Abstract:
In an arrangement for determining a temperature loading during a soldering process, a semiconductor chip ( 1 ) comprises at least one contact ( 2 ) to be soldered or is electrically conductively connected to at least one contact ( 14   d ) to be soldered that is situated outside the semiconductor chip. The semiconductor chip ( 1 ) furthermore comprises a temperature sensor device ( 3 ), which determines a measurement quantity corresponding to the temperature. A processing device ( 4, 5 ) has an analog-to-digital converter ( 5 ), which is electrically conductively connected to the temperature sensor device ( 3 ) and converts the measurement quantity into at least one storable signal that represents the temperature loading. A voltage supply device ( 10 ), which is electrically conductively connected to the temperature sensor device ( 3 ) and the processing device ( 4, 5 ), supplies these components with an operating voltage. A data memory ( 6 ) serves for storing the at least one storable signal. An electrical line ( 7, 11 ) connected to the data memory ( 6 ) serves for outputting the stored signal. As a result, it is possible to monitor temperature loadings of the semiconductor chip also outside the sphere of influence of the semiconductor manufacturer.

Description:
This application claims priority to German Patent Application 103 58 357.2, which was filed Dec. 12, 2003, and is incorporated herein by reference. 
   TECHNICAL FIELD 
   The present invention relates to an arrangement for determining a temperature loading of an integrated circuit, in particular caused by a soldering process. The invention additionally relates to an operating method for such an arrangement. 
   BACKGROUND 
   During the production of semiconductor components such as, by way of example, memory chips, in particular DRAM memories (“dynamic random access memories”), the individual integrated circuits are firstly produced at the wafer level and then singulated into semiconductor chips. After singulation, the functional chips are fitted in suitable housings, contact-connected and encapsulated. Afterward, the encapsulated chips, for producing a memory module, are applied to a module board and soldered thereto. Equally, it is also possible for a plurality of encapsulated or non-encapsulated chips to be soldered on one another. Sometimes, rework soldering steps are additionally carried out on the finished module. 
   Accordingly, the semiconductor components undergo a multiplicity of temperature-critical process steps on the way from the semiconductor chip to the finished component. Since the temperature-critical process steps during soldering can lead to parameter alterations in the individual semiconductor chips, for example to an alteration of the retention time in the case of DRAM memory chips, the maximum soldering temperature and also the soldering profile are specified precisely. The retention time is that time during which the information stored in a memory cell is retained in recognizable fashion. 
   In this case, the problem arises, on the one hand, that the temperature loading actually acting on the semiconductor chip cannot be determined exactly. Although the temperature of the soldering tip can be determined, it is not readily possible to demonstrate what temperature the chip itself experiences. Many of the soldering steps after production of the individual semiconductor chip may also be carried out outside the responsibility of the chip manufacturer, for example by subcontractors or by the customer itself. 
   Overall, it would be desirable, therefore, to be able to determine and store the actual temperatures to which a semiconductor chip has been exposed during the soldering process, and in particular the associated temperature profiles. 
   U.S. Pat. No. 6,630,754 B1 describes a semiconductor arrangement in which a temperature sensor monitors a chip temperature and instigates a corresponding action when a threshold value is exceeded. During operation of a processor arranged on a circuit board, the operating temperature of said processor is determined and, when a threshold value is exceeded, by way of example a fan is activated or the clock frequency is reduced. The temperature is determined in analog fashion. A temperature signal is subsequently processed further by the processor. Voltage is supplied to the arrangement outside the processor. 
   In U.S. Pat. No. 5,444,637, the temperature on a semiconductor wafer during wafer processing is determined in order to monitor a fabrication process step. The semiconductor wafer has, inter alia, a processor and a battery and stores respective temperature values in a nonvolatile manner when a temperature threshold value is exceeded. 
   The stored temperature values can subsequently be read out. Voltage supply and signal processing and also temperature sensor are arranged at a distance from one another on the semiconductor wafer. 
   SUMMARY 
   The present invention is based on the object of providing an arrangement and also a method for determining a temperature loading during a soldering process. 
   According to the present invention, this object is achieved by means of an arrangement for determining a temperature loading of an integrated semiconductor chip, comprising: a semiconductor chip, which contains at least one contact to be soldered or is electrically conductively connected to at least one contact to be soldered that is situated outside the semiconductor chip, a temperature sensor device, which is coupled to the semiconductor chip and which is suitable for determining a measurement quantity that can be assigned to a temperature of the semiconductor chip, a processing device, which is integrated in the semiconductor chip and comprises an analog-to-digital converter, which is electrically conductively connected to the temperature sensor device and is suitable for converting the measurement quantity into at least one storable signal that represents the temperature loading, at least one voltage supply device, which is connected to the temperature sensor device and the processing device and which provides an operating voltage for the temperature sensor device and for the processing device, a data memory, which is integrated in the semiconductor chip and is connected to the processing device, for storing the at least one storable signal, a housing, in which the semiconductor chip, the temperature sensor device and the voltage supply device are arranged, and at least one electrical line connected to the data memory and serving for outputting the stored signal outside the housing. 
   The arrangement according to the invention thus comprises a semiconductor chip that stores the temperature loading during a soldering process at the contact to be soldered. If the arrangement is treated in the same way and is subjected to the same soldering process as a memory chip or a multiplicity of memory chips of a processing batch, the arrangement according to the invention experiences the same temperature loading. 
   The semiconductor chip is accommodated in a housing, in particular a housing that is customary for memory chips. In this case, it is electrically and thus thermally conductively connected to a contact to be soldered at the housing. 
   A temperature sensor device, which is suitable for determining a measurement quantity that can be unambiguously assigned to a temperature of the semiconductor chip, is furthermore provided. The temperature sensor device may be arranged at an arbitrary location of the semiconductor chip and, in particular, be integrated into the latter. However, it may also be adhesively bonded on the chip surface by means of a thermally conductive paste. The temperature sensor device may be designed for example in such a way that it determines a temperature-dependent voltage, for example the temperature-dependent threshold voltage of a diode or the threshold voltage of a MOSFET. 
   The analog-to-digital converter may be suitable for comparing the determined measurement quantity with a threshold value, for example a voltage threshold value, and for feeding a digital quantity corresponding to the result to the data memory. 
   In this case, by way of example, the exceeding of a set maximum temperature can be reliably determined in a particularly simple manner. 
   In accordance with a further embodiment of the present invention, the processing device, which is suitable for converting the measurement quantity into at least one storable signal that represents the temperature loading, furthermore comprises: a processor device, which is connected to the analog-to-digital converter and also a clock generator connected to the processor device and the analog-to-digital converter and serving for generating an operating clock, the analog-to-digital converter being suitable for converting a measurement quantity output by the temperature sensor device into a digital signal in accordance with the operating clock, and the processor device being suitable for converting a digital signal output by the analog-to-digital converter into a digital signal representing a temperature value and for generating a time signal representing the measurement instant and for feeding said time signal together with the signal representing the temperature value to the data memory. 
   This configuration of the invention makes it possible, in particular, to determine the temporal profile of the temperature occurring at the semiconductor chip, that is to say a temperature profile. Accordingly, the temperature loading can be determined particularly effectively since often what is responsible for impairing a component is, in particular, a high temperature that persists for a relatively long time rather than an individual peak temperature value. In particular, it is thereby possible to check whether a specification-conforming temperature profile has been used. 
   The arrangement according to the invention may furthermore comprise at least one signal line set, which is connected to the processor device and by which the arrangement for determining a temperature loading can be driven externally, the electrical line, for outputting the stored signal, being connected to the processor device. 
   As a result, the data stored in the data memory can be read out by driving the processor device and are available externally outside the arrangement. 
   According to the present invention, particular preference is attached to the fact that the processor device can be operated in at least one test mode. Provision is made of at least one programmable arrangement for storing an at least one test mode sequence. 
   As a result, specific temperature recording parameters, for example the temperature threshold value or the recording interval, can be programmed by a tester. As a result, the parameters of the temperature recording method can be varied individually in accordance with the external conditions, for example the soldering method used or the capacity of the data memory. 
   In particular, the processing device may be suitable for checking whether a signal output by the analog-to-digital converter exceeds a threshold value signal stored in the programmable memory device. 
   As a result, only those temperature values which exceed the set temperature threshold value are stored in the data memory. As a result, it becomes possible to operate the arrangement over a relatively long period of time even with a limited storage capacity of the data memory since only the data that are actually relevant are stored. By way of example, the arrangement according to the invention may be supplied to customers, the soldering temperature profile used by the customer being recorded as long as the soldering temperatures used there exceed the temperature threshold value. Furthermore, this embodiment ensures that only data that are actually relevant are stored and output afterward, thereby limiting the volume of data to be stored and to be processed afterward. 
   According to the present invention, the data memory and also the processing device and, if appropriate, the temperature sensor device is part of the semiconductor chip. The corresponding component may be monolithically integrated with the semiconductor chip. 
   In this case, if at least the component is integrated into the semiconductor chip, the latter can be realized in a particularly compact and space-saving manner. The arrangement according to the invention is preferably accommodated in a housing with a multiplicity of electrical terminals. At least one terminal is a contact to be soldered that is conductively connected to the semiconductor chip via an electrical line. The signal line set is connected to the chip via other terminals. 
   In particular, the arrangement according to the invention may be accommodated in a housing that is customarily used for memory chips, by way of example. This affords the advantage that the further processing conditions can be checked as realistically as possible and, in particular, the soldering profiles employed outside the sphere of influence of the semiconductor manufacturer can be practically checked. This may serve for better analyzability and subsequent fault-finding. 
   In the case of a method for determining a temperature loading of a soldering process applied to the contact of an arrangement according to the invention, the soldering process at the contact to be soldered and at the same time the following steps are carried out: (1) determining a measurement quantity that can be assigned to the temperature of the semiconductor chip, (2) converting the measurement quantity into a digital signal corresponding to the measurement quantity, (3) comparing the digital signal with a threshold value stored in the programmable memory device, (4) storing the digital signal together with a time signal, which specifies the measurement instant, in the data memory as long as the digital signal exceeds the threshold value, and (5) repeating steps (1) to (4). 
   The method makes it possible to record the temporal profile of the temperature prevailing at the semiconductor chip. Only those temperature values which exceed a temperature threshold value that can be set by means of a test mode are stored in this case. 
   According to the present invention, particular preference is attached to the fact that, after a storage process, the next digital signal is stored together with the time signal in the data memory only after a predetermined time interval. 
   As a result, it becomes possible to record data over a relatively long period of time even with a limited storage capacity. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention is explained in more detail below with reference to the accompanying drawings, in which: 
       FIG. 1  shows a first exemplary embodiment of the present invention, 
       FIG. 2  shows an exemplary temperature profile during a soldering process, and 
       FIG. 3  shows a third exemplary embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
     FIG. 1  shows a first exemplary embodiment of the present invention, in which the arrangement for determining a temperature loading during a soldering process is accommodated in a housing  13  that is customary for memory chips. Thus, the housing  13  has 54 terminals  14   a  to  14   k  in the case of the so-called TSOP54 housing and the TSOP66 housing has 66 terminals  14   a  to  14   m , the allocation of which can be gathered from the associated data sheets. 
   The arrangement for determining a temperature loading comprises a silicon chip  1 , which contains at least one electrical terminal pad region or terminal pad  16 , which is electrically conductively connected to at least one contact  14   d  to be soldered on the chip housing via an electrical line  15 , for example a bonding wire. 
   A temperature sensor device  3  is adhesively bonded on the semiconductor chip  1  by means of a thermally conductive paste. In the present case, the temperature sensor device  3  comprises a MOSFET and also a circuit for determining the threshold voltage of the MOSFET. In this case, the circuit and the MOSFET are designed in such a way that the circuit outputs a temperature-dependent voltage value. However, the temperature sensor device may also be realized in any other desired manner and, in particular, also comprise circuits with temperature-dependent resistance elements that are known per se. 
   Furthermore, an analog-to-digital converter  5 , a processor  4 , a clock generator  9  for generating an operating clock and also a memory device  8  for storing the test modes and a data memory  6  for storing the measured temperature value determined are arranged on the silicon chip  1 . The data memory  6  is preferably nonvolatile, for example a flash or EEPROM memory, so that it stores data even without an external voltage supply device. These components may be adhesively bonded on the silicon chip or alternatively be integrated into the latter. 
   The clock generator  9  is connected to the rest of the components via a clock line  18 . The processor  4  is connected to the data memory  6  via a first signal line set  7 . The processor  4  is furthermore connected to suitable address, data and command terminals  14   a  to  14   m  of the housing via a second signal line set  11 . Data are exchanged between the arrangement according to the invention and the outside world via said second set of signal lines  11 . In other words, the arrangement according to the invention can be driven and output measurement data, for example, via the second set of signal lines  11 . The processor  4  is connected to the memory device  8  via a third signal line  17 . 
   The temperature sensor device  3 , that is to say the circuit with the MOSFET, is connected to the voltage source  10  for supply with the required operating voltage. 
   In the present case, the voltage source  10  is rechargeable and connected via the lines  12   a ,  12   b  to the corresponding voltage supply terminals of the housing  13 , for example to the supply voltage terminals V DD , V SS  of the housing in the case of a TSOP or BGA housing used at the present time. The voltage source  10  may likewise be adhesively bonded on the semiconductor chip  1  or alternatively be fitted to the semiconductor chip  1  at an arbitrary location. 
   By way of example, if the housing is now soldered onto a module board by soldering of a contact  14   d , then the semiconductor chip experiences a temperature loading since it is thermally conductively connected to the contact  14   d  on the housing  13  via the electrical line  15 . This temperature loading is identical to that experienced by a memory chip which is accommodated in an identical housing and is likewise soldered onto the circuit board. The temperature sensor device  3  outputs a quantity that can be unambiguously assigned to the temperature of the semiconductor chip, namely the temperature-dependent threshold voltage of the MOSFET. 
   This temperature-dependent threshold voltage is converted into a digital signal representing the temperature of the semiconductor chip in the analog-to-digital converter device S. Afterward, the digital signal is temporally continuously compared with a temperature threshold value in the processor  4  and, if it exceeds the temperature threshold value, is stored together with a value for the associated measurement instant in the data memory  6 . 
     FIG. 2  shows an exemplary view of a soldering profile in which the soldering temperature is plotted against the soldering time. Typical maximum values of the soldering temperatures are generally approximately 260° C. Typical soldering times are approximately 5 to 6 minutes. 
   According to the present invention, particular preference is attached to the fact that the temperature recording is not effected temporally continuously, but rather only takes place as soon as a threshold value set beforehand is exceeded. This ensures that only relevant temperature data, that is to say temperatures in proximity to the critical temperature for the memory chips, are recorded. As a result, the temperature recording process is optimized because the limited memory space of the data memory  6  is used only for data that are actually relevant. 
   Furthermore, according to the present invention, preference is attached to the fact that, after the set temperature threshold value has been exceeded, the temperature data are not stored continuously, but rather in time-discrete fashion spaced apart at defined time intervals, which permit a meaningful temperature profile. 
   If the temperature threshold value is undershot in the course of the soldering process, the storage of data is interrupted until the temperature threshold value is exceeded again. 
   The comparison of the measured temperature with the temperature threshold value is thus effected continuously in order to ensure that an exceeding of the temperature threshold value is reliably determined. After the temperature threshold value has been exceeded, however, the storage is effected in time-discrete fashion in defined time intervals that are stipulated in such a way that, on the one hand, the temperature fluctuations of interest are reliably determined, but also, on the other hand, the number of measurement points recorded is not too many and they do not unnecessarily take up the memory space of the data memory  6 . The length of a time interval is thus selected in accordance with the size of the data memory and the desired temporal resolution. 
   According to the present invention, the temperature threshold value is preferably set by means of a test mode. The time intervals for storing the determined data may also be set by means of a test mode. Furthermore, the read-out and also the erasure of the data memory may be initiated by means of test modes. 
   Test modes are programs that are not normally accessible to the customary user and are only initiated if, by way of example, three key addresses defined beforehand are input via the corresponding address lines. On the basis of the key addresses input, the processor  4  recognizes that a test mode is activated, and which one, and retrieves the latter from the memory device  8 . The memory device  8  is usually realized as hardware, that is to say that the test modes are implemented as circuit constituents, and the processor activates the associated circuit constituent when a test mode is addressed. However, the memory device  8  may also be a program memory from which the corresponding program sequence is read when a test mode is activated. The memory device  8  contains the control information in order to instigate and control the affected test mode. 
   After the addressing of the test mode for setting the temperature threshold value, the temperature threshold value can be input manually by an operator, for example via the data lines of the housed arrangement. The temperature threshold value, which is represented as T t  in  FIG. 2 , is preferably selected in such a way that it exceeds the test temperatures to which memory chips are exposed during customary functional tests. By way of example, memory chips are subjected to a reliability test at 80° C. to 90° C. Accordingly, the temperature threshold value should be approximately 100° C. 
   The time interval for the data storage can also be set by means of a test mode in a corresponding manner. 
   The arrangement according to the invention is thus incorporated as a test chip in a housing like a regular memory chip with the aid of said test chip, it is then possible to record the temperature profile during the temperature stress in the course of further processing. The housing contains the test chip instead of a functional semiconductor memory chip. Since the housing contains the test chip with the arrangement for determining a temperature loading during a soldering process and not the memory chip expected by the customer, the chip returns as a customer return in the same way as the chips are returned as test fails or stacks from subcontractors. 
   After the return, the measured temperature values stored in the test chip are read out. Customary test systems are used to read out the measured temperature values. The read-out process is initiated by means of a test mode. The content of the data memory  6  is read out via the data lines, via the data or so-called DQ lines in the case of the TSOP or BGA housings used at the present time, of the second signal line set  11 . In this case, the temperature resolution that can be achieved per read-out process depends on the number of data lines used and the read-out clock signals required for the read-out process. 
   After the read-out of the data memory  6 , a further test mode may then be initiated, by way of example, by means of which the data in the memory are erased. 
   According to the present invention, the arrangement for determining a temperature loading during a soldering process may also be used for measuring temperature during soldering, the temperature/time data also being stored if the temperature threshold value is not exceeded. 
   In accordance with this exemplary embodiment, the arrangement according to the invention has all the components shown in  FIG. 1  without the memory device  8  and the associated signal line  17 . In this case, the processor does not have to be able to be operated in a test mode, and the second signal line set  11  is connected to the data memory  6 . An external test system can directly access the data memory  6  via the signal line set  11 . 
   Firstly, the data memory  6  is erased before the beginning of the soldering process by the external test system via the second signal line set  11 . After disconnection of the electrical connection between test system and the second signal line set, the continuous recording of the measured temperature values together with the measurement instant begins. After the end of the soldering process, the data memory  6  is read by the external test system via the second signal line set  11 . Since only a limited recording duration is present in this case, the recording can be effected continuously and without a temperature threshold value. 
     FIG. 3  shows a third, particularly simple exemplary embodiment of the present invention, in which the arrangement for determining a temperature loading during a soldering process is designed in such a way as merely to ascertain whether a predetermined maximum temperature is exceeded and to store the result in a memory. 
   As shown in  FIG. 3 , an unhoused semiconductor chip  1  contains a contact  2  to be soldered. A temperature sensor device  3  is integrated into the semiconductor chip  1 . Furthermore, a processing device  4  with an analog-to-digital converter  5  are situated on the semiconductor chip  1 . A data memory  6  is connected to the processing device  4  via a first signal line  7 . Furthermore, a second signal line set  11  for external read-out of the data memory  6  is fitted to the data memory  6 . A voltage source  1 o is fitted laterally to the semiconductor chip  1 . The analog-to-digital converter  5  is electrically conductively connected to the temperature sensor device  3 . 
   The temperature sensor device may again be a temperature-sensitive semiconductor component, for example a diode or a field effect transistor, in particular MOS field effect transistor, with an associated circuit which outputs a measurement quantity corresponding to the temperature, in particular a voltage. The diode contains a pn junction, the threshold voltage of which is temperature-dependent. As the temperature rises or falls, the threshold voltage of the pn junction correspondingly decreases or increases. In the case of a field effect transistor, the gate-source threshold voltage is usually evaluated, which likewise varies as the temperature varies; the threshold voltage decreases as the temperature increases. There is a direct, unambiguous relationship between temperature and threshold voltage of diode or field effect transistor. 
   If a soldering process is carried out at the contact  2  to be soldered, then the semiconductor chip  1  is heated in exactly the same way as it would be heated if a regular memory chip were contained in the housing, the contact of which would be soldered by this soldering process. The accompanying increase in temperature is determined by the temperature sensor device  3 , which passes a voltage signal corresponding to the temperature to the analog-to-digital converter  5 . In the case of batch processing, a multiplicity of integrated circuits are processed in the same way; by way of example all the circuits of the batch are heated during a temperature treatment or the terminals of all the circuits of the batch are soldered and thereby heated. The test chip according to the invention is included in the batch and thereby processed, i.e. heated or soldered, in the same way as the rest of the semiconductor components of the batch. By virtue of the fact that the semiconductor chip according to the invention stores the temperature profile, there is therefore a good correlation between the temperature treatment which the semiconductor chip according to the invention has received and stored and the temperature treatment of the other components of the batch. By virtue of the fact that the stored temperature profile of the semiconductor chip according to the invention is read out, it can therefore be assumed with sufficient certainty that the other normal semiconductor components of the batch to be processed have also experienced a temperature treatment in accordance with said stored temperature profile. 
   In the case of this exemplary embodiment, the analog-to-digital converter  5  is embodied as a comparator that compares the voltage output by the temperature sensor device with a preset threshold value. As soon as the threshold value is exceeded, a corresponding bit is set in the data memory  6 . Analog-to-digital converter  5  and data memory  6  are designed in such a way that this set bit can no longer be overwritten during subsequent temperature measurements. By reading the data memory via the signal line set  11  by means of an external test system, it can be identified whether the preset maximum temperature was exceeded during soldering. 
   As a result, it is possible to reliably identify a temperature loading that actually occurs at the semiconductor chip during the soldering process. 
   LIST OF REFERENCE SYMBOLS 
   
       
         1  Semiconductor chip 
         2  Contact to be soldered 
         3  Temperature sensor device 
         4  Processor 
         5  Analog-to-digital converter 
         6  Data memory 
         7  First signal line set 
         8  Memory device 
         9  Clock generator 
         10  Voltage source 
         11  Second signal line set 
         12   a ,  12   b  Current lines 
         13  Housing 
         14   a – 14   m  Terminals of the housing 
         14   d  Housing terminal to be soldered 
         15  Bonding wire 
         16  Electrical terminal 
         17  Third signal line set 
         18  Clock line 
       T t  Temperature threshold value 
         20  Memory chip