JP3478273B2 - Screen printing method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a screen printing method for printing cream solder on a substrate. 2. Description of the Related Art A screen printing apparatus prints cream solder on electrodes of a substrate through pattern holes formed in a mask. In recent years, as the degree of integration of electronic components mounted on a substrate has increased, the number of fine pattern holes formed in a mask has also increased. [0003] When the pattern holes become fine, the required printing quality becomes higher, and the squeegee speed at which the squeegee slides on the mask and the relative speed between the mask and the substrate when the mask moves away from the substrate (the plate). Unless the release speed is made slower, sufficient print quality cannot be obtained. [0004] However, if the printing conditions for reducing these speeds are adopted, the tact time until printing on one substrate is completed is lengthened, and the productivity is reduced. [0005] Here, in the conventional screen printing apparatus, in order to prevent a printing defect from occurring even with the finest mask, the printing conditions at which these speeds are reduced are determined. Is used to perform all printing. However, with such a configuration,
As for a mask that is not very fine, printing is performed with an excessive print quality, and there is a problem in that an unnecessarily long tact time is required and productivity is reduced. Accordingly, an object of the present invention is to provide a screen printing method capable of well-balancing conflicting conditions of print quality and productivity. According to the present invention, there is provided a screen printing method comprising: a printing condition storage unit for storing printing conditions including a squeegee speed and a plate separation speed; Has mode information on whether to adopt,
Disk having a control unit comprising a printing condition correcting section for correcting the printing conditions of the printing condition storage unit in a different manner for each mode
This is a screen printing method that uses a lean printing device to detect the printing state, corrects printing conditions based on the detection result, and prints cream solder on the electrodes of the board. The printing condition correction unit checks whether the printing mode is the printing mode or the productivity priority mode. If the printing mode is the quality priority mode, the printing condition stored in the printing condition storage is improved so that the printing quality is improved even if the tact time is sacrificed. The squeegee speed among the conditions is corrected to be low, and in the productivity priority mode, the printing conditions among the printing conditions stored in the printing condition storage unit are shortened so that the tact time is reduced unless the printing quality becomes poor. Correction is made to increase the squeegee speed, and the cream solder is printed. According to the present invention, if the mode information instructed in advance is a quality priority mode, the squeegee speed among the printing conditions is reduced so that the print quality is improved even if the tact time is sacrificed. If the priority mode, the cream solder is printed by increasing the squeegee speed among the printing conditions so that the tact time is shortened as long as the print quality is not deteriorated, so that the necessary and sufficient print quality allows the shortest tact time. Printing can be performed, and both printing quality and productivity can be achieved. Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a side view of a screen printing apparatus according to an embodiment of the present invention, FIG. 2 is an explanatory diagram showing a relationship between print quality and printing conditions in an embodiment of the present invention, and FIG. 3 is an embodiment of the present invention. FIG. 4 is a block diagram of a screen printing apparatus according to an embodiment of the present invention, and FIG. 5 is a flowchart of the screen printing apparatus according to an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes positioning means for positioning the substrate 2. 3 is an X table, 4 is a Y table provided on the X table 3,
Reference numeral 5 denotes a Z table provided on the Y table 4, which raises and lowers a holder 6 holding the substrate 2. The substrate 2 before printing is transferred onto the holder 6 by the carry-in conveyor 7 from the left side in FIG. 1 when the positioning means 1 is at the position of the chain line. The printed board 2
The positioning means 1 moves to the right in FIG.
Is transferred to the unloading conveyor 8 and unloaded. 9 is a mask 10 (having pattern holes)
This is a board recognition camera that observes the board 2 at a position (chain line position) away from the camera. The camera 9 has a role of detecting the position of the substrate 2 when the substrate 2 is set on the holder 6, and a role of performing imaging for obtaining an area ratio described later after printing on the substrate 2. Has two roles. Reference numeral 11 denotes a mask 10 when the positioning means 1 positions the substrate 2 at a printing position (solid line position).
Is a mask frame for holding the mask 10 so as to be directly above the substrate 2. A frame 12 extending in the left-right direction of FIG. 1 is provided on an upper portion of the mask 10, and the frame 12 has a feed screw 1 driven by a squeegee moving motor 16.
3 is mounted on the shaft. The feed screw 13 has a feed nut 1
A squeegee head 15 having two squeegees 18 and 19 is fixed to a lower portion of the feed nut 14. Therefore, when the squeegee moving motor 16 is operated, the squeegee head 15 can be moved in the left-right direction in FIG.
Either 8 or 19 slides on the mask 10 and scrapes the cream solder 17, so that the cream solder 17 can be printed on the substrate 2 through the pattern holes of the mask 10. Reference numerals 20 and 21 denote elevating means such as cylinders provided on the squeegee head 15 for bringing one of the lower edges of the squeegees 18 and 19 into contact with the mask 10. Next, with reference to FIG. 2, the relationship between printing conditions such as the squeegee speed VS, the plate separation speed VL, and the distance (control section SC) for controlling the plate separation speed VL, and the print quality will be described. Here, in this embodiment, the area ratio is used as an index indicating the print quality. The area ratio is a value in which the ratio between the area of the electrode on the design value and the area of the cream solder 17 actually printed in the vicinity of the electrode in the image captured by the board recognition camera 9 is expressed as a percentage. In the present embodiment, the area ratio is less than 90% or 110%
If it exceeds, it is determined that printing is defective. That is, with this type of substrate, if the area ratio is 90% or more and 110% or less, it is determined that printing is good. For example, QFP pin pitch is 0.5m
This is the case when it is not less than m. On the other hand, for a fine substrate, the area ratio is 9
When it is 8% or more and 102% or less, it is determined that printing is good, and when it is not, it is determined that printing is defective. For example, this is the case where the pitch of the pins of the QFP is less than 0.5 mm. Of course, the above numerical values are merely examples, and may be changed for convenience. As shown in FIG. 2B, the area ratio is 1
When it is 00%, the print quality is the best. However, as described above, the print quality and the productivity have an opposite relationship, and the productivity is the lowest when the print quality is the highest (the squeegee speed VS and the plate separation speed VL are slow, and the control section SC is long).
Level. The printing conditions are changed from the state shown in FIG. 2B (the squeegee speed VS and the plate separation speed VL are increased, and the control section S
When C is shortened), a transition is made to a direction where the area ratio is insufficient as shown in FIG. 2A or to a direction where the area ratio is excessive as shown in FIG. 2C. At this time, as compared with the state shown in FIG. 2B, the print quality is reduced, but the productivity is improved. However, the direction of transition in FIG. 2 (a) or FIG. 2 (c) depends on the physical properties of the solder, and is case-by-case and cannot be foreseen. Here, considering the printing of a substrate that is not very fine, even if the area ratio is not around 100%, it is 90%.
%, Or slightly less than 110%, the printing is good and sufficient print quality is obtained. At this time, the productivity is considerably improved as compared with the case where the area ratio is around 100%. Therefore, with this type of substrate, controlling the print quality to be the highest (area ratio 100%) as in the prior art is nothing more than simply lowering the productivity. Therefore, the optimization should be performed for the state where the area ratio is slightly above 90% or the area ratio is slightly below 110%. As a result, a necessary and sufficient print quality and the highest productivity can be obtained. Next, the phenomena before and after the plate separation will be described with reference to FIG. First, immediately after the squeegee 18 slides, the cream solder 17 fills the pattern hole 23 located just above the electrode 22 of the substrate 2 as shown in FIG. Then, the control section SC1 is set longer,
When the plate release speed VL1 is reduced, the cream solder 17 smoothly comes out of the pattern holes 23 as shown in FIG. 3B, and the cream solder 17 in the pattern holes 23 as shown in FIG. All the solder 17 is transferred to the electrode 22 and printed with the area ratio being 100%. Then, in the stroke D1 following the control section SC1, the substrate 2 descends at a high speed, and the operation of one stroke ends. On the other hand, as shown in FIG. 3D, when the control section SC2 is made shorter and the plate separation speed VL2 is made faster,
As shown in (e), a part of the cream solder 17 in the pattern hole 23 remains on the mask 10, and the amount of the cream solder 17 transferred to the electrode 22 becomes insufficient (the area ratio is small). However, in the case of FIGS. 3D and 3E, the tact time is shorter and the productivity is improved as compared with the cases of FIGS. 3B and 3C. Therefore, in this embodiment, for a fine substrate, the print quality is controlled to the highest level as shown in FIGS. 3B and 3C, and for a non-fine substrate, FIG.
As shown in (d) and (e), even if the area ratio slightly varies,
If the variation is within a permissible range, control is performed to improve productivity. Therefore, in the present embodiment, the control according to the flowchart of FIG. 5 is performed using the control block shown in FIG. As shown in FIG. 4, the control unit 25 includes a printing condition storage unit 26 comprising a memory for storing printing conditions including a squeegee speed VS, a plate separation speed VL, and a control section SC.
A print condition correction which has mode information (instructed by the user from the input unit 24) as to which of the productivity priority mode and the quality priority mode is to be used, and corrects the print conditions of the print condition storage unit 26 in a different method for each mode. A unit 27 and a motor control unit 28 that controls the squeegee moving motor 16, the X table 3, the Y table 4, and the Z table 5 according to the current printing conditions in the printing condition storage unit 26. The camera 9 for recognizing the board includes the image processing unit 2.
9 is connected. In the image processing unit 29, reference numeral 30 denotes a substrate position detection unit that detects the position of the substrate on the holder 6, and the detected position is used by the motor control unit 28 for position correction. Reference numeral 31 denotes a printing state detecting unit which calculates an area ratio from the image shown in FIG. 2 and feeds back the obtained area ratio to the printing condition correcting unit 27. The screen printing apparatus of the present embodiment has the above-described configuration. Next, the control process will be described with reference to FIG. First, the substrate 2 is carried into the holder 6 from the carry-in conveyor 7 at the position indicated by the dashed line in FIG. 1 (step 1). Next, the substrate 2 on the holder 6 is imaged by the substrate recognition camera 9, the position detected by the substrate position detection unit 30 is given to the motor control unit 28, the position is corrected, and the substrate 3
Positioning is performed just below 0 (solid line position in FIG. 1, step 2). Then, the squeegee speed V in the printing condition storage unit 26
S, the separation speed VL, and the control section SC are set to initial values, and printing is performed by sliding the squeegee 18 on the mask 10 (step 3). Next, the substrate 2 is returned to the dashed line position in FIG. 1, and an image is taken by the substrate recognition camera 9 to obtain an image of the substrate 2. Then, the print state detection unit 31 calculates the area ratio based on the image. The calculated area ratio is fed back to the printing condition correction unit 27 (Step 4). Next, the printing condition correcting section 27 checks whether the mode is quality priority or productivity priority (step 5). If the mode is the quality priority mode, go to step 6; if the mode is the productivity priority mode, go to step 8. Transition. In step 6 (quality priority mode), it is checked whether or not the area ratio is 98 to 102%. VS, the plate separation speed VL is reduced, and the control section S
C is lengthened (Step 7), and the process proceeds to Step 10. On the other hand, in step 8 (productivity priority mode), the area ratio is 90 to 95% or 105 to 110%.
Check if it is%. If not, the squeegee speed VS and the plate separation speed VL stored in the printing condition storage unit 26 are increased, and the control section SC is shortened (step 9). This further improves productivity. In the productivity priority mode, if the area ratio is 10
Even if it is 0%, this is not an ideal,
Step 9 is performed to further increase the productivity.
That is, at this time, the print quality is intentionally degraded. In step 10, it is checked whether or not printing of all the substrates has been completed.
The upper substrate 2 is unloaded and the process is completed (step 1).
4). Otherwise, go to step 11. In step 11, after the substrate 2 on the holder 6 is carried out, the next substrate 2 is carried in (step 11), the substrate is aligned (step 12), and printing is performed. Here, this printing is performed under more optimized printing conditions during the previous and previous strokes. Then, returning to step 4, until printing of all the boards is completed,
Printing is repeated while optimizing the printing conditions according to the mode. In the present embodiment, inspection and correction of printing conditions are performed each time cream solder is printed on one substrate. However, the inspection may be performed every arbitrary number of substrates. The present invention is configured as described above.
Optimal printing can be performed by successfully balancing the conflicting conditions of print quality and productivity.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view of a screen printing apparatus according to an embodiment of the present invention. FIG. 2 is an explanatory diagram showing a relationship between print quality and printing conditions according to an embodiment of the present invention. FIG. 4 is a diagram illustrating a plate separation process according to an embodiment of the present invention. FIG. 4 is a block diagram of a screen printing apparatus according to an embodiment of the present invention. FIG. 5 is a flowchart of a screen printing apparatus according to an embodiment of the present invention. EXPLANATION OF SYMBOLS 1 positioning means 2 substrate 10 masks 18, 19 squeegee 23 pattern hole 25 control unit

────────────────────────────────────────────────── ─── Continuation of the front page (72) Kunihiko Tokita 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-8-207241 (JP, A) JP-A-8- 39768 (JP, A) JP-A-6-286105 (JP, A) JP-A-10-157060 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B41F 15/40 B41F 15 / 08 303 H05K 3/34 505

Claims (1)

(57) [Claims 1] A printing condition storage unit for storing printing conditions including a squeegee speed and a plate separation speed, and mode information indicating which of a productivity priority mode and a quality priority mode is to be adopted. And a control unit comprising a printing condition correction unit for correcting the printing condition of the printing condition storage unit in a different method for each mode .
This is a screen printing method that uses a screen printing device to detect the printing state, corrects printing conditions based on the detection result, and prints cream solder on the electrodes of the board. The printing condition correction unit checks whether the printing mode is the printing mode or the productivity priority mode. If the printing mode is the quality priority mode, the printing condition stored in the printing condition storage is improved so that the printing quality is improved even if the tact time is sacrificed. The squeegee speed among the conditions is corrected to be low, and in the productivity priority mode, the printing conditions among the printing conditions stored in the printing condition storage unit are shortened so that the tact time is reduced unless the printing quality becomes poor. A screen printing method characterized in that cream solder printing is performed by modifying the squeegee speed to be higher.