JPH043496A - Forming method of viahole of multilayer ceramic board - Google Patents

Abstract

PURPOSE:To improve the electrical connectability of a viahole by using copper powder as a conductor while adding zinc stearate or/and titania (TiO2) to the conductor and filling a viahole with the conductor. CONSTITUTION:The grain size of copper powder is selected in approximately 1.1mum on an average. The fill of zinc stearate is selected in approximately 0.3-3.0wt.%. When a viahole 3 filled with a conductor 4 constituted, alumina powder is also filled simultaneously. The grain size of the alumina powder is chosen in 0.3-3mum, and loading thereof is 5-10Vol.%. When the viahole is filled with the conductor 4, a protective film 10 is disposed on a surface different from the disposing surface of the mask film 2 of a green sheet 1 so as to close the viahole 3. When the protective film 10 is arranged, the upper section of the conductor 4 is filled with copper paste 4a. The copper paste 4a is filled in the thickness of approximately the half of the thickness (approximately 38mum) of the make film 2. The copper paste 4a is filled by using a rubber squeegee 7 in the same manner as the filling of copper powder.

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, in which vias for electrical connection between layers are formed by filling via holes with conductors.

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, and mechanical strength. This ceramic substrate is manufactured by firing a green sheet.

In addition, in recent years, the integration of semiconductor devices has been rapidly increasing. A ceramic substrate is provided. In this multilayer ceramic substrate, vias are formed for electrical connection between the multilayered ceramic plates. This via has a structure in which a via hole (a small diameter hole passing vertically through the ceramic plate) formed in the ceramic plate is filled with a conductor, and functions to establish electrical continuity between the ceramic plates. Therefore, if the vias are not formed properly, electrical continuity between the layers will not be established and the ceramic substrate will no longer function.

Therefore, there is a need for a via formation method that can form a hire car with high reliability.

[Conventional technology]

FIG. 4 shows a conventional method of forming a via.

Conventionally, in order to form a via, first a mask film 2 is placed on a green sheet 1 (composed of glass powder, alumina powder, an organic binder, etc.) as shown in FIG. Both the green sheet 1 and the mask film 2 are punched to form via holes 3 as shown in FIG.

Once the via hole 3 is formed, the conductor 4 is filled into the via hole 3 using a rubber squeegee 7, as shown in FIG.

Conventionally, as the conductor 4, a copper paste made of a mixture of copper powder and an organic binder has been used.

When the conductor 4 is filled in the via hole 3 as described above, a land 5 is placed on the surface of the green sheet 1 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 whose via holes 3 were filled with conductors 4 as described above were stacked and fired as shown in FIG.

However, in the conventional via forming method described above, the organic binder contained in the green sheet 1 and the conductor 4 is gasified during firing (hereinafter, this gas is referred to as binder gas), and this remains in the via hole 3 as a gaseous residue. It ends up. This gaseous residue creates a void in the conductor 4 filled in the via hole 3, causing the conductor 4 to break or increase its resistance value, resulting in a decrease in the electrical conductivity of the via. there were.

Therefore, only copper powder is filled into the via hole 3 as the conductor 4,
A conceivable method is to prevent the generation of gaseous residue by configuring the conductor 4 so that no binder gas is generated, and filling the via hole 3 with copper oxide that oxidizes and decomposes the binder gas generated from the green sheet 1. . With this configuration, no gaseous residue remains in the via hole 3 during the firing process, and the electrical connectivity of the via can be improved.

[Problem to be solved by the invention]

Is it possible to improve the electrical connectivity of the via by using copper powder as the conductor 4 as described above?
The particle size of the copper and copper oxide constituting the copper powder is small, and when the elongated via hole 3 is filled with powder with such a small particle size, the fluidity of the copper powder in the hole is poor and agglomeration is likely to occur.
A gap 8 is formed in the via hole 3 and the packing density of the conductor 4 is reduced.

If the packing density of the conductor 4 decreases in this way, the electrical connectivity of the via will deteriorate, and in the worst case, there will be no electrical continuity (and the multilayer ceramic board will no longer function). .

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

[Means to solve the problem]

In order to solve the above problems, in the present invention, holes are formed in the green sheet (1) to form ear holes (3), and then a conductor (4) is inserted into the ear holes (3). A via of a multilayer ceramic substrate, in which a plurality of green sheets (1) are laminated and fired, thereby also firing the conductor (4) to form a via (9) for electrical continuity between each layer. In the forming method, copper powder is used as the conductor (4), and this conductor (
4) Zinc stearate or/and titania (Ti
The method is characterized in that the above-mentioned ear hole (3) is filled with O2).

[Effect]

Zinc stearate functions to improve the fluidity of the conductor (4) when it is filled into the ear hole (3). Furthermore, titania has the function of improving the dispersibility of the conductor (4) when it is filled into the ear hole (3). Therefore, by adding zinc stearate and titania to the conductor (4), the packing density of the conductor (4) can be increased.

〔Example〕

Next, a first embodiment of the method of the present invention will be described with reference to the drawings. FIG. 1 is a process diagram showing a method for forming vias in a multilayer ceramic substrate according to an embodiment of the present invention. In addition, the same figure (A
), (B), and (E) to (G) 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)).

This green sheet 1 is made of a mixture of glass powder and alumina powder containing an organic binder, and the diameter of the via hole 3 is about 50 to 200 μm.

(C) and (2) are performed after the via hole 3 is formed.
The step shown in D) 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.

The first embodiment is characterized in that copper powder is used as the conductor 4 filled in the via hole 3, and in addition to the conductor 4, zinc stearate is added. The particle size of this copper powder is set to have a specific flow distribution, for example, an average of 1.
The thickness is selected to be approximately 1 μm. Moreover, the filling amount of zinc stearate is 0.3 to 3. It is selected to be approximately Owt%. Further, when filling the via hole 3 with the conductor 4 having the above structure, alumina powder is also filled. The particle size of this alumina powder is selected to be 0.3 to 3 μm, and the filling amount is set to 5 to 1 ovo 1%.

The above-mentioned zinc stearate improves the fluidity during filling of copper powder. Zinc stearate is known as a lubricant, and by mixing this zinc stearate with copper powder and filling it into the via hole 3, the zinc stearate is coated on the surface of each copper powder and the inside of the via hole 3. The fluidity of copper powder is improved. Therefore, the copper powder does not aggregate during filling, and the packing density of the conductor 4 can be improved. Note that the alumina powder is filled in order to suppress abnormal grain growth.

The method for filling the via hole 3 with this conductor 4 is the same as the conventional one, and as shown in FIG. and fill it.

After the conductor 4 is filled, a protective film 10 is then disposed on a surface of the green sheet L different from the surface on which the mask film 2 is disposed so as to close the via hole 3, as shown in FIG. Ru. This protective film 10 has the function of preventing the conductor 4 filled in the hire hole 3 from scattering and protecting the surface on which a conductor pattern, which will be described later, is formed.

After the protective film 10 is provided, the top of the conductor 4 is then filled with copper paste 4a. This copper paste 4a is filled to a thickness that is approximately half the thickness of the mask film 2 (approximately 38 μm). This copper paste 4a is filled using a rubber squeegee 7 in the same way as the filling of copper powder. The copper paste 4a formed in this manner has the function of preventing the filled conductor 4 from scattering, and also prevents the filled conductor 4 from scattering if a void is formed at the top of the via hole 3. It has the effect of filling voids.

When the conductor 4 is filled into the via hole 3 as described above, the protective film 10 is peeled off, and a copper pattern 11 is screen printed on the surface from which the protective film 10 has been peeled off, and a land is placed on the lower end of the via 9. 5 is formed (see figure (
(shown in E)). Subsequently, the mask film 2 of the thus formed ceramic plate 12 is removed as shown in FIG. 2(F), and a plurality of ceramic plates are laminated and fired as shown in FIG. 2(G). It will be done.

Before firing, a plurality of ceramic plates 12 are stacked and pressurized, so that each ceramic plate 12 stretches in the plane direction, and each stacked green sheet 1 contracts in the stacking direction. At this time, the conductor 4 filled in the via hole 3
is compressed by the contraction of the green sheet 1, but since zinc stearate, which functions as a lubricant, is added in addition to the copper powder in the via hole 3, the fluidity of each copper powder is good, and this compression The force causes the copper powder to move, and by simply filling it with the squeegee 7, the gaps between the copper powders are filled. Thereby, the packing density of the conductor 4 into the via hole 3 can be further improved.

As mentioned above, by using copper powder as the conductor 4 and adding zinc stearate to the conductor 4, it is possible to improve the packing density when filling the conductor 4, and when the ceramic 12 is laminated, this packing density can be improved. In order to further improve the electrical connectivity of the formed vias 9, it is possible to improve the reliability of the multilayer ceramic substrate.

FIG. 2 shows the relationship between the sintered density and the amount of zinc stearate added. As shown in the figure, as the amount of zinc stearate added increases, the sintered density improves, and when the amount of increase exceeds 1 wt%, the sintered density becomes constant at about 80%. Furthermore, if too much zinc stearate is added, the resistance value of the conductor 4 will increase, so the amount of zinc stearate added should be selected to be about 0.3 to 3 wt%.

Next, a second embodiment of the present invention will be described. In the method for forming vias in a multilayer ceramic substrate according to the second embodiment, the operations performed in each step are almost the same as those described using FIG. 1, as shown in FIG. 1(C).

In the process shown in (D), a mixture of copper powder and oxidized steel is used as the conductor 4, and titania (TiO2) is also added when filling the via hole 3 with the conductor 4. That is. The particle size of this copper powder is selected to be, for example, about 1.1 μm on average so as to have a specific flow distribution. In addition, the filling pattern of copper oxide is 10 to 2
It is selected to be 0wt%.

Titania has the function of improving the dispersibility of copper and copper powder, or copper and copper oxide, and by adding titania, it prevents the agglomeration of copper powder and copper oxide when filling the via hole 3 with the conductor 4. It can be prevented. By thus preventing agglomeration of the copper powder and oxidized steel, it is possible to improve the packing density of the conductor 4 in the via hole 3. In addition, since the copper powder and copper oxide are uniformly filled into the via hole 3, the binder gas generated from the green sheet 1 can be easily released, and the generation of gaseous residue can be prevented. It is also possible to improve the packing density of the conductors 4. Therefore, the electrical connectivity of the vias 9 is improved, and as a result, the reliability of the multilayer ceramic substrate can be improved.

Furthermore, titania has the function of improving the adhesion between the copper powder and the green sheet l in the via hole 3. Assuming that titania is not added, the adhesion between the copper powder and Green Sea) 1 (the inner wall of the via hole 3) is poor;
Bores occur due to the copper powder and green sheet not coming into close contact. However, by adding titania to the conductor 4 and filling the via hole 3, the adhesion between the conductor 4 and the green sheet 1 is improved and the occurrence of bores can be prevented.

Therefore, this also makes it possible to improve the electrical connectivity of the vias 9.

FIG. 3 shows the relationship between the copper agglomerated particle size and the amount of titania added. As shown in the figure, as the amount of titania added increases, the copper agglomerate particle size decreases, and the via hole 3
The packing density of the conductor 4 is improved. However, if the amount of titania added is too large, the resistance value of the via 9 will increase.

Therefore, the amount of titania added is preferably selected to be approximately 0.2 to 0.6 wt%.

Incidentally, in the above-mentioned embodiments, a configuration is shown in which zinc stearate and titania are added to the conductor 4 separately, but zinc stearate and titania may be used simultaneously.

When both are added at the same time, zinc stearate and titania each exhibit the above-described effects independently, and the electrical connectivity of the hire car 9 can be further improved.

〔Effect of the invention〕

As described above, according to the method of the present invention, the occurrence of bores in the conductor is eliminated, and the packing density of the conductor is increased, so that the electrical conductivity of the via can be improved, and the multilayer structure can be improved. It has features such as being able to improve the reliability of ceramic substrates.

[Brief explanation of drawings]

FIG. 1 is a process diagram for explaining the via forming method for a multilayer ceramic substrate according to an embodiment of the present invention; FIG. 2 is a diagram showing the relationship between sintered density and the amount of zinc stearate added; The figure is a diagram showing the relationship between the copper agglomerated particle size and the amount of titania added, and FIG. 4 is a process diagram showing an example of a conventional method for forming a pyre in a multilayer ceramic substrate. In the figure, 1 is a green sheet, 2 is a via hole, 4 is a conductor, 9 is a via, IO is a protective film, 12 is a ceramic plate, and 13 is a multilayer ceramic substrate. Figure 1 Figure 2

Claims (1)

[Claims] The green sheet (1) is made with holes (byer holes).
3), the conductor (4) is filled in the via hole (3), and then the conductor (4) is also fired by laminating and firing a plurality of green sheets (1). In a method for forming a via for a multilayer ceramic substrate in which a via (9) is formed to provide electrical continuity between layers, copper powder is used as the conductor (4), and the conductor (4)
Zinc stearate or/and titania (TiO_
2) is added to fill the via hole (3).