JPH0968418A - Soldering inspection method and apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the detection accuracy of a soldered part by matching an alignment mark on the side of a single-sided circuit board and an alignment mark on the side of a double-sided circuit board to achieve an accurate detection of the position of the alignment marks. SOLUTION: A model single-sided circuit board having an alignment mark soldered thereon is irradiated previously with X-rays of an X-ray source 1 to store an image into an image memory 4a for one side. In detection, a double- sided circuit board having an alignment mark soldered thereon is irradiated with the X-rays to store the image into an image memory 4b for two sides. More than one alignment marks are carved from the respective X-ray images of the single-sided board and the double-sided board and undergoes a binary coding to obtain correct alignment mark images. A calculator 5 determines the coordinates of the centers of gravity of the respective images from the binary-coded image. Then, both the alignment marks are made to match each other by computing a transformation of coordinate coefficient and a coordinate difference is determined to obtain a differential image. Thus, alignment mark positions of the single-sided board and the double-sided board can be detected accurately thereby improving the detection accuracy of a soldered part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an object to be inspected, which is positioned by a sample stage and soldered with electronic parts.
The present invention relates to a soldering inspection method and apparatus for inspecting a soldered portion of the electronic component by using a transmitted X-ray image obtained by irradiating a ray.

[0002]

2. Description of the Related Art As a soldering inspection method using X-rays as described above, those disclosed in, for example, JP-A-3-218409 and JP-A-5-99643 are known. These known methods utilize the fact that the X-ray absorptivity of the soldering part is larger than that of the circuit printed part made of another substrate material or copper foil, and the substrate is irradiated with X-rays to transmit the X-rays.
By binarizing the line image with a predetermined threshold value, the image of the soldered portion is extracted from the transmission X-ray image of the board to determine the presence or absence of the defect, and especially on both sides. It is intended to provide a soldering inspection method for a double-sided board on which components are mounted. In such a double-sided board, the soldered parts may overlap on the front and back sides, so simply use X.
Even if the wire is irradiated and it is binarized,
It cannot be evaluated separately from the soldered part on the back surface. Therefore, according to the above-mentioned known method, a transmission X-ray image of a board having components mounted on one side is captured in advance outside the inspection process and stored, and a transmission X-ray image of the double-sided board is captured during inspection of the double-sided board. At the same time, the previously stored transmission X-ray image for one side is subtracted from this image. As a result, a transmission X-ray image on the other surface side can be obtained. The soldering inspection of the other surface side is performed by determining the quality of the soldering portion for this image. Regarding the above one side,
This can be determined by subtracting the transmission X-ray images of the other surface from the transmission X-ray images of the both surfaces.

However, in the above-described known method, if the transmission X-ray image on both sides and the transmission X-ray image on one side cannot be accurately superposed, an error occurs in the difference image, and the accuracy of defect determination is significantly deteriorated. . Therefore, the applicant of the present application, in Japanese Patent Application No. 6-186002, obtains the position of an alignment mark provided in advance on the substrate when obtaining the difference image, and aligns the double-sided substrate and the single-sided substrate on the basis of this alignment mark position. After that, the difference image is calculated. The above alignment marks are created in the same way as a printed circuit with copper foil when creating a printed circuit for each board.
The position with respect to the printed circuit is formed extremely accurately, and the above-described method with reference to this can be used to perform positioning with substantially extremely high accuracy.

[0004]

However, the usual alignment marks as described above are either copper foil or have a thin solder coating formed on the alignment marks, and the printed circuit portion and the X-ray transmittance are not increased. The position of the alignment mark is not clear because there is almost no difference in the transmission X on one side.
There is a problem in the accuracy of alignment between the line image and the transmission X-ray images on both sides, and there is a disadvantage that the accuracy of the difference image is not good. Therefore, an object of the present invention is to improve the accuracy of alignment between the single-sided substrate and the double-sided substrate by making it possible to clearly recognize the positions of the alignment marks that serve as the position reference. As a result, even if the image detection of the soldered portion on one side and the image detection of the soldered portion on both sides are performed by different devices, the both can be accurately aligned.

[0005]

In order to achieve the above object, the main means adopted by the present invention is to irradiate an X-ray on a board having a component soldered on one side in advance, and to X-ray the one-sided board. A single-sided X-ray image storage step of pre-storing the X-ray transmission image, and a double-sided X-ray image in which X-ray transmission images of the double-sided substrates are stored by irradiating the substrate with soldered components on both sides with X-rays during inspection An X-ray transmission image of the double-sided substrate stored in the double-sided X-ray image storing step in a state where the images of common alignment marks formed on the single-sided substrate and the double-sided substrate are matched, and the single-sided X-ray image. Soldering including a difference image inspection step of superimposing the X-ray transmission image of the single-sided board stored in the line image storage step and performing a soldering inspection of the other surface side of the board by the difference image of both images. In the inspection method, An alignment mark soldering step of soldering some or all of the alignment marks common to the single-sided board and the double-sided board is provided, and the alignment mark on the single-sided board and the alignment on the double-sided board that have been soldered The soldering inspection method is characterized in that the marks are matched with each other in the difference image inspection step.

According to the present invention, by soldering the alignment mark portion, the X-ray shielding rate in the alignment mark portion can be remarkably increased as compared with other substrate portions and circuit printed portions, so that the transmitted X-rays are used. The position detection accuracy of the present invention that superimposes a single-sided image and a double-sided image on the basis of the position of the detected alignment mark can be significantly improved. In addition, since at least soldering of the double-sided board to the alignment mark is performed in the cream solder applying step in the board manufacturing process, the reproducibility of the soldering amount to the alignment mark can be improved, and the alignment mark position with high accuracy can be obtained. The detection can be repeated. In addition, the present invention as an apparatus irradiates an X-ray on a substrate having a component soldered on one side in advance, and stores an X-ray transmission image of the one-sided substrate in advance, and at the time of inspection, the component is on both sides. The soldered board is irradiated with X-rays to store an X-ray transmission image of the double-sided board, and the double-sided X-ray is imaged in a state where images of common alignment marks formed on the single-sided board and the double-sided board are matched. The X-ray transmission image of the double-sided substrate stored in the image storing step and the X-ray transmission image of the single-sided substrate stored in the single-sided X-ray image storing step are superposed, and the other surface of the substrate is determined by the difference image between the two images. In a soldering inspection device for performing a soldering inspection on one side, an alignment mark soldering means for soldering a part or all of alignment marks common to the one-sided board and the double-sided board is provided, and the soldering is performed. An alignment mark of a single-sided substrate having undergone treatment, and is configured with an alignment mark of a double-sided substrate as the soldering inspection apparatus characterized by match in the difference image inspection process.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments embodying the present invention will be described below with reference to the accompanying drawings to provide an understanding of the present invention. It should be noted that the following embodiments are examples embodying the present invention, and do not limit the technical scope of the present invention. 1 is a flowchart showing the procedure of the inspection method according to the embodiment of the present invention, FIG. 2 is a graph showing the image density of the alignment mark, FIG. 3 is a block diagram showing the entire inspection apparatus, and FIG. 6 is a flowchart showing a processing procedure for obtaining an image centroid of an alignment mark. As shown in FIG. 3, the apparatus according to this embodiment includes an X-ray source 1, an X-ray image detector 3 for detecting X-rays emitted from the X-ray source 1 through a substrate 2, and the X-ray image detector. 3 has an image memory 4 for storing the X-ray transmission amount data from the image data 3 together with the coordinates of the image, and a computer 5 for processing the data from the image memory 4 to evaluate the soldered portion on the board 2. ing. The image memory 4 includes a single-sided image memory 4a for storing an X-ray transmission image of one side of a double-sided board to be inspected prior to the inspection, and a double-sided image memory for storing an X-ray transmission image of the double-sided board taken at the time of inspection. And a memory 4b.

In this embodiment, cream solder is applied to the alignment mark portion at the manufacturing stage of the double-sided board to be inspected prior to the inspection of the soldered portion.
Also, cream solder is applied to an alignment mark common to the alignment mark provided on the double-sided board of the single-sided board in which components are mounted only on one side of the double-sided board to be inspected, and As in the prior art, the X-ray irradiation from the X-ray source 1 is performed prior to the inspection, and the image data thereof is stored in the single-sided image memory 4a. At this time, a model substrate having no defect is used as the one-sided substrate. At the time of actual inspection, X-ray irradiation is performed on the double-sided board that is the object of measurement, and a transmitted X-ray image of the double-sided board is stored in the double-sided image memory 4b each time. Next, the difference image between the X-ray image of the double-sided board and the X-ray image of the single-sided board is calculated and displayed according to the procedure as shown in FIG. In FIG. 1, S1, S2 ...
Indicates the processing procedure number.

S1 ... From the X-ray image of the single-sided substrate and the X-ray image of the double-sided substrate already obtained as described above, two or more alignment mark portions are cut out from each image. The position of the alignment mark in the transmission X-ray image is known in advance. Therefore, the alignment mark is cut out by designating a region slightly wider than the region where the alignment mark is supposed to be formed. Regarding the cut-out alignment marks, since the solder mainly contains lead or tin as a component, the X-ray absorption performance is high. Therefore, the soldered alignment marks are clearly cut out by binarization. FIG. 2 shows the case without solder (1), the case with cream soldering (2), and the case with manual soldering (3). In this way, a clear change appears in the transmitted X-ray density when compared with the case where there is soldering. In particular, when cream solder is applied, a clear parabolic concentration distribution is obtained as shown in FIG. 2B as compared with the case of hand soldering. This is due to the shaking of the hands of the operator when using hand soldering, and in the case of cream soldering, there is no shaking of the hands of an automatic machine and the surface of the solder when using cream soldering. It is considered that the solder melted by the tension becomes a hemisphere accurately. Therefore, it can be seen that by applying cream solder to the alignment mark, the cutout accuracy by binarization can be increased, and thus the position of the center of gravity calculated from the binarized image is almost equal to the center of the mark.

S2 ... Then, the cut-out alignment mark image is binarized to obtain an accurate alignment mark image. S3: The barycentric position coordinates in each of the binarized images are obtained. How to obtain this will be described later. S4 ... Sequentially, the center of gravity of the alignment mark of one-sided image (there are two or more) and the position of the center of gravity of the alignment mark of the double-sided image (2
The coordinate conversion coefficient for superimposing the above is calculated. Since the two-dimensional coordinates are superposed, the coordinate conversion coefficient can be calculated if there are at least two position coordinates. However, if the position accuracy of the cut-out alignment mark is questionable, a conversion coefficient may be obtained for three or more coordinates and the average thereof may be taken. S5: If the coordinate conversion coefficient is obtained by the above processing, the difference between the coordinate obtained by performing the coordinate conversion on one image and the other coordinate is obtained (this difference data becomes the difference image), and this is calculated. indicate. With this, a transmission X-ray image of the component on the other surface side of the double-sided board is obtained, so that the soldered portion on the other surface side can be evaluated based on this image.

A method of obtaining the barycentric coordinates of the alignment mark in S3 will be described. The computer 5 obtains the barycentric position coordinates of the binary image of the alignment mark on one side and the binary image of the alignment mark on both sides by the method described below. There are the following two methods for obtaining the barycentric position coordinates. A method in which the image of the alignment mark portion is binarized with a certain density as a threshold value, and the center of gravity (X, Y) of the binarized image is obtained by the following formula. X = Σ (X _i ) / n Y = Σ (Y _i ) / n ... X _i is the X coordinate of the binarized image, Y _i is the Y coordinate of the binarized image, and n is the binarized The number of pixels that have been processed. A method of determining the volume centroid (X, Y) of a portion of the alignment mark that exceeds a certain density. X = Σ (X _i × P _ij ) / Σ (P _ij ) (P _ij ) is the pixel density Y = Σ (Y _i × P _ij ) / Σ (P _ij ) ...

[0012]

[Embodiment] Both the method of calculating the center of gravity used in the above-described embodiments have a drawback that they are affected by the difference (sampling) in the data extracted from the alignment mark.
According to the method described below, the error in the difference image due to the difference in the data for obtaining the center of the transmission X-ray image of the single-sided substrate and the transmission X-ray image of the double-sided substrate can be reduced. N binary images are obtained when the X-ray image of the alignment mark portion is partitioned by n threshold values. The above calculation is performed for each of the n binary images to obtain n barycentric positions (XG _i, YG _i ) (where i = 1 to n). The alignment mark center position (XG _, YG) is calculated from the obtained center of gravity position (XG _i, YG _i ) by the following equation. XG = ΣXG _i / n YG is ΣYG _i / n ...

In order to further improve the accuracy in the above method, it is desirable to increase the number of data items extracted from the binarized image cut at a certain threshold value. The X-ray image of the alignment mark for cream soldering is shown in Fig. 2.
Since it is parabolic as shown in (2), it is the boundary between the alignment mark and the substrate part (outside of the alignment mark).
The closer to the line, the larger the number of data and the higher the accuracy. Image sagging occurs in the X-ray image due to the response characteristics of the imaging system, and it is desirable to obtain a threshold value within the half-value width of the sag, which is close to the contour, in order to obtain a contour that is substantially the same as the contour of the alignment mark. The half-value G of the peak density G _p of the alignment mark and the average density G _a of the substrate level is given by G = (G _p + G _a ) / 2. For this reason, the upper limit of the threshold value for obtaining a plurality of cross sections is set to a value close to G _a , and the lower limit is set to a value separated from the substrate level by the half value G, and n values (including the upper limit and the lower limit) are included therebetween. By setting the threshold value, more accurate position detection can be performed.

FIG. 4 shows a procedure for obtaining the alignment mark center position coordinates (XG _, YG) in this case.
That is, first, the alignment mark portion is cut out from the transmission X-ray image of the single-sided substrate or the double-sided substrate (P1), and the substrate level density G _a and the alignment mark peak value G _{p are obtained.}
Then, the half value G is obtained from the above equation (P2). Further, with the upper limit of the substrate level concentration G _a , the half value G
Is set as the lower limit, and n binary images are obtained with n thresholds between them (including the upper and lower limits) (P3). In the n binary images thus obtained, n barycentric positions (XG
_i, YG _i ) is obtained by an equation (P4), and the alignment mark center position coordinates (XG _, YG) are obtained from the obtained barycentric position using the above equation.

[0015]

According to the present invention, by soldering the alignment mark portion, the X-ray shielding rate in the alignment mark portion can be remarkably increased as compared with other substrate portions and circuit printed portions, so that the transmission X The position detection accuracy of the present invention that superimposes a single-sided image and a double-sided image on the basis of the position of the alignment mark detected by the line can be significantly improved. Further, by performing the soldering to the alignment mark in the cream solder applying step in the board manufacturing process, the reproducibility of the soldering amount to the alignment mark can be improved, and the position detection of the alignment mark with high accuracy can be repeated. It can be carried out. By estimating the average position of the center of gravity of the plurality of cross sections of the alignment mark portion as the position of the alignment mark, it is possible to eliminate the error in image sampling and reduce the accuracy due to the variation in sampling. Therefore, even when the X-ray imaging of the soldered portion between the single-sided board and the double-sided board is performed by another device, a difference image with less error can be obtained. Further, by taking a plurality of cross sections of the alignment mark between the substrate level and the half value between the alignment marks and the substrate level, the position detection error can be further eliminated.

[0016]

[Brief description of drawings]

FIG. 1 is a flowchart showing a procedure of an inspection method according to an embodiment of the present invention.

FIG. 2 is a graph showing the image density of alignment marks.

FIG. 3 is a block diagram showing the entire inspection apparatus.

FIG. 4 is a flowchart showing a processing procedure for obtaining an image centroid of an alignment mark.

[Explanation of symbols]

 1 ... X-ray source 2 ... Substrate 3 ... X-ray image detector 4a ... Single-sided image memory 4b ... Double-sided image memory 5 ... Calculator

Claims (5)

[Claims] 1. A single-sided X-ray image storage step of irradiating an X-ray on a substrate having a component soldered on one side in advance to previously store an X-ray transmission image of the single-sided substrate, and a double-sided image at the time of inspection. Double-sided X-ray image storing step of irradiating the substrate on which the components are soldered with X-rays and storing an X-ray transmission image of the double-sided substrate, and images of common alignment marks formed on the single-sided substrate and the double-sided substrate, respectively. In a state of matching the X-ray transmission image of the double-sided substrate stored in the double-sided X-ray image storage step and the X-ray transmission image of the single-sided substrate stored in the single-sided X-ray image storage step, In a soldering inspection method comprising a difference image inspection step of performing a soldering inspection on the other surface side of the board by a difference image of images, a part or all of alignment marks common to the single-sided board and the double-sided board are provided. Soldering A soldering step for aligning the alignment mark on the one-sided substrate side and the alignment mark on the two-sided substrate side, which have been subjected to the soldering process, in the difference image inspection step. Inspection methods. 2. The soldering inspection method according to claim 1, wherein the alignment mark soldering step for the double-sided board is performed in a cream solder applying step in the board manufacturing step. 3. The soldering inspection method according to claim 1, wherein the position of the alignment mark is determined by an average value of a plurality of sectional center of gravity of the alignment mark portion. 4. The soldering inspection method according to claim 1 or 2, wherein a plurality of cross sections of the alignment mark are obtained by binarization with a half value between the substrate level and the alignment mark as a threshold value. 5. A substrate having a component soldered on one side is irradiated with X-rays in advance, an X-ray transmission image of the one-sided substrate is stored in advance, and the components are soldered on both sides at the time of inspection. The double-sided X-ray image storing step in which the X-ray transmission image of the double-sided substrate is stored by irradiating the double-sided substrate with X-rays and the images of the common alignment marks formed on the single-sided substrate and the double-sided substrate are matched. The X-ray transmission image of the double-sided board stored in step S1 and the X-ray transmission image of the single-sided board stored in the single-sided X-ray image storage step are overlapped, and the difference image between the two images is used to solder the other side of the board. A soldering inspection device for performing a soldering inspection is provided with an alignment mark soldering means for soldering some or all of the alignment marks common to the single-sided board and the double-sided board, and the soldering process is performed. A soldering inspection apparatus characterized in that an alignment mark on the side of a single-sided board and an alignment mark on the side of a double-sided board are matched in the difference image inspection step.