Electrical connectors – Preformed panel circuit arrangement – e.g. – pcb – icm – dip,...
Reexamination Certificate
2000-12-28
2002-09-03
Ta, Tho D. (Department: 2833)
Electrical connectors
Preformed panel circuit arrangement, e.g., pcb, icm, dip,...
C439S507000, C029S840000, C029S402210, C174S260000, C174S262000
Reexamination Certificate
active
06443739
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an improved method and apparatus for repairing or reworking complex multilayer printed circuit board interconnections; and more particularly to a system of repairing circuit net connections using compression contacts.
2. Description of the Prior Art
It is known to utilize printed circuit boards to make electrical interconnections between leads of electrical components mounted thereon, including mounted integrated circuits. Printed circuit boards characteristically involve one or more discrete layers of insulating material upon which patterns of electrical conductors are formed in conjunction with a predetermined array of holes. The electrical conductors are referred to as foil. The layers are stacked, bonded, and the hole patterns formed and plated-through with electrical conductive materials. Characteristically, plated-through holes are uniform in diameter, and are often referred to as “barrels”. Selective interconnections result in selected wiring networks, or nets, being formed with various ones of the electrical conductors on different layers being interconnected through plated-through holes. This effectively provides a three-dimensional wiring system. At the mounting surfaces, it is known to provide additional electrically conductive material in electrical contact with the plated-through holes for the purposes of providing an expanded pad area for making interconnection with the component contacts, terminals, leads, or compression contacts.
It has been the usual practice to have the diameter of the plated-through holes uniform throughout the thickness of the multilayer printed circuit board. With the advent of continued reduction in size of the electronic components, the spacing of the component connections has been decreasing, and the density of the associated array of holes has been ever-increasing. As the density of integrated circuit components increase the array of interconnection points to a printed circuit board multiplies for the same integrated circuit die size. At the same time, the complexity of the interconnections that are to be made by the multilayer printed circuit boards has increased. This increase in the number of interconnections results in the requirement of providing more conductive routing paths on the various layers, where these routing paths must be constructed in ever-decreasing dimensions. The loss of routing area resulting from the reduction in pin spacing in the grid array of plated-through holes has lead to the requirement of adding additional layers to the multilayer printed circuit board assemblies, with the attendant increase in cost of manufacture.
It is known to utilize so-called surface mount components, where relatively short component leads are affixed to surface pads on the multilayer printed circuit boards. Characteristically, they are affixed through a solder process. It is also known to provide long-lead interconnection of components to the multilayer printed circuit board, wherein the component leads are formed and inserted in respectively associated ones of the plated-through holes. After such insertion, the leads are soldered in place. Both forms of interconnect have problems attendant to the manufacturing processes. The surface mount has the problem of location of all of the terminals of a component over the associated interconnection pads during the soldering process. Any misalignment or misplacement can result in missing or marginal solder interconnections. The insertion of the long-lead electrical components can result in bent leads not properly being inserted through the depth of the plated-through holes, thereby either slowing the manufacturing process if detected, or resulting in a defective assembly if not detected at the time of component insertion.
A third type of electrical interconnect involves arrays of compression contacts, known generally as land grid arrays or LGA. These can include the CIN/ASP compression contact system available from Cinch (also known as the so-called fuzz button contact system), the cLGA land grid array socket system available from InterCon Systems, the Metallized Particle Interconned (MPI) system available from Thomas & Betts, or similar compression interconnection systems, utilized to make electrical contact with an array of pads mounted to plated-through holes on a printed circuit board.
It is also well-known in the design of the electrical interconnections to be made on the printed circuit board assembly, that design problems can result in wiring network layouts that must be altered or reworked to form correct wiring network interconnections. Further, it is known that in the fabrication of multilayer printed circuit boards it can occur, for various manufacturing reasons, that one or more layers may have electrical conductors improperly electrically shorted to a plated-through hole. Unless such re-routing or shorted condition can be repaired, the entire assembly has to be scrapped. Various types of rework and repair techniques have been developed, but such known repair and rework techniques are complex; and if not accomplished with skill and precision, can result in further damage to the printed circuit board and failure to remedy the problem. As the array of printed circuit board interconnections become larger there is an increase in the number of plated-through holes of smaller diameter, and more layers, are utilized, it becomes more and more necessary to have an effective and efficient way to rework incorrect or defect wiring nets to save the boards.
The development of integrated circuits (ICs), including application specific integrated circuits (ASICs), requires on-circuit interconnection of cells and requires off-circuit interconnections to connect circuits on different ICs or to connect to connectors or other components, power, ground, and the like. When design errors, manufacturing errors, or design changes occur relative to interconnection of IC pins, the entire supporting printed circuit board must be scrapped unless a repair system is provided.
For those systems where ICs or ASICs were interconnected through metal pins soldered into plated-through holes in the printed circuit boards or to pads on the surface of the printed circuit boards it was possible to solder the repair wire directly to the pin or surface pad. Those resoldering processes usually required the pin to be disconnected from the wiring net within the printed circuit board to be accomplished by drilling out the via hole in the printed circuit board to disconnect the internal wires. It has been determined, however, that structures that utilize compression contact sockets to interconnect the ICs or the ASICs to the printed circuit board that such a drilling out and resoldering process cannot be accomplished within the tolerances of the structure. Since a compression contact socket characteristically can only accommodate an interfering object having a dimension in the order of about 0.002 inch, a replacement wire requiring soldering having a typical diameter in the order of 0.006 inch will defeat the operation of such a compression contact connector. Further, the drilling out process requires very close tolerance and often results in destruction of the compression contact pad.
Accordingly, it is desirable to have a repair system and method that overcomes the limitations for repair incident in the prior art.
OBJECTS
It is the primary objective of this invention to provide a method and apparatus to efficiently repair and rework multilayer printed circuit boards.
It is a further primary objective of this invention to provide an improved printed circuit board assembly having an improved structure for use in affixing electrical components that may be reworked as necessary to correct design and manufacturing deficiencies.
Yet another objective of the invention is to provide an improved printed circuit board assembly having a structure for affixing electrical components that is suitable for use with compression contact connectors.
Another objective
Johnson Charles A.
Starr Mark T.
Ta Tho D.
Unisys Corporation
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