Printed circuit board scrap removal and printed circuit board fabrication process

Circuit boards are formed within the boundaries of an insulative sheet or panel such that the panel may be automatably processed. The periphery of each printed circuit board is defined by at least a plurality of score lines which do not extend to the edge of the sheets and may include also uncut and/or unscored areas to provide stability to either the sheet or segments of scrap material, lending rigidity to the sheet. Following complete fabrication of the printed circuit board, the sheet is cut by a routing process to extend selected score lines to the edges of the sheet to destroy the integrity of the frame of scrap material surrounding the printed circuit boards.

FIELD OF THE INVENTION
 This invention relates to the field of printed circuit board panel
 manufacture and processing and more specifically to the excess panel
 material, surrounding the printed circuit board which remains at
 completion of processing, that is considered to be scrap and must be
 removed.
 BACKGROUND OF THE INVENTION
 Printed circuit boards are commonly manufactured in various shapes and
 sizes dependent upon the environment and the apparatus for which they are
 intended. Such diversity of shape and size is difficult to handle and
 process in the commonly used automated equipment to screen print solder,
 to populate the printed circuit boards, and to solder the electronic
 components to the printed circuit board.
 The automated equipment so economically advantageous and useful for high
 volume processing of printed circuit boards requires items to be uniformly
 sized and shaped for their transport through the machinery. Accordingly,
 to accommodate this uniform size and shape necessity, panels of printed
 circuit board substrates thus are sized larger than the printed circuit
 boards themselves and leave, for handling purposes, a "frame" of scrap or
 excess material surrounding the printed circuit board. Multiple circuit
 boards, typically identical boards, may be accommodated in varying shapes
 and quantities within each panel. These panels ultimately require trimming
 around the printed circuit board to eliminate the waste or scrap frame
 surrounding them.
 As a final finishing step, scrap or frame material surrounding the printed
 circuit board has been removed from the printed circuit board by usually
 one of two processes. One method uses a router to rout and remove material
 surrounding the edges of the printed circuit board. A router is a device
 which may be very simple or may be highly mechanized and automated whereby
 a motor drives a rotary bit, the rotary bit cutting the printed circuit
 board substrate material at the edge of the printed circuit board, easily
 severing the printed circuit board from the frame of scrap material
 between the printed circuit board and the edge of the panels. Routers of
 this type may be numerically or computer controlled and typically are used
 in facilities manufacturing a large number of circuit boards. Routing has
 been the process dictated whenever the card shapes are other than "pure"
 rectangles, i.e., having protruding tabs for contact pads.
 To rout a panel of printed circuit boards can consume several minutes.
 Reduce the routing time and a significantly higher number of panels can be
 processed by the router in the same period frame, significantly reducing
 the cost of the scrap separation step. The time consumed in the routing
 operation makes it an expensive step in printed circuit board production
 and a primary target for cost reduction.
 A second process of excess or scrap material removal scores the panels of
 the printed circuit boards in such a way as to define the exterior
 boundaries of the printed circuit boards; this scoring weakens the scrap
 frame around the printed circuit boards to the point where they may be
 easily broken or snapped in a manual scrap removal operation. Scoring of
 the panel results in score lines being formed in one or preferably both
 faces of the printed circuit board panel. The scoring of the opposite
 faces of the panel is accomplished by a machine which has two opposing
 rotary blades which cut into the surface of the printed circuit board
 panel. Rotating blades close from opposite directions onto the printed
 circuit board; and, as the printed circuit board is translated relative to
 the blades, a groove is cut into each of the opposing surfaces of the
 printed circuit board panel, leaving a thin web of material between the
 two opposing grooves or score lines.
 The remaining web of material extends between the printed circuit board and
 the scrap material surrounding it. Score lines typically extend in such a
 manner that they intersect at the corners of the printed circuit boards as
 well as extend across the frames of the scrap material. The score lines
 severely weaken the panel, as intended, but also affect the rigidity of
 the panels to the point that the panels may not be reliably handled by the
 automated processing equipment used on the panels, i.e., solder screening,
 populating of a board with electronic circuit board elements and the
 soldering of the elements to a circuit board.
 Any panel which breaks or separates from the printed circuit board during
 the processing disqualifies the printed circuit board from further
 automated processing inasmuch as it is no longer the standardized, uniform
 panel required by the equipment. Frequently, the printed circuit board
 becomes scrap once it cannot be efficiently handled by the automated
 processing equipment. The separated printed circuit boards could be
 reworked manually; however, the cost of reworking a circuit board is
 prohibitive under current manufacturing techniques. Commonly, it is more
 economical to scrap a circuit board, even one almost completely finished,
 rather than to attempt to manually rework it.
 OBJECTS OF THE INVENTIONS
 It is an object of the invention to improve printed circuit board panel
 rigidity and integrity, to enhance processing the printed circuit board
 panel in automated equipment, and to minimize processing time, removing
 the printed circuit boards from the excess material frame of the panel.
 It is another object of the invention to reduce routing operations
 necessary to remove scrap while maintaining adequate panel rigidity
 necessary to permit automated processing of the printed circuit board
 panel.
 SUMMARY OF THE INVENTION
 A panel or sheet of insulative material, such as fiberglass or other
 suitable non-conductive plastic, is plated or otherwise coated with a thin
 layer of copper or other conductive material. The conductive layer is
 etched into a pattern to form a electrical circuit pattern on the surface
 of the fiberglass sheet. This pattern may be repeated in a plurality of
 locations assuming the size of the pattern and the size of the panel
 permit.
 A border or margin around the electrical circuit pattern forms a frame of
 excess material useful only in automatic handling. Adjacent circuit
 patterns may be displaced from each other to permit an unused segment of
 scrap material to remain between the adjacent circuit patterns.
 Alternatively, the adjacent circuit patterns may be placed such that no
 unused material shall remain between the two patterns once the printed
 circuit boards are completed.
 The shape of a printed circuit board is considered to be complex if it is
 other than a rectangle, such as having a projecting tab. Score lines
 cannot be cut to end precisely; therefore, a routing operation is
 conducted to cut the complex shapes.
 The printed circuit board panel then may be scored by one or more saw
 blades, partially cutting into opposing faces or surfaces of the circuit
 board yet leaving a thin web or membrane of uncut insulative material. The
 web will be brittle by virtue of the characteristics of its material and
 can be broken later. Typically, score lines will outline the boundaries of
 the printed circuit board and, if circumstances permit, may extend
 slightly beyond the corners of the printed circuit board boundary to
 ensure that orthogonal score lines intersect. Where a routing operation
 has defined a complex shape, score lines may intersect or join the router
 cuts. Solder paste may be screened onto the contact points that the
 circuit components will make contact and be soldered. The automatic
 populating machines place the components onto the solder paste deposits,
 and the solder paste is reflowed to solder the components to the circuit
 pattern.
 Panels are subjected to router cuts which extend some of the score lines to
 the edges, saving processing time and cost. By destroying the rigidity and
 integrity of the frame, individual sections of scrap may be broken off and
 discarded without subjecting the printed circuit boards to flexing or
 bending.
 Once completely processed by the automatic processing equipment, the
 printed circuit board is separated from the scrap material and, in order
 to reduce the size of the printed circuit board to the design parameters,
 the scrap discarded. Score lines, while generally extended beyond the
 printed circuit board boundaries, do not weaken the frame sufficiently to
 cause undesired breakage; however, if subsequently router cut to the panel
 edge, these score lines permit breaking of the scrap material forming the
 frame without the flexing the printed circuit boards.
 Flexing the printed circuit boards may cause breakage of the printed
 circuit lines or cause separation of the printed circuit board and
 associated surface mounted circuit elements that are soldered onto the
 printed circuit board, thereby damaging the printed circuit board.
 By combining the scoring technique with limited routing or cutting, the
 time required to remove the scrap from the printed circuit board is
 greatly reduced. The routing occurs in very localized areas wherever the
 weakened portion of the panel, the score line, is extended to the edge of
 the panel or wherever a complex shaped printed circuit board has a portion
 which is attached for stability to the frame by an unscored or unrouted
 bridge.
 By reducing the required routing operation, the routing time may be very
 significantly reduced, by a factor of 80 to 90 percent, over that required
 for a complete routing operation separation.
 A more complete understanding of the invention may be had by reference to
 the attached drawings and the Detailed Description of the Invention to
 follow.

DETAILED DESCRIPTION OF THE INVENTION
 Referring initially to FIG. 1, a sheet or panel 10 of fiberglass material
 or other suitably insulative plastic sheet material is illustrated in a
 standard form and dimension. The outside dimension of the panels 10 may
 differ; however, any particular circuit board is configured and processed
 on panels 10 that are uniform in dimension. The maximum dimensions of any
 particular panel 10 will depend on the maximum panel dimensions that can
 be accepted by the automatic processing machinery used for component
 placement or solder screening and reflow soldering.
 The dimensions of a particular circuit board 12 are determined by the
 requirements of the device in which the circuit board 12 is intended to be
 installed. Automated machinery may be set up to process a particular sized
 panel 10. Accordingly, for high quantity production runs, panel 10, having
 an adequate area for one, two or more printed circuit boards 12, may be
 sized and the equipment set up to process that particular sized panel 10.
 Should it be desired to run panels 10 which require different outside
 dimensions, the processing machinery will have to be re-configured. Frame
 14 may have not only margins 16 surrounding the printed circuit boards 12
 but also may have an intermediate region 18 disposed between the multiple
 printed circuit boards 12.
 Score lines 22 define the periphery or boundaries of a particular printed
 circuit board 12, disposed such that they circumscribe the printed circuit
 board 12. In FIG. 1, the score lines 22 are cut by a scoring machine such
 that the orthogonal score lines 22 intersect at the corners of the printed
 circuit board 12 and extend a short distance into the margins 16 of the
 panel 10. The essential consideration in this embodiment is that the score
 lines 22, although intersecting, do not extend so far into the margins 16
 around printed circuit boards 12 that the frame 16 is weakened to the
 point that panel 10 is unstable. It is desirable to extend the score lines
 22 into the margins 16 far enough to be engaged by a router cut without
 damaging the printed circuit board 12.
 Score lines 22 may be cut into only one face of the panel 10 or,
 alternatively, may be cut into the opposing faces. The cutting of the
 score lines 22 may be accomplished, for example, by a device having a
 rotary blade similar to a saw blade, engaged with panel 10 and cutting
 into panel 10 only a small fraction of the total thickness of panel 10. In
 the event that the score line 22 is cut only on one side or into one face
 of panel 10, the depth of the cut may be substantially increased so long
 as it leaves a quantity or thickness of material sufficient to hold and
 transport the printed circuit board 12 whenever panel 10 is handled by
 frame 14.
 If the score lines 22 are cut into the faces on both sides of panel 10,
 then any remaining web or membrane of the material from which panel 10 is
 fabricated will reside generally at the center line of the thickness of
 panel 10, and the cuts on each of the opposing faces of panel 10
 necessarily must be shallower.
 The printed circuit boards 12 in FIG. 1 each have contact pads 32 on one
 surface of the printed circuit board 12 and disposed at the edge of the
 printed circuit board 12. The contact pad 32, as well as the conductors
 30, typically are formed by coating or plating one surface of the circuit
 board 12 with a thin layer of conductive metal, typically, copper or
 copper alloy. After the metal layer has been deposited on the surface of
 panel 10, a selective removal process such as etching defines the pattern
 of the conductors 30. The pattern of conductors 30 can be defined by the
 application of a photo-resist or other masking material which then may be
 light activated to cause a selective hardening of the resist layer and to
 flush away the unexposed patterns, thus exposing the copper layer or other
 electrically conductive layer to the acid for etching and removal or
 separation. Other selective removal or deposition processes may be used to
 form the conductors 30 and contact pads 32 of the electrical circuit on
 each printed circuit board 12.
 After the fabrication of the circuit pattern, panel 10 undergoes a solder
 screening process to deposit solder paste at contact points and further
 processed by a component placement apparatus, where the components of an
 electronic circuit are placed in appropriate locations on the conductors
 and solder paste deposits.
 Thereafter, the entire panel 10, including frame 14 and printed circuit
 boards 12 carrying the electrical components 20, will be sent through a
 solder reflow operation so that solder connections between the electrical
 components 20 and the conductors 30 are flowed or reflowed to form
 permanent electrical connections between the printed circuit board 12 and
 the electrical components 20.
 Score lines 22, running the longitudinal direction of panel 10 in FIG. 1,
 are interrupted in segment region 18 between printed circuit boards 12. By
 leaving unscored material or bridges in segment region 18, the rigidity of
 frame 14 is improved.
 Separation of frame 14 from printed circuit boards 12 is a combination of
 two processes, routing and scoring/breaking. The first process performed
 is the routing of the material between the ends of printed circuit board
 defining score lines 22 in one direction, preferably in the direction
 which will require the fewest number of routing operations. Routing cuts
 36 are illustrated in FIG. 1 as extending the longitudinal score lines 22
 to the edges of panel 10. Additional routing cuts 38 are made to remove an
 unscored bridge of material left between the adjacent overrun ends of
 score lines 22 in the segment 18 of frame 14.
 Routing may be accomplished by a computer controlled or numerically
 controlled router which will make a cut from the edge of the panel 10
 extended inwardly by a distance sufficient to meet with and engage the
 ends of score lines 22 extending longitudinally on panel 10.
 At this point in the process, routing operations are complete for panel 10
 and scrap frame segments 16, 18 may be manually separated from printed
 circuit board 12. Separation of frame 14 is accomplished by manually
 flexing along the longitudinal score lines 22 and router cuts 36, 38 thus
 breaking longitudinal segments of frame 14 from the ends of printed
 circuit boards 12. Once both of the pieces of scrap forming the
 longitudinal segments of frame 14 have been separated, then the transverse
 segments 16 of frame 14 may be separated by bending or flexing frame
 segments 16 relative to printed circuit board 12. Similarly, section 18
 may be separated in the same manner. Caution must be taken to not flex the
 circuit boards 12 as scrap sections are separated from the periphery of
 printed circuit board 12. Flexing the circuit boards 12 may break
 conductors 30 or cause separation between the rigid components 20 and the
 more flexible printed circuit board 12.
 With respect to FIG. 2, a printed circuit board 12 is illustrated with a
 routed pre-cut 40, having been made around the periphery of the tab 13 of
 printed circuit board 12 extending into the frame 14. Due to the size of
 printed circuit board 12 relative to panel 10 in this embodiment, there is
 insufficient material in frame 14 to permit the score line 22 to overrun
 the corners of printed circuit board 12 and still maintain rigidity and
 integrity of panel 10. Accordingly, score lines 22 only approach the
 corners of printed circuit board 12, thus leaving unscored bridging
 material at the corners to support frame 14 and printed circuit board 12.
 Understanding the desire to leave unscored material at the end of the score
 lines 22, it is necessary to subsequently rout that material and remove
 that unscored material on both of the adjoining edges of the printed
 circuit board 12, forming the corners of printed circuit board 12. A
 routing cut, in a generally jogged or "Z" path 50, is made at three of the
 four corners of printed circuit board 12. Because routing pre-cut 40 has
 been made previously and extends to the corner of printed circuit board
 12, it is only necessary to make a straight cut 52 with the router on the
 fourth corner to connect the transverse score line 22, the router pre-cut
 40 and the edge of panel 10. Thereafter, the side segments of frame 14
 designated as 54 can be broken away along score lines 22. End segments 56
 of panel 10 and particularly frame 14 then may be removed by flexing along
 their respective score lines 22.
 Circuit elements and conductors together with the contact pads illustrated
 in FIGS. 1 and 4 are only exemplary and may be formed in any desirable
 pattern to accomplish the requirements of the circuit board designer.
 While similar circuit patterns have not been illustrated in FIGS. 2 and 3,
 one should understand that one of skill in the art may incorporate any
 such desired circuits into the printed circuit boards 12 in FIGS. 2 and 3
 by one of skill in the art.
 Referring now to FIG. 3, panel 10 incorporates printed circuit boards 12 in
 what is known as a "four up pattern." In this instance, a router pre-cut
 40 has been made to form the complex shape of the tabs 60 on each of
 printed circuit boards 12. Because the router pre-cut 40 substantially
 weakens the integrity of panel 10 and jeopardizes the reliable processing
 of printed circuit board 12, a region of unscored and unrouted material is
 preserved as a bridge between at least one of the tabs 60 with frame 14
 and is later removed with router cuts 62.
 Router cuts 36 extend between the end of score line 22 and the edge of
 panel 10; router cuts 39 extend the router pre-cut 40 to the edge of panel
 10; router cuts 37 interconnect score line 22 and router pre-cut 40 on
 adjacent printed circuit boards 12; and router cuts 38 remove the bridge
 of material left by the interrupted score lines 22.
 While individual electronic components, conductors and contact pads are not
 illustrated in FIG. 3 for simplicity of illustration, conductors, contact
 pads and components may be positioned thereon and soldered, as discussed
 earlier. Scrap segments of frame 14 may be separated by bending and
 breaking without undue flexing of printed circuit boards 12.
 Referring now to FIG. 4, two printed circuit boards 12 are laid out on a
 panel 10 with router pre-cuts 40 partially defining the complex shape on
 printed circuit boards 12. Router pre-cuts 40 leave an unscored, uncut
 region subsequently removed by router cuts 62 to stabilize the frame 14
 and the complex peripheral shape of printed circuit board 12. To remove
 the scrap of frame 14 from printed circuit board 12, a routing operation
 makes cuts 36 to extend score lines 22 to the edge of panel 10; additional
 cuts 62 are made to remove the material which remained after the routing
 pre-cuts 40 were made. Once the routing cuts 36, 62 have been made, the
 scrap material forming frame 14 may be flexed about score lines 22 and
 then the remainder of frame 14 separated from printed circuit boards 12.
 In this instance, printed circuit boards 12 have a common score line 23
 intermediate printed circuit boards 12. The two printed circuit boards 12
 may be separated by merely bending and breaking the circuit boards 12
 apart at score line 23.
 FIG. 5 illustrates a flow of a preferred process of fabricating a printed
 circuit board. Beginning with Operation 100, an insulative panel 10 is
 provided. This panel 10 is plated with a conductive layer in Operation 102
 and, in Operation 104, the excess conductive material is selectively
 removed to leave the circuit conductor pattern 30.
 In Operation 106, routing cuts are made to define the boundary of the
 printed circuit boards 12 in the regions of complex shapes which do not
 lend themselves to scoring and breaking.
 Score lines are cut into the insulative panel 10 to define the boundaries
 of the printed circuit boards 12 in Operation 108. Solder paste is screen
 printed onto conductors 30 of circuit board 12 in Operation 110. Printed
 circuit boards 12 are populated in Operation 112 with electronic
 components 20 to complete the circuit. Next, in Operation 114, the
 components 20 are soldered to the circuit board 12 to permanently attach
 the components 20 to the circuit pattern.
 In Operation 116 the break lines for scrap removal are routed to destroy
 the frame integrity and to render the scrap separable. In Operation 118,
 the scrap material is broken from the printed circuit boards along the
 combined router cuts and score lines to complete the fabrication of a
 printed circuit board.
 One of ordinary skill in the art of printed circuit board manufacture will
 be capable of making changes and alterations in the above described
 printed circuit board manufacturing process without removing the resulting
 process from the scope of the appended claims.