JP3156402B2 - Solder appearance inspection method - Google Patents

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 the appearance of solder, and more particularly, to an accurate method for inspecting the appearance of solder using laser light for soldering.

[0002]

2. Description of the Related Art It is known to judge whether a solder shape is acceptable or not by sweeping and irradiating a laser beam onto solder for bonding an electronic component to a substrate and detecting the reflected light with a position detecting element (for example, see FIG. 1). JP-A-63-177042, JP-A-63-177045).

Conventionally, however, the criterion for determining the acceptability of a solder shape has not been clear, and the acceptability has been determined arbitrarily arbitrarily. Therefore, in order to establish a technique for determining the acceptability of a solder shape by sweeping irradiation of laser light, it is necessary to set a reasonable acceptance / rejection criterion as a prerequisite and perform an appearance inspection in accordance with the criterion.

[0004] To this end, the applicant of the present invention firstly (1) the upper limit height of the solder based on the lead thickness and the chip thickness, (2) the lower limit height, and (3) the solder A method for setting the lower limit wetting angle of the fillet has been proposed (Japanese Unexamined Patent Publication No. 3-183906). According to this means, arbitrary judgment can be eliminated.

[0005]

However, there is a point that this method is insufficient. First, FIG.
(A) is an enlarged view near the solder, and (b) shows a profile), when the wetting angle is small but the solder is sufficiently attached, it is determined uniformly that the solder is defective. However, in such a case, there is a strong demand for a good solder. 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, a profile as shown in FIG. 11B may be obtained in the vicinity of the solder shown in FIG. Here, it is difficult to specify a point indicating the upper edge of the solder from such a profile. Therefore,
An erroneous point P1 is often recognized as the upper edge of the solder instead of the point PO with respect to the original upper edge. In such a case, in the above-mentioned means, the angle θ1 formed by the perpendicular to the tangent to the erroneous point P1 is measured as the null angle instead of the original small null angle θO, as shown in FIG. 11A. In the case of a defective solder having an insufficient wetting angle, it is determined that the soldering is good. As described above, the conventional means has a problem that erroneous determination is easily caused.

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

[0008]

According to the present invention, an element including a base of a right-angled triangle having a height obtained by subtracting a lower limit height of solder from a lead thickness and a lower limit null angle is set as a height. Move the element along the profile,
The pass / fail of the solder shape is determined based on whether or not the profile cuts the bottom of the element.

[0009]

According to the above construction, the element moves along the profile, and the acceptability of the solder is determined based on whether the profile cuts the bottom side of the element. Here, the wetting angle is slightly below the lower limit wetting angle, but when sufficient solder is attached, this profile cuts only the hypotenuse of the triangle and does not cut the bottom, so it is determined that soldering is good. Is done. In addition, if the point corresponding to the upper edge of the solder or the edge of the lead is erroneously shifted slightly toward the base end of the lead for the target where the solder is insufficient, the profile will be near the edge of the lead. Since the profile substantially hangs, the profile cuts the bottom side, and it is determined that the soldering is defective. Furthermore, since only the process of determining whether or not the bottom and the profile intersect can be performed, it is possible to determine whether the soldering is successful or not.
Processing time can be reduced.

[0010]

Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view of a solder appearance inspection apparatus, wherein 1 is a substrate, on which an electronic component (hereinafter referred to as “chip”) 2 is mounted on a circuit pattern L on the upper surface thereof. 3
Is a lead extending from the mold 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 a mirror 6 and irradiated on the solder 4, and the reflected light is incident on a light receiving unit 7. At this time, the mirror 6 is rotated to irradiate the laser beam along the solder 4 by sweeping. Reference numeral 8 denotes a light condensing element, 9 denotes a position detecting element such as a PSD or CCD (solid-state image pickup device), and CU denotes
Is a processing device including a computer that performs the following processing by executing software according to the flowchart of FIG. 4, such as inputting the output of the above and generating a profile or setting a triangular element.

The operation will now be described with reference to the flowchart of FIG. First, laser light is scanned in the direction of the arrow N1 in FIG. 1 (the width direction of the lead 3). Then, when the step-like width direction profile as shown in FIG. 2 is obtained, 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 (the direction of arrow N2) (FIG. 3A) to obtain a raw profile (FIG. 3B) (step 3).

Next, triangular elements are set (step (c) in FIG. 4). This element is a right-angled triangle having a lower limit wetting angle θ as an apex angle and a length h as a 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 empirically determined by the type of chip. Bottom b is b = htan
It is determined by θ. Here, this element is arbitrary as long as it has a vertex and the base, and is not limited to a triangle.

Next, a point P corresponding to the upper edge of the leading end of the lead 3 is obtained after performing grouping on the profile and eliminating the influence of noise and the like (step 5).

Next, the vertices of the above element are adjusted to a point P corresponding to the upper edge. Then, while confirming that the profile does not cut the bottom b of the element, the vertex is moved along the profile as shown by the arrow in FIG. 3D until the bottom touches the circuit pattern surface (chain line). (Steps 7, 8, and 10).

Here, if the profile does not cut the bottom b until the bottom b contacts the circuit pattern surface, it is determined that the soldering is good (step 9), otherwise 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, the thickness t has high reliability, and the pattern surface (chain line) can be easily determined based on the profile. .

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

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 completely removes the element 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 bottom side b at the point Q1, and it is determined that the soldering is defective.

As shown in FIG. 7, when the height of the solder 4 is insufficient, and when the apex of the element is located at the top edge of the lead 3, the profile does not cut the bottom b. However, when the element is moved along the profile, the profile cuts the base b at the point Q2 before the base b comes into contact with 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 the solder 4 is adhered, there is a demand for good soldering as described above. is there. By the way, 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 part of the profile passes inside the oblique side of the element.
However, since the amount of solder is sufficient, the profile bends greatly to the opposite side of the lead 3 as it goes downward, cutting only the oblique side of the element and not the bottom side b. Therefore, it is determined that the soldering is good, and the above request can be met.

Finally, as explained in the section of the prior art,
When the wetting angle is insufficient and the amount of solder is small, but 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. Then, it may be erroneously determined that the soldering is good. However, in the present means, when the element moves along the profile from the state where the vertex of the element is located at the point P1, the profile always cuts the bottom side b as shown by the chain line. This is because the end face 3a of the lead 3 stands almost vertically, and even if a small amount of solder 4 having at most a small wetting angle adheres to this end face 3a, the profile corresponding to the solder 4 is at most perpendicular to the vertical direction. The profile cuts the base b since it forms only a small angle.

As described above, the reference for judging the acceptability of soldering is condensed in the element forming the right-angled triangle, and quick and accurate soldering can be performed by a simple process of cutting or not cutting the bottom. Appearance inspection can be performed.

[0025]

According to the present invention, an element including the base of a right-angled triangle having the apex of the lower limit of the wetting angle is set as the height, the length of which is obtained by subtracting the lower limit of the solder from the lead thickness. Along with the solder, and whether or not the profile cuts the bottom side of the element determines whether or not the solder shape is acceptable, so that an accurate and reasonable appearance inspection can be performed. In addition, since it is sufficient to perform the process of determining whether or not the profile cuts the bottom side, the processing time can be reduced.

[Brief description of the drawings]

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

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

FIG. 3A is a process explanatory view of an appearance inspection method according to an embodiment of the present invention. FIG. 3B is a process explanatory view of an appearance inspection method according to an embodiment of the present invention. (D) Process explanatory diagram of the visual inspection method according to one embodiment of the present invention

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

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

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

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

FIG. 8A is a process explanatory view of a visual inspection method according to one embodiment of the present invention; and FIG. 8B is a process explanatory diagram of a visual inspection method according to one embodiment of the present invention.

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

10A is a process explanatory view of a conventional visual inspection method, and FIG. 10B is a process explanatory diagram of a conventional visual inspection method.

11A is a process explanatory view of a conventional visual inspection method, and FIG. 11B is a process explanatory diagram of a conventional visual inspection method.

[Explanation of symbols]

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

Continuation of the front page (56) References JP-A-63-177042 (JP, A) JP-A-63-177045 (JP, A) JP-A-3-183906 (JP, A) JP-A-2-183104 (JP) JP-A-5-60531 (JP, A) JP-A-5-10731 (JP, A) JP-A-6-42946 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB G01B 11/24 G01N 21/93 G01N 21/95 H05K 3/34 512

Claims (1)

(57) [Claims] A method of inspecting the appearance of a solder based on a profile obtained by scanning a laser beam toward a solder and detecting a reflected light thereof by a position detecting element, wherein a lower limit height of the solder is determined from a lead thickness. An element including the base of a right triangle with the reduced length as the height and the apex of the lower limit null angle is set, and the element is moved along the profile, and the profile cuts the base of the element. A method for inspecting the appearance of solder, comprising determining whether or not the solder shape is acceptable based on the determination.