JP3059303B2 - Manufacturing method of ceramic multilayer substrate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a multi-layer substrate in which ceramic green sheets having conductive circuits are laminated and pressed, and then fired and polished.

[0002]

2. Description of the Related Art Conventionally, when manufacturing this type of multilayer substrate, first, a conductive metal paste such as tungsten is printed on a green sheet, and a conductor circuit in a through-hole and a wiring circuit pattern are formed by the paste. Then, the green sheet is laminated and pressed, and thereafter, the green sheet is subjected to degreasing, preliminary firing, and main firing.

In the process after degreasing, if a large amount of carbon exists around tungsten, tungsten is carbonized by the residual carbon, and tungsten carbide (WC, WC ₂ ) is generated. It is known that the carbide has a higher specific resistance than the tungsten single metal, and thus increases the resistance of the conductor circuit.

[0004] In this case, two types of carbon sources, one from the outside and the inside of the green sheet, can be considered. Here, the two types are carbon derived from a binder or the like contained in the green sheet and carbon derived from carbon monoxide present in the firing furnace.

[0005] Therefore, in the related art, the conductor circuit exposed on the surface of the green sheet is degreased and fired while being covered with, for example, a dummy green sheet layer. This method is intended to prevent tungsten from becoming carbide mainly by eliminating the influence of external carbon.

[0006] The dummy layer is subjected to post-processing after baking (plane polishing, GC polishing, polishing, etc.).
It is removed from the front and back surfaces of the multilayer substrate.

[0007]

However, even if a dummy layer is arranged and fired, it is difficult to reduce the influence of carbon originating from inside. Therefore, it has been difficult to sufficiently prevent tungsten from becoming carbide.

Further, in the above method, it is necessary to remove a thickness greater than the thickness of the dummy layer in post-processing after firing. However, since it takes an extremely long time to remove the dense sintered body by polishing, it is hard to say that the process is very efficient.

The present invention has been made in view of the above circumstances, and an object of the present invention is to reduce the resistance of a conductor circuit made of tungsten and to easily perform a post-process such as polishing after firing. An object of the present invention is to provide a method of manufacturing a ceramic multilayer substrate that can be performed.

[0010]

In order to solve the above-mentioned problems, the present invention provides a method of manufacturing a multi-layer substrate in which ceramic green sheets having conductive circuits are laminated and pressed, and then fired and polished. After forming a conductive circuit on the green sheet using a first conductive metal paste substantially equal to the firing shrinkage of the green sheet,
After laminating a green sheet, forming a carbon absorbing layer on the conductive circuit using a second conductive metal paste different from the firing shrinkage, the outermost layer of the green sheet through the carbon absorbing layer Place a dummy green sheet,
After the two types of green sheets are pressed, a preliminary firing is performed at a temperature lower than the sintering temperature of the ceramics.

[0011]

According to the method of the present invention, there is almost no difference in firing shrinkage between the green sheet and the first conductive metal paste, and the firing shrinkage does not occur between the green sheet and the second conductive metal paste. There is a rate difference. Therefore, when the pre-baking is performed with the arrangement as described above, the interface between the outermost green sheet and the carbon absorbing layer is peeled off, and the dummy green sheet can be easily removed from the green sheet. Therefore, the portion to be polished is reduced by the thickness of the dummy green sheet, and the post-process after firing is extremely easy.

[0012] Further, by arranging both the dummy green sheet and the carbon absorbing layer, carbon can be reliably absorbed regardless of the inside and outside of the green sheet. Therefore, tungsten carbide is reliably prevented,
The resistance of the conductor circuit is reduced.

Hereinafter, the method for manufacturing a ceramic multilayer substrate of the present invention will be described in detail in the order of steps. Fine powders of aluminum nitride, alumina, or the like having an average particle size of about 1.0 μm to 1.5 μm are used as ceramics as a main component of the green sheet.

A binder, a sintering aid, a solvent and the like are appropriately blended with the ceramic powder, and a green sheet and a dummy green sheet are formed from a high-viscosity slurry obtained by kneading the mixture. In this case, through holes for the green sheet are provided as necessary. On the other hand, it is not necessary to provide a through hole for the dummy green sheet.

Next, two types of conductive metal pastes used in the present invention will be described. A binder, a dispersant, and the like are added to the conductive metal powder that is a main component of each paste. After the mixture is adjusted to a predetermined density and viscosity, it is subjected to printing on a green sheet or a dummy green sheet.

It is preferable that the first conductive metal paste contains tungsten powder having an average particle size of 1.0 μm or more, and the second conductive metal paste contains tungsten powder having an average particle size of 0.8 μm or less.

If this condition is not satisfied, it becomes difficult to cause separation at the interface between the green sheet and the carbon absorbing layer by utilizing the difference in the firing shrinkage. As described above, it is preferable to use the latter paste for forming the carbon absorption layer. The reason is that when a paste containing fine powder is used, the carbon absorption capacity per unit volume of the carbon absorption layer is improved.

A first conductive metal paste is printed on the green sheet, and a conductive circuit in a through hole and a wiring circuit pattern are formed by the paste. On the other hand, a second conductive metal paste is printed on the dummy green sheet, and the paste forms a carbon absorbing layer.
It is preferable that the carbon absorption layer has a wider area than at least the formation area of the conductor circuit in the green sheet.

The carbon absorption layer has a thickness of 20 μm or less.
Desirably, it is 50 μm. If the thickness is less than 20 μm, the formation of tungsten carbide cannot be sufficiently prevented. On the other hand, even if the thickness is made larger than 50 μm, there is no remarkable difference in the carbon absorption effect.

The green sheets are appropriately laminated, and the dummy green sheet is disposed on the outermost layer. At this time, the conductor circuit formed on the green sheet is covered with the carbon absorbing layer of the dummy green sheet. Next, these are pressed by a laminating press or the like to form a green sheet laminate. Thereafter, the laminated body is degreased at a temperature of 600 ° C. to 900 ° C. in an inert atmosphere, and is temporarily calcined at a temperature of 1300 ° C. to 1650 ° C. under the same atmosphere.

After removing the dummy green sheet peeled from the laminate, the laminate is placed under an inert atmosphere under an inert atmosphere.
The main firing is performed at a temperature of 00C to 1900C. Thereafter, both the front and back surfaces of the sintered laminate are subjected to plane polishing, GC polishing and polishing as post-processing. Through the above steps, a desired ceramic multilayer substrate is manufactured.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is embodied in a method for manufacturing a multilayer substrate made of aluminum nitride will be described in detail with reference to the drawings.

In this embodiment, 11% by weight of an acrylic polymer as a binder, 4% by weight of yttrium oxide as a sintering aid, and 4% by weight of dibutyl phthalate as a plasticizer were added to aluminum nitride powder having an average particle size of 1.0 μm. weight%
And 40% by weight of ethanol as a solvent. Then, a high-viscosity slurry obtained by kneading the mixture was molded by a casting method to obtain a green sheet 1 having a thickness of 0.4 mm. Further, the green sheet 1 includes:
The holes 2 for forming through-holes were penetrated using a punching machine.

On the other hand, of the green sheets 1, those through which the through-hole forming holes 2 are not provided were used as dummy green sheets 1 a. In this embodiment, first, tungsten powder having an average particle diameter of 1.1 μm and tungsten powder having an average particle diameter of 0.4 μm were selected as conductive metals for forming a paste. Then, a binder and a dispersant are added to each tungsten powder,
The first paste P1 and the second paste P2 were used. These pastes P1 and P2 were subjected to printing after being adjusted to a predetermined density and viscosity.

Next, the first paste P1 was printed on the green sheet 1, and the conductor circuit 3a in the through-hole and the wiring circuit pattern 3b were appropriately formed on the green sheet 1 (see FIG. 1A).

On the other hand, one side of the dummy green sheet 1a is solid-coated and printed with a second paste P2 to have a thickness of 3 mm.
A carbon absorption layer L having a thickness of 0 μm was formed (see FIG. 1B). Then, a plurality of green sheets 1 (4 in the embodiment)
After stacking, the dummy green sheet 1 is further placed on the surface of the uppermost and lowermost green sheets 1 respectively.
a was arranged. At this time, the upper end surface or the lower end surface of the conductor circuit 3a in the through hole exposed from the green sheet 1 is completely covered with the carbon absorption layer L.

Next, the green sheet 1 and the dummy green sheet 1a are pressure-bonded by a laminating press, and
A green sheet laminate 4 as shown in (c) was obtained. After loading the laminate 4 in a firing furnace, the laminate 4 was degreased at 800 ° C. for 5 hours in a nitrogen atmosphere, and further dehydrated in the same atmosphere for 1 hour.
Preliminary baking was performed at 560 ° C. for 10 hours. Then, the organic matter in the green sheet 1 was decomposed and removed by the degreasing temporary firing step, and the green sheet 1, the dummy green sheet 1a, the conductor circuits 3a and 3b, and the carbon absorption layer L were sintered. At this stage, the dummy green sheet 1a and the carbon absorption layer L are separated from the laminate 4.

After removing the dummy green sheet 1a and the carbon absorbing layer L, only the laminate 4 was fully baked at 1800 ° C. for 1 hour in a nitrogen atmosphere, and the laminate 4 was completely sintered.

Thereafter, as shown in FIG. 1D, the front and back surfaces of the sintered laminate 4 were subjected to post-processing. In the post-processing, three types of processes, namely, planar polishing, GC polishing by SiC granulation, and polishing by diamond granulation were performed.

Through the above steps, a desired aluminum nitride multilayer substrate having the conductor circuits 3a and 3b was obtained. Further, in the comparative example, a dummy green sheet 1a having no carbon absorption layer L made of the second paste P2 was used, and was arranged and pressed on the outermost layer of the plurality of green sheets 1 in the same manner as in the previous example. Then, the laminate was degreased and calcined according to the conditions of the above example. In addition, in this method, even after the above steps, the dummy green sheet 1
a does not peel off.

Then, the laminated body provided with the dummy green sheets 1a was fully baked under the same conditions as in the above-described embodiment, and further subjected to post-processing to obtain a multilayer substrate. In order to compare and evaluate the quality of each substrate thus obtained, the following investigation was conducted.

In order to examine the effectiveness of the effect of preventing the formation of carbide, the amount (% by weight) of free carbon contained in the green sheet 1 after the degreased calcination and the conductor circuits 3a and 3 after the degreased calcination were examined.
The abundance ratio of the tungsten compound (W, W ₂ C, WC) and the sheet resistance value (mΩ / □) of the substrate were measured.

Further, in order to examine the easiness of the post-processing, the post-processing time (min / one sheet) per substrate and the thickness to be post-processed (μm) were measured. Table 1 shows the results.

[0034]

[Table 1]

As is clear from Table 1, in the example, the amount of free carbon contained in the green sheet 1 after the degreasing temporary firing was reduced to 1/5 of the comparative example. Then, in the conductor circuits 3a and 3b of the embodiment, it was found that the elemental metal of tungsten occupies 95%, and almost no carbide is formed in tungsten. On the other hand, the conductor circuit 3 of the comparative example
In a and 3b, 35% of tungsten was turned into carbide.

Next, the sheet resistance of each substrate was measured. As a result, the sheet resistance was 8 mΩ / □ in the example, but was 15 mΩ / □, which was about twice that in the comparative example. Further, as shown in Table 1, since the thickness to be post-processed is also reduced by 1/8 or more in the example, the post-processing time per substrate may be about 1/6 of the comparative example. It has been found.

Judging from the above results, it is clear that all the substrates of the examples are excellent.
Therefore, it is understood that according to the manufacturing method of the present invention, it is possible to reliably achieve tungsten carbide and low resistance of the conductor circuits 3a and 3b.

Moreover, according to the manufacturing method of the present invention, no matter how much the thickness of the dummy green sheet 1a is increased, the time required for post-processing is not adversely affected. Therefore, it is extremely convenient to arrange a green sheet 1a thicker than before in order to prevent the laminate 4 from warping.

The present invention is not limited to the above embodiment, but can be modified as follows.
For example, (a) the carbon absorption layer L may be printed on the green sheet 1 side.

(B) The carbon absorbing layer L and the dummy green sheet 1a may be arranged on the side surface of the laminate 4 and fired. With such an arrangement method, tungsten carbide can be more reliably prevented.

[0041]

As described in detail above, according to the method for manufacturing a ceramic multilayer substrate of the present invention, the resistance of a conductor circuit made of tungsten can be reduced, and post-processing such as polishing after firing can be easily performed. It has an excellent effect that it can be performed.

[Brief description of the drawings]

FIGS. 1A to 1D are process explanatory views showing a method for manufacturing an aluminum nitride multilayer substrate of an example.

[Explanation of symbols]

1 green sheet, 1a dummy green sheet, 3
a conductor circuit in through hole as conductor circuit, 3b
Wiring circuit pattern as conductor circuit, P1 (first)
Conductive metal paste, P2 (second) conductive metal paste, L 2 carbon absorbing layer.

Claims (3)

(57) [Claims] 1. A method of manufacturing a multilayer substrate, comprising laminating and pressing ceramic green sheets (1) having conductor circuits (3a, 3b), and firing and polishing them. Conductor circuits (3a, 3b) are formed on the green sheet (1) using a first conductive metal paste (P1) substantially equal to the shrinkage rate, and then the green sheet (1) is laminated, and the firing shrinkage rate is reduced. After forming a carbon absorbing layer (L) on the conductor circuits (3a, 3b) using a second conductive metal paste (P2) different from the above, the green sheet is interposed via the carbon absorbing layer (L). (1) A dummy green sheet (1a) is disposed in the outermost layer, and after the two types of green sheets (1, 1a) are pressed, pre-sintering is performed at a temperature lower than the sintering temperature of ceramics. Toss Method of manufacturing a ceramic multilayer substrate. 2. The first conductive metal paste (P1) contains tungsten powder having an average particle size of 1.0 μm or more, and the second conductive metal paste (P2) has an average particle size of 0.8 μm.
The method for producing a ceramic multilayer substrate according to claim 1, further comprising a tungsten powder of μm or less. 3. The carbon absorption layer (L) has a thickness of 20 μm or more.
The method according to claim 1, wherein the thickness of the ceramic multilayer substrate is 50 μm.