JP3591368B2 - Screen printing device and screen printing method - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a cream solder screen printing apparatus and a screen printing method for applying cream solder for soldering electronic components to a printed circuit board.
[0002]
[Prior art]
Prior to surface mounting of electronic components such as ICs, LSIs, capacitor chips, and resistor chips on a printed circuit board, cream solder is applied by a screen printing device to solder the electronic components to electrodes of a circuit pattern on the printed circuit board. .
[0003]
This type of screen printing apparatus generally opens a hole in the screen mask by bringing a printed board close to the lower surface of the screen mask and sliding a squeegee on the screen mask, as shown in, for example, Japanese Patent Application Laid-Open No. 4-65243. The cream solder is applied to a predetermined portion of the printed circuit board through the formed pattern hole.
[0004]
FIG. 9 is a front view of a conventional screen printing apparatus, and shows a state where cream solder is applied to a printed circuit board by the conventional screen printing apparatus. The screen mask 1 is configured by mounting a mask plate 2 on the lower surface of a frame-shaped holder 3. The printed circuit board 4 is held on a table 5. Nuts 6a and 6b are mounted on both sides of the table 5, and vertical feed screws 7a and 7b are screwed into the nuts 6a and 6b. One feed screw 7a is driven by a motor 8 to rotate. Timing pulleys 9a and 9b are mounted on the feed screws 7a and 7b, and a timing belt 10 is adjusted on the timing pulleys 9a and 9b. 11 is a bearing for the feed screw 7b.
[0005]
When the motor 8 is driven, one feed screw 7a rotates, and this rotation is transmitted to the other feed screw 7b via the timing pulleys 9a and 9b and the timing belt 10, and the two feed screws 7a and 7b rotate simultaneously. , Table 5 and printed circuit board 4 move up and down with respect to mask plate 2. Reference numeral 12 denotes a squeegee that slides on the mask plate 2, and reference numeral 13 denotes cream solder applied to the printed circuit board 4.
[0006]
Next, the operation will be described. The motor 8 is rotated forward to raise the printed circuit board 4, and the upper surface of the printed circuit board 4 is brought into contact with the lower surface of the mask plate 2. Next, when the squeegee 12 is slid to the left on the mask plate 2 by a driving means (not shown), the cream solder 13 is applied to the upper surface of the printed circuit board 4 through the pattern holes (not shown) opened in the mask plate 2. You. Next, by reversely rotating the motor 8, the printed circuit board 4 is lowered and separated from the mask plate 2, and the application process of the cream solder 13 is completed.
[0007]
[Problems to be solved by the invention]
Conventionally, when the cream solder 13 is applied as described above, a slight gap (generally called “snap-off”) is secured between the mask plate 2 and the upper surface of the printed circuit board 4. However, as the pitch of the leads of the electronic components becomes narrower, the snap-off becomes gradually smaller. In recent years, the snap-off has become zero, and the upper surface of the printed circuit board 4 is brought into contact with the lower surface of the mask plate 2. The application of the cream solder 13 is performed.
[0008]
However, when the upper surface of the printed circuit board 4 is brought into contact with the lower surface of the mask plate 2 to apply the cream solder 13 as described above, when the printed circuit board 4 is lowered and separated from the mask plate 2, There is a problem that the applied cream solder 13 is easily deformed. Next, the reason why the shape collapse occurs will be described with reference to FIG. FIGS. 10A to 10C are explanatory views of the operation of the conventional screen printing apparatus.
[0009]
FIG. 10A shows a state immediately after the application of the cream solder after the slide of the squeegee 12 is completed. The pattern holes of the mask plate 2 are filled with cream solder 13 by sliding the squeegee 12, and the lower surface of the mask plate 2 is adhered to the upper surface of the printed circuit board 4 due to its adhesive strength. Next, when the motor 8 is rotated in the reverse direction to lower the printed circuit board 4, the mask plate 2 is gradually bent downward by its own elasticity because the mask plate 2 is adhered to the printed circuit board 4 by the adhesive force of the cream solder 13 (FIG. 10). (B)). When the printed circuit board 4 is further lowered, the mask plate 2 is peeled off from the printed circuit board 4 at a stretch as shown in FIG. 10C, and returns to a horizontal state shown by the solid line in FIG. Incidentally, the mask plate 2 is formed of a flexible thin metal plate having a spring property such as a stainless steel plate.
[0010]
When the printed circuit board 4 is lowered to separate the printed circuit board 4 from the mask plate 2 as described above, the mask plate 2 is separated from the printed circuit board 4 at a stretch by its own elasticity when the printed circuit board 4 is lowered to some extent. The cream solder 13 in the pattern hole is disturbed by the impact at that time, or the cream solder 13 on the printed circuit board 4 is deformed because the cream solder 13 is left in the pattern hole.
[0011]
FIG. 11 is an exemplary view of cream solder applied by a conventional screen printing apparatus. In FIG. 11, the cream solder 13b on the left is a non-defective product, and the cream solder 13c on the right is a defective product that has been deformed for the above-described reason. In this example, the edge portion thereof unnecessarily protrudes upward. Depending on the cream solder 13c that has been deformed in this way, it is difficult to correctly solder the leads of the electronic component. Such deterioration of the printing-out property is remarkable when the cream solder 13 is applied at a fine pitch by the fine-pitch pattern holes, and particularly when the electronic component having the narrow pitch leads is surface-mounted on the printed circuit board 4. It becomes a problem.
[0012]
In the above-described conventional example, a screen printing apparatus that raises and lowers the printed board 4 with respect to the screen mask 1 has been described as an example. A similar problem arises.
[0013]
Therefore, an object of the present invention is to provide a screen printing apparatus and a screen printing method for cream solder that can prevent the shape of the cream solder from being lost when the printed board and the mask plate are separated.
[0014]
[Means for Solving the Problems]
2. The screen printing device according to claim 1, wherein the mask plate has a pattern hole formed therein, a substrate support for holding a printed circuit board, and the substrate support for moving an upper surface of the printed circuit board toward and away from a lower surface of the mask plate. Elevating means comprising a motor and a feed screw for elevating and lowering the portion relative to the mask plate, and moving on the mask plate while the upper surface of the printed circuit board is in contact with the lower surface of the mask plate. A squeegee for filling the pattern holes with cream solder on a mask, and after filling the pattern holes with cream solder, when separating the printed board and the mask plate, the separation speed starts at V = 0 and V = 0. The speed pattern in which the operation pattern in which the intermediate value is a positive value V2 and the operation pattern in which the intermediate value is a negative value V3 is repeated a plurality of times. To perform separation based on the emissions, and an intermediate value of the first operation pattern including a control unit for controlling the elevating means to be larger than the intermediate value of the operation pattern of the second subsequent.
[0015]
The screen printing method according to claim 2, wherein a printed circuit board is brought into contact with a lower surface of a mask plate in which a pattern hole is opened, and the mask plate and the printed circuit board are separated after filling the pattern hole with cream solder. A screen printing method for printing cream solder on a printed circuit board, wherein the separation speed starts at V = 0 and ends at V = 0, and the operation pattern has an intermediate value of a positive value V2 and a negative value V3. When the substrate and the mask plate are separated, the printed circuit board is moved up and down relative to the mask plate by elevating means including a motor and a feed screw, so that the separation speed starts at V = 0 and ends at V = 0, and the intermediate speed. A motion pattern having a positive value V2 and a motion pattern having a negative value V3 are separated based on a speed pattern that is repeated a plurality of times. To perform, and an intermediate value of the first operation pattern so as to be larger than the intermediate value of the second subsequent operation pattern.
[0016]
According to the above configuration, the printed board and the mask plate are gradually separated while repeating the movement and the stop a plurality of times. In this process, the shift speed is repeatedly generated between the solder particles of the cream solder in contact with the inner wall surface of the pattern hole of the mask plate, and the viscosity of the cream solder in this portion decreases. Thereby, the adhesive force of the cream solder to the inner wall surface of the pattern hole is also weakened, and the cream solder easily comes off from the pattern hole. Therefore, it is possible to prevent the shape of the cream solder from being lost when the plate is removed.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, an embodiment of the present invention will be described with reference to the drawings. Note that the same components as those in FIGS. 8 to 10 showing the conventional screen printing apparatus are denoted by the same reference numerals and description thereof will be omitted. FIG. 1 is a perspective view of a screen printing apparatus according to an embodiment of the present invention.
[0018]
In FIG. 1, reference numeral 14 denotes a base, and reference numeral 20 denotes a board positioning unit provided on the base 14 for positioning the printed board 4. The substrate positioning unit 20 will be described later in detail with reference to FIG. Reference numeral 70 denotes a mask holding unit for holding a screen mask in a magazine (not shown). In the mask holding portion 70, 71 and 72 are mask guides supported by a column 73 erected on the base 14 so as to bathe in the Y direction and face each other. The feed screw 75 extends in the direction of rotation and is rotatably supported by a motor 71a. The feed screw 75 is provided with a feed nut 76 integrally connected to a support plate 77 for supporting the two squeegees 12 in a vertically movable manner. It is screwed. The support plate 77 is slidably mounted on the upper surfaces of the mask guides 71 and 72 in the Y direction. Therefore, when one of the cylinders 78 is driven to lower one of the squeegees 12 and the motor 71a is driven, the squeegee 12 can be slid on the mask plate 2 in the direction of the arrow M1 or the direction of the arrow M2.
[0019]
Next, the substrate positioning unit 20 will be described with reference to FIG. FIG. 2 is a front view of a substrate positioning unit of the screen printing apparatus according to one embodiment of the present invention. 2, reference numeral 21 denotes an X table mounted on the base 14 as shown in FIG. 1 and driven by an X motor 22, and reference numeral 23 denotes a Y table mounted on the X table 21 and driven by a Y motor 24. It is a table. Reference numeral 25 denotes a first feed screw rotatably supported by a plate 23a mounted on the Y table 23, and reference numeral 26 denotes a second feed screw which is similarly supported and has the same screw portion as the first feed screw 25. Of the feed screw. A timing pulley 27 and a timing pulley 28 are respectively mounted on the lower portions of the first feed screw 25 and the second feed screw 26, and a timing belt 29 is tuned to the timing pulley 27 and the timing pulley 28. A feed nut 30 rotatably supported by the first lift plate 31 so as to be unable to move up and down is screwed to the upper portions of the first feed screw 25 and the second feed screw 26. Further, the rotational force of the first Z motor 32 fixed to the lower surface of the plate 23 a is transmitted to the first feed screw 25 via a gear train 33. Accordingly, when the first Z motor 32 is driven, the first feed screw 25 and the second feed screw 26 can be rotated via the gear train 33, the timing pulley 27, the timing belt 29, and the timing pulley 28. Thus, the first lifting plate 31 moves up and down in the direction of the arrow N1.
[0020]
An elevating guide 34 and an elevating guide 35 are erected on the first elevating plate 31. A first block 36 is fixed above the elevating guide 34, and a second block is installed above the elevating guide 35. 37 is fixed. A clamper 38 slidable in the direction of arrow N3 is provided above the first block 36. The upper surface of the clamper 38 and the upper surface of the second block 37 have a function as a lower receiving portion of the mask plate 2 and are at the same level. Further, a slide cylinder 39 is fixed to the left side of the first block 36 in FIG. 2 so that the rod 40 faces leftward in FIG. 2, and the left end of the rod 40 is connected to a clamper 38 via a connecting rod 41. 2 is connected to the left part of FIG. Therefore, when the slide cylinder 39 is driven to cause the rod 40 to protrude and retract, the clamper 38 can be moved in the direction of the arrow N3, whereby the printed circuit board 4 existing between the clamper 38 and the second block 37 can be moved. Can be clamped so as to freely contact and separate. That is, the clamper 38 and the second block 37 correspond to the clamping means. A conveyor 42 and a conveyor 43 for transporting the printed circuit board 4 in a direction perpendicular to the paper surface of FIG. 2 are provided at portions facing the first block 36 and the second block 37.
[0021]
A second elevating plate 44 is guided by the elevating guide 34 and the elevating guide 35 via bearings 45 so as to be able to move up and down in the direction of arrow N2. A feed nut 46 is rotatably supported by the first elevating plate 31. ing. A second Z motor 47 for rotating a feed nut 46 is fixed to a lower portion of the first lift plate 31 via a gear train 48, and the upper portion of the feed nut 46 is supported by a bearing 50 by a second lift plate. A third feed screw 49 which is rotatably supported by the shaft 44 is screwed. Further, a suction block 51 provided with a suction pipe 52 for suctioning the lower surface of the printed circuit board 4 is fixed to a position directly below the printed circuit board 4 on the upper surface of the second elevating plate 44. Therefore, when the second Z motor 47 is driven, the feed nut 46 and the third feed screw 49 can be rotated via the gear train 48, thereby moving the second lifting plate 44 and the suction block 51 to the second position. The first lifting plate 31 can be moved up and down in the direction of arrow N2.
[0022]
As described above, in the present embodiment, the suction block 51 corresponds to the board supporting unit that holds the printed board 4. The first Z motor 32, gear train 33, timing pulley 27, timing belt 29, timing pulley 28, first feed screw 25, second feed screw 26, second Z motor 47, gear train 48, The third feed screw 49 and the feed nut 46 correspond to elevating means for elevating the height of the upper surface of the printed circuit board 4 held by the suction block 51 as a substrate support relative to the mask plate 2. In this embodiment, the mask plate 2 is immovable and the printed board 4 is moved up and down by the elevating means. However, the printed board 4 may be immovable and the mask plate 2 is moved up and down by the elevating means. include.
[0023]
In FIG. 2, reference numeral 60 denotes a Vt diagram in which the separation speed between the printed circuit board 4 and the mask plate 2 is V, and the time is t. And a speed pattern storage unit such as a RAM (random access memory) for storing a speed pattern (to be described in detail later) composed of a combination of a plurality of operation patterns ending with V = 0. In addition to the trapezoidal pattern used in this embodiment, a triangular pattern having an intermediate value starting with V = 0 and not V = 0 and ending with V = 0 may be employed as this operation pattern. Reference numerals 61 and 62 denote driving units each including a driver for driving the first Z motor 32 and the second Z motor 47, and reference numeral 63 denotes a speed pattern storage unit 60 to output commands to the driving units 61 and 62. Thus, the control unit is a control unit such as a CPU (central processing unit) that controls the first Z motor 32 and the second Z motor 47.
[0024]
FIG. 3 shows a first example of the speed pattern. In this example, the same operation pattern P1 is repeatedly performed continuously. The first operation pattern P1 is a trapezoidal pattern in which the separation speed V starts at V = 0, has an intermediate value of V = V1 from time t1 to t2, and becomes V = 0 at time t3. In one operation pattern, the mask plate 2 and the printed circuit board 4 are set so as to be separated from each other by about several tens to several hundreds of microns.
[0025]
One embodiment of the screen printing apparatus according to the present invention has the above-described configuration. Next, the operation thereof will be described with reference to FIGS. 2, 7, and 8A to 8E.
[0026]
First, when the printed board 4 is conveyed above the suction block 51 by the conveyors 42 and 43, the second Z motor 47 is driven to raise the suction block 51, and the printed board 4 is sucked by the suction pipe 52. While holding, the upper surface is raised to a height that matches the height of the upper surface of the second block 37 and the upper surface of the clamper 38. Next, the X motor 22 and the Y motor 24 are driven to position the printed circuit board 4 on the mask plate 2, and the first Z motor 32 is driven to bring the upper surface of the printed circuit board 4 into contact with the lower surface of the mask plate 2. Thereafter, as shown in FIG. 8, the squeegee 12 is moved on the upper surface of the mask plate 2 so that the cream solder 13 on the mask plate 2 is filled in the pattern holes 2a.
[0027]
When the filling of the cream solder 13 into all the pattern holes 2a of the mask plate 2 is completed, the control unit 63 reads the speed pattern (see FIG. 3) stored in the speed pattern storage unit 60, and reads the speed pattern via the drive unit 61. The first Z motor 32 is driven to separate the printed circuit board 4 from the lower surface of the mask plate 2. FIG. 8B shows the state at this time. The cream solder 13 is made by mixing solder particles having a particle size of about several tens of microns with a flux. Therefore, when the printed circuit board 4 is lowered with the speed pattern shown in FIG. 3, a relative shift (shear) between solder particles near the inner wall surface of the pattern hole 2a, that is, a shift speed v (or a shear speed v) occurs. I do.
[0028]
FIG. 7 is a characteristic diagram showing the relationship between the rubbing speed v generated in the cream solder and the viscosity η. It is known that the viscosity η of the cream solder 13 decreases when kneading causes a shift speed between the solder particles, and it is also known that the viscosity once reduced does not recover after a certain period of time. Have been. Although such a property is called thixotropic property, as described above, when the printed circuit board 4 is intermittently lowered, the displacement speed v occurs in the cream solder 13a near the pattern hole 2a, and the viscosity η decreases. More specifically, referring to FIG. 7, assuming that the viscosity η of the cream solder 13 immediately after filling the pattern hole 2a is η1, a shift speed v occurs in the cream solder 13a near the inner wall surface in the first operation pattern P1. , The viscosity decreases along the curve m1 to become η2. When the printed circuit board 4 stops, the viscosity increases to η3, but immediately after the shift speed v due to the next operation pattern P1, the viscosity decreases along the curve m2 and changes from η4 to η6. In the conventional method, the printed board 4 was lowered at once without stopping, so that the effective displacement speed v did not occur in the cream solder 13a near the inner wall surface of the pattern hole 2a and the viscosity of the cream solder 13 did not decrease. Printing failure had occurred.
[0029]
FIG. 8C shows a state of the cream solder 13 after the separation is completed. In this method, the viscosity of the cream solder 13 at the center of the pattern hole 2a is not changed, and only the viscosity of the cream solder 13a near the inner wall surface is reduced. The cream solder 13 can be printed in an extremely favorable state without worrying that the shape will be loosened and collapsed.
[0030]
FIG. 4 shows a second example of the speed pattern. In this example, the operation pattern P2 whose intermediate value is a positive value V2 and the operation pattern P3 whose intermediate value is a negative value V3 are alternately repeated. In this case, in addition to the effects described in the first example, the printed board 4 is moved not only downward but also upward, so that the viscosity η can be further promoted to be reduced, and the removability of the cream solder 13 can be improved. it can.
[0031]
FIG. 5 shows a third example of the speed pattern. As shown in FIG. 5, in this example, the intermediate value of the first minute operation pattern P4 is larger than the intermediate value of the second and subsequent operation patterns P5, P6, P7,. Like that. In this way, immediately after the driving of the lifting / lowering means is started, that is, while the viscosity η of the cream solder 13 is large, the speed V is greatly changed and the cream solder 13 is impacted to some extent, so that the viscosity η can be reduced at once. It is suitable. In the third example, the moving distance in each of the minute operation patterns P4 to P8 is made constant, and the intermediate value of the second and subsequent minute operation patterns P5 to P8 is gradually increased.
[0032]
FIG. 6 shows a fourth example of the speed pattern. In this example, an operation pattern having a negative intermediate value is added to the third example.
[0033]
【The invention's effect】
According to the screen printing apparatus and the screen printing method of the present invention, the separation speed is set to zero a plurality of times in the process of separating the mask plate and the printed circuit board, so that the cream solder near the inner wall surface of the pattern hole of the mask plate is concentrated. Since the viscosity is reduced by applying the slippage speed, the solder removal property of the cream solder is improved, and the cream solder without shape collapse can be printed on the printed circuit board.
[Brief description of the drawings]
FIG. 1 is a perspective view of a screen printing apparatus according to one embodiment of the present invention; FIG. 2 is a front view of a substrate positioning unit of the screen printing apparatus according to one embodiment of the present invention; FIG. FIG. 4 is an exemplary diagram of a speed pattern according to an embodiment of the present invention. FIG. 5 is an exemplary diagram of a speed pattern according to an embodiment of the present invention. FIG. 6 is an embodiment of the present invention. FIG. 7 is a graph showing a viscosity characteristic of cream solder according to an embodiment of the present invention. FIG. 8 is a diagram illustrating a separating operation of a mask plate and a printed circuit board according to an embodiment of the present invention. FIG. 9 is a front view of a conventional screen printing apparatus. FIG. 10A is an operation explanatory view of a conventional screen printing apparatus. FIG. 9B is an operational explanatory view of a conventional screen printing apparatus. Operation Figure 11 is a illustration of cream was applied solder by conventional screen printing apparatus over screen printing apparatus [Description of symbols]
2 Mask plate 2a Pattern hole 3 Holder 4 Printed circuit board 12 Squeegee 32 First Z motor 47 Second Z motor 51 Suction block 60 Speed pattern storage unit 63 Control unit

Claims (2)

A mask plate having a pattern hole formed therein, a substrate supporting portion for holding a printed circuit board, and the substrate supporting portion relative to the mask plate for moving an upper surface of the printed circuit board toward and away from a lower surface of the mask plate. Elevating means comprising a motor and a feed screw for elevating and lowering, and moving the cream solder on the mask into the pattern holes by moving on the mask plate while the upper surface of the printed board is in contact with the lower surface of the mask plate. After filling the squeegee to be filled and the cream solder into the pattern hole, when separating the printed board and the mask plate, the separation speed starts at V = 0 and ends at V = 0, and the intermediate value is a positive value V2. and an operation pattern is an operation pattern and a negative value V3 is based on the speed pattern repeated several times to effect the separation, and Screen printing apparatus, wherein an intermediate value of the first operation pattern including a control unit for controlling the elevating means to be larger than the intermediate value of the operation pattern of the second subsequent. Screen printing for printing a cream solder on the printed circuit board by bringing a printed circuit board into contact with the lower surface of the mask plate having the pattern holes formed therein, filling the pattern holes with the cream solder, and then separating the mask plate and the printed circuit board. When the printed board and the mask plate are separated, the printed board is moved up and down relative to the mask plate by elevating means comprising a motor and a feed screw. = 0, and the separation is performed based on a speed pattern in which an operation pattern whose intermediate value is a positive value V2 and an operation pattern whose value is a negative value V3 are repeated a plurality of times. screen printing, characterized by greater than an intermediate value intermediate value of the second subsequent operation pattern Law.

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