Abstract:
A method for moving a workpiece having a first plurality of alignment features and a second plurality of alignment features. The method comprises attaching the workpiece to a workpiece advancer using at least a portion of the first alignment features such that the workpiece can move incrementally relative to the workpiece advancer. The method also includes shifting the workpiece using the workpiece advancer.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 09/146,702 filed Sep. 3, 1998 and issued as U.S. Pat. No. 6,029,329, which is a divisional of U.S. patent application Ser. No. 08/598,148 filed Feb. 7, 1996 and issued as U.S. Pat. No. 5,907,902. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to the continuous handling of material for processing. More particularly, the present invention relates to a belt feed machine for trimming and forming leads on semiconductor electrical components. 
     2. Description of the Invention Background 
     Solid state electrical devices are typically connected to other devices, as well as common substrates, such as printed circuit boards, through the use of electrical connectors, or leads, that are attached to input and output contacts on the device. The quality of the electrical connections between the devices depends upon the proper formation and positioning of the leads and the proper placement of the device. 
     The individual electrical devices are typically mass produced on common semiconductor substrate, or wafer, which is subsequently cut up to separate the individual dies. Electrical leads are attached to the dies as part of a preformed lead frame in which the leads are flat members extending from a common paddle that is attached to the face of the die. The leads are subsequently trimmed from the lead frame and formed to the desired shave after attachment to the die. Lead frames are often produced as a series of individual frames, each containing electrical leads for attachment to a die. The formation of multiple devices in a single lead frame or strip provides for easier handling of the lead frame during processing. In addition, the lead frames typically contain indexing holes for use in handling and alignment of the lead frame during subsequent processing. After the leads are attached, the devices are typically encapsulated in a molding compound to protect the device from moisture and other deleterious environmental conditions. The lead frames also contain dambars that are attached perpendicularly to the leads to provide structural support to the leads during processing and to prevent molding compound that extrudes from the mold during the encapsulation, known as flashing, and accumulates between the leads from flowing onto the portion of the leads to be attached to another component or onto adjacent devices. 
     After the plastic encapsulation of the device, the flashing and the dambars must be removed from between the leads. In addition, the electrical leads must be disconnected from the lead frames, trimmed and formed to a desired shape. Finally, the individual devices must be separated from the lead frame to yield the finished product. Each of these processes is generally performed through the use of die and punch tooling. 
     In the prior art, specially dedicated machines were used to perform each of the die and punch operations. The strips of lead frames would be processed in one machine for a given step and then transported to another machine to further processing. However, the transporting of the strips between machines and the required overhead with loading and feeding strips to the machines greatly increased the processing time and lowered the yield of the devices due to higher incidence of damage. Many of the problems with the use of the individual machines were overcome with development of integrated machines that can be used to perform a series of tooling operations on the framed device in one machine. In those machines, the die and punch tooling operations are linearly arranged in tooling stages and the frames are moved serially through each tooling operation. 
     The integrated machines use a “walking beam” method to advance the frames through the various stages. In a walking beam method, the lead frame or strip is fed into a track a the inlet of the machine with the lead frame and the faces of the devices in a horizontal orientation. The track supports the edges of the frame while leaving both faces of the device exposed and provides a guide for the strip through the machine as the strip is advanced by fingers extending from the walking beam. When the indexing holes on the lead frame reach the initial position of the first finger of the walking beam, a first set of pins extending from the first finger engage the indexing holes in the lead frame. Actuation of the beam causes the finger to move the lead frame to the first tooling stage. In the tooling stages, the punch tooling is reciprocated to contact and push the lead frame from above so as to disengage the lead frame from the pins on the walking beam finger and to push the lead frame onto the alignment pins attached to the stationary die. Once the lead frame is seated with the alignment pins in the indexing holes, the punch tooling stroke is continued to perform the tooling operation on the device. After the punch tooling disengages the lead frame from the walking beam finger pins, the finger is reciprocated back to its initial position where the pins on the finger engage the next pair of indexing holes in the lead frame, while during the punch operation is occurring. After the punch operation is completed, the punch tooling is reciprocated away from the stationary die and the track and lead frame lift off of the alignment pins on the stationary die. The walking beam finger is then actuated to advance the next frame into the tooling stage, which advances the preceding frame into the next tooling stage. In the final step, the devices are removed, or singulated, from the frames and the frames are discarded. While the use of the walking beam has provided a significant improvement over the prior art, the overall throughput of the machines is limited by the number of times that the strip must be engaged and disengaged by the walking beam pins, which is one of the most time consuming operation during processing. Also, the necessary reciprocal motion of the actuator results in a significant amount of unnecessary machine operations that can affect the long term reliability of the machine. Additionally in the walking beam method, the punch tooling is reciprocated not only to bring the punch into contact with the device, but to align and drive the device into the die tooling. This procedure significantly increases the stroke length of the punch, thereby increasing the possibility of damaging the devices, in addition to potentially causing tooling alignment difficulties due to bending of the frames and/or track. 
     Some of the problems associated with the unnecessary machine motion and potential overstroke of the punching tooling are resolved with the development of the pinch roller advance machines. The pinch roller machine advances the strip in a vertically oriented position through the use of a series of pinch rollers that contact the edges of the lead frame. The only advancement operation performed by the pinch roller machine operation is the rotation of the pinch rollers to advance the strip, thereby eliminating the unnecessary reciprocal operations associated with the walking beam method. Additionally, the pinch roller machine provides for reciprocal movement of both the punch and die tooling so as to reduce or eliminate many of the problems associated with the movement of only the punch tooling in the walking beam method. However, a limitation the pinch roller method is that the rollers must still be disengaged to some extent in each tooling stage to allow the alignment of the lead frame on the alignment pins of the die tooling prior to performing the tooling operation. Unlike the walking beam method, the disengagement of the strip by the rollers and the alignment of the frame on the die are not inherently interrelated operations, and therefore, must be synchronized to operate correctly, such as through the use of computer controller. The same is true after the completion of the tooling operation and the reengagement of the strip by the pinch rollers. As is the case with the walking beam method, these operations are a critical path operation and tend to limit the throughput of the machines. In addition, the performance of the pinch rollers must be closely monitored to ensure that the rollers do not apply excessive compressive forces on the lead frame during movement of the strip that may tend to damage frame, but that sufficient force is applied to prevent the strip from slipping during rotation of the roller that will cause a misalignment condition. 
     The present invention is directed to continuous belt feed design which overcomes, among others, the above-discussed problems so as to allow machines that commonly use walking beam transfer arrangements to provide for increased throughput capacities by eliminating the unproductive and time consuming machine operations that are required to reciprocate the walking beam apparatus back into position prior to handling subsequent devices. 
     SUMMARY OF THE INVENTION 
     The above objects and others are accomplished by a belt feed apparatus in accordance with the present invention. The apparatus includes at least two rotatable pulleys, an endless belt capable of retaining devices to be processed is disposed around the pulleys such that rotation of the pulleys will cause said belt to travel around said pulleys, and a plurality of paired tooling members, each of said paired tooling members having first and second tooling members disposed on opposing sides of the belt and directly opposing so as to cooperate and perform a tooling operation on the leads when reciprocated toward each other along a common axis. In a preferred embodiment, two horizontally aligned pulleys with vertical axes of rotation are used to rotate the belt in a horizontal plane. The electrical devices are contained in a lead frame which is retained by pins on the belt which pass through indexing holes in the lead frame and the faces of the electrical devices are vertically oriented. The first and second tooling member are horizontally reciprocated by a common cam to perform the tooling operations on the electrical devices and the rotation of the belt is synchronized with the reciprocation of the tooling members. Alternatively, the first and second members can be driven by different cam drives that are synchronized in conjunction with the rotation of the pulleys and the relative orientation of the pulleys, the belt, and the electrical devices can be varied to accommodate specific tooling or spacing requirements. 
     Accordingly, the present invention provides significant increase in the efficiency of handling devices during sequential operations. These and other details, objects, and advantages of the invention will become apparent as the following detailed description of the present preferred embodiment thereof proceeds. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the present invention will be described in greater detail with reference to the accompanying drawings, wherein like members bear like reference numerals and wherein: 
     FIG. 1 is a top view of the apparatus showing three pairs of tooling members; 
     FIG. 2 is a front view of the apparatus along line  2 — 2  showing three pairs of tooling members; 
     FIG. 3 is a side view of the apparatus along line  3 — 3  showing a device in position between the tooling members with a top driven pulley and a bottom driven cam; 
     FIG. 4 is a side view of the apparatus comparable to FIG. 3 showing an alternative cam embodiments without the pulleys and belt; and, 
     FIG. 5 is a front view showing a 20-lead device in a frame attached to the device side of the belt. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The operation of the apparatus  10  will be described generally with reference to the drawings for the purpose of illustrating present preferred embodiments of the invention only and not for purposes of limiting the same. In accordance with the present invention, an endless belt  30  is disposed around the periphery of at least two horizontally aligned pulleys  20  having vertical axes of rotation. A series of directly opposed first and second tooling members,  40  and  50 , respectively are disposed on opposite sides of the belt  30 . Lead frames  98  containing electrical devices  90  having leads  92  are attached to the endless belt  30  in a vertical orientation and the pulleys  20  are rotated causing the endless belt  30  travel around the pulleys  20  until the lead frames  98  are positioned between the first and second tooling members,  40  and  50 , respectively. The first and second tooling members,  40  and  50 , respectively are then horizontally reciprocated so as to cooperate and perform a tooling operation on the device  90 . The pulleys  20  are then rotated to advance the device  90  to the subsequent pairs of tooling members. After the final share of the device  90  is attained the device  90  is separated from the frame  98  and the frame  98  is discarded. 
     In a preferred embodiment, two pulleys  20  are mounted on a horizontal bench top  12  with the rotation of the pulleys  20  occurring about the vertical axis  24 , either from below or above as shown in FIGS. 2 and 3, respectively. Two pulleys  20  are preferred to minimize the area occupied by the machine (“the footprint”) and to provide for linear movement of the devices through the tooling equipment. However, any number of pulleys  20  can be used with the present invention to achieve a desired result, for example, different sized and shaped tooling members can be accommodated by adding pulleys to change the shape of the belt. Preferably, the pulleys  20  are constructed from aluminum and the bench top  12  constructed from steel. Other materials of comparable physical characteristics can be used for the pulleys  20  and bench top  12  of the present invention. The actual dimensions and materials of construction can be varied depending upon the size of the devices to be processed. 
     Preferably, the pulleys  20  are provided with a series of protrusions  22  that are spaced around the perimeters of the pulleys  20  and are capable of engaging holes in the belt  30  and preventing the belt  30  from slipping when the pulleys  20  are rotated. The protrusions  22  are preferably centered and positioned in 45° intervals around the circumference of the pulleys  20  and constructed of a hard tool steel grade to insure accuracy and long life; however, the design, location, and materials of construction of the protrusions can be varied by the skilled practitioner to achieve a desired result. 
     The endless belt  30  is preferably constructed of stainless steel or other suitable material and has a circumferential length of a size suitable to fit securely around the pulleys  20 . The belt  30  has opposing faces, a pulley face  32  that contacts the periphery of the pulleys  20  and a device face  34  that contacts the devices  90 . The belt has holes  38  through the opposing faces that are preferably centered, sized and spaced to mate with the protrusions  22  on the pulleys  20  as the belt  30  travels around the pulleys. Pins  36  are provided on the device face  34  of the belt to engage the indexing holes  96  and retain the lead frames  98 . Alternatively, the pulleys  20  can be oriented with a horizontal axis of rotation or any angle between the horizontal and the vertical and the belt faces  32  and  34  can be aligned parallel to any given plane depending on the relative elevational alignment of the pulleys. Also, the electrical devices can be oriented at an angle other than vertical to accommodate variations in the tooling layout. Preferably, a track  48  is provided for additional alignment and support for the bottom portion of the frame  98  when the frame  98  is attached to the belt  30 . Preferably, a high torque stepper servomotor is used to rotate the pulleys  20  and to provide precise stop and start control of the belt  30 . A pulley housing  26  can also be incorporated to protect the pulleys  20  and the belt  30  from accidental disruption during operation. 
     A plurality of paired first and second tooling members,  40  and  50 , respectively, are disposed on opposing sides,  32  and  34 , respectively of the belt  30 . In a preferred embodiment, each pair of tooling members are reciprocally attached to the horizontal bench top  12  in a directly opposed configuration on a monorail barrel roller assembly  58 , which is preferably provided for increased alignment accuracy and loading capability. The first and second tooling members,  40  and  50 , respectively, have opposing tooling faces  42  and  52 , respectively, which are designed to cooperate to perform a desired tooling operation on the devices  90 , when the faces are placed in close proximity by reciprocating the first tooling member  40  and the second tooling member  50  toward one another. In a preferred embodiment, the first tooling members  40  and second tooling members  50  are die and punch tooling, respectively. The actual number of paired tooling members, or stages, and the design of the tooling faces  42  and  52 , respectively, is dependent on the final design of the leads  92  as well as the shape of the leads  92  when fed into the apparatus  10 . FIGS. 1 and 2 show one possible arrangement of three paired tooling members. Additional discussion on the number of stages and the tooling is provided below by way of example. 
     In a preferred embodiment, each of the paired tooling members  40  and  50 , respectively, are reciprocated in opposite directions along the common rail  58  by a single cam  60  having first and second cam faces,  62  and  64 , respectively. The cams  60  for each tooling stage are driven by a common cam shaft  68 , which provides for synchronization of the devices  90  in each tooling stage. A trough  66  is provided in each of the cam faces,  62  and  64 , respectively, for conversion of the rotational motion of the cam  60  into reciprocal motion of the tooling members,  40  and  50 , respectively. A lever arm  70  connects the cam  60  and the tooling members  40  and  50 , respectively. The lever arm  70  has a cam end  72  that rides in the trough  66  of the cam  60 . The lever arm  70  is mounted on the bench top  12  using a sturdy bearing assembly that creates an axes about which the arm could pivot such that when the cam end  72  moves within the trough  66  the lever arm  70  and the tooling members,  40  and  50 , respectively, reciprocate a fixed distance relative to the amount of the displacement of the cam end  72 . Substantially simultaneous reciprocation of the tooling members  40  and  50  is achieved through the use of complimentary troughs  66  in the first and second cam faces.  62  and  64 . The attachment of a first lever arm  70  between the first cam face  62  and the first tooling member  40  and the attachment of a second lever arm  70  between the second cam face  64  and the second tooling member  50  allow the motion of the tooling members,  40  and  50 , to be commonly controlled. Preferably, the tooling members,  40  and  50 , are spaced equidistant from the location of the devices  90  and the troughs  66  are complimentary so as to provide for minimal translation of the tooling members,  40  and  50 . However, it will be appreciated that the relative translation of each tooling member,  40  and  50 , respectively, and the timing of the movements can be varied by changing the design of the trough  66  in each of the cam faces  62  and  64 , respectively. Also, the cams  60  and the cam shaft  68  are preferably positioned below the horizontal bench top  12  in a cam housing  14  and the lever arms  70  pass through the bench top  12  in order to provide a more compact arrangement of the components. Alternatively, the cams  60  and cam shaft  68  can be mounted on the bench top  12  in a linear arrangement Preferably, a three phase servomotor with a gear reducer and a clutch/brake device is used to provide precise start and stop control over the turning of the cam shaft  68 ; however, other methods of precisely controlling the turning of the cam shaft  68  may be used in the present invention. 
     In an alternative cam embodiment, as shorn in FIG. 4 the first tooling member  40  and the second tooling member  50  are driven by separate cam shafts,  68  and  69 , respectively. The relative movement of the first and second tooling members,  40  and  50 , respectively, can be synchronized by the use of a common servomotor in conjunction with 90° gears connecting cam shaft  68  with cam shaft  69  or through the use of separate servomotors that are synchronized in some manner such as with a computer. 
     Also in a preferred embodiment, a computer is used to provide synchronized control over both the pulley servomotor and the cam servomotors. In addition, alignment sensors can be positioned on the respective tooling members,  40  and  50 , to be used in conjunction with the holes  38  in the belt  30  and tied into the computer to ensure the proper alignment of the device  90  in the tooling stage prior to movement of the tooling members,  40  and  50 , respectively. The anticipated speed of processing devices  90  is approximately 3 to 4 strokes/second as compared to a speed of approximately 1 is stroke/second using the prior art methods. 
     An example of the use of the apparatus of the present invention will be described with respect to the trimming and forming of a 20-lead device as shown in FIG.  5 . In a preferred embodiment for processing the 20-lead device to have J-shaped leads, the pulleys  20  are preferably 5.5 inches in diameter having an axial length of 1.0 inch and constructed from aluminum and spaced apart with approximately 15.0 inches between the axes of rotation. The belt  30  is constructed of ¾ inch wide by 10 mil thick stainless steel. Seven paired tooling members are positioned on opposing sides of the belt  30  and spaced in ¾ inch intervals to perform the tooling operations on the devices. Lead frames  98  containing the devices  90  are feed to the apparatus be conventional methods and are attached to the pins  36  on the belt  30  through the  30  ovular shaped indexing holes  96  in the top portion of the lead frames  98 . The bottom portion of the lead frame  98  is engaged in the track  48 . The pulleys  20  are rotated to cause the belt  30  to travel bringing the lead frame  98  to the first tooling stage in which the die and punch tooling has been designed to remove the flashing from between the leads  92 . The die and punch tooling is reciprocated toward the device and the alignment pins on the die tooling engage the circular indexing holes  95  in the bottom portion of the lead frame  98 . The precise alignment of the lead frame  98  in the die is accommodated without disengaging the lead frame  98  by incremental slide of the ovular shaped indexing holes  96  on the pins  36 . The pulleys  20  are again rotated to move the belt  30  and the lead frame  98  to a second tooling stage where the dambars  97  which are used to provide additional structural support to the lead frame  98  and to prevent the flow of molding compound onto other devices are punched out of the lead frame  98 . The lead frame  98  is when advanced to the next tooling stage where the leads  92  are trimmed to the proper length. The lead frames  98  are then advanced through a series of four forming operations in which the free end of the leads are first bent approximately 90° with respect to the end of the lead attached to the device  90  toward the bottom side of the device  90 . The leads  92  are then bent near the attached end approximately 90° toward the bottom side of the device  90  after which the free end of the leads  92  are again bent so that the free end faces the bottom surface of the device  90 . Finally, the leads  92  is bent toward he bottom surface of the device  90  until the free end of the device  90  is in a close proximate relation with the bottom surface of the device  90 . After this final forming step, the device is singulated from the lead frame  98  by punching the device  90  out of the lead frame  98 . The lead frame  98  can then be discarded. 
     Those of ordinary skill in the art will appreciate that the present invention provides tremendous advantages over the current state of the art for efficient handling of material through staged processing. In particular, the present invention provides for a continuous feed of lead frames containing electrical devices to a trim and form machine. Also, the present invention allows for short stroke lengths of the punch and die tooling. Thus, the present invention provides a effective method of increasing the capacity of machines used to perform material handling applications. While the subject invention provides these and other advantages over the prior art, it will be understood, however, that various changes in the details, materials and arrangements of parts which have been herein described and illustrated in order to explain the nature of the invention may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.