Patent Publication Number: US-2021166997-A1

Title: Semiconductor package using conductive metal structure

Description:
FIELD OF THE INVENTION 
     The present invention relates to a semiconductor package using a conductive metal structure, and more particularly, to a semiconductor package using a conductive metal structure formed in a clip or a column, through which a semiconductor chip and a lead of a lead frame are electrically connected to each other and an area where the semiconductor chip and the metal structure are adhered may be effectively improved so that productivity may increase and durability and electrical connection properties may be improved. 
     DESCRIPTION OF THE RELATED ART 
     In general, a semiconductor package includes a semiconductor chip, a lead frame (or a board), and a package body, wherein the semiconductor chip is attached on a pad of the lead frame and is electrically connected to a lead of the lead frame by bonding a metal wire. 
     However, in a stack package using a general metal wire, the metal wire is used to exchange electric signals so that speed is lowered and a large number of wires is used. Accordingly, deterioration on electrical properties may occur in each chip. Also, in order to form metal wires, an additional area is required in a board and thus, a size of a package is enlarged. In addition, gaps used to bond wires are required in bonding pads of each chip and thus, an entire height of a package unnecessarily increases. 
     Therefore, Korean Patent No. 1208332, Utility Model No. 0482370, Korean Patent No. 1669902, and Korean Patent No. 1631232 disclosed by the inventor of the present invention provide an efficient package structure showing excellent performances in electric connection, heat emission, and thermal stability by using a metal clip structure, compared with a semiconductor package using a general metal wire. 
     In particular, Korean Patent Application Pub. No. 10-2017-0086828 (a clip bonding semiconductor chip package using a metal bump) discloses that a metal bump is formed on and protrudes from a bonding pad of a semiconductor chip and a clip is joined to the metal bump. However, in such a case, processes such as melting, sputtering, electroplating, and screen printing are needed in forming of the metal bump on the bonding pad and thus, productivity is decreased. Also, since the metal bump is formed of copper (Cu) or gold (Au) that facilitates soldering, a bonding force between the metal bump and the bonding pad is decreased due to each different thermal expansion coefficient and an electric connection property is poor. 
     SUMMARY OF THE INVENTION 
     Technical Problem 
     The present invention provides a semiconductor package using a conductive metal structure in which a conductive metal structure is directly soldered on a metal pad formed on an upper part of a semiconductor chip, instead of using an additional metal material such as a general metal bump, wherein the metal pad is prepared to be used in bonding, so that production cost and manufacturing processes may be greatly reduced and a bonding force between a clip and the semiconductor chip may be increased. 
     Technical Solution 
     According to an aspect of the present invention, there is provided a semiconductor package using a conductive metal structure including: a semiconductor chip; an aluminum pad formed on an upper part of the semiconductor chip; and a conductive metal structure adhered to the aluminum pad by a solder-based second adhesive layer, wherein the second adhesive layer includes intermetallic compounds (IMC) distributed to a lower fixed part thereof near the aluminum pad. 
     The IMCs of the second adhesive layer may include aluminum (Al) and the aluminum (Al) may hold 0.5 to 30 parts by weight with respect to 100 parts by weight of the total IMCs. 
     When the second adhesive layer is soldered using a solder including tin and when parts by weight of the tin is above 80 parts by weight of the total weight of the solder, aluminum (Al) may hold 0.5 to 30 parts by weight with respect to 100 parts by weight of the total IMCs. 
     The IMCs may be dispersed and distributed within an area at a height of approximately 30 um based on a boundary surface of the aluminum pad. 
     When more than 5 parts by weight of aluminum (Al) is included in 100 parts by weight of the IMCs, the maximum height of the IMCs is 30 um 
     When the second adhesive layer is soldered using a solder including lead and when parts by weight of the lead is above 80 parts by weight of the total weight of the solder, aluminum (Al) may hold 0.5 to 30 parts by weight with respect to 100 parts by weight of the total IMCs. 
     The IMCs may be densely distributed within an area at a height of approximately 20 um based on a boundary surface of the aluminum pad. 
     When a thickness D of the aluminum pad, which is before being adhered to the second adhesive layer, is M1≤D≤M2, a thickness D1 of the aluminum pad, which is after being adhered to the second adhesive layer, may be 0≤D1≤(2/3)×M2. 
     The thickness D1 of the aluminum pad may be 0≤D1≤4 um. 
     The conductive metal structure may be a clip structure including one end combined to the aluminum pad. 
     The conductive metal structure may be a column structure including one end combined to the aluminum pad and the other end connected to a board. 
     The semiconductor package according to the present invention includes a lead frame, the semiconductor chip, the aluminum pad, the clip structure, and a sealing member, wherein the lead frame includes a pad and a lead, the semiconductor chip is adhered to the upper part of the pad included in the lead frame, the aluminum pad is formed on the upper part of the semiconductor chip, the clip structure includes one end combined to the aluminum pad and the other end combined to the lead of the lead frame, and the sealing member is formed to surround the semiconductor chip and the clip structure using molding. A solder or an epoxy resin based first adhesive layer is adhered to an adhering part of the lead frame and a solder-based second adhesive layer is directly adhered to an adhering part interposed between the clip structure and the aluminum pad, wherein the second adhesive layer includes IMCs distributed to a lower fixed part thereof near the aluminum pad. 
     Also, the semiconductor package according to the present invention includes the lead frame, a first semiconductor chip, a first aluminum pad, a first clip structure, a second semiconductor chip, a second aluminum pad, a second clip structure, and the sealing member, wherein the lead frame includes the pad and the lead, the first semiconductor chip is adhered to the upper part of the pad included in the lead frame, the first aluminum pad is formed on the upper part of the first semiconductor chip, the first clip structure includes one end combined to the first aluminum pad and the other end combined to the lead of the lead frame, the second semiconductor chip is adhered to the upper part of the first clip structure, the second aluminum pad is formed on the upper part of the second semiconductor chip, the second clip structure includes one end combined to the second aluminum pad and the other end combined to the lead of the lead frame, and the sealing member is formed to surround the first and second semiconductor chips and the first and second clip structures using molding. The solder or epoxy resin based first adhesive layer is respectively adhered to an adhering part of the lead frame and an adhering part interposed between the first clip structure and the second semiconductor chip. Also, the solder-based second adhesive layer is adhered to adhering parts interposed between the first and second aluminum pads and the first and second clip structures so that the first and second clip structures are directly adhered to the second adhesive layer. Here, the second adhesive layer includes the IMCs respectively distributed to lower fixed parts thereof near the first and second aluminum pads. 
     In addition, the semiconductor package according to the present invention includes a lower board and an upper board each having a metal pattern, the semiconductor chip, the aluminum pad, a first column structure, a second column structure, and the sealing member, wherein the lower board and the upper board are spaced apart from each other at a lower part and an upper part of the semiconductor package and face each other, the semiconductor chip is adhered to the upper part of the lower board, the aluminum pad is formed on the upper part of the semiconductor chip, the first column structure is adhered to the aluminum pad and is connected to the upper board, the second column structure is adhered to the metal pattern of the lower board and is connected to the metal pattern of the upper board, and the sealing member is formed to surround the semiconductor chip and the first and second column structures using molding. The solder or epoxy resin based first adhesive layer is adhered to an adhering part of the lower board, and the solder-based second adhesive layer is adhered to an adhering part interposed between the aluminum pad and the first column structure so that the first column structure is directly adhered to the second adhesive layer. Here, the second adhesive layer includes the IMCs distributed to a lower fixed part thereof near the aluminum pad. 
     According to the present invention, a clip or column type conductive metal structure is adhered to an aluminum pad formed on a semiconductor chip, a separate metal bump is not formed on an aluminum pad as in the conventional art, and the metal structure is directly soldered and adhered on the aluminum pad. Therefore, manufacturing processes may be reduced to increase productivity and a structural problem occurring due to use of the metal bump may be solved to improve durability and an electrical connection property. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
         FIG. 1  illustrates a semiconductor package according to a first embodiment of the present invention; 
         FIG. 2  illustrates a second adhesive layer of the present invention; 
         FIG. 3A  is an enlarged view showing distribution of intermetallic compounds (IMCs) when tin is a main ingredient of the second adhesive layer; 
         FIG. 3B  is an enlarged view showing that distribution of the IMCs when lead is a main ingredient of the second adhesive layer; 
         FIG. 4  illustrates that an aluminum metal layer is further formed on a lower part of a clip structure according to an embodiment of the present invention; 
         FIG. 5  illustrates a semiconductor package according to a second embodiment of the present invention; and 
         FIG. 6  illustrates a semiconductor package according to a third embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. In the description, the detailed descriptions of well-known technologies and structures may be omitted so as not to hinder the understanding of the present invention 
       FIG. 1  illustrates a semiconductor package according to a first embodiment of the present invention. As illustrated in  FIG. 1 , the semiconductor package includes a lead frame  100 , a semiconductor chip  200 , an aluminum pad  300 , a clip structure  400 , and a sealing member  500 , wherein the lead frame  100  includes a pad  110  and a lead  120 , the semiconductor chip  200  is adhered to the upper part of the pad  110  included in the lead frame  100 , the aluminum pad  300  is formed on the upper part of the semiconductor chip  200 , the clip structure  400  includes one end combined to the aluminum pad  300  and the other end combined to the lead  120  of the lead frame  100 , and the sealing member  500  is formed to surround the semiconductor chip  200  and the clip structure  400  using molding. 
     A solder or an epoxy resin based first adhesive layer  600  is adhered to an adhering part of the lead frame  100  and a solder-based second adhesive layer  700  is directly adhered to an adhering part interposed between the clip structure  400  and the aluminum pad  300 , wherein the second adhesive layer  700  includes intermetallic compounds (IMC)  710  distributed to a lower fixed part thereof near the aluminum pad  300 . 
     According to the present invention, a separate metal bump for adhering the aluminum pad  300  to the clip structure  400  is not included and instead, the clip structure  400  is directly soldered on the aluminum pad  300  and adhered to the aluminum pad  300 . Accordingly, productivity may be increased and a structural problem occurring due to use of the metal bump may be solved. 
     The first embodiment above illustrates that one clip structure  400  is adhered. The clip structure  400  is connected to the lead  120  disposed at one end thereof and the lead  120  disposed at the other side of the clip structure  400  is electrically connected to the aluminum pad  300  using a bonding wire B-W. 
     The lead frame  100  of the first embodiment includes the pad  110 , on which the semiconductor chip  200  is placed, and the lead  120  electrically connected to the semiconductor chip  200 . Here, the lead frame  100  may be changed into a board having a metal pattern as illustrated in a third embodiment which will be described below. 
     The aluminum pad  300  is formed on the upper part of the semiconductor chip  200 . Since the semiconductor chip  200  is formed for wire bonding, the clip structure  400  may not be directly adhered to the semiconductor chip  200  and thus, the aluminum pad  300  is formed to have a regular thickness. Here, aluminum does not hold the entire weight of the aluminum pad  300  and impurities may be unavoidably contained in the aluminum pad  300 . Thus, it may be appropriate that aluminum holds over 95 parts by weight of the entire aluminum pad  300 . In order for the aluminum pad  300  of the present invention to form the optimized IMCs  710 , the aluminum pad  300  may have a thickness of 1 to 6 μm 
     The thickness of the aluminum pad  300  denotes a thickness before the clip structure  400  being adhered to the aluminum  300 . 
     After soldering of the second adhesive layer  700 , the aluminum pad  300  is melted and diffused to the IMCs  710  and thus, the thickness of the aluminum pad  300  may be reduced to 0 to 4 μm. 
     The thickness of the aluminum pad  300  will be described in more detail below. 
     It is assumed that an initial thickness of the aluminum pad  300 , which is before soldering, is D and a thickness changed after soldering is D1. 
     When the thickness D is in the range of M1≤D≤M2 and the thickness D1 is in the range of 0≤D1≤(2/3)×M2, it is discovered that soldering is efficiently accomplished. 
     Here, 0 denotes that the aluminum pad  300  is completely melted and (2/3)×M2 denotes a maximum soluble range when the thickness of the aluminum pad  300  is the thickest in the corresponding range. 
     Accordingly, as described above, when the range of the thickness D is 1≤D≤6, the range of the thickness D1 is 0≤D1≤4. 
     Therefore, when the thicknesses D and D1 of the aluminum pad  300  are in the above ranges, outstanding effect may be achieved in the present invention. 
     The clip structure  400  is a metal structure used to electrically connect the semiconductor chip  200  to the lead  120  of the lead frame  100  and is formed of a single metal such as copper (Cu) as a main ingredient or a metal mixture formed by partly mixing impurities added to change a property of copper (Cu) such as silicon (Si), nickel (Ni), phosphorus (P), zinc (Zn), iron (Fe), lead (Pb), manganese (Mn), tin (Sn), and chrome (Cr) to copper (cu). 
     An adhesive layer of the present invention may be formed in 2 types. That is, the first adhesive layer  600  is applied to an adhering part of the lead frame  100  and the second adhesive layer  700  is applied to adhering parts of the aluminum pad  300  and the clip structure  400 . The first adhesive layer  600  may be formed of a solder or epoxy resin based conductive adhesive and a type of the adhesive is not restricted if electrical connection is available. 
     However, the second adhesive layer  700  may be formed of a solder-based adhesive only. An epoxy resin based conductive adhesive may not be used in the second adhesive layer  700 , since the IMCs  710  may not be produced during an adhering process. Accordingly, the IMCs  710  illustrated in  FIGS. 2 through 3  are only formed in the second adhesive layer  700 . 
     The IMCs  710  are distributed to a lower fixed part corresponding to a part X near the aluminum pad  300  within the second adhesive layer  700  and are manufactured by an interface reaction between a metal material separated after melting a part of the aluminum pad  300  at above a specific temperature and metal components included in a solder. The IMCs  710  may partly include materials corresponding to the metal components included in a solder. However, according to the present invention, the IMCs  710  include a certain amount of an aluminum (Al) component. 
     Since the IMCs  710  including aluminum (Al) distributed to the second adhesive layer  700  have metallic characteristics similar to those of the aluminum pad  300 , a structural stress occurring due to a thermal expansion coefficient may be reduced, and durability and an electrical connection property may be improved. 
     The inventor identifies that when the aluminum pad  300  and the clip structure  400  are adhered to each other by soldering, when the second adhesive layer  700  is soldered using a solder including tin, and when parts by weight of the tin is above 80 parts by weight of the total weight of the solder, aluminum (Al) holds 0.5 to 30 parts by weight with respect to 100 parts by weight of the total IMCs  710 . Here, the IMCs  710  are dispersed and distributed within an area at a height of approximately 30 um based on a boundary surface of the aluminum pad  300 . In particular, when more than 5 parts by weight of aluminum (Al) is included in the IMCs  710 , the maximum height of the IMCs  710  is 30 um or below so that the IMCs  710  may be appropriately balanced and distributed and a bonding force is excellent. 
     Also, the inventor identifies that when the aluminum pad  300  and the clip structure  400  are adhered to each other by soldering, when the second adhesive layer  700  is soldered using a solder including lead, and when parts by weight of the lead is above 80 parts by weight of the total weight of the solder, aluminum (Al) holds 0.5 to 30 parts by weight with respect to 100 parts by weight of the total IMCs  710 . Here, as illustrated in  FIG. 3B , the IMCs  710  are densely distributed within an area at a height of approximately 20 um based on a boundary surface of the aluminum pad  300 . 
     When a main component of a soldering adhesive varies or a content ratio of the soldering adhesive varies, the ratio of aluminum (Al) in the IMCs  710  may be 0.5 to 30 parts by weight with respect to 100 parts by weight of the total IMCs  710 . However, when the ratio of aluminum (Al) in the IMCs  710  is below 0.5 parts by weight, effect regarding an adhering property may not be properly shown, and when the ratio of aluminum (Al) in the IMCs  710  is above 30 parts by weight, hardness of an adhering part lowers by an excessive aluminum (Al) component and a bonding force rather decreases. 
     In the present invention, in order to form the aluminum (Al) component of the IMCs  710 , the second adhesive layer  700  may further include a melting facilitator so that soldering may be smoothly accomplished. Examples of the melting facilitator may include a certain amount of stibium (Sb), wherein the stibium (Sb) effectively melts the aluminum pad  300  under the soldering condition of 200 to 300° C. so that an aluminum (Al) component may be included in the IMCs  710 . 
     Since a general adhesive does not include such a melting facilitator and thus, melting of a bonding pad formed of aluminum (Al) is not smoothly accomplished, metal bumps formed of metals such as Ag, Au, or Pb are included to perform soldering. Accordingly, in the present invention, the second adhesive layer  700  further includes a melting facilitator used to facilitate melting of the aluminum pad  300  so that the clip structure  400  may be directly adhered to the aluminum pad  300  without using additional metal bumps and a bonding property may be improved by aluminum included in the IMCs  710 . 
     In addition,  FIG. 4  illustrates the clip structure  400  according to another embodiment of the present invention, wherein the clip structure  400  formed of copper (Cu) further includes an aluminum metal layer  450  on a lower part thereof, that is, a part contacting the second adhesive layer  700  and thus, has the same metallic characteristic as that of the aluminum pad  300 . Therefore, a bonding force may be increased. 
       FIG. 5  illustrates a semiconductor package according to a second embodiment of the present invention, wherein two semiconductor chips and two clip structures are stacked. More specifically, the semiconductor package according to the second embodiment of the present invention includes the lead frame  100 , a first semiconductor chip  210 , a first aluminum pad  310 , a first clip structure  410 , a second semiconductor chip  220 , a second aluminum pad  320 , a second clip structure  420 , and the sealing member  500 , wherein the lead frame  100  includes the pad  110  and the lead  120 , the first semiconductor chip  210  is adhered to the upper part of the pad  110  included in the lead frame  100 , the first aluminum pad  310  is formed on the upper part of the first semiconductor chip  210 , the first clip structure  410  includes one end combined to the first aluminum pad  310  and the other end combined to the lead  120  of the lead frame  100 , the second semiconductor chip  220  is adhered to the upper part of the first clip structure  410 , the second aluminum pad  320  is formed on the upper part of the second semiconductor chip  220 , the second clip structure  420  includes one end combined to the second aluminum pad  320  and the other end combined to the lead  120  of the lead frame  100 , and the sealing member  500  is formed to surround the first and second semiconductor chips  210  and  220  and the first and second clip structures  410  and  420  using molding. 
     The solder or epoxy resin based first adhesive layer  600  is respectively adhered to an adhering part of the lead frame  100  and an adhering part interposed between the first clip structure  410  and the second semiconductor chip  220 . Also, the solder-based second adhesive layer  700  is adhered to adhering parts interposed between the first and second aluminum pads  310  and  320  and the first and second clip structures  410  and  420  so that the first and second clip structures  410  and  420  are directly adhered to the second adhesive layer  700 . Here, the second adhesive layer  700  includes the IMCs  710  respectively distributed to lower fixed parts thereof near the first and second aluminum pads  310  and  320 . 
     Similar to the first embodiment, the IMCs  710  of the second adhesive layer  700  in the second embodiment include aluminum (Al). Characteristics of the second adhesive layer  700  illustrated in the first and second embodiments are the same as those of the second adhesive layer  700  in a third embodiment, which will be described later. Also, characteristics regarding a thickness of the aluminum pad  300  are applied in common in the second and third embodiments and thus, repetitive descriptions will be omitted. 
       FIG. 6  illustrates a semiconductor package according to a third embodiment of the present invention, wherein electrical connection is accomplished through a column type metal structure, instead of the clip type metal structure. More specifically, the semiconductor package according to the third embodiment of the present invention includes a lower board  150  and an upper board  160  each having a metal pattern, the semiconductor chip  200 , the aluminum pad  300 , a first column structure  410   a , a second column structure  420   a , and the sealing member  500 , wherein the lower board  150  and the upper board  160  are spaced apart from each other at a lower part and an upper part of the semiconductor package and face each other, the semiconductor chip  200  is adhered to the upper part of the lower board  150 , the aluminum pad  300  is formed on the upper part of the semiconductor chip  200 , the first column structure  410   a  is adhered to the aluminum pad  300  and is connected to the upper board  160 , the second column structure  420   a  is adhered to the metal pattern of the lower board  150  and is connected to the metal pattern of the upper board  160 , and the sealing member  500  is formed to surround the semiconductor chip  200  and the first and second column structures  410   a  and  420   a  using molding. 
     The solder or epoxy resin based first adhesive layer  600  is adhered to an adhering part of the lower board  150 , and the solder-based second adhesive layer  700  is adhered to an adhering part interposed between the aluminum pad  300  and the first column structure  410   a  so that the first column structure  410   a  is directly adhered to the second adhesive layer  700 . Here, the second adhesive layer  700  includes the IMCs  710  distributed to a lower fixed part thereof near the aluminum pad  300 . 
     The first and second column structures  410   a  and  420   a  may be formed of a metal including copper (Cu) as a main component, as in the same manner as in the clip structure  400  of the first and second embodiments described above. However, as illustrated in the drawing, the first column structure  410   a , where the second adhesive layer  700  is applied, may include the aluminum metal layer  450  on the lower part thereof and a copper layer on the upper part thereof. Thus, the first column structure  410   a  may be formed of a metal combination including each different metal. Since the first column structure  410   a  is formed as described above, a metallic characteristic of the aluminum layer  450  of the first column structure  410   a  is same as that of the aluminum pad  300  disposed at the lower part of the aluminum layer  450  and thus, a bonding force may be increased. 
     While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.