JPH04291789A - Multilayer ceramic substrate - Google Patents

Abstract

PURPOSE:To substantially equalize the volumetric shrinkage rates of a layer conductor in a via hole and a multilayer ceramic substrate after baking without increasing the electric resistance. CONSTITUTION:A paste composed of mixture of at least two types of metal powder having different grain size is employed in order to equalize the volumetric shrinkage rates of a baked green sheet and a layer conductor in a via hole made in a ceramic board composed of baked green sheet.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to multilayer ceramic substrates, and in particular, it is possible to controllably controllably make the volumetric contraction rate of interlayer conductors in via holes almost the same as the volumetric contraction rate of the substrate during firing. The present invention relates to a multilayer ceramic substrate.

In recent years, in order to meet the demand for smaller and thinner electronic devices, ceramic packages and ceramic printed boards using ceramic substrates have been diversified. Ceramic substrates have been used for a long time in hybrid integrated circuits, but recently they have been used in packages to which active element chips such as semiconductor devices are directly attached, and printed boards in which passive elements such as resistors are mounted in high density. Ceramics are now being used for In order to obtain more advanced functions while making the entire circuit device smaller, multilayer ceramic substrates are being used in which several to several dozen layers are formed through via holes. Further, in order to increase the packaging density, wiring patterns are becoming finer, and the diameter of via holes is also becoming smaller, on the order of tens of micrometers.

However, multilayer ceramic substrates do not allow interlayer connections such as through-holes provided in multilayer printed boards made of insulating resin, such as stacking each layer and drilling and plating them all at once. For this purpose, a method has been adopted in which the layers are stacked one on top of the other while connecting the layers through via holes, and a technique for obtaining via holes that allows stable interlayer connections is desired.

0004

2. Description of the Related Art FIG. 1 is a partially cutaway perspective view of an example of a multilayer ceramic substrate. In the figure, 1 is a single layer substrate, 2 is a via hole, 3 is an interlayer conductor, 4 is an intermediate conductor, 5 is a surface conductor, and 6 is a multilayer ceramic substrate.

[0005] For the single-layer substrate 1, for example, alumina ceramic, aluminum nitride ceramic, glass ceramic, or the like is used. Before firing, the material powder is kneaded with a resin binder to form a soft so-called green sheet. After firing, the layer thickness is several hundred μm, and the green sheet is made thicker in advance in consideration of the volume shrinkage rate during firing.

When the single-layer substrates 1 are stacked to form a four-layer multilayer ceramic substrate 6 as illustrated here, holes called via holes 2 are provided for interlayer connections. This via hole 2 is made by punching a soft single layer substrate 1 in the form of a green sheet. In this via hole 2, an interlayer conductor 3 is formed.

The interlayer conductor 3 is formed by, for example, covering the bottom of the via hole 2 with a plastic film or the like, and filling it with a paste made from high melting point metal powder such as W (tungsten) or Mo (molybdenum). It is formed. The bottom of the via hole 2 may be filled with metal powder and then filled with paste.

Further, on the surfaces of the second layer 1a and the third layer 1c which are sandwiched between the laminated layers, an intermediate conductor 4 is formed by, for example, screen printing a thick film paste. Four single-layer substrates 1a in the form of green sheets thus obtained
- 1d are stacked and pressed so that the positions of the via holes 2 match, and the four respective layers are adhered and integrated. After that, by firing, a four-layer multilayer ceramic substrate 6 is obtained.

On the other hand, surface conductors 5 are provided on the surfaces of the first layer 1a and the fourth layer 1d. This surface conductor 5 is deposited on the via hole 2 exposed on the surface and connected appropriately so as to be electrically conductive. Wiring patterns forming soldering pads and circuits of semiconductor devices and various devices mounted on the multilayer ceramic substrate 6 are formed by the surface conductor 5.

By the way, the interlayer conductor 3 formed in the via hole 2 is formed by filling the single layer substrate 1 in the form of a green sheet, stacking them together and firing them. However, while the single-layer substrate 1 is fired from a green sheet and turned into a ceramic, the volume shrinks by, for example, 40% or 50% due to evaporation of the solvent and decomposition of the binder. At the same time, the paste constituting the interlayer conductor 3 also shrinks due to evaporation of the solvent and decomposition of the binder during firing.

[0011] If the volume shrinkage rates of both 1 and 3 are not approximately matched, serious problems such as cracks will occur in the substrate 1 and via hole 2 due to distortion after firing and disconnection of the interlayer conductor 3 will occur. Failures occur from time to time.

Therefore, conventionally, if the substrate 1 is made of alumina ceramic, alumina powder, if the substrate 1 is made of glass ceramic, glass powder, etc. is mixed into the metal powder such as W or Mo constituting the interlayer conductor 3. Adjustments are made so that the volumetric shrinkage rates of the substrate 1 and the interlayer conductor 3 are approximately the same.

[0013]

[Problems to be Solved by the Invention] In this way, in order to make the volume shrinkage rates of the ceramic substrate and the interlayer conductor almost the same when they are fired to form a ceramic, ceramic powder is added to the metal powder constituting the interlayer conductor. It has been conventional practice to mix

However, such mixed ceramics are generally highly insulating materials. Therefore, when ceramic is mixed, the electrical resistance of the interlayer conductor increases, which causes a problem of deteriorating the electrical characteristics of the multilayer ceramic substrate.

[0015] Therefore, in the present invention, metal powders having different particle sizes are appropriately mixed to form a paste, and the volume shrinkage rate of the interlayer conductor after firing is adjusted with good controllability, thereby increasing the volume of the substrate. The purpose of the present invention is to provide a multilayer ceramic substrate with substantially the same shrinkage rate.

[0016]

[Means for solving the problem] The problem described above is that the interlayer conductor of the via hole provided in the ceramic substrate formed by firing the green sheet has a volume shrinkage rate that is approximately the same as that when the green sheet is fired. This problem is solved by a multilayer ceramic substrate made of a paste made by mixing at least two types of metal powders with different particle sizes so as to have the same volumetric shrinkage rate.

[0017]

[Operation] In conventional multilayer ceramic substrates, ceramic is mixed with metal powder, and the volumetric shrinkage rate of the interlayer conductor in the via hole that occurs during firing is adjusted to match the volumetric shrinkage rate of the board. On the other hand, in the present invention, the metals are mixed with each other and adjusted with good controllability.

That is, the paste constituting the interlayer conductor of the via hole is made by mixing at least two types of metal powders with different particle sizes, whether they are the same type of metal or different types of metal. Then, by appropriately selecting the particle size and mixing ratio, various volumetric shrinkage rates can be obtained upon firing.

[0019] Then, the volumetric contraction rate of the interlayer conductor can be made almost the same as the volumetric contraction rate of the substrate, so that it is possible to prevent problems caused by a mismatch between the volumetric contraction rates of the two.

[0020]

[Embodiment] Various metal materials can be used for the metal powder constituting the interlayer conductor, and when the substrate is made of alumina ceramic or the like which is fired at a high temperature, a metal material such as W or Mo is used. On the other hand, when firing at a relatively low temperature such as glass ceramic, a metal material such as Ag (silver) or Cu (copper) is used.

[0021] Taking W as an example, Table 1 shows how the volume shrinkage rate changes after a paste is prepared by mixing metal powders of different particle sizes of these metal materials and firing.

[0022]

[Table 1]

Table 1 shows that the particle sizes are 0.5 μm and 1 μm,
and For combinations of two types of W powder, 0.5 μm and 3 μm, the average particle diameter and volume shrinkage after firing are shown when the mixing ratio is changed.

[0024] From Table 1, it can be seen that as the metal powder with a smaller particle size is increased, the volumetric shrinkage rate increases, and as the metal powder with a larger particle size is increased, the volumetric shrinkage rate tends to decrease. I understand that. Then, for example, paste with the average particle size of 1 μm:90/3 μm:10 and 0.5
The reason why the volume shrinkage rate is different between the paste with μm:70/3μm:30 is because the degree of dispersion differs depending on the particle size.
This seems to be due to the difference in powder filling rate.

In the case of the example shown here, the volume shrinkage rate after firing of the substrate is 44.4%, so for example, a paste of 1 μm:90/3 μm:10 with a volume shrinkage rate of 44.0%, Or 0.5 μm with a volume shrinkage rate of 45.0%: 5
If the interlayer conductor 3 is provided using a 0/3 μm:50 paste or the like, stable interlayer connection can be achieved.

It has been confirmed that such effects can be obtained not only with W but also with powders of metal materials such as Mo, Ag, and Cu. In any case, by mixing metal powders with different particle sizes, the volume shrinkage rate after firing can be varied. Therefore, by appropriately selecting the particle size and mixing ratio of the metal powder, it is possible to produce a multilayer ceramic substrate in which the volumetric contraction rate of the interlayer conductor of the via hole is approximately the same as that of the substrate.

[0027] Here, an example has been exemplified in which the metal powder has two types of particle sizes, but various modifications can be made to the types of particle sizes and the mixing ratio of the metal powder.

[0028]

[Effects of the Invention] Conventionally, in a multilayer ceramic substrate, ceramic powder, for example, has been mixed in to adjust the volumetric shrinkage rate upon firing of the paste used for the interlayer conductor constituting the via hole. In contrast, in the present invention, the particle size is adjusted by mixing metal powders with different particle sizes. In addition, an increase in the electrical resistance of the interlayer conductor as in the prior art is avoided.

As a result, it has become possible to create stable via holes, which is useful for realizing multilayer ceramic substrates such as ceramic packages for mounting semiconductor devices, which will become increasingly finer in the future. The present invention makes a significant contribution.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway perspective view of an example of a multilayer ceramic substrate.

[Explanation of symbols]

1 Single layer board
2 Via hole 3 Interlayer conductor
4 Intermediate conductor 5 Surface conductor
6 Multilayer ceramic substrate

Claims (2)

[Claims] Claim 1: At least at least one conductor of a via hole provided in a ceramic substrate formed by firing a green sheet has a volumetric shrinkage rate that is substantially the same as the volumetric shrinkage rate when the green sheet is fired. A multilayer ceramic substrate characterized by being composed of a paste made by mixing two types of metal powders with different particle sizes. 2. The multilayer ceramic substrate according to claim 1, wherein the metal powder comprises at least two different types of metals.