Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
1998-11-20
2001-06-05
Huson, Gregory L. (Department: 3729)
Metal working
Method of mechanical manufacture
Electrical device making
C029S412000, C029S413000, C029S414000, C029S415000
Reexamination Certificate
active
06240635
ABSTRACT:
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
Graves Scott Peter
Huston George Anton
Huson Gregory L.
International Business Machines - Corporation
Letson Laurence R.
Smith Sean
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