JP2009085923A - Void inspection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a void inspection method capable of reducing the contrast of light and darkness of an X-ray image caused by the difference in the transmission distance of X-rays transmitted through a cooling member and identifying the presence or absence of voids.
When an inspection object having a semiconductor element 60 soldered to a cooling member 50 is inspected, a direction 12 perpendicular to the plate surface of the inspection object and an irradiation direction 11 of an X-ray 10 form an imaging angle θ. The X-ray 10 is incident on the inspection object. Thereby, the transmission distance of the X-ray 10 in the rib part of the cooling member 50 becomes short. For this reason, the presence or absence of the void 80 in the solder joint 70 can be determined.
[Selection] Figure 5

Description

  The present invention relates to a method for inspecting a solder joint. More specifically, the present invention relates to an inspection method using X-rays for the presence or absence of voids (hereinafter referred to as voids) which are bonding defects in solder joints.

  The semiconductor element generates a large amount of heat during use, and dissipates heat through the substrate to prevent malfunction and damage. The semiconductor element and the substrate are joined by soldering, and voids may be generated at the soldering joint. However, when a void is generated at the solder joint, the heat dissipation effect from the semiconductor element to the substrate is reduced. In addition, the air in the voids expands due to the heat generated by the semiconductor element, and the joint part may be peeled off or the semiconductor element may be damaged.

  In order to inspect the occurrence of voids in such solder joints, an inspection method using X-rays of the solder joints may be used. X-rays emitted from an X-ray source should be detected with the same intensity when transmitted through the same material for the same distance. Therefore, it is suitable for an inspection object having a flat shape having the same thickness. This is because, if the same material is used, X-ray absorption is uniform everywhere, so that the intensity of X-rays detected at a place where there is a void is different, and voids are easily identified.

However, when the thickness of the inspection object is not uniform, or when there is a gap inside, the X-ray transmission distance varies depending on the location of the inspection object, making it difficult to identify the void. . For this reason, Patent Document 1 discloses an inspection method by image processing of voids in spherical solder bumps.
JP 2002-280727 A

  However, some inspection objects include a semiconductor element soldered to a cooling member having a heat dissipation structure as shown in FIGS. Although this cooling member is plate-like as a whole, a gap is provided on the inner side for heat dissipation to increase the contact area with a cooling medium such as outside air. When such an inspection object is inspected by X-ray transmission, the X-ray transmission distance varies greatly depending on the location of the inspection object.

  For this reason, the heat dissipation structure of the cooling member is reflected in the X-ray image and appears as a large contrast. This is because the X-ray absorption is large at the thick part of the cooling member, and the X-ray absorption is small at the thin part due to the gap. Therefore, the void image is buried in this large contrast, making it difficult to identify. Further, since the X-ray transmission distance is large in the cooling fin or rib portion of the cooling member, the X-ray absorption amount is large. That is, the X-ray image is displayed very darkly. For this reason, even if there is a void at that location, there is almost no difference. Therefore, it is more difficult to identify voids.

  Under such background contrast, void information to be detected is buried in the background. For this reason, a threshold value for identifying a void cannot be set. Therefore, it is difficult to solve by the image processing method as disclosed in Patent Document 1.

  The present invention has been made to solve the above-described problems of the prior art. That is, the subject is to provide a void inspection method that can reduce the contrast of X-ray images caused by the difference in the transmission distance of X-rays transmitted through a cooling member, and identify the presence or absence of voids. It is.

  In order to solve this problem, the void inspection method of the present invention irradiates a plate-shaped inspection object with X-rays generated from an X-ray source, and transmits the X-rays transmitted through the inspection object to the X-rays. A void inspection method for detecting the presence or absence of voids in the inspection object based on the detected X-ray intensity distribution, which is detected by an X-ray detector arranged on the other side of the inspection object as viewed from the source, The object has a structure including a place where absorption is large and a place where X-ray is transmitted in a direction perpendicular to the plate surface, and the X-ray irradiation direction is a direction inclined from the direction perpendicular to the plate surface. It is characterized by this.

  Here, the X-ray irradiation direction is the direction of the center of the X-ray to be irradiated. Such a void inspection method can reduce the difference in the X-ray transmission distance due to the gap of the inspection object. For this reason, it is possible to suppress the difference in brightness of the image.

  In the above, when the angle formed by the X-ray irradiation direction and the inspection object is changed, an angle at which the difference in X-ray contrast due to the structure of the inspection object is minimized is selected, and the inspection is performed at that angle. Good. This is because the difference in brightness of the image can be further suppressed.

  In the above, the inspection object is obtained by joining a cooling element having a structure including a place where absorption is large and a place where absorption is small when X-rays are transmitted in a direction perpendicular to the plate surface, and a semiconductor element by soldering. Yes, it is even better to check for the presence of voids inside the solder. This is because the voids in the solder joints can be inspected in a state where the difference in brightness of the X-ray image due to the ribs of the cooling member is smaller.

  According to the present invention, there is provided a void inspection method in which the contrast between light and dark in an X-ray image caused by a difference in transmission distance of X-rays transmitted through a cooling member is reduced and the presence or absence of voids can be identified.

[First embodiment]
DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the best mode for embodying the present invention will be described in detail with reference to the accompanying drawings. In the present embodiment, the present invention is embodied with respect to an inspection method using X-rays for voids in solder joints.

  The void inspection method according to this embodiment is performed under a configuration as shown in FIG. The void inspection apparatus 100 includes an X-ray source 20, an X-ray camera 30, an image processing unit 40, and a display 41. The X-ray source 20 generates X-rays 10. The X-ray camera 30 detects and images the X-ray 10 irradiated from the X-ray source 20 and transmitted through the inspection object. The image processing unit 40 outputs the intensity of the X-ray 10 at each position detected by the X-ray camera 30 as the density of the image. With this output, the display 41 displays an image.

  Here, the X-ray camera 30 faces the X-ray source 20. Further, the X-ray 10 irradiated from the X-ray source 20 toward the X-ray camera 30 is irradiated with a spread of an angle φ from the irradiation direction 11 (one-dot chain line in FIG. 4) at the center of the X-ray 10. Further, the X-ray source 20 and the X-ray camera 30 are arranged so as to be inclined so that the vertical direction 12 and the irradiation direction 11 form an imaging angle θ. Here, tilting is performed so that the imaging angle θ spreads and becomes larger than φ (θ−φ> 0).

  Next, the procedure of the inspection method will be described with reference to FIG. The inspection object used here is one in which the cooling member 50 and the semiconductor element 60 are joined by the solder joint portion 70. The cooling member 50 has a structure as shown in FIG.

  First, the X-ray 10 is generated by the X-ray source 20. The X-ray 10 is irradiated on the inspection object, passes through the inspection object, and then enters the X-ray camera 30. Thereby, the inspection object is imaged.

  When the X-ray 10 passes through the inspection object, the X-ray 10 is absorbed by the transmitted inspection object. The amount of absorption depends on the type of substance that has passed through and the distance that has passed through the substance. Thus, the X-ray 10 after being absorbed by the substance is detected by the X-ray camera 30. Thereafter, the intensity of the X-ray detected by the X-ray camera 30 is output to the image processing unit 40.

  Thereafter, the image processing unit 40 performs various image processing. At this time, the presence or absence of the void 80 is determined. This image can be viewed on the display 41. On the display 41, a portion where the X-ray 10 is less absorbed in the object to be inspected is displayed with a bright brightness, and a portion with a large amount of absorption is displayed dark.

  Next, a method for identifying the void 80 according to this embodiment will be described. The X-ray 10 is absorbed by the cooling member 50, the semiconductor element 60, and the solder joint portion 70. However, since the main part of the semiconductor element 60 is a wafer and is thin, the X-ray 10 is hardly absorbed. For this reason, the X-ray 10 detected by the X-ray camera 30 is mainly absorbed by the cooling member 50 and the solder joint 70.

  Here, the irradiation direction 11 of the X-ray 10 forms an imaging angle θ with the vertical direction 12. Therefore, the X-ray 10 is incident at an angle close to θ with respect to the vertical direction of the plate surface. The maximum value of the incident angle is θ + φ, and the minimum value is θ−φ. At this time, there is no place where the X-ray 10 is incident perpendicularly (θ−φ = 0) to the plate surface. The transmission distance of the X-ray 10 in the cooling member 50 at this time is shown in FIG. a is the thickness of the cooling member 50 where the rib portion 51 is not present, and b is the thickness of the cooling member 50 where the rib portion 51 is present.

  c1, c2, and c3 are distances at which the X-ray 10 passes through the cooling member 50 when the X-ray 10 passes through the transmission path C. d <b> 1 and d <b> 2 are distances of portions where the X-ray 10 passes through the cooling member 50 when the X-ray 10 passes through the transmission path D. e1 and e2 are distances at which the X-ray 10 passes through the cooling member 50 when the X-ray 10 passes through the transmission path E.

  At this time, the transmission distance c1 + c2 + c3 of the transmission path C of the X-ray 10 is larger than a + a and smaller than b. Similarly, the transmission distance d1 + d2 of the transmission path D of the X-ray 10 and the transmission distance e1 + e2 of the transmission path E of the X-ray 10 are also larger than a + a and smaller than b. That is, the difference between the maximum value and the minimum value of the transmission distance due to the transmission path is smaller than in the case where there is no inclination. For this reason, the brightness difference in the X-ray image by the cooling member 50 is not large.

  A part of the image displayed on the display 41 at this time is shown on the upper side of FIG. The repeated shading that appears faintly in this image is due to the presence of ribs in the cooling member 50 repeatedly. The lower side of FIG. 7 shows the intensity of X-rays on the upper one-dot chain line.

  Here, when the void 80 is present in the solder joint portion 70, the absorption of the X-ray 10 at the corresponding portion is reduced as compared with a place where there is no void 80. This appears as a remarkable brightness difference in the X-ray image. Therefore, the void 80 can be identified by setting a threshold value.

  Here, a method for identifying the void 80 will be described. F in FIG. 7 is the X-ray intensity at the place where the void 80 is present. G1 is the maximum value of the X-ray intensity at the place where there is no void 80, and G2 is the minimum value of the X-ray intensity at the place where there is no void 80. Since the cooling member 50 has a periodic structure, portions where the X-ray intensity takes values of G1 and G2 appear periodically. Therefore, G1 can be specified. Therefore, the presence or absence of the void 80 can be determined by setting a threshold value above G1 and below F.

  As described above, since the inspection is performed under the condition that the influence on the image of the cooling member 50 is small, the solder state of the solder joint portion 70 can be inspected.

  Here, the case where the imaging angle θ is 0 will be described with reference to FIGS. 8 and 9 for comparison with the present embodiment. At this time, the X-ray 10 is incident substantially perpendicularly to the plate surface of the inspection object as shown in FIG. The transmission distance of the transmission path A that passes through the cooling member 50 is a + a, and the transmission distance of the transmission path B is b.

  As is apparent from FIG. 8, the transmission distance of the X-ray 10 is approximately equal to either a + a or b. Since this appears alternately, the X-ray image becomes a striped pattern having a higher contrast than that in FIG. 7, as shown in the upper side of FIG. The portion where the transmission distance is b is dark on the display 41 because X-ray absorption is strong. In this way, the X-ray absorption is too strong at the portion that transmits the transmission distance b, so that even if the void 80 exists, it may not be detected.

  On the other hand, since the background contrast is strong, it may be buried in the background as shown in the lower side of FIG. For this reason, it becomes impossible to set a threshold value, and it becomes difficult to determine the presence or absence of the void 80.

  Thus, the maximum transmission distance can be reduced by the imaging angle θ provided in the present invention. For this reason, the image of the void 80 in the X-ray image does not disappear. Furthermore, the difference in transmission distance between transmission points can be reduced by the imaging angle θ. For this reason, the image of the void 80 can be prevented from being buried by a strong background contrast.

[Second form]
A second embodiment will be described with reference to FIG. The inspection apparatus according to the present embodiment includes the X-ray source 20, the X-ray camera 30, the image processing unit 40, and the display 41 as in the first embodiment. Further, the X-ray camera 30 and the X-ray source 20 face each other as in the first embodiment. Similarly to the first embodiment, the inspection object is also the one in which the cooling member 50 and the semiconductor element 60 are joined by the solder joint portion 70.

  The difference from the first embodiment is that the X-ray source 20 and the X-ray camera 30 are fixedly arranged so that the X-ray 10 is irradiated in the vertical direction. Instead, the inspection object is tilted at the imaging angle θ. Thereby, the same effect as the first embodiment can be obtained.

[Third embodiment]
A third embodiment will be described with reference to FIG. The inspection apparatus according to the present embodiment includes an X-ray source 20, an X-ray camera 30, an image processing unit 40, and a display 41. The functions of these parts are the same as in the first embodiment. Further, the X-ray camera 30 and the X-ray source 20 face each other as in the first embodiment. The inspection object is also the one in which the cooling member 50 and the semiconductor element 60 are joined by the solder joint 70 as in the first and second embodiments.

  The difference from the first and second embodiments is that the inspection apparatus according to the present embodiment includes a motor 90 and a motor control unit 91 in addition to the above. The motor 90 changes the imaging angle θ. The motor control unit 91 controls the motor 90 and adjusts the imaging angle θ. Thereby, an inspection can be performed under an arbitrary imaging angle θ.

  Here, when θ is rotated, the X-ray source 20 and the X-ray camera 30 may be rotated as a set around the inspection object. Further, the inspection object may be rotated while the X-ray source 20 and the X-ray camera 30 are fixed. This is because there is no change in setting the imaging angle θ.

  FIG. 12 exemplifies the relationship between the inclination angle and the difference between the maximum value and the minimum value of the transmission distance of the inspection object transmitted through the X-ray 10. At this time, the difference in transmission distance is minimized when the inclination angle is around 22 °. Therefore, by adopting this imaging angle θ = 22 °, it is possible to identify the void 80 while minimizing the influence of the contrast of the cooling member 50 as much as possible. Thereby, the presence or absence of the void 80 can be more reliably determined.

  In addition, the imaging angle θ can be automatically adjusted by feeding back to the motor controller 91 the brightness difference of the X-ray image with respect to the change in the imaging angle θ. Thereby, the presence or absence of the void 80 can be more reliably determined.

  This embodiment can obtain the same effects as those of the first embodiment and the second embodiment. Furthermore, the presence or absence of the void 80 can be more reliably determined by adopting the optimum inclination angle. In addition, by automatically correcting the imaging angle θ, it is possible to select an optimal imaging angle θ according to individual differences of inspection objects.

  As described above in detail, in the void inspection method according to the present embodiment, the plate surface of the inspection object and the X-ray are inclined from the vertical direction. The difference in the transmission distance was reduced. For this reason, the influence of the cooling member in the X-ray image can be reduced, and a threshold value for identifying the void can be set. This realizes a void inspection method that can more reliably determine the presence or absence of voids.

  Here, the inspection object is not limited to a semiconductor member soldered to the cooling member. This is because the effect of the present invention can be obtained if the influence of the background due to the shape as shown in FIGS. The same applies to a case where there is a member such as an insulating substrate having a uniform thickness on the solder joint surface side of the cooling member with the semiconductor element.

  Note that this embodiment is merely an example, and does not limit the present invention. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof. For example, the X-ray detection device may be an X-ray camera that detects X-rays in two dimensions, a point detection device, or a line counter.

  Further, the motor 90 is not limited to the one used for rotating the imaging angle θ. For example, it may be manual. This is because the effect is the same as long as the imaging angle θ can be continuously changed.

  Further, the image displayed on the display 41 is bright where the intensity of X-rays detected by the X-ray camera 30 is large and dark where it is small, but the light and dark may be reversed. This is because the void 80 can be detected by setting the threshold value.

  Moreover, the rib part 51 in the cooling member 50 does not need to be arrange | positioned periodically. This is because the void 80 can be detected by setting the threshold value.

  Alternatively, the void 80 may be identified by taking a plurality of imaging angles θ. This is particularly effective when the difference in transmission distance when the imaging angle θ is changed as shown in FIG. 12 has a plurality of minimum values. Furthermore, the determination of the presence / absence of the void 80 will be confirmed again, and the accuracy of the inspection can be further increased.

  In addition, various image processing can be performed on the obtained X-ray image. For example: First, only the cooling member 50 is carried into the void inspection apparatus 100. Next, the X-ray transmission distance data at the imaging angle θ is acquired while rotating the imaging angle θ by the motor 90. At this time, the angle at which the contrast of the X-ray image is the smallest is selected. Next, an X-ray image of the X-ray intensity at the selected inclination angle θ is stored, and an X-ray image including only the semiconductor element 60 and the solder joint portion 70 can be formed by subtracting the stored pattern. Thereby, setting of a threshold value for identifying the void 80 is facilitated, and specification of the size and range of the void 80 is facilitated.

It is a figure (the 1) which shows the structural example of a cooling member. It is FIG. (2) which shows the structural example of a cooling member. It is a figure (the 3) which shows the structural example of a cooling member. It is a block diagram (the 1) for enforcing the inspection method concerning a 1st form. It is a block diagram (the 2) for enforcing the inspection method concerning a 1st form. It is a figure explaining the transmission distance of the X-ray which permeate | transmits a cooling member when there exists an inclination. It is a figure explaining the X-ray image and X-ray intensity of the X-ray which permeate | transmitted the test target object when there exists inclination. It is a figure explaining the transmission distance of the X-ray which permeate | transmits a cooling member when there is no inclination. It is a figure explaining the X-ray image and X-ray intensity of the X-ray which permeate | transmitted the test target object when there is no inclination. It is a block diagram for enforcing the inspection method concerning the 2nd form. It is a block diagram for enforcing the inspection method concerning the 3rd form. It is a figure which illustrates the relationship between an inclination angle and the transmission distance of X-rays.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... X-ray 20 ... X-ray source 30 ... X-ray camera 50 ... Cooling member 60 ... Semiconductor element 70 ... Solder joint 80 ... Void 100 ... Void inspection apparatus (theta) ... Imaging angle

Claims (3)

X-rays generated from an X-ray source are irradiated to a plate-shaped inspection object,
X-rays that have passed through the inspection object are detected by an X-ray detection device disposed on the other side of the inspection object when viewed from the X-ray source,
A void inspection method for inspecting for the presence or absence of voids in the inspection object based on the detected X-ray intensity distribution,
The inspection object has a structure including a place where X-ray absorption is large and a place where X-ray absorption is small when X-rays are transmitted in a direction perpendicular to the plate surface.
A void inspection method, wherein the X-ray irradiation direction is a direction inclined from a direction perpendicular to a plate surface. The void inspection method according to claim 1,
The angle between the X-ray irradiation direction and the inspection object is changed to select an angle at which the difference in brightness of the X-ray intensity due to the structure of the inspection object is minimized, and the inspection is performed at that angle. Void inspection method. The void inspection method according to claim 1 or 2,
The inspection object includes a cooling member having a structure including a location where X-ray absorption is large and a location where X-ray absorption is small when X-rays are transmitted in a direction perpendicular to the plate surface, and a semiconductor element. It is joined by solder,
A void inspection method, wherein the presence or absence of voids inside the solder is inspected.

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