Abstract:
A bonding structure of device packaging includes a first substrate and a second substrate. The surfaces of the first substrate have metal pads and a first bonding layer connected to the second substrate whose surfaces have a second bonding layer and electrodes. The first bonding layer is combined with the second bonding layer, and the metal pads are in electrical communications with the electrodes. The second substrate may be a flexible substrate to decrease the strain between the first substrate and the second substrate.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of Invention  
         [0002]     The invention relates to a bonding structure and, in particular, to a bonding structure of device packaging.  
         [0003]     2. Related Art  
         [0004]     With the increasing requirements of the high device reliability, high bonding density, and device size reduction in semiconductor device packaging technology, conventional wire bonding is gradually replaced by the flip-chip technology.  
         [0005]     The flip-flop packaging technology is used to for pads or bumps at the junctions of a device and a substrate, in place of the lead frame used in the prior art, followed by coating a layer of an adhesive agent on the substrate surface. The structure is formed by directly embossing or welding the bumps of a device and the pads of a substrate together. In comparison with wire bonding, the prior art can reduce the transmission distance of electrical signals, which is suitable for the packaging of high-speed electronic devices. However, in the conventional flip-flop packaging method, the adhesive agent coated on the substrate has a serious difference in the coefficient of thermal expansion with respect to the device. When the temperature changes, the thermal stress is likely generate deformation at the bumps between the device and the substrate.  
         [0006]     The adhesive agent used in normal flip-flop packaging can be divided into non-conductive films (NCF) and anisotropic conductive films (ACF). The conventional boding technology coats NCF on a substrate and then bonds devices thereon by melting the NCF through pressing and heating procedures. The contraction stress produced after the film is completed cured bonds the devices together. The bonding technology can provide a higher bonding density. However, the bonding among the devices is maintained by a mechanical force. That is, the stress produced by the film maintains the conduction quality of the pads. Once the film experiences a too large stress, lamination will occur to the interfaces between the film and the circuit and substrate, increasing the resistance.  
         [0007]     The ACF bonding technology places an ACF with conductive particles between a device and another device to be bonded. Pressing and heating procedures are employed to melt the film, bonding the devices together. A conductive channel is thus formed among metal pads, metal bumps, and conductive particles. The drawback of this technology, however, is that if the bonding pitch between adjacent metal bumps is very small, bridging phenomena will be happened. Due to the pressure and heat, conductive particles have drifting motions to result in short circuiting between adjacent two conductive points. Therefore, it cannot satisfy the requirement of miniaturization and the bonding density allows a pitch of 40 μm.  
         [0008]     Another diffusion bonding technology makes use of high temperature to produce diffusion between the pads of devices and the substrate for bonding. However, the bonding temperature is often higher than 400 degrees of Celsius. The metal surfaces of the pads thus form metal oxide. Its covalence bond constrains free electrons of the metal, making it hard to form metal bonds at the interface. Moreover, the conduction is a result of the electron tunneling effect. There is a higher resistance at the connecting points. Therefore, it is not suitable for the applications in fine pitches.  
       SUMMARY OF THE INVENTION  
       [0009]     In view of the foregoing, the invention provides a bonding structure of device packaging to achieve the goals of improving device structures and simplifying manufacturing procedures.  
         [0010]     The disclosed bonding structure of device packaging mainly contains a first substrate and a second substrate. A surface of the first substrate has several metal pads and a first bonding metal layer. A surface of the second substrate has several electrodes and a second bonding metal layer. The first substrate is bonded with the second substrate. The first bonding metal layer and the second bonding metal layer are connected together. The metal pads and the electrodes are in electrical communications. In particular, the second substrate can be a flexible substrate, such as a polymer substrate, to buffer the stress produced by the bonding between the substrates.  
         [0011]     Using the same principle, the invention discloses another bonding structure of device packaging. The electrodes and the second bonding metal layer are embedded into the second substrate, exposing only their top surface. Likewise, the first bonding metal layer of the first substrate is fixed on the second bonding metal layer. The metal pads are in electrical communications with the electrodes.  
         [0012]     The connection between the first and second bonding metal layers and the electrical connection between the electrodes can be accomplished by direct thermocompression, ultrasonic bonding, or surface activated bonding. They can be done by first activating the surfaces or undergoing ultrasonic oscillations, followed by the thermocompression. Processing the bonding interface with surface activation or ultrasonic oscillations can reduce the required bonding temperature, solving the high-temperature problem in existing bonding procedures.  
         [0013]     The disclosed bonding structure of device packaging can be applied to the bonding between integrated circuit (IC) chips and substrates, without the need of NCF or ACF. In comparison with the prior art, the invention can increase the bonding density, achieve fine-pitch bonding, increase the fabrication reliability, reduce required steps, and lower the production cost. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     The invention will become more fully understood from the detailed description given hereinbelow illustration only, and thus are not limitative of the present invention, and wherein:  
         [0015]      FIG. 1  is a cross-sectional view of the first embodiment of the invention;  
         [0016]      FIG. 2  is a cross-sectional view of the second embodiment of the invention;  
         [0017]      FIG. 3  is a cross-sectional view of the third embodiment of the invention; and  
         [0018]     The connection between the first and second bonding metal layers and the electrical connection between the electrodes can be accomplished by direct thermocompression, ultrasonic bonding, or surface activated bonding. They can be done by first activating the surfaces or undergoing ultrasonic oscillations, followed by the thermocompression. Processing the bonding interface with surface activation or ultrasonic oscillations can reduce the required bonding temperature, solving the high-temperature problem in existing bonding procedures.  
         [0019]     The disclosed bonding structure of device packaging can be applied to the bonding between integrated circuit (IC) chips and substrates, without the need of NCF or ACF. In comparison with the prior art, the invention can increase the bonding density, achieve fine-pitch bonding, increase the fabrication reliability, reduce required steps, and lower the production cost.  
       BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]     The invention will become more fully understood from the detailed description given hereinbelow illustration only, and thus are not limitative of the present invention, and wherein:  
         [0021]      FIG. 1  is a cross-sectional view of the first embodiment of the invention;  
         [0022]      FIG. 2  is a cross-sectional view of the second embodiment of the invention;  
         [0023]      FIG. 3  is a cross-sectional view of the third embodiment of the invention; and  
         [0024]      FIGS. 4A  to  4 D are schematic views of the fabrication procedure for an embedded substrate. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]     Please refer to  FIG. 1  for a detailed description of the first embodiment of the invention. As shown in the drawing, the invention contains a first substrate  100  and a second substrate  200 . A surface of the first substrate  100  has several metal pads  110 , an adhesive metal circuit  120 , a passivation layer  140 , and a first bonding metal layer  130 . The passivation layer  140  is formed on the surface of the first substrate  110 , exposing the metal pads  110 . The adhesive metal circuit  120  is connected to the metal pads  110  and extends to cover the passivation layer  140  for the convenience of subsequent electrical connections. The first bonding metal layer  130  covers the passivation layer  140 . A surface of the second substrate  200  has several electrodes  210  and a second bonding metal layer  220 . The first substrate  100  is bonded with the second substrate  120  surface to surface, so that the first bonding metal layer  130  is fixed onto the second bonding metal layer  220 . The metal pads  110  are connected to the adhesive metal circuit  120  in order to electrically communicate with the electrodes  210 . The bonding border of the first and second substrates  100 ,  200  is filled with a little adhesive  230  to stabilize the connection of the substrates  100 ,  200  and to prevent humidity from entering the bonding structure.  
         [0026]     The metal pads on the first substrate are connected to the electrodes on the second substrate using the extension of the adhesive circuit on the first substrate. With reference to  FIG. 2 , the second embodiment of the invention also contains a first substrate  100  and a second substrate  200 . A surface of the first substrate  100  has several metal pads  110 , an adhesive metal circuit  120 , a passivation layer  140 , and a first bonding metal layer  130 . The passivation layer  140  is formed on the surface of the first substrate  110 , exposing the metal pads  110 . The adhesive metal circuit  120  is connected to the metal pads  110  and extends to cover the passivation layer  140 . The first bonding metal layer  130  covers the passivation layer  140 . A surface of the second substrate  200  has several electrodes  210  and a second bonding metal layer  220 . The first substrate  100  is bonded with the second substrate  120  in such a way that the first bonding metal layer  130  is fixed onto the second bonding metal layer  220 . The metal pads  110  on the first substrate  100  are not aligned with the electrodes  210  on the second substrate  200 . The adhesive circuit  120  on the first substrate extends to connect to the electrodes  210  on the second substrate  200 , so that the metal pads  110  are in electrical communications with the electrodes  210  via the adhesive metal circuit  120 . The bonding border of the substrates  100 ,  200  is filled with some adhesive  230 .  
         [0027]     Moreover, the invention can embed the electrodes  210  and the second bonding metal layer  220  into the second substrate  200 , exposing only their top surfaces. A cross-sectional view of the third embodiment is shown in  FIG. 3 . It includes a first substrate  100  and a second substrate  200 . The structure of the first substrate  100  is as described before. The electrodes  210  and the second bonding metal layer  220  installed on the surface of the second substrate  200  are embedded into the second substrate  200 , exposing only their top surfaces. The first substrate  100  is bonded with the second substrate  200  surface to surface, so that the first bonding metal layer  130  is fixed onto the second bonding metal layer  220 . The bonding border of the first and second substrates  100 ,  200  is filled with some adhesive agent  230 . Using the embedded second substrate structure, the packaging volume can be further reduced.  
         [0028]     In particular, the embedded substrate can be prepared using the following steps, with reference to  FIGS. 4A  to  4 D.  
         [0029]     As shown in  FIG. 4A , a metal layer  400  is deposited on the substrate  401 .  
         [0030]     As shown in  FIG. 4B , the metal layer  400  is etched to form the required electrodes  410  and the second metal bonding layer  420 .  
         [0031]     As shown in  FIG. 4C , a polymer layer  300  is coated on the substrate to cover the electrodes  410  and the second metal bonding layer  420 .  
         [0032]     As shown in  FIG. 4D , the substrate  410  is removed, exposing the surfaces of the electrodes  410  and the second metal bonding layer  420  embedded into the polymer layer  300 , thereby forming the embedded second substrate.  
         [0033]     The bonding between the first bonding metal layer and the second bonding metal layer and the electrical connections between the electrodes and the adhesive metal circuit or the metal pads are accomplished by direct thermocompression, ultrasonic bonding, or surface activation. One may also first process the bonding metal layers by surface activation or ultrasonic oscillations, followed by thermocompression or direct bonding. The surface activation removes the dust particles and oxide layer on the surfaces of the first metal layer, the bonding later and the electrodes, followed by subsequent bonding procedures to form metal bonds at the junction interface. Therefore, the bonding structure of the device packaging thus formed between the first and second substrates has very good electrical properties.  
         [0034]     The invention uses the connection between a first metal bonding layer and a second metal bonding layer to bond the first and second substrates, without the use of NCF or ACF. Since the first metal bonding layer can be formed simultaneously with the metal pads or adhesive metal circuit of the first substrate, and the second metal bonding layer can be formed simultaneously with the electrodes on the second substrate, the fabrication steps and cost can be largely reduced. The surface activation or ultrasonic processing on the junction interfaces can reduce the bonding temperature, solving the high-temperature problem in the existing bonding processes.  
         [0035]     Certain variations would be apparent to those skilled in the art, which variations are considered within the spirit and scope of the claimed invention.