Abstract:
A bonding structure with compliant bumps includes a stopper structure and a protection layer. Compliant bumps include at least a polymer bump, a metal layer and a surface conductive layer. Both the stopper structure and protection layer are formed with polymer bumps and metal layer. Compliant bumps provide bonding pad and conductive channel. Stoppers are used to prevent compliant bumps from crushing for overpressure in bonding process. The protection layer provides functions of grounding and shielding. The stoppers can be outside or connected with the compliant bumps. The protection layer has thickness smaller than the stopper structure and compliant bumps. It can be separated or connected with stoppers.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a bonding structure with compliant bumps for bonding semiconductor material or metal surface to substrate, and the bonding structure includes a stopper structure and a protection layer. It can be applied to bond integrated circuit (IC) or chip to substrate. 
     BACKGROUND OF THE INVENTION 
     Integrated circuits (IC) are conventionally made of semiconductors wafers. The manufacturing process of IC includes two steps. The first step is to manufacture the semiconductor wafer using semiconductor material, and the second step is using packaging technologies to package. The packaging technologies of the second step are mainly to dice the wafer into chips and then bond the chips to the substrate. The bonding pads are used to bond the chips to the substrate. The bottom layer of the bonding pads are usually made of aluminum covered with passivated metal. For low-profile chips, the bonding pads with a solder bump can bond the chips directly to the substrate. This technology has been developed in many packaging forms, including flip chip, tape-automated bonding and ball-grid array (BGA). 
     In general, a bonding layer is required in bonding the chips to the substrate. The bonding layer is usually made of a polymer material and the bonding is achieved using a pressurized or heating process.  FIG. 1A  and  FIG. 1B  show respectively the cross-sectional views of a conventional bonding structure before and after the bonding. A first substrate  101  has a plurality of conductive metal bonding pads  105 . The area outside of bonding pads  105  is covered with a first protection layer  102  for insulation. A plurality of metal bumps  104  are grown directly on bonding pads  105  as conductive points. An anisotropic conductive film (ACF)  106  containing conductive particles  107  is placed between first substrate  101  and a second substrate  108  for bonding. The ACF is melted by using heat and pressure in order to bond first substrate  101  and second substrate  108 . Bonding pads  105 , metal bumps  104 , conductive particles  107  and the electrode  103  on second substrate  108  form a conductive channel. The disadvantage of this technique is that it can not meet finer pitch requirement. For a finer pitch between neighboring metal bumps  104 , conductive particles  107  will flow because of heat and pressure being applied. Thereby two adjacent conductive points may be short. Thus, the technique can not meet finer pitch requirement. 
       FIG. 2A  and  FIG. 2B  show respectively the before and after bonding, cross-sectional views for another conventional bonding structure using non-conductive film (NCF). The difference between the NCF bonding technique and the ACF bonding technique shown in  FIG. 1  is that the former directly embeds conductive particles  107  on metal bumps  104  instead of in an NCF  206 . The bonding structure with NCF  206  also uses heat and pressure to melt NCF  206  in order to bond first substrate  101  and second substrate  108 . The disadvantage of the NCF bonding technique is that conductive particles  107  will be lost and escape from metal bumps  104  because of the pressure and heat. The reduction of conductive particles  107  in metal bumps  104  will increase the resistance after the bonding. 
     The aforementioned bonding technologies both use metal bumps. Because metal bumps are hard and make it difficult for processing, therefore bumps made of flexible polymer are widely used. U.S. Pat. No. 5,578,527 and U.S. Pat. No. 5,707,902 disclosed a technique using polymer bumps.  FIG. 3A  and  FIG. 3B  show respectively the before and after bonding cross-sectional views for a bonding structure using polymer bumps. The rectangular polymer bumps  310  are covered with a conductive layer  309 . This bonding technology also uses NCF  206 , which is melted by pressure and heat to bond first substrate  101  and second substrate  108 . Metal pads  105 , conductive layer  309  and electrode  103  form a conductive channel. 
       FIG. 4A  and  FIG. 4B  show respectively the before and after bonding cross-sectional view for a bonding structure using round column-shaped polymer bumps. A plurality of round column-shaped bumps  410  are placed on metal bonding pads  105 . Bumps  410  are covered with a conductive layer  309 . This bonding technology uses the polymer as the major material for bumps. The disadvantage of this technique is that when the bonding pressure is too large, the conductive layer covering the bumps tends to crack, which will lead to increase the resistance or even become non-conductive. 
     SUMMARY OF THE INVENTION 
     The primary object of the present invention is to provide a bonding structure with compliant bumps containing a stopper structure and a protection layer. The compliant bump includes a polymer bump, a metal layer and a conductive layer. The metal layer is located beneath the polymer bump to serve the purposes of bonding the first substrate and electrical conduction. The conductive layer covers the polymer bump surface to serve the purpose of electrical conduction to the electrode of the second substrate. The covering area ranges from 0.1% to 99% of the entire compliant bump area. The polymer bump is made of a polymer material with a low elasticity coefficient. Compared to the metal bumps, the polymer bumps can reduce the required pressure for bonding, although the cracking still occurs sometimes. 
     Accordingly, the stopper structure of the present invention can prevent the cracking of the compliant bump. Each stopper includes a polymer bump and a metal layer. The metal layer is located beneath the polymer bump to serve the purpose of bonding the first substrate. The height of the stopper can be adjusted by the pressure applied during the bonding process and the deformation extent of the compliant bump can be controlled precisely. The location of the stopper can be either in the external or internal area of the compliant bump. The area of distribution of the stopper can range from 0.1% to 99% of the entire first substrate area. 
     The second protection layer of the present invention is to serve the purposes of protecting the first substrate and grounding. The protection layer, manufactured using a photo-lithography process, is located outside the metal bonding pads. The second protection layer includes a polymer layer and a metal layer, and can be connected to the stopper or independently distributed. The thickness of the second protection layer is smaller than the respective thicknesses of the stopper and the compliant bump. The area of distribution of the stopper can range from 0.1% to 99% of the entire first substrate area. In other words, the stopper can substantially or partially cover the entire first substrate. 
     The compliant bump and the stopper are both manufactured using a photo-lithography process. There can be many choices for the shapes and dimensions of the compliant bump and the stopper and theft distribution of the first substrate surface. The choice depends on the pressure of the facility, the polymer material, the type of the first substrate and the second substrate. The thickness of the stopper is larger than that of the second protection layer, and is different from the thickness of the compliant bump. The surfaces of the compliant bump and the stopper may contain convexes and concaves, instead of being smooth. The bonding structure and the first substrate together form a component. The bonding film used to bond this component and the second substrate can be ACF, NCF or non-conductive glue. And the methods to bond the bonding film are thermal consolidation, thermal compressing consolidation, UV consolidation, or ultrasonic consolidation, or a combination of any of the above methods. 
     The compliant bump, the stopper and convex and the concave on their surfaces can have the following shapes: rectangle, square, trapezoid, sphere, round-column, cone, or irregular, or a combination of any of the above shapes. 
     The stopper structure of the present invention is to prevent the compliant bump from cracking during the bonding process, retain the conductive particles and improve the yield rate of the bonding. The present invention replaces the conventional metal with a more elastic polymer material in order to bond with a more fragile substrate, such as glass. This reduces the manufacturing cost. Furthermore, the second protection layer can protect the first substrate from damaging and can provide the ground connection. 
     The present invention can be applied in bonding IC, silicon chips, dices, glass substrates, polymer substrates, non-organic substrates, organic substrates, and silicon substrates. 
     The foregoing and other objects, features, aspects and advantages of the present invention will become better understood from a careful reading of a detailed description provided herein below with appropriate reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention can be understood in more detail by reading the subsequent detailed description in conjunction with the examples and references made to the accompanying drawings, wherein: 
         FIGS. 1A and 1B  show respectively a cross-sectional view of a conventional bonding structure using ACF before and after bonding; 
         FIGS. 2A and 2B  show respectively a cross-sectional view of a conventional bonding structure using NCF before and after bonding; 
         FIGS. 3A and 3B  show respectively a cross-sectional view of a conventional bonding structure using polymer bumps before and after bonding; 
         FIGS. 4A and 4B  show respectively a cross-sectional view of a conventional bonding structure using round column-shaped polymer bumps before and after bonding; 
         FIGS. 5A and 5B  show respectively a cross-sectional view of the bonding structure using compliant bumps with a stopper structure before and after bonding; 
         FIGS. 6A–6D  show respectively a cross-sectional view of different shapes of the compliant structure and the stopper; 
         FIGS. 7A and 7B  respectively show a cross-sectional view of two designs of the second protection layer; 
         FIG. 8  shows a cross-sectional view of the stopper inside the compliant bump; 
         FIGS. 9A–9C  show a cross-sectional view of the compliant bumps having different convex and concave surface designs; 
         FIG. 10  shows a top view of the entire component including the compliant bump; and 
         FIGS. 11A–11D  show a top view of the compliant bumps having different convex and concave surface designs and stopper arrangement. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 5A  shows a preferred embodiment of the bonding structure with compliant bumps containing stoppers. In this embodiment, a first substrate  101  has a plurality of metal bonding pads  105  and is covered with a first protection layer  102 . Metal bonding pads  105  serve as the conductive channel to first substrate  101 . A metal layer  511  located on first protection layer  102  is connected to polymer bumps and first protection layer  102  or bonding pads  105 . Conic bumps  510  are made of polyimide and form a stopper  512  together with metal layer  511 . Polyimide is a polymer material with high mechanical strength and high chemical resistance. Each compliant bump  513 , located on bonding pads  105  for electrical conduction, includes metal layer  511 , conic bump  510 , and conductive layer  309 . Conductive layer  309  covers the entire topmost layer of compliant bumps  513 . In this embodiment, the bonding structure includes two compliant bumps  513  at the center and two stoppers  512  on both sides. NCF  206  is located between first substrate  101  and second substrate  108 , and can be melted by heat or UV with pressure in order to bond first substrate  101  and second substrate  108 , as shown in  FIG. 5B . Metal bonding pads  105 , metal layer  511  conductive layer  309  and electrode  103  form a conductive channel. 
     Both the stoppers and the compliant bumps are conic in  FIG. 5A . In accordance with the present invention, the stoppers and the compliant bumps can have different shapes. As shown in  FIG. 6A , the two stoppers  612 A on both sides of the first substrate are made of metal layer  511  and trapezoid bumps  610 A. The compliant bump  613 A on the inner side of the first substrate is made of metal layer  511 , conic bump  610 B and conductive layer  309 . The monolithic bumps should have stronger mechanical strength. The size of the bonding area depends on the size of the bump top area. The more pressure the bonding needs, the more difficult to perform the bonding. Therefore, to achieve the sufficient mechanical strength and ease of bonding, the Convex-concave surface structure of the compliant bumps can be adopted, as shown in  FIG. 6B . Stopper  612 B is made of metal layer  511  and trapezoid bump  610 C. Compliant bump  613 B is made of metal layer  511 , the convex-concave-surfaced trapezoid bump  610 D and conductive layer  309 . Compared to the smooth-surfaced bump, the convex-concave-surfaced bump has a smaller contact surface with electrode  103  of second substrate  108 . Therefore, only a smaller pressure is required to perform the bonding. For two bumps with the identical volume and identical mechanical strength, the one with a convex-concave surface requires a smaller pressure to bond than the one with a smooth surface. 
       FIG. 6C  shows a cross-sectional view of another convex-concave-surfaced compliant bumps. The compliant bumps and the stoppers of this structure have a smaller volume but are more densely distributed. The top of metal bonding pads  105  is distributed with a plurality of trapezoidal bumps  610 F. Stopper  612 C is made of metal layer  511  and a plurality of trapezoidal bumps  610 E. Compliant bump  613 C is made of metal layer  511  and a plurality of trapezoidal bumps  610 F and conductive layer  309 .  FIG. 6D  shows a similar structure to the structure in  FIG. 6C , but the bumps in  FIG. 6D  has the shape of a round column. The top of a round column is a hemisphere. Stopper  612 D is made of metal layer  511 , a plurality of round column bumps  610 G. Compliant bump  613 D is made of metal layer  511 , a plurality of round column bumps  610 H and conductive layer  309 . 
       FIG. 7A  shows a second protection layer  715  and stopper  712  of the present invention. Second protection layer  715  is manufactured using a photo-lithography process during the manufacturing of stopper  712  and compliant bump  713 . Second protection layer  715  is made of metal layer  511  and polymer layer  714 . Polymer layer  714 , on top of metal layer  511 , uses the same material as trapezoid bumps  710 . Stoppers  712 , made of trapezoid bump  710  and metal layer  511 , are on both sides of second protection layer  715 . Compliant bumps  713  are on the two ends of first substrate  101 . Second protection layer  715  is to protect first substrate  101  from damaging during the bonding of first substrate  101  and second substrate  108  and also to provide grounding.  FIG. 7B  shows second protection layer  715  and stopper  712  are connected together. The thickness of second protection layer  715  must be smaller than the respective thicknesses of stopper  712  and compliant bump  713 . 
     In addition, the stopper can be connected to the compliant bump.  FIG. 8  shows a cross-sectional view of a stopper inside a compliant bump. A bump  810  with a surface containing a plurality of hemispheres has a bottom metal layer  511  to connect bonding pads  105 . The entire compliant bump  813  is made of metal layer  511 , bump  810  and conductive layer  309 . Stopper  812 , made of bump  810  and metal layer  511 , is located on both sides of compliant bump  813 . The center of the bump is covered with conductive layer  309 , which, together with metal layer  511  and bonding pads  105 , forms a conductive channel. 
       FIG. 9A  shows a compliant bump with an internal stopper. Stopper  912 A, made of bump  910 A and metal layer  511 , is located on both sides of compliant bump  913 A. Conductive layer  309 , covering the center of compliant bump  913 A, also covers the entire hemisphere structure.  FIG. 9B  shows another compliant bump with an internal stopper, where only one end has a stopper. Internal stopper  912 B is made of metal layer  511  and hemispheric-surfaced bump  910 B. Compliant bump  913 B is made of metal layer  511 , bump  910 B and conductive layer  309 . Conductive layer  309  only covers half of the area of the hemisphere surface. Conductive layers  309  covering two neighboring hemispheres are also connected.  FIG. 9C  shows a compliant bump without an internal stopper. Compliant bump  913 C is made of metal layer  511 , bump  910 C and conductive layer  309 . The surface of bump  910 C includes a plurality of hemispheres half covered with conductive layer  309 . 
     The compliant bumps containing the hemisphere or convex-concave surfaces can be used with both ACF and NCF bonding technologies. When ACF is used, the contact area between the compliant bump and the electrode of the second substrate is smaller so that the compliant bump requires a smaller pressure to achieve the deformation extent for bonding. Also, the conductive particles are trapped inside the convex-concave surface to avoid the flow caused by the heat and pressure. As aforementioned, the two ends of the convex-concave surface can both have stoppers or bumps not covered with conductive layer. Therefore, the two neighboring bonding pads will not become short due to the conductive particles. The reduction of the pitch between the electrodes can also improve the insulation. The present invention can also be used in substrates having fine pitch between bonding pads. If heat is applied in melting the films, the flowing adhesive material can be expelled out of the component through the gaps and controlled direction in the convex-concave surface structure. 
       FIG. 10  shows a top view of the component. First substrate  101  is surrounded with a plurality of rectangular compliant bumps  1013  and four square stoppers  1016  at the four corners. The area  1003 , distributed with the stoppers and the compliant bumps, is located at the center. The distribution of stoppers can have the shape of a spot, bar, continuous bar, delimited bar, arc, fan, or any arbitrary shape. The distribution area of the stopper or the second protection layer can range from 0.1% to 99% of the entire area of the first substrate. 
       FIG. 11A  shows a top view of a first embodiment of a rectangular compliant bump  1013 . Rectangular compliant bump  1113 A has two parallel rows of spheres  1115 , and the stoppers are distributed outside of the compliant bump. Conductive layer  309  only covers half of each sphere  1115 , and the outer half of spheres  1115  is not covered. 
       FIG. 11B  shows a top view of a second embodiment of a rectangular compliant bump  1013 . Rectangular compliant bump  1113 B has two parallel rows of spheres  1115 , and the stripe stoppers  1112  are distributed on both ends, inside the compliant bump  1113 B. Conductive layer  309  covers the entire spheres  1115 , but not the stoppers  1112 . 
       FIG. 11C  shows a top view of a third embodiment of a rectangular compliant bump  1013 . Rectangular compliant bump  1113 C has three skewed parallel rows of spheres  1115 , and the stripe stoppers  1112  are distributed on both ends, inside the compliant bump  1113 C. Conductive layer  309  covers the entire spheres  1115 , but not the stoppers  1112 . The stripe stoppers  1112  must be arranged in the direction orthogonal to the neighboring side of the first substrate to facilitate the expelling of flowing adhesive material. 
       FIG. 11D  shows a top view of a fourth embodiment of a rectangular compliant bump  1013 . Rectangular compliant bump  1113 D has four skewed parallel rows of spheres  1115 , and the stripe stopper  1112  is distributed on one end, inside the compliant bump  1113 D. The spheres  1115  at the other end without the stripe stopper  1112  are only half covered with conductive layer  309 . Conductive layer  309  does not cover the stopper  1112 . 
     The aforementioned embodiments show that the present invention can be extended to many varieties of compliant bump designs. When applied in combination with appropriate stoppers and protection layers, the present invention can be used in bonding to many types of second substrates. For different manufacturing facilities, the present invention can be adjusted to improve the yield rate and reduce the cost. 
     Although the present invention has been described with reference to the preferred embodiments, it will be understood that the invention is not limited to the details described thereof. Various substitutions and modifications have been suggested in the foregoing description, and others will occur to those of ordinary skill in the art. Therefore, all such substitutions and modifications are intended to be embraced within the scope of the invention as defined in the appended claims.