Abstract:
Provided is an adhesive tape which adheres two members to each other and decreases problems that may occur due to contraction and expansion of the adhered members when the temperature of the adhered two members changes. The adhesive tape includes: a base film having insulating properties; and an adhesive agent that adheres on both sides of the base film, wherein a coefficient of thermal expansion of the base film is 10 ppm or lower, a coefficient of thermal expansion of the adhesive tape is lower than 17 ppm, and an occupation rate of the base film in the adhesive tape exceeds 50%.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
     This application claims priority from Korean Patent Application No. 10-2009-0006015, filed on Jan. 23, 2009, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Apparatuses consistent with the present invention relate to an adhesive tape, and more particularly, to an adhesive tape used in a semiconductor package, and a semiconductor package that uses the adhesive tape. 
     2. Description of the Related Art 
     Use of semiconductor packages having detailed and various control functions is remarkably increasing according to the development of the electronic and communication industries. Accordingly, the size of the semiconductor packages is decreasing whereas data processing capacity is increasing, resulting in semiconductor packages that are less expensive and more convenient to use. As such, various research and studies are being performed in order to improve the characteristics of the semiconductor packages. 
     Despite such research and studies, improvement of the characteristics of the semiconductor packages is still limited, and thus, a semiconductor chip package having a new structure, such as a lead-on-chip semiconductor package, has been developed. 
     The lead-on-chip semiconductor package has a structure where a semiconductor chip is directly mounted on a lead by using an adhesive tape. By using such a lead-on-chip semiconductor package, the size of the semiconductor chip included in the lead-on-chip semiconductor package may be increased, and a lead frame may be freely designed. 
     SUMMARY OF THE INVENTION 
     The present invention provides an adhesive tape that adheres two members to each other and decreases problems that may occur due to contraction/expansion of the two members when the temperature of the adhered two members changes. 
     The present invention also provides a semiconductor package that uses the adhesive tape. 
     According to an aspect of the present invention, there is provided an adhesive tape, which adheres two members to each other, the adhesive tape including: a base film having insulating properties; and an adhesive agent that adheres on both sides of the base film, wherein a coefficient of thermal expansion of the base film is 10 ppm or lower, a coefficient of thermal expansion of the adhesive tape is lower than 17 ppm, and an occupation rate of the base film in the adhesive tape exceeds 50%. 
     According to another aspect of the present invention, there is provided a semiconductor package including: a semiconductor chip that controls operations of a certain apparatus; a plurality of leads electrically connecting the semiconductor chip and the certain apparatus; a plurality of bonding wires electrically connecting the plurality of leads and the semiconductor chip; adhesive tapes mutually adhering the plurality of leads and the semiconductor chip; and a molding resin entirely sealing the semiconductor chip and the plurality of bonding wires, and the adhesive tapes and partially sealing the plurality of leads, wherein each of the adhesive tapes includes a base film having insulating properties and an adhesive agent adhered to both sides of the base film, a coefficient of thermal expansion each of the adhesive tapes is lower than 17 ppm, and an occupation rate of the base film in the adhesive tape exceeds 50%. 
    
    
     
       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  is a lateral cross-sectional view illustrating a semiconductor package, according to an embodiment of the present invention; 
         FIG. 2  is a perspective view partially illustrating a semiconductor chip, a plurality of adhesive tapes, and a plurality of leads illustrated in  FIG. 1 ; 
         FIG. 3  is a perspective view illustrating one of the plurality of adhesive tapes illustrated in  FIG. 1 ; 
         FIGS. 4A through 4C  are diagrams illustrating states when the semiconductor chip, the adhesive tape, and the lead illustrated in  FIG. 2  contract and expand according to temperature; 
         FIG. 5  is a diagram for calculating a coefficient of thermal expansion of the adhesive tape of  FIGS. 3 ; and 
         FIG. 6  is a graph showing a thermal expansion coefficient of the adhesive tape of  FIG. 2  according to a thermal expansion coefficient, modulus, and thickness of a base film illustrated in  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Hereinafter, the present invention will be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. In the drawings, like reference numerals denote like elements. 
       FIG. 1  is a lateral cross-sectional view illustrating a semiconductor package  101 , according to an exemplary embodiment.  FIG. 2  is a perspective view partially illustrating a semiconductor chip  111 , a plurality of adhesive tapes  121 , and a plurality of leads  131  illustrated in  FIG. 1 . Referring to  FIGS. 1 and 2 , the semiconductor package  101  includes the semiconductor chip  111  that controls operations of an external apparatus, the plurality of leads  131  electrically connecting the semiconductor chip  111  and the external apparatus, a plurality of bonding wires  141  electrically connecting the plurality of leads  131  and the semiconductor chip  111 , the plurality of adhesive tapes  121  mutually adhering the plurality of leads  131  and the semiconductor chip  111  to each other, and a molding resin  151  entirely sealing the semiconductor chip  111  and the plurality of bonding wires  141  and the plurality of adhesive tapes  121  and partially sealing the plurality of leads  131 . 
     As illustrated in  FIG. 1 , the semiconductor package  101  that has a structure where the leads  131  are attached on the semiconductor chip  111  is called a lead-on-chip (LOC) semiconductor package, and the adhesive tapes  121  may be used in such a LOC semiconductor package  101 . 
     When the number of leads  131  is small, the number of adhesive tapes  121  may be one. 
       FIG. 3  is a perspective view illustrating one of the adhesive tapes  121  illustrated in  FIG. 1 . Referring to  FIG. 3 , the adhesive tape  121  includes a base film  321  and adhesive agents  311  and  331  adhered on both sides of the base film  321 . The base film  321  may be formed of a polyimide film that is an insulating material. 
     A coefficient of thermal expansion of the adhesive tape  121  is set to be similar to coefficients of thermal expansion of the semiconductor chip  111  and the lead  131  of  FIG. 1 . For example, when the coefficients of thermal expansion of the semiconductor chip  111  and the lead  131  are respectively 3 ppm and 5 ppm, the coefficient of thermal expansion of the adhesive tape  121  is set to be lower than 17 ppm. All objects having a low coefficient of thermal expansion have a low displacement according to temperature. Accordingly, the coefficients of thermal expansion of the semiconductor chip  111 , the lead  131 , and the adhesive tape  121  may be set to be lower than 17 ppm. Specifically, even when the adhesive tape  121  has the same coefficient of thermal expansion as the semiconductor chip  111  and the lead  131 , the displacement of the adhesive tape  121  is much bigger than that of the semiconductor chip  111  and the lead  131 , and thus the coefficient of thermal expansion of the adhesive tape  121  may be set to be lower than 17 ppm. 
     In order to decrease the coefficient of thermal expansion of the adhesive tape  121 , the coefficient of thermal expansion of the base film  321  needs to be decreased, and an occupation rate of the base film  321  on the adhesive tape  121  needs to be increased. The occupation rate of the base film  321  is a rate of the base film  321  occupying the adhesive tape  121 . Accordingly, when the coefficient of thermal expansion and a modulus of the base film  321  are respectively in a range of 1 to 5 ppm and in a range of 3 to 9 Gpa, and the coefficients of thermal expansion and moduli of the adhesive agents  311  and  331  are respectively in a range of 20 to 100 ppm and in a range of 0.5 to 4 GPa, the occupation rate of the base film  321  may exceed 50%. 
     When the coefficient of thermal expansion and the modulus of the base film  321  are respectively in a range of 3 to 4 ppm and in a range of 3 to 5 GPa, and the coefficients of thermal expansion and the moduli of the adhesive agents  311  and  331  are respectively in a range of 20 to 100 ppm and in a range of 0.5 to 4 GPa, the occupation rate of the base film  321  may exceed 60%. 
     As described above, the base film  321  having the coefficient of thermal expansion of 10 ppm or lower may be used. 
     The adhesive tape  121  is prepared by coating and hardening the adhesive agent  311  on one side of the base film  321 , and then coating and hardening the adhesive agent  331 , which is the same type as the adhesive agent  311 , on the other side of the base film  321 . The adhesive tape  121  may be stored by being rolled around a roller (not shown). In order to use the adhesive tape  121  rolled around the roller, the roller is rolled to loosen the adhesive tape  121 , and the adhesive tape  121  is cut according to the sizes of the semiconductor chip  111  and the lead  131 . 
     In order to adhere the semiconductor chip  111  and the lead  131  using the adhesive tape  121 , the adhesive tape  121  is disposed between the semiconductor chip  111  and the lead  131 , and then a high temperature, such as heat in a range of 150 to 400° C., is applied to the adhesive tape  121 . Then, the adhesive agents  311  and  331  are melted on both sides of the base film  321 . Here, the lead  131  and the semiconductor chip  111  are pressed and hardened by a pressurizing means, thereby mutually adhering the semiconductor chip  111  and the lead  131  using the adhesive tape  121 . 
     In order to prepare the semiconductor package  101 , the adhesive tape  121  is first attached to the lead  131  and then the semiconductor chip  111  is attached to the adhesive tape  121 , or the adhesive tape  121  is first attached to the semiconductor chip  111  and then the lead  131  is attached to the adhesive tape  121 . 
     Two (2) adhesive interfaces are formed between the semiconductor chip  111 , the adhesive tape  121 , and the lead  131 . When differences between the coefficients of thermal expansion of the semiconductor chip  111 , the adhesive tape  121 , and the lead  131  are big, the two (2) adhesive interfaces may be detached from each other or cracked. Accordingly, in order to prevent the adhesive interfaces from being detached or cracked, the adhesive tape  121  has a similar coefficient of thermal expansion as the coefficients of thermal expansion of the semiconductor chip  111  and the lead  131 . 
       FIG. 4A through 4C  are diagrams illustrating states when the semiconductor chip  111 , the adhesive tape  121 , and the lead  131  illustrated in  FIG. 2  contract and expand according to temperature. In detail,  FIG. 4B  shows the semiconductor chip  111 , the adhesive tape  121 , and the lead  131  in room temperature,  FIG. 4A  shows the semiconductor chip  111 , the adhesive tape  121 , and the lead  131  contracted at a low temperature, and  FIG. 4C  shows the semiconductor chip  111 , the adhesive tape  121 , and the lead  131  expanded at a high temperature. 
       FIG. 4A  and  FIG. 4C  are a phenomenon occurring during a reliability test of the semiconductor package  101  of  FIG. 1 . In other words, in order to test the reliability of the semiconductor package  101 , the functions of the semiconductor package  101  are tested by changing the temperature of the semiconductor package  101  from a low temperature to a high temperature, for example, from − 65 ° C. to 150° C. Here, the semiconductor chip  111 , the adhesive tape  121 , and the lead  131  respectively contract to first sizes ta 1 , tb 1 , and tc 1  at the low temperature, and respectively expand to second sizes ta 2 , tb 2 , and tc 2  at the high temperature. At this time, the adhesive tape  121  contracts and expands more than the semiconductor chip  111  and the lead  131 . 
     However, since the coefficient of thermal expansion of the adhesive tape  121  is similar to the coefficients of thermal expansion of the semiconductor chip  111  and the lead  131 , the semiconductor chip  111  and the lead  131  contract and expand in a similar size while testing the semiconductor package  101  for reliability. Accordingly, the adhesive interfaces between the semiconductor chip  111  and the lead  131  are not detached or do not crack. 
     Table 1 below shows displacement of the semiconductor chip  111 , the adhesive tape  121 , and the lead  131  according to temperature. 
     
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                   
                   
                   
                 Ad- 
               
               
                   
                 Semi- 
                   
                   
                 Con- 
                 hesive 
               
               
                   
                 con- 
                   
                 Cop- 
                 ventional 
                 Tape of 
               
               
                   
                 ductor 
                 Nickel 
                 per 
                 Adhesive 
                 Present 
               
               
                   
                 Chip 
                 Lead 
                 Lead 
                 Tape 
                 Invention 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Coefficient 
                   
                 3 
                 5 
                 15 
                 25 
                 5 
               
               
                 of Thermal 
                   
                   
                   
                   
                   
                   
               
               
                 Expansion 
                   
                   
                   
                   
                   
                   
               
               
                 Displace- 
                 −65° C. 
                 −1.8 
                 0.0 
                 −0.1 
                 −15.4 
                 −3.1 
               
               
                 ment (um) 
                  23° C. 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                   
                 150° C. 
                 2.7 
                 0.1 
                 0.2 
                 22.2 
                 4.4 
               
               
                 Displace- 
                   
                 4.5 
                 0.1 
                 0.3 
                 37.6 
                 7.5 
               
               
                 ment 
                   
                   
                   
                   
                   
                   
               
               
                 Width (um) 
               
               
                   
               
             
          
         
       
     
     As shown in Table 1, the displacement according to temperature decreases as the coefficients of thermal expansion of the semiconductor chip  111 , the adhesive tape  121 , and the lead  131  are decreased. Here, the lengths of the semiconductor chip  111  and the adhesive tape  121  are 7 mm, and the width of the lead  131  is 0.1 mm. 
     The coefficient of thermal expansion of the adhesive tape  121  is determined based on the thicknesses, coefficients of thermal expansion, and moduli of the base film  321  and the adhesive agents  311  and  331 . 
       FIG. 5  is a diagram for calculating a coefficient of thermal expansion of the adhesive tape  121  of  FIG. 3 . Referring to  FIG. 5 , a thickness, a coefficient of thermal expansion, and a modulus of the adhesive agent  311  formed on the top surface of the base film  321  are respectively referred to as t 1 , a 1 , and E 1 , a thickness, a coefficient of thermal expansion, and a modulus of the base film  321  are respectively referred to as t 2 , a 2 , and E 2 , and a thickness, a coefficient of thermal expansion, and a modulus of the adhesive agent  331  formed on the bottom surface of the base film  321  are respectively referred to as t 3 , a 3 , and E 3 . Here, an equivalent coefficient of thermal expansion (CTEt) and an equivalent modulus Mt of the adhesive tape  121  are respectively calculated as Equations 1 and 2 below. 
     
       
         
           
             
               
                 
                   CTEt 
                   = 
                   
                     
                       
                         t 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         × 
                         E 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         × 
                         a 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                       
                       + 
                       
                         t 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         × 
                         E 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
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                         a 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                       
                       + 
                       
                         t 
                         ⁢ 
                         
                             
                         
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                         3 
                         × 
                         E 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         × 
                         a 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                       
                     
                     
                       
                         t 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
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                         E 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                       
                       + 
                       
                         t 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         × 
                         E 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                       
                       + 
                       
                         t 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         × 
                         E 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
             
               
                 
                   Mt 
                   = 
                   
                     
                       
                         t 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         × 
                         E 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                       
                       + 
                       
                         t 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         × 
                         E 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                       
                       + 
                       
                         t 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         × 
                         E 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                       
                     
                     
                       
                         t 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                       
                       + 
                       
                         t 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                       
                       + 
                       
                         t 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                       
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
       FIG. 6  is a graph showing a thermal expansion coefficient of the adhesive tape  121  of  FIG. 3  according to a thermal expansion coefficient, modulus, and thickness of the base film  321  illustrated in  FIG. 2 . 
     In curve  640 , the moduli of the base film  321  of  FIG. 5  and the adhesive tapes  311  and  331  are 4 GPa, and a coefficient of thermal expansion of the base film  321  is in a range of 1 to 16 ppm. Since the modulus of the base film  321  is small and the moduli of the adhesive agents  311  and  331  are big, a coefficient of thermal expansion of the adhesive tape  121  of  FIG. 5  is high. Also, a coefficient of thermal expansion of the adhesive tape  121  is lower when the coefficient of thermal expansion of the base film  321  is 1 ppm at a point  641  than that of the adhesive tape  121  when the coefficient of thermal expansion of the base film  321  is 16 ppm at a point  642 . 
     In curve  630 , the moduli of the base film  321  and the adhesive agents  311  and  331  are respectively 8 GPa and 4 GPa, and a coefficient of thermal expansion of the base film  321  is in a range of 1 to 16 ppm. As the modulus of the base film  321  increases, a coefficient of thermal expansion of the adhesive tape  121  decreases. Also, a coefficient of thermal expansion of the adhesive tape  121  is lower when the coefficient of thermal expansion of the base film  321  is 1 ppm at a point  631  than that of the adhesive tape  121  when the coefficient of thermal expansion of the base film  321  is 16 ppm at a point  632 . 
     In curve  620 , the moduli of the base film  321  and the adhesive agents  311  and  331  are respectively 4 GPa and 0.5 GPa, and a coefficient of thermal expansion of the base film  321  is in a range of 1 to 16 ppm. As the moduli of the adhesive agents  311  and  331  decrease, a coefficient of thermal expansion of the adhesive tape  121  decreases. Also, a coefficient of thermal expansion of the adhesive tape  121  is lower when the coefficient of thermal expansion of the base film  321  is 1 ppm at a point  621  than that of the adhesive tape  121  when the coefficient of thermal expansion of the base film  321  is 16 ppm at a point  622 . 
     In curve  610 , the moduli of the base film  321  and the adhesive agents  311  and  331  are respectively 8 GPa and 0.5 GPa, and a coefficient of thermal expansion of the base film  321  is in a range of 1 to 16 ppm. Since the modulus of the base film  321  is big and the moduli of the adhesive agents  311  and  331  are small, a coefficient of thermal expansion of the adhesive tape  121  of  FIG. 5  is very low. Also, a coefficient of thermal expansion of the adhesive tape  121  is lower when the coefficient of thermal expansion of the base film  321  is 1 ppm at a point  611  than that of the adhesive tape  121  when the coefficient of thermal expansion of the base film  321  is 16 ppm at a point  612 . 
     Referring to  FIG. 6 , an occupation rate of the base film  321  is in inverse proportion to the coefficient of thermal expansion of the adhesive tape  121 . In other words, when the occupation rate of the base film  321  increases, the coefficient of thermal expansion of the adhesive tape  121  decreases, and inversely, when the occupation rate of the base film  321  decreases, the coefficient of thermal expansion of the adhesive tape  121  increases. 
     Also, when the coefficient of thermal expansion of the adhesive tape  121  is equal to or lower than 17 ppm, and the occupation rate of the base film  321  exceeds 50%, the coefficient of thermal expansion of the adhesive tape  121  slowly decreases. 
     As shown in Table 1, the coefficients of thermal expansion of the semiconductor chip  111  and the lead  131  are equal to or lower than 10 ppm, and thus, the coefficient of thermal expansion of the adhesive tape  121  may be set to be equal to or lower than 17 ppm. 
     Accordingly, in order to set the coefficient of thermal expansion of the adhesive tape  121  equal to or lower than 17 ppm, the occupation rate of the base film  321  may be set to exceed 50%, when the coefficient of thermal expansion and the modulus of the base film  321  are respectively in a range of 1 to 5 ppm and in a range of 7 to 9 GPa, and the coefficients of thermal expansion and the moduli of the adhesive agents  311  and  331  are respectively in a range of 20 to 100 ppm and in a range of 0.5 to 4 GPa. 
     Alternatively, in order to set the coefficient of thermal expansion of the adhesive tape  121  equal to or lower than 17 ppm, the occupation rate of the base film  321  may be set to exceed 60%, when the coefficient of thermal expansion and the modulus of the base film  321  are respectively in a range of 3 to 5 ppm and in a range of 3 to 5 GPa, and the coefficients of thermal expansion and the moduli of the adhesive agents  311  and  331  are respectively in a range of 20 to 100 ppm and in a range of 0.5 to 4 GPa. 
     According to the present invention, when a semiconductor chip is adhered on a lead by using an adhesive tape, the differences between coefficients of thermal expansion of the semiconductor chip and the adhesive tape, and between coefficients of thermal expansion of the lead and the adhesive tape are decreased since the coefficient of thermal expansion of the adhesive tape is low. 
     Accordingly, even when the temperature of a semiconductor package remarkably changes, an interface between the adhesive tape and the semiconductor chip is prevented from being detached or cracked, and a bonding wire bonded to the lead is prevented from detaching from the lead. 
     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.