Metal fusion bonding – With means to juxtapose and bond plural workpieces – Including compliant cushioning medium
Reexamination Certificate
2002-08-30
2004-08-24
Stoner, Kiley (Department: 1725)
Metal fusion bonding
With means to juxtapose and bond plural workpieces
Including compliant cushioning medium
C228S008000
Reexamination Certificate
active
06779703
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to improved method and device for pressing a workpiece, and more particularly to method and device for heat-pressing a workpiece such as a multi-layered board by applying heat and pressure simultaneously thereto.
A multi-layered board such as printed wiring board (PWB) is generally manufactured by heat-pressing a plurality of vertically stacked members such as plurality of circuitry members and prepreg members inserted between the respective adjacent pair of circuitry members.
Heat-pressing is generally carried out by employing a pressing device having a pair of opposing heating platens, one of which is arranged to be driven toward and away from the other one.
Practically, a stack of circuitry members and prepreg members is prepared and placed between the pair of heating platens to be heat-pressed therebetween. During heat-pressing process, the temperature of the heating platens is controlled such that the resin component of the prepreg members is substantially liquidized for a predetermined period of time to thereby bond the adjacent circuitry members and unite all the stacked members together to form a multi-layered printed wiring board.
As a printed wiring board manufactured as above is required to have uniform thickness, heat-pressing must be carried out with heating platens having high surface flatness. On the other hand, a printed wiring board is recently becoming thinner and thinner due to the demand for producing compact electric devices in which a printed wiring board is to be installed. For example, the thickness of a printed wiring board to be manufactured is less than 100 &mgr;m, and in this case, a heating platen must have the surface flatness variation of less than 10 &mgr;m.
If the surfaces of the heating platens do not satisfy the condition mentioned above and have relatively large undulation, the pressure exerted from the heating platens on the printed wiring board varies across the printed wiring board. Such variance in the pressure results in thickness variance of the pressed printed wiring board. In addition, poor bonding property between the circuitry members occurs at locations where the pressure was insufficiently applied.
In addition to the above, pressing devices have recently employed large heating platens in order to simultaneously press a plurality of printed wiring boards by one pressing operation. However, since the realization of the required flatness of the heating platens becomes more difficult with the size thereof, the number of defective printed wiring boards, i.e. boards having low thickness uniformity and/or poor bonding property, also increases.
In order to avoid the above defects, it has been proposed to employ a cushion member, to be placed between a workpiece and a heating platen, such as a kraft paper that has a small surface roughness and small deformation on one side of which hardly affects the surface roughness of the other side.
Materials used in such a cushion member, however, have extremely low thermal conductivity compared to the heating platen. Such low thermal conductivity requires longer heating time and results in low productivity.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide improved method and device for pressing a workpiece capable of applying uniform pressure over a workpiece irrespective the level of flatness of a pressing surface.
It is another object of the invention to provide improved method and device for pressing a workpiece capable of applying uniform pressure over a workpiece irrespective the size of a pressing surface.
It is a further object of the invention to provide improved method and device for heat-pressing a workpiece capable of applying uniform pressure over a workpiece as well as of effectively heating a workpiece.
According to an aspect of the invention, a method for pressing a workpiece with a uniform pressure across the workpiece is provided. In this method, a pressing plate is located on the pressing surface of a platen. Then a spacer thicker or deeper than the workpiece is placed beside the workpiece. The spacer is pressed by the platen to define a gap between the pressing plate and the workpiece. Then, a liquid layer formed between the platen and the pressing plate is pressurized such that the pressing plate bends toward the workpiece due to the pressure of the liquid layer and thereby presses the workpiece. Since the liquid layer exerts a uniform pressure over the pressing plate, the pressing plate applies a uniform pressure over the workpiece.
Thus, the platen can keep contacting the spacer and the distance between the platen and the workpiece remains constant while the liquid is being pressurized, which prevents the pressing plate from breaking due to too much bending toward the workpiece.
According to another aspect of the invention, a pressing method is provided in which a workpiece to be pressed is located on the pressing surface of the platen and a cushion member is provided between the platen and the workpiece. The cushion member includes a pair of plates joined to each other to form a sealed space therebetween. The sealed space is filled with liquid to form a liquid layer.
Then, the platen is forced towards the workpiece such that the workpiece is pressed by the cushion member. Since the cushion member is filled with liquid, the cushion member applies a uniform pressure across the workpiece.
Optionally, an intermediate plate may be provided between the cushion member and the workpiece before the workpiece is pressed by the cushion member. The intermediate plate may be bendable along the surface of the workpiece when the intermediate plate is pressed against the workpiece.
Alternatively, a stack of workpiece may be formed by alternatively pilling a plurality of the workpieces and the intermediate plates and placed the pressing surface of the platen for pressing.
The intermediate plates mentioned above assists in enlarging the area that the cushion member can exert uniform pressure on the workpiece.
According to another aspect of the invention, there is provided a device for pressing a workpiece, which has a platen movable towards the workpiece and a pressing plate provided between the platen and the workpiece such that the workpiece is pressed by the pressing plate when the platen is moved toward the workpiece.
A liquid layer is formed between the pressing plate and the platen. This liquid layer transfers the force for pressing the workpiece from the platen to the pressing plate. During the transmission of the force, the force exerted on the liquid layer from the platen is changed to a constant pressure of the liquid layer irrespective the surface geometry of the platen. Therefore, the force exerted on the pressing plate by the liquid layer is constant across the pressing plate and, as a result, the pressure applied on the workpiece from the pressing plate becomes uniform all over the workpiece.
The pressing plate is a thin plate so that it bends along the surface of the workpiece during pressing. Optionally, the workpiece side of the pressing plate is finished in a mirror-smooth state for smooth contact between the pressing plate and the workpiece.
In some cases, the platen is a heating platen heated to a temperature sufficient to heat the workpiece to a temperature required for heat-pressing. In such case, the liquid layer is preferably a layer of heat conductivity oil. Since the heat transfer oil has high heat conductivity, the heat of the heating platen is effectively transferred to the workpiece. Therefore the workpiece can be heated in a short time and thus the time required for the whole pressing process is reduced.
Optionally, the pressing plate is detachably mounted to the platen such that a space is defined therebetween. The space is utilized to form the liquid layer by filling the space with liquid. The pressure of the liquid filled in the space is preferably controlled by a pressure controller such that, for example, the pressure of the liquid is raised only when the workpiece is pressed.
In
Matsumoto Seiki
Okazaki Shizuaki
Kitagawa Seiki Kabushiki Kaisha
Pitney Hardin LLP
Stoner Kiley
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