JPH1048156A - Method for detecting crack - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for detecting a crack wherein the crack can be evaluated by observing an entire crack region. SOLUTION: A method for detecting a crack comprises steps of first soaking a packaged component 10 to be inspected in a beaker 1 with low viscous fluorescent liquid 2 injected (b), (c); taking the component 10 out of the beaker 1 to leave it for approximately 16 hours at a room temperature for naturally drying (d); washing off the low viscous fluorescent liquid 2 depositing to a surface in running water (e); and dividing solder joints 13a, 13b and shedding UV light 4 to the solder joints 13a, 13b from a UV lamp 3 (f). Thus a crack part emits light and is recognized, and by observing this crack face by a stereomicroscope, an SEM or the like, a depth of the crack or its advance can be easily recognized and evaluated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting cracks formed in a solder joint formed by soldering objects to be joined, and more particularly, to a method for detecting the presence or absence of cracks, the spread of cracks, The present invention relates to a crack detection method capable of detecting the size of a crack.

[0002]

2. Description of the Related Art Solder bonding is widely used in a wide range of fields to bond objects to be bonded, for example, to mount electronic components on a mounting board. However, cracks, cracks, cracks and other defects (hereinafter referred to as
Once cracks are generated), stress concentrates on the cracks, the cracks progress more and more, and finally the objects to be bonded may be separated from each other. In addition, when an electronic component is mounted on a mounting board by soldering, an electrical defect such as poor conduction occurs.

Therefore, in order to form a good solder joint, it is important to improve the solder joint method by grasping the cause of the crack and the progress of the crack and feeding it back. For that purpose, it is necessary to detect the depth of the crack and the spread in the lateral direction, grasp the progress of the crack, and evaluate the state of the crack generated in the solder joint. Conventionally, a cracked solder joint is cut along a plane orthogonal to the crack opening, the depth of the crack is measured, and the cut surface generated by the cutting is polished, and the cut surface is subjected to SEM (scanning electron microscope). ) And the like, the state of cracks generated in the solder joint was evaluated.

FIG. 3 shows a conventional crack detection method.
A mounting component formed by soldering a rectangular parallelepiped electronic component on the mounting board described above will be described as an example. 3A and 3B are diagrams showing a conventional method for detecting a crack, in which FIG. 3A is a plan view of a mounted component for observing a crack, and FIG. 3B is a cross-sectional view of a mounted component for observing a crack.

[0005] A mounting component 10 for inspection includes a plate-shaped mounting substrate 11, a rectangular parallelepiped electronic component 12 soldered onto the mounting substrate 11, and the electronic component 12 at both left and right ends of the electronic component 12. And solder joints 13 a and 13 b formed by soldering the solder joints 11.

According to the conventional crack evaluation method, the mounting component 10 is cut in a direction orthogonal to the mounting substrate 11, for example, along the line II, and the cut surface 1 orthogonal to the mounting substrate 11 is cut.
4 is formed. Here, assuming that the crack 15 is generated in the solder joint portion 13b with the spread of the crack substantially parallel to the mounting substrate 11 as shown by the broken line,
, A crack 15 as shown in FIG. Next, the depth of the crack 15 was evaluated based on the length of the crack 15 that appeared on the cut surface 14, and the cut surface 14 was polished.
The state of the crack was observed by SEM or the like.

However, in such a conventional crack detection method, a wide range of solder joints such as the rectangular parallelepiped electronic component 12 is used because a wide range of solder joints are captured and observed in all cross sections. With regard to the above, there is a problem that the length of the crack changes depending on the observation point, and it is not possible to capture the entirety of the generated crack.

[0008] That is, the conventional method for evaluating the cracks described above has the following problems. First
In the case where the component to be soldered is a component having a width like the electronic component 12 shown in FIG. 3 and the width of the soldered portion cannot be ignored, the crack depth that can be observed depends on the cutting position. Will be different. Therefore, a variation in the evaluation of cracks easily occurs. Second, since only the cut cross section can be observed, it is impossible to evaluate the spreading state and the spreading direction of the crack. Third,
Even if cracks occur in the solder joints of each mounted component under the same conditions, the depth of the crack may vary depending on each mounted component. Fourth, it has recently been attempted to predict the occurrence and spread of cracks in solder joints by simulation. However, if the depth and lateral spread of cracks cannot be detected, the simulation calculation results I can't compare. Fifth, a great amount of time is required for polishing the cut surface.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to solve the problem that the conventional method for detecting cracks cannot evaluate the state and direction of crack propagation. An object of the present invention is to provide a method for detecting a crack, which allows observation of the entire crack.

[0010]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, a method for detecting a crack according to the present invention is a method for detecting a crack formed in a solder joint formed by soldering objects to be joined. First, the fluorescent liquid is made to penetrate the solder joint so as to enter the crack. Next, the to-be-joined bodies are torn at the solder joint to detect a cracked cross section, and the ultraviolet rays (UV
The spread of the cracks (including the crack propagation speed and the crack spread direction) is characterized by irradiating the light with light and causing the remaining fluorescent liquid to enter the cracks and emit light.

According to the crack detection method of the present invention, the fluorescent liquid is caused to permeate the cracks, so that the fluorescent liquid is attached to the portions where the cracks are formed. Next, the solder joint is divided so as to spread the crack from the opening of the crack toward the inner part of the crack, and the divided solder joint is irradiated with UV light. As a result, the crack portion in which the fluorescent liquid has penetrated emits light and emerges. Therefore, the extent of the crack surface forming the crack can be easily identified, and the progress, depth, and lateral extent of the crack can be evaluated over the entire crack.

[0012]

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

First Embodiment First, a first embodiment of a crack detection method according to the present invention will be described with reference to FIG. This embodiment is an example of evaluating a crack in a solder joint of a mounted component using a low-viscosity fluorescent liquid. FIG. 1 is a diagram showing Example 1 of a crack detection method of the present invention, and (a) to (f) are explanatory diagrams for each step. Note that portions common to those described in the related art are denoted by the same reference numerals.

The apparatus used in this embodiment shown in FIG. 1A comprises a beaker 1 and a low-viscosity fluorescent liquid 2 injected into the beaker 1. A temperature controller (not shown) is attached to the beaker 1 into which the low-viscosity fluorescent liquid 2 has been injected, and the low-viscosity fluorescent liquid 2 is maintained at a constant temperature.

A mounting component 10 for inspection shown in FIG.
Is a plate-shaped mounting board 11, an electronic component 12 soldered on the mounting board 11, and a solder joint formed by soldering the electronic component 12 to the mounting board 11 at both left and right ends of the electronic component 12. It is composed of parts 13a and 13b.

In the method of this embodiment, first, the low-viscosity fluorescent liquid 2
The mounting component 10 for inspection as shown in FIG. 2B is immersed in the beaker 1 into which the metal is injected (see FIG. 2C). Next, as shown in FIG.
Is taken out of the beaker 1 and left at room temperature for about 16 hours to be naturally dried. Next, the low-viscosity fluorescent liquid 2 adhering to the surface is washed and removed with running water (see (e) in FIG. 4). Next, a tensile force perpendicular to the mounting substrate 11 is applied to both the electronic component 12 and the mounting substrate 11 of the mounting component 10 to tear the solder joints 13a and 13b along the spread surface of the crack 15, thereby forming two solder joints. Divide into parts. Further, as shown in FIG.
3b is irradiated with UV light 4 from a UV lamp 3.

Crack 1 in solder joints 13a and 13b
5, the low-viscosity fluorescent liquid 2 has entered, and by irradiating the UV light 4, a crack portion emits light and floats to be recognized. As described above, the crack surface exhibiting a clear contrast difference from the other portions is formed by a stereoscopic microscope or an S microscope.
By observing with an EM or the like, the depth and progress of the crack can be easily recognized and evaluated. In addition, a stereo microscope and S
The observation and processing can be automatically performed using an imaging device such as a CCD camera, without being limited to the method of observation using an EM or the like.

In this embodiment, since the entire area of the crack can be observed by such a simple method, it is possible to observe the state and the direction of the expansion of the crack, which were impossible in the past.
The crack depth can also be evaluated over the entire crack. Further, in the present embodiment, since the low-viscosity fluorescent liquid 2 was used as the fluorescent liquid, the crack width was nanometer (n).
m) It can be observed even if it has penetrated to the order and has fine cracks. Furthermore, the crack depth,
Since the spread or the like can be detected numerically, it can be fed back to the analysis of the crack evaluation simulation.

Second Embodiment Next, a second embodiment of the crack detection method according to the present invention will be described with reference to FIG. The present embodiment is an example in which a crack in a solder joint of a mounted component is evaluated using a high-viscosity fluorescent liquid. FIG. 2 is a diagram showing a second embodiment of the crack detection method of the present invention, and (a) to (f) are explanatory diagrams for each step.

FIG. 2A shows a mounting component 10 for inspection.
As described above, the mounting board 11, the electronic component 12 soldered to the mounting board 11, and the solder bonding formed by soldering the electronic component 12 to the mounting board 11 at both left and right ends of the electronic component 12. It is composed of parts 13a and 13b.

In the method of this embodiment, first, the high-viscosity fluorescent liquid 5
(A) is immersed in the beaker 1 into which the high viscosity fluorescent liquid 5 is injected into the dropper 6 and the high viscosity fluorescent liquid 5 is injected into the dropper 6. The liquid 5 is applied around the solder joints 13a and 13b of the mounted component 10 (FIG. 3 (c)).
reference). Next, the mounting component 10 for inspection is inserted in the same FIG.
And vacuum dried for about 10 minutes in a vacuum dryer 7 as shown in FIG. Then
As shown in FIG. 4E, the temperature of the vacuum dryer 7 is set to 125
C. and heated for about 1 hour to cure the high-viscosity fluorescent liquid 5. Next, the electronic component 12 of the mounting component 10 and the mounting substrate 1
A tensile force perpendicular to the mounting substrate 11 is applied to both the solder joints 1 and 1 to tear the solder joints 13a and 13b along the spread surface of the crack 15 and divide the two into two solder joints. Further, as shown in FIG.
The UV light 4 is radiated from the UV lamp 3 to 3a and 13b.

Crack 1 in solder joints 13a, 13b
The high-viscosity fluorescent liquid 5 has entered into 5, and by irradiating the UV light 4, the crack portion is strongly emitted and floats up and is recognized. Thus, by observing the crack surface that is strongly lifted and recognized by the high-viscosity fluorescent liquid 5 with a stereoscopic microscope, an SEM, or the like, the depth and progress of the crack can be easily recognized and evaluated.

In this embodiment, since the entire area of the crack can be observed by such a simple method, it is possible to observe the state and direction of the expansion of the crack, which was impossible in the past.
The crack depth can also be evaluated over the entire crack. In particular, in this example, since the high-viscosity fluorescent liquid 5 was used as the fluorescent liquid, a large amount of the fluorescent liquid remained in the crack and emitted light intensely, so that the crack could be reliably detected and observed. Further, since the depth, spread, and the like of the crack can be detected numerically, it can be fed back to the analysis of the crack evaluation simulation.

Although the preferred embodiments of the present invention have been described in detail above, the present invention can be implemented in various embodiments other than these embodiments. For example, the present invention can be applied to a solder connection portion or a through-hole connection portion of an electronic component other than the rectangular parallelepiped electronic component. In addition, it goes without saying that the present invention is not limited to the above embodiments, but can be developed in various forms.

[0025]

As described above, according to the crack detecting method of the present invention, the fluorescent liquid is made to penetrate the crack, and then the solder is spread from the opening of the crack toward the inner part of the crack. The joints were split, and the split solder joints were irradiated with UV light to make the cracks illuminate and recognized, so that the state and direction of the crack spread could be observed, and the crack depth Can be evaluated over the entire crack.
In addition, by applying the detection method of the present invention, crack detection can be easily performed in a short time and at low cost, which is beneficial.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of a crack detection method according to the present invention, and (a) to (f) are explanatory diagrams for each step.

FIG. 2 is a diagram showing a second embodiment of the crack detection method according to the present invention, and (a) to (f) are explanatory diagrams for each step.

FIG. 3 is a diagram showing a conventional crack detection method;
(A) is a plan view of a mounted component for observing a crack, (b)
FIG. 4 is a cross-sectional view of a cut surface of a mounted component in which a crack is observed.

[Explanation of symbols]

1: beaker, 2: low viscosity fluorescent liquid, 3: UV lamp, 4:
UV light, 5: high viscosity fluorescent liquid, 6: dropper, 7: vacuum dryer, 10: mounted component, 11: mounted substrate, 12: electronic component, 13a, 13b: solder joint, 14: cut surface, 1
5 ... crack

Claims (3)

[Claims] 1. A method for detecting cracks formed in a solder joint formed by soldering objects to be joined to each other, wherein a fluorescent liquid is permeated into the solder joint so as to enter the crack, and Identify the extent of cracks by fracturing the joints at the solder joints to detect cracked sections and irradiating the cracked sections with ultraviolet light to enter the cracks and emit the remaining fluorescent liquid. A method for detecting cracks. 2. The crack detection method according to claim 1, wherein the fluorescent liquid that enters the crack has a low viscosity such that the crack width penetrates to the order of nanometers. 3. The cracking liquid according to claim 1, wherein the fluorescent liquid that penetrates into the crack has a high viscosity so as to penetrate a predetermined crack width and emit light strongly when irradiated with ultraviolet rays. Detection method.