Active solid-state devices (e.g. – transistors – solid-state diode – Encapsulated – With specified encapsulant
Reexamination Certificate
1998-06-08
2001-03-13
Potter, Roy (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Encapsulated
With specified encapsulant
C257S787000, C438S124000
Reexamination Certificate
active
06201309
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a recyclable resin-scaled type semiconductor device. For example, a semiconductor element mounted on a lead frame is sealed with thermoplastic resin.
2. Description of the Related Art
Semiconductor devices covered by thermosetting resin may be manufactured according to the following method.
A semiconductor element bonded on a lead frame is disposed in a cavity defined by mold. The semiconductor element is interconnected with a lead frame by bonding wires comprised of a conductive material (Cu, Fe—Ni alloy). The cavity has a gate that casts the thermosetting resin into the cavity.
The epoxy resin (thermosetting resin) is cast from the gate. The epoxy resin is heated to the molding temperature by heating the mold, and the epoxy resin hardens. The epoxy resin seals the semiconductor element, the bonding wires, and a part of lead frame. The hardened resin is called a Package. Finally, the mold cools below the molding temperature of the epoxy resin.
As mentioned above, in fluidity and adhesion point of view, the thermosetting resin is applied to manufacturing the semiconductor devices.
About 60 seconds average is required for hardening the thermosetting resin, because of the step of cooling the mold. The required hardening time decreases the productivity of the semiconductor devices.
Further, generally speaking, the thermosetting resin has high fluidity, this characteristic is the cause for easily generated flashes.
Further, the package cannot be recycled because the heat-treated thermosetting resin doesn't have fluidity as before. Thus, unused packaging material must be dumped into a land fill, Unused material results from dividing the semiconductor element from the element board, dividing the package from the semiconductor element, and destroying the package by fire.
If a thermoplastic resin is substituted for the thermosetting resin, about 10 seconds average is required for hardening the thermoplastic resin. The thermoplastic resin can also be recycled because fluidity returns after heat-treating. Thus, waste material may be advantageously reclaimed and reused.
The thermoplastic resin, however, has a lower adhesion than the thermosetting resin. This characteristic allows moisturized air to enter into the semiconductor device through the interface between the package and the lead frame. It is the problem of moisture proof (or wet endurance). Therefore, thermoplastic resin has not been used.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a recyclable semiconductor device. This invention provides a reusable packaging material for semiconductor devices. The new package of semiconductor device is formed from a thermoplastic resin. This thermoplastic resin has good fluidity and good adhesion. The new package is recyclable because the thermoplastic resin's hardening process is a reversible change.
In order to achieve the aforementioned object, there is provided a thermoplastic material for sealing a semiconductor element having 4.5×10
−5
[1/.degree.C.] or less linear thermal expansivity at about 150-200 .degree.C.
The invention further provides a thermoplastic material for sealing a semiconductor element being characterized by a ratio of B1 to A1 of 0.55 or more for linear thermal expansivity where A1 is in the direction of flowing the thermoplastic material, and B1 is in the normal direction of flowing the thermoplastic material. This condition may be replaced with a ratio of A1 to B1 of 0.55 or more.
Further, the invention provides a semiconductor device comprising: a semiconductor element, a package formed by the thermoplastic material for sealing the semiconductor element, and a conductor for connecting the semiconductor element to an external element.
Further, the invention provides a process for manufacturing a semiconductor device, comprising the steps of: electrically interconnecting the semiconductor element with the one end of the conductive means, and sealing off the semiconductor element and the one end of the conductive means with a thermoplastic material.
REFERENCES:
patent: 5539218 (1996-07-01), Takahama et al.
patent: 5565709 (1996-10-01), Fukushima et al.
patent: 5827999 (1998-10-01), McMillan et al.
Adachi Masaki
Honda Tomoko
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Kabushiki Kaisha Toshiba
Potter Roy
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