Abstract:
A TAB type package on which a semiconductor chip is mounted and a method of manufacturing the same. The semiconductor package includes a plurality of inner leads to be connected to the semiconductor chip and formed on a base film, and a plurality of reinforcing leads connected to four edges of short sides of the semiconductor chip. The reinforcing leads help prevent deformation due to heat of the base film. Heat-induced stress is distributed to avoid a disconnection.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This application claims the priority of Korean Patent Application No. 2004-33377, filed on May 12, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.  
         [0002]     1. Field of the Invention  
         [0003]     The invention relates to a semiconductor package and a method of fabricating the same, and more particularly, to a semiconductor package, e.g., tape automated bonding (TAB) type package on which a semiconductor chip is mounted and a method of fabricating the same.  
         [0004]     2. Description of the Related Art  
         [0005]     Generally, TAB is a technique of electrically connecting bumps formed on a semiconductor chip and each of the inner leads patterned on a TAB tape. The use of a TAB type package is increasing due to the trend toward slim packaging, fine pitch, and multi-pining.  
         [0006]     TAB has several advantages over the conventional wire bonding. First, it is advantageous to form a multi-pin package and fine pitches since small bonding bumps can be formed on a chip. Also, all bonding work can be done simultaneously, and the bonding parts have a strong bonding force. Furthermore, in the case of a multi-chip module, manufacturing a slim package is possible by reducing the distance between the semiconductor chips.  
         [0007]     A TAB type package is one of two types: a tape carrier package (TCP) and a chip-on-film (COF). The TCP has a device hole, for mounting a semiconductor chip, in a base film. But the COF is formed via a packaging method on the base film without a device hole.  
         [0008]     Here, the TCP as an example will be described.  
         [0009]      FIG. 1  is a plan view illustrating a conventional TCP. Referring to  FIG. 1 , a device hole  12 , which is a region for mounting a semiconductor chip  14 , is formed in a base film  10 . A plurality of inner leads  16 , to be connected with the semiconductor chip  14 , are patterned on the base film  10 . An end of the inner leads  16  facing the device hole  12  are to bonding bumps  18  formed on the semiconductor chip  14 .  
         [0010]     The inner leads  16  and the bonding bumps  18  are all conductive materials. Connecting the inner leads  16  and the bonding bumps  18  is performed by bonding at a temperature of about 500° C. under a high pressure. The applied heat is transferred to the base film  10  through the inner leads  16 . The transferred heat expands the base film  10  which later contracts when the heat transferring is terminated.  
         [0011]      FIG. 2  is a plan view for describing problems of the conventional TCP of  FIG. 1 .  
         [0012]     Referring to  FIG. 2 , heat applied to the semiconductor chip  14  acts upon the base film  10  according to the length of an edge of the semiconductor chip  14 . Heat that dissipates along the X axis slightly affects the base film  10  since it is transferred easily to the outside. However, heat that dissipates along the Y axis significantly affects the base film  10  since the heat is not easily transferred to the outside. Accordingly, a width of the base film  10  expanding along the Y axis is relatively greater than a width of the base film  10  expanding along the X axis. Meanwhile, the expansion of the base film  10  is the main cause of deformation by heat since the semiconductor chip  14  expands very little by heat.  
         [0013]     When the base film  10  expands along the Y axis, the inner leads  16  arranged along the X axis deform. That is, the inner leads  16  between the base film  10  and the bonding bumps  18  deform along the Y axis. In the worst case, some of the inner leads  16  are disconnected as shown in  FIG. 2 . Also, the inner leads  16  arranged along the Y axis may disconnect due to the stress generated by the expansion caused by the thermal deformation of the base film  10 . The inner leads  16  of both ends can be disconnected since the inner leads  16  located outermost are subjected to greater stress than the inner leads  16  in the central part. When the transfer of heat is terminated, the base film  10  contracts, and in this case also, the deformation along the Y axis is greater than that along the X axis. Therefore, the deformation or disconnection of the inner leads  16  can occur when the base film  10  contracts or expands.  
       SUMMARY OF THE INVENTION  
       [0014]     According to an aspect of the invention, there is provided a semiconductor package on which a semiconductor chip is mounted, comprising: a base film, a plurality of inner leads to be connected to the semiconductor chip formed on the base film, and a plurality of reinforcing leads substantially vertically connected to four edges of short sides of the semiconductor chip.  
         [0015]     The numbers of the reinforcing leads formed on each of the four corners of the semiconductor chip may be equal to one another and at least two. The reinforcing leads formed on the four corners of the semiconductor chip have substantially identical shapes.  
         [0016]     The reinforcing leads can be bonded to the edges of the base film using a polymer adhesive and may have a length long enough to maintain a bonding force with the base film.  
         [0017]     A width of the reinforcing leads may be equal to or greater than the width of the inner leads.  
         [0018]     The reinforcing leads can be formed of a bar shaped conductive material, and a circumference of the reinforcing leads can be coated with tin or gold.  
         [0019]     The TAB type package can further comprise bonding bumps between the reinforcing and inner leads and the semiconductor chip. Also, distances between the bonding bumps may be equal to one another.  
         [0020]     The TAB type package can further comprise strengthening leads that strengthens the bonding force of the reinforcing leads in a direction substantially vertical to the reinforcing leads.  
         [0021]     A device hole in which the semiconductor chip is mounted can be formed in the base film.  
         [0022]     According to another aspect of the invention, there is provided a method of manufacturing a semiconductor package, comprising: forming reinforcing leads on a base film, and substantially vertically connecting a portion of the reinforcing leads to four corners of short sides of a semiconductor chip.  
         [0023]     The forming of the reinforcing leads comprises: coating a conductive material layer on the base film, forming a photoresist pattern that defines the reinforcing leads on the conductive material layer, and forming the reinforcing leads by etching the conductive material layer using the photoresist pattern as an etch mask.  
         [0024]     The forming of the reinforcing leads comprises: forming a device hole in which the semiconductor chip is mounted in the base film, coating a polymer adhesive layer on the base film, bonding a conductive material plate to the polymer adhesive layer, forming a photoresist pattern that defines the reinforcing leads on the polymer adhesive layer, and forming the reinforcing leads by etching the conductive material plate using the photoresist pattern as an etch mask.  
         [0025]     The connecting of a portion of the reinforcing leads comprises: forming bonding bumps on the corners of the semiconductor chip, placing a portion of the reinforcing leads on the bonding bumps, and applying heat at least greater than about 500° C. with a predetermined compression to the reinforcing leads in a substantially vertical direction to the reinforcing leads.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]     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:  
         [0027]      FIG. 1  is a plan view illustrating a conventional TCP;  
         [0028]      FIG. 2  is a plan view illustrating problems of the conventional TCP of  FIG. 1 ;  
         [0029]      FIG. 3  is a cross-sectional view illustrating a TCP according to an aspect of the present invention;  
         [0030]      FIG. 4  is a plan view of  FIG. 3 ;  
         [0031]      FIGS. 5 and 6  are cross-sectional views taken along line V-V′ in  FIG. 4  for explaining reinforcing leads and inner leads according to an embodiment of the present invention;  
         [0032]      FIGS. 7 through 12  are cross-sectional views illustrating a method of manufacturing a TCP on which a semiconductor chip is mounted, according to another embodiment of the present invention;  
         [0033]      FIG. 13  is a cross-sectional view illustrating a COF according to yet another embodiment of the present invention; and  
         [0034]      FIG. 14  is a plan view of the COF in  FIG. 13 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0035]     The invention will now be described more fully with reference to the accompanying drawings in which embodiments of the invention are shown.  
         [0036]      FIG. 3  is a cross-sectional view illustrating a TCP according to an embodiment of the invention, and  FIG. 4  is a plan view of the TCP in  FIG. 3 .  
         [0037]     Referring to  FIGS. 3 and 4 , a device hole  102 , which is a region for mounting a semiconductor chip  104 , is formed in a base film  100 . A plurality of inner leads  106  connected to the semiconductor chip  104  are patterned on the base film  100 . The end of each of the inner leads  106  facing the device hole  102  is bonded to bonding bumps  108  formed on the semiconductor chip  104 . A solder resist layer  110  is on the film  100 , to be explained later.  
         [0038]     The semiconductor chip  104  is generally shaped as a hexahedron (block-shape) having a rectangular cross-section. The rectangular cross-section can have a short side along the X axis and a long side along the Y axis, the X-Y axes being defined in  FIG. 4 . A plurality of reinforcing leads  120  are formed substantially vertically to the short sides of four corners of the semiconductor chip  104 , that is, parallel to the Y axis. Furthermore, the semiconductor chip  104  can include strengthening leads  122  for strengthening a bonding force of the reinforcing leads  120 .  
         [0039]     The purpose of forming the reinforcing leads  120  on the four corners of the semiconductor chip  104  is to obtain a balance of resistance forces to prevent thermal deformation. Here, the resistance force is a force opposing a stress caused by thermal expansion and preventing the base film  100  from thermal deformation. If one of the four corners does not have the reinforcing leads  120 , a proper balance of the resistance forces can not be achieved, and thus the base film  100  is being deformed. For balancing the resistance forces in the four corners, the reinforcing leads  120  can be formed in equal numbers and to have a substantially identical shape. The strengthening leads  122  can also be formed in the four corners, with the same numbers and a substantially identical shape, in an orthogonal direction to the reinforcing leads  120 .  
         [0040]     Meanwhile, stresses generated at the base film  100  by heat are distributed to all the reinforcing leads  120 . That is, the stresses are concentrated on the reinforcing leads  120  and act slightly on the base film  100  between the reinforcing leads  120 . If there is only one reinforcing lead  120 , the reinforcing lead  120  may be easily disconnected since all stresses are concentrated on it. Therefore, preferably, there are more than two reinforcing leads  120 . A width of the reinforcing leads  120  is preferably equal to or greater than the width of the inner leads  106  to secure a sufficient resistance force against the stresses generated by the thermal expansion.  
         [0041]     The reinforcing leads  120  formed on edges of the base film  100  are bonded using a polymer adhesive layer  124 . The reinforcing leads  120  may be long enough to maintain a bonding force with the base film  100 . That is, as long as the reinforcing leads  120  can maintain the bonding force, they can be formed as close as possible to edges of the base film  100 .  
         [0042]     The bonding bumps  108  may be formed between the semiconductor chip  104  and the reinforcing leads  120  and the inner leads  106 . The bonding bumps  108  connect the reinforcing leads  120  and the inner leads  106  to the semiconductor chip  104 .  
         [0043]      FIGS. 5 and 6  are cross-sectional views illustrating reinforcing leads and inner leads according to an embodiment of the invention.  
         [0044]     Referring to  FIGS. 5 and 6 , the reinforcing leads  120  and the inner leads  106  are formed of a bar shaped conductive material such as copper. Outer circumferences  126  of the reinforcing leads  120  and the inner leads  106  can be coated with tin (Sn) or gold (Au). Bonding bumps  108  can be formed between the reinforcing leads  120  and inner leads  106  and the semiconductor chip  104 . Distances d between the bonding bumps  108  are equal to each another. Therefore, the number of reinforcing leads  120  can be adjusted according to the distance of the bonding bumps  108  in a predetermined region. For example, as depicted in  FIG. 6 , if the distance between the bonding bumps  108  is reduced to d′, more reinforcing leads  120  can be formed.  
         [0045]      FIGS. 7 through 12  are cross-sectional views illustrating a method of manufacturing a TCP on which a semiconductor chip is mounted according to an embodiment of the invention.  
         [0046]     Referring to  FIG. 7 , the polymer adhesive layer  124  is coated on the base film  100  in which the device hole  102  for mounting the semiconductor chip  104  is formed. The base film  100  is an insulating polymer film. Generally, the base film  100  is a polyimide film. In some cases, a polyester film (not shown) can be attached on a base to protect the base film  100 . Next, a conductive material plate  120 ′ in the form of a foil and made of a conductive material such as copper is bonded on the polymer adhesive layer  124 . At this time, a thickness of the base film  100  is about 0.04 mm, and a thickness of the conductive material plate  120 ′ is about 0.008 mm.  
         [0047]     Referring to  FIG. 8 , a photoresist pattern  112  that defines the reinforcing leads  120  thereunder is formed on the conductive material plate  120 ′. The photoresist pattern  112  can be formed by a conventional method.  
         [0048]     Referring to  FIG. 9 , the reinforcing leads  120  are formed by etching the conductive material plate  120 ′ to the shape of the photoresist pattern  112 . At this time, an unwanted portion of the conductive material plate  120 ′, on which the photoresist pattern  112  is formed, is removed by spraying an etching solution. Next, the exposed polymer adhesive layer  124  is removed using a predetermined organic solvent.  
         [0049]     Referring to  FIG. 10 , a solder resist layer  110  is coated on the entire surface of the base film  100  to protect the reinforcing leads  120 . The solder resist layer  110  can be formed by coating a polymer resin such as epoxy.  
         [0050]     Referring to  FIG. 11 , the bonding bumps  108  are formed on the corners of the semiconductor chip  104 . The bonding bumps  108  are formed to electrically connect the semiconductor chip  104  to the inner leads  106  and may be formed of a conductive metal. Afterward, a portion of the reinforcing leads  120  is placed on the bonding bumps  108 . At least about 500° C. of heat with a predetermined compression in a substantially vertical direction to the reinforcing leads  120  is applied to the semiconductor chip  104  on which the reinforcing leads  120  are placed. As a result, a portion of tin plating on the circumference  126  of the reinforcing leads  120  is melted and bonded to the bonding bumps  108 . Also, a lower part of the reinforcing leads  120  is tightly bonded to the bonding bumps  108  by penetrating into the bonding bumps  108  by a pressure onto the reinforcing leads  120 . The strengthening leads  122  and the reinforcing leads  120  are formed simultaneously. Also, the strengthening leads  122  are bonded to the bonding bumps  108  by the same method as the reinforcing leads  120 .  
         [0051]     According to the embodiment of the invention, the deformation of the base film  100  caused by heat can be prevented by forming the reinforcing leads  120  that connect the four corners of the semiconductor chip  104  and the base film  100 . That is, a deformation or a disconnection of the inner leads  106  due to the deformation of the base film  100  can be prevented.  
         [0052]      FIG. 12  is a plan view illustrating a different TCP according to this embodiment of the invention.  
         [0053]     Referring to  FIG. 12 , bonding bumps  108 ′ are arranged in a zigzag pattern on the semiconductor chip  104  to allow an increased density of the inner leads  106 . Accordingly, the bonding bumps  108 ′ under the reinforcing leads  120  and the strengthening leads  122  can also be arranged in zigzag.  
         [0054]     A COF according to another embodiment of the invention will now be described.  FIG. 13  is a cross-sectional view illustrating a COF of the invention, and  FIG. 14  is a plan view of the COF in  FIG. 13 .  
         [0055]     Referring to  FIGS. 13 and 14 , a plurality of reinforcing leads  220  and strengthening leads  222  are patterned on a base film  200  as in the previous embodiment. A portion of the reinforcing leads  220  and the strengthening leads  222  facing the device hole  102  are melted and bonded to bonding bumps  208  formed on a semiconductor chip  204 .  
         [0056]     The reinforcing leads  220  and the strengthening leads  222  are formed so that first, a conductive material layer (not shown) is coated on the base film  200 ; a photoresist pattern (not shown) that defines the reinforcing leads  220  and the strengthening leads  222  is formed on the conductive material layer; and then the reinforcing leads  220  and the strengthening leads  222  are formed by etching the conductive material layer using the photoresist pattern as an etching mask.  
         [0057]     Next, a portion of the reinforcing leads  220  and the strengthening leads  222  are placed on the bonding bumps  208  formed on the four corners of the semiconductor chip  204 . Next, the reinforcing leads  220  and the strengthening leads  222  are bonded to the bonding bumps  208  by applying heat and pressure on an exposed surface of the semiconductor chip  204  or on a lower surface of the base film  200 .  
         [0058]     Here, a distance, number, length, and method of bonding to the bonding bumps  208  of the reinforcing leads  220  and the strengthening leads  222  may be the same as in the descriptions referring to  FIGS. 7 through 12 .  
         [0059]     With an aspect of the present invention, deformation of the base film by heat can be prevented by forming reinforcing leads that connect the four edges of the semiconductor chip to the base film. That is, a deformation or disconnection of the inner leads due to the deformation of the base film can be prevented.  
         [0060]     A disconnection of the inner leads can be prevented by forming a plurality of inner leads that distributes the stress applied to the reinforcing leads.  
         [0061]     While the 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 invention as defined by the following claims.