Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
1998-10-02
2001-02-20
Nakarani, D. S. (Department: 1773)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
C428S323000, C428S325000, C428S331000, C522S085000, C523S200000, C523S214000, C523S216000, C523S217000, C524S442000, C524S492000, C524S493000, C524S494000, C525S254000
Reexamination Certificate
active
06191186
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an insulating paste, and particularly relates to an insulating paste containing glass powder which is suitably used for forming an electrically insulating layer for high-frequency circuits.
2. Description of the Related Art
With trends towards high density and high speed in high-frequency electronic devices, electrically insulating materials which are associated with high-frequency circuits in these electronic devices are required to have a high dielectric constant and a high Q value. Such electrically insulating materials are used for forming electrically insulating layers which isolate two or more electrodes or transmission lines in, for example, high-frequency circuit substrates or electronic parts for high-frequency circuits.
Holes for electrically connecting upper and lower electrodes or transmission lines through conductive members, that is, via-holes, are often provided in the electrically insulating layer. In the formation of the electrically insulating layer having via-holes, for example, an insulating paste containing glass powder is used. The electrically insulating layer having the via-holes is formed with the insulating paste by, for example, screen printing, and the insulating paste is dried and then baked.
The formation of an electrically insulating layer having fine via-holes based on a photolithographic process using a photosensitive insulating resin such as a photosensitive polyimide resin is also known.
Using an insulating paste which is obtained by dispersing glass powder into a photosetting-type organic vehicle, application of the technology for forming an insulating member by a photolithographic process disclosed in, for example, Japanese Patent Laid-Open Nos. 9-110466 and 8-50811 may be possible in order to form an electrically insulating layer having fine via-holes in electronic parts for circuits which require multiple wiring.
Among the above-described conventional technologies, it is difficult in the printing method to form an electrically insulating layer having fine via-holes having a diameter of, for example, less than about 150 &mgr;m because of printing feathering due to paste viscosity and printing resolution due to the printing block. Thus, the printing method cannot deal with recent trends towards miniaturization and high-density of circuit substrates and electronic parts for circuits.
According to the method for forming an electrically insulating layer based on a photolithographic process using a photosensitive insulating resin, although fine via-holes having a diameter of, for example, less than 150 &mgr;m can be formed, the resulting electrically insulating layer has disadvantages in durability at high temperature and plating characteristics in an acidic plating solution.
On the other hand, in the insulating materials described in Japanese Patent Laid-Open Nos. 9-110466 and 8-50811 which are composed of glass powder dispersed into a photosetting-type organic vehicle and can form an electrically insulating layer having fine via-holes based on a photolithographic process, the contained glass has a relatively low softening point. When an Ag-based material is used in electrodes or transmission lines connecting to the resulting electrically insulating layer, diffusion of Ag into the electrically insulating layer is significantly noticeable and thus the formation of the electrically insulating layer having high reliability is difficult.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an insulating paste which permits formation of fine via-holes, has excellent high-temperature and plating durability, a low dielectric constant and a high Q value essential for high-frequency circuits, reduced reactivity with other materials such as electrode materials, and which is preferably used for forming an electrically insulating layer.
The preferred embodiment of the present invention provides an insulating paste comprising: an organic vehicle containing an organic binder, a photo-polymerization initiator and a photosetting monomer; and a silicate glass powder having a softening point in a range of about 700° C. to 1,050° C. and having an average particle size in a range of about 0.1 to 5.0 &mgr;m, said silicate glass powder being dispersed into said organic vehicle.
The insulating paste in accordance with the present invention is composed of the silicate glass powder dispersed in the organic vehicle containing the photo-polymerization initiator and a photosetting monomer. Therefore, an electrically insulating layer having fine via-holes which is barely formed by a printing process can be formed using a photolithographic process.
Since the insulating paste in accordance with the present invention contains the silicate glass powder, an electrically insulating layer composed of an inorganic glass material is formed after baking. Thus, durability at high-temperature and durability in an acidic plating solution can be improved compared with an electrically insulating layer composed of a resinous material. Since the silicate glass has a softening point in a range of about 700° C. to 1050° C., problems regarding reaction with other materials such as electrode materials which will occur for a softening temperature of less than about 700° C. are solved, and workability is improved by baking at a temperature of about 1,050° C. or less.
In the insulating paste in accordance with the present invention as described above, the silicate glass powder has an average particle size lies with in a range of about 0.1 to 5.0 &mgr;m. The average particle size of the silicate glass powder is determined based on Example 3 described later.
An average particle size of about 5.0 &mgr;or less can suppress light scattering on the surface of the glass powder when radiating active rays, for example, in an ultraviolet wavelength region (200 to 450 nm). Thus, fine via-holes can be formed so as to achieve a satisfactory aspect ratio, satisfactory resolution, high circularity, and a suppressed taper. At an average particle size of about 0.1 &mgr;m or more, the glass particles do not excessively absorb active rays, and thus photo-polymerization is sufficiently completed, resulting in the formation of a dense film.
Preferably, the silicate glass powder in the above described insulating paste comprises a composition represented by xSiO
2
—yB
2
O
3
—zK
2
O where x+y+z is 100 parts by weight and the values z, y and z are on lines or within a region enclosed by lines passing through four points A(65, 35, 0), B(65, 20, 15), C(85, 0, 15) and D(85, 15, 0) on a ternary diagram thereof.
A preferable composition of the silicate glass is determined based on preferred embodiments described below.
By selecting the composition of the silicate glass, the softening point of the glass is controlled to be within a range of about 700° C. to 1,050° C. The glass has, therefore, reduced reactivity with other materials such as electrode materials, and a sintered material is obtainable at a baking temperature of, for example, 900 to 1,050° C. The resulting electrically insulating layer has excellent insulating characteristics and workability. Since the glass has a low specific dielectric constant of less than about 7.0, it is suitable for substrates and electronic parts having high-frequency circuits.
More preferably, the values z, y and z are on lines or within a region enclosed by lines passing through four points E(75, 24.5, 0.5), F(75, 22, 3), G(85, 12, 3) and H(85, 14.5, 0.5) on the ternary diagram. By selecting the composition of the silicate glass, the softening point of the glass is controlled to be within a range of about 750° C. to 940° C. as shown in a first preferred embodiment described later. The glass can, therefore, be baked and sintered at a temperature of 950° C. or less to form an electrically insulating layer. Thus, workability is further improved and reactivity with other materials such as electrode materials can be further reduced.
In the above described insulating paste,
Tose Makoto
Watanabe Shizuharu
Murata Manufacturing Co. Ltd.
Nakarani D. S.
Ostrolenk Faber Gerb & Soffen, LLP
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