Patent Publication Number: US-2002008528-A1

Title: Electronic part inspection method and an electronic part assembly apparatus

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates to an electronic part inspection method which is used to inspect the conditions of bonding when solid state devices are bonded to the surface of a carrier film in an electronic part assembly process, and the present invention relates further relates to an electronic part assembly apparatus associated with such a method.  
       [0003] 2. Prior Art  
       [0004] As seen from FIG. 6, in a tape carrier system that is a type of semiconductor element assembly system, leads  76  of a specified shape 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, various types of assembly processes such as the bonding of these leads  76  to the bonding pads (surface electrodes) of silicon chips  78 , and the sealing of such elements with a resin, etc. are performed.  
       [0005] In this tape carrier system, as shown in FIG. 7, the tip ends of the leads  76  formed on the surface of the carrier film  2  overhang from the window parts  2   a  of the carrier film  2 . Silicon chips  78  are caused to approach these leads  76  from below, and the leads  76  and bonding pads  80  are thermally fused by applying heat and pressure from above by means of a bonding head containing a heater, or a molten resin material holding a dispersed conductive powder is applied to the interface between the leads and bonding pads and this material is hardened, so that the leads and bonding pads are bonded. In this system, inspection of the product quality following bonding is accomplished by detecting positional deviations between the leads  76  and bonding pads  80  by observation with a camera from above.  
       [0006] However, as the pitch of semiconductor elements has become finer, it has become impossible to ignore the deformation of the leads  76  caused by external forces and heat in the case of this conventional system. In recent years, therefore, a system (flip-chip system) in which leads  76  are formed on the surface of a board  82  consisting of an opaque phenol resin laminated material, etc., and silicon chips  78  which have been inverted are caused to approach the leads  76  from above, and are bonded (as shown in FIG. 8).  
       [0007] In such a flip-chip system, the bonding areas of the leads  76  and bonding pads  80  are located in positions that cannot be seen from the outside. Accordingly, in order to inspect the product quality, it is necessary to strip the bonded silicon chips  78  from the leads  76  on the board  82  and observe the conditions of the bonded surfaces with a microscope. As a result, the inspection process is extremely complicated. A method in which the positional deviation of the bonding pads  80  and leads  76  is inspected by irradiating the assembly with infrared light from the upper surface, causing this infrared light to pass through the silicon chips  78 , and detecting light images of the bonding pads  80  and leads  76  in reflected images of this infrared light, has been proposed as described in Japanese Patent Application Laid-Open (Kokai) No. H10270501. However, since this method uses an infrared light apparatus, the method suffers from the problem of increasing the size of the apparatus.  
       SUMMARY OF THE INVENTION  
       [0008] Accordingly, the object of the present invention is to provide a method and apparatus that allows the efficient inspection of the conditions of bonding.  
       [0009] The above object is accomplished by a unique method of the present invention for an electronic part inspection method that performs an inspection of a bonding condition between a conductive layer which is formed on an upper surface of a carrier film consisting of a light-transmitting material and bonding pads which are formed on undersurfaces of solid state devices; and in the present invention, the inspection of the bonding condition is performed based upon the light images of the bonding pads that are transmitted through the carrier film.  
       [0010] In this method of the present invention, the light transmissivity of the carrier film is utilized, and the conditions of bonding between the conductive layer formed on the carrier film and the bonding pads of the solid state devices are inspected based upon light images of the bonding pads that are transmitted through the carrier film. Accordingly, a complicated process involving the stripping of bonded silicon chips is unnecessary, and the inspection can be performed with good efficiency.  
       [0011] The above object is accomplished by another unique method of the present for an electronic part inspection method that is comprised of a bonding process for bonding bonding pads formed on undersurfaces of a plurality of solid state devices to a conductive layer formed on an upper surface of a band-form carrier film consisting of a light-transmitting material, and a detection process for detecting conditions of the bonding based upon light images of the bonding pads that are transmitted through the carrier film in a state in which the plurality of solid state devices are held in one set on a surface of the carrier film.  
       [0012] In this method of the present invention, the conditions of bonding are detected based upon light images of the bonding pads that are transmitted through the band-form carrier film in a state in which a plurality of solid state devices are held in a set on the surface of the carrier film. Accordingly, the detection of the bonding condition can be continuously performed without stopping the assembly line, and the inspection process is made even more efficient.  
       [0013] The above object is further accomplished by a unique structure for an electronic part assembly apparatus that comprises a bonding device that bonds bonding pads formed on undersurfaces of a plurality of solid state devices to a conductive layer formed on an upper surface of a band-form carrier film consisting of a light-transmitting material, and a detection device that detects conditions of the bonding based upon light images of the bonding pads that are transmitted through the carrier film in a state in which the plurality of solid state devices are held on a surface of the carrier film.  
       [0014] In the above electronic part assembly apparatus, the bonding device is comprised of an upper member and a lower member that are respectively provided above and below the carrier film, and the assembly apparatus is further provided with a moving stand on which the lower member and the detection device are provided. The lower member and the detection device are selectively positioned, by movement of the moving stand, at a location that faces the upper member; and when the lower member is positioned at a location that faces the upper member, the detection device faces solid state devices following bonding on the carrier film.  
       [0015] In this structure, the lower member and detection device are selectively positioned at a location that faces the upper member by the movement of the moving stand. Accordingly, by placing the detection device at a location that faces the upper member after bonding has been performed by the upper member and lower member, an inspection to ascertain whether or not the bonding process has been performed in a favorable manner is performed without moving the carrier film. Furthermore, the detection device faces the solid state devices following the bonding on the carrier film when the lower member is positioned at a location that faces the upper member. Accordingly, bonding by the upper member and lower member and detection by the detection device can be continuously performed in parallel by feeding the carrier film from a bonding position where the bonding is performed to an inspection position where the detection is performed. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0016]FIG. 1 is a front view of the electronic part assembly apparatus according to one embodiment of the present invention;  
     [0017]FIG. 2 is a front view of the moving stand, heater unit and inspection camera;  
     [0018]FIG. 3 is a plan view of the moving stand, heater unit and inspection camera;  
     [0019]FIG. 4 is a sectional view of the moving stand taken along the line  4 - 4  of FIG. 1;  
     [0020]FIG. 5 is an explanatory diagram of the electrical construction and operation of the embodiment;  
     [0021]FIG. 6 is a plan view of the carrier film;  
     [0022]FIG. 7 is an explanatory diagram of the conventional bonding; and  
     [0023]FIG. 8 illustrates a bonding process that uses a conventional flip-chip system. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0024] A preferred embodiment of the present invention will be described below with reference to the accompanying drawings.  
     [0025] In FIG. 1, the electronic part assembly apparatus  1  of the shown embodiment of the present invention is a die bonder or a die bonding machine. The die bonder is comprised of a loader unit  4  which accommodates an unworked carrier film  2  that is wound on a reel  8 , an unloader unit  6  which takes up the worked carrier film  2  on a reel  10 , and a bonding unit  14  which is equipped with a bonding head  12  that performs the bonding process.  
     [0026] In addition to the reel  8 , the loader unit  4  is equipped also with a spacer reel  19  that takes up a protective tape  18  when the carrier film  2  is unwound. Likewise, in addition to the reel  10 , the unloader unit  6  is equipped with a spacer reel  20  which takes up a protective tape  22  when the carrier film  2  is taken up on the reel  10 .  
     [0027] In addition to the bonding head  12 , a resin-dropping unit  24 , drying sections  26  and  28 , a heater unit  30  and an inspection camera  32  are installed in the bonding unit  14 . Furthermore, a transfer arm  31 , that places the silicon chips on the carrier film  2 , and an operating panel  33 , that operates the transfer arm  31 , are disposed in the vicinity of the bonding position  34 .  
     [0028] The resin-dropping unit  24  drops a resin material in which a conductive powder is dispersed onto the conductive layer of the carrier film  2 . The drying sections  26  and  28  both have a tubular shape that surrounds the carrier film  2 , and these drying sections  26  and  28  heat the dropped resin material by means of a hot air draft. However, the heating part  26  performs pre-heating at a temperature that is slightly lower than the curing temperature of the resin material, while the heating part  28  hardens the resin material by heating said material to its curing temperature.  
     [0029] The heater unit  30  and inspection camera  32  are mounted on a moving stand  36 . As shown in FIG. 2, the moving stand  36  consists of a fixed part  38  and a movable part  40 . The movable part  40  is formed by connecting an upper-surface plate  42  and a bottom-surface plate  44  by means of supporting columns  46 . The heater unit  30  is bolted to the upper-surface plate  42 , and the inspection camera  32  is set on the upper-surface plate  42  with a position adjustment mechanism  48  interposed.  
     [0030] The position adjustment mechanism  48  is used for the manual alteration and setting of the position of the inspection camera  32  in the XY plane. The position adjustment mechanism  48  comprises adjustment screws  50  that adjust the positions in the X and Y directions, a block  51  that is screw-engaged with these adjustment screws  50 , a guide rail  52  and slider  54  which are engaged with each other so that the slider  54  is slidable, and a lock screw  56  that fixes the set position.  57  indicates a holder on which the inspection camera  32  is set. The block  51  is moved in the X direction and Y direction (which are the axial directions of the adjustment screws  50 ) by operating the adjustment screws  50 . As a result, the inspection camera  32  moves in the range indicated by the broken line  59  in FIGS. 2 and 3.  
     [0031] Sliders  58  are fastened to the bottom surface of the bottom-surface plate  44  as shown in FIG. 4. Guide rails  60  are fastened to a fixed part  38  that faces these sliders  58 . A reciprocating type hydraulic cylinder  62  is installed parallel to the guide rails  60 , and a block  65  and stopper  66  are installed on the tip end of the rod  64  of this hydraulic cylinder  62 . The block  65  is fastened to the bottom-surface plate  44  of the movable part  40 .  68  indicates an adjustable restrictor which restricts the range of movement of the block  65  and stopper  66 . Accordingly, as a result of the protruding and retracting operation of the hydraulic cylinder  62 , the movable part  40  of the moving stand  36  is caused to move via the block  65 . In this way, the heater unit  30  and inspection camera  32  are caused to move as a unit in the X-X direction (see FIG. 2).  
     [0032] As shown in FIGS. 2 and 3, a bifurcated damper  70  is installed directly above the bonding position  34  so that the damper  70  can be raised and lowered by means of a raising-and-lowering mechanism (not shown in the figures). As a result, the carrier film  2  is pressed against the heater unit  30  in the bonding process.  
     [0033] As shown in FIG. 5, a ring-form light source  72  consisting of LEDs is disposed in the upper edge portion of the inspection camera  32 . The reason for using a ring-form light source is to avoid halation during imaging. Furthermore, the output side of the inspection camera  32  is connected to a monitor  74  via an amplifier  73 , so that a light image of the carrier film  2  can be displayed on this monitor  74 .  
     [0034] In the above embodiment, a light-transmitting heat-resistant resin film is used as the carrier film  2 . Heat-resistant polyimide films such as products marketed under the trademark Kapton by Du Pont-Toray Co., Ltd. can be used as the carrier film  2 . Products marketed under the trademark Upilex by Ube Industries, Ltd. are especially suitable for use as such a resin film. However, any other film which has a heat resistance and mechanical strength that can withstand bonding, and appropriate moisture absorption characteristics, and which consists of a material that transmits visible light, may also be used.  
     [0035] In the electronic part assembly apparatus  1  of the above embodiment, the leads  76  formed on the surface of the carrier film  2  and the bonding pads  80  of the silicon chips  78  are bonded by adhesion using a resin in which a conductive powder is dispersed. In other words, as the initial operation, the heater unit  30  is first positioned in the bonding position  34  as shown in FIG. 2; the carrier film  2  is pressed against the heater unit  30  from above by the damper  70 ; a silicon chip  78  is placed in the expected position by the transfer arm  31  (see FIG. 1); and then bonding is performed while applying heat and pressure from above by means of the bonding head  12 .  
     [0036] Next, the hydraulic cylinder  62  is actuated so that the operating rod of said cylinder  62  is caused to protrude, thus moving the movable part  40  of the moving stand  36  toward the left in the figure. As a result, the inspection camera  32  is positioned in the bonding position  34 . Since the image obtained by the inspection camera  32  is displayed on the monitor  74 , the worker operates the adjustment screws  50  while viewing this image, and checks for the presence or absence of positional deviations between the leads  76  and the bonding pads  80  by observing the bonded areas around the entire circumference of the silicon chip  78 . When any positional deviation exists, the operator operates the operating panel  33  and changes the set value of the offset of the transfer arm  31  (i.e., the positional coordinates in the horizontal direction, i.e., in the X and Y directions). The position of the silicon chip  78  is thus corrected. The above operation is the initial setting operation.  
     [0037] When this initial setting operation is completed, the hydraulic cylinder  62  is next operated so that the operating rod of said cylinder  62  is retracted, thus causing the movable part  40  of the moving stand  36  to move toward the right in the figure. As a result, the heater unit  30  is again positioned in the bonding position  34 , and the inspection camera  32  is positioned in the inspection position  35 . Afterward, the bonding process is continuously performed by the bonding head  12  and heater unit  30 , and the worker makes successive spot checks for positional deviation between the leads  76  and bonding pads  80  while observing the image on the monitor  74  obtained by the inspection camera  32 . In cases where there is an abnormality, i.e., a positional deviation between the leads  76  and bonding pads  80  that is outside the permissible range, the operation of the apparatus is stopped, and the operating panel  33  is operated in accordance with the amount of positional deviation in the image on the monitor  74 , so that the set value of the offset of the transfer arm  31  is appropriately corrected.  
     [0038] Thus, in the above embodiment, the light transmissivity of the carrier film  2  is utilized, and the conditions of bonding between the leads  76  formed on the carrier film  2  and the bonding pads  80  of the silicon chips  78  are inspected based upon light images of the bonding pads  80  that are transmitted through the carrier film  2 . Accordingly, there is no need for a complicated inspection process involving the stripping of bonded silicon chips  78 , so that the inspection can be performed with good efficiency.  
     [0039] Furthermore, the conditions of bonding are detected based upon light images of the bonding pads  80  that are transmitted through the band-form carrier film  2  in a state in which a plurality of silicon chips  78  are held in a set on the carrier film  2 . Accordingly, detection can be performed continuously without stopping the apparatus, so that the inspection process is made even more efficient.  
     [0040] In addition, the heater unit  30  (constituting the lower member) and the inspection camera  32  are selectively positioned at a location that faces the bonding head  12  (constituting the upper member) by the movement of the movable part  40  of the moving stand  36 . Accordingly, an inspection to ascertain whether or not the bonding process has been favorably completed is performed without moving the carrier film  2  by positioning the inspection camera  32  at a position that faces the bonding head  12  after bonding has been performed by the bonding head  12  and heater unit  30 . Furthermore, when the heater unit  30  is positioned at a location that faces the bonding head  12 , the inspection camera  32  faces silicon chips  78  that have already been subjected to bonding on the carrier film  2 . Accordingly, bonding by the bonding head  12  and heater unit  30  and detection by the inspection camera  32  can be continuously performed in parallel by feeding the carrier film  2  from the bonding position  34  where bonding is performed toward the inspection position  35  where detection is performed.  
     [0041] Moreover, a worker inspects for positional deviation between the leads  76  and bonding pads  80  by visual observation of the images on the monitor  74 . Instead, however, it is possible to employ a structure in which the output side of the inspection camera  32  is connected to an image processing device, positional deviations between the leads  76  and bonding pads  80  are converted into numerical data by image processing, and an abnormality is judged to have occurred when the amount of positional deviation exceeds a specified permissible value. Moreover, it is also possible to feed back the amount of positional deviation to the amount of offset of the transfer arm  31  so as to automatically correct the positional deviation.  
     [0042] In the above embodiment, the positions of the inspection camera  32  in the X and Y directions are adjusted by the manual operation of adjustment screws  50 . However, it is possible to connect respective servo motors to the adjustment screws  50 , thus adjusting the positions of the inspection camera  32  in the X and Y directions by manually operate these servo motors. Furthermore, it is also possible to operate such servo motors in accordance with the positioning pitch of the silicon chips  78 , thus positioning the inspection camera  32  in an optimal position in accordance with the positioning pitch of the silicon chips  78  in various products.  
     [0043] Moreover, in the above embodiment, a resin material in which a conductive powder is dispersed is used. Instead, various other universally known methods can be used as the bonding method in the present invention, including a method that uses a resin material that does not use a conductive powder, and a method in which the leads  76  and bonding pads  80  are bonded by thermal fusion or a eutectic reaction of both parts without using a resin material itself.  
     [0044] Furthermore, in the above embodiment, the upper member used in the bonding process is the bonding head  12 , and the lower member is the heater unit  30 . However, the positions of these members may be reversed.  
     [0045] Moreover, the above description of the present invention is made with respect to a die bonder. However, the present invention is not limited to a die bonder. The method and apparatus of the present invention is applicable to various other types of apparatuses used for semiconductor element assembly as well as to other types of electronic part assembly apparatuses utilizing carrier films. Such constructions are in the scope of the present invention.