Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Radiation sensitive composition or product or process of making
Reexamination Certificate
2003-05-09
2004-08-24
Walke, Amanda (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Radiation sensitive composition or product or process of making
C430S281100, C430S286100, C430S315000
Reexamination Certificate
active
06780565
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a photosensitive glass paste which is cured by exposure to light, particularly for making an insulation layer in multilayered electronic device, and to a method for manufacturing a multilayered interconnected circuit board using the glass paste.
2. Description of the Related Art
Conventionally, semiconductive elements, such as ICs, etc., are used mounted on a printed circuit board in which an insulating layer having a through hole is formed by processes such as printing processes, etc., on a glass epoxy resin board having fine wiring on the surface thereof.
In recent years, as the demand for high integration, fine interconnection, high speed transmission, high frequency and rapid heat dissipation increases for semiconductor elements, the demand for a printed circuit board capable of accommodating such needs has also increased.
The conventional printed circuit board, however, does not have satisfactory characteristics regarding workability, platability of through holes, adhesive property among layers, etc., resulting in problems. Also, there is a problem of thermal deformation at high temperatures in the above described glass epoxy resin board and there is a limit to increases in density.
In view of the above, a ceramic substrate which uses a ceramic having a high mechanical strength and a high thermal resistance, such as alumina, is considered to be desirable.
As a ceramic substrate, there may be mentioned a printed substrate having fine wiring on the surface thereof and having an insulating layer with through holes formed by the printing techniques, etc., on the surface thereof. In this type of printed substrate, it may sometimes be necessary to form fine through holes in order to accommodate high density packaging.
Also, in recent years, multilayer-type inductors capacitors, etc., formed by laminating a ceramic green sheet provided with electrodes (coil patterns) are being increasingly used. As the level of integration of electronic circuits increases, passive devices such as inductors, capacitors, etc., are also required to be miniaturized.
A spiral multilayer coil capable of yielding high inductance, for example, is manufactured by repeatedly forming an insulating layer, with via holes, on a ceramic green sheet (alumina green sheet) provided with a coil pattern, filling a conductor into the via hole, stacking another ceramic green sheet on the insulating layer, and connecting the coil pattern of the first layer and the coil pattern of the second layer via the via holes. When a coil is manufactured using this process, it is necessary to form fine through holes in order to achieve miniaturization of the product.
In response to the trends to higher density and miniaturization of the multilayer circuit components, a method of forming an insulating layer by using a photosensitive glass paste has been proposed, by which fine via holes which have been difficult to form by conventional printing techniques can be formed.
In this method, a photosensitive glass paste is applied on the entire surface of the substrate by way of screen-printing, etc. The applied photosensitive glass paste is dried, is then exposed and developed through a photomask, and is fired so as to form the fine via holes.
It is to be noted that, the photosensitive glass paste used in this method is a mixture of a photosensitive organic material and an inorganic mixture containing a glass or both a glass and a ceramic. As the inorganic mixture, a mixture in which ceramic material such as quartz, cordierite, alumina, zirconia, mullite, spinel, forsterite and silica are added to the glass at a predetermined proportion is generally used. As the photosensitive organic material, one including a polymer having a functional group in the side chain thereof, a photoreactive compound (monomer), a photopolymerization initiator, a solvent, etc., is generally used.
The conventional photosensitive glass paste, however, usually contains only one kind of glass component having a relatively low glass softening point. Thus, viscous flow is initiated at a low temperature, resulting in a large shrinkage ratio due to sintering and the diameter of the formed via hole will be significantly larger than the diameter after development. Another problem is that during the step of firing, the amount of Ag from the conductive leads made of Ag which constitute the circuit diffusing into the glass is large, degrading insulating characteristics between the layers.
In contrast, when the glass component of the photosensitive glass paste includes only a high melting point glass, as the photosensitive glass paste is treated with heat in the range of the optimum firing temperature so as not to cause deformation of conductive leads made of Ag and Cu, there are problems of insufficient sintering and degradation of insulative properties.
Japanese Unexamined Patent Application Publication 10-120432 discloses a photosensitive glass paste for use in plasma displays, in which a high melting point glass is added to a low melting point glass. Because the content of the low melting point glass is high (40 to 97 percent by weight), when this photosensitive glass paste is employed in a multilayered interconnected circuit board, deformations of via holes due to shrinkage cannot be avoided. Also, because viscous flow of the low temperature glass occurs at low temperatures, a conductor such as Ag will diffuse, causing the insulation properties between layers to degrade. Furthermore, because the functional group, such as carboxyl group, in the photosensitive organic component reacts with polyvalent metal such as boron contained in the glass component, the polymer chains are cross-linked and the viscosity of the paste is abnormally increased, resulting in gelation.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a photosensitive glass paste which is not susceptible to gelation, shrinkage due to sintering and diffusion of conductor compositions such as Ag, by which a glass layer having via holes of precise predetermined shape and size can be formed at predetermined positions. Another object of the present invention is to provide a method for manufacturing a multilayered interconnected circuit board using the photosensitive glass paste.
In order to achieve the above objects, a photosensitive glass paste is provided comprising an inorganic component including a glass powder, and a photosensitive organic component, in which the glass powder comprises (a) about 1 to 30 percent by weight of a low melting point glass powder having a glass softening point in a range of about 400° C. to 600° C. and (b) about 70 to 99 percent by weight of a high melting point glass powder having a glass softening point about 300° C. or more higher than the softening point of the low melting point glass powder.
Because the glass component which constitutes the main portion of the inorganic component of the photosensitive glass paste of the present invention contains a high melting point glass as the main component thereof and limits the proportion of the low melting point glass to be less, shrinkage due to sintering, diffusion of conductive components such as Ag, and gelation can be prevented.
Also, by using this photosensitive glass paste, for example, a glass layer having via holes of desired size can be reliably formed.
The photosensitive glass paste of the present invention uses about 1 to 30 percent by weight of a low melting point glass powder having a glass softening point in a range of about 400° C. to 600° C. The reason for using this type of glass powder is that when the glass softening point is lower than about 400° C., diffusion of metal contained in the leads occurs, causing defects in the insulating layers (degradation of insulating properties), and when the glass softening point exceeds about 600° C., the glass paste remains unsintered. The reason for setting the proportion of the low melting point glass powder to about 1 to 30 percent by weigh
Dickstein Shapiro Morin & Oshinsky LLP.
Murata Manufacturing Co. Ltd.
Walke Amanda
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