JPH0481724B2 - - Google Patents

Description

Detailed Description of the Invention (Technical Field) The present invention is a soldering method for inspecting the soldering surface of a printed wiring board (printed circuit board) on which electronic components, etc. are mounted, for poor mounting conditions such as proximity, bridging, and chip component misalignment. This invention relates to a mounting appearance inspection method.

(Background Art) For example, when automatically inspecting the mounting soldering state of a printed wiring board on which electronic components such as chip components are mounted, conventionally, as shown in FIG. There is a method in which an inspection area S is set around the inspection area S, an image is taken with an ITV camera, etc., image processing is performed, and if the soldering part 12 does not enter the inspection area S, it is determined that the inspection area S is normal. However, with this method, in the case of high-density mounting, the distance between multiple soldering parts becomes short, making it difficult to set the inspection area at an appropriate position, and even if it is possible to set the inspection area,
Even a small amount of deviation of the chip component, which is acceptable, will cause the soldered part to enter the inspection area.
The drawback was that there were many false positives.

In addition, as another determination method, as shown in FIG. There is a method of inspecting the mounting state and soldering state based on the area of part a, which is the difference between the two parts (part b is the common part). However, in this method, when two adjacent chip parts 11A and 11B are shifted in a direction toward each other as shown in FIG. Errors such as close proximity and bridges often occurred, resulting in erroneous judgments. In addition, when it comes to misalignment of a single chip component, even if the misalignment exceeds the allowable value, it is often not necessary to judge it as defective if the soldering is done normally, making it difficult to determine the limit level of misalignment. There was a drawback.

(Objective of the Invention) An object of the present invention is to solve the above-mentioned technical problems and provide a soldering appearance inspection method that can accurately and automatically inspect the misalignment of mounted components and the soldering condition. do.

(Disclosure of the Invention) The present invention will be described in detail below with reference to the drawings showing embodiments. Note that although chip parts will be explained below as an example, it goes without saying that other electronic parts may also be used.

FIG. 1 is a configuration diagram showing an embodiment of an inspection apparatus embodying the present invention. In the figure, reference numeral 11 denotes a chip component mounted and soldered on a printed circuit board 10, which is illuminated by diffused lighting 6 from the surroundings and imaged by an ITV camera (industrial television camera) 1 from above. There is. The image signal of the ITV camera 1 is binarized for each pixel in the binarization processing unit 2 at a threshold level that makes the soldered part appear white, and also undergoes noise processing so that the parts other than the soldered part become black, and is subjected to expansion processing. Part 3 is given.
The expansion processing unit 3 is a characteristic part of the present invention, and performs processing to expand the binarized image (land) of the soldered part by 1/2 of the proximity limit distance. Next, this expanded binarized image is stored for one frame in the frame memory 4, a scan line and an inspection area are set on the frame memory 4, the outline is scanned, and the judgment processing unit 5 selects the adjacent The quality is determined by automatically detecting whether or not the mating soldered parts are in contact.

Through these processes, we check whether separate soldered parts are closer to each other than the limit distance (proximity), whether there is a bridge between soldered parts (bridged), and whether chip components are mounted out of alignment. It is possible to detect defective mounting conditions such as chip component misalignment.

Figure 2 shows the image processing in more detail, where A is the binarized image that is the output of the binarization processing section 2, and B is the dilated binarized image that is the output of the expansion processing section 3. It is. That is, the binarized images (lands) LAND ₁ to _{LAND 4} of the soldered parts of the chip components 11A and 11B within the imaging field of view S are 1/1 of the proximity limit distance.
By performing dilation processing by 2, dilated binary images (lands) LAND ₁ ′, LAND ₂ ′, and LAND ₄ ′ are obtained.
However, this expansion process causes chip parts to shift,
If solder is close to each other or bridging occurs, separate soldered parts will appear to be connected. By checking whether or not different lands are connected by the expansion process, it is possible to inspect the mounting state of components, proximity, bridging, etc. Note that in the above explanation, the land is set to be white, but it goes without saying that the land may be reversed and set to black.

Next, a method for detecting whether different lands are connected in an expanded binarized image will be explained. In this case, a rectangular inspection area is set as shown by S' in FIG. This inspection area S' is set so that it spans two adjacent lands and does not include the entire soldering part of each land, and is
The scan line L at the center is set at a position where it will not be cut off by the land when no defects such as bridge/chip component displacement occur.

Figure 3 is an enlarged view of the inspection area S', where A and B indicate that no close contact, bridging, or chip component misalignment has occurred, and C indicates that close proximity, bridge, or chip component shift has occurred. This is the case for defective products. The specific procedure is to scan the scan line L from the starting point _P1 , and if it can reach the ending point _P2 , it is considered normal. In other words, in a case like A, the starting point P ₁
Scanning is performed straight from the point to the end point _P2 .
Therefore, in this case, inspection can be performed extremely quickly. Also, if it intersects with the contour line of the land on the scan line L as shown in (b), the branch point
Scanning is performed from _P3 to one side, for example to the left, along the contour of the land, and if it reaches a point _P4 on the side that does not intersect with the scan line L of the inspection area S', it will scan to the branch point _P3 . Returning and redoing the scan in the opposite direction, if the scan line L merges with the scan line L at point _P5 , the scan line L is scanned again to the end point _P2 .
In this case as well, the end point _P2 was reached, so it is considered normal.
On the other hand, if the left and right lands are in complete contact as shown in C, no matter which direction you scan from branch point _P6 to the left or right, you will not be able to join the scan line L, and the inspection area
Since it arrives at a side that does not intersect with the scan line L of S', in this case, it is determined that the chip is defective because proximity, bridge, or chip component displacement has occurred.

Note that the processing shown in Figure 3 (b) and (c) scans the outline of the land, so it takes longer and the scanning speed is slower than in (a), but the printed wiring boards that are actually inspected are mostly in a normal soldered state. Since the processing state (a) occupies the majority, the overall processing time is short and inspection can be performed at extremely high speed.

(Effects of the Invention) As described above, in the present invention, the soldered portion of a printed wiring board that has been mounted and soldered is imaged by a television camera, the image signal is binarized for each pixel, and an expansion process is performed. This is an inspection method that stores one frame, sets a scan line and inspection area on this frame memory, scans the contour line, and automatically detects defects such as proximity, bridging, and chip misalignment in the judgment processing section. The image of the soldered part obtained by imaging is expanded by half of the proximity limit distance, an inspection area is set in the adjacent soldered area in this expanded image, and a scan line is drawn within this inspection area. By setting this and determining normality based on the relationship between the start and end points of the scan line, it is possible to inspect for proximity, bridging, chip misalignment, etc. even in high-density packaging.

() By setting the proximity limit distance, it is possible to detect true defects regardless of the absolute amount of deviation.

() A high-speed inspection is performed for normal mounting soldering, and a detailed inspection is performed for defective parts.
The overall inspection time is shortened and inspection can be performed at high speed.

There are other effects.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an inspection apparatus embodying the present invention, FIGS. 2 and 3 are explanatory diagrams of image processing, and FIGS. 4 to 6 are explanatory diagrams of a conventional appearance inspection method. 1...ITV camera, 2...Binarization processing unit, 3
...Expansion processing unit, 4...Frame memory, 5...
Judgment processing unit, 6... Diffuse illumination, 10... Printed wiring board, 11, 11A, 11B... Chip parts, S
...Imaging field of view, S'...Inspection area, LAND ₁ ~
LAND ₄ ...Binarized image, LAND ₁ ′, LAND ₂ ′,
LAND ₄ ′...Dilated binarized image.

Claims (1)

[Scope of Claims] 1. The soldered portion of a printed wiring board that has been mounted and soldered is imaged by a television camera, the image signal is binarized for each pixel, expansion processing is performed, one frame is stored, and this frame is This is an inspection method that sets a scan line and inspection area in memory, scans the contour line, and automatically detects defects such as proximity, bridging, and chip component misalignment in the judgment processing section. The image of the part is expanded by half of the proximity limit distance, and the inspection area is set in this expanded image so that it spans two adjacent soldering parts and does not include the entirety of each soldering part. At the same time, a scan line is set within this inspection area at a position that will not break if the soldering is normal, and the scan line is scanned from the start point of the scan line, and if it intersects with the outline of the soldered part, the branch is Scans on the contour line from a point, and if it joins the scan line again, scans on the scan line, and scans from the same branching point to the end point of the scan line without reaching both sides of the inspection area that do not intersect with the scan line. A soldering appearance inspection method characterized in that if soldering is completed, it is determined to be normal.