JPH06174444A - Soldered state inspection method for discrete type electronic component - Google Patents

Abstract

PURPOSE:To accurately judge defective items in addition to the quality of the soldered state by observing the defective soldering of a discrete type electronic component by the image processing technology. CONSTITUTION:The soldered portion of a discrete type electronic component to be inspected is photographed, the image is converted into the image signal in response to the density of the preset gradation, the density histogram of the number of picture elements corresponding to each density is generated from this image signal, the sum of the frequency difference between the density histogram for each density and the standard density histogram registered in advance for soldered state items is obtained, the standard density histogram having the minimum sum is specified, and a good product and defective items of a defective product corresponding to it are judged results.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for inspecting a non-defective product or a defective product as a solder form of a discrete type electronic component by image processing.

[0002]

2. Description of the Related Art As a means for inspecting a soldered portion of a discrete type electronic component, an image processing technique has been used instead of visual inspection. In this inspection, the most difficult thing for the operator is to quantify the soldering state determined to be normal or defective by visual inspection or other inspection method and input it to the automatic inspection determination parameter of the inspection machine. is there. Conventionally, items of good products and defective products are prepared, and the values of those parameters are manually changed and set based on trial and error (dry and error), which requires a great deal of time, labor, and intuition. I needed it.

[0003]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to observe solder defects of discrete type electronic components by image processing technology, and to accurately determine defective items as well as the quality of soldering state.

[0004]

To solve the above problems, the present invention takes an image of a soldered portion of a discrete electronic component to be inspected and converts it into an image signal corresponding to a density of a predetermined gradation, and from this image signal, Create a density histogram of the number of pixels corresponding to the density, obtain the sum of the frequency difference of the density histogram and the standard density histogram registered in advance for each solder form item at each density, and specify the standard density histogram with the smallest total sum. Corresponding to this, defective items such as non-defective products and defective products are used as the determination result.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows the general construction of an illumination system and system used in the method of the present invention. A substrate 1 to be inspected is placed on a flat plate-shaped inspection table 2, and can be illuminated by an omnidirectional illumination 3 in a shadowless state from any direction. For the omnidirectional illumination 3, for example, a hemispherical holder 4 is horizontally divided into eight stages, and a light source 5 such as a ring-shaped LED is arranged at each divided position. Here, all the ring-shaped light sources 5 are arranged so as to generate light that converges toward the surface to be inspected of the substrate 1 in a range from a high angle to a low angle.

A vertical line of the substrate 1 to be inspected, in other words, a camera 6 such as a CCD camera is arranged directly above the soldered portion and is connected to the image processing device 7. The image processing apparatus 7 contains an image processing program based on the solder form inspection method of the present invention, and executes the program for the soldered portion of the board 1 after positioning.

Next, FIG. 2 shows a soldering mode, that is, a picked-up image of holes and no solder as defective items of a good product and a defective product, a vertical cross section of a soldered part, and a pattern of a standard density histogram corresponding thereto. There is.
In the case of a good soldering state, the leads 8 of the discrete type electronic component project from the through holes 9 of the substrate 1 and the land 1 on the surface of the substrate 1 through the mountain-shaped solder 10.
1 is electrically connected and physically fixed.
The imaging screen at this time appears as a circular dark portion.

On the other hand, in the case of defective soldering with holes,
Blow holes 12 are formed around the leads 8.
At this time, the imaging screen forms a ring-shaped or C-shaped bright portion corresponding to the blow hole 12. Further, in the case of defective solder without solder, a bright circular portion of the land 11 and a small black dot corresponding to the end face of the lead 8 appear on the imaging screen, corresponding to the absence of the solder 10.

Then, depending on the form of these non-defective products and defective products (with no holes and no solder), for example, when the number of pixels for each density of 256 gradations is represented, a density histogram pattern appears. The patterns of these density histograms are
Since it corresponds to each soldering form and represents the characteristics thereof, it is stored in advance in the memory of the image processing device 7 as a pattern of a standard density histogram corresponding to a defective item of a good product or a defective product.

Next, FIG. 3 shows a flow chart of the solder form inspection method of the present invention. The program for this purpose is stored in the program memory of the image processing apparatus 7. As described above, the soldered portion to be inspected has a unique shape for each solder form, that is, a good product, a defective product with holes, and a defective product without solder, and the density histogram of these images appears as a unique pattern. These density histograms are registered in advance as patterns of standard density histograms representing defective items such as non-defective products or defective products.

First, in the first step after the start, the light source 5 at the uppermost stage (just above) is turned on, and the soldered portion to be inspected is set to a brightness suitable for imaging. In the next imaging step, the camera 6 images the soldered portion to be inspected, converts it into an image signal of 256 gradations for each pixel, and sends it to the image memory in the image processing device 7 to store it.

Next, the image processing device 7 reads the image signal of the soldered portion to be inspected from the image memory, totals the number of pixels for each density, creates a density histogram, and in the next step, the density histogram The total frequency of is converted into a constant value, and the pattern of the density histogram is normalized. In the next step, it is determined which of the registered standard density histogram patterns the density histogram of the soldered portion to be inspected is closest to. Therefore, in the next histogram difference calculation step, the program obtains the sum of the frequency differences at each density of the registered standard density histogram and the density histogram of the inspection target, and in the subsequent judgment output step, the sum of the frequency differences. The smallest standard density histogram of is specified, and the item of non-defective product, defective product with holes or defective product without soldering corresponding to this standard density histogram is specified, and it is used as the determination result.

In this series of steps, the standard density histogram closest to the soldering state of the inspection object is specified. Therefore, since it is classified into any of the standard density histograms registered in advance, it is possible to make an appropriate determination for each designated item. In addition, although the above embodiment exemplifies two defective states of defective products, that is, defective drilling and defective soldering, the defective soldering state is not limited to the above, and for example, a quantitative solder amount is used. It can also be used to judge pass / fail.

Conventionally, the density histogram has been used for determining the threshold level when binarizing an image, but the method of the present invention is used as a comparison pattern for inspection as described above. It functions as an inspection parameter.

[0015]

According to the present invention, the density histogram is used as the characteristic amount of the good product and the bad product in the solder form, and the characteristic pattern of the density histogram is stored for each defective item of the good product or the bad product. Thus, the image processing inspection of the soldering state can be automatically performed. Therefore, the operator only needs to apply the solder condition judged by visual inspection or other inspection method to the inspection machine and specify the density histogram pattern as a preset item of good product or defective product. The standard can be set easily.

[Brief description of drawings]

FIG. 1 is a block diagram of a configuration of an illumination system and an inspection system.

FIG. 2 is an explanatory view showing an image pickup screen of a soldering portion, a cross-sectional view of the soldering portion, and a pattern of a density histogram of an image signal for each of a non-defective product, a defective product with a hole, and a defective product without solder.

FIG. 3 is a flowchart of a solder form inspection method.

[Explanation of symbols]

 1 substrate 2 inspection table 3 omnidirectional illumination 4 holder 5 light source 6 camera 7 image processing device 8 lead 9 through hole 10 solder 11 land 12 blow hole

Claims (1)

[Claims] 1. An image of a soldered portion of a discrete electronic component to be inspected is imaged and converted into an image signal corresponding to a density of a predetermined gradation, and a density histogram of the number of pixels corresponding to each density is created from this image signal. Then, the sum of the frequency difference between the concentration histogram at each concentration and the standard concentration histogram registered in advance for each solder form item is obtained, and the form item corresponding to the standard concentration histogram with the smallest sum is used as the determination result. Method for solder form inspection of discrete electronic components.