Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2000-09-13
2002-01-08
Lam, Cathy (Department: 1775)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C523S400000, C528S007000, C528S332000, C528S422000
Reexamination Certificate
active
06337375
ABSTRACT:
TECHNICAL FIELD
This invention relates to a high optical contrast and UV fluorescing composition such as may be used in dielectric layers of printed circuit boards, said boards in turn forming part of an electronic package.
BACKGROUND OF THE INVENTION
In the manufacture of electronic devices, such as computers, printed circuit boards are widely used to support discrete electronic components and to provide the electrical circuitry between the components. Commercial electronic computers have become much more powerful since the introduction thereof, yet these have been reduced in physical dimensions from room size to notebook size. As this size has decreased and the number of interconnections due to more powerful logic has increased, the printed circuit boards used therein have become denser and more complex. Today's printed circuit boards can be extremely dense, with very small geometries and with many layers.
Typically, printed circuit boards have at least one central core, typically a dielectric layer, such as a composite of fiber glass and a thermosetting resin such as an epoxy resin, which core has applied on at least one surface thereof a layer of conductive material such as copper. The layer or layers of conductive material are etched or otherwise processed to provide circuits of predetermined geometrical configuration. Several such cores may then be laminated to form a multilayered structure (a printed circuit board) having metal circuitry sandwiched between dielectric layers.
The dielectric material widely used today contains a composition of epoxy resins impregnated onto glass or fiber-glass reinforcing material. The dielectric layers within these circuit boards exhibit the color of the epoxy, typically white or yellow. Printed circuit boards with dielectric surfaces and layers having a white or yellow color afford low optical contrast when compared with the circuitry and make automated optical assembly pick and place operations (where components are positioned on and eventually coupled to the circuitry) very difficult.
Additionally, in the likely event that the printed circuit boards made from these dielectric layers require inspection, low optical contrast between the dielectric material and circuitry on any one layer of the printed circuit board also makes inspection difficult and inefficient. For example, circuitry defects adjacent the dielectric material on a printed circuit board with low optical contrast are difficult to optically inspect and make the process of inspecting very time consuming.
Electrical techniques to detect such circuit defects are also not effective because high electrical conductivity metals are used in circuitizing printed circuit boards. Detecting a change in current flow through a highly conductive metal circuit having a small defect is very difficult, if not impossible, without very sophisticated techniques.
To solve these foregoing and related problems, an improved composition for making a dielectric layer has been developed. It is believed that such a composition and the resultant electronic package, will constitute a significant advancement in the art.
OBJECTS AND SUMMARY OF THE INVENTION
Accordingly, it is the object of this invention to provide a new and unique composition which in turn may form part of a dielectric layer of an electronic package.
Another object of this invention is to provide a method of making such a composition.
Yet another object of this invention is to provide an electronic package including a dielectric layer of reinforcing material, a resin, a coloring agent and a fluorescing agent, the dielectric layer having enhanced ultraviolet (UV) light fluorescence characteristics and enhanced optical contrast which allows both more efficient and accurate inspection of the layer, e.g., when used in a printed circuit board.
The invention is adaptable to mass production, improves overall product quality and reduces the cost of manufacturing such products.
BEST MODE FOR CARRYING OUT THE INVENTION
In accordance with the teachings of this invention, there is provided a new composition for use in the manufacture of a circuitized substrate, (e.g., printed circuit board or chip carrier) usable as part of an electronic package. In one embodiment, this composition comprises a resin material, a coloring agent, and a fluorescing agent. It has been discovered that when this composition is utilized in the manufacture of a printed circuit board, it results in a printed circuit board dielectric layer having UV light absorbing fluorescing characteristics. As a result, the metallic conductor patterns on the printed circuit board (which do not have UV fluorescing characteristics) can be more readily, efficiently, and accurately inspected when the printed circuit board is irradiated with UV light. One application of this invention is manifested by comparing the UV light fluorescence pattern generated from a defective circuit pattern of a printed circuit board manufactured with the composition of this invention to the UV light fluorescence pattern generated from a defect free circuit pattern of a printed circuit board also manufactured with the composition of this invention. In addition, assembly processes such as those required when picking and placing components on a circuit board require high optical contrast surfaces for efficient optical equipment functionality. It has been discovered that printed circuit boards or chip carriers manufactured with the composition of this invention provide a laminate with color and high optical contrast surfaces which improve the assembly apparatus pick and place capability. The resin material of this invention is selected from a group including epoxy, cyanate or bismaleimide resins or combinations thereof. Examples of epoxy resins used in this invention include epoxy polymer resins such as epoxidized novolac polymers and polyepoxides from haloepoxy alkane polymers derived from mononuclear and polynuclear dihydric and halogenated dihydric phenols. Mixtures of epoxides can also be used. Further examples of suitable epoxides containing an oxirane ring that can be employed are known and are described in E. W. Flick, “Epoxy Resin, Curing Agents, Compounds, and Modifiers” Noyes Publications, Park Ridge, N.J. (1987); in Lee and Neville, “Epoxy Resins” McGraw-Hill, (1967) and in U.S. Pat. No. 4,680,341.
Epoxidized novolac polymers are commercially available and can be prepared by known methods by the reaction of an uncrosslinked aldehyde of a phenol with a haloepoxy alkane. The phenol can be a mononuclear or polynuclear phenol. Examples of mononuclear phenols have the formula:
wherein X, Y, and R are independently selected from the group hydrogen or hydrogen alkyl containing 1 to 9 carbon atoms, aryl containing 6 to 14 carbon atoms, and halogen. Hydrocarbon substituted phenols having two available positions ortho (o) or para (p) to a phenolic hydroxy group for aldehyde condensation to provide polymers suitable for the preparation of epoxy novolacs include o- and p-cresols, o- and p-isopropyl phenols, o- and p-tert-butyl phenols, o- and p-sec-butyl phenols, o- and p-amyl phenols, o- and p-octyl phenols, o- and p-nonyl phenols, 2,5-xylenol, 3,4-phenol, 2,5-diethyl phenol, 3,4-diethyl phenol, 2,5-diisopropyl phenol, o- and p-benzyl phenol, o- and p-phenylphenols, o- and p-tolyl phenols, o- and p-xylyl phenols, o- and p-cyclohexyl phenols, and o- and p-cyclopentyl phenols.
Various chloro-substituted phenols which can be used in the preparation of phenol-aldehyde resins suitable for the preparation of the epoxy novolacs include o- and p-chlorophenols, 2,5-dichlorophenol, 2,3-dichlorophenol, 3,4-dichlorophenol, 2-chloro-3-methylphenol, 2-chloro-5-methylphenol, 3-chloro-2-methylphenol, 5-chloro-2-methylphenol, 3-chloro-4-methylphenol, 4-chloro-3-methylphenol, 4-chloro-3-ethylphenol, 4-chloro-3-isopropylphenol, 3-chloro4-phenylphenol, 3-chloro4-chlorophenylphenol, 3,5-dichloro-4-methylphenol, 3,5-dichloro-2-methylphenol, 2,3-dichloro-5-methylphenol, 2,5-dichloro-3-methylphenol, 3-chloro-4,5-dimethylphenol, 4-chlor
Johansson Gary A.
Papathomas Konstantinos I.
Fraley Lawrence R.
International Business Machines - Corporation
Lam Cathy
LandOfFree
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