Abstract:
A semiconductor integrated circuit device has a semiconductor integrated circuit chip, a package enclosing the chip, and a plurality of conductors connecting the bonding pads of the chip to the leads of the package. The chip has an internal circuit, a plurality of bonding pads having signal paths formed between themselves and the internal circuit, and a switching circuit provided in a predetermined signal path so as to perform a switching operation to allow the internal circuit to be connected selectively to one of different bonding pads. The switching circuit is fed with an external signal to perform its switching operation in such a way as to prevent the signals passing through mutually adjacent conductors from affecting each other.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a semiconductor integrated circuit device. 
   2. Description of the Prior Art 
   In general, a semiconductor integrated circuit device has a plurality of leads provided in an edge portion of the package thereof so as to project therefrom for connection to a printed circuit board. 
   On the other hand, a semiconductor integrated circuit device has an integrated circuit chip enclosed in a central portion of the package thereof, and the chip has a plurality of bonding pads provided thereon that are connected individually to the leads of the package by wire bonding. That is, input and output of signals to and from the internal circuit of the chip is achieved by way of bonding pads corresponding to the individual signals. 
   However, the signals input to and output from the internal circuit have different amplitudes from one another, and therefore, when wires are bonded, it is necessary to select appropriate leads to prevent two signals having greatly different amplitudes from being input or output by way of leads too close to each other. This helps alleviate problems such as crosstalk, but with limited result in exchange for much inconvenience. 
   Such a chip can be enclosed also in a package of a BGA (ball grid array) type. In the case, the signals corresponding to the bonding pads provided on the chip is input thereto or output therefrom by way of solder pads from or to the bonding pads provided on the package. 
   If the two signals are transferred by way of two solder pads that are too close to each other, problems such as crosstalk occur; moreover, also on the part of the printed circuit board on which the BGA package is mounted, problems occur with the conductive patterns that are laid so as to be connected individually to those two solder pads. Such problems can be avoided by assigning the above-mentioned two signals to different bonding pads, but this requires modification of the masking pattern of the chip, and thus cannot be achieved readily. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide a semiconductor integrated circuit device that allows easy prevention of crosstalk. 
   To achieve the above object, according to the present invention, a semiconductor integrated circuit device is provided with: a semiconductor integrated circuit chip which comprises an internal circuit, a plurality of bonding pads having signal paths formed between themselves and the internal circuit, a switching circuit provided in a predetermined signal path so as to perform a switching operation to permit the internal circuit to be connected selectively to one of different bonding pads, and means for feeding a switching signal to the switching circuit; a package enclosing the semiconductor integrated circuit chip and having a plurality of leads for connection to a printed circuit board; a plurality of conductors for connecting the bonding pads of the semiconductor integrated circuit chip to the leads of the package; and means for controlling the switching operation of the switching circuit in such a way as to prevent signals passing through mutually adjacent conductors from affecting each other. 
   This semiconductor integrated circuit device allows a bonding pad that is originally assigned for input or output of a particular signal to be switched to another bonding pad. This makes it possible to handle signals having greatly different amplitudes via terminals that are located in positions well apart from each other. Thus, it is possible to prevent malfunctioning due to crosstalk and the like without any complicated process such as modification of the masking pattern. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     This and other objects and features of the present invention will become clear from the following description, taken in conjunction with the preferred embodiments with reference to the accompanying drawings in which: 
       FIG. 1  is a plan view of an integrated circuit chip embodying the invention; 
       FIG. 2  is a circuit diagram of the switching circuit used in the integrated circuit chip shown in  FIG. 1 ; 
       FIG. 3  is a plan view of a quad flat package embodying the invention; 
       FIG. 4  is a plan view of a flip ball grid array embodying the invention; and 
       FIG. 5  is a diagram showing the state of the ball grid array shown in  FIG. 4  when the chip is removed therefrom. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.  FIG. 1  is a plan view of an integrated circuit chip. This chip  1  is provided with an internal circuit  2  and bonding pads  31 ,  32 ,  33 ,  34 ,  35 ,  36 ,  37 ,  38 ,  39 ,  310 ,  311 , and  312 . Of these bonding pads, the bonding pads  32 ,  33 ,  34 ,  35 ,  37 ,  38 , and  311  form signal paths by being connected directly to the internal circuit  2  by way of conductors. 
   The bonding pads  31  and  310  are connected to the internal circuit  2  through a switching circuit  41  provided in the middle of the conductor A, so that a signal path is formed between either of those bonding pads and the internal circuit  2  through this switching circuit  41 . Similarly, the bonding pads  39  and  312  are connected to the internal circuit  2  through a switching circuit  42  provided in the middle of the conductor B, so that a signal path is formed between either of those bonding pads and the internal circuit  2  through this switching circuit  42 . 
   The switching operation of these switching circuits  41  and  42  is controlled by a switching signal (switching voltage) fed in from the outside via the bonding pad  36 . In the case of the chip  1  shown in  FIG. 1 , input and output of signals to and from the internal circuits  2  is achieved via the bonding pads  31 ,  32 ,  33 ,  34 ,  35 ,  37 ,  38 ,  39 , and  311 . 
     FIG. 2  shows the circuit configuration of the switching circuit  41 . The switching circuit  41  has a terminal  41   a  connected, as shown in  FIG. 1 , to the internal circuit  2 , a terminal  41   b  connected to the bonding pad  31 , and a terminal  41   c  connected to the bonding pad  310 . The switching circuit  41  further has a terminal  41   d  connected to the bonding pad  36 . Reference numerals  5 A and  5 B represent analog switches, of which each is composed of, for example, a p-channel MOS transistor and an n-channel MOS transistor connected in parallel and thus has two control terminals G 1  and G 2  (the control terminals of the two constituent MOS transistors). The switch  5 A is connected between the terminals  41   a  and  41   b , has its control terminal G 1  connected to the terminal  41   d , and has its control terminal G 2  connected through an inverter IV to the terminal  41   d . The switch  5 B has its control terminal G 1  connected through the inverter IV to the terminal  41   d , and has its control terminal G 2  connected directly to the terminal  41   d . Thus, the switches  5 A and  5 B operate in such a way that, when a high level is fed as the switching voltage to the terminal  41   d , the switch  5 B is turned on and the switch  5 A is turned off, and, when a low level is fed to the terminal  41   d , the switch  5 A is turned on and the switch  5 B is turned off. In  FIG. 1 , the conductor E, indicated by broken lines, for the switching voltage is laid in a different layer from the layer in which the other conductors (A, B, C, and so on) are laid. The switching circuit  42  is configured in the same manner as shown in FIG.  2 . It is to be understood that the switching circuits  41  and  42  may be configured in any manner other than shown in FIG.  2 . 
   Now, suppose that, in the above-described chip  1 , the signal output from the internal circuit  2  by way of the signal path A and the signal output therefrom by way of the signal path C so as to be fed out via the bonding pad  32  have greatly different amplitudes. In this case, the switching circuit  41  is so switched that its terminal  41   a  is connected to its terminal  41   c  so that the signal passing through the signal path A will be fed out via the bonding pad  310 . This helps reduce crosstalk between the two signals. 
     FIG. 3  is a plan view showing the structure of a QFP (quad flat package) enclosing the above-described chip  1 . This QFP has a plurality of leads  71 ,  72 ,  73 ,  74 ,  75 ,  76 ,  77 ,  78 ,  79 ,  710 ,  711 ,  712 ,  713 ,  714 ,  715 , and  716  provided in an edge portion of the package  6  thereof so as to project therefrom for connection to a printed circuit board (not shown). 
   The QFP has the integrated circuit chip  1  enclosed in a central portion of the package  6  thereof, and the bonding pads  31 ,  32 ,  33 ,  34 ,  35 ,  36 ,  37 ,  38 ,  39 ,  310 ,  311 ,  312  provided on the chip  1  are connected respectively to the leads  71 , . . . ,  712  provided on the package  6  by wire bonding. Thus, if the switching circuit  41  is switched as described above, the signal output from the internal circuit  2  to the signal path A will eventually be fed out via the lead  710  of the package  6 . 
     FIG. 4  shows a case in which a BGA (ball grid array) is used to enclose the chip  1 . This BGA has a plurality of bonding pads  81 ,  82 ,  83 ,  84 ,  85 ,  86 ,  87 ,  88 ,  89 ,  810 ,  811 ,  812 ,  813 ,  814 ,  815 , and  816  provided along an edge portion of the package  6  thereof. The BGA has the chip  1  enclosed in a central portion of the package  6  thereof, and the bonding pads  31 , . . . ,  312  provided on the chip  1  are connected respectively to the bonding pads  81 , . . . ,  812  provided on the package  6  by wire bonding.  FIG. 5  is a diagram showing the state of the BGA when the chip  1  is removed from the package  6 . In the central portion of the package  6 , a plurality of solder pads  91 ,  92 ,  93 ,  94 ,  95 ,  96 ,  97 ,  98 ,  99 ,  910 ,  911 ,  912 ,  913 ,  914 ,  915 , and  916  are arranged in a grid-like array. These solder pads  91 , . . . ,  916  are exposed also on the bottom surface of the package  6  for the package  6  for connection to a printed circuit board (not shown). 
   Now, suppose that, in the chip  1 , the switch circuit  41  is so switched that its terminal  41   a  is connected to its terminal  41   b  as shown in FIG.  1 . In this case, the output signal from the bonding pad  31  is transferred via the bonding pad  81  on the package  6  so as to be fed out via the solder pad  91  (see FIG.  5 ). On the other hand, the output signal from the bonding pad  33  is transferred via the bonding pad  83  on the package  6  so as to be fed out via the solder pad  93  (see FIG.  5 ). Here, since the solder pads  91  and  93  are close to each other, crosstalk is likely to occur. 
   To avoid this, in the chip  1 , by feeding an input signal to the bonding pad  36 , the switching circuit  41  is so switched that the signal path A is connected to the bonding pad  310 . Then, the signal is output from the bonding pad  310 , and is then transferred via the bonding pad  810  of the package  6  of the BGA so as to be fed out via the solder pad  910 . Now, the solder pad  910  is well apart from the solder pad  93 , and thus crosstalk or the like is unlikely to occur. 
   It is to be understood that the present invention may be practiced in any other way than is specifically described above. For example, the chip may be provided with any number of bonding pads, and may be provided with any number of switching circuits in any signal paths. Moreover, although the examples described above deal only with arrangements using a QFP or BGA, the present invention is applicable also to arrangements using a package of any other type.