Printing – Stenciling – Processes
Patent
1998-12-04
2000-10-17
Funk, Stephen R.
Printing
Stenciling
Processes
101126, 101DIG36, 33620, B41F 1508
Patent
active
061315117
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a screen printing method and a screen printing apparatus for implementing printing onto a circuit board by using a screen.
BACKGROUND ART
With reference to FIGS. 7 to 9 illustrating a screen printing apparatus and FIG. 10 illustrating a flow chart of a screen printing method of the prior art, the screen printing method of the prior art is described.
As an apparatus for printing solder paste to a printed board 50 equivalent to the circuit board, there has been provided a screen printing apparatus 30 which comprises a recognition device 10 and a printing device 20, as shown in FIG. 7.
The recognition device 10 comprises a stage 1, motors 3 to 5 for moving the stage 1 in X, Y and .theta. directions as illustrated, a recognition camera 2 for recognizing recognition marks 51, 52 drawn on the printed board 50 as well as recognition marks 24, 25 drawn on a screen 21, and a control device 6 electrically connected to the recognition camera 2 and the motors 3 to 5.
The printing device 20 comprises the screen 21 on which a pattern showing the arrangement of openings for printing solder paste to the printed board 50 is formed, and a squeegee 22 for spreading the solder paste 23 placed on the screen 21 over the whole surface of the screen 21.
The control device 6 controls the drive of the motors 3 to 5 based on image information obtained from the recognition camera 2 in order that the pattern of the openings of the screen 21 matches a pattern printing position on the printed board 50 where the pattern should be printed on the printed board 50.
In this screen printing apparatus 30 having such a constitution, the stage 1 reciprocatingly moves between a printed-board loading/unloading position 182 and a just-under-the-screen position 183 where the stage 1 is located just under the screen 21, relative to the screen 21 that is fixed. Due to this movement, the printing operation is executed according to the steps as shown in FIG. 10.
More specifically, at Step (represented by "S" in the FIG.) 1, the printed board 50 is placed on the stage 1 at the printed-board loading/unloading position 182. At Steps 2 to 4, positional correction of the printed board 50 relative to the screen 21, which will be detailed later, is carried out. Thereafter, at Step 5, the stage 1 is moved to the just-under-the-screen position 183. Also at Step 5, the stage 1 is moved toward the screen 21 at the just-under-the-screen position 183. At Step 6, the screen 21 and the printed board 50 are brought into contact with each other, in which state printing is performed. In this printing process, the squeegee 22 lowers to the screen 21, and the squeegee 22 is moved leftward or rightward in the figure, by which the solder paste 23 is printed to the printed board 50 according to the pattern of the openings of the screen 21. After the printing, at Step 7, the stage 1 lowers, returning from the just-under-the-screen position 183 to the printed-board loading/unloading position 182 once again, whereby the printed board 50 after the printing process is removed from the stage 1. Then, another printed board 50 to be printed is placed on the stage 1 again, and the above operations are repeated.
The positional correction of the printed board 50 in Steps 2 to 4 is now explained.
The positional correction is to correct the position of the printed board 50 relative to the screen 21 so that the printed board 50 to be printed is placed at a specified position relative to the fixed screen 21. Information for achieving such positional correction is obtained by recognizing the recognition marks 24, 25 of the screen 21 and the recognition marks 51, 52 of the printed board 50, which is implemented by the recognition camera 2 moving. A detailed description is given below with reference to FIGS. 11 and 12.
First, the recognition of the recognition marks 24, 25 of the screen 21 is explained. A distance (SX1, SY1) from the origin 2a of the recognition camera 2 with respect to the recognition mark 24, and a distance (SX2, SY2) from
REFERENCES:
patent: 4516495 (1985-05-01), Ericsson
patent: 4610200 (1986-09-01), Metso
patent: 4953459 (1990-09-01), Ericsson
patent: 5168805 (1992-12-01), Kasanami et al.
patent: 5176078 (1993-01-01), Homma et al.
Kakishima Nobuyuki
Matsumoto Masaya
Wachi Akihiko
Yanachi Seishiro
Funk Stephen R.
Matsushita Electric - Industrial Co., Ltd.
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