the scattering prevention treatment step shown in FIG. 2(d), the metal cream 8 is rubbed onto the end of the Mylar film 2 side of the via hole 3 with another squeegee, and the green sheet 1 is further turned over. A protective film 7 is attached to the side opposite to the Mylar film 2.

After this, a conductive pattern is printed on the top surface of the green sheet 1 in a printing process, a required number of intermediate layers and surface layers are laminated in a lamination process to form a multilayer, and the laminated green sheet is baked and hardened in a firing process. After removing the binder contained in the green sheet and polishing both the front and back surfaces in a polishing step, a surface conductor pattern is formed on the polished surface in a thin film forming step.

On the other hand, in the wet method (not shown), a metal paste made by mixing fine metal powder with an organic binder (vehicle) and other compounds is applied to the top surface of the green sheet, and the top surface of the green sheet is rubbed with a squeegee to fill the via holes with the metal paste. It's a method. However, in this case, there is a problem that the gaseous components generated by the decomposition of the vehicle during the firing process are encapsulated in the conductor, making the conductor porous, so today, the above-mentioned dry method is mainly adopted. .

The minimum value of the particle size of the metal fine powder 4 used for filling the metal fine powder 4 is a value that can maintain the fluidity of the metal fine powder 4, that is, larger than 0.5 μm, and the maximum value is greater than the through hole diameter. It is set to a value that does not cause the so-called wall effect that causes a rough filling part along the wall, that is, a value smaller than 1/50 of the through-hole diameter. The average particle size of Powder 4 is .

It is about 1 μm.

[Problem to be solved by the invention]

As mentioned above, from the viewpoint of the fluidity of the fine metal powder 4 and the wall effect, conventionally, the via hole 3 has a diameter of about 90 to 120 μm.
However, according to the above-mentioned conventional method, the volume of the fine metal powder 4 actually filled with respect to the volume of the via hole 3 is That is, the filling rate is only about 40 to 60%. Considering that the closest packing ratio calculated theoretically from the particle size of fine metal powder is about 74%, it can be said that the filling ratio obtained by the above-mentioned conventional method is extremely dissatisfied.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a method for filling a via hole with fine metal powder that can increase the packing density of the fine metal powder filled in the via hole. .

[Means to solve the problem]

As shown in FIG. 1, the present invention provides a method for filling a via hole with fine metal powder 4 in which a via hole 3 bored in a green sheet l is filled with fine metal powder. The above mixed powder is used.

[For production]

The particle size of the metal fine powder 4 to be filled is first determined by the size of the void formed between the particles when the metal fine powder 4 of the maximum particle size (primary particle size) is hexagonally close packed. powder 4
The next largest particle size (secondary particle size) is determined, and the primary particle size is determined from the volume of the via hole 3 and the volume of voids between particles that occur when metal fine powder 4 of the primary particle size is hexagonally close-packed. The mixing ratio of the fine metal powder 4 having the particle size and the fine metal powder 4 having the secondary particle size is determined. In addition, the size and total volume of the gaps between the particles remaining after filling the metal fine powder 4 with the primary particle size and the metal fine powder 4 with the secondary particle size are determined, and based on these, the tertiary particle size is determined. and its blending ratio is determined. In this way, grain sizes with increasing orders are determined in sequence.

The problem here is how to determine the above-mentioned primary particle size, but the minimum particle size calculated by the above procedure should be the smallest possible value of 0.5 μm or more that does not cause aggregation (fluidity can be ensured). The particle size of the first order or other orders is also determined so that

By rubbing the metal fine powder 4 made of such a mixed powder with different particle sizes into the via hole 3, the voids formed between the particles of the metal fine powder 4 in the via hole 3 can be minimized, and the metal The packing rate of fine powder can be increased to close to the closest packing rate.

〔Example〕

The procedure of filling fine metal powder into a via hole according to the present invention is exactly the same as the conventional procedure shown in FIG.

That is, as shown in FIG. 2(b), the green sheet 1 after ripening shown in FIG. 2(a) has a diameter of 90 to 120 μm.
A large number of via holes 3 are drilled.

After this, as shown in FIG. 2(c), the green sheet 1
with the Mylar film 2 side up, and place the Mylar film 2
Fine metal powder 4 made of fine copper powder is sprinkled onto the green sheet 1 from above, and by rubbing the top surface of the Mylar film 2 with a squeegee 5 made of rubber, for example, the metal is poured into the via holes 3 drilled in the green sheet 1. Fine powder 4 is filled.

After this filling step, as a treatment to prevent the fine metal powder 4 from scattering, a metal paste 8 is applied to the end of the Mylar film 2 side of the via hole 3 filled with the fine metal powder 4, as shown in FIG. 2(d). In addition, a protective film 7 made of polyethylene or the like is attached to the surface of the green sheet 1 opposite to the mylar film 2.

In the present invention, the particle size of the metal powder 4 used in the filling step is three or more types (here, five types).

That is, the next largest particle size of the metal fine powder 4 depends on the size of the voids formed between the particles when the metal fine powder 4 having the maximum particle size (primary particle size) of the metal fine powder 4 is hexagonally close-packed. (secondary particle size) is determined. Furthermore, the volume of via hole 3 and 1
From the volume of voids between particles that occur when the fine metal powders 4 of the following particle sizes are hexagonally close-packed, the fine metal powders 4 and 2 of the primary particle size are
The mixing ratio of the metal fine powder 4 having the primary particle size is determined, and the size of the void between the particles remaining after filling the metal fine powder 4 having the primary particle size and the metal fine powder 4 having the secondary particle size is determined. , and the total volume of their voids are determined, and based on these, the particle size and blending ratio of the tertiary fine metal powder 4 are determined. In this way, grain sizes with increasing orders are determined in sequence.

Table 1 and FIG. 1 show the five particle sizes sequentially determined in this manner and their blending ratios (total 100%). Here, the minimum particle size does not cause agglomeration (fluidity can be ensured)
Other particle sizes are determined to be as small as possible, 0.045 μm or more.

Table 4: Fine metal powder 4 made of these five different particle sizes
When rubbed into via hole 3, 11 of the diameter of via hole 3
Although it contains fine metal powder 4 with a diameter larger than 50 (i.e., a particle size where a wall effect appears), it contains fine powder with a small particle size, so the peripheral surface of the via hole 3 is affected by the wall effect. Fine powder with a small particle size enters between the voids generated in the vicinity, increasing the filling rate. In addition, in the center of the via hole 3, particles with different particle sizes are blended in an optimal blending ratio, so the voids between the particles are minimized, and the filling rate of the metal fine powder 4 is reduced to near the closest packing rate, for example, 71°6. %, thereby reducing the incidence of voids in via conductors, the incidence of disconnections, and the incidence of failures during thin film formation.

It was confirmed that the case of using the fine metal powder 4 made of these five different particle sizes and the case of using the conventional fine metal powder 4 with a broad distribution of particle sizes centered on an average particle size of 1.1 μm. The filling rate, micro-void occurrence rate, via disconnection occurrence rate, and failure occurrence rate during thin film formation are shown in Table 2.

Table 2 Note that the filling rate is calculated by calculating the filling amount (weight) of fine metal powder per via volume weight as the filling density, and calculating this filling density as the theoretical density, that is, the weight of fine metal powder 4 per volume weight of the via. (−
Via volume x specific gravity), and the microvoid generation rate is the diameter of the via hole exposed on the polished surface after firing and polishing.
This is the value calculated for the number of voids of 0.8m or more per 10,000 holes.
This is the occurrence rate of via disconnection between the front and back sides after firing, and the failure occurrence rate during thin film formation is the value calculated for 10,000 holes of the occurrence rate of disconnection failure after forming a thin film in the thin film forming process. .

In the above embodiment, metal fine powder 4 having five different particle sizes is used, of which 5 μm, 2 μm,
．． In the case of using fine metal powder 4 having three different particle size distributions centered on the three particle sizes of 0.07 μm and 0.58 μm, a filling rate exceeding 70% could be similarly obtained.

(Effects of the Invention) As described above, in the present invention, since the metal fine powder is a mixed powder with three or more types of particle sizes, the voids caused by the wall effect are filled by particles with small particle sizes, and the periphery of the via hole is filled with small particles. In addition to increasing the filling rate near the surface, it is also possible to prevent small-sized particles from entering the voids formed between large-sized particles in the center of the via hole, thereby preventing large voids from forming within the via hole. As a result, it is possible to increase the filling rate of metal powder into the via hole to a high filling rate comparable to that of a close-packed structure, which reduces the resistance of the conductor in the via hole after firing and reduces the occurrence of via disconnection. This can improve the reliability of via connections.

[Brief explanation of drawings]

FIG. 1 is a particle size distribution diagram showing the particle size distribution and compounding ratio of metal powder used in a method for filling fine metal powder into a via hole according to an embodiment of the present invention, and FIG. FIG. 3 is a conceptual diagram showing the steps of a method for filling fine metal powder. In the figure, l... Green sheet, 3... Beer hole, 4...
- Fine metal powder, 5... Squeegee. (a)! % & (b) North September (C) Filling (d) 4 Shikiki Todokoro Tanuki - 47 Mackerel Powder Filling 5 Sweets Flow Diagram 2nd Do 1

Claims (1)

[Scope of Claims] [1] Via hole (
3) A method for filling a via hole with fine metal powder (4), wherein the fine metal powder (4) is a mixed powder of three or more types of different particle sizes. A method of filling fine metal powder into via holes.