Coating processes – Direct application of electrical – magnetic – wave – or... – Polymerization of coating utilizing direct application of...
Reexamination Certificate
1996-05-23
2001-05-29
Utech, Benjamin L. (Department: 1765)
Coating processes
Direct application of electrical, magnetic, wave, or...
Polymerization of coating utilizing direct application of...
C427S555000, C427S123000, C427S304000, C427S305000, C427S404000, C427S437000, C427S443100, C427S443200
Reexamination Certificate
active
06238749
ABSTRACT:
The invention relates to a method of providing a metal pattern on an electrically insulating substrate in an electroless process, in which method the substrate is pretreated and subsequently locally exposed to light, whereafter the substrate is brought into contact with an aqueous metal-salt solution, thereby forming the metal pattern on the unexposed areas.
The invention relates, in particular, to a method of manufacturing a black matrix of metal on a glass faceplate of a display device, such as a colour display tube and a liquid-crystal display device.
Electroless or chemical metallization is a simple and inexpensive method of metallizing dielectric substrates such as glass, ceramics and polymer synthetic resins. For this purpose, electroless metallization baths, such as copper and nickel baths, are used (which comprise complexed metal ions and a reducing agent). On catalytic surfaces the metal ions are reduced to metal. In general, metallic Pd nuclei are provided on the surface to be metallized in order to render said surface catalytic. In a standard procedure the substrate to be metallized is nucleated (termed activation) beforehand by bringing the substrate into contact with either aqueous solutions of, in succession, SnCl
2
and PdCl
2
or with a colloidal SnPd dispersion. In either case, the Pd nuclei are surrounded by adsorbed Sn
4+
ions, thereby forming a charge-stabilized Pd sol. The activated surface is subsequently immersed in an electroless metallization bath, causing the surface to be metallized. Said activation methods are non-selective, i.e. the entire substrate surface, such as glass, is nucleated and hence metallized. These activation methods can suitably be used for electroless copper, the strongly reducing formaldehyde being used as the reducing agent.
However, for most electroless nickel baths said activation methods are less suitable due to the reduced reactivity of the reducing agents used, for example hypophosphite, in these baths and due to the lower pH value. This is caused by the use of Sn
2+
ions in the preparation of the Pd sol, which leads to the formation of Sn
4+
ions. The Sn
4+
ions adsorbed on the Pd particles, which ions are used as stabilizers in electroless nickel baths, inhibit the oxidation of the reducing agent. To bring about nickel deposition use must be made of very reactive nickel baths without stabilizers, such as a superalkaline electroless nickel bath on the basis of hypophosphite (pH>14). However, the absence of stabilizers in an electroless nickel bath leads to a poor process control and selectivity as well as the risk of bath instability, i.e. spontaneous nickel formation in the nickel bath. For this reason, commercially available electroless nickel baths comprise stabilizers, such as heavy metal ions, for example Sn
2+
, Sn
4+
and Pb
2+
, and organic sulphur compounds such as thiourea.
In electronic applications, selective or patterned metallization is often desired. This can be attained in various ways. In a subtractive process, first a uniform metal layer having the desired thickness is deposited on the substrate. Subsequently, a photoresist layer is provided which is exposed in accordance with a pattern and developed, thereby forming a pattern in the resist layer. Finally, the metal layer is etched selectively after which the resist layer is stripped off. In an additive process the substrate is activated with catalytic Pd nuclei. Subsequently, a photoresist layer is provided on the substrate, exposed in accordance with a pattern and developed, thereby forming a pattern in the resist layer. Subsequently, the surface is immersed in an electroless metallization bath, in which process metal is deposited in the desired thickness in the apertures of the resist pattern. Finally, the resist layer is stripped off and the Pd nuclei are removed by a short etching treatment. Both processes have the disadvantage that they require a relatively large number of process steps and involve the use of chemicals which are harmful to the environment, such as the resist stripper and the metal-etching bath. In addition, the provision of resist layers on large glass surfaces is difficult.
It is also known to apply a Pd-acetate or acetyl acetonate film to a substrate by means of spincoating, which film is locally decomposed to metallic palladium by means of a laser. The Pd acetate on the unexposed parts is subsequently removed. The pattern of Pd nuclei thus formed is then metallized in an electroless nickel or copper bath. The disadvantage of this method is the relatively large number of process steps and the high laser power necessary to decompose the Pd acetate. Consequently, the treatment of large glass surfaces is very time-consuming.
In United States Patent Specification U.S. Pat. No. 4,996,075 a description is given of a method of depositing a very thin silver film in accordance with a pattern on an SiO
2
surface. In this method the surface is treated with a solution of a silane with a vinyl or acetylene group in an organic solvent, such as carbon tetrachloride and chloroform. As a result of this treatment a monomolecular silane layer is formed on the SiO
2
surface, i.e. a silane layer having a thickness equal to the length of the silane molecule is formed. By locally exposing the silane layer to actinic radiation in selected areas, such as an electron beam or light beam, the vinyl or acetylene groups are chemically bonded to one another, thereby forming a polymer layer, and hence are selectively deactivated. Subsequently, the surface is first immersed in a solution of diborane in THF and then in an alkaline solution of hydrogen peroxide, so that the unexposed vinyl groups are converted to hydroxyl groups. Subsequently, the hydroxyl groups are converted to aldehyde groups. A treatment with an aqueous silver nitrate solution causes the silver ions to be reduced by the aldehyde groups to metallic silver, thereby forming a patterned silver layer having a thickness of one atom layer in the unexposed areas. A second monomolecular layer of vinyl silane can be formed on the silver oxide layer by spontaneous conversion of the monoatomic silver layer to a monomolecular silver oxide layer, whereafter the above steps for converting vinyl groups via hydroxyl groups into aldehyde groups are repeated. Subsequently, a second treatment with an aquous silver nitrate solution is carried out resulting in the formation of a second monomolecular silver oxide layer. By repeating these steps many times an alternating laminate of monolayers of silane and monolayers of silver oxide is obtained.
A disadvantage of the known method is the large number of process steps required to obtain a metal pattern of sufficient layer thickness, for example 0.1 &mgr;m or more, so that the layer is optically opaque and/or has a sufficiently low electric resistance. Another disadvantage is the use of harmful organic solvents, comprising a vinyl or acetylene group, as the solvent for the silanes. A further disadvantage is formed by the fact that the proposed irradiation of the silane layer causes said layer to be deactivated by mutual bonding of the vinyl or acetylene groups, thereby forming a polymer layer which covers the SiO
2
surface. This polymer top layer cannot easily be removed and is often undesired. Due to this polymer layer the SiO
2
surface is inaccessible to other surface reactions or causes, for example, bonding problems with other layers to be provided.
SUMMARY OF THE INVENTION
It is an object of the invention to provide, inter alia, a method of providing a metal pattern on an electrically insulating substrate in an electroless process comprising relatively few process steps, and without using photoresist layers and organic solvents. A further object of the invention is to provide a method which can suitably be used for metallizing relatively large substrate surfaces, for example 25×40 cm, in accordance with a pattern. A still further object of the invention is to provide a method which allows commercially available el
Van Den Boogaard Henricus J. A. P.
van den Brekel Cornelis H. J.
Van Der Sluis-Van Der Voort Elisabeth
Willard Nicolaas P.
Spain Norman N.
U.S. Philips Corporation
Utech Benjamin L.
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