Patent Document

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. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a printed circuit board panel with two printed circuit boards and a strip of the frame separating the two printed circuit boards. 
     FIG. 2 illustrates a single printed circuit board on a panel whereby the printed circuit board is so large that routing must occur at each corner to adequately weaken the frame if score lines do not overrun the boundaries with the printed circuit board. 
     FIG. 3 illustrates a printed circuit board panel having four printed circuit boards thereon with portions of the frame residing between the printed circuit boards and routing paths designated at portions of the periphery of the printed circuit boards. 
     FIG. 4 illustrates a printed circuit board panel with two printed circuit boards thereon with one edge of each of the two printed circuit boards common and a tab attached to the frame by a bridge, the tab shape defined by an interrupted routed path. 
     FIG. 5 is a flow diagram of a printed circuit board process of manufacture. 
    
    
     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.

Technology Category: 4