JP7599134B2 - Solder paste printing system and solder paste printing method - Google Patents

Description

The present disclosure relates to a solder paste printing system and a solder paste printing method for printing solder paste onto a substrate.

In the printing machine, the underside of a screen mask with openings is brought into contact with the substrate. Next, a squeegee moves over the screen mask, and solder paste containing solder particles and flux is forced into the openings, transferring the solder paste to the substrate. The substrate on which the solder paste has been printed is photographed by a camera. The photographed result is used to detect the presence or absence of printing defects. Printing defects include a state in which the transferred solder paste is connected to adjacent solder paste (solder bridge) and a state in which solder paste is missing from a required position (see, for example, Patent Document 1).

In the detection method described in Patent Document 1, a solder paste (cream solder) that is colored to increase the contrast with the board is used, and a camera photographs the board on which the solder paste is printed. The presence or absence of printing defects is then inspected from the shape of the solder paste photographed. If a printing defect is detected, the screen mask is cleaned.

Japanese Patent Application Publication No. 5-123892

The solder paste printing system disclosed herein includes a printer that prints a solder paste containing solder particles and flux onto a substrate, a detection unit that detects the solder particles and the flux in the solder paste printed on the substrate, and a flux state determination unit that determines whether a state of the flux is good or bad based on a detection result by the detection unit, and if the flux state determination unit determines that the state of the flux is bad, the printer performs an operation to change the state of the flux in the solder paste before the solder paste is printed onto an unprinted substrate, and the detection unit includes a camera that photographs the solder paste printed on the substrate, a first illumination unit that irradiates the substrate with a first illumination light, and a second illumination unit that irradiates the substrate with a second illumination light that is tilted more toward the substrate than the first illumination light, and detects the solder particles based on a first image captured by the camera while irradiating the first illumination light, and detects the flux based on a second image captured by the camera while irradiating the second illumination light .

The solder paste printing method disclosed herein includes the steps of printing a solder paste containing solder particles and flux onto a substrate; detecting the solder particles and the flux in the solder paste printed on the substrate to obtain a detection result; determining whether the state of the flux is good or bad based on the detection result; and, if the state of the flux is determined to be bad, performing an operation to change the state of the flux in the solder paste before the solder paste is printed on an unprinted substrate. In the step of obtaining the detection result, the solder particles are detected based on a first image taken by a camera while irradiating the substrate on which the solder paste has been printed with a first illumination light, and the flux is detected based on a second image taken by the camera while irradiating the substrate with a second illumination light that is tilted more inclined relative to the substrate than the first illumination light .

According to the present disclosure, printing defects can be prevented in advance.

FIG. 1 is a schematic configuration diagram of a screen printing system according to an embodiment of the present disclosure. FIG. 2 is a configuration diagram of a printing machine in the screen printing system shown in FIG. 1. FIG. 3 is a cross-sectional view showing a process of printing solder paste by the printer shown in FIG. FIG. 3B is a cross-sectional view showing a step of printing solder paste, subsequent to FIG. 3A . FIG. 3C is a cross-sectional view showing a step of printing solder paste, subsequent to FIG. A configuration diagram of a printed solder inspection device in the screen printing system shown in FIG. FIG. 5 is a diagram showing an example of an image captured by an inspection camera when a board on which solder paste has been printed is irradiated by a first irradiation unit of the printed solder inspection device shown in FIG. FIG. 5B is a diagram showing an example of an image taken by an inspection camera when the substrate shown in FIG. 5A is irradiated by the second irradiation unit of the printed solder inspection device shown in FIG. 4. FIG. 3 is a functional block diagram showing the configuration of a control system of the printing press shown in FIG. FIG. 5 is a functional block diagram showing the configuration of a control system of the printed solder inspection device shown in FIG. FIG. 3 is a cross-sectional view showing an example of a state of a screen mask before printing in the printing machine shown in FIG. FIG. 3 is a cross-sectional view showing an example of a state of a screen mask after printing in the printing machine shown in FIG. FIG. 8C is a cross-sectional view showing an example of the state of the screen mask after more printing has been performed than in the state shown in FIG. FIG. 8D is a cross-sectional view showing an example of the state of the screen mask after printing has been performed more times than in the state shown in FIG. FIG. 8D is a diagram showing an example of an image taken by an inspection camera after irradiating a board on which solder paste has been printed using the screen mask shown in FIG. 8C with the first irradiation unit of the printed solder inspection device shown in FIG. 4; FIG. 9B is a diagram showing an example of an image taken by an inspection camera after illuminating the board shown in FIG. 9A with the second illumination unit of the printed solder inspection device shown in FIG. 4; FIG. 8D shows an example of an image captured by an inspection camera when a board on which solder paste has been printed using the screen mask shown in FIG. 8D is irradiated by the first irradiation unit of the printed solder inspection device shown in FIG. 4 . FIG. 10B is a diagram showing an example of an image taken by an inspection camera after illuminating the board shown in FIG. 10A with the second illumination unit of the printed solder inspection device shown in FIG. 4; FIG. 8 is a diagram showing an example of a flux detection result stored in a second storage unit of the printed solder inspection device shown in FIG. 7 . 1 is a flowchart showing a part of a screen printing method according to an embodiment of the present disclosure. 1 is a flowchart showing another part of the screen printing method according to an embodiment of the present disclosure.

Before describing the embodiments of the present disclosure, the background to the conception of the present disclosure will be briefly described. In Patent Document 1, printing defects such as solder bridges are detected from the overall shape of the colored solder paste. Therefore, it is not possible to distinguish whether the solder particles or the flux contained in the solder paste have connected. However, the fluidity of solder particles and flux is different. Therefore, the behavior of the two before a printing defect such as a solder bridge occurs is also different. Therefore, there is room for further improvement in order to capture the signs of printing defects during the process of repeatedly performing screen printing and to perform appropriate improvement processing before the printing defect occurs.

The present disclosure provides a solder paste printing system and a solder paste printing method that can prevent printing defects.

The embodiments of the present disclosure will be described in detail below with reference to the drawings. The configurations, shapes, etc. described below are examples for explanatory purposes and can be modified as appropriate according to the specifications of the screen printing system, the printer, the printed solder inspection device, and the management computer. In the following, the same reference numerals are used for corresponding elements in all drawings, and duplicated explanations will be omitted. Hereinafter, the axis parallel to the substrate transport direction is defined as the X-axis, the axis perpendicular to the X-axis in the horizontal plane (left and right in FIG. 2) is defined as the Y-axis, and the axis perpendicular to the horizontal plane (up and down in FIG. 2) is defined as the Z-axis.

First, referring to FIG. 1, the configuration of a screen printing system 1, which is an example of a solder paste printing system according to an embodiment of the present disclosure, will be described. The screen printing system 1 includes a management computer 3, a printer M1 connected in series from upstream (left side of the page) to downstream (right side of the page) in the board transport direction, and a printed solder inspection device (hereinafter, inspection device) M2. The printer M1 and inspection device M2 are connected to the management computer 3 via a communication network 2. The management computer 3 stores production data, inspection result information, etc., including control programs used by each device, and transmits and receives information between the printer M1 and the inspection device M2.

The printer M1 prints solder paste onto the board brought in from upstream through an opening in a screen mask. The inspection device M2 has an inspection camera, a three-dimensional sensor, etc. Using these, the inspection device M2 inspects the condition and amount of solder paste printed on the top surface of the board transported from the printer M1. The inspection results are sent to the management computer 3 and also to the printer M1. The screen printing system 1 is positioned upstream of the mounting board production line where components are mounted on the board, and the board that has finished inspection by the inspection device M2 is transported to a component mounting device or the like positioned downstream.

Next, the configuration of the printing machine M1 will be described with reference to FIG. 2. The printing machine M1 has a pair of conveyors 5 extending along the X-axis on a base 4. A printing control unit C is provided on the base 4. The conveyors 5 are controlled by the printing control unit C, and transport the substrate 6 received from upstream of the printing machine M1 to a working position along the X-axis, and when screen printing is completed, the substrate 6 is transported downstream of the printing machine M1. A substrate holding unit 7 controlled by the printing control unit C is provided near the center of the conveyor 5 on the X-axis. The substrate holding unit 7 receives the substrate 6 transported by the conveyor 5 and holds it at a predetermined clamp position (working position).

A screen mask 8 is installed above the substrate holding portion 7. The screen mask 8 is provided with a plurality of openings 8a for printing the solder paste Pst on the substrate 6, and a mask mark (not shown). The screen mask 8 has a rectangular flat plate shape that extends in a plane defined by the X-axis and the Y-axis, and its outer periphery is supported by a frame member 8w.

On the base 4, an XY table 9, a θ table 10, and a substrate lifting mechanism 11 are arranged in this order from the bottom. The XY table 9 moves the θ table 10 in a horizontal plane (along the X-axis and Y-axis). The θ table 10 rotates the substrate lifting mechanism 11 around the Z-axis. The substrate lifting mechanism 11 supports the substrate holding part 7 from below and moves it up and down, as shown by arrow a1. The XY table 9, the θ table 10, and the substrate lifting mechanism 11 are controlled by the printing control part C.

Below the screen mask 8, a camera unit 13 incorporating a camera for substrate recognition and a camera for mask recognition is provided. As indicated by arrow a2, the camera unit 13 moves in a horizontal plane by a first moving mechanism 14, which will be described later with reference to FIG. 6. The first moving mechanism 14 is controlled by the printing control unit C. The camera unit 13 moves between the substrate 6 and the screen mask 8 to photograph a substrate mark for alignment formed on the substrate 6 and a mask mark for alignment formed on the screen mask 8. The printing control unit C recognizes the positions of the mask mark and the substrate mark based on the image photographed by the camera unit 13.

3A, a plurality of lands 6a are provided on the substrate 6. The printing control unit C controls the XY table 9, the θ table 10, and the substrate lifting mechanism 11 based on the mark recognition result. Then, the printing control unit C adjusts the position and orientation of the substrate 6 relative to the screen mask 8 so that the plurality of openings 8a formed in the screen mask 8 coincide with the plurality of lands 6a on the substrate 6 held by the substrate holding unit 7. Next, the printing control unit C raises the substrate holding unit 7 to bring the substrate 6 into contact with the screen mask 8 from below. In this way, the XY table 9, the θ table 10, and the substrate lifting mechanism 11 constitute a positioning mechanism 12. The positioning mechanism 12 moves the substrate holding unit 7 to align the substrate 6 held by the substrate holding unit 7 with the screen mask 8.

A print head 20 is provided above the screen mask 8. The print head 20 is moved along the Y axis as shown by the arrow a3 by the second movement mechanism 15 described later with reference to FIG. 6. The print head 20 includes a movement base 21 that is moved in a horizontal plane by the second movement mechanism 15. Two squeegee holding units 22 are arranged side by side along the Y axis on the movement base 21. Each of the squeegee holding units 22 holds a squeegee 23 extending along the X axis at its lower end, and moves up and down as shown by the arrow a4 by a lifting mechanism 24 provided on the movement base 21. The second movement mechanism 15 and the print head 20 are controlled by the print control unit C.

A cleaning mechanism 30 is provided below the screen mask 8 at the negative position (front side) of the Y axis to clean the solder paste Pst remaining on the back surface of the screen mask 8 and in the openings 8a. The cleaning mechanism 30 moves along the Y axis as shown by the arrow a5 by a third moving mechanism 16, which will be described later with reference to FIG. 6. The third moving mechanism 16 is controlled by the print control unit C. The cleaning mechanism 30 has a wiping head 31. The wiping head 31 extends along the X axis and moves along the Z axis as shown by the arrow a6.

In the cleaning mechanism 30, a paper roll 33A on which unused cleaning paper 32 is wound and a paper roll 33B for collecting used cleaning paper 32 are mounted in front of and behind the wiping head 31 on the Y axis. The cleaning paper 32 pulled out from the paper roll 33A slides over the top surface of the wiping head 31 and is wound up on the paper roll 33B. The paper roll 33B is rotated by a roll rotation mechanism 34 controlled by the print control unit C. The cleaning mechanism 30 further has an application unit 35. The application unit 35 is controlled by the print control unit C and applies a solvent that dissolves the flux contained in the solder paste Pst to the cleaning paper 32.

When cleaning the solder paste Pst remaining on the screen mask 8, the printing control unit C cleans the screen mask 8 using a wet cleaning method or a dry cleaning method in a preset pattern. In the wet cleaning method, the printing control unit C raises the cleaning paper 32 to which a solvent has been applied by the application unit 35 with the wiping head 31. This causes the cleaning paper 32 to abut against the back surface of the screen mask 8, and moves the cleaning mechanism 30 along the Y axis. In this way, the printing control unit C wipes off the remaining solder paste Pst. In the dry cleaning method, the printing control unit C raises the cleaning paper 32 to which no solvent has been applied with the wiping head 31 and abuts it against the back surface of the screen mask 8. Then, the cleaning mechanism 30 moves along the Y axis to wipe off the remaining solder paste Pst.

Next, referring to Figures 3A to 3C, the printing process (printing work) in which the printer M1 prints the solder paste Pst on the substrate 6 will be described. As shown in Figure 3A, a plurality of lands 6a, which are electrodes, are formed on the upper surface of the substrate 6. Resist 6b, which is an insulator, is formed on the portion of the upper surface of the substrate 6 other than the lands 6a. The substrate 6 is moved to below the screen mask 8 and is held by the substrate holding unit 7. In the printing process, first, the printing control unit C controls the positioning mechanism 12 shown in Figure 2 to align the substrate 6 with the screen mask 8. Next, the printing control unit C raises the substrate holding unit 7 as shown by arrow b1, and brings the substrate 6 into contact with the lower surface of the screen mask 8.

3B, the printing control unit C then lowers the squeegee 23 to contact the screen mask 8, and then slides it along the Y axis as shown by arrow b2. This sliding forces the solder paste Pst supplied onto the screen mask 8 into the openings 8a and is transferred to the substrate 6. In this transfer process, the printing control unit C transfers the solder paste Pst to the substrate 6 under specified printing conditions. The specified printing conditions include the pressure (printing pressure) with which the squeegee 23 is pressed against the screen mask 8, and the speed at which the squeegee 23 is moved.

3C, the printing control unit C then separates the substrate 6 from the screen mask 8 while lowering the substrate holding unit 7 as shown by the arrow b3. In this release process, the printing control unit C separates the substrate 6 from the screen mask 8 under a separation condition in which the substrate 6 is lowered at a predetermined lowering speed. This causes the solder paste Pst to be printed (deposited) on the land 6a of the substrate 6. The solder paste Pst contains solder particles S and flux F, and when printed on the substrate 6, the flux F, which has fluidity, is smudged on the periphery of the deposit of solder particles S. In this way, the printer M1 prints the solder paste Pst containing the solder particles S and flux F on the substrate 6 through the opening 8a provided in the screen mask 8.

Next, the configuration of the inspection device M2 will be described with reference to FIG. 4. The inspection device M2 has a pair of conveyors 41 extending along the X-axis on a base 40. The conveyor 41 transports the printed board (hereinafter also referred to as board) 6P received from the upstream printing machine M1 along the X-axis to an inspection position, and when the inspection is completed, it transports it downstream of the inspection device M2. A board holding unit 42 is provided near the center of the conveyor 41 on the X-axis. The board holding unit 42 receives the board 6P transported by the conveyor 41 and holds it at a predetermined clamp position (inspection position). A weighing device 43 that measures the weight of the board 6 is installed on the board holding unit 42.

An inspection head 44 is installed above the board holding part 42. The inspection head 44 moves in a horizontal plane by a moving mechanism 45, which will be described later with reference to FIG. 7. The inspection head 44 has an inspection camera (hereinafter, camera) 46, a first lighting unit 47, a second lighting unit 48, and a height detection unit 49. The camera 46 is installed with its optical axis 46a facing downward, and moves above the board 6 held by the board holding part 42 to capture an image of the solder paste Pst printed on the board 6.

The first illumination unit 47 is disposed around the camera 46 and illuminates the portion of the board 6 photographed by the camera 46. The second illumination unit 48 is disposed around the camera 46, outside the first illumination unit 47 as viewed from the camera 46, and illuminates the portion of the board 6 photographed by the camera 46. That is, the second illumination light 48a irradiated from the second illumination unit 48 is tilted more with respect to the board 6 than the first illumination light 47a irradiated from the first illumination unit 47.

In the inspection device M2, the first illumination unit 47 and the second illumination unit 48 are switched or used simultaneously depending on the object photographed by the camera 46. Alternatively, the intensity of the first illumination light 47a irradiated from the first illumination unit 47 and the intensity of the second illumination light 48a irradiated from the second illumination unit 48 are changed depending on the object photographed by the camera 46. The height detection unit 49 includes a 3D sensor and moves above the board 6 held by the board holding unit 42, and measures the position of the solder paste Pst printed on the board 6 and the shape including the height of the solder paste Pst while irradiating the measurement light 49a, and detects the state of the solder paste Pst printed on the board 6.

Next, referring to Figures 5A and 5B, an example of an image of a substrate 6P on which solder paste Pst has been printed by a printer M1, taken by a camera 46 of an inspection device M2 will be described. Figure 5A shows images 50 and 51 taken by the camera 46 of the same position on the substrate 6 while irradiating the substrate with a first illumination light 47a from a first illumination unit 47, and Figure 5B shows images 50 and 51 taken by the camera 46 while irradiating the substrate with a second illumination light 48a from a second illumination unit 48. In Figure 5A, solder paste Pst is printed in a cylindrical shape on a land 6a formed on the upper surface of the substrate 6 through a circular opening 8a formed in a screen mask 8.

Image 50 captured while irradiating first illumination light 47a shows the boundary between land 6a and resist 6b on substrate 6, as well as the deposit of solder particles S contained in solder paste Pst. In FIG. 5B, image 51 captured while irradiating second illumination light 48a shows the boundary between land 6a and resist 6b on substrate 6, the deposit of solder particles S, as well as the flux F contained in solder paste Pst. Flux F seeps outward from the deposit of solder particles S printed on substrate 6. In this way, the state of flux F on substrate 6 can be detected by irradiating second illumination light 48a at an angle.

In this way, the camera 46 and at least one illumination unit (first illumination unit 47, second illumination unit 48) that illuminates the board 6 photographed by the camera 46 function as a detection unit that detects the solder particles S and flux F of the solder paste Pst printed on the board 6. The inspection device M2 inspects the state of the solder paste Pst printed on the board 6. That is, this detection unit is provided in the inspection device M2 that the screen printing system 1 has.

Next, the configuration of the control system of the printing machine M1 will be described with reference to Figure 6. The printing control unit C of the printing machine M1 is connected to the conveyor 5, substrate holding unit 7, positioning mechanism 12, camera unit 13, first moving mechanism 14, second moving mechanism 15, third moving mechanism 16, touch panel 17, print head 20, and cleaning mechanism 30. The touch panel 17 has a display function for displaying the operation screen of the printing machine M1 on the liquid crystal panel, and an input function for inputting commands and various information by operating the displayed operation screen. Note that instead of the touch panel 17, a display device such as a liquid crystal panel and an input device such as a mouse or switch may be provided separately.

The printing control unit C has a memory unit 60, a first processing unit 61, a second processing unit 62, a planning management unit 63, a third processing unit 64, and a communication unit 65. The communication unit 65 is a network communication device that transmits and receives information between the management computer 3 and the inspection device M2 via the communication network 2. The memory unit 60 is a storage device that includes a rewritable RAM (random access memory) and the like. The memory unit 60 stores, for each type of substrate 6, printing conditions under which the print head 20 prints solder paste Pst on the substrate 6, mask cleaning conditions for performing mask cleaning, and the like.

As described above, the printing conditions include the pressure (printing pressure) with which the squeegee 23 pushes the solder paste Pst into the multiple openings 8a, the movement speed of the squeegee 23 during printing, the separation speed at which the substrate 6 is pulled away from the screen mask 8 after printing, etc. In addition, the mask cleaning conditions include the timing of performing mask cleaning and the cleaning method (wet cleaning, dry cleaning), etc.

The first processing unit 61, the second processing unit 62, the planning management unit 63, and the third processing unit 64 are configured with a CPU (Central Processing Unit) or an LSI (Large Scale Integrated Circuit). Alternatively, they may be configured with a dedicated circuit, or may be realized by controlling general-purpose hardware with software read from a transient or non-transient storage device. Two or more of these may also be configured as an integrated unit.

Based on the printing conditions stored in the memory unit 60, the first processing unit 61 controls each part of the printing machine M1, including the print head 20, to perform printing work. The second processing unit 62 controls the cleaning mechanism 30 and the third moving mechanism 16 to perform mask cleaning in accordance with commands (instructions) from the planning management unit 63. Based on the mask cleaning conditions stored in the memory unit 60, the planning management unit 63 commands the second processing unit 62 to perform mask cleaning in a predetermined manner after printing work on a predetermined number of substrates 6.

Now, referring to FIG. 11, an example of the normal cleaning process will be described. The planning management unit 63 has a counter function, and in the normal cleaning process, it counts the number of printed sheets of the substrate 6 after wet cleaning. Then, as shown on the horizontal axis and at the top of the figure, when four sheets of the substrate 6 (first to fourth sheets) have been printed, the planning management unit 63 causes the second processing unit 62 to perform dry cleaning. When four more sheets of the substrate 6 (fifth to eighth sheets) have been printed, the planning management unit 63 causes the second processing unit 62 to perform dry cleaning again. When four more sheets of the substrate 6 (ninth to twelfth sheets) have been printed, the planning management unit 63 causes the second processing unit 62 to perform wet cleaning and then resets the counter.

In FIG. 6, when a defect is detected in the printing state determination process or flux state determination process in the inspection device M2 described below, the third processing unit 64 changes the printing conditions stored in the memory unit 60 so as to improve the state of the solder paste Pst printed on the substrate 6.

Next, the configuration of the control system of the inspection device M2 will be described with reference to Figure 7. The inspection control unit 70 of the inspection device M2 is connected to the conveyor 41, the substrate holding unit 42, the weighing device 43, the moving mechanism 45, the camera 46, the first lighting unit 47, the second lighting unit 48, the height detection unit 49, and the touch panel 76. The touch panel 76 has a display function for displaying the operation screen of the inspection device M2 on the liquid crystal panel, and an input function for inputting commands and various information by operating the displayed operation screen. Like the touch panel 17, the touch panel 76 may also be replaced with a display device and an input device that are provided separately.

The inspection control unit 70 has a first memory unit 71, a second memory unit 72, an inspection processing unit 73, a flux state determination unit (hereinafter, the determination unit) 74, and a communication unit 75. The communication unit 75 is a network communication device that transmits and receives information between the management computer 3 and the printer M1 via the communication network 2. The first memory unit 71 and the second memory unit 72 are storage devices. The first memory unit 71 stores inspection conditions for each type of board 6, including the weight of the board 6 before printing, the inspection position of the solder paste Pst printed on the board 6, and the inspection criteria. The second memory unit 72 stores the inspection results, including the data of the image taken by the camera 46 (hereinafter, simply referred to as the image), the state of the detected solder particles S and flux F, and the like. The first memory unit 71 and the second memory unit 72 also include rewritable RAM, flash memory, hard disk, etc., like the memory unit 60.

The inspection processing unit 73 and the judgment unit 74 are configured with a CPU (Central Processing Unit) or an LSI (Large Scale Integrated Circuit). Alternatively, they may be configured with a dedicated circuit, or may be realized by controlling general-purpose hardware with software read from a transient or non-transient storage device. These two may also be configured as one unit.

The inspection processing unit 73 controls the camera 46, the first illumination unit 47, and the second illumination unit 48 to have the camera 46 capture an image of the board 6 while irradiating the first illumination light 47a or the second illumination light 48a. The inspection processing unit 73 further processes the captured image to detect the solder particles S and flux F printed on the board 6. The detection results are stored in the second memory unit 72. That is, the second memory unit 72 stores the detection results by the detection unit including the camera 46, the first illumination unit 47, and the second illumination unit 48.

The inspection processing unit 73 also controls the weighing device 43 to measure the weight of the printed board 6P brought into the board holding unit 42. The measurement result is stored in the second memory unit 72.

The inspection processing unit 73 also controls the height detection unit 49 to measure the three-dimensional shape of the solder paste Pst printed on the substrate 6. As a result, the inspection processing unit 73 detects the solder particles S and the flux F based on the height of the solder paste Pst from the land 6a, the height of the solder paste Pst from the resist 6b, the step between the deposit of the solder particles S and the flux F, etc. The detection results are stored in the second memory unit 72. In other words, the height detection unit 49 functions as a detection unit that detects the solder particles S and the flux F of the solder paste Pst printed on the substrate 6.

Now, with reference to Figures 8A to 8D, the state of the screen mask 8 after the printing operation will be described. Figure 8A shows the state of the screen mask 8 before printing or immediately after wet cleaning, with the solder paste Pst having been removed from the openings 8a and the underside of the screen mask 8. Figures 8B to 8D show schematic diagrams of the state of the screen mask 8 after repeated printing operations without performing mask cleaning. After the printing operation, residues such as solder particles S and flux F adhere to the openings 8a and underside of the screen mask 8, and the amount of residues increases with repeated printing operations.

Next, referring to Figures 5A, 5B, 9A, 9B, 10A, and 10B, an example of an image taken by the camera 46 on the board 6 on which the solder paste Pst is printed will be described. Figures 9A, 9B, 10A, and 10B are images of the same positions on the board 6 as in Figures 5A and 5B. Figures 5A and 5B are printed through the screen mask 8 immediately after wet cleaning shown in Figure 8A, and Figures 10A and 10B have a greater number of repeated printing operations than Figures 9A and 9B. For example, Figures 9A and 9B are printed using the screen mask 8 in the state shown in Figure 8C, and Figures 10A and 10B are printed using the screen mask 8 in the state shown in Figure 8D. Image 52 shown in Figure 9A and image 54 shown in Figure 10A are photographed while irradiating the first illumination light 47a from the first illumination unit 47. An image 53 shown in FIG. 9B and an image 55 shown in FIG. 10B are captured while irradiating the second illumination light 47 a from the second illumination section 48 .

As is clear from these figures, as the residue on the screen mask 8 increases, the shape of the deposit of solder particles S printed on the substrate 6 becomes distorted and the solder particles S spread horizontally. The area of the flux F seeping out from the solder particles S also increases. A "solder bridge" has occurred at the position indicated by the dotted circle c in image 54 of Figure 10A. That is, the deposit of solder particles S printed on land 6a spreads and connects with the adjacent deposit of solder particles S. In image 55 of Figure 10B, the flux F connects two adjacent lands 6a.

In this way, as the residue on the screen mask 8 increases, the amount of flux F printed on the substrate 6 increases. By observing the state of the flux F printed on the substrate 6 (flux state), it is possible to predict the occurrence of printing defects such as solder bridges that may occur if the printing operation is continued.

In Figure 7, the judgment unit 74 judges whether the state of the flux F on the substrate 6 is good or bad from the images 51, 53, and 55 captured by the camera 46 while irradiating the second illumination light 48a. For example, the judgment unit 74 calculates the area (flux amount) of the printed flux F, and judges the state of the flux F to be good if it is within a standard (threshold value). If it exceeds the standard, the judgment unit 74 judges the state of the flux F to be bad. Note that the judgment unit 74 may judge the state of the flux F to be good or bad from the shape of the flux F in addition to the area of the printed flux F.

Now, referring to FIG. 11, an example of the judgment of the quality of the flux F by the judgment unit 74 will be described. FIG. 11 is a graph showing the flux amount of the flux F detected from the images 51, 53, and 55 in the order in which the board 6 was printed. The white circles connected by the solid line d show a schematic representation of the normal progression of the flux amount on the board 6. That is, after wet cleaning, the flux amount gradually increases until the next wet cleaning (1st to 12th sheets), the flux amount slightly decreases after dry cleaning (5th and 9th sheets), and the flux amount suddenly decreases after wet cleaning (13th sheet). Thus, in a normal state, wet cleaning is performed before the flux amount exceeds the threshold value.

The black circles connected by the dashed dotted line e indicate that the amount of solder paste Pst remaining on the screen mask 8 after the printing operation has increased faster than normal, causing the amount of flux on the seventh board 6 to exceed the threshold value. In this case, the judgment unit 74 judges that the flux condition of the seventh board 6 is defective.

The open triangles connected by dotted line f indicate that a large amount of solder paste Pst residue adheres to the screen mask 8 after the printing operation of the sixth board 6, and the flux amount of the seventh board 6 is within the threshold value, but has increased rapidly. In this case, the judgment unit 74 predicts that the flux amount will exceed the threshold value from the eighth board onwards, resulting in a poor flux state, based on the flux amount of the sixth board and the flux amount of the seventh board. In other words, the judgment unit 74 judges the state of the flux F based on the previous detection result (sixth board) stored in the second storage unit 72 and the current detection result (seventh board) detected by the detection unit.

7 judges the state of the flux F from the image captured by the camera 46. The judgement unit 74 may also judge the state of the flux F from the flux amount of the flux F detected by the height detection unit 49. The judgement unit 74 may also calculate the weight of the printed solder paste Pst from the weight of the board 6 before printing stored in the first memory unit 71 and the weight of the board 6 after printing measured by the weighing device 43. Furthermore, the judgement unit 74 may calculate the weight of the flux F by subtracting the weight of the solder particles S calculated from the image of the solder particles S captured by the camera 46 from the weight of the printed solder paste Pst.

That is, the determination unit 74 may determine the state of the flux F from the weight of the board 6 before and after printing the solder paste Pst. In this way, the scale 43 and the camera 46 function as a detection unit that detects the solder particles S and flux F of the solder paste Pst printed on the board 6. The determination unit 74 then determines whether the state of the flux F is good or bad based on the detection results by the detection units (camera 46, first illumination unit 47, second illumination unit 48, scale 43, height detection unit 49). The determination result is sent to the management computer 3 and the printing machine M1.

When the judgment result of the judgment unit 74 of the inspection device M2 that the condition of the flux F is bad (for example, the amount of flux exceeds a threshold value) is received, the plan management unit 63 shown in FIG. 6 instructs the second processing unit 62 to perform wet cleaning and then resets the counter. Note that if printing work on the subsequent board 6 has already started, wet cleaning may be performed after printing of the board 6 currently being worked on.

A specific example will be described using the black circles shown in Figure 11. When the judgment unit 74 judges the state of the flux F on the seventh board 6 to be defective, the judgment result to that effect is sent to the printer M1. In the printer M1, the planning management unit 63 commands the second processing unit 62 to perform wet cleaning and resets the counter. Then, in the printer M1, wet cleaning is performed before the printing operation on the eighth board 6. When the wet cleaning is performed, the solder particles S and flux F adhering to the screen mask 8 are removed, and the state of the solder paste Pst printed on the board 6 is improved.

That is, when the state of the flux F is judged to be poor by the judgment unit 74, the printer M1 executes an operation to change the state of the flux F of the solder paste Pst printed on the board 6. In this case, the operation to change the state of the flux F in the printer M1 is cleaning (wet cleaning) the screen mask 8 by the cleaning mechanism 30 possessed by the printer M1. This makes it possible to prevent the printing state of the solder particles S from becoming poor.

When the determination unit 74 transmits a determination result indicating that the state of the flux F is poor, the third processing unit 64 shown in FIG. 6 may change the printing conditions stored in the storage unit 60. That is, when the determination unit 74 determines that the state of the flux F is poor, the operation of changing the state of the flux F of the solder paste Pst to be printed on the board 6 may be a change (update) of the printing conditions.

That is, the conditions under which the printer M1 brings the substrate 6 into contact with the screen mask 8 to transfer the solder paste Pst to the substrate 6, and the conditions under which the printer M1 separates the substrate 6 from the screen mask 8 after transferring the solder paste Pst to the substrate 6 are changed. More specifically, the printing pressure, the movement speed of the squeegee 23, the separation speed, and the like are changed. This makes it possible to prevent the printed state of the solder particles S from becoming defective. It is not necessary to change the printing conditions every time a result is received indicating that the flux state is defective. For example, the printing conditions may be changed if defects occur twice consecutively during normal cleaning, or if the occurrence of defects exceeds a predetermined frequency.

In the above embodiment, an example has been described in which the judgment unit 74 is provided in the inspection device M2, and the plan management unit 63 and the third processing unit 64 are provided in the printing machine M1, but the screen printing system 1 is not limited to this form. For example, the management computer 3 may have the judgment unit 74, the plan management unit 63, and the third processing unit 64. In addition, the printing machine M1 may have a weighing device 43 that measures the weight of the substrate 6 before and after printing.

Next, the screen printing method in the screen printing system 1 will be described with reference to Figures 12 and 13. In Figure 12, first, the conveyor 5 carries the substrate 6 into the printer M1 of the screen printing system 1 (ST1). Next, the substrate holder 7 holds the substrate 6, and the positioning mechanism 12 aligns the substrate 6 with respect to the screen mask 8 (ST2), and brings the substrate 6 into contact with the screen mask 8 (ST3). Next, the print head 20 transfers the solder paste Pst through the screen mask 8 to the substrate 6 in contact with the screen mask 8 (about ST4), and then the substrate lifting mechanism 11 separates the substrate 6 from the screen mask 8 (ST5).

As a result, the solder paste Pst is printed on the board 6, and a printed board 6P is produced. That is, steps ST2 to ST5 are a printing process (ST30) for printing the solder paste Pst on the board 6. Next, the printed board 6P is transferred to the inspection device M2 (ST6). Next, at least one illumination unit (first illumination unit 47, second illumination unit 48) illuminates the board 6P (ST7), and the camera 46 photographs the solder paste Pst printed on the board 6 (ST8). Next, the inspection processing unit 73 performs image recognition on the photographed image to recognize the solder particles S and flux F of the solder paste Pst printed on the board 6 (ST9).

Next, the weighing device 43 measures the weight of the substrate 6P after the solder paste Pst has been printed (ST10). Thus, steps ST7 to ST10 constitute a detection process (ST31) for detecting the solder particles S and flux F of the solder paste Pst printed on the substrate 6. Next, the detection results in the detection process (ST31) are stored in the second memory unit 72 (ST11).

13, the inspection processing unit 73 determines whether the condition of the solder particles S is good or bad from the image captured in ST8 (ST12). If the printing condition is bad (bad in ST12), that fact is transmitted to the downstream component mounting device. In addition, the printer M1 performs printing defect processing such as cleaning the screen mask 8 (dry cleaning) and changing the printing conditions (ST13). If the printing condition is good (good in ST12) or if the printing condition is bad and printing defect processing (ST13) is performed, the substrate 6P is then removed from the screen printing system 1 (ST14).

If the production of the printed board 6P has not been completed (No in ST15), the judgment unit 74 judges whether the state of the flux F of the already inspected printed board 6P exceeds a predetermined standard, i.e., whether the flux state is good or bad, based on the detection result in the detection process (ST31) (ST16). The judgment unit 74 may also judge the state of the flux F based on the stored previous detection result and the current detection result detected in the detection process (ST31). Specifically, the judgment unit 74 judges the state of the flux F from the image captured in ST8. The judgment unit 74 may also judge the state of the flux F from the weight of the board 6 before printing and the weight after printing measured in ST10.

If the condition of the flux F is judged to be poor in ST16, the planning management unit 63 causes the second processing unit 62 to perform wet cleaning (ST17) and resets the counter to zero (ST18). Next, the third processing unit 64 changes the printing conditions stored in the memory unit 60 (ST19). This changes the conditions for transferring the solder paste Pst to the substrate 6 in ST4 and/or the conditions for separating the substrate 6 from the screen mask 8 in ST5.

Thus, steps ST17 to ST19 are a change operation step (ST32) in which, if the condition of the flux F is determined to be defective in ST16, an operation is performed to change the condition of the flux F in the solder paste Pst printed on the board 6. This makes it possible to prevent printing defects from occurring.

If the condition of the flux F is judged to be good in ST16, the planning management unit 63 executes normal cleaning according to the count of the counter (ST20). After the change operation process (ST32) or the normal cleaning process (ST20), the process returns to ST1 and the next substrate 6 is loaded.

As described above, the screen printing system 1 has a printer M1. The screen printing system 1 has a detection unit that detects the solder particles S and flux F of the solder paste Pst printed on the board 6, and a judgment unit 74 that judges whether the state of the flux F is good or bad based on the detection result by the detection unit. Then, when the judgment unit 74 judges that the state of the flux F is bad, the printer M1 executes an operation to change the state of the flux F of the solder paste Pst printed on the board 6. This makes it possible to prevent printing defects in advance. Note that the detection unit only needs to be able to detect the state of the flux F of the solder paste Pst. Therefore, the detection unit does not need to have all of the camera 46, the first illumination unit 47, the second illumination unit 48, the measuring device 43, and the height detection unit 49. For example, if the detection unit can sufficiently detect the state of the flux F using at least one of the camera 46, the first illumination unit 47, and the second illumination unit 48, the measuring device 43 and the height detection unit 49 may not be provided.

The above embodiment also describes an example in which the quality of the flux F state is fed back to trigger cleaning of the screen mask 8 or to change printing conditions in screen printing. However, the determination of the quality of the flux F state is not limited to these uses. For example, it may be used to determine the formation state of the solder portion when forming the solder portion on the land 6a by a method other than screen printing. Furthermore, based on the determination result, an operation to change the state of the flux in the solder paste may be performed in that method.

The solder paste printing system and solder paste printing method disclosed herein have the effect of preventing printing defects in advance, and are useful in the field of mounting electronic components to substrates.

1 Screen printing system 2 Communication network 3 Management computer 4, 40 Base 5, 41 Conveyor 6 Substrate 6a Land 6b Resist 6P Printed substrate (substrate)
Reference Signs List 7 Substrate holding section 8 Screen mask 8a Opening 8w Frame member 9 XY table 10 θ table 11 Substrate lifting mechanism 12 Positioning mechanism 13 Camera unit 14 First moving mechanism 15 Second moving mechanism 16 Third moving mechanism 17, 76 Touch panel 20 Print head 21 Moving base 22 Squeegee holding section 23 Squeegee 24 Lifting mechanism 30 Cleaning mechanism 31 Wiping head 32 Cleaning paper 33A, 33B Paper roll 35 Coating section 42 Substrate holding section 43 Measuring device 44 Inspection head 45 Moving mechanism 46 Inspection camera (camera)
46a Optical axis 47 First illumination unit 47a First illumination light 48 Second illumination unit 48a Second illumination light 49 Height detection unit 49a Measurement light 50, 51, 52, 53, 54, 55 Image 60 Storage unit 61 First processing unit 62 Second processing unit 63 Plan management unit 64 Third processing unit 65, 75 Communication unit 70 Inspection control unit 71 First storage unit 72 Second storage unit 73 Inspection processing unit 74 Flux state determination unit (determination unit)
C Printing control section F Flux M1 Printer M2 Printed solder inspection device (inspection device)
Pst Solder Paste S Solder Particles

Claims (15)

a printer that prints a solder paste containing solder particles and flux onto a substrate;
a detection unit that detects the solder particles and the flux of the solder paste printed on the board;
a flux state determination unit that determines whether the state of the flux is good or bad based on a detection result by the detection unit,
If the flux state determination unit determines that the state of the flux is poor, the printer performs an operation to change the state of the flux of the solder paste before the solder paste is printed on an unprinted board ;
The detection unit is
a camera for photographing the solder paste printed on the substrate;
a first illumination unit that irradiates the substrate with a first illumination light;
a second illumination unit that irradiates the substrate with second illumination light that is tilted with respect to the substrate more than the first illumination light,
Detecting the solder particles based on a first image captured by the camera while irradiating the solder particles with the first illumination light;
A solder paste printing system that detects the flux based on a second image taken by the camera while irradiating the second illumination light . A storage unit that stores the detection result by the detection unit,
2. The solder paste printing system according to claim 1, wherein the flux state determination unit determines the state of the flux based on a previous detection result stored in the memory unit and a current detection result detected by the detection unit. 3. The solder paste printing system according to claim 1 , wherein the flux state determination unit determines that the state of the flux is defective based on a determination result that an area of the flux printed on the board in the second image exceeds a standard. the detection unit has a weighing device that measures a pre-printing weight of the board before the solder paste is printed and a post-printing weight that is a total weight of the board and the solder paste after the solder paste is printed,
The solder paste printing system according to claim 1 , wherein the flux state determining unit determines the state of the flux based on the pre-printing weight and the post-printing weight. 5. The solder paste printing system according to claim 4 , wherein the flux state determination unit determines that the state of the flux is defective based on a determination result that the amount of the flux calculated from the difference between the pre-printing weight and the post-printing weight exceeds a threshold value. The method further includes a printed solder inspection device that inspects the state of the solder paste printed on the board,
The solder paste printing system according to claim 1 , wherein the detection unit is provided in the printed solder inspection device. The printer includes a screen mask having an opening for printing the solder paste on the substrate, and a cleaning mechanism for cleaning the screen mask;
The solder paste printing system of claim 1 , wherein the operation that changes the state of the flux in the printer is cleaning of the screen mask by the cleaning mechanism. the printer includes a screen mask having openings for printing the solder paste onto the substrate;
7. The solder paste printing system of claim 1, wherein the operation of changing the state of the flux in the printer is to change the conditions under which the printer contacts the unprinted substrate with the screen mask to transfer the solder paste on the screen mask to the unprinted substrate. the printer includes a screen mask having openings for printing the solder paste onto the substrate;
7. The solder paste printing system of claim 1, wherein the operation of changing the condition of the flux in the printer is to change the conditions under which the printer separates the unprinted substrate from the screen mask after the printer transfers the solder paste to the unprinted substrate. printing a solder paste containing solder particles and flux onto a substrate;
detecting the solder particles and the flux of the solder paste printed on the substrate to obtain a detection result;
determining whether the state of the flux is good or bad based on the detection result;
if the condition of the flux is determined to be poor, performing an operation to change the condition of the flux of the solder paste before the solder paste is printed on an unprinted board ;
In the step of obtaining a detection result,
detecting the solder particles based on a first image captured by a camera while irradiating the substrate on which the solder paste is printed with a first illumination light;
A solder paste printing method comprising: detecting the flux based on a second image captured by the camera while irradiating the board with second illumination light that is tilted more inclined with respect to the board than the first illumination light . The method further comprises the step of storing the detection result.
The solder paste printing method according to claim 10 , wherein the condition of the flux is judged to be good or bad based on a stored previous detection result and a detected current detection result. When obtaining the detection result, a pre-printing weight of the substrate before the solder paste is printed and a post-printing weight, which is a total weight of the substrate and the solder paste after the solder paste is printed, are measured;
The solder paste printing method according to claim 10 or 11 , wherein the condition of the flux is determined based on the pre-printing weight and the post-printing weight. The solder paste is printed onto the substrate through a screen mask having openings;
13. The method of claim 10 , wherein the operation that changes the state of the flux is cleaning of the screen mask. When printing the solder paste on the substrate, the solder paste is transferred to the substrate through a screen mask having openings in contact with the screen mask;
13. The method of claim 10 , wherein the operation of changing the state of the flux is to change the conditions for transferring the solder paste to the unprinted substrate. When printing the solder paste on the substrate, the solder paste is transferred to the substrate through a screen mask having openings in contact with the screen mask;
After transferring the solder paste to the substrate, the substrate is separated from the screen mask;
13. The method of printing solder paste according to claim 10 , wherein the operation of changing the state of the flux is to change the conditions under which the unprinted substrate is separated from the screen mask.

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