LEAD FRAME FEEDING DEVICE

Abstract: A device for successively feeding integrated circuit lead frames from a stack comprises a bin (24) having an inwardly-directed projection (90) on one side thereof, and a pair of picker blades (70, 80) slidably disposed immediately atop one another on the opposite side of the bin (24). The first, upper picker blade (70) has an extending abutement (76) for edgewise contacting successive lead frames (20) stacked in the bin (24) and laterally pushing the frames (20) against the side (34) of the bin (24) having the projection (90). The second, lower picker blade (80) functions as a shelf, supporting the stack of frames below, together with the projection (90). The upper picker blade (70) is continually urged against the stack of frames by an air cylinder (66). A motor (44) rotating eccentric bearings (52, 56) mounted on a shaft (46) is provided for alternately reciprocating the picker (70, 80). The stack of frames is held by the first picker blade (70) against the bin wall (34) while the lowermost lead frame falls away when the lower picker blade (80) is withdrawn from beneath the stack of frames. Thereafter, the second picker blade (80) is advanced underneath the stack of frames by the eccentric bearing (52) and the frames are held from beneath by the edge (86) of the second picker blade in conjunction with the projection (90).

Description: LEAD FRAME FEEDING DEVICE Cross Reference to Related Application This application is a ∞ntinuation-i_n-part of my copending application Serial No. 380,243, filed May 20, 1982. Field of the Invention This invention relates to the field of feeding of delicate articles, and in particular to automatic feeding of lead frames for integrated circuits. Description of the Prior Art The leads of an integrated circuit ("IC") represent a peculiar problem for automatic handling systans. Frames are made in which the lead patterns for a series of integrated circuit packages are mounted together in a row, forming a lead frame of approximately one inch width and six inches length. The leads and frames of leads are delicate, and also tend to nest when stacked. The frames simply cannot be dependably moved laterally with respect to one another, without causing damage. The two problems of nesting and fragility have made feeding IC lead frames such a problem that, notwithstanding the tremendous rate of development in IC processing and in automatic handling equipment therefore, lead frames have heretofore been unstacked predαninantly manually. Autαnatic scheπes have been tried with some success including lifting the top lead frame frcm a stack by a vacuum head or adhesive strip, the latter having to be frequently replaced. Manual unstacking is, of course, quite time consuming, expensive, labor intensive, and not fully reliable. Moreover, contamination of the metal leads by perspiration and the like can cause difficulties in further processing. Lead frames for dual-in-line packs and flat packs are relatively thin metal strips which, upon completion of mounting, connect a semiconductor chip to a circuit card. The leads are stamped out frcm flat stock in groups, for example, all the leads for eight integrated circuits contained on a single unit. The ends of the leads are disposed iiπ ediately adjacent to the semiconductor chip position, and the leads are also joined to continuous metal strips on the edges of the frames. The strips are termed "flashing", the successive lead patterns being thereby joined into a unit for processing. Adjacent the semiconductor chip position, or "pad", which is relatively small, the leads come into close proximity with one another. Lead positioning is -Important both electrically and to facilitate automatic handling. The leads must not be bent, in order to avoid their -Shorting together or being erroneously processed in subsequent steps. In processing subsequent to feeding and unstacking, seniconductor chips are attached to the lead frames, and hair-thin wires attach connection areas on the semi-conductors to the ends of the leads, adjacent the semiconductor pad. The leads, which were initially stamped from a flat piece of stock, eventually are bent ninety degrees to connect the semiconductor chip, housed inside a plastic or ceramic body, to a printed circuit card, IC socket or connector. In order to facilitate automatic processing, the pads upon which the semiconductor chips are mounted are offset downwards from the plane of the leads. Upon ιr_->unting the semiconductor chip, the surface of the lead frames and the surface of the attached chip will be disposed flush, that is, on a straight line across the top of the IC package. Prior to mounting the semiconductor chip, the series of lead frames in a single unit therefore include a series of offset mounting areas, slightly lower than the plane of the leads. Until chips are mounted therein, when the units are stacked, the offset mounting areas nest into depressions left by the offset areas of the neighboring lead frames in the stack. In addition, because the lead frames are stamped from sheet metal, fine burrs remain at the cut edges, further causing the frames to nest even in the absence of intentionally-offset areas. Accordingly, a lead frame unit in a stack cannot be dependably moved transversely to the stack, that is sliding over the surface of another frame, lateral to a feeding direction, without catching and bending or damaging the leads against one another and against the offset mounting pads. Accordingly, the frame units must be lifted perpendicularly away from one another at least partially, in order to be handled individually. My oopending application Serial No. 380,243, filed May 20, 1982 concerns lifting the nested frames frcm one another using a pair of picker wheels which engage each successive lead frame by the ends of the flashing strips, bowing the frame out of contact with the stack. for handling. The device of that application employs the springy and resilient nature of the lead frames and attached flashing to separate successive lead frames frαn a stack and direct them to a receiving station. Unlike the former application, in which lead frames are engaged by the ends, the present device employs the force of gravity to . substantially perpendicularly remove a lowermost lead frame frcm a stack. Insofar as the lead frames are subjected to any lateral force, they are not slided across one another's surfaces. Force is directed transversely (ie, inward frcm the sides) rather than longitudinally (ie, inward from the end) during feeding. ]_ * owing is not employed to resiliently unnest successive lead frames. Instead, the inclined surface of a stationary projection on one side of the feeding bin is employed to encourage the successive lead frames to move downwardly and laterally frcm the stack, as the remainder of the stack is held in position by picker blades on the side of the bin opposite the projections. A number of devices have been conceived for feeding stacked articles, nested and otherwise. Such devices primarily have been employed in feeding sheets of paper or cardboard which may be caused to slide across one another as well as to freely deform, without permanent damage. The basic problem in such devices is to separate the endmost sheet frαn the stack, and at the same time avoid carrying along the second-last sheet due to the action of static electricity, and due to the vacuum produced when the endmost sheet is suddenly engaged and drawn away. The prior art has therefore scmetimes employed pickers which bow the endmost sheet away from the stack before engaging it. Such pickers are sometimes accompanied by means for holding the remainder of the stack in position while bowing up the endmost sheet. Air pressure or other means are frequently employed to prevent a vacuum between the fed sheet and the second-endmost sheet. No effort is usually made to move an endmost sheet directly upwards, at least initially parallel to the second sheet. Instead, the sheets are at least partly slid across one another in feeding. Integrated circuit lead frames are susceptible to damage from rough handling of the usual pickers and pinch rollers employed in feeding paper, cardboard and similar sheet like material. The lead frames cαrprise a series of fragile lead patterns, which would be disturbed and damaged by the usual pickers or rollers. Where moving the articles transverse to the stack could not be conveniently accomplished, for exaπple when articles such as trays or dishes were nested, the prior art has employed helical screw feeding techniques to separate and feed an endmost article. The present invention employs the forces of gravity and the motion of edge engaging picker blades to smoothly feed delicate integrated C-Lrσuit lead frames. The feeding is accomplished primarily by moving the endmost frame in the direction of feed, perpendicular to the plane of the lead frame. The motion, however, is executed frcm the bottom of a stack, using a pair of picker blades reciprocated alternately, gently feeding the lowermost frame under power of gravity. Summary of the Invention It is an object of this invention to delicately yet dependably unstack and convey integrated circuit lead frames using automatic apparatus. It is another object of the invention to employ the force of gravity as the prime mover of a lead frame unstacking device, thereby avoiding excessive mechanical manipulation of the fed articles. It is also an object of the invention to provide a lead frame feeding device which is inexpensive and dependable. It is another object of the invention to feed lead frames frcm a single picker mechanism. It is yet another object of the invention to avoid damage to lead frames by engaging them only laterally at the sides. These and other objects are accomplished by a device for successively feeding integrated circuit lead frames frcm a stack, the device having a bin for guiding the stack toward a feeding station, and inwardly-directed projection being disposed on a first side of the bin, and a pair of alternately driven picker blades being disposed on an opposite side of the bin. The picker blades are slidably and alternately movable toward and away from the stack, directly out of phase with one another. A first, upper picker blade engages the edge of the second-lowermost lead frame, pressing sideways. A second, lower picker blade is simultaneously retracted, allowing the lowermost lead frame to fall over the projection and away. When the first picker blade is retracted, the second picker blade advances and functions as a shelf, together with the projection, allowing the stack to advance into position for feeding another frame. Means are provided for alternately reciprocating the first and second picker blades, and a receiving station is positionable below the feeding station to receive fed frames. O PI Brief Description of the Drawings There are shown in the drawings the enπbod-urents of the invention which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and -Instrumentalities shown. Fig. 1 is a perspective view of the frame feeder of the , invention. Fig. 2 is a section view taken along lines 2-2 in Fig. 1. Fig. 3 is a section view taken along lines 3-3 in Fig. 2. Figs. 4a through 4c are enlargements of the section view taken along line 3-3 in Fig. 2, showing successive stages of operation. Detailed Description of the Preferred Ξrnbodiments The lead frame feeding device according to the invention is shown generally in Fig. 1. A stack of lead frames is loaded into bin 24, for separation into individual lead frames to be fed along shelf 28. In general, the stack of individual lead frames 20, each of which lead . frames is in fact a series of approximately eight lead "spiders" attached to one another by continuous edge strips, is to be serialized. The individual lead frames will be separated frcm the bottom of the stack one at a time, and dropped onto shelf 28, from which they will be pushed into a further processing station by a pushing means (not shown) . Bin 24 need only be roughly the same dimensions as the lead frames. In order to facilitate loading, the bin walls are chamfered such that the upper end of the bin is slightly wider than the lower end, making loading easier. The bin is otherwise an open-ended box, wall 34 having a central gap to facilitate loading by hand. The bin is loaded by the user sirrply placing a supply of lead frames into bin 24, between sides 32, 34 and ends 36, 36, forming a stack. The stack of lead frames rests within bin 24 on supports extending inwards frcm walls 32 and 34. On wall 32, the picker assembly formed by a pair of blades is movably mounted to extend through wall 32. On the other side, the stack is supported by stationary projections 90. Projections 90 are adjustably positionable by means of threads, but are locked in position once they are adjusted for smooth operation. Inasmuch as projections 90 do not move, the operation of the machine may be described as holding the stack of lead frames while periodically releasing the lowermost lead frame frcm one side only. The wall 34 extends below the bin to form a vertical wall attached to foot member 30. The picker mechanism is supported along side 32 of bin 24 by means of shelf 62 which is mounted directly to bin wall 32. A wide slot 64 is formed in shelf 62, slidably acxoππodating a pair of picker blades 70, 80. Eoth picker blades are driven by eccentrically mounted bearings upon the shaft 46 of electric motor 44. The eccentric bearings 52, 56 are force fit on eccentric disks 54, 58, mounted exactly out of phase on shaft 46. The disks may be attached to shaft 46 by soldering, or other rigid attachment means. As motor shaft 46 is turned, for example at one revolution per second, the upper picker blade 70 is retracted frαn the bin while the lower picker blade 80 is extended toward the bin, and vice-versa. The blades 70, 80 extend through an opening in bin wall 32, aligned with wide slot 64. The upper picker blade 70 is urged toward the stack of lead frames fcy air cylinder 66, by means of threadably adjustable shaft 72. upper picker blade 70 is adapted to resiliently hold the stack of lead frames by pressing laterally against one of the lead frames. The upper picker blade is not directly driven against the stack by the motor. Instead, the upper picker blade is resiliently urged toward the stack by the air cylinder, and is only driven by motor 44 upon being retracted. The effect is to more gently handle the lead frames, and also to permit a very fine adjustment of the force exerted laterally against the lead frame, namely by means of air pressure and length of threadable shaft 72. Alternatively, the air cylinder 66 can be replaced by a spring, adjustably mounted to urge upper picker blade 70 toward the stack in bin 24. In the preferred embodiment, enlargement 82 contacts threadable shaft 72, but is not directly attached. Enlargement 82 limits the stroke of the air cylinder, preventing damage to the leadframes due to excessive air pressure. The indirect connection also permits seme misalignment between the air cylinder and slide 64. The particular operation of the feeding mechanism is shown in cross section in Fig. 3. M-.tor.44 turning shaft 46 causes picker blades 70, 80 to alternately extend into the area of bin 24. In Fig. 3, the eccentric bearings 52, 56, mounted upon motor shaft 46, are shown at the half point of their cycle, namely, both picker blades 70, 80 being shown near the center of their stroke. As motor shaft 46 continues to rotate, upper picker blade 70 will be extended while lower picker blade 80 is retracted, and vice versa. A counter mechanism may be adapted using slotted disk 48, mounted to a collar on shaft 46 and attached thereto by set screw 50. Disk 48 is opaque except at a slot at a certain point around its circumference. A photoelectric cell, combined with a light source opposite the disk, can be used to count the number of revolutions of the motor, and therefore the number of lead frames fed, by sensing the OMH ° periodic passage of the slot between the light source and the photoelectric cell. Air cylinder 66, in contact to upper picker blade 70 by means of shaft 72, is the operative force behind upper picker blade 70. The opening in picker blade 70 enclosing eccentric bearing 52 only contacts the eccentric bearing on a side of the opening opposite the .motor shaft frcm the bin. In other words, eccentric shaft 52 drives picker blades 70 back frcm the bin, against the force of air cylinder 66, but it is the air cylinder, not the motor, which drives picker blade 70 forward toward the bin. Unlike the upper picker blade 70, the lower picker blade 80 is driven entirely by the action of the motor, the force being transmitted by eccentric bearing 56. Bearing 56 fits precisely into the rectangular opening in lower picker blade 80, causing lower picker blade 80 to smoothly and periodically move both towards and away frcm the bin. As shown in Fig. 4a, at the midpoint of the cycle, the stack of lead frames 20 is supported by means of the lower picker blade 80, more particularly by the edge 86 of lower picker blade 80 on one side of the bin, and by the upper rounded surface 92 of projection 90 on the other side of the bin. The lead frames are therefore supported by the flashing on their edges, on both sides of the bin, and are held stablely in a horizontal position. As shown in Fig. 4b, as shaft 46 continues to rotate, the eccentric bearing 52 is rotated back from the rear edge of the opening in upper picker blade 70, permitting air cylinder 66 to press upper picker blade 70 toward the stack of lead frames, blade 70 sliding in track 64. Upper picker blade 70 is flattened upon the extreme end thereof, forming abutment 76 which is placed laterally against the second lowermost lead frame. A cut out 78 allows the lowermost lead frame to slip underneath any extending portion of upper picker blade 70. The lowermost lead frame is held up by the lower picker blade, but is left free of the upper picker blade as the upper blade is brought forward to support the stack. The upper picker blade supports the stack by exerting a lateral force on the second lowermost lead frame, which is now supported by the upper rounded surface 92 of projection 90 on one side of the bin, and by a fractional attachment. increased by the lateral force of picker blade 70, between the edge of the second lowermost lead frame and abutment 76. At the mcirient in the sequence shown in Fig. 4b, the tipper picker blade 70 is holding the second lowermost lead frame, and the lower picker blade 80 is retracted. Therefore, the lowermost lead frame 98 is no longer sτ-pported by either blade 70 or 80. Lead frame 98, unsupported on the bottom of the stack, is dropped clear on the side of the bin closest to the picker blades. Projection 90 does not move, and in dropping away frcm the stack, lead frame 98 must rotate and the edge thereof must move slightly laterally relative to the stack, in order to clear projection 90. In other words, the edge of the lead frame is forced downwards and inwards along the sloping upper edge of projection 92, tending to thereby unnest frcm the stack and drop evenly onto removal shelf 28. After dropping the lowermost lead frame, lower picker blade 80 is again brought forward, whereby the stack of lead ' frames is supported by the upper surface 86 of lower picker blade 80, in the manner of a shelf. At the same time, upper picker blade 70 is retracted, whereby the weight of the lead frames in the stack is taken over by lower picker blade 80, and the cycle may continue. As shown in Fig. 2, it is presently preferred that a plurality of projections 90 be provided opposite a single picker blade station, having two relatively wide blades. In this manner, the lead frames are supported neither only by their ends, nor only by their middle, either of which conditions could force the lowermost lead frame to bend. Fine adjustments in the feeding operation can be accomplished by adjusting the position of extensions 90 inward toward the bin area. Lead frames 20 include depressed pad areas at the center of each IC spider, which depressions tend to resist lateral sliding between the lead frames. Inasmuch as the present invention allows the lowermost lead frame to initially move perpendicularly away from the stack, it tends to unleaf the lowermost lead frame. After being unleafed, or separated from surface engagement with the next lead-frame, the dropping lowermost leadframe passes easily around the curved edge 92 of protrusion 90. Nesting is not a problem, and in addition, the frames are quite delicately handled. The device of the invention engages the lead frames 20 only by the metal strips which run along the edges of the frame. The lead OM wiring contact areas and the central pad areas are not engaged by the handling equipment, even at catch shelf 28, which is channeled along the center of its upper surface. Catch shelf 28 also has an upward extending outer edge, guiding the falling lead frame into a P-_ede * termined position. In this manner abrasion problems do not arise and dirt accumulating on the mechanism remains clear of the lead .frames, except along the edge flashing. anooth and dependable feeding of lead frames according to the invention is accomplished by precision of dimensions and positioning of the various elements. As will be appreciated, lower picker blade 80 must be allowed to remain under the stack until upper picker blade 70 exerts a sufficient force on the lowermost lead frame to hold the remainder of the stack. The stack may not be of such weight as to overcome the friction exerted by the lateral pressure of upper picker blade 70. A few pounds of pressure is adequate. The cut- out 78 on the lower edge of upper picker blade 70 is a means of spacing abutment 76 from lower picker blade 80, in order to avoid engaging the lowermost lead frame with the upper picker blade. Another method of insuring that the upper picker blade remains free of the lowermost lead frame (which is to be released) is to position projection 90 such that the lowermost lead frame, resting on the curve surface 92 of projection 90, is tilted slightly downwards toward the picker blades. In other words, the carrying surface 92 of projection 90, at a point defined by the edge of the lowermost lead frame, is located slightly higher than the upper edge 86 of lower picker blade 80. The picker blades 70, 80 slide directly upon one another. It is presently preferred that the upper picker blade 70 be made of stainless steel, the lower picker blade 80 of brass, for purposes of wear. Either picker blade can be replaced without a great deal of expense. Upper blade 70 is preferably channeled along its underside, whereby blade 70 slidably contacts blade 80 along two spaced runners, aligned to the sliding direction. This improves the precision of motion. The operative surfaces of the two picker blades, namely abutment 76 and shelf surface 86, are separated by the depth of cut out 78. It will be appreciated that various other means could be provided to space abutment 76 frαn support surface 86, and to positively slide the OM " - 1 blades relative to one another. Enough room must be left between abutment 76 and surface 86 to clear the lowermost lead frame. The clearance must not be so much, however, that the second lowermost lead frame is less than adequately engaged by abutment 76. It is presently preferred that cut out 78 be only one or two thousandths of an inch wider than a lead frame, which is typically about ten thousandths wide. The invention is capable of various eιr--X-5diments, and additional variations will now be apparent to persons skilled in the art. Reference should be made to the appended claims rather than the foregoing specification as indicating the true scope of the subject invention.

Claims: What is claimed is: 1. A device for successively feeding integrated circuit lead frames frcm a stack, the device comprising: a bin for guiding the stack toward a feeding station; a projection disposed on a first side of the bin and .directed inwardly toward the bin; a first picker blade disposed on a second side of the bin opposite the projection, the first picker blade having an extending abutment for laterally contacting the successive lead frames, the first picker blade being movable toward and away frcm the stack, whereby the successive lead frames are laterally pushed against the first side of the bin; a second picker blade disposed below the first picker blade on the side of the bin opposite the projection, the second picker blade being spaced from the abutment by a width of a lead frame, a second picker blade also being movable toward and away from the stack; and, means for alternately reciprccating the first and second picker blades, whereby the first picker blade holds the stack laterally against the first side of the bin while the lowermost lead frame falls away, and the second picker blade, together with the projection, holds the stack as the stack advances to the feeding station. 2. The device of claim 1, wherein said inwardly directed projection comprises at least two rounded pins, spaced apart on the first side of the bin, successive lead frames being moved downwards from the stack and outwards from the first side of the bin in rounding the projection. 3. The device of claims 1 or 2, further comprising means for resiliently urging the first picker blade against the stack, said means for reciprocating operating to move the first picker blade against the force of said means. 4. The device of claim 1, wherein said first and .second picker blades are slidably mounted one atop the other. 5. The device of claim 4, wherein said first picker blade is cut away on a lower edge thereof facing the stack, an upper edge adj cent said cut away forming the abutment. 6. The device of claims 1 or 5, wherein said means for alternately reciprocating the first and second picker blades includes a motor having a pair of eccentrics mounted on opposites sides of the shaft, said first and second picker blades each being cut out to form an opening for engaging one of said eccentrics. 7. The device of claim 6, wherein said first and second picker blades are in sliding contact with one another, the first picker blade being steel and the second picker blade being brass.

Inventors: STRAUS PETER L, STRAUS, PETER, L.
Applicants: STRAUS PETER L, STRAUS, PETER, L.
Application year: 1983
Main classification: B65G59
IPC codes: B65G59