Active solid-state devices (e.g. – transistors – solid-state diode – Lead frame
Reexamination Certificate
1998-12-23
2003-09-02
Williams, Alexander O. (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Lead frame
C257S696000, C257S698000, C257S787000, C257S790000, C257S788000, C257S684000, C257S796000, C257S784000, C257S693000, C257S692000, C257S730000, C257S795000, C174S050000, C361S709000
Reexamination Certificate
active
06614100
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a lead frame for the installation of an integrated circuit in an injection-molded package. The lead frame has a lead (i.e., a conductor element for electrically connecting the integrated circuit) provided with a contact surface. After the completion of the injection-molded package, the contact surface becomes an external contact for electrically bonding the integrated circuit from outside the package.
Particularly if the injection-molded package is a chip card or the like, it is sometimes desirable for the contact surfaces not to be in the direct vicinity of the integrated circuit in the injection-molded package. This has the result that the leads extend relatively far within the package or on its surface. The packages are usually produces with a two-part injection mold which has a cavity into which the integrated circuit, with the lead frame connected to it, is inserted. The integrated circuit is thereby usually provided with a thermoset enclosure (the so-called mold body), from which the leads with the contact surfaces protrude. In the case of so-called in-mold labeling, a decorative film or label is placed on each of two sides of the cavity formed in the injection mold. Between the two decorative films and in direct contact with them is the enclosure of the integrated circuit. The actual card body is then produced by forcing a thermoplastic polymer into the cavity which remains between the two decorative films.
This may result in two undesirable effects: On the one hand, the relatively long leads that protrude from the enclosure of the integrated circuit may be deformed by the relatively high injection pressure (sometimes far in excess of 1000 bar) during the injection of the thermoplastic polymer composition. On the other hand, there is the risk of so-called flash forming on the contact surfaces of the leads, whereby a thin film of thermoplastic polymer composition is formed on the contact surfaces. This is, of course, disadvantageous, since the contact surfaces must be free from polymer for the later electrical bonding. The flash is removed by detaching the thin polymer film from the contact surfaces by a cleaning process. Another prior art solution that prevents flash formation is to use thin hold-down pins, which are component parts of the injection mold and, when the halves of the injection mold are fitted together, press the contact surfaces through the cavity formed as a result against one of the inside walls of the injection mold. The thermoplastic polymer is thereby prevented from getting onto that side of the contact surface which is in contact with the inside of the injection mold. However, the hold-down pins are associated with the disadvantage that, after injecting the polymer composition into the cavity and subsequently removing the hold-down pins, holes remain in the injection-molded package thus produced.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a lead frame for mounting an integrated circuit in an injection molded package, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which specifies another solution with which the formation of polymer flash on the contact surfaces of the leads can be avoided.
With the foregoing and other objects in view there is provided, in accordance with the invention, a lead frame for mounting an integrated circuit in an injection-molded package, comprising:
at least one lead formed with a contact face for electrically bonding an integrated circuit;
the at least one lead including a spring element to be compressed during an injection molding of the package in an injection mold, whereby the contact surface is pressed against an inside wall of the injection mold during the injection molding.
In other words, each lead is provided with a spring element that can be compressed by the injection mold during the injection molding of the package. The resultant force of the compressed spring element has the effect that the contact surfaces of the leads are biased against the inside wall of the injection mold. The compression is a resilient, reversible deformation of the spring element.
The spring elements according to the invention render the use of the prior art hold-down pins unnecessary. This overcomes the associated disadvantages of more complex handling of the injection mold, and the holes produced in the injection-molded package after removal of the hold-down pins are avoided. Nevertheless, because the contact surface, and consequently the lead, is fixed, flash formation on the contact surfaces and deformation of the leads during the injection of the polymer composition into the injection mold are avoided by the invention.
In accordance with an added feature of the invention, the spring element is integrally formed at one end of the lead.
In accordance with an additional feature of the invention, the spring element is a hook anchoring the lead in the package after completion thereof.
In accordance with another feature of the invention, the spring element is a J-shaped element. In the alternative, the spring element has a semicircular shape.
In accordance with a further feature of the invention, the spring element is at least partially zigzag-shaped.
In accordance with again a further feature of the invention, the spring element is disposed in vicinity of the contact surface.
In accordance with a concomitant feature of the invention, the injection mold is formed with two injection mold halves defining a given thickness of the package, and wherein the spring element projects relative to the contact surface by more than the given thickness of the package.
If the spring element is designed in the form of a hook, at the same time an anchoring of the lead in the package can be achieved. Consequently, coming away of the lead, or the contact surface, as a result of mechanical or thermal loading of the completed package can be avoided.
Although the invention is illustrated and described herein as embodied in a lead frame for the installation of an integrated circuit in an injection-molded package, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
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“Technique Fo
Hauser Christian
Schmidt Helge
Winderl Johann
Greenberg Lawrence A.
Infineon - Technologies AG
Locher Ralph E.
Williams Alexander O.
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