Active solid-state devices (e.g. – transistors – solid-state diode – Encapsulated – With specified filler material
Reexamination Certificate
2000-09-20
2002-07-02
Clark, Sheila V. (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Encapsulated
With specified filler material
C257S789000
Reexamination Certificate
active
06414398
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to resin ceramic compositions. More particularly, the resin ceramic compositions of the invention include a ceramic that provides the composition with magnetic properties.
2. Description of the Prior Art
A variety of resins are used in connection with devices having magnetic or electronic uses. Often the resin serves as a package or as a support structure onto which other devices are attached. Hence, the resin must be further processed to provide a finished product.
Semiconductor devices are packaged and encapsulated in a variety of resinous materials, including epoxy. Epoxy resins have excellent heat resistance, moisture resistance, electrical characteristics and adhesion properties, and they can acquire various characteristics with the addition of modifying agents. Accordingly, epoxy resins are used for packaging microelectronic components, such as integrated circuits.
The epoxy compositions used in electronic applications may include a hardener and fillers. The fillers are utilized to provide the epoxy resin with desirable characteristics such as a low coefficient of thermal expansion and high thermal conductivity. Commonly used fillers include inorganic fillers used in combination with epoxy include silica, quartz, alumina, fiber glass, calcium silicate, a variety of earths and clays, and combination thereof. Examples of epoxy compositions which include various types of fillers which are used in electronic applications are described in U.S. Pat. No. 4,042,550.
One type of semiconductor device which utilizes epoxy compositions, are proximity sensing devices, such as a Hall effect sensor. A Hall effect sensor relies on a change of magnetic flux density applied to a sensing plane of a Hall effect element. A detailed description of Hall effect sensors is set forth in U.S. Pat. Nos. 5,729,130, 5,694,038, 5,650,719, 5,389,889 and 4,970,463, and the operation of a number of different Hall effect type sensors is described in Allegro (formerly Sprague) Data Book SN-500.
In a representative Hall effect sensor as shown in U.S. Pat. No. 4,970,463, a magnet is mounted a fixed distance from a sensing plane of a Hall effect sensor element, defining an air gap and forming an assembly. The manufacture of such assemblies requires that the magnet be mounted in a particular orientation relative to the sensing plane. Various techniques are known for fixing the position of the Hall effect sensor, such as potting or overmolding. In one known overmolding technique, the magnet is overmolded onto an existing semiconductor which is already encapsulated in a package. The addition step of adding or overmolding a magnet to the semiconductor increases the complexity and cost of manufacture of such devices.
In addition to the increased manufacturing cost, a common shortcoming of such sensing devices is the dependence of the output of the device on the airgap between the device and the magnet which may vary on a part to part basis. More specifically, as the air gap between the magnet and the semiconductor increases, the maximum output range of the device decreases, decreasing the sensitivity of the sensor. Thus, there is a need to provide a reduced cost Hall effect sensor with relatively consistent repeatable output characteristics.
SUMMARY OF THE INVENTION
Briefly, the present invention relates to a resin ceramic composition and provides a number of properties heretofore not available in a single composition. In an important aspect of the invention, the resin ceramic composition is capable of providing a magnetic field. Hence, the use of the resin ceramic compositions of the invention eliminates the need to use a separate magnet and thus significantly reduces the cost of such devices requiring external magnet fields.
In one aspect of the present invention, the resin ceramic composition is an epoxy ceramic composition suitable for encapsulating an integrated circuit. Two embodiments of this aspect the invention are contemplated. In one embodiment the composition is overmolded over an already encapsulated integrated circuit. In another embodiment of the invention, the composition is used as the only encapsulation for the integrated circuit die. In both embodiments, the use of the composition eliminates the need for an external magnet, significantly reducing the cost of the sensor and providing relatively consistent repeatable output characteristics. Further, the use of the resin ceramic composition of the invention as a package or overmold provides a relatively repeatable and consistent air gap, and thus, increases the sensitivity of the device used with a similar type magnetic material. Since the magnetic field strength is temperature dependent in one aspect of the invention, the composition may be based on a resin that is able to provide suitable output over an anticipated temperature range of −40° C. to 150° C., which makes the composition attractive for sensors used in automotive applications.
The composition of the invention includes a resin, and an amount of ceramic filler effective for providing the composition with a magnetic field strength of at least about 1 gauss. The ceramic filler may include strontium ferrite, barium ferrite, or mixtures thereof. When the resin is an epoxy, and the epoxy ceramic composition is used to encapsulate an integrated circuit, the ceramic filler may have a particle size of about 1.5 microns or less. The relatively small particle size and shape provides an additional advantage in that it provides less stress on the semiconductor than other compositions used for encapsulation.
The present invention also provides a process for preparing a resin ceramic composition. In accordance with the process of the present invention, a resin is blended with a ceramic filler in an amount effective for providing the resulting composition with a magnetic field of at least about 1 gauss. The resin ceramic filler blend is exposed to a magnetic field to orient magnetic dipoles within the composition.
The present invention also provides a process for preparing a resin molding composition capable of conversion to a thermoset condition upon application of heat which is suitable for encapsulating semiconductor devices. The process provides a composition having properties compatible for use with semiconductor device, and a magnetic field of at least about 1 gauss. In accordance with this aspect of the present invention, a resin composition is blended with a hardener, if necessary, and a ceramic filler in an amount effective for providing the resulting composition with a magnetic field of at least about 1 gauss. In an important aspect of the invention, the ceramic filler may include a dielectric that has magnetic properties such as barium ferrite, strontium ferrite, and mixtures thereof. The resin/hardener/ceramic filler blend is heated to a temperature for a predetermined time effective for crosslinking the composition. The resin/hardener/ceramic filler blend may be isotropic or anisotropic (i.e. non-magnetically oriented or magnetically oriented).
DETAILED DESCRIPTION
The present invention provides a resin having magnetic properties. In one aspect of the invention, the resins may be used in connection with various types of magnetic responsive sensors. Examples of magnetic flux responsive sensors include Hall effect sensors, discrete, hybrid or integrated circuits which include Hall effect sensors such as application specific integrated circuits (ASIC), reed switches, magneto resistive sensors (MRS) such as a hybrid, discrete or integrated circuit including an MRE, and magnetic axial contact switches and the like as generally described in U.S. Pat. No. 4,970,463, herein incorporated by reference. Any sensor which provides an output signal in response to a change in magnetic flux density can be fabricated by the method in accordance with the present invention.
Resins useful in the present invention may include thermoplastic and thermoset resins. Representative examples of resins that may be used in the pr
Clark Sheila V.
Dana Corporation
Katten Muchin Zavis & Rosenman
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