JPH06167315A - Inspecting method for appearance of solder - Google Patents

Abstract

PURPOSE:To correctly and rationally inspect the outer appearance of a solder by setting an element including the base of a right triangle which has the height of the length obtained by subtracting the lowest height of the solder from the thickness of a lead and also the vertical angle of the lowest wet angle, and judging the shape of the solder from whether or not a profile cuts the base of the element when the element in moved along the profile. CONSTITUTION:An element including the base of a right triangle which has the height of the length obtained by subtracting the lowest height of a solder 4 from the thickness of a lead and the vertical angle of the lowest wet angle is set. The spot laser light from a laser device 5 is cast to the solder 4 after being reflected by a mirror 6, and the reflecting light enters a photodetecting part 7. At this time, the mirror 6 is rotated to sweep and cast the laser light along the solder 4. When an output of a position detecting element 9 is input to a processing device CU, the processing device CU generates a profile or sets the rectangular element. The element is moved along the profile. The shape of the solder is detected to be good or bad from the fact whether or not the profile cuts the base of the element.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solder visual inspection method, and more particularly, to a solder visual inspection method using laser light for solder, which enables accurate visual inspection.

[0002]

2. Description of the Related Art It is known that a solder for adhering an electronic component to a substrate is swept and irradiated with a laser beam, and the reflected light is detected by a position detecting element to judge whether the solder shape is acceptable or not (for example, JP-A-63-177042 and JP-A-63-177045).

In the past, however, the criteria for judging the pass / fail of the solder shape have not been clear, and the fact is that the pass / fail judgment is made quite arbitrarily. Therefore, in order to establish the pass / fail judgment technique of the solder shape by the sweep irradiation of the laser light, it is necessary to set a reasonable pass / fail judgment standard as a premise and perform the visual inspection along the standard.

For this reason, the applicant has previously established, as the acceptance criteria for the solder shape, (1) the upper limit height of the solder based on the lead thickness and the chip thickness, (2) the same lower limit height, and (3) the solder. A method for setting the lower limit wetting angle of the fillet has been proposed (Japanese Patent Laid-Open No. 183906/1993). By this means, arbitrary judgment can be eliminated.

[0005]

However, even with this means, there are insufficient points. First, FIG. 10 ((a))
Is a magnified view near the solder, and (b) shows a profile), when the wetting angle is small but the solder is sufficiently attached, it is uniformly determined that the solder is defective. However, in such a case, there is a strong demand for good soldering. In addition, 3 is a lead, 4 is a solder, L is a circuit pattern, θT is a lower limit wetting angle, and θS is a measured wetting angle.

Further, in the vicinity of the solder shown in FIG. 11A, a profile as shown in FIG. 11B may be obtained. Here, it is difficult to specify the point indicating the upper edge of the solder from such a profile. Therefore,
In many cases, the wrong point P1 is recognized as the upper edge of the solder instead of the original point PO for the upper edge. In such a case, the above-mentioned means measures not the original excessively small wetting angle θO but the angle θ1 formed by this tangent to the erroneous point P1 and the perpendicular as the wetting angle, and as shown in FIG. Therefore, it is determined that the soldering is good for the defective solder having the insufficient wetting angle. As described above, the conventional means has a problem that an erroneous determination is likely to occur.

Therefore, an object of the present invention is to provide a solder visual inspection method capable of performing an accurate visual inspection.

[0008]

According to the present invention, an element including a base of a right-angled triangle having a lower limit wetting angle as an apex angle is set by setting a length obtained by subtracting a lower limit height of solder from a lead thickness as a height. Move the element along the profile,
Whether or not the solder shape is acceptable depends on whether or not this profile cuts the bottom of this element.

[0009]

According to the above construction, the element moves along the profile, and whether the solder is acceptable or not is determined by whether the profile cuts the bottom of the element. Here, the wetting angle is slightly below the lower limit wetting angle, but when sufficient solder is attached, this profile only cuts the hypotenuse of the above triangle and does not cut the bottom, so it is determined that soldering is good. To be done. In addition, if the point corresponding to the upper edge of the solder or the edge of the lead is erroneously misaligned slightly toward the lead base end side for the object with insufficient solder, the profile will be near the edge of the lead. Since it droops substantially, the profile cuts the bottom side and it is determined that soldering is defective. Further, since it is possible to determine whether the soldering is successful or not, only by the process of determining whether or not the profile intersects the bottom side,
The processing time can be shortened.

[0010]

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 1 is a perspective view of a solder visual inspection apparatus, in which 1 is a substrate, and an electronic component (hereinafter referred to as "chip") 2 is mounted on a circuit pattern L on the upper surface thereof. Three
Is a lead extending from the molded body 2a of the chip 2, and 4 is a solder for bonding the lead 3 to the substrate 1. Reference numeral 5 denotes a laser device. The laser spot light emitted from the laser device 5 is reflected by the mirror 6 and applied to the solder 4, and the reflected light enters the light receiving portion 7. At that time, by rotating the mirror 6, laser light is swept and irradiated along the solder 4. Reference numeral 8 is a light-collecting element, 9 is a position detecting element such as a PSD or CCD (solid-state image sensor), and CU is this position detecting element 9.
Is a processing device including a computer that performs the processing described below by executing the software according to the flowchart of FIG.

Now, description will be made below with reference to the flowchart of FIG. First, laser light is scanned in the direction of arrow N1 in FIG. 1 (width direction of the lead 3). Then, if the stepwise widthwise profile as shown in FIG. 2 can be acquired, the center of the convex portion on this scanning line is set to the start point ST (steps 1 and 2).

Next, a laser beam is scanned in the length direction of the lead 3 (direction of arrow N2) (FIG. 3A) to obtain a raw profile (FIG. 3B) (step 3).

Next, triangular elements are set (step (4) in FIG. 4C). This element is a right-angled triangle having the lower limit wetting angle θ as the apex angle and the length h as the height. The length h is obtained from h = H-Hmin (where H is the thickness of the lead 3 (known data) and Hmin is the lower limit height of the solder 4). Hmin is a height that is empirically determined depending on the type of chip. Bottom b is b = h · tan
Calculated by θ. Here, this element is arbitrary as long as it has a vertex and the above-mentioned base, and is not limited to a triangle.

Then, the profile is grouped to eliminate the influence of noise and the like, and then the point P corresponding to the upper edge of the tip of the lead 3 is obtained (step 5).

Next, the vertex of the above element is aligned with the point P corresponding to the upper edge. Then, while confirming that the profile does not cut the bottom side b of the element, move this apex along the profile as shown by the arrow in FIG. 3D until the bottom side contacts the circuit pattern surface (chain line). (Steps 7, 8, 10).

Here, until the bottom side b contacts the circuit pattern surface, if the profile does not cut the bottom side b, it is determined that the soldering is good (step 9), and if not, it is determined that the soldering is bad (step 11). Since the circuit pattern L is accurately formed on the substrate 1 by etching or the like, its thickness t is highly reliable, and the pattern surface (chain line) can be easily determined based on the profile. .

Next, each pattern of solder adhesion and its determination will be described with reference to FIGS. 5 to 9, (a) is an enlarged side view of the tip of the lead 3, and (b) is a diagram showing its profile.

First, as shown in FIG. 5, when the solder 4 has a sufficient height and wetting angle, the profile cuts only the oblique side of the element or the element completely until the bottom side b of the element contacts the circuit pattern surface. Do not disconnect. Therefore, it is determined that the soldering is good.

As shown in FIG. 6, when the wetting angle is insufficient, the profile cuts the above-mentioned bottom side b at the point Q1 and is judged to be defective in soldering.

Further, as shown in FIG. 7, when the height of the solder 4 is insufficient and the apex of the element is located at the upper edge of the tip of the lead 3, the profile does not cut the bottom side b. However, when the element is moved along the profile, the profile cuts the base b at the point Q2 before the base b contacts the circuit pattern surface (see the chain line). Therefore, it is determined that the soldering is defective.

Next, as shown in FIG. 8, when the wetting angle is slightly insufficient but a sufficient amount of solder 4 is attached, there is a request for good soldering as described above. is there. Now, in this case, when the apex of the element is located at the upper edge of the tip of the lead 3 (see the solid line), the upper portion of the profile passes inside the element rather than the hypotenuse of the element.
However, since the amount of solder is sufficient, the profile bends largely toward the opposite side of the lead 3 as it goes downward, cutting only the oblique side of the element and not cutting the bottom side b. Therefore, it is determined that the soldering is good, and it is possible to meet the above request.

Finally, as explained in the section of the prior art,
Although the wetting angle is insufficient and the amount of solder is small, when the point corresponding to the upper edge of the tip of the lead 3 is mistakenly recognized as the point P1 (FIG. 9), the apparent wetting angle θ1 is sufficiently large and the conventional means is used. Then, it can be erroneously determined as good soldering. However, in this means, when the element moves along the profile from the state where the apex of the element is located at this point P1, the profile always cuts the bottom side b as shown by the chain line. This is because the end surface 3a of the lead 3 stands almost vertically, and even if a small amount of solder 4 having a small wetting angle is attached to this end surface 3a, the profile corresponding to this solder 4 is at most perpendicular to the vertical direction. Therefore, the profile cuts the bottom side b, because it forms only a small angle.

As described above, the criteria for determining whether the soldering is acceptable or not are condensed in the element forming the above-mentioned right triangle, and the simple process of whether or not to cut the bottom side of the element allows quick and accurate soldering. Appearance inspection can be performed.

[0025]

According to the present invention, the length obtained by subtracting the lower limit height of the solder from the lead thickness is defined as the height, and the element including the base of the right triangle whose apex angle is the lower limit wetting angle is set, and this element is set as the profile. It is possible to perform an accurate and rational visual inspection because the pass / fail of the solder shape is judged depending on whether or not this profile cuts the bottom side of this element by moving along. Moreover, since it is sufficient to perform the determination process as to whether or not the profile cuts the bottom side, the processing time can be shortened.

[Brief description of drawings]

FIG. 1 is a perspective view of an appearance inspection apparatus according to an embodiment of the present invention.

FIG. 2 is a process explanatory diagram of an appearance inspection method according to an embodiment of the present invention.

3A is a process explanatory diagram of an appearance inspection method according to an embodiment of the present invention. FIG. 3B is a process explanatory diagram of an appearance inspection method according to an embodiment of the present invention. Process explanatory drawing of the said appearance inspection method (d) Process explanatory drawing of the external appearance inspection method which concerns on one Example of this invention.

FIG. 4 is a flowchart showing an appearance inspection method according to an embodiment of the present invention.

5A is a process explanatory diagram of an appearance inspection method according to an embodiment of the present invention. FIG. 5B is a process explanatory diagram of an appearance inspection method according to an embodiment of the present invention.

6A is a process explanatory diagram of an appearance inspection method according to an embodiment of the present invention. FIG. 6B is a process explanatory diagram of an appearance inspection method according to an embodiment of the present invention.

7A is a process explanatory diagram of an appearance inspection method according to an embodiment of the present invention. FIG. 7B is a process explanatory diagram of an appearance inspection method according to an embodiment of the present invention.

8A is a process explanatory diagram of an appearance inspection method according to an embodiment of the present invention. FIG. 8B is a process explanatory diagram of an appearance inspection method according to an embodiment of the present invention.

9A is a process explanatory diagram of an appearance inspection method according to an embodiment of the present invention. FIG. 9B is a process explanatory diagram of an appearance inspection method according to an embodiment of the present invention.

10A is a process explanatory diagram of a conventional appearance inspection method. FIG. 10B is a process explanatory diagram of a conventional appearance inspection method.

11A is a process explanatory view of a conventional appearance inspection method. FIG. 11B is a process explanatory view of a conventional appearance inspection method.

[Explanation of symbols]

 3 Lead 4 Solder 9 Position detection element θ Lower limit wetting angle h Element height b Element bottom side H Lead thickness

Claims (1)

[Claims] 1. A method of inspecting the appearance of solder on the basis of a profile obtained by scanning a laser beam toward the solder and detecting the reflected light by a position detecting element, and determining the lower limit height of the solder from the lead thickness. Set an element that includes the base of a right-angled triangle with the reduced length as the height and the lower corner angle as the apex, and move this element along the profile, and whether this profile cuts the base of the element. A method for inspecting the appearance of solder, which comprises determining whether the shape of the solder is acceptable or not.