Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – To produce composite – plural part or multilayered article
Reexamination Certificate
1993-11-24
2001-01-23
Ortiz, Angela (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
To produce composite, plural part or multilayered article
C264S272150, C264S272170
Reexamination Certificate
active
06177040
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to improvements in integrated circuit protective packages and in methods for manufacturing same. More specifically, this invention relates to improvements in protective packages for erasable programmable read only memory devices (conventionally, “EPROMs”). In particular, this invention relates to fabrication of a light transparent window in a molded protective package for an EPROM.
BACKGROUND INFORMATION
An EPROM circuit of the type of interest herein is an erasable programmable read only integrated circuit in which memory circuitry is erasable by exposure to light. Following such exposure, electric charge on the memory cells is dissipated, and consequently data stored in the memory cells is removed, or erased, from the circuit. Thereafter, new data may be programmed into the circuit in known manner. One form of light used to irradiate an EPROM is ultraviolet (“UV”) light.
Generally, EPROM devices are sealed in packages to protect the EPROMs from damage during transit between the manufacturer and the end user, from damage during use of the EPROM, and to insure reliability of the circuit. In EPROM circuit packages, a window is typically provided through which light, generally light in the UV wavelength region, may pass to irradiate the contained memory circuit.
A variety of methods are used to form integrated circuit packages, while also providing a light transparent window to the circuit. One variety of packages include those that are molded around the contained integrated circuit. For example, a package may be fabricated by providing a circuit mounted on a circuit board, and applying a light transparent epoxy resin over the circuit. The light transparent epoxy resin is cured to form a light transparent cover over the circuit. Such a method has several limitations, including being package outline specific, thus limiting the market for the fabricated package. Further, UV transparent epoxy resin has a thermal expansion coefficient substantially greater than standard plastic molding compounds, which introduces reliability problems in the circuit. In such conventional packages, little, if any, effort is made to select a conformable epoxy resin, or to shape the quantity of epoxy resin applied to the circuit. Consequently, the thickness of the cured epoxy resin may vary from package to package. Further, differences in thickness may distort the incidence of light transmitted through the cured epoxy cover.
Another method for fabricating an EPROM package is to manufacture a hermetically sealed protective package that includes a ceramic lid with a UV transparent lens. A variety of such ceramic packages exist. Most of the various ceramic packages belong to one of three major groups: (i) packages which have a ceramic or metal base and lid, and an all glass wall; (ii) packages which have a ceramic wall, base, and lid; and (iii) packages which have a glass base and wall, and a glass, ceramic, or metal lid. The UV transparent lens permits irradiation of the EPROM circuit through the lens. The lens often is made of quartz, which in turn has dictated that the protective package materials be made of carbon, graphite, and compounds of barium and titanium because of the nonwetting characteristic of the glass with respect to carbon and graphite.
Fabrication of the individual components of ceramic packages and assembly of the packages themselves are expensive in comparison with encapsulated or plastic molded packages. For example, each lens must be individually constructed at significant cost. Because each lens is not constructed or fabricated integrally with other components of the finished package, each lens must be individually mounted on a separately manufactured lid, a step in the manufacturing process which further increases the price of the finished product. The lid of the protective package that houses the lens must be manufactured with a special recess, depression, or preformed aperture to receive the lens, another step that adds to the cost of the finished package.
In addition, it has been common practice to hermetically seal the transparent lens in the preformed aperture, a step necessitating sandwiching the lid and lens within paired fixtures, which fit together. Following the step of fitting the fixtures together, the protective package assembly is fired to form the desired hermetic seal between the lens and the lid. The firing process often deposits foreign particles on the lens, principally carbon, and the lens surface also may be damaged from the process of firing. Particle deposition on the lens surface inhibits the ability of the lens to transmit UV light through the lens without diffusing the light. To remove such foreign particles, a solvent may be applied to clean the surface of the lens. However, that step may further roughen the surface of the lens. The roughened surface may then have to be further fired to fire-polish the surface of the lens. All of the foregoing steps are time consuming and expensive, and each step may itself induce impurities or a rough surface on the lens requiring additional expensive steps to correct.
Much of the cost of an integrated circuit of any kind is incurred in the packaging. The costs associated with fabricating and assembling conventional plastic molded protective packages for integrated circuits is much less than the costs associated with fabricating and assembling a ceramic type of protective package. Economics and market demand indicate a need to provide for a light transparent plastic package for an EPROM, particularly an ultraviolet light transparent window.
Accordingly, there is a need to provide an EPROM protective package with a light transparent window to substantially reduce the costs associated with producing conventional ceramic hermetically sealed protective packages for EPROMs, particularly a window which is transparent to ultraviolet light.
SUMMARY
In light of the above, therefore, it is an object of the invention to provide an improved package, and method for making the improved package, for an integrated circuit having light erasable elements.
Another object of the invention is to provide an EPROM package having a light transparent window that is inexpensive to produce and assemble in comparison with prior packages.
Yet another object of the invention is to provide an EPROM package that has a UV transparent window, and which can be formed into a wide variety of package outlines, such as Chip-On-Board (“COB”) applications, DIPS, chip carriers, and other integrated circuit structures.
Another object of the invention is to provide an EPROM package assembly that provides a UV receptive window to erase the EPROM, and which may be fabricated from inexpensive light transparent compounds.
A technical advantage of a plastic EPROM package with a light transparent window constructed according to the invention is substantially reduced fabrication and assembly costs are associated with the package.
Another technical advantage of the preferred embodiment of the invention is that fabrication of a window integral with the package that is transparent to ultraviolet light is enabled.
Yet another technical advantage of a plastic EPROM package with a light transparent window constructed according to the invention is that fabrication of the device is possible in a wide variety of package outlines. The invention is not limited to use in connection with a particular outline such as COB, DIP, or any other limited use.
Another technical advantage of a plastic EPROM package with a light transparent window constructed according to the invention is that increased protection is afforded the EPROM by the finished package, in comparison with other varieties of EPROM packaging.
According to a broad aspect of the invention, an integrated circuit having light erasable elements includes a light transparent material having a top, a bottom, and lateral sides. The bottom side is located conformally on a first region of the integrated circuit overlying the light erasable elements. The top si
Brady III Wade James
Franz Warren L.
Ortiz Angela
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
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