Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making electrical device
Reexamination Certificate
1999-09-15
2002-08-27
Huff, Mark F. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making electrical device
C430S270100, C430S280100, C428S411100, C428S901000
Reexamination Certificate
active
06440642
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to the field of dielectric compositions. In particular, this invention relates to dielectric compositions having low volatile organic compound content.
A present trend in the printed wiring board industry is toward high density interconnected circuitry. Such circuitry has an increased number of circuit layers in a board with a decreased width of formed lines and spaces. Typically, a circuit board is manufactured by first constructing all circuits separately and laminating these layers together. Drilling and metallization of the drilled holes is then performed to electrically connect the layers. Recently, a new method of manufacturing multilayer circuit boards has been developed to address increased densification. Such new method sequentially builds circuit layers on a substrate. Substrates used in conventional multilayer printed circuit boards typically include glass cloth reinforced copper-clad plastic substrates that range in thickness from 4-8 mils for the insulative plastic alone.
In a typical process for sequential building of circuit layers, a definable dielectric material is coated onto an appropriate substrate either as a solution in a solvent, which includes a drying step, or as a pre-dried film resident on polyester. The definable coating is then lithographically processed by exposure and development to provide lines, spaces and vias as required by the circuit design. Alternatively, such structures may be defined by laser drilling which uncovers an area onto which an electrical connection can be made from the upper, just coated, layer. The definable coating is then adhesion promoted and plated, followed by a print and etch operation that defines the next circuit layers. The above process is then repeated until the desired number of layers and interconnections are achieved.
In general, the definable dielectric materials are dissolved in a solvent. For example, U.S. Pat. No. 5,262,280, herein incorporated by reference, describes a process of sequentially building a printed circuit board using a dielectric material in a solvent. Once a coating of the dielectric material is applied to the substrate, it must be dried prior to lithographic processing. In this drying step, a large amount of volatile organic material is generated, e.g., from evaporation of the solvent. In some areas of the world the emissions of volatile organic compounds (“VOC”) are regulated or prohibited. Thus, the volatilized solvent from the drying step in the dielectric coating process must be contained, which greatly adds to the cost and inconvenience of the process.
Another method of application is from a dry film construction. In this method, a solvent-borne dielectric coating is first coated onto a carrier sheet, then the solvent is removed by heating.
Photodefinable dielectrics must contain components that make the coating developable, that is, components which make the dielectrics either more or less soluble in the developer. Thus, photodefined areas are created during exposure of the photodefinable coatings to the developer, upon which copper can be later deposited. The developable components used in the dielectric coatings are typically highly polar compounds, which helps their solubility. Unfortunately, such developable components increase the dielectric constant of the dielectric coatings, which must be as low as possible for circuitry applications.
Low surface tack is an important property of known dielectric coatings as such dielectric coating will come into direct contact with artwork during the photodefining process. The surface tack of the dielectric coating needs to be low enough such that the artwork can slide over the surface of the dielectric coating for ease of registration with the dielectric coated substrate. Such low surface tack concerns limit the available low dielectric material formulations.
In the course of applying the dielectric, either from solvent or from dry film construction, the problem of planarization occurs since the coatings are applied over three-dimensional structures. When solvent-borne dielectric material is used, the liquid will planarize, however, during evaporation of the solvent, the thickness of the material shrinks to a percentage of the formulation. The amount of shrinkage will be the same whether over a raised circuit or in the valley between. As the solvent evaporates, the remaining dielectric will shrink to conform to the different heights, resulting in a three-dimensional surface. This is also true of dry film construction which has a uniform film thickness. When applied to a three-dimensional structure, the film will conform to the uneven surface.
Thus, there is a need in the art for dielectric coatings that have low volatile organic compound content, low dielectric constants, avoid the issue of surface tack and have improved planarization.
SUMMARY OF THE INVENTION
The present invention provides such dielectric compositions. The advantages of the present invention are that the amount of volatile organic components are greatly reduced, post exposure bake is avoided, development of the dielectric compositions is avoided, planarization is improved and surface tack issues are avoided.
In a first aspect, the present invention provides a composition including: a) from 1 to 99% by weight of at least one low dielectric constant, crosslinkable material; b) from 1 to 99% by weight of at least one reactive diluent; and c) optionally one or more additives; wherein the composition is substantially free of organic solvent.
In a second aspect, the present invention provides a composition including: a) from 20 to 80% by weight of at least one low dielectric constant, crosslinkable material; b) from 10 to 80% by weight of at least one crosslinking agent; c) from 0.1 to 25% by weight of at least one catalyst including acid generators, photoacid generators, thermal base generators, photobase generators, or mixtures thereof; d) from 5 to 60% by weight of a reactive diluent; and e) optionally one or more additives; wherein the composition is substantially free of organic solvent.
In a third aspect, the present invention provides a process for manufacturing circuit boards including the steps of applying a dielectric composition to a substrate; thermally curing the dielectric composition; providing one or more or lines, spaces or vias in the dielectric composition; promoting adhesion; and plating the dielectric layer with a conductive metal; wherein the dielectric composition includes a) from 1 to 99% by weight of at least one low dielectric constant, crosslinkable material; b) from 1 to 99% by weight of at least one reactive diluent; and c) optionally one or more additives; wherein the composition is substantially free of organic solvent.
In a fourth aspect, the present invention provides a process for manufacturing circuit boards including the steps of applying a dielectric composition to a substrate; thermally curing the dielectric composition; providing one or more or lines, spaces or vias in the dielectric composition; promoting adhesion; and plating the dielectric layer with a conductive metal; wherein the dielectric composition includes a) from 20 to 80% by weight of at least one low dielectric constant, crosslinkable material; b) from 10 to 80% by weight of at least one crosslinking agent; c) from 0.1 to 25% by weight of at least one catalyst including thermal acid generators, photoacid generators, thermal base generators, photobase generators, or mixtures thereof; d) from 5 to 60% by weight of a reactive diluent; and e) optionally one or more additives; wherein the composition is substantially free of organic solvent.
In a fifth aspect, the present invention provides a substrate coated with a dielectric composition as described above.
In a sixth aspect, the present invention provides a process for providing a dielectric coating on a substrate including the steps of preparing a melt of a dielectric polymer, and applying the melt to the substrate.
In a seventh aspect, the present invention provides a pr
Aubry James L.
Canlas Jennifer Patricia
Shelnut James G.
Sonnenberg Wade
Barreca Nicole
Cairns S. Matthew
Huff Mark F.
Shipley Company L.L.C.
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