JPH083472B2 - Appearance inspection method of solder part - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a method for inspecting the appearance of a solder portion, in which whether the appearance of the solder portion is acceptable or not is determined from the light reflection characteristics of the solder portion after reflow. Is.

(Prior Art) A substrate on which an electronic component is mounted by an electronic component mounting device is sent to a soldering device, where the cream solder applied to the grounded portion of the lead is heated. After this reflow, a visual inspection of the solder part is performed to check whether the solder part is normally formed, and defective products are excluded from the line.However, conventionally, such visual inspection is performed by visual inspection by an inspector. It was being appreciated.

(Problems to be Solved by the Invention) However, there are problems that the inspection efficiency is not improved by the visual inspection work of the inspector, the inspection standard is likely to vary due to the individual error of the inspector, and an erroneous judgment is easily caused due to an error.

By the way, the upper surface of the solder portion after reflow that has been subjected to heat treatment is generally a glossy corrugated or mountain-shaped uneven surface, and when illuminating this from above and observing with an upper camera, the uneven surface A horizontal plane or a substantially horizontal plane among them reflects light upwardly and is detected by the camera as a bright and bright area, but most of the light is reflected sideways on the inclined surface and is incident on the camera above. Without
Therefore, it is observed by the camera as a dark black color with low brightness. Further, on the upper surface of the normal solder portion after the reflow, there are a portion having high luminance and a portion having low luminance as described above, but there is no or almost no portion having intermediate luminance.

Therefore, the present invention was made by focusing on the light reflection characteristics of the upper surface of the solder portion after such reflow, and by utilizing such light reflection characteristics, the appearance of the solder portion can be accurately and accurately determined by an optical method. The purpose is to provide a method that can be inspected with good workability.

(Means for Solving the Problem) For this purpose, the present invention sets a check area in front of the lead extending from the electronic component mounted on the board, and irradiates the check area with light from above to check the upper area. By observing this check area with a camera, obtaining a histogram of the brightness of this check area, and detecting whether the brightness histogram is bright or dark, it is possible to judge whether the appearance of the solder portion after reflow is acceptable or not. It was done like this.

(Operation) In the above configuration, when the check area is irradiated with light from above and the check area is observed by the camera above, the normal solder portion is observed as a surface in which bright and dark portions in which bright and dark portions are mixed are separated. From this observation result, it is distinguished from the defective solder portion.

Example 1 Next, an example of the present invention will be described with reference to the drawings.

FIG. 1 shows a visual inspection device for a solder portion,
Reference numeral 1 denotes an electronic component mounted on a substrate 2, on which a camera 3 and a ring-shaped light source 4 are arranged. Reference numeral 5 denotes a control device such as a computer connected to the camera 3.
The electronic component is mounted on the substrate 2 by the mounting device and then heat-treated by the soldering device. The electronic component 1 is an electronic component with leads, and leads L are provided on both sides of the molded body 6.
Is extended. The mold body 6 is made of a material having a low brightness such as black synthetic resin, while the lead L is made of a material having a high brightness such as a glossy metal.
The lead L has a horizontal base end a and a steep downward slope b.
And has a horizontal tip portion c that is grounded to the substrate 2. FIG. 2 shows a plane of the lead L, and 7 is a substrate 2
The tip portion c of the lead L is grounded on the solder portion 7. d is a solder fillet that rises at the tip of the lead L, and the upper surface thereof is an inclined surface having an upward slope from the substrate 2 toward the tip of the lead (first
(See the enlarged view of the figure). When the lead portion L is irradiated with light from above and observed by the camera 3 above, the horizontal base end portion a and the tip end portion c reflect light upward, and the reflected light is sufficiently incident on the camera 3. Although it is observed as a bright part with high brightness, the light incident on the inclined part b and the fillet d is not reflected right above, and most of it is reflected sideways and hardly enters the camera 3, so Observed as low dark areas.

Now, as shown in FIG. 3, the upper surface of the reflowed solder portion 7 which has been subjected to the heat treatment by the soldering device has a corrugated or chevron-shaped uneven surface, and is also a glossy and highly bright mirror surface. . Therefore, when light is emitted from above and observed by the camera 3 above, the light incident on the horizontal or substantially horizontal surface M such as the upper surface or the bottom surface is strongly specularly reflected upward and is observed as a bright portion with high brightness. However, since most of the light incident on the inclined surface N is reflected to the side, it is hardly incident on the camera 3, and therefore the inclined surface N is observed as a dark portion with low brightness. In the figure, the broken line arrow indicates light. That is, as described in the section of the problem to be solved by the invention, the luminance histogram is observed on the surface of the solder portion 7 after the reflow with bright and dark separation, and there is no or almost no portion having an intermediate luminance. .
Therefore, by setting the check area A ahead of the lead L and observing the light reflection characteristics of the check area A, the appearance of the solder portion 7 can be inspected as described below. In FIG. 3, the shape and the thickness of the solder portion 7 are exaggerated for easy understanding.

FIG. 4 shows a histogram of the luminance and the number of pixels when the appearance of the solder portion 7 is normal as shown in FIG. 3, and in this case, the check area A shows the luminance as described above. High and low parts are mixed, and there is no or almost no intermediate brightness. TH is a threshold value that is a measure of high and low brightness. Further, as shown in FIG. 5, when the preliminary solder is exposed or when the amount of the solder is too small, almost no light is incident on the camera 3, and the check area A
The brightness of is quite low. Preliminary solder is solder that is applied before regular solder application in order to improve adhesion to the copper foil on the substrate. Further, FIG. 6 shows the case where the copper foil is exposed without applying the solder at all, or the heat treatment in the soldering device is insufficient and the solder is melted. Light incident from is diffusely reflected on these surfaces and is observed as intermediate brightness by the camera. From the above, if the luminance histogram is bright and dark separated as shown in FIG. 4, the solder portion is good, and if it is not bright and dark separated as shown in FIG. 5 and FIG. The part is determined to be defective.

As described above, the solder portion 7 has different light reflection characteristics depending on its shape and state when irradiated with light from above and observed by a camera above. Therefore, by observing the light reflection characteristic, it is possible to determine whether the solder portion is acceptable or not. The pass / fail judgment criteria are arbitrarily determined in consideration of the required quality or accuracy of the soldered part, but for example, those with a TH value or more of 90% or more are
If it is OK or lower, it is judged as NG, or if the intermediate brightness is 5% or more, it is judged as NG. The calculation such as the pass / fail judgment is performed by the control device 5.

(Effect of the Invention) As described above, according to the present invention, a check area is set in front of a lead extending from an electronic component mounted on a board, and light is emitted to the check area from above and a camera above is used. By observing this check area, obtaining the brightness histogram of this check area, and detecting whether the brightness histogram is bright or dark, it is possible to judge whether the appearance of the solder part after reflow is acceptable or not. Therefore, the pass / fail of the solder portion can be accurately determined from the light reflection characteristics.

[Brief description of drawings]

FIG. 1 shows an embodiment of the present invention. FIG. 1 is a side view of a solder appearance inspection device, FIG. 2 is a plan view near a lead, FIG. 3 is a side view during observation, and FIG. FIG. 5, FIG. 5 and FIG. 6 are histogram diagrams. 1 ... Electronic parts 2 ... Substrate 3 ... Camera 7 ... Solder A ... Check area L ... Lead

Claims (1)

[Claims] 1. A check area is set in front of a lead extending from an electronic component mounted on a board, light is emitted from above to the check area, and this check area is observed by an upper camera to make this check. Obtaining the brightness histogram of the area and detecting whether or not the brightness histogram is separated into bright and dark areas, the pass / fail appearance of the solder part after reflow is judged. Appearance inspection method.