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
2002-05-24
2003-05-06
Baxter, Janet (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
C430S270100, C430S320000
Reexamination Certificate
active
06558874
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to a photosensitive silver conductor tape which exhibits improved development latitude by the selection of a polymer binder containing butyl methacrylate.
BACKGROUND OF THE INVENTION
Since it is the trend in the industry to make smaller and cheaper electronic devices and provide higher resolution for performance, it has become necessary to reduce the size and cost of the conductor layers. However, it has become difficult to create conductor patterns having line widths of less than 100 microns by means of screen printed thick film pastes. Moreover the lithographic precision of the screen becomes poor and errors tend to arise, which makes it difficult to increase pattern density.
Photosensitive materials are one representation of thick film materials commonly applied to a substrate by screen printing, and the organic binder is dissipated by means of a subsequent firing step. However, it is difficult to apply a uniform thickness of a thick film paste by screen printing and the dissipation is often uneven, particularly over large areas. Furthermore, screen printing is a labor intensive process which is expensive. Therefore, the substitution of a tape for a thick film paste is appealing to the industry. Application of a tape to a substrate by hot roll lamination is very cost effective because it provides high throughput and results in high, reliable circuit yields.
Development latitude, wherein the range in the time involved in forming an acceptable latent image during an exposure is developed in a dilute aqueous base solution and is washed off, is a key performance characteristic in utilizing tapes in the construction of a circuit. It is beneficial to the manufacturer that a tape has properties which provides a range in development times resulting in acceptable resolution with little variation in fired line width and thickness. The industry has been lacking tapes with improved development latitude. Therefore, the need exists for a photosensitive silver tape with improved development latitude.
SUMMARY OF THE INVENTION
The present invention relates to a composition of a photosensitive silver conductor tape comprising: (1) finely divided inorganic solids comprising (a) finely divided particles of silver solids; (b) finely divided particles of inorganic binder having a glass transition temperature (Tg) of 325-700° C., the inorganic solids being dispersed in (2) an organic medium comprising a solution of (c) an organic polymeric binder which is a copolymer, interpolymer or mixture thereof selected from (1) nonacidic comonomers comprising butylmethacrylate or mixtures of butylmethacrylate and C
1-10
alkyl acrylates, C
1-10
alkyl methacrylates, styrene, substituted styrenes, or combinations thereof and (2) acidic comonomers comprising ethylenically unsaturated carboxylic acids containing moiety that are at least 15wt. % of the total polymer weight; and having a Tg of 50-150° C. and weight average molecular weight in the range of greater than 55,000 but less than or equal to 300,000; (d) a photoinitiation system; (e) a photohardenable monomer; and with the proviso that the composition is fireable in an oxidizing or substantially nonoxidizing atmosphere at temperature of no higher than 7000° C.
The invention is also directed to a method for forming an electrode arrangement for a plasma display panel device comprising the steps of: (a) forming a tape with the photosensitive silver composition of the above; (b) applying the tape to a substrate; (c) imagewise exposing the film to actinic radiation to define the specified pattern; (d) developing the exposed composition in an aqueous solution to remove the composition in area not exposed to actinic radiation; and (e) firing the developed conductive composition.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is a photosensitive silver conductor tape which exhibits improved development latitude by the selection of a polymer binder containing butyl methacrylate. Components, formation and processing of the photosensitive silver conductor tape are discussed below.
A. Conductive Component
Virtually any shape silver particle in powder form, including spherical particles and flake (rods, cones, plates) may be used in practicing the invention. It is preferred that the particles be in the range of 0.2 &mgr;m and 20 &mgr;m. It has been found that the dispersion of the invention must contain no significant amount of solids having a particle size of less than 0.2 &mgr;m. When particles of this small size are present it is difficult to adequately obtain complete burnout of the organic medium when the films or layers thereof are fired to dissipate the organic medium and to effect sintering of the inorganic binder and the silver solids. In using the dispersion to make dry photosensitive tape, the maximum particle size must not exceed the desired thickness of the tape. It is preferred that at least 80 percent by weight of the silver solids fall within the 0.5-10 &mgr;m range.
In addition, it is preferred that the surface area/weight ratio of the silver particles not exceed 20 m
2
/g. When silver particles having a surface area/weight ratio greater than 20 m
2
/g are used, the sintering characteristics of the accompanying inorganic binder are adversely affected. It is difficult to obtain adequate burnout and blisters may appear.
It is known that small amounts of other metals, such as: Au, Pd, Pt and Cu or mixtures thereof, may be added to silver conductor compositions to improve the properties of the conductor. Generally the metal particles are spherical -in shape, preferably approximately 0.1 to 10 microns in diameter. When present, the other metal powders comprise from about 0.05 to 5.0 percent by weight of the total tape composition, and preferably from about 0.1 to about 2.0 percent.
Often, copper oxide is added to improve adhesion. The copper oxide should be present in the form of finely divided particles, preferably ranging in size from about 0.5 to 5 microns. When present as Cu
2
O, the copper oxide comprises from about 0.1 to about 3 percent by weight of the total composition, and preferably from about 0.1 to 1.0 percent. Part or all of the Cu
2
O may be replaced by molar equivalents of CuO.
B. Inorganic Binders
The inorganic binders, which can also be referred to as glasses or frits, used in this invention help sinter the conductive component particles and can be any composition known in the art providing it has a softening point below the melting point of the conductive components. The softening point of the inorganic binder has considerable influence on the sintering temperature. For the conductive composition of the present invention to be sufficiently sintered on an underlying layer, the glass transition temperature (Tg) is about 325-700° C., preferably about 350-650° C. and more preferably about 375-600° C.
If significant melting takes place below 325° C., organic material will likely be encapsulated and blisters will tend to form in the composition as the organic materials decompose. On the other hand, a Tg above 700° C. will tend to produce a composition with poor adhesion.
The glass frit most preferably used are the borosilicate frits, such as lead borosilicate frit, bismuth, cadmium, barium, calcium or other alkaline earth borosilicate frits. The preparation of such glass frits is well known in the art and consists, for example, of melting together the constituents of the glass in the form of the oxides of the constituents and pouring such molten composition into water to form the frit. The batch ingredients may, of course, be any compound that will yield the desired oxides under the usual conditions of frit production. For example, boric oxide will be obtained from boric acid, silicon dioxide will be produced from flint, barium oxide will be produced from barium carbonate, etc.
The frit is passed through a fine mesh screen to remove large particles since the solid composition should be agglomerate free. The inorganic binder has a preferred surface to weight ratio of no mo
Baxter Janet
E. I. du Pont de Nemours and Company
Thornton Yvette C.
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