JPH06188561A - Via forming method for thick film printed board - Google Patents

Abstract

PURPOSE:To improve the fillability of the thick film copper via hole to be formed in an ultra multilayer glass-ceramic wiring board which is widely used for large type electric machines, and to form a highly minute conductive via hole under an intrinsic baking condition by a method wherein the characteristics of conductor powder are properly controlled. CONSTITUTION:In the manufacture of a low-temperature-baked glass-ceramic wiring board having copper as conductive material, conductive powder 2, consisting of copper powder having area/weight ratio of 0.3 to 0.6m<2>/g, 50% value of particle-size distribution of 5.0 to 7.0mum in particle diameter, liquidity index of 70 to 79 and coating amount of oxidation preventing agent of 12 to 17wt.%, is put in the via hole 1a provided on a green sheet 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of forming a thick film copper via of an ultra-multilayer glass ceramic wiring board which is widely used in the construction of large electronic equipment.

Recently, a printed wiring board used for a large-scale electronic device such as a large-scale general-purpose computer has been required for an increase in circuit scale and a high speed while utilizing the characteristics of inorganic materials such as glass ceramic. The formed wiring patterns and interlayer connection vias are required to be miniaturized and densified and to be multilayered.

Therefore, since the printed wiring board is limited in expansion in the two-dimensional direction due to downsizing, it is inevitable to increase the number of layers in the thickness direction, and the increase in the number of layers increases the number of connections in the three-dimensional direction. Accordingly, higher reliability of connection without breakage is required. In order to achieve this, the thick film copper vias for interlayer connection must have sufficient stability not only for thermal stress but also for various stresses, etc., so the filling property of the conductor powder is improved and the connection reliability is high. There is a need for a new method of forming vias for thick film printed circuit boards that can form vias.

[0004]

2. Description of the Related Art A method of forming a via for a thick film printed board, which has been widely used in the past, is as follows. As shown in FIG.
By supplying the paste-like or powder itself of the conductor powder 2 made of copper to one end edge and moving the conductor powder 2 to the other end side of the green sheet 1 by the squeegee 3, the green sheet 1 is punched. About 100,000 via holes 1a were filled with the above-mentioned conductor powder 2, and 60 green sheets 1 were positioned and laminated and baked by the heating time chart A as shown in FIG. Vias are formed.

The conductor powder 2 filled in the via holes 1a of the green sheet 1 has the powder characteristics shown in Table 1.

[0006]

[Table 1]

The fluidity index and the fluidity index of the fluidity index are numerical values comprehensively judged from the seven items of fluidity and fluidity measured using a "powder tester" manufactured by Hosokawa Micron.

[0008]

A problem with the conventional method of forming vias for thick film printed boards described above is that the diameter of the via hole 1a formed in the green sheet 1 is about 100 μm.
m, which has a high aspect ratio (green sheet thickness / via hole diameter) with respect to the thickness of the green sheet 1 of about 300 μm, in order to increase the filling density in the via holes 1a, it is inevitable to make the conductor powder finer. As a result, the agglomeration of the conductor powder and the deterioration of the fluidity impede the filling property, thereby lowering the filling density and causing the disconnection defect as shown in the filling property section of Table 2.

[0009]

[Table 2]

However, even if the characteristics of the conductor powder that achieves a good filling property and a high filling density are set for one via hole 1a, there are variations in the defects and the filling density for 100,000 via holes 1a per sheet. It is not easy to fill without sinter, and the instability of sinterability caused by this variation is unavoidable.

Further, the selection of the conductor powder with an emphasis on the filling property does not always give good sinterability, and in the conventional conductor, the time chart A for heating the laminated green sheet is shown in FIG. On the other hand, the shrinkage behavior of the glass-ceramic has a curve like B, but the shrinkage behavior of the conductor powder filled in the via hole is as shown by the curve C in the time zone when the shrinkage of the glass-ceramic rapidly increases. The fluctuations become large and small vias (cracks) are generated in the formed vias.

Therefore, as shown in the sinterability section in Table 2 above, initial disconnection defects: 2 cases / 6 million connections are caused by the above-mentioned cracks after the application of thermal stress due to the mounting of electronic components on the formed thick film printed board. The number of disconnection defects is 1 due to the growth of
The number has increased significantly to 20 cases / 6 million connections.

Therefore, the characteristics of the conductor powder set only for achieving good filling do not always achieve good sintering / shrinking behavior in the firing step, and the conductor powder is well balanced. The problem is that it becomes difficult to design the characteristics.

In view of the above-mentioned problems, the present invention makes the filling property of the via hole good by controlling the characteristics of the conductor powder, and further, under a specific firing condition, a more dense conductor can be obtained. It is an object of the present invention to provide a new method for forming a via for a thick film printed circuit board that can form a via and has few disconnections.

[0015]

According to the present invention, as shown in the following table, in the manufacture of a low temperature fired glass ceramic wiring board using copper as a conductor material,

[0016]

[Table 3]

The specific surface area of the spherical powder made of copper is 0.3 to
0.6 m ² / g, 50% value of particle size distribution is 5.0-
7.0 μm particle size, copper powder fluidity index 70 ~ 7
9. The coating amount of antioxidant is 0.12-0.17
Filling the via hole formed in the green sheet with wt% of the conductor powder.

[0018]

In the present invention, the characteristics of the conductor powder with which the via holes are filled are such that the specific surface area is 0.3 as shown in FIGS.
The number of filling defects is 0 when the particle size distribution is up to 0.6 m ² / g and the 50% value of the particle size distribution is between 5.0 and 7.0 μm, and the fluidity as shown in FIGS. When the index value is 70 to 79, the filling rate of the via hole is 6
0% or more, antioxidant coating amount is 0.12-
Since experimental values have been obtained that the number of occurrence of via pores is the lowest at 0.17 wt%, the conductor powder satisfying these values is filled into the via holes to form a low temperature fired glass ceramic wiring board. As a result, good results as shown in the following table are obtained.

[0019]

[Table 4]

As shown in Table 4, there are 1.2 disconnection defects due to the filling property / 6 million connections and 0 disconnection defects due to the sinterability.
9 cases / 6 million connections, the increase due to the application of heat stress has decreased significantly to 0 cases. Therefore, by controlling the characteristics of the conductor powder, the filling properties into the via holes are improved and the unique firing conditions are set. Under this condition, it is possible to form a finer conductor via.

[0021]

Embodiments of the present invention will be described in detail below with reference to FIGS. 2 is a diagram showing the relationship between the specific surface area of the conductor powder and the number of filling defects according to one embodiment of the present invention, FIG. 3 is a diagram showing the relationship between the particle size distribution of the conductor powder according to the present embodiment and the number of filling defects, and FIG. FIG. 5 is a diagram showing the relationship between the flow index and the filling rate of the conductor powder according to the present embodiment, FIG. 5 is a diagram showing the antioxidant coating amount of the conductor powder according to the present embodiment and the number of pores of 10 μm or more, and FIG. It is a figure which shows the difference of the shrinkage behavior of the glass ceramic of an Example, and a conductor powder.

The characteristics of the conductor powder used according to one embodiment of the present invention are as follows:

[0023]

[Table 5]

It is as follows. In order to secure a good filling property, it is necessary to satisfy all the conditions of to in Table 3, and when the liquidity index is not within this range, it is 10
Insufficient filling of several holes occurs for every 10,000 holes.

The good sinterability is influenced by the insufficient filling amount (filling density), and therefore it is necessary to indirectly satisfy all the conditions 1 to 3 shown in Table 1, but this is considered to be a direct factor. Are specific surface area, particle size distribution, antioxidant, and particle shape. In particular, the specific surface area of (5) sensitively affects the relationship of the sintering behavior between the glass ceramic and the conductor powder shown in FIG.

In the method of forming a via of a thick film printed board using the above member, a paste of conductor powder 2 made of copper or the powder itself is supplied to one edge of the green sheet 1 as in the conventional example shown in FIG. Then, about 100,000 via holes 1a formed in the green sheet 1 with a squeegee are filled with the conductor powder 2 and the 60 green sheets 1 are positioned and laminated, and the heating time shown in FIG. Chart A
The vias of the thick film printed board are formed by firing at.

As a result, as shown in FIG. 6, the contraction behavior curve of the conductor powder of the present invention changes gently as shown by D with respect to the contraction behavior B of the glass ceramic, so that a small grain boundary rupture of the via formed. Less. As a result, as shown in the final quality section of Table 5 above, 1.0 cases of disconnection defects in the initial stage were due to insufficient filling amount (fillability) of 6 million connections, and grain boundary fracture (cracks) during sintering. The result was 0.6, and the increase in grain boundary rupture after applying thermal stress due to mounting electronic components on the formed thick film printed board was 0.
Therefore, by controlling the characteristics of the conductor powder, the filling property in the via hole can be improved and a more dense conductor via can be formed.

[0028]

As is apparent from the above description, according to the present invention, it is possible to prevent the disconnection defect by a very simple method by making the filling property of the conductor powder into the via hole of the green sheet good. It is possible to provide a via forming method for a thick film printed circuit board, which has advantages such as the above, and which can be expected to have a remarkable economic effect and reliability improvement effect.

[Brief description of drawings]

FIG. 1 is a diagram showing a method of forming a via in a thick film printed board.

FIG. 2 is a diagram showing the relationship between the specific surface area of conductor powder and the number of filling defects according to the present embodiment.

FIG. 3 is a diagram showing the relationship between the particle size distribution of conductor powder and the number of filling defects according to the present embodiment.

FIG. 4 is a diagram showing the relationship between the flow index and the filling rate of the conductor powder according to this example.

FIG. 5 is a diagram showing the coating amount of an antioxidant on a conductor powder and the number of pores of 10 μm or more according to the present embodiment.

FIG. 6 is a diagram showing a difference in shrinkage behavior between the glass ceramic and the conductor powder of the conventional example and the present example.

[Explanation of symbols]

1 is a green sheet, 1a is a via hole, 2 is a conductor powder,
3 is a squeegee,

Claims (1)

[Claims] 1. In the production of a low temperature fired glass ceramic wiring board using copper as a conductor material, a spherical specific surface area made of copper is 0.3 to 0.6 m ² / g and a particle size distribution of 5 is obtained.
The above conductor powder (2) having a 0% value of 5.0 to 7.0 μm, a powder fluidity index of 70 to 79, and an antioxidant coating amount of 0.12 to 0.17 wt%. A method for forming a via for a thick film printed circuit board, characterized in that the number of filling defects is controlled by filling the via holes (1a) of the green sheet (1).