METHOD FOR CONTROLLING SCREEN PRINTING MACHINE

Abstract: The present invention relates to a control method for improving the productivity of a screen printer for an electronics-mounting machine. Thus, a screen printer according to this invention uses a recognition camera to inspect the results of printing of a circuit board concurrently with a cleaning operation of the rear surface of a screen, thereby enabling the effective use of time. This screen printer also enables cream solder to be automatically supplied to reduce the operation time by determining whether the next screen to be used is unused. During automatic screen replacement, this screen printer enables a desired screen stored in the corresponding stocker to be automatically specified in order to replace the current screen in response to a selected NC program.

Description: The present invention relates to a control method for improving the productivity of a screen printer for an electronics-mounting machine. A screen printer for an electronics-mounting machine prints cream solder on a circuit board of an electronic part. There are several problems to be solved in order to improve the productivity of this printer. A first problem is the correction of locational offset between a printed pattern of a screen and a pattern on the circuit board. A procedure for improving the printing accuracy of a conventional screen printer is described with reference to FIGS. 2 to 5. FIG. 2 is a perspective view of a screen printer. A circuit board loaded by a loader 1 is fixed to a stage section 2. A recognition camera 3 recognizes a circuit board target mark, and a stage moving section 4 and a stage elevating section 5 position the circuit board in a screen 6. Subsequently, a print head section 7 moves in the lateral direction for printing and the stage elevating section 5 lowers to perform a print separating operation. Then, a cleaner section 8 moves forward and backward to clean the rear surface of the screen, but at this point, the stage moving section 4 on the rear surface of the screen is located so as to contact the cleaner section 8, so the stage moving section must retreat to the loader 1 side together with the circuit board. Once the cleaning operation is finished, the stage moving section 4 moves to an unloader 9 side, where the circuit board is unloaded to the unloader 9. FIG. 3 is a flowchart describing a process of a conventional general screen printer. The operation of each step is described based on the flowchart with reference to FIG. 3. When the program starts at #1 and a circuit board waiting state (upstream side) is exited at #2, a circuit board is loaded by the loader 1 at #3 and fixed to the stage section 2 at #4, and the recognition camera 3 recognizes the circuit board target mark. At #5, the stage moving section 4 and the stage elevating section 5 position the circuit board at a screen target mark that has been already recognized, and at #6, the print head section 7 performs a printing operation. At #7, the stage elevating section 5 retreats the stage, and at #8, the cleaner section 8 cleans the rear surface of the screen. When the circuit board waiting state (downstream side) is exited at #11, the stage moving section 4 moves at #12 to unload the circuit board, thereby finishing the production of the single one circuit board. Furthermore, if production is to be continued, the process returns to #2 from #13 to repeat the same steps. If production is to be finished, the process finishes at #14. The occurrences of #2 and #11 depend on the production conditions of the mounting machine on the upstream and downstream sides. FIG. 4 is a flowchart describing a procedure for improving the printing accuracy of a conventional screen printer having no inspection function. Steps #1 to #8, #11, and #12 are the same as in FIG. 3 and their description is omitted. When a circuit board is loaded at #12, the machine is stopped at #15, and an operator uses a microscope to measure the results of printing at #16 and registers the locational difference between a screen pattern and a circuit board pattern, in the machine as an offset to reflect the measured offset in the subsequent printing correction operation at #17. At #18, the operator re-operates the machine, and the subsequent steps are the same as in FIG. 3. FIG. 5 is a flowchart describing a procedure for improving the printing accuracy of a conventional screen printer having a function for inspecting the results of printing. Steps #1 to #8 are the same as in FIG. 3. When the cleaning operation is finished at #8, the machine inspects the results of printing at #9 and registers the locational difference between the screen pattern and the circuit board pattern at #10 to reflect it in the subsequent printing correction operation. The subsequent steps are the same as in FIG. 3. In the process executed by the conventional screen printer having no inspection function, the machine must be halted to measure the offset between the screen pattern and the circuit board pattern, and a step is required in which the operator inspects the results of printing, thereby reducing productivity. In addition, in the conventional screen printer having a function for inspecting the results of printing, a step for inspecting the results of printing is required that follows the cleaning operation. The inspection of the results of printing requires a large amount of time, thereby reducing the productivity of the printer. A conventional screen printer is described in US-A-5 197 384. The screen printer comprises a table unit, a mask unit and a mask cleaning unit. The table unit carries the matter to be printed. The mask unit is attached with a mask having at least a perforated through hole of a printing pattern. During a printing operation, the table unit which carries the matter to be printed is moved to a position below the mask. The mask is put into contact with an upper surface of a printed circuit board disposed on a table of the table unit and ink on the mask is squeezed out through the holes of the mask so that a pattern of the mask is printed on the printed circuit board. During a cleaning operation of the mask, the table unit is moved away from the printing position and the cleaning unit is moved to the position below the mask. Reference DE-A-39 28 525 relates to a screen printer for the production of printed circuit boards. The screen printer comprises a cleaning device in the form of a doctor blade. The cleaning of the screen is carried out by employing a two step cleaning procedure. A method for registered printing on an electronic circuit with respect to reference holes in a substrate is disclosed in EP-A-0 204 901. The circuits to be printed are provided with holes therein. A screen comprises hole patterns to be printed around the holes on the circuit board. After the hole patterns have been printed onto a circuit board, the circuit board is moved to another position for being inspected as to whether or not the hole patterns are printed correctly. Recognition means generate images from the hole patterns on the circuit board which are displayed on monitors for being inspected. Detected deviations of the printed hole patterns are used to correct the position of the screen for subsequent printing operations. It is the object of the present invention to provide a more efficient method for controlling a screen printer. This is achieved by the features of claim 1. To solve this problem, this invention provides a method for controlling a screen printer having an automatic cleaning function according to claim 1. This control method can correct the offset between a pattern of a screen and a pattern on the circuit board.during the screen cleaning operation. Thus, this invention reduces the number of steps required to inspect the result of printing and the time required to inspect the result of printing to improve the productivity of the screen printer. FIG. 1 is a flowchart describing a process executed by a screen printer according to an embodiment of this invention; FIG. 2 is a perspective view of a screen printer; FIG. 3 is a flowchart describing a process executed by the screen printer; FIG. 4 is a flowchart describing a procedure for improving the printing accuracy of a conventional screen printer having no inspection function; FIG. 5 is a flowchart describing a procedure for improving the printing accuracy of a conventional screen printer having an inspection function. An embodiment of this invention that solves the problem is described below with reference to FIGS. 1 and 2. The configuration of a screen printer according to the embodiment of this invention is the same as in FIG. 2. FIG. 1 is a flowchart describing a process executed by the screen printer according to the embodiment of this invention. Steps #1 to #7 are the same as in FIGS. 3 to 5. When the program starts at #1 and a circuit board waiting state (upstream side) is exited at #2, a circuit board is loaded by the loader 1 at #3 and fixed to the stage section 2 at #4, and a recognition camera 3 recognizes a circuit board target mark. At #5, a stage moving section 4 and a stage elevating section 5 position the circuit board at a screen target mark that has been already recognized, and at #6, a print head section 7 performs a printing operation. At #7, the stage elevating section 5 retreats the stage section. During the subsequent cleaning operation at #8, a cleaner section 8, which is shown in FIG. 2, moves forward and backward to clean the rear surface of the screen 6, but at this point, the stage moving section 4 on the rear surface of the screen is located so as to contact the cleaner section 8, so the stage moving section must retreat to the loader 1 side together with the circuit board. According to this invention, concurrently with the cleaning operation, at #9, the recognition camera 3 inspects the results of printing for the circuit board that has retreated to the loader 1 side in order to detect the locational difference between a screen pattern and a circuit board pattern. At #10, the machine automatically registers this offset to reflect it in the subsequent circuit board printing correction operation. When the circuit board waiting state (downstream side) is exited at #11, the stage moving section moves at #12 to unload the circuit board, thereby finishing the production of the one circuit board at #13. Each of these steps is the same as in FIG. 3.

Claims: A method for controlling a screen printer having an automatic cleaning function, said method concurrently performs the steps of: cleaning (#8) a screen, and inspecting (#9) the result of printing (#6) a circuit board by using a recognition camera (3), so that the inspection result can be off-set registered (#10) and reflected in the subsequent printing correction operation.

Inventors: NISHIKAWA NOBORU, SAITO HIROYOSHI, WACHI AKIHIKO, NISHIKAWA, NOBORU, SAITO, HIROYOSHI, WACHI, AKIHIKO
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1997
Main classification: B41F15
IPC codes: H05K3, B41F35, B41F15, H05K1