Printing – Stenciling – Processes
Reexamination Certificate
2001-04-02
2003-01-14
Evanisko, Leslie J. (Department: 2854)
Printing
Stenciling
Processes
C101S123000, C101S126000, C101S127100
Reexamination Certificate
active
06505553
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a screen-printing method and a screen-printing apparatus and particularly to the art of facilitating the separation from a screen of a print material printed on a substrate.
2. Discussion of Related Art
A screen printing is carried out by filling, in a state in which a screen is contacted with a substrate such as a printed wiring board, through-holes of the screen with a print material such as creamed solder, and thereby applying the print material to the substrate. After the printing operation, the screen is separated from the substrate, so that the print material is separated from the screen and is left on the substrate. Thus, the print material is printed on the substrate.
However, there is a problem that when the screen and the substrate are separated from each other after the printing operation, a certain amount of the print material remains adhered to respective inner surfaces of the through-holes of the screen, so that an amount of the printing material left on the substrate may be short or a print pattern formed on the substrate may have a defect.
SUMMARY OF THE INVENTION
The present invention provides a screen-printing method and a screen-printing apparatus which have one or more of the following technical features that are described below in respective paragraphs given parenthesized sequential numbers (1) to (19). Any technical feature that includes another technical feature shall do so by referring, at the beginning, to the parenthesized sequential number given to the latter feature. However, the following technical features and the appropriate combinations thereof are just examples to which the present invention is by no means limited. In addition, in the case where one technical feature recites a plurality of items, it is not essentially required that all of those items be simultaneously employed. That is, it is possible to select and employ only a portion (one, two, . . . , but not all) of those items.
(1) According to a first feature of the present invention, there is provided a screen-printing method, comprising the steps of filling, in a state in which a screen having a plurality of through-holes is contacted with a print surface of a substrate, the through-holes with a print material, and thereby applying the print material to the print surface of the substrate, moving, after the filling step, at least one of the screen and the substrate relative to the other of the screen and the substrate, in at least one cycle, on a plane parallel to the print surface of the substrate, in at least one direction parallel to at least one straight line, and separating, after the moving step, the screen and the substrate from each other.
When one of the screen and the substrate is moved relative to the other of the screen and the substrate, in a direction parallel to the print surface of the substrate, the print material, i.e., a print pattern formed by the print material filled in a through-hole and applied to the substrate is moved relative to the through-hole, so that a clearance is produced between a portion of the entire periphery of the print pattern and an inner surface of the through-hole. Therefore, when the screen and the substrate are separated from each other after the relative movement thereof, the print pattern is easily separated from the through-hole, such that no print material, or only a small amount of print material, if any, is left on the side of the screen. Thus, the present screen-printing method is free of the problems that the print material is short or the print pattern has a defect.
The number of cycles in which the screen and the substrate are moved relative to each other may be determined depending on, for example, the degree of difficulty of printing or the degree of difficulty of separation of the print pattern from the through-holes. For example, in the case where the screen has a constant thickness and the through-holes have a substantially identical cross-sectional shape, the degree of difficulty of separation of the print pattern increases as the cross-sectional area of the through-holes decreases. Therefore, the number of cycles increases. In this case, a circular through-hole and a square through-hole are defined as having a substantially identical cross-sectional shape. In addition, in the case where the screen has a constant thickness, and the through-holes have different cross-sectional shapes but have a substantially identical cross-sectional area, the degree of difficulty of separation of the print pattern increases and the number of cycles increases as a value (i.e., a ratio) obtained by dividing a maximum inner dimension of each through-hole by a minimum inner dimension thereof increases. For example, in the case where the through-holes have a rectangular, shape, the above ratio increases as the length of the short sides of the rectangular through-holes decreases. Moreover, as a value (i.e., a ratio) obtained by dividing the depth of each through-hole by the cross-sectional area thereof increases, the degree of difficulty of separation of the print pattern increases and the number of cycles increases. If the number of cycles is determined in this way, then it is assured that respective clearances are produced between the print pattern and the respective inner surfaces of the through-holes, according to the shape, dimensions, and/or height (i.e., depth) of each through-hole, and that the screen and the substrate are moved relative to each other with a small amount of waste.
(2) According to a second feature of the present invention that includes the first feature (1), the one cycle comprises a first forward movement of the at least one of the screen and the substrate by a distance &agr;, a backward movement of the at least one of the screen and the substrate by twice the distance &agr;, and a second forward movement of the at least one of the screen and the substrate by the distance &agr;, in an order of description.
According to this feature, in a state after the second forward movement following the backward movement, two clearances each having a dimension substantially equal to the distance &agr;, are produced between opposite end portions of each print pattern as seen in the direction of relative movement of the screen and the substrate, and opposite end portions of an inner surface of a corresponding through-hole as seen in the same direction. Although the size of each print pattern is decreased since the clearances are produced, the center of the each print pattern is not moved in the above-indicated direction and accordingly the each print pattern is formed at a correct position. Thus, for example, in the case where the substrate is a printed wiring board and the print material is creamed solder, when an electric component having a lead wire is mounted on the wiring board, the lead wire is placed at the center of a print pattern in a widthwise direction thereof, so that an electric circuit (i.e., an electric-conductor pattern) is produced with reliability.
(3) According to a third feature of the present invention that includes the second feature (2), the distance a is not smaller than one hundredth of an inner dimension of one of the through-holes in the one direction and not greater than one fifth of the inner dimension.
In the case where all the through-holes are elongate in the one direction parallel to the one straight line, the relative movement of the screen and the substrate in one or more cycles in only the one direction suffices in many cases. More specifically described, providing that an elongate through-hole is divided into unit-length portions in a lengthwise direction thereof lengthwise opposite end unit-length portions of the through-hole are more contacted with a print pattern than intermediate unit-length portions of the through-hole and, when the screen is separated from the substrate, the print material has a difficulty to separate from the inner surface of the through-hole and accordingly a certain amount of the material
Ishida Nobumichi
Mizuno Manabu
Shimizu Toshinori
Evanisko Leslie J.
Fuji Machine Mfg. Co., Ltd
Oliff & Berridg,e PLC
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