JP4830993B2 - Degradation detection method for semiconductor device - Google Patents

Description

  The present invention detects power module degradation in power conversion devices using power semiconductor elements, such as inverters and uninterruptible power supplies (UPS), and in particular, degradation of solder used for joining semiconductor chips and insulating substrates. On how to do.

In an inverter, a UPS, or the like, power conversion is generally performed by switching a power semiconductor element such as a bridge-connected bipolar transistor, MOS-FET, or IGBT (insulated gate bipolar transistor).
As an example of such a converter, a configuration example of a single-phase bridge inverter is shown in FIG. This supplies power to the motor 5 that is a load by alternately switching power semiconductor elements (IGBT) 3a and 3b and diodes (FWD: freewheeling diodes) 4a and 4b connected in series in the vertical direction. . Reference numeral 1 denotes a DC power source, 2 denotes a module container, and 2a to 2c denote terminals.

A power semiconductor element applied to such a circuit is generally used by storing a plurality of elements (chips) in one package (module) in order to simplify connection and cooling. A package with a built-in is usually called a power module.
FIG. 6 shows an example of the appearance of a module containing two IGBTs connected in series to form a bridge circuit, and FIG. 7 shows a sectional view of the module.

The module container 2 shown in FIG. 6 is provided with input terminals 2a and 2b from the DC power supply 1, a connection terminal 2c to the load, and a gate terminal 2d for inputting an on / off signal.
As shown in FIG. 7 , the semiconductor chips 3a and 3b are fixed to the circuit pattern surface (upper surface side) of the ceramic insulating substrate 12 having the circuit patterns 12a to 12c formed on the surface thereof by a brazing material such as solder. The circuit patterns 12a to 12c and the chips are bonded to each other by aluminum wires 9a and 9b to form a circuit as shown in FIG.

  A solid pattern 12d is also provided on the back surface of the ceramic insulating substrate 12, and is brazed to the heat radiating plate 11 such as a copper alloy with solder or the like. Since the electric circuit side such as the semiconductor chips 3a and 3b and the wiring patterns 12a to 12c and the heat sink 11 are insulated by the ceramic substrate 12, the heat sink 11 may be grounded for the purpose of preventing electric shock. Good configuration.

By the way, in the power module configured as described above, due to a rapid temperature change due to intermittent operation of the device, the solder material used for bonding is deteriorated and deteriorated, and a crack (crack) is generated. There is a problem that the heat transfer of the chip is hindered, the temperature of the semiconductor chip rises, and the element is finally destroyed. As described above, the semiconductor chip is brazed to the electrode mainly by a solder material, but the semiconductor chip (silicon material) and the electrode (steel material) have different linear expansion coefficients (steel material: 17 × 10 ⁻⁶ / ° C., (Silicon: 8 × 10 ⁻⁶ / ° C., which is a difference of about 3 times), a shear stress is generated in the solder material sandwiched between them.

  Therefore, when intermittent energization is performed for a long time, a crack (crack) progresses in the joint due to repeated shear stress due to the temperature change. When the crack progresses to some extent, the thermal conductivity decreases at the cracked portion (so-called thermal resistance increases), so the heat dissipation of the semiconductor chip is hindered, the chip overheats, and eventually the semiconductor chip is destroyed. . This deterioration and life of the power module due to repeated heat generation of the semiconductor chip is called power cycle tolerance (or power cycle life), and is one of the very important items for judging the reliability of the power module. .

FIG. 8 is an example of a power cycle life characteristic curve of the power module. When the temperature change amount (ΔTj) of the joint portion increases, the deformation (expansion) amount of each portion also increases and the above-described shear stress increases. It shows that the number of times decreases.
FIG. 9 illustrates the progress of cracks, and shows that cracks 13a have occurred in the solder material 13 that joins the back surface of the chip and the circuit pattern. FIG. 9A shows the deterioration of the center portion of the chip where the temperature is relatively high, and FIG. 9B shows the occurrence of cracks spreading from the end portion of the chip.

FIG. 10 shows the transition of the thermal resistance (Rth) from the semiconductor chip surface to the metal base 11. It was found that the thermal resistance value gradually increased with the number of power cycles, and at the end of the life, the thermal resistance value rapidly increased from 40% to about 60% with respect to the initial value, leading to destruction.
There is a demand for the realization of preventive maintenance functions to prevent troubles in equipment by detecting such deterioration of power semiconductor elements and prompting replacement immediately before the element breaks down. For example, it is disclosed in Patent Documents 1 and 2.

In Patent Document 1, as a method of detecting solder deterioration of a semiconductor chip, a temperature sensor such as a thermocouple is provided on the surface of the semiconductor chip and the case portion, and the thermal resistance is calculated by measuring the temperature difference to determine the deterioration. Technology to do is shown.
However, it is necessary to attach the sensor to the chip surface, so the assembly process becomes complicated, and a weak signal from the sensor must be wired to the control circuit, so it is necessary to pay attention to the noise superimposed on the wiring. Become. In addition, in the course of long-term use, there is a problem that if the sensor is removed, temperature detection becomes impossible and life detection becomes impossible.

On the other hand, Patent Document 2 compares a power cycle life characteristic curve (a power cycle dependency characteristic with respect to a temperature change width) of a semiconductor element obtained in advance as shown in FIG. A technique for performing life estimation in comparison with a curve is disclosed. However, here, the count is a simple number, and since an actual solder deterioration state is not observed, an estimation error becomes large. Usually, the load state of the conversion device is not constant, and the temperature change width varies depending on the operating conditions. Therefore, it is extremely difficult to estimate the actual power cycle life from the number of cycle lifes under a single temperature condition.
In addition, it is necessary to obtain a power cycle life characteristic curve of the semiconductor element in advance, which takes time for evaluation. Furthermore, it is necessary to store a life curve, a temperature change value, and an operation history of the apparatus in a memory or the like, which complicates the apparatus configuration.

JP 2003-172760 A JP 2005-354812 A

  Therefore, the problem to be solved by the present invention is to enable efficient and accurate detection of deterioration of the solder joint portion of the power module.

In order to solve the above problem, in the invention of claim 1, in a semiconductor device having a semiconductor module connected in series between DC power supplies,
The semiconductor elements connected in series are simultaneously given an on-pulse, and a short-circuit current value in the on-pulse period is detected, thereby making it possible to detect deterioration of the semiconductor element.

In the first aspect of the invention, the detected short-circuit current value is compared with a preset reference level, and when the short-circuit current value is different from the reference level, deterioration of the semiconductor element can be detected (invoice) invention of claim 2), in the invention of claim 2, wherein the reference level may be a level corresponding to the initial short-circuit current value (the invention of claim 3).

  In the present invention, a pair of elements connected in series in a semiconductor module bridge-connected between DC power supplies are simultaneously turned on to cause a short-circuit current to flow, thereby causing the semiconductor chip to generate heat and measuring the flowing short-circuit current. Since a constant short-circuit current can flow regardless of the load state, it is possible to accurately detect the deterioration of the thermal resistance and to grasp the life before the power module is destroyed.

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and shows one phase of a bridge circuit in which IGBTs 3a and 3b are connected in series. Drive circuits 8a and 8b are connected to the IGBTs 3a and 3b. The drive signals 15a and 15b generated from the control circuit 10 are amplified to drive the IGBT. Then, the current detector 16 detects the current flowing through the IGBT 3a driven in this way.
The current signal detected by the current detector 16 is compared with the reference voltage value 7 by the comparator 6, and when the short-circuit current value is below or above the reference level (when different from the reference level), the output 14 of the comparator 6 is output. Is reversed. By detecting this output as the end of life signal, it is possible to detect the end of life before the power module breaks down.

  In addition, in order to stably generate heat in the IGBT regardless of the load state, in the present invention, the IGBTs 3a and 3b of the upper and lower arms are simultaneously turned on for a very short time so as not to be broken by a short circuit (life measurement pulse). Is input, and a large short-circuit current is allowed to flow, so that the thermal resistance can be measured by utilizing the temperature dependence of the short-circuit current value.

  FIG. 2 shows an output characteristic curve (collector-emitter voltage-collector current) of the IGBT. The value of the short-circuit current that flows at the time of a short circuit is determined by the operating point indicated by a black circle on the output characteristic curve. That is, the short-circuit current value flowing through the IGBT is determined by the collector-emitter voltage, that is, the voltage value of the DC power supply 1, the junction temperature Tj, and the gate voltage value. Generally, the short-circuit current value has a positive temperature coefficient, and it can be seen that the short-circuit current tends to decrease as the junction temperature increases.

FIG. 3 shows a timing chart of the life measurement pulse.
Here, short-time simultaneous on-pulse signals as shown in FIG. 3A are input to the IGBTs 3a and 3b, respectively. Accordingly, a direct current power supply voltage is directly applied between the collector and emitter terminals of the IGBT, so that a large pulsed short-circuit current flows through the IGBT as shown in FIG. 2 (see FIG. 3C). . The peak of this pulse current is generally about 5 to 10 times the IGBT rating.

  When a short-circuit current flows, a large loss occurs in the IGBT, and the junction temperature Tj rapidly increases as shown in FIG. On the other hand, the short-circuit current (the collector current value of the IGBT) gradually decreases as Tj increases during the short-circuit period. However, when the thermal resistance is deteriorated, that is, when the solder joint is deteriorated, heat dissipation is performed as described above. Since it is hindered by cracks, the increase in the junction temperature Tj is also higher than in the normal state (see the dotted line in FIG. 3B). As a result, the short-circuit current value is as shown by the dotted line in FIG. , Lower than normal.

The short-circuit current value is compared with a reference level 7 (normal short-circuit current value) in the comparator 6, and if it is below the reference level, it is determined that the temperature rise is high, that is, the solder joint is deteriorated.
On the other hand, when the temperature coefficient of the IGBT is negative, the short-circuit current value increases as the temperature increases. Therefore, when a short-circuit current exceeding the reference level flows, it is determined that the thermal resistance has deteriorated. .

FIG. 4 shows another embodiment of the present invention. This utilizes a current detection emitter terminal provided in the IGBT 3a as means for detecting the collector current. When a current of several hundreds to several thousandths of the collector current is supplied to the current detection emitter terminal, a current signal proportional to the collector current is generated in the current detection resistor 17. By comparing the magnitudes of the current signals, it is possible to detect the deterioration of the solder joint as in FIG.
In addition, the short circuit withstand capability (time) of the IGBT is generally about 10 microseconds, and a life measurement pulse less than this time may be input.

The life measurement pulse may be input at the start of operation or every certain accumulation period as necessary. Further, the upper and lower arm pulses 15a and 15b do not need to have the same timing and pulse time width as long as a period during which a short-circuit current flows is ensured.
In addition, during the lifetime measurement pulse generation, it is possible to suppress the short-circuit current and extend the measurement time by reducing the gate voltage of the IGBT.

  In the above, an example of a two-level inverter in which two IGBTs are connected between DC power supplies has been described, but the same applies to all three or more inverters in which a large number of IGBTs are connected in series by simultaneously turning on all the IGBTs. Of course, this effect can be obtained.

Configuration diagram showing an embodiment of the present invention IGBT output characteristics curve FIG. 1 is an explanatory diagram of the operation. The block diagram which shows another embodiment of this invention Circuit diagram showing a general inverter circuit External view of power module Sectional view of FIG. Characteristic curve diagram showing power cycle life Illustration of cracks in solder joints Transition diagram of thermal resistance (Rth) in power cycle

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... DC power supply, 2 ... Module container, 2a-2d ... Terminal, 3a, 3b ... IGBT, 4a, 4b ... Diode, 5 ... Load (motor), 6 ... Comparator, 7 ... Reference value, 8a, 8b ... Drive Circuits 9a, 9b ... wire wiring, 10 ... control circuit, 11 ... heat sink, 12 ... insulating substrate, 12a-12c ... wiring pattern, 13 ... solder material, 13a ... crack, 15a, 15b ... drive signal (upper and lower arm pulses) ), 16 ... current detector, 17 ... current detection resistor.

Claims (3)

In a semiconductor device having a semiconductor module connected in series between DC power supplies,
A degradation detection method for a semiconductor device, wherein degradation of a semiconductor element can be detected by simultaneously applying an on-pulse to the semiconductor elements connected in series and detecting a short-circuit current value during the on-pulse period . 2. The semiconductor device according to claim 1 , wherein the detected short-circuit current value is compared with a preset reference level, and deterioration of the semiconductor element is detected when the short-circuit current value is different from the reference level. Degradation detection method. 3. The semiconductor device deterioration detection method according to claim 2 , wherein the reference level is a level corresponding to an initial short-circuit current value.

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