Abstract:
Disclosed is a semiconductor IC device capable of suppressing the interference of noise generated in one functional block with other functional blocks therein while protecting against electrostatic breakdown. A plurality of isolated pads are connected to a first terminal through respective wires, and further connected to a plurality of isolated pads each connected to a second terminal having the same function as that of the first terminal, so as to reduce noise interference based on the pad isolation and protect against electrostatic breakdown based on the inter-pad connection.

Description:
RELATED APPLICATION 
     This application is based on Japanese Patent Application No. 2006-151439, the contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a technique for reducing the influence of noise generated in a functional block on other functional blocks in a semiconductor integrated circuit (IC) device, and more particularly to a semiconductor IC device adapted to balance the protection against noise interference with the protection against electrostatic breakdown, i.e., surge. 
     Late years, in semiconductor IC devices, a noise level has become increasingly higher due to increase in operating frequency associated with progress in higher processing speed. Under such a situation, there has been proposed a technique of reducing noise interference between a plurality of functional blocks (each hereinafter referred to simply as “block”) based on isolation of a pad.  FIG. 8  shows one example of this type of technique. In this semiconductor IC device, a lead frame  801  and a pad  803  are electrically connected to each other through a wire  802 . The pad  803  is connected to a plurality of blocks through respective intra-chip wires  804 . 
     Specifically, as shown in  FIG. 8 , in order to prevent noise occurring in one of three blocks A to C from interfering with other two blocks, the three blocks A to C are connected at a single point in or near the pad  803 . In this technique, if the single connection point has a sufficiently low impedance, noise interference can be reduced as expected. In reality, elements, such as the wire  802  and the lead frame  801 , in a terminal area between the pad  803  and the outside of a semiconductor package, have a certain level of impedance, and it is difficult to adequately lower the impedance at the single connection point, which is liable to cause the problem of noise interference between the blocks. 
     There has therefore been proposed another technique of more effectively preventing noise interference, as disclosed in R. Jacob Baker, Harry W. Li, and David E. Boyce, “CMOS Circuit Design, Layout, and Simulation”, ISBN 0-7803-3416-7 (referred to as “Publication 1” hereinafter). This technique will be described below with reference to  FIG. 9 . 
     As shown in  FIG. 9 , a wire to be connected to a lead frame  801  is divided into three wires  121 ,  122 ,  125  which are connected, respectively, to three pads  131 ,  132 ,  135 , and isolated from each other. The pads  131 ,  132 ,  135  are not connected to each other in a wiring layer on a semiconductor substrate but through the wires. Specifically, a position for connecting the wires at a single point is set on the lead frame  801 . Thus, as compared with the technique illustrated in  FIG. 8 , an impedance value at the single connection point can be lowered to more effectively reduce the noise interference. 
     In the conventional technique illustrated in  FIG. 9 , each functional terminal, such as a source terminal or a ground terminal, is provided in a number of only one, and there is no specific problem as long as a current supplied from the terminal falls within an allowable range. However, if the current supplied from the terminal is increased beyond the allowable range, or a plurality of terminals are provided for the purpose of noise reduction, the following problem will occur. If the technique illustrated in  FIG. 9  is used for reducing noise interference under the above conditions, electrostatic breakdown level will be undesirably lowered due to the wires which are not connected together in a wiring layer, although noise interference can be reduced. 
     SUMMARY OF THE INVENTION 
     In view of the above conventional problem, it is an object of the present invention to provide a semiconductor IC device capable of balancing the protection against noise interference with the protection against electrostatic breakdown. 
     In order to achieve this object, the present invention provides a semiconductor integrated circuit device which includes a plurality of terminals having a same function. The terminals consist of a plurality of source terminals or ground terminals. The semiconductor integrated circuit device comprises: a plurality of lead frames having the terminals, respectively; a plurality of wire groups each consisting of two or more wires, wherein the wire groups are connected to each other at a single point on the respective lead frames; and a plurality of pad groups each consisting of two or more pads, wherein the pad groups are associated, respectively, with the terminals, and at least one of the pads making up of one of the pad groups is connected to the remaining pad groups, to define an inter-pad connection line. While each of the pad groups is separated from an associated one of the lead frames before a wire bonding process, it is connected to the associated lead frame using one of the wire groups which is connected to the associated lead frame, with relatively low impedance, through the wire bonding process. Although impedance in source and ground lines relative to functional blocks is not changed, the single point connection with the relatively low impedance makes it possible to suppress noise interference. After the wire bonding process, the terminals are connected to each other through an intra-chip wiring layer and the wires to prevent electrostatic breakdown between the terminals. 
     In contrast to the conventional device having the problem about lowering an electrostatic breakdown level in conjunction with suppressing noise interference, the semiconductor IC device of the present invention makes it possible to balance the protection against noise interference with the protection against electrostatic breakdown. 
     As above, the semiconductor IC device of the present invention can suppress noise interference while protecting against electrostatic breakdown, in a smaller surface area. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various characteristics and advantages of the present invention will become clear from the following description taken in conjunction with the preferred embodiments with reference to the accompanying drawings throughout which like parts are designated by like reference numerals, in which: 
         FIG. 1  is a block diagram of a semiconductor IC device according to a first embodiment of the present invention; 
         FIG. 2  is an explanatory diagram of a parasitic element in the semiconductor IC device according to the first embodiment; 
         FIG. 3  is a block diagram of a semiconductor IC device according to a second embodiment of the present invention; 
         FIG. 4  is a fragmentary block diagram showing one example of modification of the semiconductor IC device according to the second embodiment; 
         FIG. 5  is a schematic diagram showing the configuration of a semiconductor substrate of a semiconductor IC device according to a third embodiment of the present invention; 
         FIG. 6  is an explanatory diagram of a scheme of electrostatic breakdown protection in the semiconductor IC device according to the third embodiment; 
         FIG. 7  is a block diagram of the semiconductor IC device according to the third embodiment; 
         FIG. 8  is an explanatory diagram of one conventional technique of reducing noise interference; and 
         FIG. 9  is an explanatory diagram of another conventional technique of reducing noise interference, in the Publication 1. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to the drawings, various embodiments of the present invention will now be described. 
     First Embodiment 
     With reference to  FIGS. 1 and 2 , a first embodiment of the present invention will be described below. As shown in  FIG. 1 , a semiconductor IC device according to the first embodiment comprises a first lead frame  101 , and two block-dedicated pads  131 ,  132  which are associated, respectively, with a block A and a block B, and provided for connection between the first lead frame  101  and each of the blocks A, B. The block-dedicated pad  131  is connected to an intra-chip wire  111  connected to the block A, and further connected to a block-dedicated wire  121  for the block A, and an inter-lead-frame connection line  110  for interconnecting between the first lead frame  101  and other lead frame, such as an after-mentioned second lead frame  102 . The block-dedicated pad  132  is connected to an intra-chip wire  112  connected to the block B, and further connected to a block-dedicated wire  122  for the block B, and the inter-lead-frame connection line  110 . The semiconductor IC device further includes two electrostatic-breakdown protection diodes  140  associated, respectively, with the block A and the block B, a connection pad  133 , and a connection wire  123  connected to connection pad  133 . The block-dedicated wire,  121 , the block-dedicated wire  122  and the connection wire  123  are wire-boded onto the first lead frame  101  in such a manner as to be connected to each other at a single point on the first lead frame  101 . 
     Furthermore, the semiconductor IC device includes a second lead frame  102 , and two block-dedicated pads  135 ,  136  which are associated, respectively, with a block C and a block D, and provided for connection between the second lead frame  102  and each of the blocks C, D. The block-dedicated pad  135  is connected to an intra-chip wire  114  connected to the block C, and further connected to a block-dedicated wire  125  for the block C, and the inter-lead-frame connection line  110 . The block-dedicated pad  136  is connected to an intra-chip wire  115  connected to the block D, and further connected to a block-dedicated wire  126  for the block D, and the inter-lead-frame connection line  110 . The semiconductor IC device includes two electrostatic-breakdown protection diodes  140  associated, respectively, with the block C and the block D, a connection pad  134 , and a connection wire  124  connected to the connection pad  134 . The block-dedicated wire  125 , the block-dedicated wire  126  and the connection wire  124  are wire-boded onto the second lead frame  102  in such a manner as to be connected to each other at a single point on the second lead frame  102 . 
     In the semiconductor IC device illustrated in  FIG. 1 , the first lead frame  101  and each of the blocks A, B are not wired or electrically connected to each other by a wiring layer on a semiconductor substrate but through the use of the block-dedicated wires  121 ,  122  connected to the block-dedicated pads  131 ,  132 . In the same manner, the second lead frame  102  and each of the blocks C, D are not wired or electrically connected to each other by the wiring layer but through the use of the block-dedicated wires  125 ,  126  connected to the block-dedicated pads  135 ,  136 . In the first embodiment, instead of the two connection pads  133 ,  134 , a single pad  702  may be provided as shown in  FIG. 7 . 
     When the number of blocks connected to one lead frame is “n”, the number of pads is preferably “n+1”. However, if the number of blocks as a noise source is “m”, at least (m+1) isolated pads may be connected to one lead frame to efficiently isolate respective noises. 
     The one pad (“+1”) in the (n+1) pads is exclusively used as the connection pad ( 133  or  134 ) wired to the block-dedicated pads ( 131 ,  132 ; or  135 ,  136 ) of the first or second lead frame ( 101  or  102 ) for the purpose of protection against electrostatic breakdown. The inter-lead-frame connection line  110  which connects between a first group of the block-dedicated pads  131 ,  132  and the connection pad  133  associated with the first lead frame  101  and a second group of the block-dedicated pads  135 ,  136  and the connection pad  134  associated with the second lead frame  102  makes it possible to reliably ensure a noise reduction effect. If only (m+1) pads are minimally provided, and there is at least one block which is a non-noise source, a wire of the non-noise-source block can be used to serve as the inter-lead-frame connection line  110 . That is, in this case, if there are “m” noise-source blocks, a wire of one non-noise-source block can be used to serve as the inter-lead-frame connection line  110  so as to achieve the same function as that of the first embodiment only by (m+1) pads. Generally, when the semiconductor substrate is a p-type, and the lead frame has a ground terminal, a wire on the p-type substrate is preferably used to serve as the inter-lead-frame connection line  110 . Alternatively, the pad  702  as illustrated in  FIG. 7  may be used without using the inter-lead-frame connection line  110 . 
     In the first embodiment, the block-dedicated pads  131 ,  132  are connected onto the first lead frame  101  at a single point through the block-dedicated wires  121 ,  122 , and the block-dedicated pads  135 ,  136  are connected onto the second lead frame  102  at a single point through the block-dedicated wires  125 ,  126 , as described above. Thus, as shown the left side of  FIG. 2 , a parasitic inductance  201  is generated in each of the block-dedicated wires. Therefore, as shown in a capacitance  204  may be connected to each of the block-dedicated wires which is intended to be protected against noise interference, to form an LC low-pass filter so as to facilitate noise reduction. Alternatively, a capacitance  204  may be connected between two of the block-dedicated wires from the block-dedicated pads as a noise source, to form a #-type low-pass filter so as to obtain enhanced noise reduction effect as compared with the LC low-pass filter. 
     Further, as shown the right side of  FIG. 2 , a capacitance  205  may be connected to the inter-lead-frame connection line  110  for electrostatic breakdown protection, to form a T-type low-pass filter in combination with respective parasitic inductances of the connection wires  123 ,  124  so as to more effectively prevent noise interference between the first and second lead frames. 
     Second Embodiment 
     With reference to  FIG. 3 , a second embodiment of the present invention will be described below. In  FIG. 3 , the same component or element as that in the first embodiment illustrated in  FIG. 1  is defined by the same reference numeral or code, and its detailed description will be omitted. In the semiconductor IC device according to the first embodiment which is designed to connect the block-dedicated and connection wires to each other at a single point on the lead frame ( 101 ,  102 ) by a wire bonding process so as to reduce noise interference, the wire connections and the inter-lead-frame connection line  110  are effective in preventing electrostatic breakdown after the wire bonding process. However, the semiconductor IC device according to the first embodiment cannot prevent electrostatic breakdown during and before the wire bonding process. 
     In a semiconductor IC device according to the second embodiment, as shown in  FIG. 3 , an electrostatic-breakdown protection element  301  is connected to a block-dedicated pad  131  to prevent electrostatic breakdown during and before the wire bonding process. Further, as an electrostatic-breakdown protection element, an electrostatic-breakdown protection diode  302  is connected to a block-dedicated pad  132 , and an electrostatic-breakdown protection transistor  303  and an electrostatic-breakdown protection transistor  304  are connected, respectively, to a block-dedicated pad  135  and a block-dedicated pad  136 . Each of the electrostatic-breakdown protection elements is provided as a means for protection against electrostatic breakdown during and before the wire bonding process although they have no electrostatic-breakdown protection effect after the wire bonding process because the block-dedicated and connection pads ( 131 ,  132 ,  133 ;  134 ,  135 ,  136 ) are connected to each other by the block-dedicated and connection wires ( 121 ,  122 ,  123 ;  124 ,  125 ,  126 ), and equalized in potential. Alternatively, as shown in  FIG. 4 , an electrostatic-breakdown protection element  401  may be connected to each of the block-dedicated pads, and an electrostatic-breakdown protection line  402  may be provided, so as to maintain the electrostatic-breakdown protection effect even after the wire bonding process. 
     Third Embodiment 
     With reference to  FIGS. 5 to 7 , a third embodiment of the present invention will be described below. In  FIGS. 6 and 7 , the same component or element as that in the first embodiment illustrated in  FIG. 1  is defined by the same reference numeral or code, and its detailed description will be omitted. As compared with the first and second embodiments, a semiconductor IC device according to the third embodiment is deigned to more efficiently protect against electrostatic breakdown in more small surface area. 
     Specifically, as shown in  FIG. 5 , in the semiconductor IC device according to the third embodiment, a semiconductor substrate having a first conductivity type has a first well having a second conductivity type which is opposite to the first conductivity type, and a second well having the first conductivity type exists in the first well. Further, an electrostatic-breakdown protection element is connected between a source line and a ground line. The ground line is divided in the same manner as that in the first embodiment illustrated in  FIG. 1  to prevent noise interference. In this configuration, given that a lead frame has a ground terminal, and the first conductivity type and the second conductivity type are, respectively, a p-type and an n-type, a circuit is formed by an inter-source electrostatic-breakdown protection element  607  and a parasitic diode  605 , as shown in  FIG. 6 . Then, the electrostatic-protection breakdown diode  140  (see  FIG. 1 ) serving as an electrostatic-breakdown protection element can be simply connected between the inter-lead-frame ground line (i.e., inter-lead-frame connection line  110 ) and the isolated pad (i.e., pad  604 ) to obtain the layout as shown in  FIG. 1  so as to protect against electrostatic breakdown during and before the wire bonding process. 
     Given that the lead frame has a ground terminal, and the first conductivity type and the second conductivity type in  FIG. 5  are, respectively, an n-type and a p-type, a polarity of each electrostatic-breakdown protection diode to be connected may be set in the same manner as that of the diode  701  illustrated in  FIG. 7 . In  FIG. 6 , an n-type first well  602  exists in a p-type semiconductor substrate  601 , and a p-type second well  603  exists in the first well  602 . The second well  603  is connected to the pad  604 . 
     Given that the lead frame has a source terminal, and the first conductivity type and the second conductivity type in  FIG. 5  are, respectively, a p-type and an n-type, a polarity of each electrostatic-breakdown protection diode to be connected may be set in the same manner as that of the diode  701  as shown in  FIG. 7 . Otherwise if the first conductivity type and the second conductivity type in  FIG. 5  are, respectively, an n-type and a p-type, a polarity of each electrostatic-breakdown protection diode to be connected may be set in the same manner as that of the diode  140  as shown in  FIG. 1 . 
     As mentioned above, the semiconductor integrated circuit device is effective in reducing noise interference and preventing electrostatic breakdown, and suitable for use as a semiconductor integrated circuit. 
     Although the present invention has been fully described by way of example with reference to the accompanying drawings, it is to be understood that various changes and modifications will be apparent to those skilled in the art. Therefore, unless otherwise such changes and modifications depart from the scope of the present invention hereinafter defined, they should be construed as being included therein.