Metal working – Means to assemble or disassemble – Work-supported apparatus
Reexamination Certificate
2000-03-13
2004-03-30
Hong, John C. (Department: 3726)
Metal working
Means to assemble or disassemble
Work-supported apparatus
C029S559000, C072S020100, C269S020000
Reexamination Certificate
active
06711797
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a tooling fixture to support a workpiece. In particular, this invention relates to a hydraulic fixture for supporting a flexible substrate such as a printed circuit board to be used in a screen printing machine or placement machine.
BACKGROUND OF THE INVENTION
Fabrication of large volumes of electronic circuitry is economically accomplished using automated equipment. According to one known process a viscous solder paste is applied to selected areas of a printed circuit board through a stencil in a screen printing machine. Electronic components are then placed on the applied solder paste using a placement machine (also known as a pick-and-place machine). The printed circuit board and components are then heated in a reflow oven to a temperature sufficient to melt the paste, causing it to flow over the leads of the components and adjacent areas of the printed circuit board, thereby forming solder joints and completing the electronic circuit.
Within the screen printing machine a pair of conveyor belts support the printed circuit board by its edges. The conveyor belts move the board into the machine and position it relative to the stencil. A tooling fixture below the underside of the board is raised so that it presses upward on the lower surface of the board t) provide support for the board during the printing process. The board and tooling are then raised until the top surface of the board contacts the stencil. A printhead applies the solder paste to the top surface of the stencil and presses the paste against the stencil. Pressure applied by the printhead forces solder through holes in the stencil and onto the top surface of the board. The tooling fixture prevents the board from flexing away from the stencil as pressure is applied by the printhead.
Conveyor belts also move the circuit board through the placement machine. After solder is applied to the board by the screen printing machine, the board is moved into the placement machine and positioned relative to a robotic pick-and-place head. A tooling fixture located below the board is raised to support the underside of the board. Under the control of a program that defines the proper location of each of the components of the circuit, the pick-and-place head sequentially presses each component onto its proper location on the printed circuit board. The tooling fixture prevents the board from flexing as pressure is applied by the pick-and-place head.
Where components are placed on only one surface of the board, the tooling fixtures merely have to support a flat surface, and only slight modifications to the fixtures need to be made to accommodate boards with different linear dimensions. However, in order to better utilize the surface area of printed circuit boards and produce more compact circuitry, components are often placed on both surfaces of the board. In such cases, after components have been applied to one side of the board, the board is then turned over and components are placed on the other side of the board. Consequently, a second tooling fixture is required that conforms to the three-dimensional surface created by the components placed on the board. Since each different circuit layout has a different three-dimensional shape, this second tooling fixture must be customized for each layout.
One way to provide a customized, three-dimensional tooling fixture is to manually assemble blocks on the top surface of the tooling fixture that are arranged to contact the portions of the board not populated by components. However, this method is time consuming because an operator must reposition the blocks each time a different board is processed. This method is particularly cumbersome when a large number of different types of circuit boards are fabricated on the same assembly line.
Another method is to provide an array of electronically addressable posts that are either retracted in positions where a component is attached or extended where they can contact the board surface to provide support. A computer program directs the tooling fixture to configure the posts to conform to each printed circuit board that is fabricated. This method provides a faster means to change from one tooling configuration to another than the manual assembly of blocks. However, a separate computer database must be created for each layout of each board. Further, since no support is provided to the board in areas covered by components, certain portions of the board may be inadequately supported. Unsupported portions of the board may flex during processing resulting in misalignment between the stencil or the pick-and-place head and the board.
Yet another method is to provide a robot mechanism to automatically take support pillars from a reservoir and place them in the required positions to support the board. This method is faster and more consistent than manually placing support blocks, but needs a separate computer database for each board type to define where pillars should be placed and can only provide support where there is clear space on the board for the pillar.
Prior to using a customized fixture with a new board layout, an operator must carefully inspect the fit between the tooling fixture and the board to make certain that misalignment and dimensional tolerances do not cause an extended post, positioned pillar, or a manually positioned block to contact a component. Such contact will cause the tooling fixture to flex the board upward resulting in misplacement of the solder paste or components. More importantly, flexure of the board upward against the stencil can cause damage to the stencil or printhead of the screen printing machine.
Inspection of the tooling fixture each time a new type of board is fabricated complicates the manufacturing process and lowers throughput. Further, if the operator fails to properly inspect the fit between the board and the fixture, large numbers of misaligned boards may be produced or costly damage to the equipment may result.
Furthermore, even when a fabrication line produces only a single type of printed circuit board, each side of the board requires a different tooling fixture surface. A “flat” tooling fixture supports the unpopulated side of the board while the first side is screen printed and populated with components, and then a customized fixture supports the now populated side while the second side of the board is screen printed and populated. Even this tooling change reduces the throughput of the fabrication line.
SUMMARY OF THE INVENTION
In view of the above-identified problems with know methods for forming tooling fixtures, it is an object of the present invention to provide a tooling fixture that conforms to an uneven surface without having been configured beforehand.
It is another object of the invention to provide a tooling fixture that supports an uneven surface formed by a printed circuit board with components fixed thereon within a screen printing machine.
It is yet another object of the invention to provide a tooling fixture that supports an uneven surface formed by a printed circuit board with components fixed thereon within a placement machine.
It is still a further object of the invention to provide a tooling fixture that adapts to the surface of populated and unpopulated printed circuit boards.
It is still a further object of the invention to provide a tooling fixture that supports a workpiece using an array of hydraulic cylinders driving a respective array of pistons.
It is still a further object of the invention to provide a tooling fixture that supports a workpiece using an array of bearing and seal assemblies for directing an array of support rods to be driven.
According to one aspect of the present invention a block is provided with a plurality of cylinders. Each cylinder surrounds a piston that drives a rod extending out of the top surface of the block. The cylinders are connected with a pressure sensor and an accumulator. A controllable valve is connected between the accumulator and the cylinders. Opening the valve allows hydraulic fluid to flow bet
Bennett Ricky Paul
Edelstein Jason Mark
Moncavage Charles D.
Starke Bernward
Wood Ian Gordon
Dek International GmbH
Hong John C.
Shanks & Herbert
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