Patent Publication Number: US-2015069593-A1

Title: Semiconductor device and method of manufacturing same

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2013-189548, filed on Sep. 12, 2013, the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate to a semiconductor device and a method of manufacturing the same. 
     BACKGROUND 
     In a pressed lead frame including a chip mounting portion and a lead portion, the chip mounting portion to be mounted with a semiconductor chip is shifted upward from the lead portion in order to provide a space to be filled with a molding resin on the rear face side of the semiconductor chip. Such a structure is formed by bending (pressing) a metal plate to serve as the lead frame. The pressed lead frame therefore has to include a region used to bend the lead frame, in addition to regions corresponding to the chip mounting portion and the lead portion. Accordingly, the size of the semiconductor chip that can be mounted is limited in the pressed lead frame. It is therefore difficult to improve the chip mounting capability of the lead frame. In addition, the lead frame has to be made larger in order to mount a large-size semiconductor chip. This requirement leads to an increase in material costs. 
     An etched lead frame has been proposed as an alternative to the pressed lead frame. The etched lead frame is formed by etching a metal plate. In the etched lead frame, the thickness of a chip mounting portion is smaller than the thickness of a lead portion. Therefore, a space to be filled with a molding resin is present on the rear face side of a semiconductor chip. Accordingly, the etched lead frame need not have a region used to bend the lead frame. Consequently, the etched lead frame is not restricted in size of the semiconductor chip that can be mounted, and therefore has a high chip mounting capability. 
     However, since the etched lead frame requires an etching process, the etched lead frame is expensive compared with the pressed lead frame. In addition, it is difficult to uniformly heat the etched lead frame in a case where heat is applied to the etched lead frame in order to mount the semiconductor chip, since the thickness of the etched lead frame is not uniform. Accordingly, a temperature difference arises in the etched lead frame, and therefore warpage may be generated in the etched lead frame. The semiconductor chip mounted on the chip mounting portion may be broken due to this warpage, causing a failure in a semiconductor device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  are drawings of a semiconductor device of a first embodiment; 
         FIGS. 2A and 2B  are drawings of a lead frame of the first embodiment; 
         FIG. 3  is a flowchart showing a method of manufacturing the semiconductor device of the first embodiment; 
         FIG. 4  is a drawing illustrating a cross section of a semiconductor device of a modified example of the first embodiment; and 
         FIGS. 5A and 5B  are drawings of semiconductor devices of a second embodiment and its modified example. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments will now be explained with reference to the accompanying drawings. The present invention is not limited to these embodiments. Common components are denoted by common reference numerals throughout the drawings and will not be discussed again. The drawings are schematic views used to facilitate the description and understanding of the invention, and may therefore differ in shape, dimension, ratio and the like in some places from actual devices. Design changes can be made to these devices as appropriate by taking into consideration the following description and known technology. In the following embodiments, a vertical direction of a semiconductor device, a semiconductor chip and the like indicates a relative direction when a surface of the semiconductor chip where semiconductor elements are arranged is faced up, and may therefore differ from a vertical direction based on gravitational acceleration in some cases. Also, expressions such as “same”, “uniform” and “planar” used for thicknesses, shapes and the like not only mean that they are mathematically (geometrically) identical, but also signify that they include those degrees of difference, roughness and the like which are industrially acceptable in a process of manufacturing semiconductor devices. 
     In one embodiment, a semiconductor device includes a lead frame including a chip mounting portion and a lead portion separated from the chip mounting portion and having the same thickness as the chip mounting portion, a level of an upper face of the chip mounting portion being same as a level of an upper face of the lead portion. The device further includes a semiconductor chip mounted on the upper face of the chip mounting portion and electrically connected to the lead portion. The device further includes a molding resin which collectively seals up the lead frame and the semiconductor chip. The device further includes a metal film covering parts of rear faces of the chip mounting portion and the lead portion. 
     First Embodiment 
     (1) Semiconductor Device 
       FIGS. 1A and 1B  are drawings of a semiconductor device  10  of a first embodiment. 
       FIG. 1A  illustrates a cross section of the semiconductor device  10 , and  FIG. 1B  illustrates a rear face of the semiconductor device  10 . The semiconductor device  10  of the first embodiment will be described with reference to  FIGS. 1A and 1B . 
     The semiconductor device  10  of the first embodiment includes a lead frame  11 , a semiconductor chip  12 , a wire  13 , and a molding resin  14 . The lead frame  11  includes a chip mounting portion  111  and a lead portion  121  separated from the chip mounting portion  111 . The semiconductor chip  12  is mounted on an upper face of the chip mounting portion  111 . An electrode arranged on an upper face of the semiconductor chip  12  is electrically connected to an upper face of the lead portion  121  via the wire  13 . In addition, the molding resin  14  collectively seals up the lead frame  11 , the semiconductor chip  12 , and the wire  13 . 
     The respective leading ends of the chip mounting portion  111  and the lead portion  121  protrude from the molding resin  14 . A metal film  15  is formed on these protruding portions. In addition, as illustrated in  FIG. 1B , parts of rear faces of the chip mounting portion  111  and the lead portion  121  are exposed out of the molding resin  14  also on the rear face of the semiconductor device  10 . A metal film  15  is also formed on these exposed portions. 
     (2) Lead Frame 
       FIGS. 2A and 2B  are drawings of the lead frame  11  of the first embodiment. 
       FIG. 2A  illustrates a cross section of the lead frame  11 , and  FIG. 2B  illustrates the upper face of the lead frame  11 . The lead frame  11  of the first embodiment will be described with reference to  FIGS. 2A and 2B . Note however that a lead frame actually used in a manufacturing process is a continuous chain of the lead frames  11  illustrated in  FIGS. 2A and 2B . 
     As described earlier, the lead frame  11  includes the chip mounting portion  111  and the lead portion  121  separated from the chip mounting portion  111 . In addition, as illustrated in  FIG. 2A , the chip mounting portion  111  and the lead portion  121  have the same thickness, and no steps are present between the chip mounting portion  111  and the lead portion  121 . In other words, the lead frame  11  has a uniform thickness, and a level of the upper face of the chip mounting portion  111  is same as a level of the upper face of the lead portion  121 . Accordingly, the lead frame  11  can be inexpensively manufactured without the need for an etching process and a bending process (pressing process). 
     (3) Method of Manufacturing Semiconductor Device 
       FIG. 3  is a flowchart showing a method of manufacturing the semiconductor device  10  of the first embodiment. The method of manufacturing the semiconductor device  10  will be described with reference to  FIG. 3 . 
     In step S 1 , the semiconductor chip  12  is mounted on the upper face of the chip mounting portion  111  of the lead frame  11 . At this time, heat is applied to the lead frame  11 . Since the heat can be uniformly applied to the lead frame  11  having a uniform thickness, a temperature difference is less likely to arise in the lead frame  11 . Accordingly, it is possible to avoid the warpage of the lead frame  11  due to the temperature difference and the breakage of the semiconductor chip  12  due to the warpage. 
     In step S 2 , the wire  13  for electrically connecting the electrode and the lead portion  121  is bonded to the electrode arranged on the upper face of the semiconductor chip  12  and to the upper face of the lead portion  121 . 
     In step S 3 , the lead frame  11 , the semiconductor chip  12 , and the wire  13  are collectively sealed up with the molding resin  14 . A sealing process is carried out by injecting the molding resin  14  into a metal mold including the lead frame  11 . At this time, the sealing is performed by using the metal mold so as to expose the parts of the rear faces of the chip mounting portion  111  and the lead portion  121  out of the molding resin  14 . It is possible, by sealing up the semiconductor device by using the metal mold, to cover the rear face of the semiconductor chip  12  with the molding resin  14 , while exposing the parts of the rear faces of the chip mounting portion  111  and the lead portion  121  of the lead frame  11  out of the molding resin  14 , even when the lead frame  11  which is neither bent (pressed) nor etched and has a uniform thickness is used. 
     In step  4 , the metal film  15  is formed on the parts of the chip mounting portion  111  and the lead portion  121  exposed out of the molding resin. 
     In step  5 , a plurality of semiconductor devices  10  coupled by the lead frame  11  is uncoupled (divided into individual pieces). 
     In the lead frame  11  of the first embodiment, the chip mounting portion  111  and the lead portion  121  have the same thickness, no steps are present between the chip mounting portion  111  and the lead portion  121 , and the level of the upper face of the chip mounting portion  111  is same as the level of the upper face of the lead portion  121 . In a pressed lead frame, a bent region where a semiconductor chip cannot be mounted is present between a chip mounting portion and a lead portion. However, such a region is not present in the lead frame  11  of the first embodiment. It is therefore possible to mount a large-size semiconductor chip by the use of the lead frame  11 , and thereby improve the chip mounting capability of the semiconductor device. In addition, the lead frame  11  can be manufactured inexpensively without the need for etching and bending processes. Even in a case where such a lead frame  11  is used to perform the sealing, the rear face of the semiconductor chip  12  can be covered with the molding resin  14  while exposing the parts of the rear faces of the chip mounting portion  111  and the lead portion  121  out of the molding resin  14 , by performing the sealing using the metal mold. 
     According to the first embodiment, the lead frame  11  has a uniform thickness. Therefore, heat is uniformly applied to the lead frame  11  when the lead frame  11  is heated, and a temperature difference is less likely to arise in the lead frame  11 . Consequently, it is possible to avoid the warpage of the lead frame  11  due to the temperature difference. The semiconductor chip  12  therefore does not become broken due to the warpage. That is, it is possible to avoid the failure of the semiconductor device  10  due to the breakage of the semiconductor chip  12 . 
       FIG. 4  is a drawing illustrating a cross section of a semiconductor device  20  of a modified example of the first embodiment. 
     The semiconductor device  20  includes solder balls  16  which are formed on the rear face side of the semiconductor device  20  and are in contact with the metal film  15 . The semiconductor device  20  differs from the semiconductor device  10  of the first embodiment in this regard. When the semiconductor device  20  is mounted on an application substrate, the semiconductor device  20  is electrically connected to the application substrate via the solder balls  16 . At this time, since the electrical connection can be made by the solder balls  16  located immediately under the semiconductor device  20 , it is possible to reduce the area of a region (foot pattern) on the application substrate to be mounted with the semiconductor device  20 , compared with a case in which the electrical connection is made by terminals located on a lateral side of the semiconductor device. 
     Second Embodiment 
     (1) Semiconductor Device 
       FIGS. 5A and 5B  are drawings of semiconductor devices  30  and  40  of a second embodiment and its modified example. 
     The method of mounting the semiconductor chip  12  of the second embodiment differs from that of the first embodiment.  FIG. 5A  illustrates a cross section of the semiconductor device  30  of the second embodiment. The second embodiment will be described using  FIG. 5A . 
     Similarly to the first embodiment, the semiconductor device  30  of the second embodiment includes the semiconductor chip  12 , the wire  13  and the molding resin  14 . In addition, the semiconductor device  30  includes the lead frame  11  having the same structure as that of the lead frame  11  in the first embodiment. Unlike the first embodiment, however, the semiconductor chip  12  is mounted so as to extend over the upper faces of the chip mounting portion  111  and the lead portion  121 . That is, the semiconductor chip  12  is mounted on both the chip mounting portion  111  and the lead portion  121 . The semiconductor chip  12  is mounted on the chip mounting portion  111  and the lead portion  121  via an insulating adhesive material  37 . The insulating adhesive material  37  is, for example, an insulating die attach film (DAF), an adhesive agent, or paste. 
     According to the second embodiment, the chip mounting portion  111  and the lead portion  121  of the lead frame  11  have the same thickness as similar to the first embodiment. In addition, no steps are present between the chip mounting portion  111  and the lead portion  121 , and therefore the level of the upper face of the chip mounting portion  111  is same as the level of the upper face of the lead portion  121 . Accordingly, it is easy to mount the semiconductor chip  12  so as to extend over the upper faces of the chip mounting portion  111  and the lead portion  121 . As a result, it is possible to mount the semiconductor chip  12  wider in area than the chip mounting portion  111  without having to make the lead frame  11  larger. That is, it is possible to further improve the chip mounting capability of the semiconductor device. 
     In addition, since the second embodiment uses the same lead frame  11  as that of the first embodiment, it is possible to obtain the same advantageous effects as those of the first embodiment. 
     The semiconductor device  30  of the second embodiment can be formed by mounting the semiconductor chip  12  so as to extend over the upper faces of the chip mounting portion  111  and the lead portion  121  in the manufacturing method of the first embodiment. 
       FIG. 5B  illustrates a cross section of the semiconductor device  40  of the modified example of the second embodiment. In this semiconductor device  40  of the modified example, the semiconductor chip  12  is connected to the chip mounting portion  111  and the lead portion  121  via metal bumps  48 . In this modified example, electrodes (for example, through silicon via (TSV) electrodes) are arranged on the rear face of the semiconductor chip  12 , and these electrodes are electrically connected to the chip mounting portion  111  and the lead portion  121  via the metal bumps  48 . As a result, it is possible to keep the thickness of the semiconductor device  40  smaller, compared with the electrical connection using the wire  13 . 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel devices and methods described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the devices and methods described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.