Patent Document

BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a die bonder. 
     2. Description of the Related Art 
     A die bonder is an apparatus which bonds a die (silicon wafer chip integrating electric circuits) to a lead frame, substrate or the like (hereinafter, referred to as “substrate”) using solder, gold plate or resin as a bonding material. An engineering plastic is used as a die bond material (paste, film) for bonding the die and the substrate together. After positioning, the die is bonded to the lead frame or the like. A method of implementing bonding using a resin as the bonding material is now predominant. 
     In semiconductor die bonding, solder or resin paste for die bonding (Ag epoxy and Ag polyimide) is used as an adhesive for fixing a semiconductor chip (IC, LSI) to the lead frame, ceramic case, substrate or the like. 
     The adhesive for bonding the die to the substrate is applied by a syringe which is vertically movable and ejects a paste adhesive. Specifically, the syringe enclosing therein the paste adhesive applies a predetermined amount of adhesive to a predetermined place on the substrate. 
     In this regard, the syringe containing therein the paste adhesive and a pattern on the lead frame need be checked by capturing an image thereof with a recognition camera before a bonding operation is carried out. It is therefore a conventional practice to move the recognition camera to an imaging position for acquiring the image and to detect a proper bonding position before carrying out the bonding operation. After bonding, the recognition camera is moved again to the imaging position to acquire an image for determination as to whether the paste adhesive is properly applied or not. 
     In this manner, the conventional die bonder causes the recognition camera to make two runs to the imaging position for image acquisition each time the paste adhesive is applied to the lead frame. These are quite wasteful steps. Namely, the conventional die bonder involves an inefficient movement to lower throughput per unit time. 
     In addition, a clear image free from the moiré phenomenon is necessary for making an exact determination of an application position of the paste adhesive and an amount of applied paste adhesive, to thereby prevent product failure. 
     However, the above JP-A No.2001-127080 and JP-A No.2004-288715 do not give due consideration to the increase in the throughput of an adhesive application job although a camera for image recognition and an illumination element are provided. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a die bonder that eliminates the need for an operation of moving a recognition camera for capturing an image related to adhesive application and achieves high reliability with high throughput. 
     According to an aspect of the invention, the above object is accomplished in a die bonder which comprises: a syringe located above a lead frame and enclosing therein a paste adhesive; a recognition camera fixed to place lateral to the syringe; an illumination element disposed in the vicinity of the recognition camera; and a reflector plate disposed in opposed relation to the illumination element, wherein the reflector plate reflects light from the illumination element onto a die at an application surface of the paste adhesive. 
     According to another aspect of the invention for achieving the above object, it is preferred that the recognition camera, the illumination element and the reflector plate are arranged in a manner that the reflector plate is disposed on a front side of the die bonder and the recognition camera and the illumination element are disposed on a back side of the die bonder with respect to the syringe located above the lead frame transported in X direction. 
     According to another aspect of the invention for achieving the above object, it is preferred that the illumination element is disposed below the recognition camera. 
     According to another aspect of the invention for achieving the above object, it is preferred that the illumination element is an illumination device including a plurality of LEDs arranged in a ring form and the illumination device surrounds an outside circumference of a lens of the recognition camera. 
     According to another aspect of the invention for achieving the above object, it is preferred that a reflective surface of the reflector plate is provided with a white matte coating. 
     According to another aspect of the invention for achieving the above object, it is preferred that the white matte coating has a thickness of 0.02 mm or more and 0.04 mm or less. 
     The object of the invention can be achieved by providing the die bonder that eliminates the need for the operation of moving the recognition camera for capturing the image related to adhesive application and achieves high reliability with high throughput. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a conceptual diagram of a die bonder according to a first embodiment of the invention as seen from above; 
         FIG. 2  is an external perspective view showing a preform portion according to the first embodiment of the invention; 
         FIG. 3  is a schematic diagram showing a structure of the preform portion according to the first embodiment of the invention; 
         FIG. 4  is a schematic diagram showing a structure of a preform portion according to a second embodiment of the invention; 
         FIG. 5  is a front view showing an illumination device according to the second embodiment of the invention; and 
         FIG. 6  is a flow chart showing the steps of an operation according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the invention will hereinbelow be described with reference to the accompanying drawings. 
     First Embodiment 
       FIG. 1  is a conceptual diagram of a die bonder according to a first embodiment of the invention as seen from above. 
     Referring to  FIG. 1 , a die bonder  10  principally includes a wafer feeder  1 , a frame feeding/transporting portion  2  and a die bonding portion  3 . The frame feeding/transporting portion  2  includes a stack loader  21 , a frame feeder  22  and an unloader  23 . A frame (hereinafter, referred to as “lead frame”) supplied by the stack loader  21  to the frame feeder  22  is transported to the unloader  23  via two processing positions on the frame feeder  22 . 
     The die bonding portion  3  includes a preform portion  31  and a bonding head portion  32 . The preform portion  31 , preceding the die bonding portion  3  in operation, applies a die attach adhesive (hereinafter, referred to as “paste adhesive”) onto the frame delivered by the frame feeder  22 . Picking up a die from a pickup device  12 , the bonding head portion  32  is moved up and parallel, thus transferring the die to a bonding point above the frame feeder  22 . The bonding head portion  32  lowers the die so as to bond the die onto the frame to which the paste adhesive is applied. 
     A recognition camera  33  is installed in the vicinity of the preform portion  31 . The recognition camera  33  is used for recognizing a pattern on the lead frame and determining whether or not a predetermined amount of paste adhesive is applied to a predetermined position. As will be described hereinlater, the preform portion  31  is provided with a vertically movable syringe  36  at an upper part thereof. A paste adhesive  37  is enclosed within this syringe  36  so as to be ejected through a nozzle tip by air pressure. 
     The wafer feeder  1  includes a wafer cassette lifter  11  and the pickup device  12 . The wafer cassette lifter  11  includes a wafer cassette loaded with wafer rings (not shown) for sequentially feeding the wafer rings to the pickup device  12 . 
     The present inventors first investigated a fixing position of the recognition camera, and found a problem occurs in a case where the recognition camera is fixed in place on a front side of a main body  4  of the die bonder with respect to the syringe (on the −Y side of the preform portion as seen in  FIG. 1 ). 
     Specifically, when replenishing the paste adhesive enclosed within the syringe, the syringe is extracted in the −Y direction as seen in  FIG. 2  so that a work area for a worker to extract the syringe lies in the same direction as the recognition camera mentioned. Hence, if the recognition camera is located on the front side of the main body of the die bonder, it interferes with the syringe extracting job. Accordingly, the present inventors conducted various tests with the recognition camera fixed in place on the back side of the main body of the die bonder (on the +Y side of the preform portion as seen in  FIG. 1 ) and arrived at the following embodiments. 
       FIG. 2  is an external perspective view showing the preform portion according to the first embodiment of the invention. 
     Referring to  FIG. 2 , a lead frame  34  is moved in the X direction indicated by an arrow in the figure. The syringe  36  is disposed above the lead frame  34 . The paste adhesive  37  is enclosed within this syringe  36 . With the syringe  36  moved up in Z direction, the recognition camera  33  is operated for determination of the position of the lead frame  34  and the amount of applied paste adhesive  37 . This recognition camera  33  is fixed in an angled position so as to direct a lens  33   a  thereof to an application surface of the paste adhesive  37  at all times. An illumination lamp  38  is disposed under the recognition camera  33 . The illumination lamp  38  includes a plurality of LEDs  38   a . A reflector plate  39  is angularly disposed at place opposed to the illumination lamp  38  and reflects light from the illumination lamp  38  on the lead frame  34  at a pattern recognition surface or at the application surface of the paste adhesive  37 . 
     The preform portion  31  having the above structure operates as follows to apply the paste adhesive. 
     Specifically, the lead frame  34  is moved from the X direction indicated by the arrow. The lead frame  34  stops when arriving at place directly under the syringe  36 . Meanwhile an image captured by the fixed recognition camera  33  is checked to determine whether the lead frame  34  is stopped at a correct position or not. If it is determined that the stop position of the lead frame corresponds to a predetermined position, the syringe  36  is lowered to apply the paste adhesive  37  to a predetermined place on the lead frame  34 . When the application of the paste adhesive  37  by the syringe  36  is done and the syringe  36  is moved up in the Z direction, the recognition camera  33  checks to determine whether a proper amount of paste adhesive  37  is applied or not, or whether dripping of the paste adhesive occurred or not. If it is determined that the proper amount of paste adhesive is applied without dripping, the operation proceeds to the next application job. 
     It is noted that the syringe  36  indicated by a dotted line in the figure represents a position to apply the paste adhesive while the one indicated by a solid line represents a position to which the syringe  36  is moved up (Z direction). That is, the figure illustrates a state where the syringe  36  is moved up so as not to block the light from the illumination lamp  38 , allowing the recognition camera  33  to observe the amount of applied paste adhesive. 
       FIG. 3  shows the preform portion in side view. 
     Referring to  FIG. 3 , with the syringe  36  moved up, an area where the paste adhesive is applied is observed by the fixed recognition camera  33 . At this time, the light from the illumination lamp  38  is applied toward the reflector plate  39  and reflected by this reflector plate  39  to illuminate the application surface of the paste adhesive, as indicated by a dotted line in the figure. 
     By the way, the illumination lamp  38  includes a plurality of LEDs (In this embodiment, an investigation was made using six LEDs). A reflector plate having a glossy surface (mirror polished surface) was provided to reflect the light from the illumination lamp  38  onto the lead frame  34  at the application surface of the paste adhesive. However, it was found that captured images sustained disturbances or distortion. This is the so-called moiré phenomenon on image or image distortion which occurs when periodic patterns overlap with each other. 
     After making various investigations on what caused the moiré phenomenon, the present inventors reasoned that the mirror polished reflector plate  39  was responsible for the moiré phenomenon. A white matte coating was applied to the reflector plate  39  (coating thickness on the order of 0.03 mm). As a result, favorable images free from the moiré phenomenon were obtained. Incidentally, the coating having thickness in the range of 0.02 to 0.04 mm affords favorable results. 
     Thus, this embodiment accomplishes the high-throughput adhesive application job by eliminating the need for moving the recognition camera for image acquisition. In addition, the embodiment can set the fixing position of the recognition camera in a place that is not affected by the removal of the syringe. 
     Furthermore, this embodiment can prevent the acquired images from being affected by the moiré´ phenomenon, thereby ensuring a reliable adhesive application. 
     Second Embodiment 
       FIG. 4  is a schematic diagram showing a structure of a preform portion according to a second embodiment of the invention. 
     Referring to  FIG. 4 , the syringe  36  is disposed above the lead frame  34 . This syringe  36  encloses therein the paste adhesive  37 . With the syringe  36  moved up, the recognition camera  33  observes the position of the lead frame  34  or the amount of applied paste adhesive. A ring-like illumination lamp  38  is attached to an outside circumference of the lens  33   a  mounted in the recognition camera  33  (The lamp  38  will be specifically described with reference to  FIG. 5 ). This illumination lamp  38  includes a plurality of LEDs  38   a . The reflector plate is angularly disposed at place opposed to the illumination lamp  38  and reflects light from the illumination lamp  38  on the lead frame  34  at the pattern recognition surface or at the application surface of the paste adhesive  37 . 
     The preform portion  31  having the above structure operates as follows to apply the paste adhesive. 
     Specifically, the lead frame  34  stops when arriving at place directly under the syringe  36 . Meanwhile an image captured by the fixed recognition camera  33  is checked to determine whether the lead frame  34  is stopped at a correct position or not. If it is determined that the stop position of the lead frame corresponds to the predetermined position, the syringe  36  is lowered to apply the paste adhesive  37  to the predetermined place on the lead frame  34 . When the application of the paste adhesive  37  by the syringe  36  is done and the syringe  36  is moved up, the recognition camera  33  checks to determine whether the proper amount of paste adhesive  37  is applied or not. When it is determined that the proper amount of paste adhesive is applied, the operation proceeds to the next application job. 
     It is noted that the syringe  36  indicated by the dotted line in the figure represents the position to apply the paste adhesive while the one indicated by the solid line represents the position to which the syringe  36  is moved up (Z direction). That is, the figure illustrates a state where the syringe  36  is moved up so as not to block the light from the illumination lamp  38 , allowing the recognition camera  33  to observe the amount of applied paste adhesive. 
       FIG. 5  is a front view showing an illumination device according to the second embodiment of the invention. 
     Referring to  FIG. 5 , the ring-like illumination lamp  38  is attached in a manner to surround the lens  33   a  of the recognition camera  33 . This ring-like illumination lamp  38  is a single illumination device including a plurality of LEDs arranged in a case shaped like a ring (In this embodiment, the investigation was made using six LEDs). 
     Needless to say, this embodiment applied the white matte coating to the reflector plate  39  in order to prevent images captured by the recognition camera  33  from suffering from the moiré phenomenon. 
     According to this embodiment, a clear image free from the moiré phenomenon can be acquired because the ring-shaped illumination is provided to apply the light to the area of the applied adhesive in a focused way. 
       FIG. 6  is a flow chart showing the steps of an operation according to an embodiment of the invention. 
     In  FIG. 6 , 
     Step  101 : With the lead frame delivered to the predetermined position, the preform portion prepares for the application of the paste adhesive. 
     Step  102 : The recognition camera observes to check if the lead frame is delivered to the predetermined position. 
     Step  103 : If any displacement of the lead frame is observed in the camera&#39;s field of view, an amount of displacement from the predetermined position is calculated so as to be used for correction of the position to apply the paste adhesive. If, on the other hand, the lead frame is displaced out of the camera&#39;s field of view or the position thereof is unrecognizable, an error is detected to suspend the job (Step  104 ). 
     Step  105 : The syringe is lowered to apply the predetermined amount of paste adhesive onto the lead frame . 
     Step  106 : When the syringe finished with the application of past adhesive is moved up, the recognition camera checks the condition of the applied paste adhesive. 
     Step  107 : If the amount of applied paste adhesive is insufficient or abrasion is observed, an application job error is detected to suspend the job (Step  108 ). If it is determined that there is no problem, the step of applying the paste adhesive is completed. 
     According to the embodiment as described above, the predetermined amount of paste adhesive can be applied to the lead frame without displacement because the job of applying the paste adhesive is always monitored by the recognition camera. If the lead frame should be displaced, the application job error due to displacement will not occur because the displacement is corrected when the paste adhesive is applied. In the event that the lead frame is displaced out of the camera&#39;s field of view, that the paste adhesive is applied in an amount other than the predetermined amount, or that abrasion on the adhesive application surface results from an insufficient amount of paste adhesive applied, the application job error is immediately detected to suspend the job. Hence, there is no fear of any defective product coming on the market. 
     According to the invention as described above, the need for moving the recognition camera is eliminated so that an increased throughput is achieved, leading to higher productivity. Further, the syringe becomes more maintainable because the nozzle tip of the syringe can be checked by the recognition camera. 
     Furthermore, the quality improvement can be achieved because the recognition camera also facilitates determination as to whether or not the paste adhesive is applied properly or checking for dripping. What is more, an even higher quality improvement can be achieved because the reflector plate of the embodiment affords the image free from moiré disturbance or distortion for checking of the application surface.

Technology Category: 5