JP2004268475A - Stencil printing method and its apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a stencil printing method which can always and stably carry out printing by preventing occurrence of printing defects such as misregistration, printing blur, oozing or missing irrespective of change and the like of an time interval for printing, and to provide its apparatus. <P>SOLUTION: A process for coating solder paste 32 on an upper surface of the stencil 2 by moving one side squeegee 4 along the upper surface of the stencil 2 while a circuit printed wiring board 1 and the stencil 2 are positioned in a specific relative position to be kept in a mutually opposed positioning state by keeping a specific space between a tip part 4a of one side squeegee 4 and an upper surface of the stencil 2; and a process for filling the solder paste 32 in a pattern opening part 33 of the stencil 2 by moving the other squeegee 7 along the upper surface of the stencil 2 while a printing pressure is added to the other squeegee 7 on the upper surface of the stencil 2, are provided. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method and an apparatus for stencil printing a solder paste for soldering an electronic component to a circuit board on a circuit board.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, most of solder paste for soldering electronic components to a circuit board is printed on a land of a circuit pattern of the circuit board by stencil printing. In this case, the solder paste is required to be printed in a good finished state in which bleeding, rubbing or chipping does not occur. There are many types of solder pastes, and these solder pastes have different characteristics such as physical properties such as viscosity and thixotropy and storage properties. In particular, in recent years, as solder pastes have become lead-free, not only diversification of metal components but also diversification of flux components have progressed, and as a result, the types of solder pastes have increased significantly. For this reason, the manner in which the solder paste changes in response to environmental changes such as temperature and humidity has also been diversified. Therefore, the operator of the printing apparatus needs to move the squeegee at the time of printing, the printing pressure when pressing the squeegee against the stencil, and separate the printed circuit board from the stencil in order to maintain a good finish state of the solder paste printing. The production is performed while adjusting the speed at which the plate is released.
[0003]
As a general specific adjustment operation performed by the operator, the printing pressure of the squeegee is reduced when bleeding tends to occur in printing, and the printing pressure is increased when blurring tends to occur. Further, when the print pattern is complicated and exists from a large print pattern to a small print pattern, the squeegee moving speed is reduced and the plate separation speed is reduced. When bleeding occurs in printing, it is general to clean the lower surface of the stencil.
[0004]
Conventionally, the operator has to set the print parameters by repeating test printing many times while changing the print parameters such as the squeegee moving speed, the plate release speed, and the printing pressure in various ways, which requires a long time and labor. In addition, there is a problem that a large amount of material is wasted. Therefore, in recent years, a screen printing method of cream solder capable of automatically setting print parameters has been proposed (for example, see Patent Document 1). This screen printing method will be described below with reference to the drawings.
[0005]
FIG. 6 shows a schematic configuration of a printing apparatus embodying the above-described screen printing method. In FIG. 6, a pattern opening (not shown) corresponding to a printing pattern to be printed on the circuit board 1 is formed. The stencil 2 is held by a stencil holder 3 generally called a screen frame. The pair of left and right squeegees 4 and 7 are attached to the rods 10 and 11 of the cylinders 8 and 9, respectively, and come into and out of contact with the upper surface of the stencil 2 as the rods 10 and 11 move up and down. The nut 12 to which the cylinders 8 and 9 are connected is screwed to a feed screw 13 rotatably supported by a screw holder 14 in a horizontal arrangement. The feed screw 13 is rotated by a drive motor 17. Accordingly, the pair of left and right squeegees 4 and 7 move in the horizontal direction while maintaining a state in contact with the upper surface of the stencil 2 as the nut 12 is moved along the feed screw 13 by the forward and reverse rotations of the drive motor 17. Is to be moved to.
[0006]
The movable table unit 18 for positioning the circuit board 1 at a predetermined position includes an X-axis table 19 for moving the circuit board 1 in the X direction, a Y-axis table 20 for moving the circuit board 1 in the Y direction, and a circuit. A configuration in which an elevating table 21 for vertically displacing the substrate 1 is arranged in a stacking order from below, and a substrate holder 22 for holding the circuit board 1 is provided on the upper surface of the elevating table 21. It has become. The board holder 22 has a function of holding and rotating the circuit board 1.
[0007]
The X-axis table 19 receives the transmission of the rotational force of the X-axis motor 23 and moves the substrate holder 22 in the X direction. The Y-axis table 20 receives the rotational force of the Y-axis motor 24 and moves the substrate holder 22 in the Y direction. The lifting table 21 receives the rotational force of the Z-axis motor 27 and displaces the substrate holder 22 in the vertical direction. The substrate holder 22 is rotated in a horizontal plane by receiving the rotation force of the rotation motor 28, so that the circuit pattern of the circuit board 1 held by the substrate holder 22 is moved to the pattern opening of the stencil 2 located above. Adjusted to match. Further, the circuit board 1 is transported by the carry-in conveyor 29 and is placed and held on the board holder 22. At this time, the circuit board 1 is positioned on the board holder 22 based on the image captured by the recognition camera 31. On the other hand, the solder paste 32 for printing is placed on the upper surface of the stencil 2. The printed circuit board 1 is taken out of the board holder 22 and carried out by the carry-out conveyor 30.
[0008]
A printing operation on the circuit board 1 by the printing apparatus will be described. When the circuit board 1 is carried in by the carry-in conveyor 29 and placed on the board holder 22, the recognition camera 31 images and detects a recognition mark (not shown) on the upper surface of the circuit board 1, and the detection result is obtained. Then, the relative relationship between the position of the circuit board 1 and the position of the stencil 2 is calculated. The circuit board 1 is moved to a predetermined position below the stencil 2 by controlling the rotation of the X-axis motor 23, the Y-axis motor 24, and the rotation motor 28 based on the calculation result of the positional relationship. Positioned. After that, the circuit board 1 is raised via the board holder 22 by the rotation control of the Z-axis motor 27, and the upper surface of the circuit board 1 is brought into contact with the lower surface of the stencil 2.
[0009]
Next, the rod 10 of one cylinder 8 projects downward, and the squeegee 4 attached to the rod 10 is pressed against the upper surface of the stencil 2 with a predetermined force. The squeegee 4 is moved along the upper surface of the stencil 2 while the feed screw 13 is controlled to rotate by the drive motor 17. Thereby, as shown in FIG. 7A, the solder paste 32 placed on the upper surface of the stencil 2 on the moving direction side of the squeegee 4 fills the pattern opening 33 of the stencil 2 with the squeegee 4.
[0010]
Then, when the squeegee 4 has finished moving on the upper surface of the stencil 2, the circuit board holder 22 holding the circuit board 1 is lowered as shown in FIG. When separated from the stencil 2, the solder paste 32 filled in the pattern opening 33 of the stencil 2 is transferred and printed on the circuit board 1.
[0011]
By the way, the conventional printing condition adjusting method lowers the printing pressure on the stencil 2 of the squeegees 4 and 7 when the printing bleeding tends to occur, and reduces the printing pressure of the squeegees 4 and 7 when the printing bleeding tends to occur. I try to increase the printing pressure. When the printing pattern of the circuit board 1 is large or small and printing stability is required, the plate separation speed when the circuit board 1 is separated from the stencil 2 is adjusted to be slow. This is because when the plate separation speed is reduced, the shearing strain speed of the solder paste 32 can be reduced, so that printing stability can be effectively obtained.
[0012]
[Patent Document 1]
JP-A-2001-219537
[0013]
[Problems to be solved by the invention]
In the above-described printing method, since the occurrence of bleeding or bleeding of the printing is prevented by adjusting the printing pressure, the bleeding of the printing caused by the insufficient filling force of the solder paste 32 into the pattern opening 33 of the stencil 2 is performed. It is possible to effectively prevent the occurrence of print bleeding due to excessively large filling power and the like, or the occurrence of print blurring due to the difference in the removability of the solder paste 32 depending on the size of the print pattern. is there.
[0014]
However, in the above-described printing method, there remains a problem that it is not possible to prevent the displacement of the relative position between the circuit board 1 and the stencil 2 and the occurrence of blurring due to the change of the printing time interval. This will be described below.
[0015]
The solder paste 32 is a mixture of a metal powder made of solder and a liquid composed of a flux and a solvent, and has a thixotropic property in order to improve printability. Therefore, the solder paste 32 has such a property that the viscosity decreases when the shearing force continues to act, and the viscosity increases and increases when the shearing force is left for a long time. Furthermore, since the solder paste 32 contains a solvent, the solvent having a low specific gravity easily floats when left for a long time, and has a property that the surface of the solvent easily dries. Therefore, the solder paste 32 that has been stored for a long time is supplied to the upper surface of the stencil 2 after the solvent is made uniform and the viscosity is reduced before stirring for use in printing. ing.
[0016]
However, when the printing apparatus is stopped for a relatively long time for some reason, the viscosity of the solder paste 32 supplied to the upper surface of the stencil 2 recovers and becomes high, and at the same time, the solder paste 32 comes into contact with air in the solder paste 32. Solvent on the surface of the existing flux evaporates. Particularly in recent years, many factories have air conditioning, and inside such factories, the humidity tends to be low, and the evaporation of the solvent in the solder paste 32 tends to be accelerated. This tendency is even more pronounced in hot countries other than Japan and in regions inside the continent.
[0017]
When the viscosity of the solder paste 32 is increased as described above, it becomes difficult for the solder paste 32 to enter the pattern openings 33 of the stencil 2, and the filling of the solder paste 32 into the pattern openings 33 becomes difficult. Will be enough. In such a case, as shown in FIG. 8A, a cavity 34 in which the solder paste 32 does not exist may be formed in the pattern opening 33 filled with the solder paste 32. If the cavity 34 is formed, the solder paste 32 located above the cavity 34 remains in the pattern opening 33 of the stencil 2 as it is after the plate separating step shown in FIG. On the circuit board 1, a pattern smaller than a predetermined size indicated by a two-dot chain line is printed. When printed in this small size, it is called "printing", and when there is a portion which is not printed locally, it is called "chip", and both are defective printing.
[0018]
Further, when the solder paste 32 remaining in the pattern opening 33 is left as it is without being removed, the viscosity is further increased and the adhesive force to the stencil 2 is also increased. When the next printing step is performed in that state, the solder paste 32 is filled by the movement of the squeegees 4 and 7 into the pattern openings 33 in a state where the solder paste 32 remains. In the solder paste 32, the portion remaining during the previous printing and the portion newly filled by the current printing coexist. Since the solder paste 32 remaining during the previous printing has been left for a long period of time to maintain the same shape, the viscosity is high, and the solder paste 32 filled during the current printing is in a rolling state when the squeegees 4 and 7 are moved. Since the shearing force is generated at that time, the viscosity remains reduced. Therefore, in the plate separation step after the printing step, the high-viscosity portion of the solder paste 32 remains in the pattern opening 33 due to a large force for maintaining the previous state, and only the low-viscosity portion remains on the circuit board. As a result, not only the "scratch" at the time of printing is not corrected, but also the printing proceeds further.
[0019]
On the other hand, even when various printing conditions are properly set, as shown in FIG. 9, a thin film-like film is formed on the upper surface side of the stencil 2 where the solder paste 32 is supplied and on the hole side surface of the pattern opening 33. Flux film 37 may be formed and remain. Since the thickness of the flux film 37 is very small, from several microns to several tens of microns, the surface area per unit volume is very large. If even a small amount of the solvent contained in the flux film 37 evaporates, the Becomes larger.
[0020]
That is, when the flux film 37 is left for a long time after printing, a small amount of the remaining solvent evaporates and the viscosity increases, and at the same time, the adhesiveness increases. For this reason, in the next printing process of the circuit board 1, when the solder paste 32 is filled in the pattern opening 33 of the stencil 2, the solder powder existing near the side surface of the pattern opening 33 is The solder powder is adhered to the flux film 37 on the side surface of the hole, and the adhered solder powder remains as it is on the pattern opening 33 side in the plate separating step, causing print blurring. FIG. 9 shows a state in which the flux film 37 has been generated after printing has been performed properly without any printing failure, and this flux film 37 causes the above-described printing blur in the subsequent printing process. This can cause
[0021]
By the way, once the print flaring has occurred, it is necessary to take measures to increase the filling force of the solder paste 32 into the pattern openings 33 of the stencil 2 in order to return to the original proper printing state. It is known that a method of increasing the printing pressure to perform printing is effective as one of the countermeasures. That is, when the printing pressure is increased, the contact angle 38 of the squeegee 4 with the stencil 2 is reduced by bending the squeegee 4 as shown in FIG. On the other hand, the dynamic pressure generated in the solder paste 32 existing on the moving direction side of the squeegee 4 is increased, and the filling force of the solder paste 32 into the pattern opening 33 is increased. Will be improved.
[0022]
However, as described with reference to FIG. 9, when the thin flux film 37 remains on the upper surface of the stencil 2, when the printing pressure is increased as described above, the tip 4a of the squeegee 4 and the upper surface of the stencil 2 are removed. Are bonded via the thin flux film 37. In this state, when the squeegee 4 is moved along the upper surface of the stencil 2 in the direction of the arrow in FIG. 10, the stencil 2 is pulled by the squeegee 4 with a strong force accompanying the movement of the squeegee 4. In other words, the flux film 37 contained in the solder paste 32 acts as a lubricant between the tip 4a of the squeegee 4 and the upper surface of the stencil 2 when printing at a normal printing pressure. Will function as an adhesive. Therefore, the stencil 2 shifts from the regular relative position positioned with respect to the circuit board 1, causing a serious problem in that the printing by the solder paste 32 on the circuit board 1 shifts.
[0023]
Furthermore, this is because, in the double squeegee system in which one reciprocating squeegee is performed on one circuit board pair 1 using a pair of squeegees 4 and 7 as a measure against flaring during printing, one squeegee 4 is used. In the first squeegee and the second squeegee by the other squeegee 7, the stencil 2 is displaced from the circuit board 1 alternately in the opposite direction. As a result, the stencil 2 is pressed against the solder paste 32 that has been printed first, and printing bleeding occurs.
[0024]
In view of the above, the present invention has been made in view of the above-described conventional problems, and prevents the occurrence of printing defects such as printing displacement, printing blur, blurring or chipping, regardless of changes in printing time intervals, and the like. It is an object of the present invention to provide a stencil printing method and a printing apparatus which can always perform stable printing.
[0025]
[Means for Solving the Problems]
In order to achieve the above object, a stencil printing method according to the present invention provides a method of printing a solder paste at a predetermined position on a circuit board by a double squeegee system in which a pair of squeegees are sequentially moved along an upper surface to which the solder paste is supplied in the stencil. After the circuit board is positioned and held at a predetermined relative position with respect to the lower surface of the stencil, the tip of one of the squeegees is positioned with respect to the upper surface of the stencil. A step of coating the upper surface of the stencil with a solder paste by moving the one squeegee along the upper surface of the stencil while maintaining the positions of the stencils facing each other at a predetermined interval; and While applying a predetermined printing pressure to the other squeegee against the upper surface, the stencil A step of filling the pattern opening of the stencil with the solder paste by moving the solder paste along the upper surface, and a step of relatively separating the circuit board and the stencil so that the solder paste in the pattern opening is filled with the circuit paste. And a step of transferring onto a substrate.
[0026]
In this stencil printing method, the flux film remaining on the stencil in a highly viscous state is reduced in viscosity and adhesive strength by the movement of one of the squeegees due to the solder paste coated on the upper surface of the stencil. As a result, strong adhesive force does not act between the contact portion between the tip of the other squeegee and the upper surface of the stencil, and even when the printing time interval is long, the stencil moves with the movement of the other squeegee. Since the stencil is not pulled, the stencil can maintain a predetermined relative position with respect to the circuit board, and perform accurate printing without displacement. In addition, since the other squeegee is moved in a state where the printing pressure is applied, the solder paste is sufficiently filled in the pattern opening, so that printing by the double squeegee method increases the printing time interval. Even in this case, printing can be performed without causing defects such as blurring and blurring.
[0027]
The first printing step is a printing step in which the step of coating the upper surface of the stencil with the solder paste and the step of filling the solder paste in the pattern openings of the stencil in the above invention are the first printing step, and the step of coating the solder paste is performed. A second printing step of holding the squeegee under a predetermined printing pressure and moving the squeegee along the upper surface of the stencil to directly fill the pattern opening with the solder paste, It is preferable to select the first and second printing steps according to the printing state of the solder paste printed on the circuit board. According to this, even if the time interval for printing greatly changes due to a change in the production situation, the occurrence of printing defects such as blurring and blurring of printing can be prevented by appropriately selecting and using the first and second printing processes. Prevention and good printing can be performed.
[0028]
In the above-described printing method, the amount of deviation of the printing position of the solder paste after printing on the circuit board from a predetermined position is set as a printing state value, and printing of the solder paste is performed based on a comparison between a predetermined printing reference value and the printing state value. The state can be determined, and when a result of the determination that the printing state value exceeds the printing reference value is obtained, the second printing step can be changed to the first printing step. According to this, the solvent contained in the solder paste is of a type that is relatively easy to evaporate, and even if the flux film remaining on the upper surface of the stencil tends to have a high viscosity with the passage of time, the second By changing the printing process from the first printing process to the first printing process, it is possible to prevent the occurrence of printing position shift.
[0029]
Further, in the above printing method, at least one of the length, area, and volume of the solder paste after printing on the circuit board is used as a printing state value, and a predetermined printing reference value and the printing state value are compared. It is also possible to determine the printing state of the solder paste based on the comparison and change the second printing step to the first printing step when a determination result that the printing state value is less than the printing reference value is obtained. . According to this, even if the solder paste used has thixotropy, the printing is changed by changing the second printing step to the first printing step at an appropriate timing according to the printing state of the solder paste. And the occurrence of chipping and chipping can be effectively prevented and good printing can be performed.
[0030]
In each of the above inventions, it is preferable to change from the second printing step to the first printing step when the time interval for printing on the circuit board becomes equal to or longer than a preset time. According to this, the second printing step can be changed to the first printing step at the time when the viscosity of the solder paste having a thixotropic property due to the evaporation of the solvent contained in the flux in the solder paste and the recovery of the viscosity can be changed to the first printing step. In this case, it is possible to effectively prevent the occurrence of the positional deviation and perform good printing.
[0031]
In each of the above inventions, it is preferable to fill the solder paste into the pattern opening of the stencil and hold the filling state until a preset holding time has elapsed, and then relatively separate the circuit board and the stencil. . According to this, even when using a solder paste having poor plate-removing property, after the elapse of the holding time, the viscosity is increased while maintaining the shape filled with the solder paste in the pattern opening, and the shape is reduced. Since the plate is removed while being held, it is possible to effectively prevent the occurrence of printing defects such as print blurring and chipping.
[0032]
In the above printing method, it is preferable that a holding time for holding the pattern opening with the solder paste filled therein is changed according to a printing state of the solder paste on the circuit board. According to this, since the holding time is changed according to the printing state of the solder paste on the circuit board, it is possible to more effectively prevent the occurrence of printing defects such as print blurring and chipping.
[0033]
In the above-described printing method, at least one of the length, area, and volume of the solder paste after being printed on the circuit board is used as a first printing state value, and a predetermined position of the printing position of the solder paste printed on the circuit board is used. Is used as a second printing state value, the two printing state values are compared with individually set printing reference values, and the first and second printing processes are selected based on the comparison result. It is preferable to determine both the pattern retention time and the retention time for keeping the pattern opening filled with the solder paste. According to this, when printing is performed in a factory in a relatively dry atmosphere, even if the solvent of the flux of the solder paste is likely to evaporate, the first and second printing steps are selected and the solder paste is inserted into the pattern opening. Since both the holding time and the holding time for holding the state filled with are set respectively, it is possible to effectively prevent the occurrence of printing failure.
[0034]
In each of the above inventions, the solder paste is printed on a predetermined number of circuit boards at a predetermined printing location, and the printing state of the solder paste on each of the circuit boards is sampled while being inspected by an inspection unit, and the sampled data is obtained. It is preferable to select one of the first and second printing steps based on this. According to this, even if the printing state fluctuates so that the tendency of printing bleeding occurs irregularly, a printing process is selected based on a plurality of sampling data, so that highly reliable printing is performed. Can be.
[0035]
Further, the stencil printing apparatus according to one configuration of the present invention is a pre-printing standby station that can detect whether a circuit board before printing is waiting at a predetermined position, a printing station that prints the circuit board, and a printing station that prints the circuit board. A post-printing standby station that can detect whether the circuit board is waiting at a predetermined position, and a control unit, wherein the control unit is configured such that the circuit board exceeds the preset time set in the post-printing standby station. When it is determined that the stencil is present, at the printing station, after positioning the circuit board carried in from the standby station before printing at a predetermined relative position with respect to the stencil, the tip of the squeegee is positioned on the upper surface of the stencil. By moving along the upper surface of the stencil while holding at opposing relative positions with an interval After coating the solder paste on the upper surface of the stencil, control is performed to select whether to hold this state for a preset holding time or to hold the circuit board in the waiting station after printing until the circuit board is discharged. It is characterized by having a function.
[0036]
This stencil printing apparatus is provided with a configuration capable of appropriately setting a printing process selection and a holding time in a state where the solder paste is coated, so that the stencil printing method of the present invention is faithfully embodied, and the printing method is The same effect as described above can be reliably obtained.
[0037]
A stencil printing apparatus according to another aspect of the present invention includes a pre-printing standby station that can detect whether a circuit board before printing is waiting at a predetermined position, a printing station that prints a circuit board, and a circuit after printing. A post-printing standby station capable of detecting whether or not the board is waiting at a predetermined position; and a control unit, wherein the control unit is provided with a circuit board that is present for more than a predetermined time set in the post-printing standby station. When it is determined that the stencil is in a predetermined position relative to the stencil at the printing station, the squeegee is positioned at a predetermined position relative to the stencil. By moving along the upper surface of the stencil while holding at opposing relative positions with a gap, After coating the upper surface of the stencil with the solder paste, the other squeegee is moved along the upper surface of the stencil while applying a predetermined printing pressure to fill the pattern opening of the stencil with the solder paste. And a control function for selecting whether to hold for a preset holding time or to hold the circuit board of the waiting station after printing until the circuit board is discharged.
[0038]
The stencil printing apparatus of the present invention is also provided with a configuration in which the selection of a printing step and the holding time in a state where the solder paste is filled in the pattern opening after coating the solder paste can be appropriately set. By faithfully embodying the method, it is possible to reliably obtain the same effect as that of the printing method.
[0039]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram showing a printing apparatus embodying a stencil printing method according to a first embodiment of the present invention. 6, the same or corresponding components as those in FIG. 6 are denoted by the same reference numerals, and redundant description will be omitted. This printing apparatus is different from that shown in FIG. 6 in that the cylinders 39 and 40 have a function of adjusting the position including the bottom dead center position of the squeegees 4 and 7 held through the respective rods 10 and 11. In addition, board detection sensors 41 and 42 which detect whether or not the circuit board 1 is present at predetermined positions in the vicinity of each of the carry-in conveyor 29 and the carry-out conveyor 30 are provided in a non-contact manner. By providing each of them, a pre-printing standby station 43 that can wait for the circuit board 1 to be printed and a post-printing standby station 44 that can wait for the printed circuit board 1 are installed. , 40 are provided only with a control section 47 for controlling the entire apparatus including the operation of the apparatus.
[0040]
When the squeegees 4 and 7 move along the upper surface of the stencil 2, the control unit 47 projects the cylinders 39 and 40 by the projection length set by the rods 10 and 11, in addition to the normal printing operation. By controlling the operation as described above, the squeegees 4 and 7 are moved in a state where a space is provided between the squeegees 4 and 7 and the upper surface of the stencil 2 so that the solder paste 32 is coated on the upper surface of the stencil 2. I do. Further, the control unit 47 controls the operation of the cylinders 39 and 40 to arbitrarily change the distance between the tip portions 4a and 7a of the squeegees 4 and 7 with respect to the upper surface of the stencil 2 so as to change the thickness of the coating with the solder paste 32. It controls so that it may adjust arbitrarily.
[0041]
Next, a printing operation of a stencil printing method using the stencil printing apparatus having the above configuration will be described below. When the circuit board 1 is carried in by the carry-in conveyor 29 and placed on the board holder 22, the control unit 47 controls the rotation of the X-axis motor 23 and the Y-axis motor 24 so that two points are moved rightward. The movement of the board holder 22 is controlled so that the circuit board 1 is located directly below the recognition camera 31 as shown by the chain line. Next, when the recognition camera 31 captures an image of a recognition mark (not shown) on the upper surface of the circuit board 1 and detects it, the control unit 47 determines the position of the circuit board 1 and the position of the stencil 2 based on the detection result of the recognition mark. By calculating the relative relationship with the position and controlling the rotation of the X-axis motor 23, the Y-axis motor 24 and the rotation motor 28 based on the calculated relative relationship, the circuit board 1 is positioned below the stencil 2. Is moved to a predetermined position for positioning, and thereafter, the circuit board 1 is raised via the board holder 22 by controlling the rotation of the Z-axis motor 27 so that the upper surface of the circuit board 1 is placed on the lower surface of the stencil 2. Make contact.
[0042]
Subsequently, the control unit 47 operates the one of the cylinders 39 (left side in the figure) so as to protrude the rod 10 downward, so that the one (left side in the figure) squeegee 4 approaches the upper surface of the stencil 2. . At this time, as shown in FIG. 2, the squeegee 4 is positioned such that the tip 4 a faces the upper surface of the stencil 2 at a predetermined interval. After that, the control unit 47 controls the rotation of the drive motor 17 to move the squeegee 4 in the direction of the arrow in FIG. At this time, the squeegee 4 is moved along the upper surface of the stencil 2 while the tip 4a of the squeegee 4 keeps the above-mentioned set interval with respect to the upper surface of the stencil 2. As a result, a part of the solder paste 32 supplied to the upper surface of the stencil 2 is coated on the upper surface of the stencil 2 with a thickness corresponding to the distance between the tip 4a of the squeegee 4 and the upper surface of the stencil 2.
[0043]
At the time of coating the solder paste 32, even if the flux film 37 (same as that described in FIG. 9) generated in the previous printing process remains on the upper surface of the stencil 2, the tip 4a of the squeegee 4 Since the stencil 2 is separated from the upper surface, no large force acts on the stencil 2 by the moving squeegee 4, so that the stencil 2 is not displaced from the circuit board 1. When the solder paste 32 is coated on the upper surface of the stencil 2, the solvent contained in the solder paste 32 naturally diffuses into the flux film 37. Accordingly, the flux film 37 attached to the upper surface of the stencil 2 and the side surface of the hole of the pattern opening 33 in a state where the viscosity is increased and the viscosity is increased due to the evaporation of the solvent is reduced in viscosity and adhesive strength, and the original film is formed. It is restored to the characteristic state.
[0044]
Then, when one squeegee 4 has finished moving on the upper surface of the stencil 2, then the other squeegee 7 is moved in a direction opposite to the moving direction of the one squeegee 4, as shown in FIG. , Double squeezing is performed. In this case, the squeegee 7 is moved while the tip 7a thereof is pressed against the upper surface of the stencil 2 with a predetermined printing pressure as in the conventional case, but the flux film 37 is coated by the solder paste 32 coated on the upper surface of the stencil 2. Since the viscosity and the adhesive strength of the stencil 2 are reduced, the flux film 37 does not exert a strong adhesive force between the contact portion between the tip 7a of the squeegee 7 and the upper surface of the stencil 2. Therefore, even when the printing time interval becomes longer, the stencil 2 is not pulled by the movement of the squeegee 7, so that the stencil 2 maintains a predetermined relative position with respect to the circuit board 1 and is displaced. It is possible to perform accurate printing without any problem.
[0045]
In addition, when the solder paste 32 is coated by moving the one squeegee 4, as shown on the left side of FIG. When the other squeegee 7 is moved while the printing pressure is applied, the solder paste 32 is sufficiently filled in the pattern opening 33 as shown on the right side of FIG. By performing printing using such a double squeegee method, printing can be performed without causing defects such as blurring and blurring even when the printing time interval is long. When the printing by the squeegees 4 and 7 is completed, the board holder 22 holding the circuit board 1 is lowered, and when the circuit board 1 is separated from the stencil 2, the stencil is placed on the circuit board 1. The solder paste 32 filled in the second pattern opening 33 is transferred and printed.
[0046]
FIG. 4 is a schematic configuration diagram showing a printing apparatus embodying the stencil printing method according to the second embodiment of the present invention. In the figure, the same or corresponding elements as those in FIG. 1 are denoted by the same reference numerals, and redundant description will be omitted. This printing apparatus differs from that of FIG. 1 only in the configuration in which an inspection camera 48 for inspecting the printed state of the printed circuit board 1 is added. In this embodiment, the printing is performed in accordance with the inspection result based on the image of the printed state of the circuit board 1 captured by the inspection camera 48, that is, in accordance with the printing status of the solder paste 32 printed on the circuit board 1. Change the method as appropriate. For example, a printing method only by moving a squeegee to which a printing pressure is applied in the same manner as in the related art, and a coating process of the solder paste 32 and moving the squeegee 4 or 7 while applying a printing pressure as in the first embodiment. A printing method that uses the printing step in combination is appropriately used.
[0047]
That is, in the printing method using the double squeegee method as in the first embodiment, since the filling force of the solder paste 32 into the pattern openings 33 of the stencil 2 is strong, the printing process by this printing method is continuously repeated. In such a case, there is a possibility that printing bleeding may occur. Therefore, the printed circuit board 1 is imaged by the inspection camera 48, and the printing state is inspected based on the imaged screen. If the printing bleeding tends to occur, the coating process of the solder paste 32 is omitted. Then, the printing method is executed only by moving the squeegee 4 or 7 to which the printing pressure is applied. On the other hand, as a result of the above-described inspection of the printing state, if the printing tends to be flared, the coating process of the solder paste 32 and the printing pressure are applied to the squeegee 4 or 7 as in the first embodiment. The printing step of moving the sheet in the added state is used together. As a result, even when the time interval for printing greatly changes, it is possible to always perform good printing without printing defects such as blurring and blurring of printing.
[0048]
If the solvent contained in the solder paste 32 to be used is of a type that evaporates relatively easily, the adhesion of the flux film 37 remaining on the upper surface of the stencil 2 increases as the printing time interval increases. Therefore, misregistration of printing is likely to occur. Therefore, based on the image captured by the inspection camera 48, a print state value, which is a shift amount of the print position of the solder paste 32 from a predetermined position, is obtained, and the print state value is compared with a preset print reference value. Now, when only the printing step of moving the squeegee 4 or 7 while applying the printing pressure is performed, and when the printing state value exceeds the printing reference value, the coating step of the solder paste 32 and the squeegee 4 are performed. Alternatively, the printing method is changed to a printing method in which a printing step of moving the printing sheet 7 while applying a printing pressure is used together. For example, when the allowable range of the printing position shift is 0.1 mm, the shift amount of 0.05 mm is set as the printing reference value, and when the printing state value becomes 0.05 mm or more, the coating process of the solder paste 32 is performed. And a printing step of moving the squeegee 4 or 7 while applying a printing pressure.
[0049]
In addition, when the solder paste 32 having a large thixotropic property is used for the purpose of improving the printability, if the time interval of the printing is long, the viscosity of the solder paste 32 is increased, and the printing tends to be flared. Therefore, at least one of the length, area, and volume of the solder paste 32 printed on the circuit board 1 is set as a printing state value, and the printing state value is compared with a preset printing reference value. If the printing state value is less than the printing reference value, the printing method using only the movement of the squeegee 4 or 7 to which the printing pressure has been applied is changed to the coating process of the solder paste 32 and the printing pressure applied to the squeegee 4 or 7. The printing method is changed to a printing method that uses the moving printing step together. As a result, it is possible to perform good printing without printing defects such as print blurring and chipping.
[0050]
A specific method for inspecting the printing state of the solder paste 32 based on dimensions will be described with reference to FIG. FIG. 5A shows a normal printing state, in which the solder paste 32 is finely printed on the land 49 of the circuit pattern on the circuit board 1. As described above, if the solder paste 32 is normally printed, the electrodes of the electronic component can be correctly connected and mounted on the lands 49. The print pattern of the solder paste 32 in the normal printing state is set as a reference dimension, and as shown in FIG. 4B, the case where the print pattern of the solder paste 32 is larger than the reference dimension is set as printing blur. As shown in FIG. 7C, the case where the print pattern of the solder paste 32 is smaller than the reference size is set as print blur. Then, as shown in (b) and (c), the critical dimension is determined for the bleeding and bleeding of the print, respectively. to decide.
[0051]
Then, when it is determined that the printing is flared, when the next circuit board is printed, the coating process of the solder paste 32 and the squeegee 4 Alternatively, the printing method is changed to a printing method in which a printing step of moving the printing sheet 7 while applying a printing pressure is used together. On the other hand, when it is determined that the bleeding of the printing occurs, the printing pressure is applied from the printing method using both the coating process of the solder paste 32 and the printing process of moving the squeegee 4 or 7 while applying the printing pressure. The printing method is changed to a printing method only by moving the squeegee 4 or 7.
[0052]
Next, a stencil printing method according to a third embodiment of the present invention will be described. In a printing apparatus having no inspection camera after printing as shown in FIG. 1, the state of the solder paste 32 after printing on the circuit board 1 cannot be inspected. The time from the end of the printing process to the start of the printing process of the next circuit board 1 is measured. If the time interval of the timed printing is equal to or longer than a predetermined time, the printing method using only the movement of the squeegee 4 or 7 to which the printing pressure is applied is changed to the solder paste 32 coating process and the squeegee 4 or 7. The printing method is changed to a printing method in which a printing step of moving the printing paper while applying a printing pressure to the printing paper is used together.
[0053]
The reason for changing the printing direction as described above is that as the printing time interval becomes longer, the solder paste 32 becomes high due to evaporation of the solvent contained in the flux or recovery of the viscosity of the solder paste 32 showing thixotropic properties, as described above. This is to prevent the viscosity from becoming too high and the misalignment of printing and the occurrence of flaring to occur easily. That is, in this embodiment, the printing time interval is managed and the printing method is changed as appropriate, thereby preventing the occurrence of print displacement and blurring.
[0054]
By the way, in the case where the solder paste 32, which has been reduced recently but does not have good print-out properties, is used, the following printing method is adopted to improve the print-out properties. That is, after filling the solder paste 32 into the pattern opening 33 of the stencil 2, the circuit board 1 is lowered or the stencil 2 is raised after a predetermined holding time has elapsed while maintaining this state. Accordingly, the viscosity of the solder paste 32 is increased by the recovery of the viscosity while maintaining the shape filled in the pattern opening 33, so that when the plate is separated, the plate is removed while maintaining the shape, and printability is improved. Be improved. Further, by appropriately changing the holding time according to the state of the solder paste 32 in the pattern opening 33 captured by the inspection camera 48, it is possible to effectively prevent the occurrence of print blur or chipping. .
[0055]
On the other hand, when printing is performed in a factory in a relatively dry atmosphere, the flux solvent is easily evaporated even when a solder paste 32 having a hardly evaporating solvent and a thixotropic flux is used. . In such a case, if two or more types of printing means are selectively used based on two printing state values, ie, a printing state and a printing position detected based on an image captured by the inspection camera 48, the occurrence of printing failure is effectively reduced. Can be prevented.
[0056]
That is, at least one of the length, area and volume of the solder paste 32 printed on the circuit board 1 detected based on the image captured by the inspection camera 48 is set as a first print state value, 1, the amount of deviation of the printing position of the solder paste 32 after printing from a predetermined position is set as a second printing state value, and based on a comparison result between these two printing state values and each printing reference value, the solder paste 32 (A) a printing step using both the coating step of (1) and a printing step of moving the squeegee (4 or 7) while applying a printing pressure, and (ii) a printing means solely by moving the squeegee 4 or 7 to which the printing pressure is applied; Two items, that is, the length of the holding time for holding the pattern opening 32 as it is filled in the pattern opening 33, are determined. Thereby, the occurrence of printing failure can be effectively prevented.
[0057]
In the printing apparatus including the inspection camera 48 and the control unit 47 shown in FIG. 4, the coating process of the solder paste 32 and the squeegee 4 or 7 are moved in a state where the printing pressure is applied according to the situation of the solder paste 32 after printing. Although it is possible to selectively use a printing unit that uses a printing step to perform the printing process and a printing unit that only moves the squeegee 4 or 7 to which the printing pressure is applied, the printing state may slightly fluctuate. For example, even if the printing bleeding tendency occurs at one time, the printing bleeding may have subsided on the next circuit board 1. In such a case, while printing on the set number of circuit boards 1 at a preset printing place, the printing state is sampled, and the coating process of the solder paste 32 is performed based on the inspection result of the sampled data. The control unit 47 determines whether to use the printing unit that uses the printing step of moving the squeegee 4 or 7 while applying the printing pressure together with the printing unit that uses only the movement of the squeegee 4 or 7 that applies the printing pressure. I do. As a result, a highly reliable inspection can be performed, so that the above-described fluctuation of the printing state can be prevented, and stable printing can always be continued.
[0058]
Further, the printing method of changing the printing means in response to the change of the printing time interval can be faithfully embodied by providing the following configuration in the printing apparatus. That is, as shown in FIGS. 1 and 4, the board detection sensor 41 that detects whether or not the circuit board 1 exists at a predetermined location of the carry-in conveyor 29 is provided. A standby station 43 for pre-printing the circuit board 1 is installed at the same time, and a board detection sensor 42 for detecting whether or not the circuit board 1 is present at a predetermined position of the unloading conveyor 30 is provided. The post-printing standby station 44 of the circuit board 1 is installed at the disposition location, and the substrate holder 22 is used as a printing station. Further, a manufacturing line is provided in which an electronic component mounting machine is connected to a post-process of the printing process by the printing apparatus.
[0059]
When the board detection sensor 42 detects that the circuit board 1 does not exist in the post-printing standby station 44 of the unloading conveyor 30 at the time of normal printing, the controller 47 The substrate 1 is carried into and held by the substrate holder 22, and is controlled to perform printing. Further, when the time during which the board detection sensor 42 detects the circuit board 1 exceeds the set time, the control section 47 sets the circuit board 1 to the post-printing standby station 44 due to something in a post-process. After determining that the circuit board 1 has been stagnating for more than a predetermined time, the upper surface of the stencil 2 on which the circuit board 1 is polymerized in a predetermined positioning state is coated with the solder paste 32 at the printing station. For example, the user selects either to hold for a while, or to hold until the circuit board 1 of the post-printing standby station 44 is carried out. Thereby, the stencil printing method described above can be realized. When this printing method is adopted, even if a trouble occurs in the subsequent electronic component mounting process and the production tact changes suddenly to stop the operation of the printing apparatus without fail, the printing failure may occur. It is possible to appropriately select and adopt an appropriate printing unit that does not cause the printing.
[0060]
【The invention's effect】
As described above, according to the stencil printing method of the present invention, the flux film remaining on the stencil in a high-viscosity state has a viscosity and an adhesion due to the solder paste coated on the upper surface of the stencil by moving one squeegee. Since the force is reduced, a strong adhesive force is not applied between the contact portion between the tip of the other squeegee and the upper surface of the stencil by the flux film, and even when the time interval of printing is long, Since the stencil is not pulled with the movement of the other squeegee, the stencil can maintain a predetermined relative position with respect to the circuit board, and can perform accurate printing without displacement. In addition, since the other squeegee is moved in a state where the printing pressure is applied, the solder paste is sufficiently filled in the pattern opening, so that printing by the double squeegee method increases the printing time interval. Even in this case, printing can be performed without causing defects such as blurring and blurring.
[0061]
In addition, the stencil printing apparatus according to the present invention has a configuration in which the selection of a printing step and the holding time in a state where the solder paste is coated can be appropriately set. The present invention can be embodied to reliably obtain the same effect as that of the printing method.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing a printing apparatus embodying a stencil printing method according to a first embodiment of the present invention.
FIG. 2 is a longitudinal sectional view showing a step of coating a solder paste on an upper surface of a stencil by moving a squeegee in the printing apparatus.
FIG. 3 is a longitudinal sectional view showing a step of filling a solder paste into a pattern opening of a stencil by moving a squeegee in the printing apparatus.
FIG. 4 is a schematic configuration diagram showing a printing apparatus embodying a stencil printing method according to a second embodiment of the present invention.
FIGS. 5A to 5C are explanatory diagrams of various printing patterns by a solder paste on a circuit board.
FIG. 6 is a schematic configuration diagram showing a conventional printing apparatus.
FIGS. 7A and 7B are longitudinal sectional views sequentially showing a printing process using a solder paste on a circuit board.
FIGS. 8A and 8B are longitudinal cross-sectional views sequentially showing a printing process in a case where the printing with the solder paste on the circuit board causes a deficiency in scuffing.
FIG. 9 is a longitudinal sectional view showing a state in which a solder paste is normally printed on a circuit board while a flux film is present on the stencil.
FIG. 10 is a vertical cross-sectional view showing a state of bending of the squeegee when a printing pressure is applied to the squeegee in a printing process.
[Explanation of symbols]
1 circuit board
2 Stencil
22 Substrate holder (printing station)
32 Solder paste
33 pattern opening
43 Standby station before printing
44 Standby station after printing
47 Control section
48 inspection camera

Claims (11)

A stencil printing method of printing solder paste at a predetermined position on a circuit board by a double squeegee method of sequentially moving a pair of squeegees along an upper surface to which a solder paste in a stencil is supplied,
After positioning and holding the circuit board at a predetermined relative position with respect to the lower surface of the stencil, the leading end of one of the squeegees faces the upper surface of the stencil with a predetermined interval therebetween. Moving the one squeegee along the upper surface of the stencil while holding, thereby coating a solder paste on the upper surface of the stencil;
Filling the solder paste into the pattern openings of the stencil by moving the stencil along the upper surface of the stencil while applying a predetermined printing pressure to the other squeegee against the upper surface of the stencil;
Transferring the solder paste in the pattern opening onto the circuit board by relatively separating the circuit board and the stencil. A step of coating the solder paste on the upper surface of the stencil according to claim 1, wherein the step of coating the upper surface of the stencil with the step of filling the pattern opening of the stencil with the solder paste is a first printing step. A second printing step of holding the squeegee at a predetermined printing pressure and moving the squeegee along the upper surface of the stencil to directly fill the pattern opening with the solder paste without passing through. 2. The stencil printing method according to claim 1, wherein the first and second printing steps are selected according to a printing state of the solder paste printed on the circuit board. The amount of deviation of the printing position of the solder paste after printing on the circuit board from a predetermined position is used as a printing state value, and the printing state of the solder paste is determined based on a comparison between a printing reference value set in advance and the printing state value, 3. The stencil printing method according to claim 2, wherein a change from the second printing step to the first printing step is performed when a determination result that the printing state value exceeds the printing reference value is obtained. At least one of the length, area, and volume of the solder paste after printing on the circuit board is used as a print state value, and the print state of the solder paste is determined based on a comparison between a preset print reference value and the print state value. 3. The stencil printing according to claim 2, wherein when the determination result is that the printing state value is less than the printing reference value, the second printing process is changed to the first printing process. Method. The stencil printing according to any one of claims 2 to 4, wherein the second printing step is changed to the first printing step when the time interval for printing on the circuit board is equal to or longer than a preset time. Method. 6. The pattern opening of the stencil is filled with solder paste, and the state of filling is maintained until a predetermined holding time has elapsed, and then the circuit board and the stencil are relatively separated from each other. The stencil printing method according to any one of the above. 7. The stencil printing method according to claim 6, wherein a holding time for holding the pattern opening with the solder paste filled therein is varied according to a printing state of the solder paste on the circuit board. At least one of the length, area, and volume of the solder paste printed on the circuit board is used as a first printing state value, and the amount of deviation of the printing position of the solder paste printed on the circuit board from a predetermined position is defined as a second printing state value. These two print state values are compared with individually set print reference values. Based on the comparison result, selection of the first and second printing steps and selection of the pattern opening are performed. The stencil printing method according to claim 7, wherein both the holding time for holding the solder paste in a filled state and the holding time are determined. While printing the solder paste on a predetermined number of circuit boards at a predetermined printing place, the printing state of the solder paste on each of the circuit boards is sampled while being inspected by inspection means, and the first and the second are determined based on the sampling data. 9. A stencil printing method according to claim 2, wherein one of the second printing steps is selected. A pre-print standby station that can detect whether the circuit board before printing is waiting at a predetermined position,
A printing station for printing circuit boards;
A post-print standby station that can detect whether the printed circuit board is waiting at a predetermined position,
With a control section,
The control unit, when determining that the circuit board is present in the post-printing standby station for more than a preset time, at the printing station, stencils the circuit board loaded from the pre-printing standby station. After being positioned at a predetermined relative position with respect to the stencil, by moving the squeegee along the upper surface of the stencil while holding the squeegee at a relative position opposing the upper surface of the stencil at an interval to the upper surface of the stencil, After coating the solder paste on the upper surface of the stencil, control is performed to select whether to hold this state for a preset holding time or to hold the circuit board in the waiting station after printing until the circuit board is discharged. A stencil printing device characterized by having a function. A pre-print standby station that can detect whether the circuit board before printing is waiting at a predetermined position,
A printing station for printing circuit boards;
A post-print standby station that can detect whether the printed circuit board is waiting at a predetermined position,
With a control section,
The control unit, when it is determined that the circuit board is present in the post-printing standby station for more than a preset time, when the printing station, at the printing station, stencils the circuit board loaded from the pre-printing standby station. After being positioned at a predetermined relative position with respect to the stencil, by moving the squeegee along the upper surface of the stencil while holding the squeegee at a relative position opposing the upper surface of the stencil at an interval to the upper surface of the stencil, After the solder paste is coated on the upper surface of the stencil, the other squeegee is moved along the upper surface of the stencil while applying a predetermined printing pressure to fill the pattern opening of the stencil with the solder paste. Is held for a preset holding time, or the standby mode after printing is performed. Stencil printing device in which a circuit board Shon is characterized in that it is configured to have a control function for selection of hold up is discharged.

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