Abstract:
In a semiconductor device, each of the leads is provided with guided-surfaces that are inclined surfaces and each of the bumps is provided with a recess that has guide-surfaces formed by inclined surfaces. The leads are smoothly guided toward the centers of the upper surfaces of the bumps with the aides of the inclined surfaces formed on the leads and bumps, so that the attitude of the leads is corrected and the leads are snugly brought into the recess and prevented form falling off of the bump.

Description:
This is a Divisional Application of application Ser. No. 09/998,467, filed Nov. 29, 2001. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a semiconductor device and to a method for manufacturing semiconductor devices that reduces the size of semiconductor devices and improves the yield. 
     2. Prior Art 
     One type of semiconductor device assembly method is a tape carrier method. Essentially, in this assembly method, as seen from FIG. 7, numerous leads  76  consisting of a conductive layer are formed on the upper surface of a carrier film  2  that is made of a band-form heat-resistant resin film. Then, these leads  76  are bonded to bumps that are surface electrodes of semiconductor chips  78 . In addition, these elements are sealed with a resin. 
     More specifically, in this tape carrier method, the tip ends of the leads  76  formed on the surface of the carrier film  2 , as seen from FIG. 8, overhang from windows  2   a  of the carrier film  2 , and the semiconductor chip  78  is caused to approach the leads  76  from below. Then, the leads  76  and bumps  80  are thermally fused while being heated and pressed from above by a bonding tool that has a heater, thus bonding the leads  76  and bumps  80 . Bonding of the leads  76  and bumps  80  can be done by another way. A molten resin material in which a conductive powder is dispersed and held is applied to the interfacial surfaces of the leads  76  and bumps  80  and then hardened. 
     In recent years, a flip-chip method is also used. In this method, as seen from FIG. 9, leads  76  are formed on the surface of a carrier film  82 , and semiconductor chips  78  that are set upside down are caused to approach the leads  76  from above, and bonding is performed on the leads and bumps. 
     However, even in this flip-chip method, there are problems. When achieving a finer pitch, it is likely that more defective products are produced, thus causing yield drop. A detailed investigation of such defective products done by the inventor found the causes of such defective bonding. When the lead  76  contacts a position that is away from the center of the corresponding bump  80 , the application of pressure in this state causes the lead  76  to slip on the upper surface of the bump  80  as shown in FIG.  10 . As a result, the deviation S increases, and the lead  76  falls from the upper surface of the bump  80 . 
     SUMMARY OF THE INVENTION 
     Accordingly, the object of the present invention is to provide a semiconductor device that, in its manufacturing process, is able to prevent slipping between the leads and bumps, thus preventing falling of the leads from the bumps. 
     A further object of the present invention is to provide a manufacturing method of semiconductor devices that is able to realize a much greater reduction in the size of semiconductor devices and also realize an improvement in the yield. 
     The above object is accomplished by a unique structure for a semiconductor device in which bumps formed on the surface of a semiconductor chip and leads are set to face each other and bonded, wherein 
     a recess is formed in the surface of each one of the bumps that faces a lead, 
     the recess comprises guide-surfaces that are inclined surfaces and are formed between the bottom of the recess and the opening edges of the recess, and 
     each of the leads is provided with a projection at one end thereof, the projection being to be bonded to a bump and provided with guided-surfaces that are inclined surfaces. 
     In this structure, when the bump and the lead are faced and pressed each other, the lead is guided toward the center of the upper surface (or the bottom) of the bump by the guide-surfaces of the bump and by the guided-surfaces of the lead that are inclined. Accordingly, even when the lead contacts a position that is away from the center of the bump, the lead does not fall from the bump. Furthermore, since the lead is guided by the inclined surfaces, a stress acts toward the lead from the opening edges of the bump, and the lead is held firmly on the bump. Accordingly, an assured bonding is performed, reduced size semiconductor devices are produced, and it is possible to realize the improvement in the yield. 
     In the above structure, the inclined guide-surfaces are formed for the entire periphery of the recess of each bump. Also, the guided-surface are formed so as to be inclined for the entire periphery of each lead and so as to surround a bonding point (a point that is bonded to the corresponding bump) of the lead. 
     Accordingly, the lead is guided into the recess of the bump from any directions around the entire periphery of the lead. 
     Furthermore, in the above semiconductor device, the width of the end surface of the lead that faces the bump is set to be narrower than the width of the lead. 
     By way of designing the end surface of the lead that faces the bump so as to be narrower than the width of the lead, the lead is accurately guided into the recess of the bump. In addition, this structure provides the lead with a structural strength, the deformation thereof is thus prevented, and it is ideal for meeting a required finer pitch. 
     The above object is further accomplished by unique steps of the present invention for a method for manufacturing a semiconductor device in which bumps formed on the surface of a semiconductor chip and leads are set to face each other and bonded; and in the present invention, the method includes: 
     a step of forming a recess in the surface of each of the bumps that faces the lead, the recess having inclined surfaces between the bottom of the recess and the opening edges of the recess, and 
     a step of forming a projection at one end of each of the leads, the projection being to be bonded to each of the bumps and provided with guided-surfaces that are inclined surfaces. 
     In this method, each bump has guide-surfaces that are inclined surfaces and each lead has guided-surfaces that are inclined surfaces that mate the inclined surfaces of the bump. Accordingly, when the bump and the lead are faced and pressed each other, the lead is guided into the center of the upper surface (or the bottom) of the bump by the guide-surfaces of the bump and the guided-surfaces of the lead. Accordingly, even when the lead contacts a position that is away from the center of the bump, the lead does not fall from the upper surface of the bump. Furthermore, since the lead is guided by the inclined surfaces of the bump, a stress acts toward the lead from the opening edges of the bump, and the lead is held firmly on the bump. Thus, bonding is performed securely, reduced size semiconductor devices can be produced, and it is possible to realize the improvement in the yield. 
     In the above method, the inclined guide-surfaces are formed around the entire periphery of the recess of each bump, and the guided-surfaces are formed around the entire periphery of the bonding point (a point that is bonded to the corresponding bump) of each lead. Thus, the lead is guided into the recess of the bump from any directions around the entire periphery of the lead. 
     Furthermore, in the above method, the width of the end surface of a lead that faces a bump is formed so as to be narrower than the width of the lead. Since the end surface of the lead that faces the bump is narrower than the width of the lead, the lead is accurately guided into the recess of the bump. In addition, the lead has a structural strength, the deformation thereof is prevented, and it is ideal for manufacturing finer pitch semiconductor devices. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front view in cross section that illustrates the bump formation process in one embodiment of the present invention; 
     FIG. 2 is a perspective view of an obtained bump; 
     FIG. 3A is a side view of a lead in the lead-side-bump formation process, and FIG. 3B shows a lead in the lead-side-bump formation process in which half-etching has been performed; 
     FIG. 4 is a perspective view of a tip end portion of a lead; 
     FIG. 5 is a front view that illustrates the bonding process of the leads and bumps, showing that the leads and bumps face each other; 
     FIG. 6 is a front view that illustrates the bonding process of the leads and bumps, showing that the leads and bumps are pressed; 
     FIG. 7 is a top view of a semiconductor device in one step of a semiconductor device manufacturing process that uses a carrier film; 
     FIG. 8 is a side view of a semiconductor device in one step of a semiconductor device manufacturing process that uses a carrier film; 
     FIG. 9 is a side view of a semiconductor device in one step of a semiconductor device manufacturing process that uses flip-chip method; and 
     FIG. 10 is a front view illustrating a defective lead and bump bonding in a conventional semiconductor device. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     One embodiment of the present invention will be described below with reference to the accompanying drawings. 
     FIG. 1 shows the formation of bumps  10 . The bumps  10  are formed by electroplating. 
     More specifically, a mask layer  4  consisting of a synthetic resin is first formed by a silkscreen process on portions of the surface of the semiconductor chip  8  except for the electrodes (not shown). As a result, through-holes  4   a  are formed in the mask layer  4 . Next, this semiconductor chip  8  is subjected to electroplating, so that a gold-plating layer is grown on the electrodes. The growth of this gold-plating layer is not performed to the point that the gold-plating layer reaches the edges of the through-holes  4   a  in the mask layer  4 . Instead, this growth is completed at an intermediate point in the depth of each through-hole  4   a . The growth of the gold-plating layer proceeds along the peripheral wall surfaces of the through-holes  4   a ; as a result, a recess  10   a  is formed in the upper surface of each bump  10 . Then, the mask layer  4  is removed by solvent. 
     As shown in FIG. 2, the recess  10   a  has the shape of a truncated square pyramid, and it has inclined guide-surfaces  10   c  between the bottom  10   b  and the opening edges  10   d.    
     FIGS. 3A and 3B illustrate the process of forming a projection or a lead-side-bumps  6   a  on a lead  6 . 
     First, mask layers  7  consisting of a synthetic resin are formed on the tip end portion and base portion (with respect to the direction of length) of the surface of each lead  6  that is held on a carrier film  12 . This surface that has the mask layers  7  is one that faces a corresponding bump  10  (i.e., the upper surface in FIG.  3 A). 
     Next, this lead  6  is subjected to half-etching as shown in FIG.  3 B. As a result, the portions of the lead  6  that are not masked by the masking layers  7  are etched and removed. Here, a projection or a lead-side-bump  6   a  is formed at the tip end portion of the lead  6  that is masked by the masking layer  7 . Since the etching acts uniformly on the surfaces of the material of the lead  6 , the side surfaces of the lead-side-bump  6   a  are formed as a guided-surface  6   b . The side surfaces of the guided-surface  6   b  are inclined outward from the upper surface side (that faces the corresponding bump  10 ) toward the lower surface side. Then, the mask layers  7  on the lead  6  are removed by solvent. 
     As shown in FIG. 4, the guided-surface  6   b  of each lead-side-bump  6   a  is formed around the entire periphery of the lead-side-bump  6   a.    
     The bonding of the leads  6  and bumps  10  is performed using a gang bonding method in which all bonding is performed simultaneously for a single semiconductor chip  8 . As shown in FIG. 5, the carrier film  12  and semiconductor chip  8  are positioned in relative terms so that the leads  6  and bumps  10  are set to face each other. Then, beginning from this state, the respective leads  6  and bumps  10  are pressed toward each other by means of a heated bonding tool (not shown) as shown in FIG.  6 . The width  6   c  (see FIG. 4) of the surfaces of the leads  6  that face the bumps  10  in FIG. 5 is approximately 6 to 8 micrometers (μm). 
     Here, as shown in FIGS. 5 and 6, the center of the lead  6  located in the central position more or less coincides with the center of the corresponding bump  10 . Accordingly, during bonding, the lead-side-bump  6   a  contacts the bottom  10   b  of the corresponding bump  10  from the beginning and is bonded so that the lead-side-bump  6   a  bites of the lead  6  into the bump  10 . 
     On the other hand, the centers of the leads  6  located in the left and right positions deviate from the centers of the corresponding bumps  10 , and these leads  6  contact the corresponding bumps  10  with a deviation S of, for instance, approximately 5 to 7 micrometers (μm). However, when the leads  6  and bumps  10  are pressed, the leads  6  are guided toward the centers of the upper surfaces of the bumps  10  via the inclined guide-surfaces  10   c  of the bumps  10  and the guided-surfaces  6   b  (that are also inclined) of the leads  6 . As a result, the attitudes of the leads  6  are corrected. Furthermore, as a result of the leads  6  being guided, stress acts toward the guided-surface  6   b  of the lead-side-bumps  6   a  from the opening edges  10   d  of the bumps  10 . As a result, the leads  6  are firmly held on the bumps  10 . In this case, the change in the attitudes of the leads  6  is accomplished while causing deformation of the carrier film  12  or is accomplished with the constraint of the leads  6  released as a result of the leads  6  leaving the carrier film  12 . 
     Then, in this state, the leads  6  and bumps  10  are bonded by way of thermal fusion. 
     In the above embodiment, the leads  6  (more specifically the projections of the leads) are guided toward the centers of the upper surfaces of the bumps  10  by the inclined guide-surfaces  10   c  of the recesses  10   a  of the bumps  10  and by the inclined guided-surfaces  6   b  of the leads  6 . Accordingly, even in cases where the leads (or projections thereof)  6  contact the bumps  10  in positions that are away from the centers of the bumps  10 , the leads  6  are prevented from slipping off of the upper surfaces of the bumps  10 . In addition, since the leads  6  are thus guided, stress acts toward the leads  6  from the opening edges of the bumps  10 , so that the leads  6  are firmly held on the bumps  10 . Accordingly, bonding is performed more securely, and a much greater reduction in the size of the semiconductor device is realized. In addition, the yield is increased. 
     Furthermore, the inclined guide-surfaces  10   c  are formed around the entire circumference of the recess  10   a  of each bump  10 . Also, the guided-surface  6   b  that are also inclined are formed around the entire circumference of each lead  6  so as to surround the bonding point (an area that is bonded to the corresponding bump  10 ) of the lead. Accordingly, guidance of the leads  6  by the guide-surfaces  10   c  and guided-surface  6   b  is performed with accuracy in any directions around the entire circumference. 
     Furthermore, as seen from FIG. 4, the width  6   c  of the surfaces of each lead  6  that face the bumps  10  is formed so as to be narrower than the width  6   d  of the leads  6 . Accordingly, the edge portions of the surfaces of the leads  6  that face the bumps  10  are guided with higher reliability by the inclined guide-surfaces  10   c  of the bumps  10 . As a result, the leads  6  are guided accurately. In addition, since the width  6   d  of each lead  6  is wider than the width  6   c  of the surface that faces a bump  10 , the strength of the leads  6  is ensured, a deformation thereof is suppressed. Thus, it is ideal for obtaining a finer pitch. 
     In the shown embodiment, the recesses  10   a  are formed by way of interrupting the formation of the electroplating layers of the bumps  10 . The recesses  10   a , however, can be formed by other methods. The recesses can be made by way of cutting or etching the upper surfaces of the bumps  10 . 
     Moreover, in the above embodiment, the lead-side-bumps  6   a  are formed by way of half-etching the leads  6 . However, the lead-side-bumps  6   a  can be formed by other methods. One way to form the lead-side-bumps  6   a  or a projection on each of the leads  6  is to cut the lead  6  so that a portion that makes the lead-side-bumps  6   a  or a projection is allowed not to be cut and remain. Another way is to separately form the lead-side-bumps  6   a  or projections and bond them to the leads  6 . 
     Furthermore, in the above embodiment, the inclined guide-surfaces  10   c  are formed around the entire circumference of the recess  10   a  of each bump  10 , and guided-surface  6   b  are formed so as to incline around the entire circumference of each lead-side-bump  6   a . However, the guide-surfaces  10   c  and/or the guided-surfaces  6   b  can be formed partially with reference to the entire circumference of each bump and each lead. For instance, it is possible to form the guided-surface  6   b  only on the left and right surfaces of the lead  6  with respect to the direction of width and form the guide-surfaces  10   c  in two places in the recesses  10   a  so as to correspond to such a guided-surface  6   b.    
     In the above embodiment, the leads  6  and bumps  10  are bonded by thermal fusion. However, the leads  6  and bumps  10  can be bonded by various other known methods. Thus, they can be bonded by a synthetic resin material in which a conductive powder is dispersed and held. Such methods are within the scope of the present invention.