Abstract:
A method of detaching a film of material ( 2 ) from the surface ( 5 ) of a substrate ( 1 ). An outlet ( 11 ) of a fluid delivery device ( 10 ) is engaged with an aperture ( 7, 8 ) in the substrate ( 1 ) from the opposite side of the substrate ( 1 ) from the surface ( 5 ) to which the film ( 2 ) is attached. Fluid is passed out of the outlet ( 11 ) and through the aperture ( 7, 8 ) to generate a detaching force between the film of material ( 2 ) and the surface ( 5 ) adjacent to the aperture ( 7, 8 ).

Description:
FIELD OF THE INVENTION  
         [0001]    The invention relates to a method of detaching a film of material from a substrate.  
         BACKGROUND OF THE INVENTION  
         [0002]    Recently, semiconductor device packaging techniques have been developed in which a semiconductor chip is mounted on a substrate and an epoxy resin material is molded around the semiconductor chip on only one side of the substrate. Hence, the underside of the substrate is left substantially free of the epoxy resin material. One particular type of packaged device where this technique is used is commonly known as a quad, flat, no lead (QFN) package where the substrate is a metal lead frame. In order to prevent epoxy resin material seeping onto the underside of the lead frame and causing flashing, it is conventional practice to attach an adhesive masking tape to the underside of the lead frame. The lead frame with semiconductor chip and masking tape is then placed into a mold and epoxy resin material is molded around the semiconductor chip. The masking tape minimises seepage of epoxy resin molding material onto the underside of the lead frame, and so helps reduce flashing.  
           [0003]    However, one of the problems with using masking tape to minimise flashing on the underside of the lead frame is the subsequent processing of the lead frame to detach the adhesive masking tape from the lead frame without damaging the lead frame or the packaged device.  
         SUMMARY OF THE INVENTION  
         [0004]    In accordance with a first aspect of the present invention, there is provided a method of detaching a film of material from the surface of a substrate, the method comprising engaging a fluid delivery device with an aperture in the substrate from the opposite side of the substrate from which the film is attached to the substrate, and causing the fluid delivery device to pass a fluid through the aperture to generate a detaching force between the film of material and the surface of a substrate adjacent to the aperture.  
           [0005]    Preferably, the method further comprises inserting the fluid delivery device through the aperture from the opposite side of the substrate to which the film is attached, and pressing the fluid delivery device against the film to separate the film from the surface of the substrate adjacent to the aperture prior to passing the fluid through the aperture.  
           [0006]    In accordance with a second aspect of the present invention, there is provided a method of detaching a film of material from a surface of the substrate, the method comprising attaching a detachment member to the external surface of the film opposite to the surface of a substrate such that the attachment force between the detaching member and the film is greater than the adhesion force between the film and the surface of a substrate, and moving the detachment member away from the surface of the substrate to cause the film to detach from the substrate.  
           [0007]    Preferably, the first aspect of the invention may be used in combination with the second aspect of the invention to remove the film from the substrate.  
           [0008]    Typically, the first aspect of the invention is used to initiate detachment of the film from the substrate and the second aspect of the invention is used to remove the film from the substrate.  
           [0009]    In one example of the invention, the detaching member may comprise a second film of material which is attached to the exposed side of the first film, typically by an adhesive. Typically, where the first aspect is used in combination with the second aspect, the second film is attached to the first film before the fluid is passed through the aperture in the substrate by the fluid delivery device.  
           [0010]    Preferably, the second film comprises a layer of adhesive.  
           [0011]    In a further example of the invention, the detaching member comprises a clamp device adapted to clamp onto an edge portion of the first film  
           [0012]    Preferably, the aperture in the substrate is adjacent the edge portion of the first film which is engaged by the clamp device.  
           [0013]    Preferably, the clamp member comprises a wedge shaped member which is adapted to be inserted between the first film and the substrate and a clamp member movable relative to the wedge shaped member to cause the film to be clamped between the wedge shaped member and the clamp member when the clamp member moves to a clamping position. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    Examples of a method for detaching a film of material from a substrate in accordance with the invention will now be described with reference to the accompanying drawings, in which:  
         [0015]    [0015]FIGS. 1A to  1 C are cross-sectional schematic views of an air purge mechanism showing initiating detachment of a masking tape from a lead frame;  
         [0016]    [0016]FIGS. 2A to  2 C are schematic cross-sectional views showing removal of the masking tape from the substrate following initiation of the detachment using a clamp mechanism; and  
         [0017]    [0017]FIGS. 3A and 3B show removal of the masking tape from the substrate using an adhesive tape. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0018]    [0018]FIGS. 1A to  1 C show a lead frame  1  with a polyimide adhesive tape  2  attached to a surface  5  of the lead frame  1 . In this example, the lead frame  1  is a lead frame for a QFN semiconductor device package and a semiconductor chip (not shown) would be mounted on surface  6  of the lead frame  1  on a die attach portion (not shown) of the surface  6 . The masking tape  2  is attached to the surface  5  of the lead frame  1  so that during molding of epoxy resin material around a chip mounted on the surface  6 , seepage of epoxy resin material onto the surface  5  (commonly known as flashing) is minimised.  
         [0019]    However, after molding, it is necessary to remove the masking tape  2  from the surface  5  of the lead frame  1 . Therefore, after the molded lead frame is removed from the mold, it passes to a position in an air purge mechanism  10  as shown in FIG. 1A. The air purge mechanism  10  includes a hollow probe  11  and a passage within the probe  11  communicates with an air inlet chamber  12  located in an air purge block  13 . The air purge mechanism  10  is movable relative to the lead frame  1  along an axis  14  so that the probe  11  can be inserted into an aperture  7  formed in a recess  8  in surface  6  of the lead frame  1 . Surface  50  of the air purge block  13  is configured to be parallel to surface  52  of the recess  8 . The aperture  7  is a through aperture between the recess  8  and surface  5  of the lead frame.  
         [0020]    Hence, when the probe  11  is inserted into the aperture  7  through the recess  8 , the end of the probe  11  hits the surface of the masking tape  2  which is adhered to the surface  5  and further movement of the probe  11  into the hole  7  (see FIG. 1B) causes detachment of the film  2  from the lead frame  1  in the region adjacent to the hole  7  to form a cavity  16 . At the same time a seal  15  on the probe  11  seals between the probe  11  and the hole  7 . The air inlet  14  is connected to a pressurised air source (not shown) which is then actuated to cause air to flow through the probe  11  into the cavity  16  formed by the probe  11  pushing against the tape  2 . The change in volumetric flow rate and pressure within the cavity  16 , caused by air from the inlet  14  entering the cavity  16  through the probe  11 , causes separation of the masking tape  2  from the surface  5 , as shown in FIG. 1C.  
         [0021]    During the air purge operation, a support member  17  is moved into engagement with the tape  2  so that the tape  2  is supported on one side the probe  11 , as shown in FIG. 1C. This ensures that the masking tape  2  separates from the surface  5  on the left hand side of the probe  11 , as shown in FIG. 1C, as air is prevented from separating the masking tape  2  from the lead frame  1  on the right hand side by the support member  17 . This ensures that if the recess  8  and hole  7  are located adjacent to an edge  3  (see FIG. 2A) of the lead frame  1 , the tape  2  separates from the lead frame  1  at the edge  3  to enable a clamping mechanism  20  to engage with the edge of the masking tape  2  to enable the clamping mechanism  20  to remove the masking tape  2  from the lead frame  1 .  
         [0022]    After separation of the tape  2  from the lead frame  1 , as shown in FIG. 1C, the tape  2  may be removed from the lead frame  1  using a clamp mechanism  20  which comprises a wedge shaped member  21  and a gripping member  22  (see FIG. 2A). The clamp mechanism  20  is moved in the direction of arrow  23  so that the wedge shaped member  21  is inserted between the tape  2  and the substrate  1 . The gripping member  23  is on the opposite side of the tape  2  from the wedge shaped member  21 , as shown in FIG. 2A. As shown in FIG. 2B, the gripping member  23  is then moved upwards, with respect to the wedge shaped member  21 , to clamp the end of tape  2  between the gripping member  23  and the wedge shaped member  21 . The clamp mechanism  20  is then moved away from the lead frame  1  in the direction of arrow  24  at a shearing angle θto the position shown in FIG. 2C. Further movement of the clamp mechanism  20  parallel to the lead frame  1  causes the tape  2  to be sheared away from surface  5  of the lead frame  1  to remove the masking tape  2  from the surface  5 .  
         [0023]    It should be noted that use of the air purge mechanism  10  is not essential to permit removal of the masking tape  2  using the clamp mechanism  20 , as it is possible that the edge  3  of the lead frame  1  could be configured to enable the clamping mechanism  20  to engage with the end of the tape  2  without requiring an edge portion of the masking tape  2  to be first separated from the lead frame  1 .  
         [0024]    In addition, the use of the clamp mechanism  20  following use of the air purge mechanism  10  is not essential. After use of the air purge mechanism  10  to cause separation of a portion of the masking tape  2  from the lead frame  1 , removal of the masking tape  1  from the lead frame could be performed using any other suitable means. For example, the masking tape  2  could be removed using an adhesive tape  32  which is adhered to the exposed side of the masking tape  2  (i.e. the side of the masking tape  2  not attached to the lead frame  1 ), as shown in FIGS. 3A and 3B.  
         [0025]    [0025]FIGS. 3A and 3B show an adhesive masking tape removal mechanism  30  which includes a supply drum  31  on which is mounted a roll of adhesive tape  32 . The adhesive tape  32  extends around the tension roller  33 , an idling roller  34 , through a pair of guide rollers  35  to a waste drum  36 . The adhesive tape removal mechanism  30  also includes a press roller  37  which can be moved vertically in the direction of the arrow  38  with respect to the idle roller  34  and the guide rollers  35  and horizontally in the direction of the arrow  39 .  
         [0026]    In use, a roll of adhesive tape  32  is mounted on the supply drum  31  and fed around the tensioning roller  33 , the idle roller  34 , through the guide rollers  35  and attach to the waste drum  36 . The adhesive tape  32  is orientated so that the adhesive side of the tape  32  is directed upwards towards a lead frame clamp  40 . When a lead frame  2  is mounted in the clamp  40  after molding, the masking tape  2  attached to the surface  5  of the lead frame is located above the adhesive tape  32  between the idle roller  34  and the guide rollers  35 . The press roller  37  is then moved upwards to cause the adhesive tape  32  to contact the exposed side of the masking tape  2  and moved left and right in the direction of the arrow  39  to press the adhesive tape  32  onto the exposed side of the masking tape  2  so that the adhesive tape  32  adheres to the exposed side of the masking tape  2 . The press roller  37  is then lowered away from the lead frame  1  and the adhesive tape removable mechanism  30  is moved in the direction of arrow  41  to peel the masking tape  2  away from the lead frame  1 , as shown in FIG. 3B.  
         [0027]    The masking tape  2  is peeled away from the lead frame  1  as the adhesive tape  32  is chosen such that the adhesion of the tape  32  to the exposed side of the masking tape  2  is greater than the adhesion of the masking tape  2  to the lead frame  1 .  
         [0028]    After adhesive tape  32  and masking tape  2  have been removed from the lead frame  1 , the waste drum  36  is rotated by a drive mechanism (not shown) to wind the tape  32  onto the waste drum  36 .  
         [0029]    After the masking tape  2  has been removed from the lead frame  1 , the waste drum  36  continues to be driven until a new section of adhesive tape  32  is located between the idle roller  34  and the guide rollers  35 . The adhesive tape removal mechanism  30  then moved in a reverse direction to the arrow  41  to return it to its original position and the new section of adhesive tape  32  between the idle roller  34  and guide rollers  35  can be used to remove another masking tape  2  from another lead frame  1 .  
         [0030]    In addition, as shown in FIG. 3B, the air purge mechanism  10  described above, and shown in FIGS. 1A to  1 C can also be used to aid detachment of the masking tape  2  from the lead frame  1 . It should be noted that the air purge mechanism is used to aid detachment of the masking tape  2  after the adhesive tape  32  has been pressed on to the masking tape  2  by the press roller  37 .