JP2767188B2 - Via forming method for ceramic laminate - 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 forming a via connection portion in a ceramic laminate, and more particularly, to a method for forming an electrical connection between layers by using a metal material in a large or small via hole provided in a corresponding portion of an adjacent layer. The present invention relates to a method of forming a via connection portion for performing a dynamic connection. This technique is useful for electrical connection between layers in a multilayer ceramic circuit board, a multilayer capacitor, a multilayer piezoelectric element, and the like.

[0002]

2. Description of the Related Art In a laminated ceramic substrate and various laminated ceramic elements, there is a via connection structure as a technique for electrically connecting layers within the substrate or the element. This is because, when laminating ceramic green sheets (unsintered sheets), via holes are provided at corresponding locations on adjacent sheets, and metal powder (actually, metal powder such as silver particles and an organic binder) are placed inside. (Using a mixed conductive paste), and sintering after lamination and integration to achieve electrical connection between layers by a metal material in a via hole.

[0003] The diameter of a conventionally used via hole varies from about 0.08 to 0.8 mm depending on the type and size of the element. However, in any case, the via holes in one laminated body are all formed with the same diameter from the upper green sheet to the lower green sheet. Then, the respective green sheets are strictly aligned and laminated and integrated so that the center positions of all the via holes at the corresponding locations coincide.

[0004]

The metal powder and green sheet filled in the via hole are integrally fired as a laminate.
At this time, the metal powder and the ceramic (green sheet) have different firing shrinkage rates, and the metal powder generally shrinks more. Due to this and the condensation effect of the metal, a gap is formed between the via hole wall and the metal material. For this reason, especially when the via hole diameter is small, the amount of the metal powder to be filled is small, and a slight shift of the center position of the upper and lower via portions may have a great effect. Or, an electrical connection failure occurs between the via portion and the internal electrode pattern,
There were problems such as a loss of reliability due to insufficient connection.

[0005] If the diameter of the via hole is made considerably large, the amount of the metal powder to be filled is increased, and the possibility of occurrence of defective electrical connection is reduced. However, when the diameter of the via hole is increased, there is a disadvantage that the area of an effective portion that performs the original function as an element is reduced. For example, in the case of a laminated piezoelectric element, the area of the via hole becomes an inactive area (part that does not contribute to the piezoelectric operation), and therefore it is desirable to reduce the area as much as possible. Also, if the via hole diameter becomes extremely large,
During the period from filling of the metal powder to lamination, there is a risk that the metal powder may fall off, resulting in poor workability.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned drawbacks of the prior art, to facilitate alignment between via portions, and to provide a space between upper and lower via portions or between a via portion and an internal electrode pattern. An object of the present invention is to provide a method for forming a via connection portion of a ceramic laminate that can reliably perform an electrical connection and improve reliability and a production yield.

[0007]

According to the present invention, when laminating ceramic green sheets, via holes are provided in corresponding portions of adjacent green sheets, metal powder is filled therein, and firing is performed after lamination and integration. In the method of forming a via in which electrical connection between layers is performed by the metal material in the via hole, one of the via holes to be formed in a corresponding portion of the adjacent green sheet is one large via hole and the other is a small via hole. This is a method of forming a via connection portion of a ceramic laminate having the following combination. Here, it is desirable that the diameter of the large via hole is about 1.2 to 2 times the diameter of the small via hole.

[0008]

When firing the laminated body, the firing shrinkage of the metal powder filled in the via hole differs from that of the ceramic of the green sheet. As described above, the metal powder generally has a higher shrinkage rate, and the metal powder is aggregated. In the configuration in which the large via hole and the small via hole are combined as in the present invention, when the metal powder is agglomerated, the metal powder is also supplied from the large via hole side into the small via hole due to a capillary phenomenon, and there is no gap. Completely filled. On the other hand, in the large via hole, the amount of the metal powder is slightly reduced, and although a slightly larger gap is generated between the metal material and the via hole wall, since most of the metal material remains in the center portion, The connection between the upper and lower via portions can be sufficiently performed.

[0009] Further, since one is a large via hole and the other is a small via hole, a slight positional deviation of approximately the difference between the radii of the upper and lower vias is allowed during the alignment between the upper and lower vias. Therefore, the electrical connection between the upper and lower via portions can be performed more reliably.

[0010]

1 is an explanatory view showing one embodiment of a via forming structure of a ceramic laminate according to the present invention, wherein A is a plan view of a green sheet before lamination, and B is a side sectional view of each green sheet. is there. This example is a case where the present invention is applied to a laminated piezoelectric element (piezoelectric actuator). When laminating ceramic green sheets, via connections are made by forming via holes in the corresponding locations of adjacent sheets, filling metal powder inside, and sintering after lamination and integration. In this structure, electrical connection between layers is performed.

A large via hole 12 and a small via hole 14 are respectively formed in a ceramic green sheet (unsintered sheet) 10 in a circular shape, and a predetermined internal electrode pattern 16 (portion shaded) is formed on the surface of the green sheet. Is printed, and the inside of the large via hole 12 and the small via hole 14 is filled with the metal powder 18. A ring-shaped non-electrode portion 20 (a portion with fine dots) is formed around the large via hole 12 to separate the large via hole 12 from the metal powder 18 filled in the large via hole 12. For the hole 14, the internal electrode pattern 16 is printed up to the edge of the hole, and the metal powder 18 filled in the small via hole 14 is formed.
Is configured to be continuous. Here, the ceramic green sheet 10 is formed by kneading a ceramic powder such as PZT (lead zirconate titanate) and an organic binder, and forming a thin sheet by a doctor blade method, a rolling roll method, or the like. For the internal electrode pattern 16 to be printed on the surface of the green sheet, for example, a paste-like material obtained by mixing silver particles and a binder is used. The metal powder 18 to be filled in each of the via holes 12 and 14 is also a paste obtained by mixing the metal powder and an organic binder. Typically, this is the same material used to form the internal electrode pattern.

As shown in FIG. 1B, such green sheets 10 are combined and laminated such that the large via holes 12 and the small via holes 14 face each other. That is, large via hole 1
2 are alternately stacked so that the center of the small via hole 14 coincides with the center of the small via hole 14. After being integrated under pressure, it is baked. FIG. 2 shows a cross section of the fired product. In this fired product 30, the internal electrodes 34 are connected every other layer through the large and small via portions 32,
Thus, a structure in which voltages of different polarities can be applied to every other internal electrode 34 is obtained. Although FIG. 2 shows only four stacked layers for easy understanding of the drawing, the number of stacked layers is several tens to one hundred and several tens in an actual stacked piezoelectric element.

FIG. 3 shows details of the via portion. This is a schematic diagram in which the fired product is cut and observed. In the state of the green sheet, the diameter of the large via hole is set to 0.25 mmφ, and the diameter of the small via hole is set to 0.125 mmφ, so that the diameter after sintering is smaller. However, the relative ratio between the diameter of the large via hole and the diameter of the small via hole does not change. Although a void is formed in the large via hole 12 near the hole wall, the small via hole 14
The inside is almost completely filled with the metal material 32. This is because both the ceramic green sheet and the metal powder shrink during firing, and the metal powder shrinks more, creating a gap between the two via holes. And the metal powder is first filled in the small via hole. In addition, although the metal powder remaining in the large via hole becomes spherical due to cohesive force and separates from the via hole wall, it maintains good connection with the metal material and internal electrode pattern in the small via hole, so that good electrical The connection state is realized. In addition, even if the center of the large via hole and the center of the small via hole are slightly displaced from each other, as long as the difference is about the difference between the radii of the two via holes, the above-described favorable connection state is ensured.

However, as in the prior art, the same diameter (0.125
FIG. 4 is a schematic view of a fired product when via connection is performed with a via hole of (mmφ). This is a typical state where a connection failure has occurred. As described above, in the conventional product, the metal powder filled in each via hole shrinks during firing and becomes spherical, respectively, so that the metal material in the upper and lower via holes becomes discontinuous, and the electrical connection between the internal electrodes is reduced. You cannot do it. In many laminated sintered products,
If there is even one such discontinuity (disconnection), the element becomes defective and cannot be used. In particular, if the center positions of both via holes are shifted, such poor connection is likely to occur.

It is desirable that the ratio of the diameter of the large via hole to the diameter of the large via hole is in the range of about 1.2 to 2.0 times the diameter of the small via hole. If the ratio of the hole diameters is less than 1.2, the deviation tolerance of the lamination cannot be covered, and conversely, the ratio of the hole diameters is 2.
If it is larger than 0, the inactive portion increases, which is not preferable.

It goes without saying that the present invention can be applied not only to the above-described laminated piezoelectric element, but also to a laminated circuit board, a laminated capacitor, a laminated microwave dielectric element and the like.

[0017]

As described above, the present invention has a structure in which the large via portions and the small via portions are combined so as to be alternately stacked, so that the firing shrinkage of the metal powder is smaller than that of the ceramic green sheet. Despite being much larger, the small via holes are filled with metal powder, and in the large via holes, the metal material becomes spherical due to the cohesive action of the metal material, and between the upper and lower via portions and between the via portion and the internal electrode. The electrical connection is made reliably. Further, a slight displacement between adjacent large and small via portions, which is equivalent to a difference between the radii of the two via holes, is allowed, and does not hinder the electrical connection. For these reasons, electrical connection failure at the via connection portion can be prevented, reliability is greatly improved, and the production yield is improved.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing one embodiment of a via forming method according to the present invention.

FIG. 2 is a cross-sectional view of a laminated sintered product via-connected according to the present invention.

FIG. 3 is an enlarged explanatory view of a via portion of the laminated sintered product according to the present invention.

FIG. 4 is an enlarged explanatory view of a via portion of a conventional laminated sintered product.

[Explanation of symbols]

 Reference Signs List 10 ceramic green sheet 12 large via hole 14 small via hole 16 internal electrode pattern 18 conductive paste 20 non-electrode part

Claims (2)

(57) [Claims] When laminating ceramic green sheets, via holes are provided in corresponding portions of adjacent green sheets, metal powder is filled therein, and sintering is performed after lamination and integration. In the method of forming a via for electrically connecting layers with a metal material, a via hole formed in a corresponding portion of an adjacent green sheet is a combination in which one is a large via hole and the other is a small via hole. Via forming method for a ceramic laminate. 2. The via forming method according to claim 1, wherein the diameter of the large diameter via portion is 1.2 to 2 times the diameter of the small diameter via portion.