JPH03295295A - Formation of multilayer ceramic board via - Google Patents

Abstract

PURPOSE:To improve a via-hole in fill density of conductor and electrical conduction by a method wherein conductor composed of two types of conductor particles, one large in grain diameter and the other small, is filled into a via- hole (small through-hole) in this sequence. CONSTITUTION:When a conductor 4 is filled into a via-hole 3, copper powder 10 small in grain diameter is filled into the hole 3 first with a squeegee. At this point, as the copper powder 10 is small in grain diameter, it is liable to cohere to induce voids. In succession, copper powder 11 large in grain diameter is filled into the via-hole S. As the copper powder 11 is large in grain diameter, it is hard to be filled into the via-hole 3 as compared with the copper powder 10, so that the copper powder 11 is filled by a larger filling power as compared with the copper powder 10. In result, the small copper powder 10 is pressed by the large copper powder 11 to eliminate voids (E), so that a conductor 4 is enhanced in fill density and consequently a via 9 is improved in electrical conduction, and therefore a multilayered ceramic board is improved in reliability.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for forming vias in a multilayer ceramic substrate.
In particular, the present invention relates to a method for forming vias in a multilayer ceramic substrate, which improves the connectivity of the vias that make electrical connections between layers.

Generally, ceramic substrates are widely used as circuit boards on which semiconductor elements are mounted. Ceramic substrates have good properties in terms of heat resistance, heat dissipation, electrical properties, mechanical strength, etc. This ceramic substrate is manufactured by firing a green sheet.

In addition, in recent years, the integration of semiconductor devices has been rapidly increasing, and in response to this trend, multilayer ceramic substrates have been developed to increase the density of conductor patterns by forming multiple layers of thin ceramic plates on which conductor patterns are formed. is provided. In this multilayer ceramic substrate, vias are formed to provide electrical continuity between the multilayered ceramic plates. This via is a via hole (
It has a structure in which a conductor is filled in small diameter holes that penetrate the ceramic plates up and down, and functions to establish electrical continuity between each ceramic plate. Therefore, if the buyer is not formed properly,
Electrical conduction between each layer becomes impossible, and the ceramic substrate no longer functions.

Therefore, a method for forming vias that can form vias with high reliability is desired.

[Conventional technology]

FIG. 3 shows a conventional method of forming a via.

Conventionally, in order to form a via, a mask film 2 is first placed on a green sheet 1 as shown in FIG. A via hole 3 is formed as shown in Figure (B).

Once the via hole 3 is formed, the conductor 4 is filled into the via hole 3 using a squeegee 7, as shown in FIG. At this time, the side of the green sheet 1 that is different from the filling side of the conductor 4 is under negative pressure, and is configured to easily fill the via hole 3 with the conductor 4. This conductor 4 is a mixture of copper powder and a binder, and the particle size of the copper powder is 0.3 to 10.0 μm relative to the diameter of the via hole 3, which is 50 to 200 μm.
It was selected that the size was around m. In this way, the conventional conductor 4 was composed only of copper powder having a small particle size and having only one type of particle size.

When the via hole 3 is filled with the conductor 4 as described above, a land 5 is formed on the surface of the green sheet l that is different from the surface on which the mask film 2 is disposed so as to close the via hole 3, as shown in FIG. The mask film 2 is then peeled off from the green sheet 1 as shown in FIG.

The green sheets 1 in which the via holes 3 are filled with the conductors 4 as described above are stacked and fired as shown in FIG. 3(F) to form a multilayer ceramic substrate. still,
The figure (F') shows various ways in which the gap 8 is generated.

[Problem to be solved by the invention]

As described above, in the conventional via forming method, copper powder having a small particle size or having only one type of particle size is used as the conductor 4. When the elongated via hole 3 is filled with powder having a small particle size in this way, the fluidity of the copper powder in the hole is poor and agglomeration is likely to occur, and as shown in FIG. If it occurs in the hole 3, a gap 8 will be formed in the via hole 3, reducing the packing density of the conductor 4.

If the packing density of the conductors 4 is reduced in this way, the electrical conductivity of the vias will deteriorate, and in the worst case, electrical continuity will not be established and the multilayer ceramic substrate will no longer function.

The present invention has been made in view of the above points, and it is an object of the present invention to provide a method for forming vias in a multilayer ceramic substrate that can improve the packing density of conductors.

[Means to solve the problem]

In order to solve the above-mentioned problems, the present invention processes holes in a green sheet (1) to form via holes (3), and then fills the via holes 3) with a conductor (4). Next, by laminating and firing a plurality of green sheets (1), the conductor (4) is also fired to form a via (9) for electrical continuity between each layer, forming a via of a multilayer ceramic substrate. In the method, two types of the conductor (4), a small-grain conductor (10) and a large-grain conductor (11), are prepared, and the small-grain conductor (10) is first filled into the via hole (3). Later, large-grain conductors (
11).

[Effect]

According to the above via forming method, after filling the via hole (3) with the small particle diameter conductor (10), the large particle diameter conductor (11) is filled into the via hole (3). Even if agglomeration occurs and gaps are formed during filling of the small particle conductor (11), the large particle conductor (11) filled afterwards will
10) is pushed in, so the gap that occurs is crushed. This improves the packing density of the conductor (4) and improves the electrical conductivity of the via (9).

〔Example〕

Next, an embodiment of the method of the present invention will be described with reference to the drawings. FIG. 1 is a process diagram of a method for forming vias in a multilayer ceramic substrate, which is an embodiment of the present invention. In addition, the same figure (A), (
The steps shown in B) and (E) to (H) are completely the same as the conventional via forming method. Therefore, the steps shown in each figure will be briefly explained.

To form a via, first place a mask film 2 on a green sheet 1 (as shown in FIG. (shown in Figure (B)). The diameter of this via hole 3 is 50 to 20
It is said to be about 0 μm.

The steps (C) to (C) in the same figure are performed after the via hole 3 is formed.
The step shown in E) is a characteristic step of the method of the present invention. The process shown in each figure is the process of filling the via hole 3 with the conductor 4.

To fill the via hole 3 with the conductor 4, two types of copper powder with different particle sizes are prepared. Of these, 10 copper powders with small particle size (
The copper powder (hereinafter referred to as small particle size copper powder) is the same as the conventionally used copper powder, and has a particle size of about 0.3 to 10.0 μm. Further, the particle size of the copper powder 11 having a large particle size (hereinafter referred to as large particle size copper powder) is selected to be, for example, 70 μm. The particle size of this large particle size copper powder 11 is at least larger than the particle size of the small particle size copper powder 10, and
Is it necessary to select a diameter smaller than that of the ? To fill the via hole 3 with the conductor 4, as shown in the same figure (C),
First, small particle size copper powder 1O is filled using a squeegee 7. At this time, as described above, since the small particle size copper powder 1O has a small particle size, there is a possibility that agglomeration may occur and the gap 8 may be generated.

When the via hole 3 is filled with the small particle size copper powder 10, the large particle size copper powder 11 is subsequently filled into the via hole 3 as shown in FIG. Since the large particle size copper powder 11 has a large particle size, it is difficult to enter the via hole 3 compared to the small particle size copper powder lO. For this reason, it is preferable that the large-particle copper powder 11 be filled with the squeegee 7 with a stronger filling force than when the small-particle copper powder 10 is filled.

As described above, after the via holes 3 are filled with the small-particle copper powder 1O, by filling the large-particle copper powder 11, as shown in the figure (
As shown in E), the small particle size copper powder IO is pressed down by the large particle size copper powder 11, and the gap 8 is in a crushed state. This increases the packing density of the conductor 4 in the via hole 3, thereby improving the electrical conductivity of the via 9, and thus improving the reliability of the multilayer ceramic substrate.

Figure 2 shows the relationship between the diameter of large-particle copper powder and the packing density of the conductor, which the inventor found through experiments.
(Experimental results are shown for a via hole with a diameter of 90 μm.) As shown in the figure, when the particle size of the large-particle copper powder is very small or about the same as the diameter of the via hole, the packing density is low. Therefore, large particle diameter copper powder 1
When selecting the particle size of the conductor 1, the packing density of the conductor 4 can be improved by selecting the particle size to be approximately half the diameter of the via hole 3 or slightly larger than this.

When the via hole 3 is filled with the conductor 4 as described above, a land 5 is formed on a surface of the green sheet I that is different from the surface on which the mask film 2 is disposed so as to close the via hole 3 (first
(shown in Figure (F)), then the mask film 2 is peeled off from the green sheet 1 (as shown in Figure (G)). continue,
A plurality of the ceramic plates 12 on which the vias 9 are formed as described above are laminated and fired to form a multilayer ceramic substrate 13, as shown in FIG.

When this ceramic plate 12 is laminated, the ceramic plate 1
Since the packing density of the conductors 4 in the vias 9 formed in the multilayer ceramic substrate 2 is high, the electrical connection between the adjacent ceramic plates 12 is ensured, and the reliability of the multilayer ceramic substrate 13 can be improved.

Incidentally, in the above-mentioned embodiments, an example was given in which copper powder was filled as a conductor, but the conductor is not limited to copper powder.
Of course, powder of other conductive metals may also be used.

〔Effect of the invention〕

As described above, according to the present invention, since the packing density of the conductor is improved, the electrical conductivity of the via is improved, and the reliability of the multilayer ceramic substrate can be improved.

[Brief explanation of drawings]

Fig. 1 is a process diagram for explaining the via formation method for a multilayer ceramic substrate according to an embodiment of the present invention in the order of the forming steps, and Fig. 2 shows the relationship between the diameter dimension of large-particle copper powder and the packing density. FIG. 3 is a process diagram showing an example of a conventional method for forming vias in a multilayer ceramic substrate. In the figure, I is a green sheet, 3 is a via hole, 4 is a conductor, 9 is a via, 10 is a small particle diameter copper powder, 11 is a large particle diameter copper powder, 12 is a ceramic plate, and 13 is a multilayer ceramic substrate.

Claims (1)

[Claims] The green sheet (1) is made with holes (3).
), the conductor (4) is filled into the via hole (3), and then the conductor (4) is also fired by laminating and firing a plurality of the green sheets (1), and the conductor (4) is also fired. In a method for forming vias of a multilayer ceramic substrate for forming vias (9) for electrical conduction, two types of conductors (4) are prepared: a small-grain conductor (10) and a large-grain conductor (11). , the via hole (3) is first filled with the small particle diameter conductor (10), and then the large particle diameter conductor (10) is filled into the via hole (3).
1) A method for forming vias in a multilayer ceramic substrate, characterized by filling the vias.