Patent Publication Number: US-2020294895-A1

Title: Semiconductor device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2019-044014, filed on Mar. 11, 2019; the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments relate to a semiconductor device. 
     BACKGROUND 
     There is a semiconductor device in which a semiconductor chip is mounted on a die pad and sealed in a resin package. Such a semiconductor device has a die pad shrinking in size corresponding to downsizing. When the die pad and the semiconductor chip are connected using a bonding member such as solder, the bonding member may extend around and cover an unintended portion of the die pad, thus, reducing air tightness of the resin package. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  are schematic views showing a semiconductor device according to a first embodiment; 
         FIGS. 2A to 2C  are schematic views showing a back surface of a semiconductor chip according to the first embodiment; 
         FIGS. 3A to 3C  are schematic views showing a manufacturing process of the semiconductor device according to the first embodiment; 
         FIGS. 4A and 4B  are schematic views showing a semiconductor device according to a second embodiment; and 
         FIGS. 5A to 5C  are schematic views showing a manufacturing process of the semiconductor device according to the second embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     According to one embodiment, a semiconductor device includes a die pad; a semiconductor chip mounted on a front surface of the die pad; a bonding layer placed between the die pad and the semiconductor chip; a first resin member being positioned between the bonding layer and the semiconductor chip; and a second resin member covering the semiconductor chip and the front surface of the die pad. The first resin member is provided along a periphery of the semiconductor chip. The bonding layer includes a first portion and a second portion. The first portion is positioned between the semiconductor chip and the die pad, and contacts the semiconductor chip. The second portion is positioned between the first resin member and the die pad. 
     Embodiments will now be described with reference to the drawings. The same portions inside the drawings are marked with the same numerals; a detailed description is omitted as appropriate; and the different portions are described. The drawings are schematic or conceptual; and the relationships between the thicknesses and widths of portions, the proportions of sizes between portions, etc., are not necessarily the same as the actual values thereof. The dimensions and/or the proportions may be illustrated differently between the drawings, even in the case where the same portion is illustrated. 
     There are cases where the dispositions of the components are described using the directions of XYZ axes shown in the drawings. The X-axis, the Y-axis, and the Z-axis are orthogonal to each other. Hereinbelow, the directions of the X-axis, the Y-axis, and the Z-axis are described as an X-direction, a Y-direction, and a Z-direction. Also, there are cases where the Z-direction is described as upward and the direction opposite to the Z-direction is described as downward. 
     First Embodiment 
       FIGS. 1A and 1B  are schematic views showing a semiconductor device  1  according to a first embodiment. FIG.  1 A is a perspective view showing an appearance of the semiconductor device  1 .  FIG. 1B  is a schematic view showing a cross section parallel to a Y-Z plane. The semiconductor device  1  includes, for example, a MOSFET. 
     As shown in  FIG. 1A , the semiconductor device  1  includes a resin package  10 , and lead terminals  13 ,  15  and  17 . The resin package  10  houses, for example, a semiconductor chip  20  (see  FIG. 1B ). The semiconductor chip  20  is, for example, a MOSFET chip. 
     The lead terminals  13 ,  15  and  17  are disposed, for example, so as to extend from one of side surfaces of the resin package  10 . The lead terminal  13  is connected to, for example, the drain of the semiconductor chip  20 , and the lead terminal  15  is connected to, for example, the source of the semiconductor chip  20 . The lead terminal  17  is connected to, for example, the gate of the semiconductor chip  20 . The lead terminals  13 ,  15  and  17  include, for example, copper or copper alloy. 
     As shown in  FIG. 1B , the semiconductor device  1  includes the semiconductor chip  20 , a resin member  25 , a die pad  30 , and a connector  15   M . The die pad  30  is, for example, a lead type die pad including copper or copper alloy, and the lead terminal  13  is a portion of the die pad  30  (see  FIG. 3A ). The lead terminal  13  may be electrically connected to the die pad  30  by a metal wire (not shown). The lead terminal  15  is a portion of the connector  15   M . 
     The semiconductor chip  20  is mounted on a front surface  30   F  of the die pad  30  via a bonding layer  33 . A bonding layer  33  is, for example, a solder layer. The bonding layer  33  contacts, for example, a back electrode of the semiconductor chip  20 , for example, a drain electrode (not shown), and electrically connects the semiconductor chip  20  and the die pad  30 . 
     The resin member  25  is provided on a back surface side of the semiconductor chip  20 . The resin member  25  is provided, for example, on the back electrode (the drain electrode) of the semiconductor chip  20 . The resin member  25  is positioned between the semiconductor chip  20  and a portion of the bonding layer  33 , and extends along a periphery of the semiconductor chip  20  (see  FIG. 2A ). 
     The connector  15   M  is electrically connected via a bonding layer  23  to a front electrode of the semiconductor chip, for example, a source electrode (not shown). The connector  15   M  is, for example, a metal plate including copper or cooper alloy. The bonding layer  23  is, for example, a solder layer. 
     The resin package  10  is provided to cover the semiconductor chip  20 , the die pad  30  and the connector  15   M . The resin package  10  includes, for example, epoxy resin and is formed by a vacuum molding method. 
     As shown in  FIG. 1B , the resin package  10  is provided to cover the front surface  30   F , a back surface  30   B  and a side surface  30   S  of the die pad  30 . The semiconductor chip  20  is connected to an external circuit via the lead terminals  13 ,  15  and  17  that extend from the resin package  10 . The lead terminal  17  is electrically connected to a gate pad (not shown) of the semiconductor chip  20  at a portion (not shown) in the resin package. 
     The embodiment is not limited to the above example. For example, there may be a configuration where the back surface  30   B  of the die pad  30  is exposed at the resin package  10  (see  FIG. 4A ), and the lead terminal  13  electrically connected to the die pad  30  is omitted. 
       FIGS. 2A to 2C  are schematic views showing the back surface  20   B  of the semiconductor chip  20  according to the first embodiment. The back surface  20   B  is, for example, a surface of the back electrode (the drain electrode). 
     As shown in  FIG. 2A , the resin member  25  is provided on a back surface  20   B  of the semiconductor chip  20 . The resin member  25  is provided, for example, in a line shape along the periphery of the semiconductor chip  20 . The resin member  25  is a member of one body extending continuously, and includes polyimide, for example. 
     The resin member  25  is formed in a predetermined shape by a photolithography after a resin film is formed on a back surface of the semiconductor wafer in a manufacturing process of the semiconductor chip  20 . 
     As show in  FIG. 2B , multiple resin members  27  are arranged on the back surface  20   B  of the semiconductor chip  20 . The resin members  27  may be provided in place of the resin member  25 . The resin members  27  are spaced from each other along the periphery of the semiconductor chip  20 . The resin members  27  include, for example, polyimide. The resin members  27  are formed, for example, using photolithography or a printing method. 
     As shown in  FIG. 2C , a cutout portion  25 S may be provided in the resin member  25 . The cutout portion  25 S is provided, for example, in a portion of the resin member  25  along at least one of four sides of the semiconductor chip  20  having the square shape. The resin member  25  may be formed, for example, by a printing method such as a screen printing. The resin member  25  in this example is suitable to be formed using a printing method. 
     A manufacturing method of the semiconductor device  1  will be described here with reference to  FIGS. 3A to 3C .  FIGS. 3A to 3C  are schematic views showing in order the manufacturing process of the semiconductor device  1  according to the first embodiment. 
     As shown in  FIG. 3A , a lead frame is prepared which includes a lead terminal  13  and a die pad  30 . The die pad  30  is provided in a plurality, and the plurality of die pads  30  are arranged, for example, in the X-direction and the Y-direction. The die pad  30  is linked to a frame body (not shown) via the lead terminal  13 . 
     As shown in  FIG. 3B , a bonding member  35  is provided in drops on the front surface  30   F  of the die pad  30 . The bonding member  35  is, for example, liquid solder paste. For example, a predetermined amount of bonding member  35  falls in drops from a movable nozzle  37  on each of the plurality of die pads  30 . 
     As shown in  FIG. 3C , the semiconductor chip  20  is mounted on the front surface  30   F  of the die pad  30  with the bonding member  35  interposed. The semiconductor chip  20  is mounted so that the back surface  20   B  on which the resin member  25  is provided faces the die pad  30 . Subsequently, heating the die pad  30  on which the semiconductor chip  20  is mounted is performed to convert the bonding member  35  to the bonding layer  33 . The die pad  30  is heated, for example, through a reflow process of solder. 
     The bonding member  35  spreads in a space between the semiconductor chip  20  and the die pad  30 , and contacts the back surface  20   B  of the semiconductor chip  20  and the front surface  30   F  of the die pad  30 . Moreover, a portion of the bonding member  35  tends to spread outside the space between the semiconductor chip  20  and the die pad  30 . 
     The resin member  25  includes, for example, a material having low affinity for the bonding member  35 . Thus, the resin member  25  prevents the bonding member  35  from spreading outside the space. For example, the resin member  25  prevents the bonding member  35  from spreading outside the space at the contact portion of the resin member  25  and the bonding member  35  by a surface tension of the bonding member  35 . 
     In the process shown in  FIG. 3C , the amount of the bonding member  35  falling from the movable nozzle  37  is controlled at a level of filling the space between the semiconductor chip  20  and the die pad  30  and spreading into a space between the resin member  25  and the die pad  30  (see  FIG. 1B ). Thereby, it is possible to prevent the bonding member  35  from spreading outside the space between the semiconductor chip  20  and the die pad  30 . 
     For example, in the case where the resin member  25  is not provided on the back surface  20   B  of the semiconductor chip  20 , when pressing force is applied to the semiconductor chip  20  toward the die pad  30  in order to form a uniform bonding layer between the semiconductor chi  20  and the die pad  30 , the space is narrowed between the semiconductor chip  20  and the die pad  30 . Thus, most of the bonding member  35  falling onto the die pad  30  is pushed out of the space between the semiconductor chip  20  and the die pad  30 . 
     The amount of the bonding member  35  pushed out of the space depends on a case, for example, how the semiconductor chip  20  and the die pad  30  are bonded, and is not always the same. When the amount of the bonding member  35  pushed out of the space is large, the bonding member  35  spreads, for example, along the front surface  30   F  of the die pad  30  through the process of heating the die pad  30 , and may cover the side surface  30   S  and the back surface  30   B  (see  FIG. 1 ). Thus, there may be a case, for example, where the electrodes disposed respectively on the front and back sides of the die pad  30  are short-circuited. Moreover, the adhesion strength may be reduced between the resin package  10  and the die pad  30 , thereby, making the air tightness of the resin package  10  to be lowered. When the falling amount of the bonding member  35  is decreased to avoid such a case, a void space may be generated between the semiconductor chip  20  and the die pad  30 , consequently reducing the reliability of the semiconductor device  1 . 
     In contrast, in the semiconductor device  1  according to the embodiment, as the resin member  25  is provided on the back surface  20   B  of the semiconductor chip  20 , it is possible to secure the predetermined space between the semiconductor chip  20  and the die pad  30 . Thereby, it is possible to hold a constant amount of bonding member  35  in the space between the semiconductor chip  20  and the die pad  30 . Accordingly, the bonding member  35  may be provided with at least an amount being held in the space between the semiconductor chip  20  and the die pad  30 . Thus, it is easy to control the falling amount of the bonding member  35  so that the void space is not generated between the semiconductor chip  20  and the die pad  30 , and the bonding member  35  is not spread over the die pad  30  into the side surface  30   S  and the back surface  30   B . In other words, it is possible to reduce the amount of the bonding member  35  pushed out the space between the semiconductor chip  20  and the die pad  30 . 
     Furthermore, the resin member  25  prevents the bonding member  35  from spreading through the heating process of the die pad  30  with the semiconductor chip  20  mounted. As a result, it is possible to prevent the bonding member  35  from spreading into the side surface  30   S  and the back surface  30   B  and to improve the reliability of the semiconductor device  1 . 
     In the case where the resin members  27  shown in  FIG. 2B  are used in place of the resin member  25 , it is preferable to make a space width between the adjacent resin members  27  so that the bonding member  35  cannot pass therethrough. In other words, it is preferable to set the space width to prevent the resin members  27  from spreading outside through the space between the adjacent resin members  27  due to the surface tension of the bonding member  35 . 
     Second Embodiment 
       FIGS. 4A and 4B  are schematic views showing a semiconductor device  2  according to a second embodiment.  FIG. 4A  is a schematic view showing a cross section parallel to the X-Z plane.  FIG. 4B  is a plan view showing a resin member  40  provided on the front surface of the die pad  30 . 
     As shown in  FIG. 4A , the semiconductor chip  20  is mounted on the die pad  30  with the bonding layer  33  interposed. Moreover, the connector  15   M  is bonded on the semiconductor chip  20  with the bonding layer  23  interposed. 
     In the embodiment, the resin member  40  is disposed on the front surface  30   F  of the die pad  30 . The resin package  10  is molded so that the back surface  30   B  of the die pad  30  is exposed. The embodiment is not limited to this example. For example, the resin package  10  may be formed so as to cover the whole surface of the die pad  30  (see  FIG. 1B ). 
     As shown in  FIG. 4B , the resin member  40  is, for example, provided with a line shape along the periphery of the die pad  30 . There may be a case where the resin member  40  is provided in a plurality along the periphery of the die pad  30  (see  FIG. 2B ). The resin member  40  is provided outside a region on which the semiconductor chip  20  is mounted, and is not placed between the semiconductor chip  20  and the die pad  30 . 
     A manufacturing method of the semiconductor device  2  will be described here with reference to  FIGS. 5A to 5C .  FIGS. 5A to 5C  are schematic views showing in order the manufacturing process of the semiconductor device  2  according to the second embodiment. 
     As shown in  FIG. 5A , the resin member  40  is formed on the front surface  30   F  of the die pad  30 . The resin member  40  is selectively formed, for example, using a printing method or an inkjet method. The resin member  40  is not formed on the region of the front surface  30   F  on which the semiconductor chip  20  is to be mounted. 
     As shown in  FIG. 5B , the bonding member  35  falls in drops on the front surface  30   F  of the die pad  30 . The bonding member  35  is, for example, liquid solder paste. The bonding member  35  falls on a region surrounded by the resin member  40 . 
     As shown in  FIG. 5C , the semiconductor chip  20  is mounted on the front surface  30   F  of the die pad  30  with the bonding member  35  interposed. Then, the die pad  30  on which the semiconductor chip  20  is mounted is heated to convert the bonding member  35  to the bonding layer  33 . 
     The resin member  40  serves as a blocking bank preventing the bonding member  35  from spreading over the front surface  30   F  of the die pad  30 . Thereby, it is possible to prevent the bonding member  35  from spreading over the die pad  30  into the side surface  30   S  and the back surface  30   B , and to improve the reliability of the semiconductor device  2 . 
     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 embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments 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 invention.