Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package – With contact or lead
Reexamination Certificate
2002-05-21
2004-08-10
Elms, Richard (Department: 2824)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
With contact or lead
C257S692000, C257S693000, C257S730000
Reexamination Certificate
active
06774479
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to an electronic device having a semiconductor chip on a semiconductor chip connection plate, and to a leadframe having the semiconductor chip connection plate. The invention also relates to corresponding production methods.
If bond connections to a ground potential are additionally required by the semiconductor chip, it is possible to lead corresponding bonding wires from contact areas on the semiconductor chip, which are to be grounded, to the semiconductor chip connection plate. To that end, the semiconductor chip connection plate has a larger top side than the base area of the semiconductor chip. However, it is found that the reject rate is increased on statistical average by virtue of the fault rate in the case of devices with drawn-down additional ground lines to the semiconductor chip connection plate.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to investigate the cause of this increased reject rate and to avoid it to the greatest possible extent.
With the foregoing and other objects in view there is provided, in accordance with the invention, an electronic device having a semiconductor chip, a plastic housing and a leadframe for assembling the semiconductor chip. The semiconductor chip is mounted on a semiconductor chip connection plate of a flat conductor frame of the leadframe. The area of the semiconductor chip connection plate of the flat conductor frame is greater than the base area of the semiconductor chip. However, this larger semiconductor chip connection plate is structured in such a way that it has elongate openings along the edge sides of the semiconductor chip, so that the flat conductor frame has a ring that is defined by the elongate openings and that surrounds the semiconductor chip.
This electronic device has the advantage that the reject rate after the press molding of the plastic housing is lower than in previous constructions with a non-structured semiconductor chip connection plate having a larger top side than the base area of the semiconductor chip fitted thereon. Since the elongate openings surround the semiconductor chip, the bonded ground lines are arranged on the annular structure of the formed semiconductor chip connection plate. By virtue of the elongate openings between the ring structure and the semiconductor chip, the ring is mechanically decoupled from the semiconductor chip. Bond connections on the ring can shift with the ring and the pressed-on molding compound, with the result that the shear stress on the bond connection by the plastic molding compound during the press molding operation is reduced, and interruption or delamination of bond connections on the structured semiconductor chip connection plate is advantageously avoided in the region of the ring.
After the press molding operation, during the cooling of the plastic composition of the housing, the ring with the bond connections can follow the shrinking process of the plastic, with the result that the shear loads between the ring and the bond connection remain minimized in this phase as well. Without the invention's openings all around the semiconductor chip, the shear loads between the bond connections and the semiconductor chip connection plate are in some instances so high that the bond connections tear and malfunctions of the electronic device thus occur. This problem is solved by the invention's structuring of the semiconductor chip connection plate.
In order to ensure a ground line between the semiconductor chip connection plate and the surrounding ring—in one embodiment of the invention—at least one electrically conductive bridge is provided between the ring of the semiconductor chip connection plate and the region of the semiconductor chip connection plate on which the semiconductor chip is arranged. The bond connections are arranged spaced apart from the mechanical bridge on regions of the ring that are mechanically decoupled from the region that carries the semiconductor chip. Hereinafter the region of the semiconductor chip connection plate on which the semiconductor chip is fitted is referred to as the island region or the island while the region of the semiconductor chip connection plate that is of annular design is defined as ring.
By virtue of the mechanical decoupling of the ring, which has bond connections to the ground connection, from the island region with the semiconductor chip, this ring region can be shifted and moved more freely in the molding compound. Relative movements between the bond connection and the ring are minimized so that, in the event of thermal cycling, delamination of the bond connection on the ring is avoided, and consequently, there is a reduction in the rejects in particular during the soldering test and after thermal cycling for the device. Although hitherto delamination of the chip on the island has necessarily led to delamination of the bond connections on the semiconductor chip connection plate, this inevitable coupling is overcome by the invention's structuring of the semiconductor chip connection plate. In other words, even in the event of delamination of the chip in the island region, the ground connection is completely preserved via the bond connections and the ring, so that, after thermal cycling, the soldering and moisture test yields a significantly reduced reject rate.
In a further embodiment of the invention, the ring has a smaller thickness than the thickness of the island. Reducing the thickness of the ring reduces the stiffness thereof, and this minimizes the stresses, in particular shear stresses on account of relative movements between the island region of the molding compound and the ring with regard to the bond connection on the ring, and thus with regard to the ground line. Furthermore, on account of the smaller thickness of the ring, the ring with its bond connections can be completely embedded in the plastic compound. As a result, the region of the bond connections on the ring is better protected against mechanical stress including those from the outside, e.g. during the bending of the leadframe, during the cleaning of molding compound from the rear side or through stresses on account of the electronic device being pressed into a measurement receptacle, so that the reject rate which can occur during further processing likewise remains minimized.
A further embodiment of the invention provides for the semiconductor chip connection plate to be electrically connected to the ring and to be put at ground potential. To that end, provision is made of the mechanical bridge that connects the ring to the island.
A further embodiment of the invention provides for the semiconductor chip to have contact areas on its active top side. These contact areas are electrically connected to the ring via bond connections and are put at ground potential via the ring. Whereas on the island itself, the semiconductor chip with its passive rear side can be electrically connected to the island, and thus to ground potential directly by using a conductive adhesive or a soft solder, specific semiconductor structures on the active top side of the semiconductor chip cannot be connected directly to a ground potential. For these regions, corresponding contact areas are connected to the ring via bond connections, while the ring itself is in turn electrically grounded to the island using at least one electrically conductive mechanical bridge.
In one embodiment of the invention, therefore, it is provided that the ring is electrically connected to the semiconductor chip connection plate by at least one mechanical bridge located in the corner regions of the semiconductor chip connection plate. The bond connections are arranged in central regions of the elongate openings of the semiconductor chip connection plate. Providing the bond connections in the central regions of the elongate openings and fitting bridges only in the corner regions of the ring ensures mechanical decoupling of the central region of the ring, so that the bond connections i
Ernst Georg
Lee Tan Loon
Schätzler Bernhard
Elms Richard
Stemer Werner H.
Wilson Christian D.
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