Abstract:
An integrated circuit includes an electronic circuit in a housing and a first contacting device for soldering the circuit to a corresponding second contacting device of a circuit board. The first and second contacting devices are each divided into a first section and a second section, the sections of one of the contacting devices being fixedly electrically connected to each other, and the sections of the other contacting device being selectively connectable to a device for resistance determination.

Description:
BACKGROUND INFORMATION 
       [0001]    An integrated circuit includes an electronic circuit which is situated on a semiconductor substrate and accommodated in a housing having contact elements. Different housings having different contact elements are available, depending on a planned application or field of application. The contact elements are usually electrically connected to corresponding contact elements of a circuit board using a soldering process. The circuit board usually connects the integrated circuit to additional electronic components. 
         [0002]    In vehicle electrical systems, for example, it is often necessary to ensure that the electrical connection between the corresponding contact elements is inspected after the soldering process, for example when a security-relevant system is affected, such as a brake control system. The inspection may be carried out visually, for example. If the solder joints are not immediately visible, as is the case, for example, in a QFN or LGA housing, an inspection may be carried out with the aid of x-ray light. However, this is cost-intensive and may produce ambiguous results if other elements, a bonding wire, for example, is visible in the x-ray image. Alternatively, the reliability of the soldering process may be ensured, for example, by providing the contact elements with solder prior to the soldering process. A so-called presoldering process of this type also generates additional costs. 
         [0003]    An object of the present invention is therefore to provide a cost-effective solder joint inspection. 
       SUMMARY OF THE INVENTION 
       [0004]    According to a first aspect of the present invention, an integrated circuit includes an electronic circuit in a housing and a first contacting device for soldering the circuit to a corresponding second contacting device of a circuit board. The first and second contacting devices are each divided into a first section and a second section, the sections of one of the contacting devices being fixedly electrically connected to each other, and the sections of the other contacting device being selectively connectable to a device for resistance determination. 
         [0005]    The first sections and the second sections may each be connected to each other with the aid of a soldering process. A total resistance of both series-connected connections may be determined by measuring the resistance between the first and second sections, which are not electrically connected to each other. If one of the two connections is faulty, this is reflected in the determined resistance. A solder joint inspection may thus be carried out electrically without additional measuring equipment. 
         [0006]    The electronic circuit may include the device for resistance determination. The contacting device whose sections are connected to each other is situated on the circuit board in this case. After soldering to the circuit board, the integrated circuit may carry out a function test and determine whether its connection to the circuit board is faulty. No special precautions need to be taken on the circuit board for this purpose. The functionality of the resistance determination may be implemented at no appreciable added cost, in particular in the case of application-specific integrated circuits (ASICs). This makes it possible to increase process reliability without significantly raising manufacturing costs at the same time. 
         [0007]    The electronic circuit may have a switching device for selectively connecting the device for resistance determination to one of the sections. The resistance determination may thus be selectively activated or deactivated, so that no current flow through the connections needs to be generated during normal operation of the integrated circuit, which follows a resistance determination, thereby making it possible to reduce the electrical power loss of the integrated circuit during normal operation. 
         [0008]    The electronic circuit may include a device for comparing the determined resistance with a threshold value. The level of the resistance with regard to the threshold value may be an indicator of whether or not one of the connections is faulty. In one specific embodiment, multiple threshold values are provided, it being possible to determine a quality of the connections from the level of resistance with regard to the threshold values. 
         [0009]    The electronic circuit may be configured to output a signal which indicates the comparison result. This makes it possible, for example, to prevent the integrated circuit from starting up if the integrated circuit does not have an adequate electrical connection to the circuit board. 
         [0010]    In one specific embodiment, one of the sections of the contacting device of the integrated circuit is fixedly connected to the device for resistance determination. The other section may be assigned to a functionality of the integrated circuit which is independent of the resistance determination. The functionality of the integrated circuit may thus be completely decoupled from the connection inspection according to the present invention. 
         [0011]    According to a second aspect, a method is provided for determining a resistance between a contacting device of an integrated circuit which is connected to an electronic circuit and a corresponding contacting device of a circuit board, the contacting devices each being divided into a first section and a second section, the method including steps which involve electrically connecting the sections of one of the contacting devices to each other and determining an electrical resistance between the sections of the corresponding contacting device. 
         [0012]    The method preferably also includes a comparison of whether the determined resistance falls below a predetermined threshold value. In particular, a plurality of contacting devices and corresponding contacting devices may be provided, the method including outputting a signal which indicates whether all resistances are below the threshold value. The resistance measurements of the connections of the individual contacting devices are preferably carried out sequentially. 
         [0013]    According to a further aspect, a computer program product includes program code means for carrying out the method when the computer program product runs on a processing device or is stored on a machine-readable data carrier. This applies, in particular, if the electronic circuit includes the processing device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  shows an integrated circuit which is connected to a circuit board. 
           [0015]      FIG. 2  shows the integrated circuit from  FIG. 1  having a faulty connection. 
           [0016]      FIG. 3  shows an equivalent circuit diagram of the integrated circuit from  FIGS. 1 and 2 . 
           [0017]      FIGS. 4 through 6  show variants of the integrated circuit from  FIGS. 1 and 2 . 
           [0018]      FIG. 7  shows a flow chart of a method for inspecting the connections on the integrated circuit from  FIGS. 1 through 6 . 
       
    
    
     DETAILED DESCRIPTION 
       [0019]      FIG. 1  shows a system  100  of an integrated circuit  110 . Integrated circuit  110  includes a housing  115  in which an electronic circuit  120  is situated. Solder pads  130 ,  140 , which are electrically connected to electronic circuit  120  with the aid of bonding wires, are located on the outside of housing  115 . A circuit board  150 , which has a further solder pad  160 , is located beneath integrated circuit  110 . In one specific embodiment, solder pads  130 ,  140  have a miniaturized design and together are approximately the same size as solder pad  160  on circuit board  150 , solder pad  160  preferably having a standardized size. Electrical connections  170  and  180 , which are formed by a shared solder joint  190 , are situated between solder pad  160  and solder pads  130 ,  140  of the integrated circuit. 
         [0020]    For normal operation of integrated circuit  110 , only one of solder pads  130 ,  140  is needed to connect electronic circuit  120  to solder pad  160  of circuit board  150 . To increase the operating reliability of integrated circuit  110  during normal operation, a resistance measurement is carried out between solder pads  130  and  140  of integrated circuit  110  in a test phase which precedes normal operation. In doing so, a current flows through connection  170  from first solder pad  130  to solder pad  160  of circuit board  150 , and from there to second solder pad  140  of integrated circuit  110  via connection  180 . A flow in the opposite direction is also possible. 
         [0021]    A resistance is determined which includes the two series-connected connections  170  and  180 . If both connections  170  and  180  are fault-free, a resistance value between solder pads  130  and  140  typically lies in the range of just a few mΩ. 
         [0022]      FIG. 2  shows integrated circuit  110  from  FIG. 1 , which has a faulty connection  180 . Connection  180  is only partially established because solder joint  190  has only partially wetted solder pad  140 . A connection of this type is also known as a “cold solder joint.” In this case, the electrical resistance between solder pads  130  and  140  lies in the range of several Ω. The resistance value between solder pads  130  and  140  may be even higher if other connection  170  is also faulty or if one of solder pads  130 ,  140  is not at all wetted by solder joint  190 . In this case, the resistance between solder pads  130  and  140  typically lies in the range of several mΩ to an infinite value. 
         [0023]      FIG. 3  shows an equivalent circuit diagram of integrated circuit  110  from  FIGS. 1 and 2 . Housing  115 , on whose outside solder pads  130  and  140  are situated, is shown in a schematic representation. Electronic circuit  120  is accommodated in housing  115  and connected to solder pads  130  and  140  with the aid of bonding wires. 
         [0024]    Electronic circuit  120  includes a first function module  310  and a second function module  320 . A first switch  330  selectively connects solder pad  130  to first function module  310  or to second function module  320 . A second switch  340  selectively establishes a connection between solder pad  140  and second function module  320 . 
         [0025]    First function module  310  represents the portion of electronic circuit  120  which is used during normal operation of integrated circuit  110 . Second function module  320  is the portion of electronic circuit  120  which may be used to carry out a resistance measurement between solder pads  130  and  140 . This measurement is usually carried out before integrated circuit  110  goes into normal operation. 
         [0026]    To determine the resistance between solder pads  130  and  140 , first switch  330  is in the illustrated position, in which solder pad  130  is connected to second function module  320 . Second switch  340  is closed as illustrated. 
         [0027]    For normal operation, first switch  330  is flipped so that it connects solder pad  130  to first function module  310 . At the same time, second switch  340  is opened to prevent a current from flowing from second function module  320  to first function module  310  via switch  340 , solder pad  140 , solder joint  190 , solder pad  130  and first switch  330 . If a current of this type is negligible or desired, second switch  340  may be omitted and replaced by a fixed connection. 
         [0028]      FIG. 4  shows a variant of integrated circuit  110  from  FIGS. 1 and 2 . In contrast to the representation in  FIG. 1 , solder pads  130  and  140  of integrated circuit  110  are spaced farther apart and are located opposite separately formed solder pads  160  on circuit board  150 . Solder pads  160  on circuit board  150  are electrically connected to each other with the aid of a printed conductor. Connection  170  between solder pad  130  and left solder pad  160  is established by a first solder joint  190 , and connection  180  between solder pad  140  and right solder pad  160  of circuit board  150  is established by a second solder joint  190 . The specific embodiment uses solder pads  130 ,  140  which have a common size and grid spacing, so that it is not necessary to provide miniaturized solder pads  130 ,  140  on integrated circuit  110 , as described above with reference to  FIG. 1 . This makes it possible, for example, to increase a current carrying capacity of connections  170  and  180 . If necessary, the producibility of solder joints  190  may also be improved. In addition, this makes it possible to reduce a probability that, while a solder joint  190  has good connections to solder pads  130  and  140 , it nevertheless has a poor connection or no connection at all to solder pad  160  of circuit board  150 . 
         [0029]      FIG. 5  shows a further variant of integrated circuit  110  from  FIGS. 1 and 2 . In contrast to the representation in  FIG. 4 , solder pads  160  of circuit board  150  are not electrically connected to each other. In determining a resistance of connections  170  and  180 , this specific embodiment takes the opposite approach in that solder pads  130  and  140  are electrically connected to each other within electronic circuit  120  using a function of electronic circuit  120  according to  FIG. 3 . The resistance is then determined on the part of circuit board  150  by determining the resistance between the two solder pads  160 . In this case, second function module  320  from  FIG. 3  may correspond to a predetermined resistance, in particular the short-circuit of 0 Ω. 
         [0030]    In another specific embodiment, second function module  320  may include a predetermined resistance which is greater than 0Ω and above which a voltage drops which is proportional to a current flowing through solder pads  160  of circuit board  150 . The resistance is then measured by applying a predetermined voltage between solder pads  160 , for example with the aid of further components on circuit board  150 , and by determining the current flowing through connections  170  and  180  on the basis of the voltage drop in second function module  320 . In addition to using components which are situated on circuit board  150 , the voltage between solder pads  160  may also be produced with the aid of external test equipment, for example with the aid of test pins which contact solder pads  160  during the test phase. 
         [0031]      FIG. 6  shows a further variant of integrated circuit  110  from  FIGS. 1 through 5 . In contrast to the representation in  FIG. 1 , only one connection  170  exists between integrated circuit  160  and circuit board  150 . In addition to solder pad  130 , there is also a pin terminal  610  which is accessible on the side of housing  115  and which is part of an electrical connection between solder pad  130  and electronic circuit  120 . The quality of electrical connection  170  may be determined by determining the electrical resistance between pin terminal  610  and solder pad  160  of circuit board  150 . 
         [0032]      FIG. 7  shows a flow chart of a method  700  for inspecting the connections on integrated circuit  110  from  FIGS. 1 through 6 . In a first step  705 , adjacent sections of solder pad  160  on circuit board  150  are electrically connected to each other. This may be provided, for example, in the form of a printed circuit, during the manufacture of circuit board  150 . In a subsequent step  710 , connections  170  and  180  are established between corresponding solder pads  130 ,  140  and  160 . This step may include producing solder joints  190 . In step  715 , second function module  320  is connected to solder pads  130  and  140  with the aid of first switch  330  and second switch  340 . In step  720 , a resistance measurement is subsequently carried out between solder pads  130  and  140 . 
         [0033]    In a step  725 , it is determined whether the determined resistance is less than a predetermined threshold value. This threshold value usually lies in the range of just a few Ω. If the determined resistance falls below this threshold value, it may be assumed that connections  170  and  180  are in proper condition. If it is determined in step  725  that the resistance determined in step  720  exceeds the threshold value, a signal is output in a step  730  which indicates at least one faulty connection  170 ,  180  between integrated circuit  110  and circuit board  150 . In the illustrated variant, method  700  ends in step  730 . In a further variant, the method may continue in a step  735 , which otherwise follows step  725 , after the signal has been output. In step  735 , a check is carried out to determine whether all contacting elements  130 ,  140  of integrated circuit  110  have already been checked. If this is not the case, method  700  continues with step  715 , where a different contact element  130 ,  140  is checked. 
         [0034]    If it is determined in step  735  that all contact elements  130 ,  140  have been checked, a signal which indicates fault-free connections  170 ,  180  is output in an optional final step  740 . In the event that the method is continued with step  735  after step  730 , a more differentiated result may be output in step  740 , for example an indication of which of connections  170 ,  180  are faulty and which are not.