JP2008036958A - Screen printing apparatus and screen printing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a screen printing apparatus which can ensure good printing plate releasing properties and a stable quality of printing, and a screen printing method. <P>SOLUTION: In a screen printing for printing a soldering paste on a substrate, an initial retention time TO in a printing plate releasing operation is set in advance as a specified timer value based on a viscosity recovering time inherent to the kind of the soldering paste, and on the printing plate releasing after squeezing operation, after the initial retention time TO passes, under a condition that the viscosity of the soldering paste is recovered, releasing of the substrate 10 from a mask plate 12 is started. It is possible thereby to suppress collapse of the soldering paste in releasing the printing plate and to ensure the good printing plate releasing properties and the stable quality of printing. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a screen printing apparatus and a screen printing method for printing a paste on a substrate.

  A screen printing method is known as a solder supply method when soldering an electronic component to a substrate. In this method, the solder paste containing solder particles in the flux component is printed on the electrode surface of the substrate through the pattern holes provided in the mask plate, and the substrate is in contact with the lower surface of the mask plate. A screen printing apparatus provided with a screen printing mechanism that slides a squeegee on the upper surface is used (for example, Patent Document 1).

  In order to ensure good print quality in screen printing, the solder paste is patterned when the plate is separated from the lower surface of the board after filling, as well as the filling ability to reliably fill the pattern holes with the solder paste. It is required that the stencil release property to be removed from the hole without losing the mold is good. For this reason, in the screen printing operation, various attempts have been made to optimally set the operation speed and operation pattern for separating the substrate from the mask plate according to the properties of the solder used.

For example, in the above-mentioned patent document example, when the substrate is separated from the mask plate, a motion that promotes the flow of the solder paste in the pattern hole is imparted, thereby reducing the viscosity of the solder paste and releasing the plate. To improve.
Japanese Patent Laid-Open No. 7-80083

  In recent years, from the viewpoint of diversification of applications of electronic parts and environmental protection, solder having a composition different from that of conventionally used solder has been used for soldering electronic parts. For example, lead-free solder that contains almost no harmful solder components has been widely used for environmental protection requirements, and in-vehicle electronic devices use acrylic resin as a flux component. Is used.

  These solder pastes have significantly different properties and viscosity characteristics compared to conventional Pb-Sn eutectic solder contained in a general-purpose flux such as rosin. It has become difficult to apply as it is. That is, since the tin-based alloy constituting the lead-free solder has a specific gravity smaller than that of the Pb—Sn eutectic solder, there is a feature that the plate pull-out effect due to its own weight is small and the shape is easily broken. Furthermore, when an acrylic resin is used as the flux, it is easy to induce a loss of shape when the plate is released due to a small thixo ratio. As described above, in the printing of solder paste using lead-free solder, there is a problem that it is difficult to maintain the shape when the plate is separated, and it is difficult to ensure good print quality.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a screen printing apparatus and a screen printing method that can ensure good plate separation and stable printing quality.

The screen printing apparatus according to the present invention is a screen printing apparatus for printing a paste on a substrate through the pattern hole by bringing the substrate into contact with the lower surface of the mask plate in which the pattern hole is formed, and receiving the substrate. Holding the substrate support, plate release means for separating the substrate from the lower surface of the mask plate by raising and lowering the substrate support, plate release control means for controlling the plate release means, and A timer setting unit for setting an initial stop time in the plate separating operation by the plate separating means as a predetermined timer value based on a viscosity recovery time specific to the type, and the plate separating control means is provided on the lower surface of the mask plate. While the substrate is in contact, the substrate is held stationary for the initial stop time, and after the initial stop time has elapsed, the lowering of the substrate receiving portion is opened. Controlling said detaching means so as to.

  The screen printing method of the present invention is a screen printing method in which a substrate is brought into contact with the lower surface of a mask plate in which pattern holes are formed, and a paste is printed on the substrate through the pattern holes, and is specific to the type of paste. A timer setting step for setting, as a predetermined timer value, an initial stop time in the plate separating operation for separating the substrate from the lower surface of the mask plate based on the viscosity recovery time of the mask plate, and bringing the substrate into contact with the lower surface of the mask plate A mask mounting step, a filling step of filling the pattern hole with a paste by moving a squeegee on the mounted mask plate, and a plate separation step of separating the substrate from the lower surface of the mask plate, In the plate separation step, the initial stop is performed while the substrate is in contact with the lower surface of the mask plate. Course of the holding the substrate in a stationary state, to initiate the separation from the mask plate of the substrate after the initial dwell time has elapsed.

  According to the present invention, the initial stop time in the plate separation operation is set as a predetermined timer value based on the viscosity recovery time specific to the paste type, and the substrate contacts the lower surface of the mask plate in the plate separation step. In this state, the substrate is held in a stationary state for the initial dwell time, and after the initial dwell time has elapsed, the separation of the paste from the mask plate is started in the state in which the viscosity of the paste has been recovered. It is possible to suppress the loss of shape and to ensure good plate separation and stable printing quality.

  Next, embodiments of the present invention will be described with reference to the drawings. 1 is a side view of a screen printing apparatus according to an embodiment of the present invention, FIG. 2 is a front view of the screen printing apparatus according to an embodiment of the present invention, and FIG. 3 is a screen printing apparatus according to an embodiment of the present invention. FIG. 4 is a flowchart of the printing operation by the screen printing apparatus according to the embodiment of the present invention, and FIG. 5 is the operation of the printing operation by the screen printing apparatus of the embodiment of the present invention. FIG. 6 is an explanatory diagram of the plate separation operation in the screen printing operation according to the embodiment of the present invention.

  First, the structure of the screen printing apparatus will be described with reference to FIGS. In FIG. 1, the screen printing apparatus is configured by disposing a screen printing mechanism above a substrate positioning unit 1. The substrate positioning unit 1 is configured by stacking a Y-axis table 2, an X-axis table 3, and a θ-axis table 4, and further combining a first Z-axis table 5 and a second Z-axis table 6 thereon. Yes.

  The configuration of the first Z-axis table 5 will be described. Similarly, on the upper surface side of the horizontal base plate 4 a provided on the upper surface of the θ-axis table 4, the horizontal base plate 5 a is held up and down by an elevating guide mechanism (not shown). The base plate 5a is moved up and down by a Z-axis lifting mechanism configured to rotationally drive a plurality of feed screws 5c through a belt 5d by a motor 5b.

A vertical frame 5e is erected on the base plate 5a, and a substrate transport mechanism 8 is held at the upper end of the vertical frame 5e. The substrate transport mechanism 8 includes two transport rails arranged in parallel to the substrate transport direction (X direction—the direction perpendicular to the paper surface in FIG. 1), and both end portions of the substrate 10 to be printed by these transport rails. It supports and conveys. By driving the first Z-axis table 5, the substrate 10 held by the substrate transport mechanism 8 can be lifted and lowered with respect to the screen printing mechanism described later together with the transport rail 8.

  The configuration of the second Z-axis table 6 will be described. A horizontal base plate 6a is disposed between the substrate transport mechanism 8 and the base plate 5a so as to be movable up and down along a lifting guide mechanism (not shown). The base plate 6a is moved up and down by a Z-axis lifting mechanism configured to rotationally drive a plurality of feed screws 6c through a belt 6d by a motor 6b. On the upper surface of the base plate 6a, a lower table 7 having a lower receiving surface for holding the substrate 10 is provided on the upper surface.

  By driving the second Z-axis table 6, the lower table 7 moves up and down with respect to the substrate 10 held by the substrate transport mechanism 8. The lower table 7 supports the substrate 10 from the lower surface side when the lower surface of the lower table 7 contacts the lower surface of the substrate 10. A clamp mechanism 9 is disposed on the upper surface of the substrate transport mechanism 8. The clamp mechanism 9 includes two clamp members 9a that are arranged opposite to each other on the left and right sides. The substrate 10 that is supported by the lower table 7 is moved forward and backward by the drive mechanism 9b. And clamp from both sides. The receiving table 7 and the clamp mechanism 9 are substrate receiving portions that receive and hold the substrate 10. The first Z-axis table 5 constitutes a plate separating means for separating the substrate 10 from the lower surface of the mask plate 12 by moving the substrate receiving portion up and down.

  Next, the screen printing mechanism disposed above the substrate positioning unit 1 will be described. 1 and 2, a mask plate 12 is extended on the mask frame 11, and the mask plate 12 corresponds to the shape and position of the electrode 10a to be printed on the substrate 10 (see FIG. 3). Pattern holes 12a are provided. A squeegee head 13 is disposed on the mask plate 12. The squeegee head 13 has a configuration in which a squeegee raising / lowering mechanism 15 for raising and lowering the squeegee 16 is disposed on a horizontal plate 14. By driving the squeegee lifting mechanism 15, the squeegee 16 moves up and down and comes into contact with the upper surface of the mask plate 12. In this state, the plate 14 is moved in the Y direction by a horizontal movement mechanism (not shown), so that the squeegee 16 slides on the upper surface of the mask plate 12, thereby filling the pattern holes 12a with solder paste (paste). Is done.

  Next, the configuration of the control system will be described with reference to FIG. Here, of the functions of the screen printing apparatus, only the function related to the plate separation operation for separating the substrate from the lower surface of the mask plate after screen printing is shown. In FIG. 3, the control unit 20 is a calculation processing function by the CPU of the control device, and has a function of controlling the operation and processing of each unit described below.

  The timer setting unit 21 sets an initial stop time T0 (see FIG. 6A) in the plate separation operation by the first Z-axis table 5 based on a viscosity recovery time specific to the type of solder paste used. Set as timer value. Here, the viscosity recovery time is the time required for the solder paste in a state where the fluidity is increased and the viscosity is reduced by stirring to return to the viscosity state before stirring, and this viscosity recovery time is the composition of the solder paste. It will be different depending on. For example, a solder paste that uses an acrylic resin with a low thixo ratio as a flux component will recover to its original viscosity after the viscosity has been reduced by agitation, compared with general solder pastes that use general-purpose fluxes such as rosin. Is known to require a long time.

And, when using a solder paste containing lead-free solder particles having such a characteristic that the viscosity recovery time is long and the specific gravity of the solder particles is smaller than that of the conventional Pb—Sn eutectic solder, In the plate separating operation for separating the substrate from the mask plate, the solder paste tends to lose its shape, and it is difficult to ensure good printing quality. In order to solve such a problem, in this embodiment, prior to the start of the plate separation operation after squeezing, the substrate is placed in a stopped state for a predetermined time defined by the timer value and filled in the pattern hole. The viscosity of the solder paste is recovered, and then the plate separation operation is started.

  This timer value is set by the operator inputting data from the input device of the operation panel. In an actual setting example, 3-10 sec. Set to the time of the order. The plate separation pattern storage unit 22 stores the combination of the plate separation pattern in the printing operation, that is, the plate separation speed pattern by the first Z-axis table 5 and the timer value of the above-described initial stop time for each substrate and solder paste type. Remember.

  The drive unit 23 drives a Z-axis motor 5b that is a drive source of the first Z-axis table 5 as a plate separating means. The control unit 20 controls the drive unit 23 according to the plate separation pattern stored in the plate separation pattern storage unit 22 so that the plate separation operation can be performed under an appropriate plate separation condition according to the type of the target substrate and solder paste. Executed. Therefore, the control unit 20 is a plate separation control unit that controls the first Z-axis table 5 that is a plate separation unit. Then, as will be described later, the control unit 20 holds the substrate 10 in a stationary state for the initial holding time while keeping the substrate 10 in contact with the lower surface of the mask plate 12, and after the initial holding time has elapsed, The first Z-axis table 5 is controlled so as to start the lowering of the part.

  Next, the screen printing operation will be described along the flow of FIG. 4 with reference to FIG. The screen printing performed here is to print a solder paste to form solder bumps on the substrate 10. As the mask plate 12, a thin plate in which pattern holes 12a (pattern holes) having a very small size (for example, about 0.4 mm × 0.2 mm) are formed at a high density is used. A composition having a characteristic of having a long viscosity recovery time is used in which the flux contains a lead-free solder that does not contain lead as a component.

  Screen printing performed under such printing conditions has a high degree of printing difficulty. In particular, it is difficult to perform good plate separation that is uniform over the entire range of the substrate and does not lose the shape of the solder paste in the plate separation operation after squeezing. That is, since the pattern holes are present at a high density, the tack force at the time of separating the plate is large. On the other hand, the mask plate itself is thin and easily bent, so that the mask plate tends to be pulled downward during the plate separating operation for lowering the substrate. . As a result, there is a difference in plate separation timing between the outer peripheral portion and the central portion of the substrate, and it has been difficult to realize uniform plate separation.

  Furthermore, when using a lead-free solder as described above and a type having a long viscosity recovery time, the viscosity of the solder paste in the pattern hole 12a is reduced and the fluidity is high. As a result of starting the plate separation, when the solder paste adhering to the surface of the substrate 10 descends together with the substrate 10, a so-called thread that is partially connected to the solder paste adhering to the inner wall of the pattern hole 12a. Pulling phenomenon occurs. Such a stringing phenomenon causes the shape of the solder paste on the surface of the substrate 10 to be out of shape, and this tendency becomes prominent particularly when a pattern hole of a small size is an object, resulting in a printing defect. It was. In the screen printing shown in the present embodiment, for the screen printing for forming solder bumps having such a high degree of difficulty, it is possible to ensure uniform plate separation and print quality by the following method. Yes.

First, prior to the start of the printing operation, based on the viscosity recovery time specific to the type of solder paste, the initial stop time in the plate separation operation for separating the substrate 10 from the lower surface of the mask plate 12 is set as a predetermined timer value ( Timer setting process). This timer setting process is performed by operating the timer setting unit 21.

  When the printing operation is started, first, the first Z-axis table 5 is driven to raise the receiving table 7, and the substrate 10 is received by the receiving table 7 as shown in FIG. Next, the substrate 10 on the lower receiving table 7 is sandwiched and held from both sides by the clamper 9 a, and the Z-axis table 5 is driven to raise the substrate lower receiving portion (the lower receiving table 7 and the clamping mechanism 9) together with the substrate 10. The substrate 10 thus raised comes into contact with the lower surface of the mask plate 12 (mask mounting process). At this time, the upper surface of the substrate 10 is raised from the normal height position of the lower surface of the mask plate 12 to a position higher by a predetermined push-up allowance h, and the contact state between the substrate 10 and the mask plate 12 is set up arbitrarily.

  Next, as shown in FIG. 5B, the squeegee 16 is brought into contact with the mask plate 12, and the squeegee 16 is moved in a state where the cream-like solder paste 17 is supplied onto the mask plate 12 (ST1). By this squeezing operation, as shown in FIG. 5C, the solder paste 17 is filled in each pattern hole 12a (ST2) (filling step). In this filling step, the solder paste 17 can be satisfactorily filled into the minute pattern holes 12a because the viscosity of the solder paste 17 is lowered and the fluidity is increased by the stirring action of the squeegee 16 during the squeezing operation. .

  Next, a plate separation operation is performed. Here, when starting to release the plate, timer value measurement is performed (ST3). That is, the substrate 10 is held in a stationary state for a preset initial dwell time T0 while the substrate 10 is in contact with the lower surface of the mask plate 12. Then, after the timer value has expired and the initial stop time T0 has elapsed, plate separation is started (ST4).

  That is, the Z-axis table 5 is driven to lower the support table 7 and the clamp mechanism 9 together with the substrate 10, and the substrate 10 is masked while the solder paste 17 filled in the pattern holes 12 a is adhered onto the substrate 10. Separated from the lower surface of the plate 12. At this time, as shown in FIG. 5 (d), the separation between the substrate 10 and the mask plate 12 is started from the outer peripheral portion of the substrate 10, and in the state where the separation of the outer peripheral portion is started, the central portion is still in a close contact state. .

  Thereafter, by further lowering the receiving table 7, the mask plate 12 is separated from the upper surface of the substrate 10 in the entire range of the substrate 10 as shown in FIG. 5E, and the plate separation is completed (ST5). (The plate separation process). Thereby, the screen printing operation for printing the solder paste 17 on the upper surface of the substrate 10 through the pattern hole 12a is completed.

  Next, an operation pattern of the plate separation operation in the above-described screen printing operation will be described with reference to FIG. FIG. 6A shows a descending speed pattern of the first Z-axis table 5 in the plate separating operation. Here, the temporal change in the lowering speed V (plate separation speed) when lowering the substrate 10 is illustrated in relation to the lowering stroke S indicating the lowering amount of the substrate 10. A general trapezoid pattern is assumed as the speed pattern, and the area of the trapezoid (formed by the speed line and the time axis) indicating the speed pattern corresponds to the descending stroke in the descending operation.

As shown in FIG. 5A, at the start of the plate separation operation, first, an initial stop time T0 corresponding to the timer value is set. During this period, the first Z-axis table 5 does not operate, The substrate 10 is held in a stationary state. As described above, the initial retention time T0 is set according to the viscosity recovery time specific to the type of solder paste 17 to be used. Therefore, by holding the substrate 10 in the stationary state for the initial retention time T0, The viscosity of the solder paste 17 once lowered by the stirring action during the squeezing operation is restored to the viscosity before squeezing. Thereby, the solder particles in the solder paste 17 are in a state in which the cohesive force is increased by the flux component whose viscosity has been recovered. The plate separation shown below is started in such a state that the viscosity of the solder paste 17 in the pattern hole 12a is recovered and the cohesive force of the solder particles is increased.

  The plate separation operation is performed in two stages of a first fall time T1 and a second fall time T2. Here, during the first descending time T1 and the second descending time T2, the substrate 10 descends by the first descending stroke S1 and the second descending stroke S2, respectively. That is, as shown in this plate separation operation pattern, in the plate separation step in the above-described screen printing method, the substrate 10 is held stationary for the initial dwell time T0 while the substrate 10 is in contact with the lower surface of the mask plate 12. The separation of the substrate 10 from the mask plate 12 is started after the initial stop time T0 has elapsed.

  Then, after the separation of the substrate 10 from the mask plate 12 starts, the first lowering speed is low (for example, about 0.1 mm / s) until the lowering stroke reaches the first lowering stroke S1. The lowering speed V1 (first plate separation speed) is set, and the lower table 7 is slowly lowered. When the descending stroke reaches the first descending stroke S1, the descending speed is once returned to zero, and then the descending speed is increased again, and the second descending speed is higher than the first descending speed V1 (for example, about 5 mm / s). The lower receiving table 7 is lowered at a lowering speed V2 (second plate separation speed). Accordingly, the lower table 7 is lowered by the second lowering stroke S2 and stopped at the lowering position.

  That is, as shown in FIG. 6B, the solder paste 17 is filled in the pattern holes 12a, and the upper surface of the substrate 10 is first from the lower surface of the mask plate 12 as shown in FIG. 6B. The lowering is performed at a low speed (first lowering speed V1) until it is separated by the lowering stroke S1. Here, the first downward stroke S <b> 1 is set according to the thickness t of the mask plate 12. In the present embodiment, the thickness t is set to a range of 1/2 to 2 times (preferably a range of 1/2 to 9/10 times, more preferably 2/3 to 3/4 times). The

  During the first descending time T1 during which the substrate 10 descends by the first descending stroke S1, the descending speed of the substrate 10 is a low speed of the order of 0.1 mm / s, and therefore the solder paste in the pattern hole 12a. 17, the solder paste 17 at a position in contact with the side wall surface of the pattern hole 12 a remains in the pattern hole 12 a while remaining attached to the side wall surface even after the substrate 10 starts to descend, as shown in FIG. There is a strong tendency to remain. The solder paste 17 that is printed on the upper surface of the substrate 10 and descends together with the substrate 10 is connected to the solder paste 17 that is stretched in a string-like manner in a suspended state. At this time, since the viscosity of the solder paste 17 on the substrate 10 is recovered by the rest during the initial retention time T0 and the solder particles are aggregated by the flux component, the solder paste by the above-described stringing is used. 17 shape loss is suppressed as much as possible.

  FIG. 6D shows the state of the solder paste 17 in the second lowering time T2 when the substrate 10 is lowered by the second lowering stroke S2. That is, at the timing of FIG. 6C, the descending speed is suddenly increased from the low first descending speed V1 to the second descending speed V2, so that the side in the pattern hole 12a in FIG. The solder paste 17 that is attached to the wall surface and partially connected to the solder paste 17 on the substrate 10 is torn off by an impact tensile force at the time of speed increase. As a result, most of the solder paste 17 filled in the pattern hole 12a in FIG. 6B is lowered with the substrate 10 in a state where a part of the solder paste 17 is left on the side wall surface of the pattern hole 12a, and the plate separation is performed. Is called. At this time, the solder paste 17 is in a state where the viscosity is recovered and the cohesive force of the solder particles is increased as described above, so that the deformation of the solder paste 17 on the substrate 10 is suppressed.

  That is, in the above-described plate separation operation pattern, the upper surface of the substrate 10 is 1/2 to 2 times the thickness of the mask plate 12 from the lower surface of the mask plate 12 from the state where the substrate 10 is in contact with the lower surface of the mask plate 12. The substrate lowering portion is lowered at the first plate separation speed V1 until it is separated by a predetermined gap set between them, and then at a second plate separation speed V2 that is higher than the first plate separation speed V1. The plate separating means is controlled so as to lower the substrate support part.

  As a result, even when the solder paste 17 used for printing undergoes a change in viscosity due to changes over time, the degree of separation of the plate greatly depends on the viscosity state, and in any case, the plate is within an allowable range. Separation can be ensured. Therefore, even when a solder paste having a high printing difficulty, such as lead-free solder or acrylic solder, is used, it is possible to ensure good plate separation and stable printing quality.

  The first descending stroke S1 and the initial descending time T1 are advantageously set as small as possible from the viewpoint of the tact time. In order to prevent the solder paste 17 from losing its shape as much as possible, it is desirable that the substrate 10 be separated from the lower surface of the mask plate 12 by a certain amount. For this reason, the actual first descending stroke S1 is determined after comparing the allowed tact time and the required print quality.

  The screen printing apparatus and the screen printing method of the present invention have an effect that it is possible to ensure good plate separation and stable printing quality even when a solder paste having different properties and viscosity characteristics is used. In particular, it is useful for applications in which lead-free solder is printed on a substrate.

1 is a front view of a screen printing apparatus according to an embodiment of the present invention. The side view of the screen printing apparatus of one embodiment of this invention The block diagram which shows the structure of the control system of the screen printing apparatus of one embodiment of this invention FIG. 4 is a flowchart of a printing operation performed by the screen printing apparatus according to the embodiment of the present invention. Operation explanatory diagram of printing operation by screen printing apparatus of one embodiment of the present invention Explanatory drawing of plate separation operation | movement in screen printing operation of one embodiment of this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Board | substrate positioning part 5 1st Z-axis table (plate separation means)
5b Z-axis motor 7 Lower table (Substrate lower part)
9 Clamp mechanism (PC board receiving part)
10 Substrate 12 Mask Plate 12a Pattern Hole 13 Squeegee Head 16 Squeegee 17 Solder Paste
20 Control unit (plate separation control means)
T0 Initial stop time T1 1st descent time T2 2nd descent time V1 1st descent speed V2 2nd descent speed S1 1st descent stroke S2 2nd descent stroke

Claims (2)

A screen printing apparatus for bringing a substrate into contact with the lower surface of a mask plate in which pattern holes are formed and printing paste on the substrate through the pattern holes,
A substrate receiving part for receiving and holding the substrate, a plate separating means for separating the substrate from the lower surface of the mask plate by raising and lowering the substrate receiving part, and a plate separating control for controlling the plate separating means Means, and a timer setting unit for setting an initial stop time as a predetermined timer value in the plate separation operation by the plate separation means based on the viscosity recovery time specific to the type of paste,
The plate separation control means holds the substrate in a stationary state for the initial stop time while keeping the substrate in contact with the lower surface of the mask plate, and lowers the substrate receiving portion after the initial stop time has elapsed. A screen printing apparatus for controlling the plate separating means so as to start printing. A screen printing method in which a substrate is brought into contact with the lower surface of a mask plate in which pattern holes are formed, and a paste is printed on the substrate through the pattern holes,
A timer setting step for setting an initial stop time in a plate separating operation for separating the substrate from the lower surface of the mask plate based on the viscosity recovery time specific to the paste type as a predetermined timer value; and on the lower surface of the mask plate A mask mounting step for contacting the substrate, a filling step for filling the pattern holes with paste by moving a squeegee on the mounted mask plate, and a plate for separating the substrate from the lower surface of the mask plate A separation step,
In the plate separation step, the substrate is held stationary for the initial dwell time while the substrate is in contact with the lower surface of the mask plate, and after the initial dwell time has elapsed, the substrate is removed from the mask plate. A screen printing method comprising starting separation.

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