Patent Application
20060000872
1. Field of the Invention
The present invention relates to a technique for checking whether mounted parts are correctly soldered on a printed circuit board, and particularly relates to an inspection technique for accurately predicting soldering defects before soldering the parts in a reflow oven.
2. Description of the Related Art
In printed circuit board assemblies, visual inspections by human eyes or by appearance inspection devices that replace human eyes have been conducted to check whether mounted parts are correctly soldered.
For example, Japanese Patent Laid-Open Publication No. 10-311807 (hereinafter referred to as Reference 1) discloses a technique for calculating reference states of solders deformed by area array parts such as BGA (Ball Grid Array) and CSP (Chip Scale Package) and checking the soldering quality with reference to the reference states by an inspection device using X-rays. Japanese Patent Laid-Open Publication No. 10-170455 (hereinafter referred to as Reference 2) discloses a technique for detecting a shadow of lead in a solder alloy with use of X-rays and checking the soldering quality based on the shadow.
Japanese Patent Laid-Open Publication P No. 2002-134899 (hereinafter referred to as Reference 3) discloses an inspection line technique. According to this technique, an inspection is performed after each process, including an inspection of solder printed states after a printing process, an inspection of part mounted states of mounted parts after a mounting process, and an inspection of soldered states after a reflow process. Detecting defects in theses processes with this technique assures high density mounting quality, contributes to part size reduction, and facilitates repair of defected defects. Additionally, measurement values obtained in each process are fed back and fed forward so as to provide accurate and efficient quality control.
Japanese Patent Laid-Open Publication No. 2003-110299 (hereinafter referred to as Reference 4) discloses an inspection device capable of simultaneously inspecting mounted chip parts and solder printed states of area array parts. As this inspection device can perform inspections that have been conventionally performed by two inspections devices, the amount of equipment investment is reduced.
With recent advances in high density mounting on printed circuit boards for facilitating size reduction, performance enhancement and speed improvement of products, a need for assembly inspection methods for high density mounting is increasing. On the other hand, for example, with the rise of China in the field of printed circuit board assembly, many mass-production type printed circuit boards, including printed circuit boards of easy-to-assemble and non-high density mounting types, are now produced in China. This, in turn, has increased production of a wide variety of printed circuit boards in small quantities (and occasionally large quantities) or a high-mix low-volume production in Japan.
Combinational use of a high-speed chip mounting device and an odd-shaped part mounting device, which is used to mount odd-shaped parts such as IC (Integrated Circuit) or connectors, has been popular so far. However, it is being shifted to combinational use of plural odd-shaped part mounting devices. This is because the increase of ASICs (Application Specific Integrated Circuits) has reduced the number of mounted parts. Time that can be used for arrangements and setup of these mounting devices is becoming tight.
These circumstances demonstrate a growing need for solder inspection devices, processes, and methods that are applicable in production of printed circuit boards with reduced number of parts and in high-mix low-volume production.
Conventional inspections by appearance inspection devices or human eyes after soldering cannot assure inspection quality when facing future challenges such as part size reduction, use of area array parts and improvements of mounting density.
In the case of the methods using X-rays disclosed in References 1 and 2, soldered states of area array parts that cannot be checked by appearance inspections can be checked by irradiating X-rays. However, the methods are disadvantageous in that X-ray devices are expensive, the number of X-ray operators is limited, and defect repair is difficult even if defects are detected.
The technique disclosed in Reference 3 can realize efficient quality control by providing an inspection device for each assembly process performed before a soldering process. However, with this technique, it is not possible to detect defects that occur after a part mounting (placement, installation) process, including adhesion of foreign materials such as small parts to solder printed areas of area array parts. Another issue with this technique is that an inspection device is required to be provided for each assembly process, resulting in increase of equipment investment and extra task of setting-up each inspection device. That is, this technique is effective in large volume production, but is not effective in small volume production.
The technique disclosed in Reference 4 and other similar techniques known in the art uses an inspection device, which has a function of measuring solder printed shapes on areas where parts are not mounted and measuring mounted states of the parts on areas where the parts are mounted, installed at a most effective inspection point between a high-speed chip part mounting device and an odd-shaped part mounting device, instead of using an inspection device provided for each process. These techniques are somewhat useful in high density mounting. However, soldered states on the area where the parts are mounted cannot be checked, and therefore soldered states of chip parts mounted in high density cannot be checked.
A problem with the techniques described above is that a printed state of a solder paste and mounted states of parts cannot be efficiently checked with low cost.
An object of the present invention is to solve at least one problem described so as to improve the quality of printed circuit boards and the productivity of printed circuit boards.
To achieve the above and other objects of the present invention, in an inspection of a printed circuit board on which a solder paste is printed such that a part or parts are mounted on the solder paste, the quality is checked by not merely performing print pattern matching of a solder paste and examining the solder shapes and deformation after mounting parts, but also by calculating the amount of the solder paste not covered by electrodes after mounting the parts. In other words, the amount of the solder paste not covered by the electrodes of the parts mounted on the solder paste is calculated based on image data, which is captured by an imaging device such as a CCD camera and/or a laser measuring device, showing a state of the part mounted on the solder paste. Then, if the non-covered amount is greater than a predetermined upper limit or smaller than a predetermined lower limit, it is determined that the solder paste is incorrectly printed.
According to the present invention, states of a solder printed on the printed circuit board, mounted states of parts, and deformation of the solder under the mounted parts can be efficiently measured with a simple structure. Therefore, the present invention allows a significant reduction of defect rates of printed circuit boards and is applicable in high-density mounting and multi-mix variable-quantity production.
An exemplary embodiment of the present invention is described below with reference to the accompanying drawings.
A mounting inspection device 10 shown in
The inspecting section 10a provides a function for checking the quality by not merely performing print pattern matching of a solder paste and examining the solder shapes and deformation after mounting parts, but also calculating the amount of the solder paste not covered by electrodes after mounting the parts.
More specifically, the inspecting section 10a provides a function for storing image data, which image data is captured by the camera 11 and the laser measuring machine 12 and shows a mounted state of the part with respect to the solder paste, into a storage unit (not shown), a function for calculating the amount of solder not covered by an electrode of the part mounted on the solder paste, and a function for determining whether solder paste is incorrectly printed if the calculated non-covered amount is greater than a predetermined upper limit or lower than a predetermined lower limit.
The inspecting section 10a further provides a function for finding a mounted state of the part on the solder paste based on the image data, and a function for determining that the part is not correctly mounted if the found mounted state is different from a predetermined correct state.
The inspecting section 10a further provides a function for finding the height of the part mounted on the solder paste relative to the surface of the printed circuit board, and a function for determining that the solder paste is insufficient or that the part is missing if the height is smaller than a predetermined lower limit associated with the part and determining that a foreign material is adhered to the solder paste if the height is greater than a predetermined upper limit associated with the part.
The inspecting section 10a further provides a function for finding the height of the part mounted on the solder paste relative to the surface of the printed circuit board and detecting whether the solder paste has a portion not covered by the electrode at a position lower than the height of the part, a function for determining that the solder paste is insufficient or that the part is missing if the found height of the part is smaller than a predetermined lower limit associated with the part, determining that a foreign material is adhered to the solder paste if the found height of the part is greater than a predetermined upper limit associated with the part, and determining that the solder paste is insufficient if it is detected that the solder paste does not have a portion not covered by the electrode at a position lower than the height of the part.
The inspecting section 10a further provides a function for detecting insufficiency of the solder paste, print misalignment, part misalignment on the solder paste, missing parts, wrong parts, parts mounted in a wrong orientation, and lifted parts, and a function for detecting insufficiency of the solder paste, print misalignment, print smudge, and foreign materials on the solder paste based on image data, which is captured by the camera 11 and the laser measuring machine 12 before mounting the part, showing the solder paste printed on the printed circuit board.
To provide these functions, the inspecting section 10a has a foreign material inspecting section 13, a print smudge inspecting section 14, a solder insufficiency inspecting section 15, a print misalignment inspecting section 16, a part misalignment inspecting section 17, a missing part inspecting section 18, an orientation error inspecting section 19, and an under-electrode solder insufficiency inspecting section 20.
The camera 11 and the laser measuring machine 12 can be used in combination for inspecting a state of the solder printed on the printed circuit board, a state of the mounted part, and a state of the solder under the electrode of the part. The camera 11 and the laser measuring machine 12 are not necessarily used in combination, and it is possible to use only one of them.
The inspecting section 10a provides a function for inspecting a state of the solder printed on the printed circuit board before part mounting, and a function for inspecting a state of the mounted part and a state of the solder printed on the printed circuit board after the part mounting. To provide the function for inspecting a state of the solder printed on the printed circuit board before the part mounting, the inspecting section 10a includes the foreign material inspecting section 13 for detecting foreign materials, the print smudge inspecting section 14 for detecting print smudge due to excess solder, the solder insufficiency inspecting section 15 for detecting solder insufficiency, and the print misalignment inspecting section 16 for detecting solder print misalignment.
To provide the function for inspecting the mounted part, the inspecting section 10a includes the part misalignment inspecting section 17 for detecting misalignment of the mounted part, the missing part inspecting section 18 for checking missing parts, the orientation error inspecting section 19 for detecting parts mounted in a wrong orientation, the under-electrode solder insufficiency inspecting section 20 for detecting solder insufficiency under the electrode of the part, a solder deformation inspecting section (not shown) for inspecting deformation of the solder under the electrode of the part, and a wrong part inspecting section (not shown) for detecting parts mounted in a wrong position.
The print smudge inspecting section 14, the solder insufficiency inspecting section 15, and the print misalignment inspecting section 16 serve not only in inspections before the part mounting but also in inspections after the part mounting.
There are two types of printed circuit board assembly lines. One is the type that includes different types of part mounting devices, and the other one is the type that includes the same type of part mounting devices. The number of the part mounting devices is not limited to two.
With this printed circuit board assembly and inspection line configuration, the mounting inspection device 10 is able to detect the cause of defects before soldering in the reflow oven 60. Therefore, occurrence of defects can be significantly reduced while assuring high density mounting. Moreover, such a line configuration allows changing of the position of the mounting inspection device 10 depending on the type of parts to be mounted. Accordingly, high-mix variable-volume production is easily achieved without increasing investment in inspection equipment and setup time.
The following describes inspection operations of the inspecting section 10a of
A foreign material (body 3 of a part) such as a chip part that is failed to be mounted or a piece of a tape of a part supply cassette is sometimes unexpectedly put on the printed circuit board depending on the state of the part mounting device (40) after the solder is printed by the solder printer (30).
The mounting inspection device 10 according to this embodiment captures image data of the state of the solders 4 on the pads 1 in a mount area on the printed circuit board with use of the camera (11), measures the area of the solders 4 based on the image data, and compares the measured area with an allowable value so as to check the presence of the foreign material (body 3 of the part). If the foreign material (body 3 of the part) is present, the area of the solders 4 that can be observed is reduced. Therefore, the presence of the foreign material (body 3 of the part) can be confirmed based on the area of the solders 4 portion.
It is difficult to detect such defects caused by the presence of a foreign material (body 3 of the part) after the area array parts are mounted on and soldered to the foreign material (body 3 of the part), because joint sections are located under the body 3 and therefor can not be seen from outside. If this foreign material inspection is not performed, these defects are not detected until a function inspection is performed. According to this embodiment, the presence of a foreign material (body 3 of the part) is checked before the part mounting. This makes it possible to take a measure such as removal of the foreign material (body 3 of the part) before the part mounting, and thereby avoiding difficult repairs after the soldering.
According to this embodiment, occurrence of print smudge is checked by capturing image data of the print state of the mount area on the printed circuit board with use of the camera (11) before the part mounting, measuring the area of the solders based on the image data, and comparing the measured area with an allowable value so as to check the presence of print smudge. If there is print smudge, the area of the solders that can be observed is larger than a predetermined upper limit. Therefore, the print smudge can be detected based on the measured area of the solders.
In this inspection, solder insufficiency is detected by capturing image data of the solders 4 on the pads 1 in the mount area on the printed circuit board with use of the camera (11), measuring the area of the solders 4 based on the image data, and comparing the measured area with a predetermined allowable value. For example, if the measured area of the solders r is equal to or lower than a predetermined lower limit, it is determined that the solders are insufficient. This inspection can also be performed in the same way after the part mounting.
According to this embodiment, image data of the states of the pads 1 and the solders 4 in the mount area on the printed circuit board are captured by the camera (11), and occurrence of print misalignment is checked based on the image data. Misalignment may be detected by finding positions of the solders 4 based on the image data of the solders 4 and comparing the found positions with reference positions provided in advance in the form of data. This inspection can also be performed in the same way after the part mounting.
As can be seen, in this mounting inspection device, defects due to solder print states that occur after the melting and reflow soldering can be detected both before (
According to this embodiment, image data of the states of the pads 1, the body 3 of the part, and the electrodes 2 of the part in the mount area on the printed circuit board are captured by the camera (11), and occurrence of part misalignment is checked based on the image data. Misalignment such as parallel displacement of
According to this embodiment, image data of a state around the pads 1 in the mount area on the printed circuit board is captured by the camera (11), and missing parts are checked based on the image data. If the outlines of the body 3 and the electrodes 2 of the part are not detected in the mount area on the printed circuit board, it is determined that the part is missing. In this inspection, detection of missing parts may also be performed by checking the presence of a region that is higher than the surfaces of the pads 1 by the height of the part in the mount area for the part with use of the laser measuring machine (12).
According to this embodiment, a wrong part is detected by capturing image data of a state around the pads 1 in the mount area on the printed circuit board with use of the camera (11), and reading a part ID, e.g. “102”, printed on the top of the body 3, and comparing the read part ID with a correct part ID, e.g. “103”.
According to this embodiment, such an orientation error is detected by capturing image data of a state around the pads 1 in the mount area on the printed circuit board with use of the camera (11), and reading a polar mark 7 based on the image data, and comparing the read polar mark 7 with a correct orientation. An IC part 14 shown in
In this inspection, the mounting inspection device 10 captures an image around the mount area on the printed circuit board with use of the camera (11) before reflow, acquires a section with a color indicating the solder (image data) through image processing, determines whether there is a portion of the solder not covered by the electrode 2 of the part based on the image data, and detects insufficiency of the solder under the electrode based on the determination result.
If there is a sufficient solder under the electrode 2 of the part, a portion of the solder 4 not covered by the electrode 2 of the part can be detected as shown at the left side of
Such solder insufficiency under the electrodes can also be detected with use of the laser measuring machine (12). First, a height (A) is measured by irradiating a laser beam onto the surface of the printed circuit board. Next, a height (B) of the electrode 2 of the part is measured by irradiating a laser beam at a position of the electrode 2 of the part based on the position information of the electrode 2. Then, it is determined whether a height (C) between the height (A) of the printed circuit board and the height (B) of the electrode 2 of the part is present, so that the solder insufficiency under the electrode is checked.
In this case, a portion of the solder 4 not covered by the electrode 2 can be detected by image capturing and image processing with use of the camera (11) or by height measuring with use of the laser measuring device in the same manner as in the case described above.
According to this embodiment, the area of a solder portion not covered by electrodes of the odd-shaped parts is calculated, and the measured area is compared with an allowable value so as to detect the presence of the foreign material. If the foreign material is present, the area of the solder portion that can be observed in image data captured by the camera (11) is reduced. Therefore, the presence of the foreign material can be detected based on the area of the solder portion.
Moreover, as shown in
Three-dimensional measuring techniques using a CCD camera or a laser measuring machine, for example, may be employed for the height measurement described above. An example of a technique for measuring an object in three dimensions with use of a CCD camera includes a technique disclosed in Japanese Patent Laid-Open Publication No. 2000-304520 wherein six lights are turned on, the image of reflowed solder fillet is captured by a CCD camera each time the lights are turned on, and the shape of the solder fillet is measured based on the luminance of pixels in the image.
An example of a technique for measuring an object in three dimensions with use of a laser includes a technique disclosed in Japanese Patent Laid-Open Publication No. 07-208948 wherein a laser beam is irradiated onto an object, and the reflected light is measured and computed to find the height of the object, and a technique wherein a plurality of laser beams are irradiated to realize highly accurate measurements.
The following explains “allowable value” with reference to
To find these allowable values, for example, a CCD camera or a laser measuring machine is moved to coordinates of a specified address so as to measure the area of the non-covered amount of the solder. Then, based on quality data after reflow soldering, if solder insufficiency occurs, the allowable value is set to a value of the measured non-covered area of the solder to which “1” is added. On the other hand, if a bridge occurs after reflow soldering, the allowable value is set to a value of the measured non-covered area of the solder from which “1” is subtracted.
As described above with reference to
More specifically, the quality of the solders are examined by computing the area of the solder not covered by the electrodes based on image data obtained by the camera or the laser measuring device, and comparing the computed area with predetermine allowable values. With these operations, a presence of foreign materials, solder insufficiency, print smudge, and print misalignment can be detected after mounting the parts.
In addition, part misalignment, missing parts, wrong parts, orientation errors of the mounted parts, solder insufficiency under the electrodes of the mounted parts, and openings due to lead curvature can also be detected after mounting the parts.
The use of the printed circuit board inspection device of the present invention eliminates the need for inspections after the melting and soldering process. This is very effective and efficient in view of future improvements in high density mounting techniques. In particular, it is sometimes difficult to check the appearance of joint sections because of interference of the height of mounted parts in inspections after soldering. If solder joint sections are located under the body of the mounted parts or the like, soldered states can not be checked by inspections after reflow soldering. If the printed circuit board inspection device of the present invention is employed, there is no need to perform such inspections after the reflow soldering. That is, because the printed circuit board inspection device of the present invention can predict defects that will occur after the soldering, areas that can not be checked after the soldering can be checked before the soldering. Therefore, circulation of defective printed circuit boards can be prevented. This makes it possible to provide high-quality and efficient printed circuit boards and electronic devices.
While the present invention has been described in terms of a preferred embodiment with reference to the examples illustrated in
It is understood that the inspecting section 10a does not necessarily have a computer including a keyboard and an optical disc drive device is used in the above embodiment. A computer not including them may be used alternatively. While an optical disc is used as a recording medium in the above embodiment, a FD (Flexible Disk) and the like may be used alternatively. As for program installation, the program may be downloaded and installed via a network with use of a communication device.
The present application is based on Japanese Priority Application No. 2004-193001 filed on Jun. 30, 2004, with the Japanese Patent Office, the entire contents of which are hereby incorporated by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-193001 | Jun 2004 | JP | national |
