JP2530788B2 - Electronic parts joint 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 a joint portion of an electronic component, and more particularly to a method for inspecting a joint state of a joint portion by soldering an electric circuit board by temperature distribution.

[0002]

2. Description of the Related Art Conventionally, a joint portion of an electronic component, for example, a soldering portion of an electric circuit board has many defects, and various proposals have been made as a method of inspecting the joint portion.

The inspection device developed by Van Zetti, Inc. of the United States is a device for automatically inspecting each joint of printed circuit boards [Sensor Technology, August 1982, (Vol.2.
No. 9) p. 47-50].

In this method, the temperature of the joint surface is measured by heating the solder joint portion with a laser beam and detecting infrared rays emitted from the solder joint portion, and the solder joint is measured by the temperature change of the joint surface. It is to judge the state of the department. That is, the defective joint is based on the principle that the temperature rises faster than the normal joint. This method is epoch-making in terms of automating the inspection of the joint portion of the electronic component, which has conventionally relied on visual inspection.

However, since the quality of the joint is judged only from the local temperature information on the surface of the solder joint, there is a fundamental weakness that the inspection accuracy is low. Therefore, many improved techniques have been proposed.

[0006] For example, Japanese Patent Application Laid-Open No. 60-73347 (Japanese Patent Application No. 58-180687) "Inspection method and inspection apparatus for joint state" heats an inspection object having a joint and measures the radiation temperature of the heated portion. However, the present invention provides a method and apparatus for determining the presence / absence of a defect in a joint based on the measurement result of the radiation temperature.

In this method, the temporal change of the radiation temperature of the heated portion is measured, and based on the short-time temperature change which is not affected by the presence or absence of a defect in the joint portion, the atmospheric conditions (inspection target) The surface condition etc. of an object is detected, and the presence or absence of a defect in the joint is determined by adding a correction based on the atmospheric conditions to a temperature change for a relatively long time that is affected by the presence or absence of a defect in the joint. .

That is, in the case of defective soldering, the thermal capacity of the joint is smaller than in the case of normal soldering, and the phenomenon in which the temperature of the heated object rises sharply is the same as the technology of the Vanzetti Company. However, this inspection apparatus is improved in that the influence of the surface condition of the soldered portion is corrected. As another improved technology,
JP-A-63-49362 (Japanese Patent Application No. 61-193223)
There is a "solder inspection device".

The above-mentioned Van Zetti Company and JP-A-60
While the device of −73347 locally irradiates a laser from a direction perpendicular to the circuit board, this device includes a pair of opposing heating means in a flat package LSI.
Is obliquely upward with respect to the terminal surface and is rotated by 45 degrees with respect to the longitudinal direction of the terminal about the vertical direction of the terminal surface as an axis, and heating is performed simultaneously from both sides of the soldered portion.

Local heating may be affected by the amount of solder and the like, and the temperature change in a defective soldering state may be included in the range of variation in the normal soldering state. Is difficult to do. In order to solve the problem, by irradiating the laser obliquely from above, the terminal and the solder surface are heated at the same time, and there is a very small gap between the terminal portion and the solder portion due to poor soldering. The laser beam enters the gap and repeats reflection between the terminal and the solder part, further heating the terminal part.

As a result, the temperature of the terminal portion with poor soldering is increased by the small heat capacity and the temperature is increased by the reflection of the laser beam, and the difference from the normal temperature increase of the soldered portion is increased and the detection sensitivity is improved. Can be raised. Furthermore, by arranging a pair of laser devices as described above, it is possible to reduce the
Both terminals can be inspected at the same time without changing the arrangement of the laser device.

However, in the series of methods for inspecting the soldered portion, the temporal change in the local temperature of the joint portion of the electronic component is measured, and the quality of the joint portion is judged by the temperature change. They are common and do not overcome the fundamental weaknesses of Van Zetti's technology.

Furthermore, the technology of Banzetti Co., Ltd. or an improved technology thereof is disclosed in JP-A-60-73347 (Japanese Patent Application No.
8-180687) "Joining state inspection method and inspection apparatus", and Japanese Patent Application Laid-Open No. 63-49362 (Japanese Patent Application No. 61-1).
93223) The principle of the "solder inspection apparatus" is to judge a defective joint by a change in heat capacity of the joint. That is, it is based on the fact that the temperature rise rate due to thermal energy is higher in the case of an insufficiently soldered joint having voids than in the case of a normal joint.

In the same electronic component, the size of each wiring and the connection destination of the wiring are different, and therefore the degree of heat diffusion through the wiring is different, or the size of each lead connected to the external wiring is different. When the heat capacities of the leads are different, there is a fundamental problem that the temperature rising rate becomes different even in the case of a normal soldering joint having no defect, which makes it indistinguishable from the defective joint.

There are many defects such as bridges, solder balls, voids, bonding defects, blow holes, insufficient solder, insufficient wetting, and misalignment of lead positions at soldered joints of electric circuit boards. With respect to these defects, some of the above defects can be identified only by a temporal change in a certain local temperature based on the difference in heat capacity, but all the defects are identified, and the joint portion is comprehensively determined. In many cases, when an inspected electric circuit board is incorporated into a product, a defect occurs.

In order to solve such a problem, the inventors of the present application do not judge the quality of the joint by detecting only a temporal change in a certain temperature, but consider the whole joint as a surface. , The temperature distribution corresponding to the shape of the defect of the joint is recorded as a thermal image, the defect of the soldering of the joint is determined by image processing of the image, and the quality of the joint is determined. An inspection method is proposed [Japanese Patent Application Laid-Open No. 63-305238 (Japanese Patent Application No. 62-141182).
[Method for inspecting joints of electronic components)].

In the method of inspecting the joint portion, which captures the shape of the defect as a surface as proposed above, it is necessary to detect an image corresponding to the defect from the thermal image.

In general, the simplest method of detecting a specific image from an image is to set a specific value and divide the image with the specific value as a boundary. That is, this is a method of extracting a pixel group having a brightness value that exceeds a specific value (threshold value) or is less than a specific value (threshold value) as a specific image.

Even in the joint inspection method which catches the shape of a defect as a surface proposed above, if an appropriate threshold value is set and the binarization processing is performed, the brightness exceeding or below the threshold value is obtained. A group of pixels with values can be drawn as a surface. Further, by calculating the number of pixels having a luminance value that exceeds the threshold value or is less than the threshold value, the area of the pixel group can be easily calculated.

However, in this case, the method of setting the threshold value becomes a problem.

One of the typical methods for setting the threshold value is a histogram method. This is a method in which the value of the valley between two peaks is used as the threshold value when the histogram of the number of pixels for the temperature obtained by performing image processing on the thermal image of the inspection object shows bimodality.

However, the histogram of the number of pixels for the temperature obtained by image-processing the thermal image of the joint where the defect exists generally has a complicated shape, and it is difficult to determine the threshold value from the shape of the histogram. is there.

Another one is a P-tile method using a histogram. This is a method in which a histogram is used to calculate a brightness value having a cumulative distribution of P percent from the smaller brightness value, and the calculated brightness value is used as a threshold value.

However, in the thermal image of the joint where the defect exists, the proportion occupied by the defect is not known in advance in the thermal image, and on the contrary, the proportion occupied by the defect is calculated by the threshold value. Therefore, this method cannot be used either.

A thermal image obtained by irradiating an object to be inspected with heat energy, receiving infrared rays radiated from the object to be inspected by an infrared camera, converting the infrared signal into an electric signal, and image-processing the thermal energy to be irradiated. , And the time at which infrared rays are captured. That is, as the irradiation heat energy increases and the time for capturing infrared rays elapses after the start of heat energy irradiation, the histogram of the number of pixels for the temperature obtained by image processing the thermal image shifts to the high temperature side.

Therefore, the threshold value for discriminating a defect must also shift to the high temperature side as the amount of thermal energy and the time at which infrared rays are taken in elapses.

Further, on a general printed wiring board, hundreds of parts are mounted through thousands of soldered joints, but the mounting density is high in order to miniaturize the equipment and to enhance its functionality. It is getting higher and higher. Accordingly, the lead pitch, lead width and lead length are reduced. When the joint portion is miniaturized, fine defects that have not been a problem in the past affect the quality of the joint portion, and higher inspection accuracy is required.

In the inspection method in which defects are discriminated by the threshold value and the quality of the joint is determined, the setting of the threshold value has a significant influence on the inspection accuracy.

Further, when the joint portion is miniaturized, the influence of heat diffusion through the wiring connected at the joint portion increases.
When the heat diffusion is large like the wiring connected to the power source or the ground, the temperature rising speed of the joint portion due to the heat energy is reduced. On the contrary, in the case of a short wiring connected to the adjacent electronic component, the temperature rise of the joint portion is accelerated. In this way, when the influence of heat diffusion through the wiring connected to the joint comes out, the area of the defect cannot be accurately calculated with the same threshold value for the thermal image of each joint of the same electronic component. .

On the other hand, there are cases where the same electronic component has different lead sizes. In this case as well, due to the difference in the lead size, the difference in the heat capacity of the lead and the difference in the temperature rising speed of the joint due to the thermal energy also occur, and the same threshold is applied to the thermal image of each joint of the same electronic component. The value cannot accurately calculate the area of the defect.

High reliability is required for the inspection of the joint portion, and demand for workability of the inspection is also increasing. In order to improve the workability of the inspection, it is required to shorten the judgment time, but for that purpose, a threshold value is required that can judge many kinds of defects at the same time and judge the quality of the joint portion at the same time.

[0032]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and the amount of heat energy to be radiated,
Regardless of the time at which infrared rays are captured, the type of wiring connected to the joint, or the size of individual leads connected to external wiring, the types of various defects are determined at once, and the An object of the present invention is to provide a method for inspecting a joint part of an electronic component, which sets an optimum threshold value for determining the quality and accurately determines the quality of the joint part of the electronic component.

[0033]

In order to achieve the above object, the present invention provides a portion to be inspected, which comprises a joint portion including a heat conductive member to be connected to a wiring pattern on a substrate according to claim 1. Thermal energy is radiated, infrared rays radiated from the inspected portion are imaged by an infrared camera, and the obtained thermal image is free from defects and has a number of pixels in a range outside the temperature range indicated by a normal surface. In the method of inspecting the joint of an electronic component for determining the quality of the joint state of the portion to be inspected by obtaining the ratio to the number of pixels, the wiring pattern is set to the upper limit value or the lower limit value of the temperature range indicated by the normal surface. The temperature range threshold value is determined by correcting the number of pixels within the temperature range of the joint to be inspected and the number of pixels outside the temperature range are determined using this threshold value. The method for inspecting a joint part of an electronic component, wherein a ratio between the number of pixels within the temperature range and the number of pixels outside the temperature range is obtained. Thermal energy was applied to a portion to be inspected including a joint to be connected to a wiring pattern on a substrate including a heat conductive member, and infrared rays emitted from the portion to be inspected were imaged by an infrared camera to obtain an infrared ray. Regarding the thermal image, the ratio of the number of pixels in the range outside the temperature range indicated by a normal surface having no defect to the number of pixels of the inspected part is obtained, and by this, the bonding of electronic components for judging the quality of the bonded state of the inspected part In the method of inspecting a portion, the upper limit value or the lower limit value of the temperature range indicated by the normal surface is corrected according to the size of the joint to determine a temperature range threshold value, and the inspection is performed using this threshold value. Should The number of pixels within the temperature range of the joint and the number of pixels outside the temperature range are calculated, and the ratio between the number of pixels within the temperature range and the number of pixels outside the temperature range is calculated. The method for inspecting a joint part of an electronic component, and the number of pixels within the temperature range in the method according to claim 1 or 2 and a range outside the temperature range. The present invention provides a method for inspecting a joint part of an electronic component, which determines the type of defect based on the size of the ratio to a certain number of pixels.

[0034]

In this method, the upper limit value or the lower limit value of the temperature range of the normal surface without the defects of the same kind of electronic parts joint under the same heating and imaging conditions is set as the threshold value,
The defect type is determined by the ratio (defect area ratio) of the number of pixels in the temperature region that exceeds the threshold value or is below the threshold value to the number of pixels of the inspection object, and the quality of the joint is determined.

When there is a difference in the type of wiring connected to the electronic component or the size of the individual leads of the electronic component, there is no defect in the standard joint and the upper or lower limit of the normal surface temperature range. The threshold value is the value obtained by multiplying the value by a constant coefficient according to the wiring type and the size of each lead, and the number of pixels in the temperature range that exceeds or falls below the threshold value. The type of defect is determined by the ratio (defect area ratio) to the number of pixels of the object to be inspected, and the quality of the joint is determined.

As a result of the above method, first, the threshold value shifts to the high temperature side according to the magnitude of the thermal energy to be irradiated and the time at which infrared rays are captured and a thermal image is captured. When determining the threshold, set the normal heating conditions and imaging conditions of the same type of electronic parts without defects
By making the heating conditions and the imaging conditions for the actual joint inspection of the electronic component joint the same, it is possible to determine the threshold value that is suitable for the inspected object and correctly identify the defective portion and the normal portion. You can

Second, since the upper limit value or the lower limit value of the temperature range indicated by a normal surface without defects of the same kind of electronic part joint under the same heating and imaging conditions is used as the threshold value, There is no ambiguity in the determination of threshold values, and highly reliable and highly accurate inspection can be performed.

Thirdly, when there is a difference in the type of wiring connected to the electronic component or the size of the individual leads of the electronic component, there is no defect in the standard joint and the upper limit of the normal temperature range of the surface is obtained. The threshold value is the value obtained by multiplying the value or the lower limit value by a constant coefficient according to the wiring type and the size of each lead, etc. It is possible to cancel the influence of the difference in heat capacity on the thermal image.

Fourthly, the ratio of the number of pixels in the temperature region exceeding the threshold value or below the threshold value to the number of pixels of the object to be inspected (defect area ratio) accurately corresponds to the type of defect. Therefore, the type of defect can be determined at once by the value of the defect area ratio.

Fifth, in the electronic part joint, the ratio of the number of pixels in the temperature range exceeding the upper limit of the normal temperature range of the joint surface without defects to the number of pixels of the inspection object (defect area ratio) is Since it closely corresponds to the joint strength of the joint, the quality of the joint can be simultaneously judged by the value of the defect area ratio.

Sixth, the ratio of the number of pixels in the temperature region below the lower limit of the temperature range of a normal surface having no defect to the number of pixels of the inspection object (the defect area The rate closely corresponds to whether or not a short circuit due to solder has occurred between the leads, so that the quality of the joint portion can be determined at the same time by the value of the defect area ratio.

Seventh, in the area adjacent to the electronic component joint, the ratio of the number of pixels in the temperature range in which there is no defect and exceeds the upper limit of the temperature range of the normal surface to the number of pixels of the inspection object (defect area ratio). Since () closely corresponds to the occurrence of a short circuit between the wiring and the lead during the use period, it is possible to simultaneously judge the quality of the joint portion based on the value of the defect area ratio.

[0043]

EXAMPLE A joint part of an electronic component to which the present invention is applied is
Soldering, brazing, diffusion bonding (bonding due to mutual diffusion of both molecules during contact, pressurization, and heating), thermocompression bonding (destruction of oxide film due to slippage at bonding interface caused by material deformation) And the subsequent bonding based on mutual diffusion), bonding (bonding with an adhesive), and the like. However, in the examples described below, the case of a soldered joint of an electronic component was taken up.

The object to be inspected is a resin-molded gull-wing type QFP [100 pins, lead material is Fe].
-Ni alloy (42 alloy), lead pitch 650 μm,
Lead width is 300 μm, lead length (joint part) is 120
0 μm, lead thickness is 150 μm], 63Sn-37Pb eutectic solder paste is printed on a glass epoxy substrate on which a copper pattern (wiring) having a thickness of 35 μm is formed, and reflow is performed using an infrared soldering device. After being prepared, it was ultrasonically cleaned with acetone for 5 minutes and used.

FIG. 1 shows the size and shape of the object to be inspected. In the figure, 1 is a lead, 2 is a pattern, 3 is solder, and 4 is a substrate. The portion of the lead 1 joined to the substrate 4 by the solder 3 is the joint to be inspected.

This inspection object is irradiated with thermal energy by an automatic inspection system (not shown), infrared rays radiated from the inspection object are received, and the captured thermal image is image-processed to obtain the temperature distribution on the surface of the inspection object. Was measured.

A YAG laser was used as the thermal energy, and the laser was irradiated vertically from directly above the joint, coaxial with the microscope. Laser irradiation output is 24W, irradiation diameter is 20
The center of the irradiation diameter was made to coincide with the center of the joint portion of the lead at 00 μmΦ, and the entire surface of the lead portion of the joint portion was irradiated. The irradiation time is 66.7 ms, and the imaging time is 33.3 ms after the start of irradiation.
It is 33.4 ms between 66.7 ms. Since the upper limit of the temperature range of the normal joint surface without defects was 94 ° C, 94 ° C was used as the threshold value.

For easy viewing, FIG. 2 shows a histogram of the number of pixels and a threshold value with respect to the temperature obtained by image-processing the thermal image of the inspection object. In the figure, 5 is a histogram of the number of pixels in a 1200 × 300 μm range of a normal junction having no defects, and 6 is an upper limit value (threshold value) of temperature. Pixels exceeding the threshold value in the thermal image of the bonded portion correspond to defects such as voids, insufficient solder, insufficient wetting, and unbonded.

FIG. 3 shows a histogram of the number of pixels and a threshold value with respect to the temperature in the range of 1200 × 300 μm in the joint portion including a defect (void) at the joint interface. In the figure, 6 is a threshold value and 7 is a histogram of a joint portion including a defect (void).

The area of the defect was 98817.20 μm ^{2 when} the area of the defect was calculated from the number of pixels in the temperature region which exceeded the threshold value of the histogram of the joint portion containing the defect (void). On the other hand, the area of the defect (void) measured by breaking the bonded portion was 96193.36 μm ² , and the inspection result proved that the dimension of the defect was measured with high accuracy (error within 3%). As can be seen in FIG. 1, the pattern in this case is shown to be as short as necessary.

FIG. 4 shows an example of a pattern (wiring) connected to an electronic component. In the figure, the wiring 8 is the case where it is connected to an adjacent electronic component and is as short as a necessary minimum, the wiring 9 is the case of an intermediate length, and the wiring 10 is the case where it is the longest connected to a power supply or ground.

When the type of wiring connected to each lead is different, the threshold value for each lead is set to a different value according to the type of wiring. That is, a value obtained by multiplying the upper limit value of the temperature of the normal joint surface without defects by the coefficient shown in Table 1 according to the type of wiring to be connected was used as the threshold value.

[0053] The threshold is 94 ° C for the minimum required minimum (in this case, this value is the standard), 84.6 ° C for the intermediate length, and 75.2 ° C for the longest. Is.

Using this threshold value, the area of the defect was determined from the number of pixels in the temperature region exceeding the threshold value, and it was in good agreement with the area of the defect measured by breaking the joint.

FIG. 5 shows an example of electronic components. In the figure, 11 is a standard lead, 12 is a larger standard, and 13 is a smaller standard.

As described above, when there is a difference in the lead size in one electronic component, the threshold value for each lead is set to a different value according to the lead size. That is, the value obtained by multiplying the upper limit value of the temperature range of the normal joint surface without defects by the coefficient shown in Table 2 was used as the threshold value.

[0057] In the case of the standard lead of this electronic component, the maximum temperature of the normal joint surface without defects was 81 ° C. This is the case when the wiring to be connected is as short as necessary. The threshold for reads larger than standard is 72.9 ° C and the threshold for reads smaller than standard is 89.1 ° C.

Using this threshold value, the area of the defect was determined from the number of pixels in the temperature region that exceeded the threshold value, and it was in good agreement with the area of the defect measured by breaking the joint.

When both the wiring to be connected and the lead of the electronic component are changed, the standard threshold value is multiplied by the coefficient obtained by multiplying the respective coefficients shown in Table 1 and Table 2 by the threshold value. And For example, in an electronic component in which the threshold value for the standard lead is 81 ° C., when the longest wiring is connected to the lead larger than the standard, the coefficient 0.9 for the lead larger than the standard and the coefficient 0. A coefficient of 0.72 multiplied by 8 was multiplied by a threshold value of 81 ° C. for a standard lead, and a value of 58.3 ° C. was used as a threshold value.

Also in this case, when the area of the defect was obtained from the number of pixels in the temperature region exceeding the threshold value, it was in good agreement with the area of the defect measured by breaking the joint.

In order to discriminate the kind of defect by the ratio of the number of pixels in the temperature region exceeding the temperature indicated by the threshold value to the number of pixels of the object to be inspected (defect area ratio), the judgment standard shown in Table 3 was applied. . The inspection results were in good agreement with the types of defects observed by breaking the joint.

_{Table 3} Defect area ratio (%) Judgment standard 0 to 30 Good 31 to 70 Void 71 to 90 Insufficient solder or insufficient wetting 91 to 100 Unbonded (Lead floating) In Table 3, it was determined that the bonded portion with a defect area ratio of up to 30% was good. This is because it was confirmed as a result of an experiment that the defect area ratio does not affect the strength of the bonded portion up to 30%.

The above is an example of actual measurement of defects existing in the joint itself.

At the soldered joint portion of the electric circuit board, defects existing in regions adjacent to the joint portion such as bridges and solder balls also occur. An example of this case will be described below.

FIG. 6 shows a copy of a thermal image in which a bridge exists. In the figure, 14 is a lead, 15 is a substrate, 1
6 is a thermal image of the bridge. As shown, the bridge is shown cooler than the glass epoxy substrate.

Under the same object to be inspected, the same heating and imaging conditions as those of the actual measurement examples described in FIGS. 1 and 2, the temperature of the substrate was measured by providing a measurement visual field in the portion of the substrate between the leads. Since the lower limit of the temperature range of a normal substrate without defects was 86 ° C, 86 ° C was used as the threshold value.

FIG. 7 shows a substrate 120 having a bridge.
The histogram of the number of pixels with respect to temperature and the threshold value in the range of 0 × 350 μm are shown. In the figure, 17
Is a threshold value for detecting the bridge, and 18 is a histogram of the substrate on which the bridge exists.

The area of the bridge obtained from the number of pixels in the temperature range below the threshold value and the area of the actually measured bridge were in good agreement.

The standard for judging the quality in the presence of the bridge is shown in Table 4. It was judged that the bonded portion with a defect area ratio of up to 15% was good. This is because it was empirically confirmed that the bridge does not exist up to the defect area ratio of 15%.

[0070] FIG. 8 shows a copy of a thermal image in which solder balls are present.
In the figure, 14 is a lead, 15 is a substrate, and 19 is a thermal image of a solder ball. As shown, the solder balls are shown at a higher temperature than the glass epoxy resin substrate.

The temperature of the substrate was measured by providing a measurement field of view in the portion of the substrate between the leads under the same object to be inspected, the same heating and imaging conditions as the actual measurement example described in the case of the bridge. Since the upper limit of the temperature range of a normal substrate without defects was 108 ° C, 108 ° C was set as the threshold value.

In FIG. 9, one of the substrates having solder balls is shown.
The histogram of the number of pixels with respect to temperature and the threshold value in the range of 200 × 350 μm are shown. In the figure,
20 is a threshold value for detecting a solder ball,
21 is a histogram of the substrate on which the solder balls are present.

The solder ball area obtained from the number of pixels in the temperature range exceeding the threshold value and the actually measured solder ball area were in good agreement.

Table 5 shows the standard for judging the quality when the solder balls are present. It was judged that the bonded portion with a defect area ratio of up to 20% was good. This is because it is empirically confirmed that a short circuit between the wiring and the lead does not occur during the use period up to the defect area ratio of 20%.

[0075] Although the embodiments of the present invention have been specifically described with reference to the drawings, the scope of application of the present invention is not limited thereto.

[0076]

Since the present invention is configured as described above, it has the following effects. First, according to the method of claim 1, the upper limit value or the lower limit value of the temperature range indicated by the normal joint surface of the electronic component is corrected according to the length of the wiring pattern to be joined to obtain the temperature range threshold value. The number of pixels within the temperature range of the joint to be inspected and the number of pixels outside the temperature range are determined using this threshold value, and the number of pixels within the temperature range and the temperature range are determined. Since the ratio with the number of pixels in the outlying range is calculated,
It is possible to provide a method for determining the quality of a joint in which the determination error due to the length of the wiring pattern to be joined is extremely reduced. Next, according to the method of claim 2, the upper limit value or the lower limit value of the temperature range indicated by the normal joint surface of the electronic component is corrected according to the size of the joint portion to determine the temperature range threshold value. , The number of pixels in the temperature range of the joint to be inspected and the number of pixels in the range out of the temperature range are obtained using this threshold value, and the number of pixels in the temperature range and the temperature range are out of the range. Since the ratio with the number of pixels in the range is obtained, it is possible to provide a method for determining the quality of a joint, in which the determination error due to the size of the joint is extremely small. Further, according to the method of claim 3, the type of defect is determined by the magnitude of the ratio of the number of pixels within the temperature range and the number of pixels outside the temperature range in the method according to claim 1 or 2. By doing so, it is possible to accurately grasp what kind of defect has occurred and to lead to a subsequent defective product prevention measure.

When the type of the wiring connected to each joint of the electronic component is different, a constant coefficient is applied to the upper limit value or the lower limit value of the temperature range of a normal surface without defects depending on the type of the connected wiring. Since the value multiplied by is used as the threshold value, highly reliable and highly accurate inspection can be performed without being affected by heat diffusion due to the type of wiring.

When the lead size is different in one electronic component, the threshold value is a value obtained by multiplying the upper limit value or the lower limit value of the temperature range of a normal surface having no defect by a constant coefficient according to the lead size. Therefore, unlike the prior art, highly reliable and highly accurate inspection can be performed without being affected by the heat capacity due to the size of the lead.

[0079]

[0080]

[0081]

By grasping the entire joint as a surface, the temperature distribution corresponding to the shape of the defect in the joint is stored as a thermal image, the soldering defect in the joint is determined based on image processing, and the quality of the joint is determined. In the method for inspecting the joint part of an electronic component, the thermal image of the inspected object is tested outside the normal temperature range without defects of the same type of inspected object under the same heating and imaging conditions. If you extract the pixels in the temperature range,
Since the shape of the defect of the joint can be detected with high accuracy, the reliability of the inspection is high, and when the electric circuit board inspected by applying the method of the present invention is incorporated into a product, a failure due to a solder defect is caused. Etc. will not occur.

Further, since the type and size of the defect can be discriminated, if the discrimination result is fed back to the soldering process which is the previous process, it contributes to the improvement of the soldering process and the occurrence of the defect is prevented beforehand. It is possible to make industrial contributions, such as

[Brief description of drawings]

FIG. 1 is a plan view and a side view of a joint portion of an electronic component.

FIG. 2 is a histogram of the number of pixels for a defect-free and normal junction temperature.

FIG. 3 is a histogram of the number of pixels with respect to the temperature of a joint including a defect (void).

FIG. 4 is a perspective view of wiring connected to a joint portion of an electronic component.

FIG. 5 is a plan view showing a lead of an electronic component.

FIG. 6 is a copy of a thermal image having a defect (bridge).

FIG. 7 is a histogram of the number of pixels with respect to the temperature of a substrate having a defect (bridge).

FIG. 8 is a copy of a thermal image in which defects (solder balls) are present.

FIG. 9 is a histogram of the number of pixels with respect to the temperature of a substrate having a defect (solder ball).

[Explanation of symbols]

1 Lead 2 Pattern 3 Solder 4 Substrate 5 Histogram of Number of Pixels at Normal Temperature without Defects 6 Upper Limit (Threshold) 7 Histogram of Number of Pixels at Temperature of Junctions Containing Defects (Voids) 8 Minimum required short wiring 9 Intermediate length wiring 10 Longest wiring 11 Standard lead 12 Lead larger than standard 13 Lead smaller than standard 14 Thermal image of lead 15 Thermal image of glass epoxy resin substrate 16 Defect (bridge) Thermal image 17 Threshold for detecting bridge

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Susumu Aono 3-6-40, Koyodai, Kawanishi-shi, Hyogo (72) Inventor Minoru Nakamura 1-20-14, Koji Higashi, Ikuno-ku, Osaka, Osaka (72) ) Inventor Takeo Sakai 2-8-65, Yoshinodai, Kawagoe City, Saitama Denyo Co., Ltd. Saitama Factory (56) References JP-A-2-12046 (JP, A) JP-A-2-198347 (JP, A) JP-A-50-74167 (JP, A) JP-A-2-278105 (JP, A)

Claims (3)

(57) [Claims] 1. An infrared camera irradiates an infrared ray emitted from the inspected portion by irradiating thermal energy to an inspected portion including a joint portion which includes a heat conductive member and is to be connected to a wiring pattern on a substrate. Then, for the obtained thermal image, the ratio of the number of pixels in the range outside the temperature range indicated by a normal surface having no defects to the normal area is obtained, and the ratio of the number of pixels in the inspected part to the quality of the bonding state of the inspected part is determined. In the method of inspecting a joint part of an electronic component, the upper limit value or the lower limit value of the temperature range indicated by the normal surface is corrected according to the length of the wiring pattern to determine a temperature range threshold value. The number of pixels in the temperature range of the joint to be inspected and the number of pixels in the range out of the temperature range are obtained by using the number of pixels in the temperature range and out of the temperature range. Characterized in that so as to obtain a ratio of a prime number, method of inspecting a joint portion of the electronic component. 2. An infrared camera irradiates an infrared ray radiated from the inspected portion with an infrared camera by irradiating the inspected portion including a heat conductive member to be connected to a wiring pattern on a substrate with thermal energy. Then, for the obtained thermal image, the ratio of the number of pixels in the range outside the temperature range indicated by a normal surface having no defects to the normal area is obtained, and the ratio of the number of pixels in the inspected part to the quality of the bonding state of the inspected part is determined. In the method of inspecting a joint portion of an electronic component, the upper limit value or the lower limit value of the temperature range indicated by the normal surface is corrected according to the size of the joint portion to determine a temperature range threshold value. The number of pixels in the temperature range of the joint to be inspected using and the number of pixels in the range out of the temperature range are obtained, and the number of pixels in the temperature range and the pixel in the range out of the temperature range Characterized in that so as to obtain a ratio between a method of inspecting a joint portion of the electronic component. 3. The method according to claim 1 or 2, wherein the type of defect is determined by the ratio of the number of pixels within the temperature range and the number of pixels outside the temperature range. A method of inspecting joints of electronic components.