JPH0446375B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method for inspecting a soldered portion of an electronic component soldered onto a board.

[Background of the invention]

FIG. 1A shows a state in which a component lead 101 of a flat package type component is connected to a pad 102 on a board via a soldering portion 103. In addition, in FIG.
Figure c also shows the state where the surface-mounted part 107 is connected to the soldered part 108 on the board 108.
9 shows the bonded state, but the reality is that small fillet defects have not been detected with good accuracy until now. Figure 2 a and b are the first
A cross-section of the soldered portion 103 and its surroundings in Figure A is shown for good and bad fillets, respectively.As a conventional fillet inspection method, the method disclosed in Japanese Patent Application Laid-Open No. 55-51342 is cited. . According to this method, the inspection object is irradiated with light from directly above, while the light reflected from the inspection object is detected directly above the inspection object. If the object to be inspected is scanned by sequentially moving the light irradiation area, the quality of the fillet can be known from the signal waveform of the detected light.

However, when the light 112 is irradiated in a spot shape from directly above and the reflected light is detected as shown in FIG. There is a problem in that the reflected light amount distribution is almost the same regardless of the difference. As shown in FIG. 3b, there is almost no difference between the light quantity distribution A for a small fillet and the light quantity distribution B for a good fillet.

On the other hand, by irradiating the light 112 from obliquely upward as shown in FIG.
It is also thought that there will be a big difference between However, when performing an inspection in this manner, there is a problem in that the optical path is interrupted by surrounding components, making it impossible to perform the inspection. Note that reference numerals 110 and 111 in FIGS. 2a and 2b, 3a and 4a indicate solder and a substrate, respectively.

[Purpose of the invention]

Therefore, it is an object of the present invention to provide a method for inspecting soldered parts that is not influenced by surrounding parts and that can inspect fillets with good precision even in the case of miniaturized soldered parts. It is in.

[Summary of the invention]

To this end, the present invention focuses on the fact that organic materials such as polyimide and glass epoxy that constitute the base material have a low band gap, but that the band gap of the solder, iron, and copper that constitute the soldering part is high. By irradiating light with a wavelength sufficiently shorter than the wavelength corresponding to the energy from directly above the inspection object as excitation light, fluorescence is generated only from the base material, and the quality of the fillet can be determined by the way this fluorescence is reflected at the fillet. It was made so that it could be known.

[Embodiments of the invention]

The present invention will be explained below with reference to FIGS. 5 to 9.

First, the principle of the present invention will be explained. Figure 5a
If the excitation light 5 is irradiated onto the inspection object from directly above the inspection object as shown in FIG.
There is also reflected fluorescence 7 that is reflected by the fillet as the outer surface of the solder 110 and reaches directly above. The degree to which the reflected fluorescent light 7 is reflected directly above the fillet differs depending on the shape of the fillet. That is, when looking at the reflected fluorescence 7 from the fillet from directly above, if the fillet is good, the reflected fluorescence 7 will be detected as a band with a large reflecting surface, but if the fillet is small, it will actually be detected as a band. Even if the reflective surface is large, the reflective surface will be made small and therefore detected as a band with a small width.
Alternatively, almost no reflected fluorescence 7 can be detected. FIG. 5b shows the light quantity distribution F when the fillet is good and the light quantity distribution E when the fillet is small, and it is clear that there is a difference. Therefore, if the width of the difference is greater than a certain value, it can be determined that the fillet is good, and if it is less than that, it can be determined that the fillet is small.

Now, the present invention will be specifically explained below with respect to flat package type parts, but it can be similarly applied to fillet inspection of pin type and surface mounted parts as soldering parts.

First, the soldering state of the flat package type component onto the board will be explained. FIG. 6 shows this state. As shown in the figure, a flat package type component 10 is connected to a pad 13 formed in advance on a substrate 12 by a solder fillet 14, so that a component lead 11 led out from the side surface of the component 10 is mounted on a substrate 12. Although the solder fillet 14 is mounted, the soldering part inspection apparatus shown in FIG. 7 is used to inspect whether or not a small defect has occurred in the solder fillet 14. That is, the inspection apparatus according to the present invention is entirely composed of a light irradiation system 19, a fluorescent image detection system 23, and a control system 27.
7, the drive of the X-Y table 28 on which the substrate 12 is mounted is controlled. First, the irradiation of excitation light onto the soldered portion will be explained. This is done by the light irradiation system 19. The spot-shaped excitation light from the Ar laser 15 is made into a slit by cylindrical lenses 16 and 17, and is then irradiated onto the soldering portion through a dichroic mirror 18 that reflects only the wavelength of the excitation light.
By irradiating this excitation light, the substrate 1 near the soldering part
Fluorescence is emitted from the two parts, and an image of this fluorescence is detected by a fluorescence image detection system 23. Direct fluorescence from the substrate 12 portion and reflected fluorescence from the solder fillet are transmitted to the solid-state TV via a dichroic mirror 18, an imaging optical system 20, and an excitation light cut filter 21.
It is designed to be detected by the camera 22.

Prior to the inspection, first, the X-Y
The table 28 is moved to the inspection starting position, and
The Ar laser 15 is turned on.
Therefore, by repeating the following operations, the soldered portion can be inspected.

That is, with the component lead to be inspected in the flat package component 10 positioned in the area to be inspected by driving the X-Y table 28, a fluorescent image in the area to be inspected is detected by the solid-state TV camera 22. It is something to do. FIG. 8 shows an example of a fluorescent image detected in this manner, with only the soldered portion extracted. As shown in the figure, the ground is the detected image 29 of the substrate reaction, and there are detected images G and H corresponding to the soldered parts, but both of the detected images G and H include the solder fillet image 30. It is becoming included. Incidentally, the detected images G and H show a solder fillet with a good solder fillet and a solder fillet with a small defect, respectively. In the case of a good solder fillet, the solder fillet image 30 is detected as having a large width, but in the case of a small defect in the solder fillet, the width is detected as being small, or the solder fillet image 30 cannot be detected at all. be. Therefore, solder fillet image 3
The quality of the solder fillet can be determined by detecting the width of 0 and determining whether the width is greater than a certain value.

To explain this determination in detail, the defect determining section 24 first compares the fluorescence image as shown in FIG. Or extract only the soldered parts. Next, by adding this in the y direction, a one-dimensional light intensity function with the position x as a parameter is obtained as shown in Figure 9b, and the value of the light intensity function is set to a predetermined threshold value. It is now possible to convert it into two values. If it is above the threshold value, it is set as "1", and if it is less than that, it is set as "0" and binarized as shown in Figure 9c. In the binarized light amount function obtained in this way, By measuring the width of the "1" portion and comparing this value with a predetermined threshold, it is possible to easily and quickly determine whether the solder fillet at that pad or soldering section is good or bad. It is. In addition, in the above processing, addition of the fluorescent images in the y direction is performed as follows.
This is to ensure that the quality of the solder fillet is determined without error by considering the entire solder fillet without being affected by minute irregularities or noise.

The present invention is as described above, but as an excitation light source, a laser having a wavelength of 600 mm or less, or a combination of a light source containing a wavelength component of 600 mm or less, such as a mercury lamp or an ultraviolet fluorescent lamp, and an optical filter can be used. In addition, devices for detecting fluorescent images include a TV camera using an image pickup tube, a combination of a linear sensor and a scanning mechanism such as a galvano mirror, and a sensor for detecting the amount of light at one point such as a photomultiplier tube and a scanning device. There are various possibilities, such as combinations of mechanisms.

〔Effect of the invention〕

As explained above, the present invention uses excitation light irradiated from directly above the object to be inspected to generate fluorescence only from the substrate portion, and detects the degree of reflection of this fluorescence at the solder fillet from directly above the object to be inspected. This allows you to know whether the solder fillets are good or bad. Therefore, in the case of the present invention, it is possible to check the quality of the solder fillet, that is, the quality of the soldered part, without being affected by surrounding components, and with good accuracy even in the case of miniaturized soldered parts. It has the effect of being able to be inspected.

[Brief explanation of drawings]

Figures 1a, b, and c are diagrams showing the mounting and joining states of various components on the board by soldering parts, and Figures 2a and b are cross-sectional views of the soldering parts and their surroundings in Figure 1a. Figures 3a and 3b are diagrams showing good and bad fillets, and Figures 3a and 4b are diagrams for explaining problems when light is irradiated from directly above a steeply sloped fillet and reflected light is detected. a, b are
Figures 5a and 5b are diagrams for explaining that the quality of fillets can be inspected by irradiating light from diagonally above the inspection object, and Figure 6 is a diagram for explaining the principle of the present invention. Figure 7 shows the soldering state of flat package type components onto the board.
FIG. 8 is a diagram showing the soldering part inspection apparatus according to the present invention together with a component mounting board, FIG. FIG. 3c is a diagram for explaining an example of processing by the defect determination section in the same configuration. 10...Flat package type part, 11...
Component lead, 12... Board, 14... Solder fillet, 15... Ar laser, 16, 17... Cylindrical lens, 18... Dichroic mirror, 20... Imaging optical system, 21... Excitation light cut filter, 22...Solid TV camera, 24...
Defect determination section, 25... Overall control section, 26... Table controller, 28... X-Y table.

Claims (1)

[Claims] 1. A method for inspecting the quality of solder fillets at the soldered parts of various components mounted on a board,
Fluorescence is generated from only the base material of the board by irradiating excitation light from directly above the soldered part to be inspected, and the size of the area where the fluorescence is reflected on the solder fillet is detected directly above the soldered part. A method for inspecting a soldering part, characterized in that the quality of the solder fillet at the soldering part is inspected based on the size of the reflective area involved in the detection.