JP2015039865A - Screen printer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a screen printer capable of preventing reduction in productivity of a substrate without causing a delay in the start of screen printing work even when a mask is cleaned or inspected for clogging.SOLUTION: A screen printer comprises: a mask imaging camera 29 for imaging a mask 21 from below with the mask 21 separated from the substrate 2; a substrate imaging camera 31 for imaging the substrate 2 from above with the substrate 2 separated from the mask 21; and a mask cleaner 33 for cleaning the mask 21 by sliding on an under surface of the mask 21 with the mask 21 separated from the substrate 2. The mask imaging camera 29 and the mask cleaner 33 are mounted on a first moving beam 25 which horizontally moves under the mask 21, and the substrate imaging camera 31 is mounted on a second moving beam 27 which horizontally moves under the first moving beam 25 independently of the first moving beam 25.

Description

  The present invention relates to a screen printing machine that transfers a paste onto a substrate by sliding a squeegee on a mask in contact with the substrate.

  The screen printing machine slides a squeegee on a mask in contact with the upper surface of the substrate to transfer the paste to the substrate, and then separates the substrate from the mask (releases the plate) to print the paste on the substrate. Such a screen printing machine includes a mask imaging camera that images the mask separated from the substrate from below, and a substrate imaging camera that images the substrate separated from the mask from above. A mask cleaner is provided for cleaning the mask by sliding the lower surface of the mask. The mask imaging camera captures the mark (mask side mark) provided on the mask to recognize the position of the mask when the mask is first installed, and recognizes the clogged state of the paste in the mask pattern hole after releasing the plate. In order to do so, the entire lower surface of the mask is imaged. The substrate imaging camera captures the mark (substrate side mark) provided on the substrate to recognize the position of the substrate carried under the mask, and the mask cleaner slides on the lower surface of the mask after separating the plate. And wipe off the paste attached to the mask.

  In such a screen printing machine, the mask imaging camera and the board imaging camera are usually attached to a moving body that horizontally moves below the mask as one camera unit, and the mask cleaner is moved by the moving body that moves the camera unit. It is moved (see, for example, Patent Document 1). The screen printing machine recognizes the position of the substrate based on the image of the substrate side mark every time a new substrate is carried in, and brings the substrate into contact with the mask based on the relationship with the mask position recognized at the time of initial mask installation. . Although the mask cleaning by the mask cleaner is performed every time several screen printings are finished, the fine pitch type substrate may be performed every time the screen printing is performed once.

JP2013-10240A

  However, in the configuration in which the mask cleaner is moved together with the camera unit as described above, it is necessary to recognize the position of the newly loaded substrate after the mask cleaning operation is completed. There has been a problem that the start of production may be delayed and the productivity of the substrate as the whole screen printing machine may be reduced. In addition, since the position of the substrate cannot be recognized by the substrate imaging camera while the mask clogging inspection is performed by the mask imaging camera, the same problem occurs when the mask clogging inspection is performed. It was.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a screen printing machine capable of preventing a decrease in substrate productivity without delaying the start of screen printing work even when mask cleaning or mask clogging inspection is performed. And

  The screen printing machine according to claim 1, wherein the paste is transferred to the substrate by sliding a squeegee on a mask in contact with the upper surface of the substrate, and then the substrate is separated from the mask to be pasted on the substrate. A screen printing machine that prints the mask separated from the substrate from below, a substrate imaging camera that images the substrate separated from the mask from above, and the substrate. A mask cleaner that cleans the mask by sliding on the lower surface of the mask in a separated state, and the mask imaging camera and the mask cleaner are attached to a first moving body that horizontally moves below the mask. The board imaging camera is attached to a second moving body that horizontally moves below the first moving body independently of the first moving body. That.

  The screen printing machine according to claim 2 is the screen printing machine according to claim 1, wherein the board imaging camera is configured to move the first moving body and the second moving body independently of each other. Imaging of the substrate and cleaning of the mask by the mask cleaner or imaging of the substrate by the substrate imaging camera and imaging of the mask by the mask imaging camera are performed in parallel.

  The screen printer according to claim 3 is the screen printer according to claim 1 or 2, wherein imaging of the substrate by the substrate imaging camera is performed for inspection of a paste printed on the substrate. Is included.

  In the present invention, the mask imaging camera and the mask cleaner are attached to the first moving body that horizontally moves below the mask, while the substrate imaging camera moves horizontally below the first moving body independently of the first moving body. Since the first moving body and the second moving body can be moved independently of each other, the substrate imaging by the substrate imaging camera and the mask cleaning by the mask cleaner (or the substrate imaging) It is possible to perform in parallel the imaging of the substrate by the camera and the clogging inspection of the mask by imaging the mask of the mask imaging camera. For this reason, even when mask cleaning (or mask clogging inspection) is performed, the start of the screen printing operation on the substrate is not delayed, and a reduction in substrate productivity can be prevented.

The top view of the screen printer in one embodiment of the present invention The front view of the screen printer in one embodiment of the present invention The side view of the screen printer in one embodiment of the present invention The enlarged side view of the mask cleaner with which the screen printer in one embodiment of the present invention is provided The block diagram which shows the control system of the screen printer in one embodiment of this invention The flowchart which shows the execution procedure of the screen printing operation which the screen printer in one embodiment of this invention performs (A) (b) Operation | movement explanatory drawing of screen printing work which the screen printer in one embodiment of this invention performs (A) (b) Operation | movement explanatory drawing of screen printing work which the screen printer in one embodiment of this invention performs (A) (b) Operation | movement explanatory drawing of screen printing work which the screen printer in one embodiment of this invention performs (A) (b) Operation | movement explanatory drawing of screen printing work which the screen printer in one embodiment of this invention performs (A) (b) Operation | movement explanatory drawing of screen printing work which the screen printer in one embodiment of this invention performs

  Embodiments of the present invention will be described below with reference to the drawings. The screen printing machine 1 shown in FIGS. 1, 2 and 3 is a device that screen prints a paste Pt such as solder on the electrode 2a of the substrate 2, and is placed on the base 11 in the left-right direction as viewed from the operator OP ( A carry-in conveyor 12, a positioning conveyor 13, and a carry-out conveyor 14 that convey the substrate 2 from the left to the right in the X-axis direction are provided in this order.

  2 and 3, the positioning conveyor 13 is a component of the substrate holding unit 16 provided on the base 11 via the unit moving mechanism 15, and the substrate holding unit 16 includes the positioning conveyor 13 and the lower part. A receiving unit 17 and a pair of clamp members 18 are provided. The lower receiving unit 17 is driven by the lower receiving cylinder 17a to move up and down, and supports the substrate 2 positioned at the work position by the positioning conveyor 13 from below. The clamp member 18 is opened and closed in the front-rear direction (Y-axis direction) viewed from the operator OP by the clamp member opening / closing mechanism 18a, and clamps and holds the substrate 2 supported by the lower receiving unit 17 from the Y-axis direction. The unit moving mechanism 15 is composed of an XYθ robot, and moves the substrate holding unit 16 with respect to the base 11 in a horizontal plane and raises / lowers the base 11.

  1, 2, and 3, the mask 21 is held in a horizontal position above the positioning conveyor 13. The mask 21 is made of a rectangular plate-like member, and four sides are supported by a rectangular frame-shaped mask frame 21w. A large number of pattern holes 21 h corresponding to the electrodes 2 a of the substrate 2 are provided in the central portion of the mask 21.

  In FIG. 1, two substrate-side marks 2m are provided at one diagonal position on the substrate 2 (only one is shown in FIG. 1), and the mask 21 corresponds to these two substrate-side marks 2m. Two mask side marks 21m are provided (only one is shown in FIG. 1). The substrate 2 is raised with the two substrate-side marks 2m and the two mask-side marks 21m facing each other up and down (the substrate holding unit 16 holding the substrate 2 is raised by the unit moving mechanism 15) to the mask 21. When the substrate 2 is brought into contact, the electrode 2a of the substrate 2 and the pattern hole 21h of the mask 21 are brought into a matched state.

  1, 2, and 3, a squeegee base 22 extending in the X-axis direction is provided above the mask 21. At both ends of the squeegee base 22, two first ball screws 22 a extending in the Y-axis direction and supported by four support columns 11 a extending upward from the four corners of the front and rear of the base 11 are threaded. When the two first ball screws 22a are synchronously rotated by the two first ball screw driving motors 23, the squeegee base 22 moves in the Y-axis direction.

  1, 2, and 3, the squeegee base 22 is provided with two squeegees 24. The two squeegees 24 are each composed of a bowl-shaped member extending in the X-axis direction, and are disposed to face each other in the Y-axis direction. Each squeegee 24 is raised and lowered individually by a squeegee lifting cylinder 24 a attached to the squeegee base 22.

  A first moving beam 25 serving as a first moving body extending in the X-axis direction is provided below the mask 21. At both ends of the first moving beam 25, two second ball screws 25a supported by the above-mentioned four support columns 11a and extending in the Y-axis direction are threaded, and these two second ball screws 25a are inserted. When synchronously rotated by the two second ball screw drive motors 26, the first moving beam 25 moves in the Y-axis direction (hereinafter, the horizontal plane on which the first moving beam 25 moves is referred to as the first horizontal plane S1).

  Below the first moving beam 25, a second moving beam 27 as a second moving body extending in the X-axis direction is provided. At the both ends of the second moving beam 27, two third ball screws 27a supported by the four columns 11a and extending in the Y-axis direction are threaded through, and these two third ball screws 27a are two. When the three third ball screw drive motors 28 are synchronously rotated, the second moving beam 27 moves in the Y-axis direction (hereinafter, a horizontal plane on which the second moving beam 27 moves is referred to as a second horizontal plane S2).

  1, 2, and 3, the first moving beam 25 is provided with a mask imaging camera 29 with an imaging field of view facing upward. A fourth ball screw 25 b provided along the first moving beam 25 is threaded through the support portion 29 a of the mask imaging camera 29, and the fourth ball screw 25 b is driven by the fourth ball screw driving motor 30. When rotated, the mask imaging camera 29 moves in the X-axis direction. As described above, the mask imaging camera 29 is movable in the first horizontal plane S1 below the mask 21 and is separated from the substrate 2 by the synchronous rotation of the two second ball screws 25a and the rotation of the fourth ball screw 25b. The state of the mask 21 is imaged from below.

  The second moving beam 27 is provided with a substrate imaging camera 31 with an imaging field of view directed downward. A fifth ball screw 27 b provided along the second moving beam 27 is threaded through the support portion 31 a of the board imaging camera 31, and the fifth ball screw 27 b is driven by a fifth ball screw driving motor 32. When rotated, the board imaging camera 31 moves in the X-axis direction. In this way, the board imaging camera 31 moves in the second horizontal plane S2 below the mask 21 (further below the first horizontal plane S1) by the synchronous rotation of the two third ball screws 27a and the rotation of the fifth ball screw 27b. The substrate 2 that is free and separated from the mask 21 is imaged from above.

  1, 2, and 3, a mask cleaner 33 extending in the X-axis direction is fixedly provided on the first moving beam 25. When the two second ball screws 25a are synchronously rotated by the two second ball screw driving motors 26, the mask cleaner 33 moves in the Y-axis direction in the first horizontal plane S1 together with the mask imaging camera 29. As described above, the mask cleaner 33 is movable in the first horizontal plane S1 below the mask by the rotation of the two second ball screw drive motors 26, and slides on the lower surface of the mask 21 in a state of being separated from the substrate 2. Then, the mask 21 is cleaned.

  In FIG. 4, the mask cleaner 33 includes a first reel 35a on the feeding side and a second reel 35b on the take-up side which are rotatably provided around the X axis in the housing 34, and the first reel 35a and the second reel 35b. The paper member 36 spanned between the reels 35b and the X-axis direction can be freely moved up and down with respect to the housing 34. When the paper member 36 is moved up by the nozzle vertical movement mechanism 37a, a part of the paper member 36 is moved upward. It has a nozzle 37 that pushes it up. A portion of the paper member 36 pushed upward by the nozzle 37 becomes a mask contact surface 36 a that comes into contact with the lower surface of the mask 21. The mask contact surface 36a can be updated by driving the first reel 35a and the second reel 35b in the same direction by the reel drive motor 35c and moving the paper member 36 in the Y-axis direction.

  In FIG. 5, the substrate 2 is transported and positioned to the work position by the control device 40 provided in the screen printing machine 1 by controlling the operation of the carry-in conveyor 12, the positioning conveyor 13, and the carry-out conveyor 14. The receiving operation is performed by the control device 40 controlling the operation of the lower receiving cylinder 17a. The clamping operation of the substrate 2 by the pair of clamping members 18 is performed by the control device 40 controlling the operation of the clamping member opening / closing mechanism 18a, and the moving operation and the raising / lowering operation of the substrate holding unit 16 in the horizontal plane are performed by the control device 40. Is performed by controlling the operation of the unit moving mechanism 15.

  The movement operation of the squeegee base 22 in the Y-axis direction, that is, the movement operation of the two squeegees 24 in the Y-axis direction is performed by the control device 40 controlling the operation of the two first ball screw drive motors 23. Moreover, the raising / lowering operation | movement of each squeegee 24 with respect to the squeegee base 22 is made | formed when the control apparatus 40 performs operation | movement control of the squeegee raising / lowering cylinder 24a (FIG. 5).

  For the movement operation of the first moving beam 25 in the Y-axis direction, that is, the movement operation of the mask imaging camera 29 and the mask cleaner 33 in the Y-axis direction, the control device 40 controls the operation of the two second ball screw drive motors 26. The movement of the mask imaging camera 29 in the X-axis direction is performed by the control device 40 controlling the operation of the fourth ball screw drive motor 30. In addition, the movement of the second moving beam 27 in the Y-axis direction, that is, the movement of the substrate imaging camera 31 in the Y-axis direction is performed by the control device 40 controlling the operation of the two third ball screw drive motors 28. The movement of the board imaging camera 31 in the X-axis direction is performed by the control device 40 controlling the operation of the fifth ball screw drive motor 32.

  The imaging operation of the mask imaging camera 29 and the imaging operation of the substrate imaging camera 31 are controlled by the control device 40, and the image data obtained by the imaging operation of the mask imaging camera 29 and the image data obtained by the imaging operation of the substrate imaging camera 31 are controlled. Is sent to the control device 40 and subjected to image processing in the image processing section 40a of the control device 40 (FIG. 5).

  The vertical movement of the nozzle 37 of the mask cleaner 33 is performed by the control device 40 controlling the operation of the nozzle vertical movement mechanism 37 a, and the paper member 36 of the mask cleaner 33 is advanced to be passed over the upper surface of the nozzle 37. The operation of updating the 36 mask contact surfaces 36a is performed by the control device 40 controlling the operation of the reel drive motor 35c. The negative pressure supply operation for applying a vacuum pressure to the nozzle 37 is performed by the control device 40 controlling the operation of the negative pressure supply mechanism 41 (FIG. 5).

  Next, the execution procedure of the screen printing operation by the screen printer 1 will be described with reference to the flowchart of FIG. 6 and the operation explanatory diagrams of FIGS. When the mask 21 is set by the operator OP, the control device 40 first moves the mask imaging camera 29 in the first horizontal plane S1, and the mask imaging camera 29 images the mask 21 separated from the substrate 2 from below. (FIG. 7A. Step ST1 shown in FIG. 6). Here, the two mask-side marks 21m provided on the mask 21 are imaged, and the images of the two obtained mask-side marks 21m are recognized to recognize the position of the mask 21.

  When the control device 40 performs imaging of the mask 21 by the mask imaging camera 29 and recognizes the position of the mask 21, the substrate 2 sent from the outside of the screen printing machine 1 is carried in by the carry-in conveyor 12, and is moved by the positioning conveyor 13. After the substrate 2 is positioned at the work position (step ST2), the substrate 2 is held by the substrate holding unit 16 (FIG. 7B, step ST3). The substrate 2 is held by supporting the lower surface by the receiving unit 17 (arrow A1 shown in FIG. 7B) and clamping the substrate 2 by the clamp member 18 (arrow B1 shown in FIG. 7B). ).

  After holding the substrate 2 by the substrate holding unit 16, the control device 40 moves the substrate imaging camera 31 in the second horizontal plane S <b> 2 and images the substrate 2 separated from the mask 21 from above by the substrate imaging camera 31. (FIG. 8A. Step ST4). Here, the two substrate-side marks 2m provided on the substrate 2 are imaged, and the image of the obtained two substrate-side marks 2m is recognized to recognize the position of the substrate 2.

  In parallel with the imaging of the substrate 2, the control device 40 cleans the mask 21 with the mask cleaner 33 as necessary (FIG. 8B, step ST5). The mask 21 is cleaned before the screen printing on the next substrate 2 is performed on the remaining residue of the paste Pt adhering to the lower surface of the mask 21 when the paste Pt is printed on the substrate 2 in steps ST6 to ST9 described later. Wipe it off. In the cleaning of the mask 21, the control device 40 moves the nozzle 37 of the mask cleaner 33 upward by the nozzle vertical movement mechanism 37 a so as to protrude above the housing 34, and the mask contact surface 36 a of the paper member 36 is the lower surface of the mask 21. The first moving beam 25 is moved in the Y-axis direction while being in contact with the arrow (arrow C shown in FIG. 8B). At this time, the control device 40 operates the negative pressure supply mechanism 41 to increase the wiping effect of the remaining residue of the paste Pt by the mask cleaner 33, and the paste through the mask contact surface 36 a of the paper member 36 to the nozzle 37. The vacuum suction of Pt is performed.

  Thus, in the screen printing machine 1 according to the present embodiment, the mask imaging camera 29 and the mask cleaner 33 are attached to the first moving beam 25 that horizontally moves below the mask 21, and the substrate imaging camera 31 is the first moving beam. Since it is attached to the second moving beam 27 that moves horizontally below the first moving beam 25 independently of the first moving beam 25, the first moving beam 25 and the second moving beam 27 are moved independently of each other. Accordingly, it is possible to perform the imaging of the substrate 2 by the substrate imaging camera 31 (imaging of the substrate side mark 2m) and the cleaning of the mask 21 by the mask cleaner 33 in parallel.

  Here, as described above, the cleaning of the mask 21 is to wipe off the remaining residue of the paste Pt adhering to the lower surface of the mask 21 by executing the screen printing before performing the next screen printing. If the paste Pt is not attached to the lower surface of the mask 21 for the first screen printing performed after the step ST5, the step ST5 can be omitted. Further, the step ST5 may be executed every time (that is, every time one screen printing is finished) or may be executed every time several screen printings are finished. When the mask 21 is not cleaned, after the substrate 2 is held by the substrate holding unit 16 (step ST3), only the substrate side mark 2m is imaged (step ST4) by the substrate imaging camera 31. Further, instead of cleaning the mask 21 or following the cleaning of the mask 21, the entire surface of the lower surface of the mask 21 is imaged by the mask imaging camera 29, so that the paste Pt in the pattern hole 21 h of the mask 21 is clogged. A clogging inspection of the mask 21 to be inspected may be performed.

  The control device 40 performs imaging of the substrate 2 and, if necessary, cleans the mask 21 in parallel with imaging of the substrate 2, moves the substrate holding unit 16 in the horizontal plane, The substrate 2 is aligned with the mask 21 so as to face the mask side mark 21m vertically (step ST6). Then, the substrate holding unit 16 is raised with respect to the base 11 (arrow D1 shown in FIG. 9A), and the upper surface of the substrate 2 clamped and held by the clamp member 18 is brought into contact with the lower surface of the mask 21 ( 9A, step ST7). As a result, the electrode 2a on the substrate 2 and the pattern hole 21h of the mask 21 are brought into a matched state.

  When the control device 40 brings the substrate 2 into contact with the mask 21, the paste Pt is transferred to the substrate 2 by the squeegee 24 (step ST8). In the transfer of the paste Pt, one of the two squeegees 24 is moved downward with the paste Pt supplied in advance on the mask 21, and the lower end thereof is brought into contact with the upper surface of the mask 21 (FIG. 9B). The arrow E1 shown in FIG. 10 is performed by moving the squeegee base 22 in the Y-axis direction while maintaining the contact state (arrow F shown in FIG. 10A). As a result, the paste Pt is scraped by the squeegee 24 on the mask 21 and pushed into the pattern hole 21h of the mask 21, and is transferred onto the electrode 2a of each substrate 2.

  After transferring the paste Pt to the electrode 2a of the substrate 2, the control device 40 moves the unit up after moving the squeegee 24 in contact with the mask 21 (arrow E2 shown in FIG. 10B). The substrate holding unit 16 is lowered by the mechanism 15 (arrow D2 shown in FIG. 11A), and the substrate 2 is separated from the mask 21 to release the plate (step ST9). When the control device 40 releases the plate, the clamp member 18 is opened (arrow B2 shown in FIG. 11B), and the lower receiving unit 17 is lowered (arrow shown in FIG. 11B). A2) The holding of the substrate 2 is released by lowering both ends of the substrate 2 onto the positioning conveyor 13 (FIG. 11 (b), step ST10).

  When the control device 40 releases the holding of the substrate 2, the substrate holding unit 16 is moved in the horizontal plane by the unit moving mechanism 15, the orientation of the positioning conveyor 13 is adjusted, and the substrate 2 is sent from the positioning conveyor 13 to the carry-out conveyor 14. Then, the substrate 2 is carried out of the screen printer 1 (step ST11). When the control device 40 carries out the substrate 2, it enters a waiting state for the newly sent substrate 2 (step ST12). If there is a substrate 2 newly sent within a certain time, the process returns to step ST2 to carry in and position the substrate 2, hold the substrate 2 (step ST3), and perform the substrate imaging camera 31. The substrate 2 is imaged by (step ST4), and the mask 21 is cleaned by the mask cleaner 33 (step ST5). On the other hand, in step ST12, when there is no substrate 2 newly sent within a certain time, the screen printing operation is terminated.

  As described above, in the screen printing machine 1 according to the present embodiment, the mask imaging camera 29 and the mask cleaner 33 are attached to the first moving beam 25 as the first moving body that horizontally moves below the mask 21. The substrate imaging camera 31 is attached to a second moving beam 27 as a second moving body that horizontally moves below the first moving beam 25 independently of the first moving beam 25. Since the second moving beams 27 can be moved independently of each other, the substrate imaging camera 31 images the substrate 2 and the mask cleaner 33 cleans the mask 21 (or the substrate imaging camera 31 images the substrate 2 and the mask imaging camera). (Inspection of clogging of the pattern hole 21h of the mask 21 by imaging of the mask 21 of 29) is performed in parallel. Possible it is. Therefore, even when the mask 21 is cleaned (or the clogging inspection of the mask 21), the start of the screen printing operation on the substrate 2 is not delayed, and the productivity of the substrate 2 can be prevented from being lowered. This effect is particularly significant when the mask 21 needs to be cleaned after each screen printing, such as when screen printing is performed on the fine pitch type substrate 2.

  In the above-described embodiment, the imaging of the substrate 2 by the substrate imaging camera 31 in step ST4 is for imaging the substrate-side mark 2m of the substrate 2 held by the substrate holding unit 16, but the imaging of the substrate 2 is performed. Can include imaging for inspection of the paste Pt printed on the substrate 2 (inspection of whether or not the paste Pt is normally printed).

  Provided is a screen printing machine capable of preventing a reduction in substrate productivity without delaying the start of a screen printing operation even when a mask cleaning or a mask clogging inspection is performed.

DESCRIPTION OF SYMBOLS 1 Screen printer 2 Board | substrate 21 Mask 24 Squeegee 25 1st moving beam (1st moving body)
27 Second moving beam (second moving body)
29 Mask Imaging Camera 31 Board Imaging Camera 33 Mask Cleaner Pt Paste

Claims (3)

A screen printing machine that slides a squeegee on a mask in contact with the upper surface of the substrate to transfer the paste to the substrate, and then separates the substrate from the mask to print the paste on the substrate,
A mask imaging camera for imaging the mask in a state of being separated from the substrate from below;
A substrate imaging camera for imaging the substrate in a state separated from the mask from above;
A mask cleaner that cleans the mask by sliding on the lower surface of the mask in a state of being separated from the substrate;
The mask imaging camera and the mask cleaner are attached to a first moving body that horizontally moves below the mask,
The screen printing machine, wherein the board imaging camera is attached to a second moving body that horizontally moves below the first moving body independently of the first moving body.   By moving the first moving body and the second moving body independently of each other, the imaging of the substrate by the substrate imaging camera, the cleaning of the mask by the mask cleaner, or the imaging of the substrate by the substrate imaging camera The screen printing machine according to claim 1, wherein the mask imaging by the mask imaging camera is performed in parallel.   3. The screen printing machine according to claim 1, wherein imaging of the substrate by the substrate imaging camera includes imaging for inspecting a paste printed on the substrate. 4.

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