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 250xc2x0 C. If the heating continues, for instance above 300xc2x0 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. 270xc2x0 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 300xc2x0 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.
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 threshold is exceeded.
The inventive semiconductor module thus includes a temperature sensor and an interruption device for irreversibly interrupting the load current in the case of a malfunction. The irreversible break is characterized by two distinct successive steps:
(1) First, a temperature sensor is provided which detects and monitors the temperature of the semiconductor chip and which is activated at a trip temperature. The term xe2x80x9ctrip temperaturexe2x80x9d refers to a critical temperature threshold TS upon whose crossing the protective mechanism engages (i.e. the temperature sensor is activated).
(2) Secondly, an interruption device is provided which irreversibly interrupts the load circuit of the monitored power MOSFET given that the ignition temperature has been exceeded. The ignition temperature is greater than the trip temperature. The ignition signal by means of which the interruption device is ignited is the temperature of the activated temperature sensor. The term xe2x80x9cignition temperaturexe2x80x9d refers to the temperature at which the thermally active material of the interruption device ignites. When the thermally active material of the interruption device ignites, its volume rapidly expands. This volume expansion can be expressed in a strongly oxidizing or exploding or heavily frothing character.
The particular advantage of the invention consists in the linking of two conditions that must exist simultaneously in order to trigger the irreversible interruption which ultimately leads to the destruction of the MOSFET:
(a) The first condition is the presence of an overtemperature (trip temperature) and the simultaneous presence of an operating voltage. The trip temperature can be set arbitrarily low as a precondition for tripping given the achievement of this temperature. In case this temperature should be attained during the processing of the semiconductor module, for instance during the soldering of the terminals, the other requirement for satisfying the first condition, namely the application of the operating voltage, is not satisfied, and thus the temperature sensor is not activated.
(b) The second condition is the ignition temperature. The ignition temperature of the actual thermally active and thus destructive material can be any temperature above the trip temperature. This temperature is achieved in that, given the attainment of the trip temperature and the presence of the operating voltage, a mechanism is set in motion which induces this ignition temperature. For instance, this temperature can be generated by the temperature sensor, which has been activated and is therefore heating up intensely.
The advantage of this arrangement is that the ignition signal is released only if an ignition temperature is exceeded and the operating voltage is simultaneously being applied, i.e. not during the soldering of the unit, because at this time the required operating voltage could not be present, although the ignition temperature may be.
The following advantages are gained by combining the two conditions:
I. Because the trip mechanism is separate from the ignition mechanism, this ignition temperature can be selected sufficiently far from the trip temperature. It is therefore possible to avoid, as far as possible, accidental ignition of the interruption device, for instance during the processing of the semiconductor module or upon the triggering of the temperature sensor.
II. The overall interruption process can also be switched from outside, either directly via the supply voltage or via a separately provided terminal of the power MOSFET. The overall tripping process can thus be sparked either internally or externally.
III. Lastly, the overall tripping process can be advantageously dimensioned in view of the sensitivity of the temperature sensor, so that the trip temperature can be set to a specific value in a highly precise fashion.
Typically, the load systems of the semiconductor component and the temperature sensor are arranged in parallel fashion between the terminals for the supply voltage. The temperature sensor is supplied by the supply voltage of the protected MOSFET. But the temperature sensor may also conceivably have a separate supply voltage and thus function independently of the MOSFET.
Typically, the temperature sensor is not connected to the external connecting leads. Rather, it is connected within the housing to at least one load terminal of the semiconductor component and alternatively to a drive circuit which drives the semiconductor component. In this case, a separate external terminal for the temperature sensor can be forgone.
What is essential to the functioning of the inventive semiconductor module is that the second temperature threshold is higher than the first temperature threshold. Typically, the first temperature threshold is in the range between 250xc2x0 C. and 300xc2x0 C., whereas the second temperature threshold greater than 300xc2x0 C.
It is particularly important for the function of the inventive temperature sensor that the temperature sensor, and alternatively the interruption device as well, be arranged in the immediate vicinity of the semiconductor component. This produces a thermal coupling between the temperature sensor and the MOSFET, which guarantees an immediate reaction of the temperature sensor in the case of a malfunction.
A triac or thyristor is utilized as a temperature sensor, whereby the thyristor or triac advantageously does not have a control terminal.
If the temperature sensor is constructed as a triac, an additional advantage is gained in that the temperature sensor also trips if the poles are connected the wrong way. If the poles of the power MOSFET are connected the wrong way, a load current which is limited only by the load and the diode flow voltage flows through the inverse diode, which is usually inherent in the power MOSFET. In this case, the power MOSFET no longer functions as a controllable switch. Because of the large voltage drop of the inverse diode, the power MOSFET heats up intensely, and it is no longer possible to cut off the current flow. In the extreme case, absent a separately provided reverse polarity circuit, the power MOSFET can heat up to an extreme degree. In this case, the sensor signal provided by the triac can be utilized as a trigger signal for a trip mechanism of any type which also acts given pole inversion. The switching characteristic of the temperature sensor could also be laid out thermally asymmetrically for a mispole operation and a normal operation; i.e., the current-voltage characteristic curve of the triac can be optimally designed with respect to its first and third quadrants.
Given the utilization of a thyristor as a temperature sensor, the trip temperature can be purposefully set and thus adapted to the requirements.
Instead of a thyristor or triac, it is possible to utilize any temperature sensor that causes a rapid and intense current rise when the trip temperature is exceeded. This temperature sensor can also be constructed as a rapidly heating destructive resistance, a bimetal switch, or the like.
It is particularly important to the function of the inventive semiconductor module that the interruption device is arranged in the immediate vicinity of the bonding wires carrying the load current. In particular, it can be arranged precisely underneath these bonding wires.
In accordance with an added feature of the invention, a fuse can be alternatively or additionally provided as an interruption device. This fuse is connected in series with the load system of the semiconductor component and the temperature sensor.
In accordance with an additional feature of the invention, besides its primary function as a temperature sensor, the thyristor (or triac) simultaneously functions as an interruption device. Here, the intense heating of the thyristor or triac leads directly to the bursting of the housing, and thus the destruction of the semiconductor module.
In accordance with another feature of the invention, the interruption device contains an ignitable, volume-expansive material. The volume-expansive material exhibits a foaming and/or strongly oxidizing and/or explosive characteristic when the second temperature threshold is exceeded.
In accordance with a further feature of the invention, the semiconductor component is a controllable power semiconductor component, in particular a power MOSFET. But it would also be possible to utilize any other semiconductor switch, for instance an IGBT, a JFET, a bipolar transistor, and so on.
In accordance with a concomitant feature of the invention, the semiconductor component and the temperature sensor are integrated monolithically in a single chip. This is particularly advantageous from a production standpoint. The advantage of a chip on chip assembly is that the sensor is usually not destroyed when the MOSFET is destroyed.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a semiconductor module, 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.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.