DE3830299A1 - Method and arrangement for determining internal thermal resistances of wafer-shaped semiconductor components - Google Patents

Abstract

Known methods for determining the internal thermal resistance of semiconductor components require measurement of the housing temperature, as a result of which it is possible to determine different thermal resistances depending on the choice of the type of probe (sensor) and of the measurement location. In order to solve this problem, the invention proposes abandoning direct measurement of the housing temperature and instead performing calculations through an indirect measurement of the depletion layer temperatures via a temperature-dependent parameter, e.g. the forward voltage across a gate cathode junction whose temperature dependence has previously been determined, of two or more semiconductor components, connected back to back, while combining the dissipation flowing through the semiconductor components. The method permits calculation of the thermal resistances on the anode and cathode sides. The method is suitable for all wafer-shaped semiconductor components, and can be applied with particular advantage to components having a structured cathode. The single figure of the drawing applies. <IMAGE>

Description

The invention relates to a method for determining Internal heat resistance of pressure contacts th disk-shaped semiconductor components after the Preamble of claim 1. In addition, the Invention on an arrangement for performing the Ver driving. The method can be used to determine the interior Thermal resistance from one or both sides cooled th disc-shaped semiconductor components with constant ter power loss in stationary operation the.

According to DIN 41 781 and DIN 41 786, the internal heat resistance is stand defined as the quotient of the difference between the internal replacement temperature and the housing temperature rature on the one hand and that occurring in the semiconductor component  tendency constant power loss on the other hand, in sta domestic case. Therefore:

R _thJC = ( T _VJ - T _c ) / P ; (K / W)

With
T _thJC = thermal resistance junction box housing,
T _VJ = equivalent junction temperature,
T _c = housing temperature at a specified point,
p = power loss,
K = Kelvin,
W = watt.

During the power loss and the case temperature A measurement is accessible from the outside Junction temperature only over a temperature dependent current electrical parameters are closed. This can e.g. the temperature dependence of the forward chip voltage drop of a pn junction. In DIN IEC 747 Part 6, Chap. 2.2 "thermal resistance and transient heat such a measuring method is described.

Deviating from this, it can occur with large disc-shaped Semiconductor devices that have a small internal heat exhibit resistance, be more advantageous, the so-called Flow method for the determination of the internal heat to apply. Here, e.g. as diffe limit of the measured anode temperature and cathode temperature temperature drop across the entire component divided by a known heat flow, this Temperature drop causes the so-called passage or series thermal resistance. This measuring method is in BBC textbook, power semiconductors, Dr. H. Buri, out given in 1983 by Giradet-Verlag, Essen, on page 49 and 50 described.  

Finally, a standard proposal from IEC, TC 47, SEMI- CONDUCTOR DEVICES, in which the Swiss Na tional committee proposes the chapter already mentioned 2.2 in IEC 747, Part 6. The supplement be makes a further development of the above Flow method, according to which a division of the heat resistance of the anode-side and cathode-side portion is made possible.

Such a division of the thermal resistance into anode and partial heat resistance on the cathode side is desirable worth it because these partial heat resistors differed a lot Lich and when dimensioning cooling equipment depending on the installation position of the semiconductor device mentes are to be considered.

All known measuring methods with the associated arrangement Common is that to determine the inner Thermal resistance or partial thermal resistance Housing temperature on the semiconductor component at a fixed increasing point must be measured. So there are some Disadvantages with regard to the accuracy of the determined Thermal resistance connected.

The thermal resistance to be determined can be manipulated by choosing the housing reference point. In many disk-shaped semiconductor components, the heat flow - mostly from the cathode side - does not emerge homogeneously (for example in the case of structured cathodes, such as in GTO thyristors). This means that different thermal resistances can be measured depending on the choice of the reference point.

One is used for measuring the case temperature Resistance thermometer, a occurs at the measuring point elevated temperature because practical at this point is not cooled. The internal heat resistance determined in this way stand is less than the true value. The error is from depending on the nature of the resistance thermometer.

The use of thermocouples instead of contra level thermometers can also lead to an error ren, whereby here, due to a thermal secondary conclusion of the thermocouple, a too low housing temperature is measured and the determined thermal resistance is greater than the true value.

The invention has for its object a method indicate after which the internal thermal resistance of disc-shaped semiconductor components and indeed divides by anode-side and cathode-side part and determined while avoiding the disadvantages mentioned can be. In addition, a suitable Meßan order can be specified.

This task is carried out in a procedure according to the Oberbe handle of claim 1 by its characteristic note times solved. Advantageous embodiments are in the Subclaims specified. In further claims are Arrangements for performing the procedure are given.

The invention proposes to determine the anode and cathode side thermal resistances only elec to use measurable parameters that depend on the tem temperature of a pn junction. That invented Process according to the invention requires in an advantageous manner  only a simple measurement arrangement and leads to measurement result with comparatively high accuracy. The main one part of the invention is the fact that no measurement the housing temperature is required.

The invention is described below with reference to a preferred Embodiment described in more detail in the Drawing is shown. As outlined below the procedure is also with others Arrangement variants feasible.

The measuring arrangement 10 shown in the drawing includes a stack of three disk-shaped semiconductor components, which are provided with reference numerals 1 to 3 . These can be, for example, turn-off thyristors (GTO), as indicated by dashed symbols in the drawing, or other types of semiconductor components, such as non-turn-off thyristors or diodes. It is essential that the semiconductor components are not poled in the same direction, but are inserted into each other in the arrangement, so that two anodes A and two cathodes K follow each other. In the drawing, the cathodes are opposite to the K of the first semiconductor component 1 and the second semiconductor component 2 and also the anodes of the second semiconductor component 2 and of the third semiconductor component 3 .

A heat source 4 is arranged above the first semiconductor component 1 . The heat source 4 is expediently made of a copper blank 8 , in which an electrical heating coil 7 is housed covering the entire surface. The winding 7 should be umschlos sen on all sides of copper, so that a small temperature gradient is achieved. The diameter of the copper blank 8 is adapted to the semiconductor components 1 , 2 , 3 . This distributes the heat flow evenly over the surface. So that leads 14 to the heat source 4 can be made thin and neither conduct nor conduct heat through heat conduction, the heating winding 7 is designed to be high-resistance.

On the second side of the stack components, a cooling device 5 is disposed, that of the third semiconductor component 3 is thermally conductive advantage kontak to the cathode K, and also with respect to its surface is matched to the semiconductor devices. The Kühleinrich device 5 is advantageously flowed through by cooling water and should ideally dissipate all of the heat supplied by the heat source 4 .

To achieve this goal, the entire arrangement is surrounded by thermal insulation 6 . For precision measurements with particularly high accuracy requirements, a vacuum vessel with internal radiation protection can be used for thermal insulation.

The further demand for thin test leads can can be complied with without any problems since there are no high currents are required to record the temperature-dependent pn transition.

Finally, the stacked arrangement must be contacted with the aid of a tensioning device, not shown in the drawing, and a force F applied with the aid thereof.

For a reliable determination of the thermal resistances, it is necessary to ensure even heat transfer at the joints, so that no distortion of the isothermal surfaces occurs. For this reason, the contact surfaces must be carefully provided with thermal paste 9 before clamping.

The measures described for guiding the heat flow through the measuring arrangement 10 as uniformly and completely as possible make it possible to use the electrical heating power of the heat source 4 , which can be grasped simply and precisely, as power loss P in the equations for calculating the internal thermal resistance. The measuring currents also cause power losses, but they do not need to be taken into account if they are much smaller than the heating power embossed with the heat source 4 .

Since an electrical parameter is to be used to determine the junction temperature, the temperature dependence of this parameter must be measured in advance. The forward voltage U of the gate-cathode path, which is measured at a measuring current I in the forward direction, is preferred as the electrical parameter. But it could also be used, for example, the reverse current or the reverse voltage in the avalanche sector. In the case of GTOs that have been shorted on the odor side, the gate anode section can be used instead of the gate cathode section.

Measuring the temperature dependence of the electrical Parameters, so to speak a calibration, can be done with the same Chen measuring device are carried out with the performed the measurement to determine the thermal resistance leads.  

Below, the measuring device will first be considered described on the thermal resistance measurement.

The measuring device consists of three galvanically separated measuring circuits, each consisting of a measuring device 11 , measuring lines 12 and one of the semiconductor components 1 , 2 or 3 . From the measuring devices 11 , a measuring current I is fed via the gate connection G into the gate cathode path of the semiconductor component and fed back via the auxiliary cathode connection HK . The measuring current I is adapted to the respective semiconductor component type and is fed in as a constant current. In order to keep the heating by the measuring current small, it can be expedient to impress it in a pulsed manner. Its amplitude should correspond to the control current with which the semiconductor component is operated in practical operation.

With the devices 11 , the adjustable, stabilized measuring current I is generated and also measured together with the voltage drop at the gate section, that is the forward voltage U. With the help of a relationship between forward voltage U and junction temperature T _VT (with the measurement current I used as a parameter) determined beforehand as a table or curve, the associated junction temperature T _VJ can be determined for a measured forward voltage U.

In the measuring arrangement 10 shown in the drawing, a heat flow flows from the heating source 4 through the semiconductor components 1 , 2 , 3 to the cooling device 5 . The heating power of the heating source 4 is to be adjusted with a stabilizing power supply 13 , which also shows the heating power, so that the maximum permissible junction temperature of the hottest component is not exceeded. To increase the accuracy of measurement, it is appropriate to dimension the thermal resistance of the cooling system so that a heat flow of at least 2/3 of the maximum permissible power loss of the semiconductor components flows through them. A temperature drop occurs on this route due to the thermal resistance. For the determination of the thermal resistances, only the temperatures T _{VJ 1} , T _{VJ 2} and T _{VJ 3} at the pn junctions of the semiconductor components 1, 2, 3 are required, which are determined indirectly by measuring the forward voltage U. The thermal resistances are given in an equivalent circuit diagram in the drawing and provided with designations insofar as these are relevant for the further explanations. Thereby, anode-side thermal resistances R _{thJC (A)} and cathode-side thermal resistances R _{thJC (K) of} the semiconductor _components 1, 2, 3 are given, as well as _{contact resistances} R _thü between the semiconductor _components .

The thermal resistances between the barrier layers (pn- Transitions) of two semiconductor components, i.e. two Temperature detection points, each consists of two cathode-side or two anode-side heat resistors stand together and an intervening over passage heat resistance. Because the transition heat resistance is small compared to the other thermal resistances and also when determining the internal thermal resistance only half by the method of the invention would be taken into account, he can neglect for simplification be relaxed.  

With this simplification and the assumption that the inserted semiconductor components 1, 2 and 3 are of the same type, and their thermal resistances are the same, can be determined from the junction temperatures T _{VJ 1} , T _{VJ 2} and T _{VJ 3} and the heating power P the Calculate thermal resistances as follows:

R _{thJC (K) 1.2} = ( T _{VJ 1} - T _{VJ 2} ) / 2 P ; (K / W)
R _{thJC (A) 2.3} = ( T _{VJ 2} - T _{VJ 3} ) / 2 P ; (K / W)

With
R _{thJC (K) 1,2} = cathode-side thermal resistance of the semiconductor _component 1 or 2 ,
R _{thJC (A) 2,3} = anode-side thermal resistance of the semiconductor _component 2 or 3
P = heating power (W)
T _{VJ 1} , T _{VJ 2} , T _{VJ 3} = junction temperatures of the semiconductor components 1, 2, 3 (K)

In the above equations, a divisor 2 is included because between two temperature measurement points two lie on odenseitige or cathode-side heat resistance gene. The inserted into the equations loss or heating power P is supplied in a heating source 4 to the power supply unit 13 is measured and displayed.

The measuring arrangement 10 shown can also be used when semiconductor components of different types are to be used. In this case, the semiconductor component 2 arranged in the middle is to be regarded as a test object, whose anode-side and cathode-side thermal resistance is to be determined. The cat-side thermal resistance of the semiconductor device 1 and the anode-side thermal resistance of the semiconductor device 3 must then be measured beforehand. In practice, the semiconductor components 1 and 3 will be firmly connected to the clamping device, that is to say the semiconductor component 1 with the heating source 4 and the semiconductor component 3 with the cooling device 5 , so that with one measurement both thermal resistances of the test object, that is to say the semiconductor component 2 , can be determined simultaneously.

In this case:

R _{thJC (K) 2} = ( T _{VJ 1} - T _{VJ 2} ) / P - R _{thJC (K) 1} ; (K / W),
R _{thJC (A) 2} = ( T _{VJ 2} - T _{VJ 3} ) / P - R _{thJC (A) 3} ; (K / W),

With
R _{thJC (K) 2} = cathode-side thermal resistance of the test specimen 2 ,
R _{thJC (A) 2} = anode-side thermal resistance of test specimen 2 ,
R _{thJC (K) 1} = cathode-side thermal resistance of the (reference) component 1 ,
R _{thJC (A) 3} = anode-side thermal resistance of the (reference) component 3 ,
T. . . = Junction temperatures of components 1, 2, 3

It goes without saying that the forward voltage U must be measured in the steady state, that is to say only when the semiconductor components are heated and the forward voltage U no longer changes. Since the heat source 4 can remain switched on continuously and the entire device is at the temperature provided for the test, only the specimen used has to be brought to the required temperature. A comparatively short time is required for this.

Automation of the test process can e.g. he be enough by processing the measured electri parameters in e.g. programmed Facility, then the desired heat resistance status values can be output.

As already mentioned, the measuring arrangement 10 can also be used for the previous measurement of the relationship between the electrical parameter, for example the forward voltage U , and the junction temperature T at a selected measuring current I. The semiconductor device element stack is heated from both sides, so probably by the heat source 4 as well as by the Kühlein device 5 , which for this purpose is flowed with hot water from a thermostat 15 instead of with cold water. The thermostat 15 is in this case connected to the power supply 13 by an indicated temperature control circuit 16 . The temperatures at both ends of the semiconductor stack are matched to one another using the temperature control circuit 16 . The respective uniform temperature of the stack is increased in stages, the forward voltages U of the three semiconductor components 1 , 2 and 3 being measured in each stage. If the two semiconductor components 1 and 3 reference components are elements with a known relationship between forward voltage and temperature, the barrier layer temperature of an interposed new component type can be concluded.

The measuring arrangement with three semiconductor components is made preferred for the reasons set out. If only two half conductor components can be used with a measuring  process only either the anode side or the catho partial heat resistance can be determined. For the second measurement, both semiconductor components are reversed turns used.

It is also possible to arrange more than three Semiconductor devices to provide multiple semiconductors to be able to measure components at the same time. Also there must each have two anodes or two cathodes follow.

Claims (11)

1. A method for determining internal heat resistances of pressure-contacted disc-shaped semiconductor components, wherein a measuring arrangement is used, with the aid of which a stationary heat flow is generated by the semiconductor components, characterized in that

• - At least two semiconductor components ( 1 , 2 , 3 ) are stacked one above the other in the measuring arrangement ( 10 ) in such a way that main connections of the same type, for example two cathodes ( K ) or two anodes ( A ) of the semiconductor components ( 1 , 2 , 3 ) oppose each other,
• - A heating power ( P ) of a heat source ( 4 ) is measured, which generates the heat flow through the stacked semiconductor components ( 1 , 2 , 3 ),
• - a is measured from a junction temperature (T _VJ) of the semiconductor components (1, 2, 3) dependent electrical parameters shear (U) to all semiconductor devices (1, 2, 3),
• - the current measured at the semiconductor components (1, 2, 3) parameter (U) is in each case used to determine the junction temperature (T _VJ) of the respective semiconductor component (1, 2, 3) by means of a link to prior determined for the devices to be tested Type between the electrical parameter ( U ) and the junction temperature ( T _VJ ) and
• - The internal heat resistances ( R _{thJC (K)} , R _{thJC (A)} ) are calculated by _{forming the} difference from the junction temperatures ( T _VJ ) and linking them with the measured heating power ( P ).

2. The method according to claim 1, characterized in that as the junction temperature ( T _{VJ )} dependent electrical parameters ( U ) the forward voltage is selected at a pn junction, both in the outgoing determination of the component type-appropriate coherence between the forward voltage ( U ) and the junction temperature ( T _VJ ) and in the measurement of the forward voltage ( U ) of the semiconductor devices to be tested ( 1 , 2 , 3 ) is measured at a uniform and constant measuring current ( I ). 3. The method according to claim 1 or 2, characterized in that two semiconductor components ( 1 , 2 ) are used in the measuring arrangement ( 10 ) and two measurements are carried out in succession to determine the required junction temperature ( T _VJ ), for which second measurement, both semiconductor components ( 1 , 2 ) are used upside down. 4. The method according to claim 1 or 2, characterized in that three semiconductor components ( 1 , 2 , 3 ) are used in the measuring arrangement ( 10 ). 5. The method according to claim 1 or 2, characterized in that in the measuring arrangement ( 10 ) more than three semiconductor components are used to with a measuring process of the junction temperature ( T _VJ ) dependent electrical parameters ( U ) from a larger number of semiconductor components at the same time. 6. The method according to claim 4, wherein all three semiconductor components ( 1 , 2 , 3 ) in the measuring arrangement ( 10 ) of the same component type with the same thermal resistance, characterized in that the calculation of the internal thermal resistances according to the following equations, it follows: R _{thJC (K) 1.2} = ( T _{VJ 1} - T _{VJ 2} ) / 2 P ; (K / W),
R _{thJC (A) 2.3} = ( T _{VJ 2} - T _{VJ 3} ) / 2 P ; (K / W), with
R _{th (K) 1,2} = cathode-side thermal resistance of the semiconductor component ( 1 or 2 ),
R _{thJC (A) 2,3} = anode-side thermal resistance of the semiconductor _{component (} 2 or 3 ),
P = heating power (W),
T _{VJ 1} , T _{VJ 2} , T _{VJ 3} = junction temperatures of the semiconductor components ( 1, 2, 3 ) (K). 7. The method according to claim 4, wherein the three semiconductor components used ( 1 , 2 , 3 ) have different thermal resistances, and the anode and cathode side thermal resistances of the upper and lower semiconductor components ( 1 , 3 ) in the stack are known and the calculation the thermal resistances of the second semiconductor _component ( 2 ) arranged therebetween are calculated according to the following equations: R _{thJC (K) 2} = ( T _{VJ 1} - T _{VJ 2} ) / P - R _{thJC (K) 1} ; (K / W),
R _{thJC (A) 2} = ( T _{VJ 2} - T _{VJ 3} ) / P - R _{thJC (A) 3} ; (K / W), with
R _{thJC (K) 2} = cathode-side thermal resistance of the test specimen ( 2 ),
R _{thJC (A) 2} = anode-side thermal resistance of the test specimen ( 2 ),
R _{thJC (K) 1} = cathode-side thermal resistance of the (reference) component ( 1 ),
R _{thJC (A) 3} = anode-side thermal resistance of the (reference) component ( 3 ),
T. . . = Junction temperatures of the components ( 1, 2, 3 ). 8. Measuring arrangement for performing the method according to any one of the preceding claims, wherein

• - A heat source ( 4 ) is provided, with a to be tested semiconductor components ( 1 , 2 , 3 ) adapted and electrically uniformly heated surface and with a device ( 13 ) for measuring the heating power fed in,
• - A cooling device ( 5 ) for removing a semiconductor component ( 1 , 2 , 3 ) flowing through heat flow,
• - A tensioning device with which a contact pressure required for Druckkon ( F ) is brought up, and
• - A thermal insulation ( 6 ), which causes the heat flow to be dissipated as completely as possible through the cooling device ( 5 ), characterized in that
• - At least two semiconductor components ( 1 , 2 , 3 ) are arranged between the heat source ( 4 ) and the cooling device ( 5 ) in such a way that in each case two identical main connections of the semiconductor components ( 1 , 2 , 3 ), for example two anodes ( A ) or two cathodes ( K ), on each other and
• - Measuring devices ( 11 ) are provided for feeding egg nes electrical current ( I ) in the semiconductor devices ( 1 , 2 , 3 ) and for measuring the electrical current fed ( I ) and the selected, depending on the junction temperature electrical Pa parameters, for example forward voltage ( U ).

9. Measuring arrangement according to claim 8, characterized in that three semiconductor components ( 1 , 2 , 3 ) are inserted, the semiconductor component arranged in the middle ( 2 ) is a test specimen and the upper and lower semiconductor components ( 1 , 3 ) Reference elements with known internal thermal resistances are. 10. Measuring arrangement according to claim 9, characterized records that a device for measured value processing is provided, which is a mathematical link of the determined measured values and directly on the anode side and cathode-side partial thermal resistance values of the test lings issues. 11. Use of the measuring arrangement according to claim 9 for determining the relationship between the selected electrical parameter and the junction temperature, with heating of the semiconductor component stack both by the heating source ( 4 ) and from the side of the cooling device ( 5 ), which for this measurement solution is operated as a heating device, for example by switching from a cold water to a hot water flow, and forms a temperature-controlled circuit together with the heating source ( 4 ).