Abstract:
The purpose of the present invention is to provide a thermal flow-rate sensor that is capable of self-diagnosis. Provided is a thermal flow-rate sensor provided with a semiconductor element that detects a flow rate and that is equipped with electrode pads for electrical conduction with the outside, wherein at least two of the electrode pads are provided, and other electrode pads proximate to the electrode pads are arranged and have an electric potential beyond the scope of output to be used at the time of flow rate detection.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a sensor that detects a physical quantity, in particular relates to a thermal flow rate sensor that detects an intake airflow rate of an internal combustion engine. 
       BACKGROUND ART 
       [0002]    As for a flow rate sensor detecting an intake air amount that is provided in an intake air passage of an internal combustion engine of a motor vehicle or the like, thermal sensors have conventionally been prevailing because they can directly detect a mass air quantity. 
         [0003]    Recently, attention has been given to an air flow rate element in which after a resistor and an insulation layer film are accumulated on a silicon substrate using a semiconductor micromachining technology, a part of the silicon substrate is removed by a solvent such as KOH, and a thin film section (diaphragm) is formed, because the air flow rate element includes a high-speed responsiveness and is capable of a backward flow detection. 
         [0004]    On the other hand, inmost cases, a semiconductor circuit element such as an LSI and a microcomputer is used in order to drive the air flow rate element by heating using a heater, where the semiconductor circuit element and the air flow rate element are directly connected at each electrode pad via a gold wire or the like or they are electrically connected to the electrode pad and a substrate wiring section via a ceramic wiring substrate that supports the semiconductor circuit element and the air flow rate element or the like. 
         [0005]    On the other hand, recent requirements for motor vehicle components include a functional safety. With the functional safety, when, for example, any sort of abnormality occurs in sensors or actuators that make up a fuel injection system of an engine, an engine control unit (ECU) stores and detects the occurrence of the abnormality and turns on a warning indicator of an instrument panel or the like in order to let the driver know the occurrence of the abnormality, so that the driver recognizes that there is an abnormality in some part of the motor vehicle components, stops the driving of the vehicle for early repair, exchange of parts, or the like, and returns the vehicle to a safe state. This can prevent a dangerous traveling in which the driver continues a normal driving even in a state in which a motor vehicle component has an abnormality. The most important thing about the functional safety is whether each component (a sensor, for instance) diagnoses whether a current state is normal or abnormal and, if there is an abnormality, it can accurately transfer it to the ECU. In other words, it is whether a single component includes a function to output a failure signal by itself when an abnormality occurs in a part of the single component. In general, this is called a self-diagnosis function. Examples of these technologies include the one described in the patent literature 1. 
       CITATION LIST 
     Patent Literature 
       [0006]    PTL 1: Japanese Patent Application Laid-Open No. 2014-1993 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0007]    When a self-diagnosis is carried out, one of the failure modes of a thermal flow rate sensor may be a short circuit between adjacent electrode pads. For instance, a method to detect short circuit using a comparator is commonly employed in a case where short circuit occurs between an electric power source potential and a ground potential. However, short circuit between midpoint potentials when abridge circuit is configured and its midpoint potential is removed has not been taken into consideration so far. 
         [0008]    A short circuit occurring between electrode pads may be caused via a void in a resin. This problem will be explained in detail using  FIG. 3  and  FIG. 4 . 
         [0009]    As presented in  FIG. 3 , a thermal flow rate sensor  50  is inserted into an air intake duct  40 . The thermal flow rate sensor  50  includes an air flow rate detection element  10  and an LSI  70 , which is a drive circuit. In a configuration of  FIG. 3 , the air flow rate detection element  10  is adhered on a ceramic substrate and connected with an electrical wiring layer  65  in the ceramic substrate using a gold wire  90  as for electrical conduction. Similarly the LSI  70  is also adhered on the ceramic substrate and connected with an electrical wiring in the ceramic substrate using the gold wire  90  as for electrical conduction. In this way, the air flow rate detection element  10  and the LSI  70  are electrically connected. In the configuration described above, air flowing inside the air intake duct is partially taken into the thermal flow rate sensor and flows on the air flow rate detection element  10 , and thus flow rate detection is made possible. 
         [0010]    In addition, an electrical conduction portion of the air flow rate detection element  10  will be explained using  FIG. 4 . Since the element is directly exposed to engine intake air as described above, a variety of materials such as water, sulfur gas, and oil scatter onto the element. It is common that a resin seal  100  is provided so as to protect an electrode pad section  30  and a gold wire section  90  from such materials. 
         [0011]    On the other hand, a void  101  may be formed inside the resin seal. Formation of a void itself is not any problem at all as a product. However, since this seal section is exposed to a very harsh environment as engine intake air as described previously, a case is assumed in which a liquid (gas) material such as water is collected in a void over a long period of time. 
         [0012]    What is a problem now is, as presented in  FIG. 4 , a void that is formed across adjacent gold wires. If an electrically conductive material such as water is collected in the void in this state, a problem of short circuit occurs between the adjacent gold wires. 
         [0013]    On the other hand, the patent literature 1 presents an example of arrangement of electrode pads of an element of a thermal flow rate sensor. However, the patent literature 1 is insufficient in terms of consideration for short circuit between adjacent pads described above. More specifically, there is a case in which short circuit occurs between adjacent midpoint potential electrode pads. This problem will be explained using  FIG. 5  to  FIG. 9 . 
         [0014]      FIG. 5  is a drawing that presents a simplified illustration of a wiring section of an element of a drive circuit of a common thermal flow rate sensor that is described in the patent literature 1. A flow rate detection bridge is configured with a bridge circuit that controls a heat resistor (heater)  21  and temperature measuring resistors  22  and  23  that are arranged in the upstream and the downstream of the heater.  FIG. 6  is a drawing that presents a simplified illustration of an arrangement of the electrode pads that are described in the patent literature 1.  FIG. 7  presents an output of the thermal flow rate sensor when this circuit works normally. When the circuit works normally, Vmax and Vmin, which correspond to a maximum value Qmax of the flow rate and a minimum value Qmin of the flow rate, respectively, are output. In contrast,  FIG. 8  presents output voltage when a short circuit occurs between S 2  and V 2 MA terminals of  FIG. 6 . Since S 2  and V 2 MA are both electrical potentials corresponding to midpoint potentials of the bridge circuit, output voltages (S 1 -S 2 ) slightly change compared with a normal case. While  FIG. 8  presents a change in a negative direction, there may be a change in a positive direction. The greatest problem here is that changed properties are within the output range that is used normally presented in  FIG. 7 . In this case, even if the property changes as in  FIG. 8 , the ECU on the engine control side is not capable of recognizing that it is an abnormality, and hence the engine control may be carried out with the original property presented in  FIG. 7 . 
         [0015]    In addition, the greatest effect on the property after short circuit is a case in which a short circuit occurs between S 1  and S 2 , which are flow rate output signals. In this case, as presented in  FIG. 9 , since a short circuit has occurred, a voltage VO, which corresponds to a zero output, is constantly output regardless of the air flow rate. Also in this case, the greatest problem here is that changed properties are within the output range that is used normally presented in  FIG. 7 . In this case, even if the property has changed as in  FIG. 9 , the ECU on the engine control side is not capable of recognizing that it is an abnormality, and hence the engine control may be carried out with the original property presented in  FIG. 7 . 
         [0016]    As given above, not only the patent literature 1 but also other conventional arts have not considered an output change when a short circuit occurs between electrode pads that correspond to mainly adjacent midpoint potentials. Depending on the short circuit pattern, an output value after short circuit occurs falls within an output range that is used normally and the ECU described above is not capable of recognizing that the component state is an abnormality. As a result, there has been a possibility that a dangerous driving state is caused by carrying out an engine control using a signal that contains a great error. 
         [0017]    An object of the present invention is to provide a thermal flow rate sensor that is capable of carrying out a self-diagnosis. 
       Solution to Problem 
       [0018]    The above problem can be solved by, for instance, a thermal flow rate sensor that is provided with electrode pads for electrical conduction with the outside and includes a semiconductor element that detects a flow rate, in which two or more of the electrode pads are provided, and an electrode pad that has an electrical potential outside the output range used at a time of flow rate detection is arranged in an electrode pad that is adjacent to the electrode pad. 
       Advantageous Effects of Invention 
       [0019]    According to the present invention, a thermal flow rate sensor that is capable of carrying out a self-diagnosis even when a short circuit occurs between pads that are adjacent to each other in an electrode pad provided in an element that detects a flow rate can be provided. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0020]      FIG. 1  is an illustration of an embodiment of a thermal flow rate sensor according to the present invention. 
           [0021]      FIG. 2  is an illustration of an embodiment of the thermal flow rate sensor according to the present invention. 
           [0022]      FIG. 3  is an outline illustration of the thermal flow rate sensor. 
           [0023]      FIG. 4  is an illustration of an electrical connection of an air flow rate detection element. 
           [0024]      FIG. 5  is an illustration of an embodiment of a conventional thermal flow rate sensor. 
           [0025]      FIG. 6  is an illustration of an embodiment of a conventional thermal flow rate sensor. 
           [0026]      FIG. 7  is an illustration of an embodiment of a conventional thermal flow rate sensor. 
           [0027]      FIG. 8  is an illustration of an embodiment of a conventional thermal flow rate sensor. 
           [0028]      FIG. 9  is an illustration of an embodiment of a conventional thermal flow rate sensor. 
           [0029]      FIG. 10  is a cross-section view of the air flow rate detection element. 
           [0030]      FIG. 11  is an illustration of an embodiment of the thermal flow rate sensor according to the present invention. 
           [0031]      FIG. 12  is an illustration of an embodiment of the thermal flow rate sensor according to the present invention. 
           [0032]      FIG. 13  is an illustration of an embodiment of the thermal flow rate sensor according to the present invention. 
           [0033]      FIG. 14  is an illustration of an embodiment of the thermal flow rate sensor according to the present invention. 
           [0034]      FIG. 15  is an illustration of an embodiment of the thermal flow rate sensor according to the present invention. 
           [0035]      FIG. 16  is an illustration of an embodiment of the thermal flow rate sensor according to the present invention. 
           [0036]      FIG. 17  is an illustration of an embodiment of the thermal flow rate sensor according to the present invention. 
           [0037]      FIG. 18  is an illustration of an embodiment of the thermal flow rate sensor according to the present invention. 
           [0038]      FIG. 19  is an illustration of an embodiment of the thermal flow rate sensor according to the present invention. 
           [0039]      FIG. 20  is an illustration of an embodiment of the thermal flow rate sensor according to the present invention. 
           [0040]      FIG. 21  is an illustration of an embodiment of the thermal flow rate sensor according to the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0041]    An embodiment according to the present invention will be hereinafter described. 
       First Embodiment 
       [0042]    A production method of the air flow rate detection element  10  will be described with reference to the cross-section view presented in  FIG. 5 . An insulating oxide film  11  is formed on a silicon substrate  12 , a resistance wiring layer  13  is formed on the insulating oxide film  11  formed on a silicon substrate  12 , and patterning is provided by etching. The insulating oxide film  11  is further formed on it. After that, in order to obtain electrical conduction, a contact section is formed on an insulating oxide film of an upper layer by etching, an electrode wiring layer  14  made of aluminium or the like is formed on that, and, similarly, patterning is provided by etching, so that an electrode pad is formed. In the end, the silicon substrate is etched with KOH (potassium hydroxide) from the rear side, so that the silicon substrate is partially removed and a diaphragm section  20  is formed. This is a common production method of an air flow rate detection element. 
         [0043]    Embodiments according to the present invention will next be described using  FIG. 1  and  FIG. 2 .  FIG. 2  presents a circuit diagram of the air flow rate element  10 . This circuit includes a heat resistor Rh and a bridge circuit that is formed by upstream temperature measuring resistors Ru 1  and Ru 2  and downstream temperature measuring resistors Rd 1  and Rd 2 . In addition, an arrangement of the resistors is presented in  FIG. 1 . A heat resistor is arranged in a central part of the diaphragm  20 , and a temperature measuring resistor is arranged on an upstream side and a downstream side of it. This element and an LSI are electrically connected and, by applying a constant voltage from the LSI to between Rh-GNDH terminals, heat is applied and a temperature distribution is formed in the diaphragm section. Due to this, a difference in temperature between the upstream and the downstream is detected and the air flow rate can be measured. 
         [0044]    In addition,  FIG. 1  presents an arrangement of an electrode pad  30  of each electrical potential presented in  FIG. 2 . These electrode pads are arranged so that an electrode pad adjacent to the electrode pads (S 1  and S 2 ) through which a flow rate signal is output becomes an electrode pad that has an electrical potential outside the output range used at the time of flow rate detection.  FIG. 11  presents a truth value of a short circuit occurring between electrode pads adjacent to S 1  and S 2  in the arrangement described above. In addition, each electrical potential level used in this calculation is presented. Each value shows an electrical potential of a common thermal flow rate sensor, and, even in a case where the power supply voltage and the output range are different depending on each product, the table of truth value shows the same result. In addition, there is no problem as for a short circuit occurring between VH and VCC 1  because the same electrical potential is set. 
         [0045]    Thus, by employing the arrangement of the configuration of the present invention, the output value after short circuit as mentioned in the problem described above is out of the range used normally, and hence the thermal flowmeter can carry out a self-diagnosis and can accurately detect a product abnormality on the ECU side. 
         [0046]    As above, the first embodiment can provide a thermal flow rate sensor that is capable of carrying out a self-diagnosis in all the cases where a short circuit occurs in adjacent electrode pads. 
         [0047]    In addition, regardless of the circuit diagram of the present first embodiment, as long as at least the pads described above are provided, an advantageous effect of a self-diagnosis of the thermal flow rate sensor can be achieved if the arrangement relationship of the electrode pads meets the conditions described above. 
       Second Embodiment 
       [0048]    Next, a clearer self-diagnosis method using the element configuration of the first embodiment and the LSI of the drive element will be explained using  FIG. 13  and  FIG. 14 .  FIG. 13  presents a simplified signal diagram when the element  10  and the LSI  70  are connected. The output voltage (S 1 -S 2 ) of the element is input into an A/D converter inside the LSI and converted to a digital value. After that, calculation processing is carried out at a DSP, and the digital value is converted to a desired output value at an output conversion circuit and output as an output QOUT of the thermal flow rate sensor. 
         [0049]    Now, a general property of an A/D converter is presented in  FIG. 14 . While an input is linearly converted to a digital value in a specific input range (−VD to +VD), an input other than that is fixed to a HIGH level and a LOW level. Since in  FIG. 14 , a 16-bit A/D converter is assumed, the HIGH level is 32767 and the LOW level is −32768. However, taking a product variation into consideration, the voltage VD, which is 32767, has a slight variation, and hence the voltage value of a digital value is different for each product. On the other hand, since an input of VD or greater is always fixed to the HIGH level, the digital value becomes constant regardless of the product. 
         [0050]    Now, (S 1 -S 2 ), which is an input voltage of the A/D converter, is defined as S 1 =OUT 1  and S 2 =OUT 2  and an electrical potential (VCC 1  in  FIG. 1 ) of a pad provided between the electrode pads of S 1  and S 2  is defined as OUT 3 , and, when a short circuit occurs between the VCC 1  electrode pad and either of the electrode pads of both ends, each input becomes either OUT 3 −OUT 2  or OUT 1 −OUT 3 . If the absolute value of the input value at this time is greater than a value of the VD described above, the input is always fixed to the HIGH level or the LOW level. 
         [0051]    In other words, by setting the OUT 3  electrical potential in which |OUT 3 −OUT 1 |&gt;|VD| and |OUT 3 −OUT 2 |&gt;|VD| are constantly true regardless of the presence of air flow and change in environment and temperature, an identical self-diagnosis is made possible because an input is always fixed to the HIGH level or the LOW level even if a short circuit occurs between adjacent pads regardless of the product performance variation. 
         [0052]    In an example of product, when an output conversion circuit that outputs 5 V at the time of HIGH level and 0 V at the time of LOW level is designed, QOUT is always 5 V or 0 V at the time of short circuit described above. On the other hand, in case of a normal use, it is commonly practiced that the input voltage is set so that it falls into a linear region of the A/D converter and set so that a slight margin from the saturation region is given (input range in which the digital value becomes about −20000 to 20000 at the normal time, for instance), and therefore 5 V or 0 V is not output at the normal time. Due to this, a clearer self-diagnosis whether it is normal or abnormal is made possible on the ECU side regardless of product variation of the thermal flow rate sensor. 
         [0053]    In addition, while in the first embodiment, VH and VCC 1  are power supplies with the same electrical potential, they may be set with different electrical potentials depending on the product. In that case, it is necessary to diagnose a short circuit occurring between VH and VCC 1 . As for this, two source circuits  77  as presented in  FIG. 13  with the same electrical potential are formed and compared using an operational amplifier, and thus short circuit detection is easily made possible. 
       Third Embodiment 
       [0054]    A configuration of the present invention with a heater drive method different from that in the first embodiment will next be explained using  FIG. 15 ,  FIG. 16 , and  FIG. 17 . 
         [0055]      FIG. 16  presents a circuit diagram of the air flow rate element  10 , and  FIG. 17  presents a signal diagram in a case where it is connected with the drive element LSI  70 . In this circuit configuration, a bridge with which temperature of heat applied by the heater is controlled is added to the circuit configuration of the first embodiment. In addition, an arrangement of each resistor is presented in  FIG. 15 . In addition to the configuration of the first embodiment, a heater temperature-sensitive resistor (Rhs)  24  is arranged on the periphery of a heater  21 , and due to this, the temperature of Rhs also rises by heat generated by the heater. Following this, the temperature of Rhs resistance rises and a V 2 P terminal and a V 2 MA terminal of the bridge circuit are heated until they become the same electrical potential. Due to this, the temperature of the heater is controlled so that it becomes a certain temperature. Fixed resistances (Rc 1 , Rc 2 , and Rc 3 )  26  of the heater temperature control bridge are formed not on the diaphragm section but on the silicon substrate. 
         [0056]    In addition,  FIG. 15  presents an arrangement of the electrode pad of each electrical potential presented in  FIG. 16 . These electrode pads are arranged so that the electrical potential of the pads adjacent to each of the electrode pads (S 1  and S 2 ) through which the flow rate signal is output, the electrode pads (V 2 P and V 2 MA) through which the midpoint potential of the bridge circuit that controls the temperature of the heater is output, and the electrode pad (VH) through which the heater power source is output become the electric power source potentials (VCC 1  and VC 2 ) of the bridge circuit, its ground potential (GND 1 ), or the ground potential (GNDH) of the heater. The difference in the idea from the first embodiment lies in that the heater power source VH is handled as a midpoint potential. In the first embodiment, VH is driven on constant voltage by the LSI fixed power source. In the present embodiment, on the other hand, VH is a feedback circuit and changes due to the presence of air flow and temperature change, and thus VH needs to be handled as a midpoint potential similarly with S 1 , S 2 , and the like. 
         [0057]    At first, at the electrode pads (S 1  and S 2 ) through which a flow rate signal is output, adjacent pads are arranged with the identical condition to that of the first embodiment, and therefore a self-diagnosis is made possible in all the short circuit modes. 
         [0058]    Next, at the electrode pads (V 2 P and V 2 MA) through which the midpoint potential of the bridge circuit that controls the temperature of the heater is output, the condition of the electrical potential of the adjacent electrode pad is identical to the condition of the electrode pad through which the flow rate signal described above is output but output change at the time of short circuit is different. When a short circuit occurs between the midpoint potential of the bridge circuit that controls the temperature of the heater and the bridge power-source voltage or the ground potential, an input of an operational amplifier presented in  FIG. 17  is in a state with a constant offset, and hence VH, which is an output voltage of the operational amplifier, constantly keeps the HIGH level. By monitoring this state using a heater voltage judgment circuit  73 , the short circuit described above can be detected. An example of detection method is to store the VH voltages in a memory in the LSI for a certain period of time, to judge that it is abnormality if all of the VH voltages are the HIGH level (or the LOW level) for a certain period of time, and to output a self-diagnosis output signal. 
         [0059]    Next, at the electrode pad (VH) through which the heater power source is output, since the adjacent pad has a ground potential in  FIG. 15 , in case of short circuit, by monitoring it using the heater voltage judgment circuit  73  described above, the short circuit described above can be detected. 
         [0060]    In a case where the adjacent pad has the bridge circuit electric power source potential (VCC 1  or VCC 2 ), if the electrical potential has the same electrical potential (let it be 5 V in this case) as that of a power source PVCC that is supplied to the thermal flow rate sensor, VH constantly keeps 5 V (HIGH) in case of short circuit, and hence by monitoring it using the heater voltage judgment circuit  73  described above, the short circuit described above can be detected. On the other hand, in a case where the electrical potential is driven on an electrical potential that is lower than PVCC, there is a case where the heater voltage judgment circuit  73  described above is not capable of detecting the short circuit. In that case, the arrangement may be made so that the electrical potential of the electrode pad adjacent to VH becomes the ground potential as in the present embodiment. 
         [0061]    In a case where the form of the output QOUT of the thermal flow rate sensor is a voltage output or a frequency output, the self-diagnosis output signal described above is set as presented in  FIG. 21 , so that it is outside the output range that is used normally, and thus a diagnose can be carried out most easily. Using a specific setting method in which when the heater voltage judgment circuit described above detects an abnormality, the signal is input to the DSP and the digital value of the flow rate output signal is forcibly replaced with 32767 or −32768, QOUT falls into outside the output range that is used normally similarly to the first embodiment. 
         [0062]    In addition, as for another self-diagnosis output signal, in a case where the form of the output QOUT of the thermal flow rate sensor is a digital output such as SENT and LIN, a failure flag is allocated to a specific bit and output, and thus a diagnose can be carried out most easily. If an abnormality flag is put up to even only one of the many bits that are transmitted, the ECU can recognize that an abnormality has occurred in the thermal flow rate sensor. The bit described above may be set in consistency with the ECU on an output signal reception side. 
         [0063]    As seen above, in the present third embodiment, a thermal flow rate sensor that is capable of self-diagnosis in all the cases where a short circuit occurs between adjacent electrode pads can be provided. 
         [0064]    In addition, regardless of the circuit diagram of the present third embodiment, as long as at least the pads described above are provided, an advantageous effect of a self-diagnosis of the thermal flow rate sensor can be achieved if the arrangement relationship of the electrode pads meets the conditions described above. 
       Fourth Embodiment 
       [0065]    A configuration of the present invention with the heater drive method different from that in the third embodiment will next be explained using  FIG. 18 ,  FIG. 19 , and  FIG. 20 . 
         [0066]      FIG. 19  presents a circuit diagram of the air flow rate element  10 , and  FIG. 20  presents a signal diagram in a case where it is connected with the drive element LSI  70 . In this circuit configuration, a resistance (Rm)  26  for adjustment with which temperature of heat applied by the heater is controlled more accurately is added to the circuit configuration of the third embodiment. Following that, also on the LSI side, a circuit is formed in which an arbitrary voltage value V 2 MC can be selected from the electrical potential of both ends of the resistance for adjustment described above. Due to this, while V 2 MA is the only choice of the adjustment electrical potential in the third embodiment, the temperature of heat applied by the heater can be controlled more accurately because the adjustment electrical potential can be arbitrarily selected in a certain range. 
         [0067]    In addition,  FIG. 18  presents an arrangement of the electrode pad  30  of each electrical potential presented in  FIG. 19 . These electrode pads are arranged so that the electrical potential of the pads adjacent to each of the electrode pads (S 1  and S 2 ) through which the flow rate signal is output and the electrode pad (VH) through which the heater power source is output is the electric power source potentials (VCC 1  and VCC 2 ) of the bridge circuit, its ground potential (GND 1 ), or the ground potential (GNDH) of the heater, and the electrode pads (V 2 MA and V 2 MB) of the both terminal electrical potentials of the resistance for adjustment described above are not adjacent. 
         [0068]    The difference in the idea from the third embodiment lies in that the short circuit between the midpoint potential (V 2 P) on the heater temperature-sensitive resistor side of the bridge circuit and the electrical potentials (V 2 MA and V 2 MB) of the both terminals of the resistance for adjustment described above is not limited. In a case where a short circuit occurs between V 2 MA and V 2 MB, while a relationship of V 2 MA&gt;V 2 MC&gt;V 2 MB is always true before the short circuit occurs, a relationship of V 2 MA=V 2 MC=V 2 MB is true after the short circuit occurs. As a result, V 2 MC, which is an input of an operational amplifier  71 , changes. In that case, the temperature of heat applied by the heater changes and hence the output property becomes as the one presented in  FIG. 8 . In this case, abnormality cannot be detected because it is not an abnormal circuit drive also on the LSI side in addition to the fact that a self-diagnosis cannot be carried out from the output property. Accordingly, a pad arrangement needs to be configured so that a short circuit does not occur between the electrical potentials of the both terminals of the resistance for adjustment described above. 
         [0069]    On the other hand, in a case where a short circuit occurs between V 2 P and V 2 MA (or V 2 MB), there is a relationship of V 2 MA&gt;V 2 MC&gt;V 2 MB similarly to the above, and hence V 2 P and V 2 MC do not become the same electrical potential. Due to this, the output (VH) of the operational amplifier is constantly fixed to HIGH, and thus, similarly to the third embodiment, by monitoring it using the heater voltage judgment circuit  73 , the short circuit described above can be detected. 
         [0070]    As for the electrode pads (S 1  and S 2 ) through which another flow rate signal is output and the electrode pad (VH) through which a heater power source is output, adjacent pads are arranged with the identical condition to that of the third embodiment, and therefore a self-diagnosis is made possible in all the short circuit modes. 
         [0071]    As seen above, in the present fourth embodiment, a thermal flow rate sensor that is capable of self-diagnosis in all the cases where a short circuit occurs between adjacent electrode pads can be provided. 
         [0072]    In addition, regardless of the circuit diagram of the present fourth embodiment, as long as at least the pads described above are provided, an advantageous effect of a self-diagnosis of the thermal flow rate sensor can be achieved if the arrangement relationship of the electrode pads meets the conditions described above. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           10  air flow rate detection element 
           11  insulating oxide film 
           12  silicon substrate 
           13  resistance wiring film 
           14  electrode wiring layer 
           20  diaphragm 
           21  heat resistor (heater); Rh 
           22  upstream side temperature resistor; Ru 
           23  downstream side temperature resistor: Rd 
           24  heater temperature-sensitive resistor: Rhs 
           25  heater temperature control bridge configuration resistances; Rc 1 , Rc 2 , and Rc 3   
           26  resistor for adjustment: Rm 
           30  electrode pad 
           40  air intake duct 
           50  thermal flow rate sensor 
           60  ceramic substrate 
           65  electrical wiring layer of ceramic substrate 
           70  LSI 
           71  operational amplifier 
           72  bridge power supply circuit 
           73  heater voltage judgment circuit 
           74  A/D converter 
           75  DSP 
           76  output conversion circuit 
           77  heater power supply circuit 
           80  aluminium wire 
           90  gold wire 
           100  resin seal region 
           101  void in resin