JP2011210921A - Junction inspection method and junction inspection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correctly identify the junction marks of a wire bonding junction after a shear test is performed, and to find a highly accurate wire residual rate.SOLUTION: The junction inspection test has: a step S1 to detect shear strength and perform a shear test, while wire bonding junctions 22 are sheared by a shear tester unit 32 at a fixed shear height H; and a step S2 to obtain the real picture 43 (i.e. pick-up image) of the junction marks 23 after the shear test is performed, to measure the height within a surface including the junction marks 23, to identify the aluminum residual section b of the junction marks 23 based on the height distribution within the surface including the junction marks 23 and the shear height H, and to identify the external form c of the junction marks 23 based on the real picture 43. The wire residual rate is calculated based on the aluminum residual area of the aluminum residual section b and the external form area of the external form c.

Description

  The present invention relates to a technique for inspecting a wire bond junction between an electrode such as a semiconductor chip and a wire.

  Generally, in a power semiconductor device, a surface electrode and a peripheral electrode of a semiconductor chip are connected to a conductive wire such as a gold wire, a copper wire, or an aluminum wire by ultrasonic bonding or the like. A power semiconductor device used as a switching element is used in a severe environment subject to thermal stress by repeatedly raising and lowering temperature from room temperature to 150 ° C. or more with power on / off. When such thermal stress is repeatedly applied, thermal strain due to the difference in linear expansion coefficient between the semiconductor chip and the wire (for example, aluminum wire) is applied to the surface electrode or wire of the semiconductor chip, resulting in cracks in the wire bond joint and progress. To do. When the crack progresses, the bonding area between the chip surface electrode and the wire decreases, and the electrical resistance increases, so the heat generation increases, the area of the heat dissipation path through the chip surface electrode and the wire also decreases, and the heat dissipation is also improved. As a result, the temperature of the semiconductor chip rises abnormally. Finally, melting of the chip surface electrode and the wire occurs, the semiconductor chip reaches the heat limit, the rectification function is lost, and a failure state occurs. The evaluation of the bonding reliability between the surface electrode and the wire is a heat shock cycle test in which the temperature is changed very rapidly by passing a large current intermittently through the semiconductor chip and the number of times is very high. A power cycle test is performed. The durability of the power cycle test, the so-called power cycle tolerance, is greatly affected by the bonding state of the wires.

  As a method for evaluating the bonding state of the wire, a “peel test” for measuring the tensile strength of the wire and a shear test for measuring the shear strength of the wire bond bonded portion are generally performed. The shear test device is equipped with a displaceable sample stage, shearing the wire bond joint with a tool that applies horizontal force to the sample, and the shear load (shear strength) applied to the tool from the sensor output. A shear tester (shear test device) for measuring is known.

  Generally, the shear strength is evaluated by the maximum load applied to the tool during shearing. In the evaluation by this maximum load, the state where the center part of the wire bond joint is not sufficiently joined and the wire bond joint It is difficult to make a difference in value between the state where the joint is sufficiently joined to the center of the part, and these states cannot be detected. Considering the fact that the center of the wire bond joint is not sufficiently bonded, the power cycle resistance is inferior compared to the state where it is fully bonded to the center, the difference between these bonded states cannot be detected. Since this is a problem in evaluating durability reliability, it is required to quantitatively grasp such a joining state.

  Thus, it has been proposed to use the wire remaining rate as an index for evaluating the bonding state. The wire remaining rate is the ratio of the wire remaining area in the outer area of the wire bond joint. This wire remaining area is obtained, for example, by binarizing the image of the wire bond bonded portion after the shear test by an image processing computer and based on the ratio of the wire remaining area and the bonded area (outer area) (for example, patent Reference 1).

Japanese Patent No. 4220286

However, in measuring the outer shape of the wire bond joint and the remaining area of the wire, the technique for obtaining the area from the binarized image after the shear test is based on the influence of the image state before the binarization processing and the shape peculiar to the wire. There are large variations in the measured wire remaining area. For example, when aluminum wires of the same color are bonded on a semiconductor chip having a silver-white aluminum electrode surface, the contrast between the chip surface and the wire bond junction is difficult to attach on the image, so the threshold level for binarization is selected. Is difficult and accurate quantification is difficult.
In addition, the wire touches the chip surface during wire bonding, and the part where the wire material such as aluminum is slightly adhered to the chip surface, or the part where the wire is sheared and then torn after the shear test For a portion that is not joined but that shows an image similar to a wire bond joined portion, it is difficult to determine a boundary between joined and unjoined even by binarizing the image, and accurate quantification is difficult.

  The present invention has been made in view of the above-described circumstances, and accurately identifies the bonding trace of the wire bond bonded portion after the shear test, and can determine the wire remaining rate with high accuracy, and It aims at providing a junction inspection device.

  In order to achieve the above object, the present invention includes a step of shearing a wire bond joint with a shear tester at a certain shear height, detecting a shear strength and performing a shear test, and a joint mark after the shear test. A step of measuring an in-plane height including the bonding trace, and an in-plane height distribution including the bonding trace and a wire remaining portion of the bonding trace based on the shear height. And specifying the outer shape of the bonding trace based on the captured image, and calculating a wire remaining ratio from the wire remaining area of the wire remaining portion and the outer shape area of the outer shape. A method for inspecting a joint is provided.

According to the present invention, the captured image of the joint trace after the shear test is acquired, the height in the plane including the joint trace is measured, and the height distribution in the plane including the joint trace and the shear height are determined. Since the remaining wire portion of the bonding trace is specified based on the above, the remaining wire portion can be accurately specified even when the contrast between the chip surface and the wire bond bonding portion is difficult to be obtained on the captured image.
In addition, since the outer shape of the joint trace is specified based on the captured image, even if the base exposed portion where the base is exposed without any wire remaining is close to or connected to the base, The outline can be specified by accurately determining the boundary of the mark.
Thereby, a wire residual rate can be calculated | required correctly and it becomes possible to grasp | ascertain the joining state of a wire bond junction part more correctly now together with a shear test result.

Further, the present invention provides the above-described bonding portion inspection method, wherein an area in which an in-plane height including the bonding mark falls within a predetermined height range based on the shear height is specified as the wire remaining portion. Features.
According to the present invention, a wire material such as aluminum adhering to the chip surface, or a portion similar to the wire bond bonded portion that is not originally bonded, such as a portion where the wire bond bonded portion extends during shearing, and is a captured image. Thus, the remaining wire portion can be specified by accurately excluding the portion that cannot be identified by the binarization process.

Further, the present invention, in the above-described joint inspection method, during the shear test, the shear speed is set to be equal to or higher than a speed at which the wire bond joint does not generate elongation, and the peak value of the shear strength is detected. The tool provided in the shear tester is not less than a distance that does not leave a wire member in the joint trace, and the joint trace is applied to the joint trace by the reaction when the warp generated in the tool is released by the stress at the time of shearing of the wire bond joint portion. The movement of the tool is stopped when it is moved by a distance in a range that does not cause deformation.
According to the present invention, unnecessary deformation of the bonding marks after the shear test is prevented, and the wire remaining rate can be accurately obtained, so that the bonding state can be determined more accurately.

  In order to achieve the above object, the present invention shears the wire bond joint at a certain shear height, detects a shear strength and performs a shear test, and a joint test after the shear test. An image pickup means for acquiring a picked-up image, a height measurement means for measuring an in-plane height including the joint trace, an in-plane height distribution including the joint trace, and the shear height based on the shear height. Analysis means for specifying a wire remaining portion, specifying an outer shape of the bonding trace based on the captured image, and calculating a wire remaining ratio of the wire remaining portion and the outer shape area of the outer shape. There is provided a junction inspection apparatus characterized by the above.

According to the present invention, the captured image of the joint trace after the shear test is acquired, the height in the plane including the joint trace is measured, and the height distribution in the plane including the joint trace and the shear height are determined. Since the remaining wire portion of the bonding trace is specified based on the above, the remaining wire portion can be accurately specified even when the contrast between the chip surface and the wire bond bonding portion is difficult to be obtained on the captured image. In addition, since the outer shape of the joint trace is specified based on the captured image, even if the base exposed portion where the base is exposed without any wire remaining is close to or connected to the base, The outline can be specified by accurately determining the boundary of the mark. Thereby, a wire residual rate can be calculated | required correctly and it becomes possible to grasp | ascertain correctly the joining state of a wire bond junction part with a shear test result.
In the present invention, the wire remaining portion can be accurately identified by identifying an area where the in-plane height including the joint trace falls within a predetermined height range based on the shear height as the wire remaining portion. Can be specified.
Further, in the present invention, during the shear test, a tool provided in the shear tester is set after a shear speed is set to be equal to or higher than a speed that does not cause elongation in the wire bond joint portion and a peak value of the shear strength is detected. , A distance that does not leave a wire member in the bonding trace, and does not cause deformation in the bonding trace due to a reaction when the warp generated in the tool is released due to a stress at the time of shearing of the wire bond joint portion. By stopping the movement of the tool when moved by a distance, unnecessary deformation of the joint marks after the shear test is prevented, and the wire remaining rate can be obtained accurately, so the joining state can be determined more accurately. it can.

It is a figure which shows typically the structure of the junction part test | inspection apparatus which concerns on embodiment of this invention. It is a schematic diagram of the cross section of the power semiconductor device to be examined. It is a figure which shows the test | inspection procedure of the joining state of a wire bond junction part. It is explanatory drawing of a share test. It is a figure which shows the relationship between a wire bond junction part and a shear direction. It is a figure which shows an example of the entity image of a joining trace. It is a figure which shows the height distribution image obtained by measuring height for the same joining trace as the entity image shown in FIG. It is explanatory drawing of generation | occurrence | production of the elongation of the base material by a share speed. It is a figure which shows the time change of the detected value of the shear strength (shear load) at the time of a shear test. It is a figure which shows the distance which a tool moves before the detection value of a share intensity | strength falls 10%, 30%, and 90% from a peak value.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram schematically showing a configuration of a joint inspection apparatus 1 according to the present embodiment, and FIG. 2 is a schematic cross-sectional view of a power semiconductor device 3 to be inspected.
The joint inspection device 1 is a device for inspecting the bonding state of the wire bond joint 22 (FIG. 2) of the power semiconductor device 3, and the power semiconductor device 3 will be briefly described prior to the description of the device.

A power semiconductor device 3 shown in FIG. 2 is a package of a circuit for one phase of an AC output of a three-phase inverter circuit used in a power conversion device such as an electric vehicle. That is, the power semiconductor device 3 mounts a semiconductor chip 5 and a circuit element such as a diode constituting a circuit for one phase on the insulating circuit board 7 via the solder 6, and the insulating circuit board 7 forms the bottom surface of the package. The resin case 13 as a side wall surrounding the periphery of the base plate is provided on the heat sink 9 with the packing 14 interposed therebetween, and the inside of the resin case 13 is a silicone gel as a resin agent. 15 and sealed.
The semiconductor chip 5 is a switching element for supplying power corresponding to a large current, such as an IGBT, a power MOSFET, a thyristor, or a diode, and the insulating circuit board 7 is between a top board 7A and a bottom board 7B made of a metal plate. A substrate having a three-layer structure in which an insulating substrate 7C is sandwiched and bonded by a brazing material or the like. The upper substrate 7A and the lower substrate 7B may be formed of a conductor layer instead of a metal plate. The heat sink 9 is a plate material made of a metal having high thermal conductivity such as copper or aluminum.

  Further, the power semiconductor device 3 is provided with an external terminal 17 that is a peripheral electrode of the semiconductor chip 5 through the resin case 13 from the inside of the package to the outside. The external terminal 17 is electrically connected to the semiconductor chip 5 by an aluminum wire 20 made of aluminum as a conductive wire. That is, the aluminum wire 20 is a wire having a thickness of several tens μm to several hundreds μm, and one end thereof is bonded to the chip surface 5A of the semiconductor chip 5 by a load and ultrasonic waves, and the other end is similarly connected to the external terminal 17. It is joined. At the time of manufacturing the power semiconductor device 3, the bonding process is performed, and then sealing is performed with the silicone gel 15.

  The joint inspection apparatus 1 measures the shear strength of the wire bond joint 22 which is a joint between the chip surface 5A of the semiconductor chip 5 and the aluminum wire 20, and the wire remaining rate at the joint surface Q (FIG. 5). It is an apparatus for inspecting the joining state. That is, the joint inspection apparatus 1 includes a shear tester unit 32 for a shear test for measuring the shear strength and a wire residual ratio measuring unit 34 for measuring a wire residual ratio. And a computer 30 for controlling and analyzing the remaining rate measuring unit 34.

The share tester unit 32 fixes the semiconductor chip 5 as a sample to be inspected so as not to move at least in the movement direction (share direction) M of the tool 36 described later at the time of the shear test, and to the stationary stage 38. The chip surface 5A of the semiconductor chip 5 fixed to the fixed stage 38 is positioned at a predetermined shear height H with reference to the chip surface 5A, and is maintained in the predetermined shear direction M while maintaining the shear height H. And a tool 36 for shearing the wire bond joint portion 22 on the chip surface 5A and a load cell 40 for detecting a shear load during shearing.
During the shear test, the computer 30 detects the shear load at a plurality of measurement points with time based on the detection signal of the load cell 40 from the start to the end of the shearing of the wire bond joint 22, and the largest shear among them. The load is measured as the shear strength, which is an index of bonding strength.

The wire remaining rate measurement unit 34 includes a base 42 on which the semiconductor chip 5 after the shear test by the shear tester unit 32 is placed, and a solid image 43 of a bonding mark 23 formed by shearing the wire bond joint 22 by the tool 36. It incorporates a microscope 44 that is an imaging device that captures (FIG. 5) from the opposite side and outputs it to the computer 30, a laser light source and optical system of a 3D measurement laser microscope, a light receiving sensor for the amount of reflected light, etc. Scanning head 46.
The computer 30 acquires a multi-valued entity image 43 such as a grayscale image or a color image from the microscope 44, and the chip surface 5A in a range including the joint mark 23 based on the detection signal of the scanning head 46. Measure height.
The computer 30 may be provided separately for each of the shear tester unit 32 and the wire remaining rate measurement unit 34. Further, the wire residual ratio measuring unit 34 may be configured to obtain the substantial image 43 by causing the scanning head 46 of the 3D measurement laser microscope to function as the microscope 44.

FIG. 3 is a diagram illustrating an inspection procedure by the bonding portion inspection apparatus 1 in a bonding state of the wire bond bonding portion 22.
In evaluating the power cycle tolerance of the power semiconductor device 3, it is important to evaluate the bonding state of the aluminum wire 20, and the evaluation is performed as follows using the bonding portion inspection apparatus 1.
That is, as shown in FIG. 3, first, a shear test is performed to measure the shear strength of the wire bond joint portion 22 using the shear tester unit 32 (step S1). In this shear test, as shown in FIG. 4, the tool 36 of the shear tester unit 32 is held at a certain shear height H from the chip surface 5 </ b> A that is the bonding surface of the semiconductor chip 5, and this shear height H is maintained. As it is, the tool 36 is moved horizontally in the shear direction M (parallel to the joint surface), and the wire bond joint 22 is sheared. During this shearing process, the shear load applied to the tool 36 is sequentially detected by the computer 30, and the maximum value is measured as the shear strength.
The shear direction M is preferably parallel (0 degree) or perpendicular (90 degrees) to the aluminum wire width direction J. However, in this embodiment, as shown in FIG. The ultrasonic wire is joined in the direction parallel to the wire width direction J of the aluminum wire 20 which is perpendicular to the ultrasonic amplitude direction when the aluminum wire 20 is joined, ie, the length direction K of the aluminum wire 20.

Here, at the bonding surface Q between the chip surface 5A and the aluminum wire 20, as shown in FIG. 5, an unbonded portion R that is not sufficiently bonded is generated at the central portion O or the like of the bonding surface Q. The joining state of the joining surface Q is inspected by the following procedure.
That is, as shown in FIG. 3, the shape of the bonding mark 23 of the wire bond bonded portion 22 sheared by the shear test is measured by the wire residual ratio measuring unit 34 after the shear test in step S1 (step S2). In this shape measurement, the computer 30 captures a front image (an image captured facing the chip surface 5A) of the bonding mark 23 on the chip surface 5A, and an in-plane of the chip surface 5A including the bonding mark 23. Are obtained, and based on these, the outer area of the bonding mark 23 and the remaining wire area are specified.

FIG. 6 is a diagram illustrating an example of a substantial image 43 obtained by imaging the joint mark 23 with the microscope 44 serving as an imaging device.
In the figure, the base a in the entity image 43 corresponds to the chip surface 5A, and this chip surface 5A is, for example, a silver-white aluminum electrode surface, and therefore has substantially the same color as the aluminum wire 20. For this reason, it is difficult to provide contrast between the aluminum remaining portion b where the aluminum wire 20 remains after the shear test and the base exposed portion d where the base a which is the chip surface 5A is exposed without the aluminum wire 20 remaining, and the aluminum remaining portion b. However, the brightness is slightly darker than the base a and the base exposed portion d. Therefore, in the binarization process, if the base exposed portion d is whitened with reference to the base exposed portion d and the threshold value is reduced to distinguish it from the aluminum remaining portion b, the region of the aluminum remaining portion b is also whitened. The number of places will increase. On the other hand, if the remaining aluminum portion b is blacked on the basis of the remaining aluminum portion b and the threshold value is increased to distinguish it from the exposed base portion d, a portion that is blackened also in the region of the exposed base portion d. It will increase. As described above, when the threshold value is set based on one of the aluminum remaining portion b and the base exposed portion d, the other region becomes inaccurate, and the area ratio between the aluminum remaining portion b and the base exposed portion d is accurately set. It cannot be determined, and the bonding state of the wire bond bonding portion 22 cannot be accurately evaluated.
Therefore, in this embodiment, the share height H is kept constant during the share test so that the height of the remaining aluminum portion b of the joint mark 23 is substantially the same as the share height H, so that the joint mark The remaining aluminum portion b is specified on the basis of the height distribution in the surface of the chip surface 5A including 23 and the share height H at the shear test.

FIG. 7 is a diagram showing a height distribution image 50 obtained by measuring the height of the same joint mark 23 as the entity image 43 shown in FIG.
As shown in FIG. 7A, the height distribution image 50 has a height of share height H based on height distribution data 52 indicating the height distribution of the chip surface 5A obtained by laser height measurement. An area that falls within the range of ± margin α (in this embodiment, the share height H = 10 μm, margin α = 2 μm) is extracted as the remaining aluminum portion b, and the rest is binarized as the base a or the base exposed portion d. . Thus, by extracting the area based on the share height H, the remaining aluminum portion b after the share test can be accurately extracted. At this time, by excluding the range of the shear height H + the margin α or more, the wire material adhered to the chip surface during the wire bonding process or the aluminum wire 20 is sheared during the shear test, It is possible to accurately exclude a portion that is not originally joined, such as a portion that has been extended. The margin α is appropriately selected in order to accurately extract the remaining aluminum portion b in consideration of the parallelism between the moving direction of the tool 36 and the chip surface 5A at the shear test and the sheared surface roughness. It is a value set to. The share height H is desirably a height that exceeds the measurement error of the share tester unit 32 from the viewpoint of measurement accuracy. For example, if the measurement error is ± 2 μm, the share height H is desirably 4 μm or more.

In the height distribution image 50, the aluminum remaining portion b can be accurately extracted. However, when the base exposed portion d is close to or connected to the base a as shown in FIG. Alternatively, the boundary between the base exposed portion d and the base a becomes unclear at the connected portion X. Therefore, when the contours of the remaining aluminum portion b and the base exposed portion d are extracted from the height distribution image 50 and the outer shape c of the joint mark 23 is specified based on the respective contours, the base exposed portion d and the base exposed portion 50 The outer shape c at the location X where a is close or connected is unclear, and the outer shape c of the joint mark 23 cannot be accurately specified.
On the other hand, as shown in FIG. 6, in the entity image 43, by performing binarization processing, the outer shape c including the portion X where the base exposed portion d and the base a are close or connected can be extracted as a whole. . Therefore, in the present embodiment, for the outer shape c, the computer 30 binarizes the entity image 43 and specifies the outer shape c of the joint mark 23 based on the binarized image.

Through the processing as described above, as shown in FIG. 7B, the aluminum remaining portion b and the outer shape c in the bonding mark 23 are accurately specified. Then, based on the aluminum remaining portion b and the outer shape c, the computer 30 determines the outer area that is the area surrounded by the outer shape c and the aluminum remaining area (wire remaining area) that can be the area extracted as the aluminum remaining portion b. ) Is calculated. For this calculation, for example, an arbitrary calculation method such as calculation based on the number of pixels occupied by the outer shape c and the remaining aluminum portion b in the entity image 43 or the height distribution image 50 is used.
Note that the outline c is not specified only from the entity image 43, but may be obtained more accurately based on data of both the entity image 43 and the height distribution image 50. For example, the outer shape c obtained from the entity image 43 is corrected based on these contours so as to be consistent with the contours of the remaining aluminum portion b and the base exposed portion d extracted from the height distribution image 50. The accuracy of the outer shape c can be increased.

  Returning to FIG. 3, the computer 30 divides the aluminum remaining area obtained in step S2 by the outer shape area, thereby obtaining the wire remaining ratio, which is the ratio of the aluminum remaining area to the joint mark 23 (step S3). Then, the computer 30 displays the wire remaining rate and the shear strength measured in step S1 on, for example, a monitor device. The bonding state of the wire bond bonding part 22 can be evaluated in an integrated manner (step S4). This evaluation may be performed appropriately by the computer 30 and the evaluation result may be output.

  Here, as described above, even when the shear strength is the same, the bonding state of the wire bond bonding portion 22 may be different. For example, depending on the relationship between the wire remaining rate and the position and presence of the unbonded portion R on the bonding surface Q, there may be an equivalent shear strength despite the bonding state of the wire bond bonding portion 22 being different. Therefore, the joining state cannot be judged sufficiently only by the shear strength. The inventors investigated the relationship between the bonding state and the power cycle resistance, and found that the power cycle resistance correlated with the remaining area of the aluminum wire 20. The inventors obtained knowledge that a high power cycle resistance can be ensured by setting a determination value of the wire remaining rate that satisfies the power cycle resistance based on the Q correlation value.

  Therefore, when displaying the wire remaining rate and the share strength on, for example, a monitor device in step S4, the computer 30 outputs a power cycle withstand capability determination based on the wire remaining rate. As a result, based on the shear strength, the wire remaining rate, and the power cycle tolerance, it is possible to comprehensively evaluate the bonding state of the wire bond bonding portion 22 on the assumption that the power semiconductor device 3 is used.

By the way, in the joining part inspection apparatus 1 of this embodiment, since a joining state is evaluated based on the external shape c and the aluminum remaining part b of the joining trace 23 after a shear test, the joining trace 23 is formed when the shear test is sheared. If it is deformed, the accuracy of evaluation of the bonding state is lowered.
Specifically, when the shear speed is slow, as shown in FIG. 8, the base material of the aluminum wire 20 is stretched, and it is difficult to observe the state of the unjoined portion R (base exposed portion d) due to the stretch. . That is, the faster the share speed during the share test, the better. In this embodiment, the share speed is set to 700 μm / second.

  In the shear test, when the tool 36 begins to shear the wire bond joint 22, as shown in FIG. 9, the detected value of the shear strength (shear load) sequentially increases with the start of shearing and reaches a peak. Later, it drops quickly. At this time, when the shear strength peak value detection time point is recognized as the point where the wire bond joint portion 22 is broken and the shear test is completed, the aluminum wire 20 remains without being peeled off from the wire bond joint portion 22. In some cases, the wire remaining rate cannot be accurately obtained from the bonding mark 23.

FIG. 10 shows the measurement results of the distance that the tool 36 moves until the detected value of the shear strength decreases by 10%, 30%, and 90% from the peak value. As shown in this figure, the moving distance of the tool 36 increases every time the detected value of the shear strength decreases sequentially from the peak value to 10%, 30%, and 90%. Therefore, in the case where the measurement is terminated when the aluminum wire 20 is surely peeled off from the wire bond joint portion 22, the time when the detected value of the shear strength is lowered from the peak value to 90%, for example, is determined. Is set in the computer 30 as the recognition timing (destruction recognition point) at which the damage is destroyed, and the share by the tool 36 is stopped at the destruction recognition point to end the measurement.
However, if the movement distance of the tool 36 is increased by setting the fracture recognition point when it is 90% lower than the peak value, the warp generated in the tool 36 due to the stress at the time of shearing of the wire bond joint 22 is released. As a result of this reaction, a shared location is generated within the measurement range, and the outer shape c of the bonding mark 23 is deformed, so that the outer area of the bonding mark 23 cannot be obtained accurately. That is, the measurement end point at the shear test (timing when the shearing by the tool 36 is stopped) is after the peak value of the shear strength is detected, and the aluminum wire 20 is surely peeled off from the wire bond joint portion 22. It is necessary to make the timing at which the tool 36 moves within a range where no share is generated due to the reaction of the warp of the tool 36. In the present embodiment, since the knowledge that the aluminum wire 20 remains when the fracture recognition point is set when the peak value is reduced by 10% from the peak value and the share due to the reaction of the warp is generated when the fracture recognition point is set when the value is reduced by 90% is obtained by experiments. Then, the 30% drop during that time is set as the fracture recognition point so that the outer shape c of the joining mark 23 can be obtained accurately.

As described above, according to the present embodiment, the substantial image 43 of the joint trace 23 after the shear test is acquired, the height in the plane including the joint trace 23 is measured, and the height in the plane including the joint trace 23 is measured. Based on the distribution and the shear height H, the aluminum remaining portion (wire remaining portion) b of the bonding mark 23 is specified. Thereby, even when the contrast between the base a which is the chip surface 5 </ b> A and the wire bond bonding portion 22 is difficult to attach on the actual image 43, the remaining aluminum portion b can be accurately specified.
In addition to this, according to the present embodiment, since the outer shape c of the bonding mark 23 is specified based on the entity image 43, the bonding is performed even when the base exposed portion d is close to or connected to the base a. The outline c can be specified by accurately determining the boundary of the mark 23.
Thereby, a wire residual rate can be quantified correctly and it becomes possible to grasp | ascertain the joining state of a wire bond junction part more correctly now together with a shear test result.

  Further, according to the present embodiment, in the height distribution image 50, the area in which the in-plane height including the joint mark 23 falls within the range of the share height H ± the predetermined margin α is specified as the aluminum remaining portion b. did. As a result, a wire material such as aluminum attached to the chip surface 5A, a portion where the wire bond joint portion 22 is stretched at the time of shearing, etc. are portions that are not originally joined but are similar to the wire bond joint portion 22 and are substantial images. The aluminum remaining portion b can be specified by accurately excluding the portion that cannot be identified by the binarization processing of 43.

Further, according to the present embodiment, at the time of the shear test, the shear tester unit 32 includes a tool that is set after the shear speed is set to a speed that does not cause the wire bond joint portion 22 to be stretched and the peak value of the shear strength is detected. 36 is equal to or longer than a distance that does not leave a wire member in the bonding mark 23, and the bonding mark 23 is not deformed by a recoil when the warp generated in the tool 36 is released by the stress at the time of shearing of the wire bond bonding portion 22. The movement of the tool 36 is stopped when it is moved by a distance in the range.
Thereby, unnecessary deformation of the bonding mark 23 after the shear test is prevented, and the wire remaining rate can be accurately quantified, so that the bonding state can be determined more accurately.

  The above-described embodiment is merely an aspect of the present invention, and can be arbitrarily modified and applied without departing from the spirit of the present invention.

  For example, in the above-described embodiment, the 3D measurement laser microscope is used for the measurement of the height distribution in the plane including the bonding marks 23. However, the measurement is not limited to this, and for example, length measurement in a height direction such as a laser displacement meter can be performed. Any length measuring device can be used. Further, the measurement is not limited to the non-contact type measurement by the laser, and the contact type may be used as long as the chip surface 5A is not scratched at the time of measurement.

In the above-described embodiment, the aluminum wire 20 is exemplified as the conductive wire. However, the material of the conductive wire is not limited to aluminum but may be gold, copper, or the like.
Further, in the above-described embodiment, the bonding portion inspection apparatus 1 sets the chip surface 5A of the semiconductor chip 5 and the wire bond bonding portion 22 of the aluminum wire 20 to be inspected, but the present invention is not limited thereto, and the peripheral electrode (external terminal 17) and A wire bond joint with the aluminum wire 20 may be an inspection target. Furthermore, the present invention can be applied not only to the semiconductor chip 5 and the external terminal 17 that is an electrode, but also to the evaluation of the bonding state of the wire bond bonding portion of an electronic component provided in any device other than the power semiconductor device 3.

DESCRIPTION OF SYMBOLS 1 Junction inspection apparatus 5A Chip surface 20 Aluminum wire 22 Wire bond junction 23 Bond trace 30 Computer (analysis means)
32 Share tester unit (Share tester)
34 Wire remaining rate measurement unit 36 Tool 43 Real image (captured image)
44 Microscope (Imaging means)
46 Scanning head 50 Height distribution image 52 Distribution data H Shear height M Shear direction Q Joint surface R Unjoined part b Aluminum remaining part (wire remaining part)
c Outline d Base exposed part

Claims (4)

Shearing wire bond joints at a certain shear height with a shear tester, detecting the shear strength and performing a shear test,
Acquiring a captured image of the joint trace after the shear test, measuring the height in the plane including the joint trace,
Specifying a wire remaining portion of the bonding trace based on an in-plane height distribution including the bonding trace and the shear height, and specifying an outer shape of the bonding trace based on the captured image. ,
A wire remaining rate is calculated from the wire remaining area of the wire remaining portion and the outer shape area of the outer shape.   2. The joint inspection according to claim 1, wherein an area in which a height in a plane including the joint trace falls within a predetermined height range based on the shear height is specified as the remaining wire portion. Method. At the time of the shear test, the shear speed is set to a speed that does not cause elongation in the wire bond joint, and
The tool provided in the shear tester after the peak value of the shear strength is detected is longer than the distance that does not leave a wire member in the joint trace, and is generated in the tool due to the stress at the time of shearing of the wire bond joint portion. The joint inspection method according to claim 1, wherein the movement of the tool is stopped when the joint is moved by a distance within a range that does not cause deformation of the joint trace due to a reaction when the warp is released. A shear tester that detects the shear strength and performs a shear test while shearing the wire bond joint at a certain shear height,
An imaging means for acquiring a captured image of the joint mark after the share test;
A height measuring means for measuring an in-plane height including the joint mark;
The wire remaining part of the bonding mark is specified based on the height distribution in the plane including the bonding mark and the shear height, the outer shape of the bonding mark is specified based on the captured image, and the wire remaining part Analyzing means for calculating the wire remaining rate from the wire remaining area and the outer area of the outer shape,
A joint inspection apparatus comprising: