METHOD OF PLACING A COMPONENT ON A SUBSTRATE AND COMPONENT PLACEMENT MACHINE FOR CARRYING OUT THE METHOD

Abstract: The invention relates to a method of and a component placement machine for placing a component (10) onto a substrate (7), in which, after a component has been picked up by a placement head (6) secured to an arm (5) of a robot (2), the component is moved into an image field (18) of a stationary first imaging device (12) and the component is imaged, after which a second imaging device (13), which is also secured to said arm (5) of the robot, images a mark (21) of the substrate (7), subsequently the positions of the component and the position where the component is to be placed onto the substrate are calculated from the resulting image data, and finally the placement head places the component onto the substrate at the desired position. During imaging of the component (10), in order to compensate for inaccuracies in the distance between the placement head and the second imaging device, the first imaging device (12) also images at least one mark (16) situated on a reference plate (14) and at the same time the second imaging device (13) images a second mark (17) on the reference plate, after which the position of the component (10) relative to the second imaging device (13) is calculated from the resulting image data.

Description: Method of placing a component on a substrate and component placement machine for carrying out the method. The invention relates to a method of placing a component onto a substrate, in which, after a component has been picked up by a placement head secured to an arm of a robot, the component is moved into an image field of a stationary first imaging device and the component is imaged, a second imaging device, which is also secured to said arm of the robot, images a mark of the substrate, after which the position of the component and the position where the component is to be placed onto the substrate are calculated from the resulting image data and the placement head subsequently places the component onto the substrate at the desired position. Such a method is known from US-A-5, 084,959. In this known method the position of the component relative to the second imaging device is calculated after an image of the component has been made by means of the first imaging device. This is possible since a reference point of the placement head is always moved to a fixed position in the image field of the first imaging device and the distance between the reference point of the placement head and a reference point of the second imaging device is known. However, in practice this distance is not always found to be constant, which gives rise to an inaccuracy in the placement of the component on the substrate. The fact that this distance is not constant is caused in particular by temperature differences. However, other influences, such as undesired vibrations, may also give rise to erroneous measurements. It is an object of the invention to place a component at the desired position on a substrate with a high accuracy. To this end, the invention is characterized in that during imaging of the component the first imaging device also images at least one mark situated on a reference plate and at the same time the second imaging device images at least one other mark on the reference plate, after which the position of the component relative to the second imaging device is calculated from the resulting image data. The advantage of this method is that the position of the component picked up by the placement head relative to the second imaging device can be determined during the placement process of each component on the substrate. The desired position where the component is to be placed on the substrate is determined by means of the second imaging device. By means of the data of these two positions the robot can direct the placement head with the component exactly to the desired position in order to place the component. Preferably, for imaging the component the component is positioned at substantially the same image distance as the first mark. The invention also relates to a component placement machine comprising a frame, a robot, a transport system for the transport of substrates, a placement head for placing components onto the substrate, which placement head is secured to an arm of the robot, a first imaging device, which is fixedly connected to the frame, for determining the position of the component, and a second imaging device, which moves along with the placement head, for detecting a mark of the substrate. In order to place a component at the desired position on the substrate with a higher accuracy, the placement machine is characterized in that the placement machine comprises a reference plate having at least a first mark and a second mark, which marks are situated at a fixed distance from one another and which first mark is situated within the image field of the first imaging device during imaging of the component, while at the same time the second mark is situated within the image field of the second imaging device. The marks on the reference plate have been applied with a very high accuracy. Their exact position relative to one another is stored in an image processor, which calculates the instantaneous position of the component with the aid of the image data. Preferably, the reference plate has an opening which allows a component picked up by the placement head to pass through and the reference plate has at least one first mark adjacent the opening. This enables the component to be positioned in the opening in such a manner that the component, particularly contact faces or pins thereof, are disposed in the same image plane of the imaging device as that in which the mark of the reference plate is situated. Moreover, the reference plate is preferably disposed at substantially the same level as the substrate. This raises the imaging accuracy and hence the placement accuracy of the component. The invention will now be described in more detail with reference to an exemplary embodiment shown in the drawings, in which Fig. 1 shows a component placement machine for carrying out the method, Fig. 2 is a plan view showing a reference plate and a substrate, and Fig. 3 is a side view of the placement head and the imaging devices in a position for imaging. The component placement machine in Fig. 1 comprises a machine frame 1 carrying an X-Y robot 2. The robot is formed by a slide 3, which is movable in the Y- direction over two parallel guide members 4 of the frame and which is movable along the slide 3 in the X direction by means of an arm 5. The arm carries a component placement head 6. The machine has a transport mechanism for the transport of substrates, for example printed circuit boards, through the machine. Of this transport mechanism only the conveyor belt 8 is shown. The component placement head 6 comprises a suction nozzle 9 by means of which components 10 are picked up from a component feeder 11, which are subsequently placed onto the substrate 7. The suction nozzle can be driven in a Z direction and a φ direction. In the φ direction means that the nozzle can perform an angular rotation φ about its longitudinal axis. In order to place the components very accurately at the desired position on a substrate, the machine comprises a first imaging device 12, which is fixedly secured to the frame, and a second imaging device 13, which is secured to the arm 4 of the robot, adjacent the placement head. The machine further comprises a reference plate 14. The reference plate has an opening 15. This opening is so large that the component can pass through the opening. Near the opening the reference plate has first marks 16, in then present example four. The reference plate has a second mark 17 at some distance from the opening. The second mark has a very accurate and known position relative to the first marks. The stationary first imaging device 12 is disposed underneath the opening 15 of the reference plate. Both the opening 15 and the first marks 16 surrounding this opening are situated within the image field 18 of the imaging device. The reference plate is preferably made of a transparent material. The method of placing a component onto a substrate will be described hereinafter with reference to Figures 2 and 3. The robot is first directed to the component feeder 11 , where the suction nozzle 9 of the placement head 4 picks up a component 10 with the aid of a partial vacuum. The placement head 4 is then positioned above the reference plate 14 and the component is moved into the opening 15 of the reference plate. At this instant the second mark 17 is within the image field 19 of the second imaging device 13. The first imaging device 12 now images the component 10 and the marks 16 surrounding it and the second imaging device 13 images the second mark 17. Preferably, these images are made at the same time. The image data is applied to an image processor 20, which calculates the instantaneous position of the component relative to the second imaging device. Subsequently, the robot positions the second imaging device 13 above a mark 21 of the substrate 7. The position of this mark 21 relative to the position where the component is to be placed onto the substrate is know accurately and is stored in the image processor. Now the second imaging device 13 images the second mark 21 on the substrate and applies the resulting image data to the image processor. The image processor calculates the position of the second imaging device 13 relative to the position where the component is to be placed onto the substrate. Since the position of the component relative to the second imaging device is also known, the relative position of the component with respect to the position where the component is to be mounted on the substrate is now also known accurately, in the X, Y and Z directions and in the φ direction. By means of this data the placement head 6 can be directed accurately to the desired position in order to place the component 10 onto the substrate 7. In practice, the position of the component is generally defined by the positions of the contact pins 22 and the position of the substrate, with which the contact pins should make contact, is defined by the positions of the contact pads 23. For determining the position relative to the second imaging device this device has a reference point 24. The reference plate does not require an opening in order to image the component. However, the advantage of an opening is that the component can be positioned in the opening, as a result of which the component and the mark of the reference plate are disposed at substantially the same level and, consequently, at the same image distance from the imaging device. This results in an increased accuracy of the measurement. Preferably, the reference plate is disposed at the same level as the substrate. The imaging sequence is not essential. For example, it is also possible that first a mark of the substrate is imaged and subsequently the component is imaged.

Claims: CLAIMS: 1. A method of placing a component onto a substrate, in which, after a component has been picked up by a placement head secured to an arm of a robot, the component is moved into an image field of a stationary first imaging device and the component is imaged, a second imaging device, which is also secured to said arm of the robot, images a mark of the substrate, after which the position of the component and the position where the component is to be placed onto the substrate are calculated from the resulting image data and the placement head subsequently places the component onto the substrate at the desired position, characterized in that during imaging of the component the first imaging device also images at least one mark situated on a reference plate and at the same time the second imaging device images at least one other mark on the reference plate, after which the position of the component relative to the second imaging device is calculated from the resulting image data. 2. A method of placing a component onto a substrate as claimed in Claim 1, characterized in that for imaging the component the component is positioned at substantially the same image distance as the first mark. 3. A component placement machine comprising a frame, a robot, a transport system for the transport of substrates, a placement head for placing components onto the substrate, which placement head is secured to an arm of the robot, a first imaging device, which is fixedly connected to the frame, for determining the position of the component, and a second imaging device, which moves along with the placement head, for detecting a mark of the substrate, characterized in that the placement machine comprises a reference plate having at least a first mark and a second mark, which marks are situated at a fixed distance from one another and which first mark is situated within the image field of the first imaging device during imaging of the component, while at the same time the second mark is situated within the image field of the second imaging device. 4. A component placement machine as claimed in Claim 2, characterized in that the reference plate has an opening which allows a component picked up by the placement head to pass through and the reference plate has at least one first mark adjacent the opening. 5. A component placement machine as claimed in Claim 3, characterized in that reference plate is disposed at substantially the same level as the substrate.

Inventors: OTTEN JOSEPH GERTRUDIS LEONARD, OTTEN, JOSEPH, GERTRUDIS, LEONARDUS
Applicants: PHILIPS ELECTRONICS NV, PHILIPS NORDEN AB, PHILIPS ELECTRONICS N.V.
Application year: 1997
Main classification: H05K13
IPC codes: H05K13