Electricity: electrical systems and devices – Safety and protection of systems and devices – Circuit interruption by thermal sensing
Reexamination Certificate
2002-05-09
2004-05-11
Sircus, Brian (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
Circuit interruption by thermal sensing
C361S104000
Reexamination Certificate
active
06735065
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a semiconductor module with a housing, a semiconductor component that is surrounded by the housing, and an integrated temperature sensor and interrupt device housed in the housing.
This type of semiconductor component can have any construction; i.e. it can be an MOS (Metal Oxide Semiconductor) transistor, an IGBT (Insulated Gate Bipolar Transistor), a JFET (Junction Field Effect Transistor), a thyristor, and so on. The structure and function of such semiconductor components are known from multiple sources, so that it is unnecessary to provide a detailed description of these semiconductor components here. The exemplary semiconductor component herein is a field-effect-controlled power MOS transistor, also known as a power MOSFET (Metal Oxide Semiconductor Field Effect Transistor), although the invention is not limited to this semiconductor component.
When semiconductor components such as power MOSFETs are utilized, the possibility of an error or failure can never be completely ruled out. Minor errors, which have almost no effect on the function of the semiconductor component, are distinguishable from serious errors, which cause functional impairment, and which in extreme cases, cause destruction of the power MOSFET. A particularly serious error is what is known as alloying-through or melting of a power MOSFET. In a MOSFET that is constructed as a high-side switch, a short can occur between the positive supply potential and the output terminal. In a MOSFET that is constructed as a low-side switch, the output terminal can be shorted to the device ground. The shorted load current of the respective power MOSFET can no longer be controlled by its drive logic. Thus, the load current is limited only by the impedance of the load and the defective transistor in the load circuit.
If a MOSFET is melted through and therefore shorted, the current flow is uncontrolled, and is determined by the voltage source and the resistances of the load and the melted MOSFET. The current is therefore smaller than in normal operation, and the fuse does not trip. The maximum power loss at the destroyed MOSFET occurs when its resistance reaches the order of magnitude of the load resistance. A voltage shearing between the MOSFET and the load then occurs, i.e. a matching for power transfer, or a power maximum. Depending on the size of the load resistance and the possibilities for cooling the melted, nonfunctional MOSFET, this leads to an extreme temperature rise of the MOSFET and ultimately the MOSFET or the chip environment will catch on fire.
As a precaution against overheating, a temperature sensor is typically provided, which switches the power MOSFET off given excessive overheating of the power MOSFET, for instance, as a consequence of a short-circuit current. But such a remedy only works as long as the power MOSFET is not defective. Besides this, the problem with this type of arrangement is that, in a semiconductor module with a plurality of power MOSFETs, it is extremely difficult technically to place a temperature sensor in the vicinity of such a MOSFET. Furthermore, it is disadvantageous to utilize a single temperature sensor that detects the temperature of the entire semiconductor module, because due to the poor heat conductivity inside the housing, the temperature sensor only senses an overtemperature after a long delay. Therefore, an overtemperature of a defective power MOSFET is only detected by the temperature sensor when the MOSFET is already disabled.
Beyond this, even in protected circuits such as this, extreme conditions occur, which can cause damage to the power MOSFET. The injury to the power MOSFET can manifest itself in the flowing of an uncontrollable load current though the power MOSFET and the presence of a forward bias at the drain and source terminals. The problem with this is that the power MOSFET can go out of control while remaining fully functional and continuing to conduct the short- circuit current. The current flow through the load circuit of the power MOSFET is not even stopped when the power MOSFET and the motherboard on which the power MOSFET is disposed is heated above the melting point of the solder, for instance above 250° C. If the heating continues, for instance above 300° C., the MOSFET is still not destroyed, but merely damaged. This effect is particularly serious when the heating of the power MOSFET and its environment is not abrupt, but rather occurs relatively slowly over several minutes. The power MOSFET and its environment can heat up progressively until the environment ignites and a fire starts.
Furthermore, a malfunction may not necessarily always be due to a short circuit. Rather, uncontrollable errors comparable to the errors just described can already occur given a nominal load current and a defective semiconductor component.
Issued German Patent DE 198 05 785 C1 describes a power semiconductor module that irreversibly interrupts the load circuit in case of an impermissible heating of the load circuit of a power semiconductor component. To accomplish this, interruption means are provided, which exhibit a volume expansion property in the case of an impermissibly high temperature, and which force open the load terminals and thus interrupt the load circuit in a defined and irreversible manner when a temperature threshold is crossed.
The interruption means described in Issued German Patent DE 198 05 785 C1 is problematic with respect to finding suitable materials that respond precisely at the desired temperature threshold. A still greater problem is that the processing temperature of this material approximately corresponds to the temperature at which this thermally ignitable material will react. For instance, the highest processing temperature in the assembly of the semiconductor module is approx. 270° C. The reaction temperature of this thermally ignitable material must thus be sufficiently greater than this maximum processing temperature in order to avoid a potential false activation, so that the thermally ignitable material may only ignite at a temperature above 300° C. In any case, there are many instances of application in which the semiconductor component already does serious harm at a temperature approximately corresponding to the processing temperature.
There also exists the need to furnish a power semiconductor module with a thermal protection mechanism that trips in a defined fashion at an arbitrary temperature, preferably a low temperature. The subsequent fate of the power semiconductor module is irrelevant, the only need is to guarantee a reliable interruption.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a semiconductor module which overcomes the above-mentioned disadvantages of the prior art apparatus of this general type.
In particular, it is an object of the invention to reliably interrupt the load circuit of a housed semiconductor component in the case of a malfunction in the load circuit of the semiconductor component, given that the processing temperature is not excessive.
With the foregoing and other objects in view there is provided, in accordance with the invention, a semiconductor module, including: a housing; terminals for receiving a supply potential; at least one output line for carrying a load current; at least one semiconductor component disposed in the housing, the semiconductor component being conductively connected to the output line; an integrated temperature sensor being housed in the housing, the temperature sensor having a load terminal connected to one of the terminals for receiving the supply potential; and an interruption device housed in the housing. When a first temperature threshold is being exceeded and a first supply potential is being supplied to the terminals for receiving the supply potential, then the temperature sensor conducts a load current causing heating of the temperature sensor. The interruption device is configured for irreversibly interrupting at least the output line when a second temperature th
Graf Alfons
Tihanyi Jenoe
Tröger Wolfgang
Greenberg Laurence A.
Infineon - Technologies AG
Kitov Z
Mayback Gregory L.
Sircus Brian
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