Coating processes – Electrical product produced – Integrated circuit – printed circuit – or circuit board
Reexamination Certificate
1998-09-25
2001-03-27
Talbot, Brian K. (Department: 1762)
Coating processes
Electrical product produced
Integrated circuit, printed circuit, or circuit board
C427S282000, C101S126000, C101S129000
Reexamination Certificate
active
06207220
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to the field of circuit board manufacturing and more specifically to a method and apparatus for improving the performance of circuit board stenciling operations.
BACKGROUND OF THE INVENTION
As it is known in the art, the success of circuit board manufacturers is measured in terms of the number of defect-free products they are able to supply in a given time period. Unfortunately, the achievement of desired productivity levels is hampered by the accuracy requirements inherent in providing such defect-free products. The accuracy requirements become even more difficult to attain as technological advances command smaller component sizes and more pins per package fitting on a circuit board with very closely spaced pads. Defective boards may be either rejected outright or reworked, both of which costs time and increases expense.
For example, the typical circuit board manufacturing process includes three basic operations, each of which is usually performed by an independent machine. These operations include stenciling of a pattern of solder onto the pads of an incoming circuit board, placement of components on the pads of the board, and heating the board to establish the integrity of the contact between the solder and the board, the pins of the components, and the pads.
The stenciling and the placement operations must be performed in a precise manner to ensure that a defect-free product is provided. The stenciling operation is typically performed by a stencil machine. Boards that are fed into the stencil machine have a pattern of pads or other, usually conductive surface areas onto which solder will be deposited. In addition, one or more small holes, or marks, called fiducials, are provided on the board for alignment purposes. The stencil machine also typically includes a stencil (or screen) having a pattern of apertures etched through the stencil that matches the expected solder pattern to be placed on the circuit board.
When the circuit board is fed into the stencil machine, it first must be aligned with the stencil to make sure that the circuit board is appropriately aligned with the apertures of the stencil. One apparatus for performing this task is an optical alignment system that is introduced between the circuit board and the stencil for aligning the fiducials of the board with one or more fiducials on the stencil. For example, optical alignment systems provided by MPM™ Corporation, such as those described in U.S. Pat. No. 5,060,063, issued Oct. 21, 1991, by Freeman and in U.S. Pat. No. RE 34,615 issued Jan. 31, 1992 by Freeman, each of which is incorporated herein by reference, may alternatively be used.
When the board has been aligned with the stencil, it is raised to the stencil, solder is dispensed on the stencil, and a wiper blade (or squeegee) traverses the stencil to dispense the solder through the apertures of the stencil onto the board. After stenciling is complete, the board is lowered and forwarded to a pick and place machine that places electrical components at specific locations on the board.
The pick and place machine provides the components that are required by the board. Components are placed at the appropriate locations (the location of solder deposition performed by the stencil machine) and with the proper orientation on the circuit board. Because of the number of pins of a component and the proximity between the pins, it is essential that the pick and place machine operate to precise standards to ensure the correct placement of the component upon the soldered connections. Thus the pick and place machine must also perform alignment checks before operation.
The next step in the process is to forward the circuit board having the components laid upon the stenciled solder to a reflow machine. The reflow machine heats the existing solder to cause the solder to form tight connections with the pins of the components that were placed by the pick and place machine and the pads or other surfaces of the board.
In the systems described above, the accuracy required in the printing of solder on circuit boards and in the placement of components on the printed solder leads to the use of alignment procedures for the circuit board which cause delays in the manufacturing process. In addition, there is an added element of delay, referred to as ‘dwell time’ at the pick and place machine as the pick and place machine waits to receive a board from the stenciling machine. Each of these delays reduces the overall performance and productivity of the manufacturing process. It would be desirable to develop a method and apparatus for increasing the throughput of the circuit board manufacturing process.
SUMMARY OF THE INVENTION
According to one aspect of the invention, a stenciling device for use in a circuit board manufacturing process includes a plurality of sets of rails, each of the plurality of sets of rails supporting a corresponding plurality of circuit boards as the circuit boards propagate through the stenciling system. With such an arrangement, in a preferred embodiment, a dual track system may be provided that allows for the reduction of dwell time in the circuit board manufacturing process.
According to another aspect of the invention, a method for providing processing of circuit boards in a stenciling system having first and second tracks, the stenciling system comprising a stencil having two patterns, one associated with each track, and a solder dispensing mechanism, suspended above and between the two patterns of the stencil includes the steps of: receiving a first board on the first of the tracks, engaging the board, stencil, and solder dispensing unit, stroking the solder dispensing unit from a first position between the patterns to an outer position of the one of the tracks receiving the board, disengaging the first board, advancing the first of the tracks to receive a second board, engaging the second board, stencil and solder dispensing unit, stroking the solder dispensing unit from the output position of the first of the tracks to the first position, and repeating the above steps using the second of the two tracks.
With such an arrangement, a processing sequence is provided that allows for existing stenciling components to be used in a dual track system, thereby minimizing the extent of additional hardware by eliminating the need for a second stencil apparatus and minimizing the overall cost of the system.
According to another aspect of the invention, a dual track stenciling system having shortened rails is described. With such an arrangement, the stencil machine may be used at circuit board manufacturing processes having existing pre- and post-print queue stations on loading and unloading equipment.
According to a further aspect of the invention, a dual track stenciling system for stenciling of palletized material includes a first set of rails for receiving boards from a loader/unloader, a second set of rails for returning boards to the loader/unloader, a shuttle device for transporting boards from the first set of rails to the second set of rails and a plurality of palettes, for supporting boards as they are transported through the stenciling system. With such an arrangement, the dual track stencil machine may be used for printing of palletized materials.
According to a further aspect of the invention, a dual track stenciling comprises a pair of tracks, each track for forwarding in parallel a circuit board to a work nest of the stencil machine for processing.
According to one aspect of the invention, a stenciling system for use in circuit board manufacturing includes a plurality of sets of parallel rails mounted perpendicular to a plurality of spacing tracks, each of the sets of rails for supporting a corresponding plurality of circuit boards as the circuit boards are moved through said stenciling system, wherein each rail of is separately controllable to be moved in along said spacing tracks. With such an arrangement, a stenciling system capable of stenciling varying size boards in one process is provided. In
Doyle Dennis G.
Hall Steven W.
Mintz Levin Cohn Ferris Glovsky and Popeo PC
Speedline Technologies, Inc.
Talbot Brian K.
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