Active solid-state devices (e.g. – transistors – solid-state diode – Responsive to non-electrical signal – Temperature
Reexamination Certificate
2000-01-03
2001-11-27
Lee, Eddie (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Responsive to non-electrical signal
Temperature
C257S252000, C257S499000
Reexamination Certificate
active
06323531
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a two-chip power IC, in which a sensor chip having a sensor is mounted on a switch chip having a switch. The sensor is electrically connected to the switch in order to switch it off when the temperature detected by the sensor exceeds a preset threshold value.
Examples of such two-chip power ICs includes a Tempfet (“temperature protected FET”) and a Profet (“protected FET”). These two-chip power ICs are effectively resistant to short-circuits, in the event of the short-circuit current being reduced as well, only if the temperature detection (“temperature sensing”) can be carried out reliably by means of the sensor chip which is bonded to the switch chip. This means that the temperature sensor (also referred to, for short, as the “sensor” in the following text) must reliably be able to detect a temperature rise in order to be able to switch the switch in the switch chip off in good time before it is destroyed by a short-circuit current. However, this presents a problem when the short-circuit current values are reduced and do not result in the sensor on the sensor chip being heated sufficiently.
In general, the maximum permissible gate-source voltage of a switch, which is generally an FET, in the switch chip must not exceed a specific maximum value in order that the switching-off process in the event of a short-circuit can still be carried out in good time before the switch is destroyed. Even in the case of a sensor chip which is bonded on to the switch chip, it has been found that it is impossible to ensure that the switch chip is reliably switched off in good time, since in many cases the sensor chip is heated only relatively slowly. This is due to the fact that the encapsulation compound which encloses the switch chip and the sensor chip causes the sensor chip to be additionally cooled. As a result, the heating of the switch chip produced before a short-circuit occurs is not sufficient to heat the sensor chip so that the sensor can switch off the switch in the switch chip.
European patent application EP 0 262 530 A1 describes a configuration comprising a power semiconductor chip and a control circuit which is integrated in a second semiconductor chip. The semiconductor chip, together with the control circuit, is thereby mounted on one of the surfaces of the power semiconductor chip, with the two semiconductor chips being connected to one another by means of an insulating layer and a solder layer. The semiconductor chip together with the control circuit is electrically connected via electrical lines to the power semiconductor chip.
The configuration is mounted on a lead frame. The source contact of the power semiconductor chip is connected via two bonding wires to in each case one connecting finger of the lead frame and to one contact of the sensor chip.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a two-chip power IC having an improved short-circuit response, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which ensures that the switch in the switch chip is reliably switched off by means of the sensor on the sensor chip, before a short circuit occurs.
With the foregoing and other objects in view there is provided, in accordance with the invention, a two-chip power IC, comprising:
a switch chip having a switch;
a sensor chip mounted on the switch chip, the sensor chip having a sensor electrically connected to the switch of the switch chip for switching the switch off when a temperature detected by the sensor exceeds a preset threshold value;
a direct supply line connecting the switch chip to an outer conductor and being routed in a vicinity of the sensor for enabling good heat transfer between the supply line and the sensor.
In accordance with an added feature of the invention, the switch of the switch chip comprises a MOSFET, the supply line is a source supply line for the MOSFET, and the supply line touches a surface of the sensor chip, at least in certain parts.
In accordance with an additional feature of the invention, the supply line is connected to the surface of the sensor chip by stitch-bonding. In a preferred embodiment, the sensor chip is formed with an aluminum surface and the supply line is connected to the aluminum surface of the sensor chip.
In accordance with another feature of the invention, the switch chip, the sensor chip, and the supply line are encased in an encapsulation compound.
In accordance with a concomitant feature of the invention, the supply line is routed in a loop or in a curve.
In other words, the objects of the invention are satisfied with a two-chip power IC of the type mentioned in the introduction, in which the direct supply line is routed in the vicinity of the sensor, from an outer interconnect to the switch chip. Heat is transferred well between the supply line and the sensor. In this case, the term “vicinity” means that the supply line may also touch the sensor chip of the sensor.
The proper heat transfer mechanism can be assured when the supply line of the sensor touches the surface of the sensor chip at least in places. An advantageous development of the invention in this case provides for the supply line to be connected to the surface of the sensor chip by stitch-bonding. In this case, the supply line may be connected to an aluminum surface of the sensor chip, in order to ensure good heat transfer between the sensor and the supply line leading to the switch in the switch chip. Both chips and the supply line may be enclosed by an encapsulation compound. The supply line is preferably the source supply line for the switch in the switch chip. In an advantageous development of the invention, the supply line may be routed in the form of a loop or curve from the switch in the switch chip to the surface of the sensor chip.
In summary, the invention thus comprises the source bonding wire being routed in the vicinity of the sensor chip in a preferred manner. Before a short-circuit occurs, this bonding wire is heated and, as a result of the proximity between the bonding wire and the sensor chip, the sensor is heated not only from “underneath” by the switch chip, but also from “above” by means of the heat emitted from the bonding wire.
This means that the sensor assumes higher temperatures more quickly, and responds more rapidly to any short-circuit that occurs. The sensor of the sensor chip can thus switch the switch in the switch chip off in good time before it is destroyed by the full-magnitude of the short-circuit current that flows.
Finally, the yield of reliable two-chip power ICs is greater, with the permissible short-circuit load also rising, since the rapid heating of the sensor chip ensures that the switch in the switch chip is switched off reliably.
The contact between the supply line, or the bonding wire, and the surface of the sensor chip may, of course, be designed such that the contact point is electrically insulated from the sensor chip circuit. The above-mentioned aluminum surface must therefore be electrically isolated from the sensor chip circuit, and this can be achieved, for example, without any problems by the aluminum surface being deposited on silicon dioxide.
However, it must be stressed that the supply line, or the bonding wire, does not need to touch the surface of the sensor chip. It is even sufficient for the supply line, or the bonding wire, to be routed close to the surface of the sensor chip in order that the latter is heated by the current flowing in the supply line.
In addition to the sensor, the sensor chip may contain other integrated circuits. It is even possible to fit further chips having integrated circuits on the switch chip in addition to the sensor chip, as well. The term “two-chip power IC” should thus be understood to mean that a switch chip is connected to a sensor chip which protects the switch chip and, if required, may also have further circuits.
Other features which are considered as characteristic for the invention a
Sander Rainald
Schlögel Xaver
Tihanyi Jenoe
Greenberg Laurence A.
Infineon - Technologies AG
Lee Eddie
Lerner Herbert L.
Stemer Werner H.
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