JP4047737B2 - Degradation diagnosis method for lead-free solder - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a lead-free solder deterioration diagnosis method, apparatus, and lead-free solder alloy for diagnosing deterioration of a tin-zinc based lead-free solder.
[0002]
[Prior art]
Conventionally, with respect to a solder alloy containing lead, as shown in Patent Document 1, by measuring the roughness of the surface of the solder and determining the relationship between the measured roughness of the solder surface and time, There is known a method for estimating the time until a crack occurs, in other words, the life of a solder.
[0003]
[Patent Document 1]
JP 2002-310888 A
[0004]
[Problems to be solved by the invention]
However, as for lead-free solders, it is not clear what the deterioration index that shows the signs of deterioration is, so it is difficult to diagnose deterioration of lead-free solder because there is no standard for determining deterioration. .
[0005]
Accordingly, the present invention has been made in view of the above circumstances, and by making a deterioration index showing signs of deterioration clear, a lead-free solder deterioration diagnosis method can be easily performed. And an apparatus.
[0006]
Furthermore, another object of the present invention is to provide a lead-free solder alloy with a long life.
[0007]
[Means for Solving the Problems]
In order to solve the above problems, the first invention is a lead-free solder deterioration diagnosis method for diagnosing lead-free solder deterioration from a change in the cross-sectional shape of the lead-free solder, wherein the lead-free solder is polished by polishing the surface of the lead-free solder. The surface polishing process that exposes the metal structure of the cross section of the lead, the observation process that observes the metal structure of the cross section of the lead-free solder polished by the surface polishing process, and the observation results of the observation process, obtained from the metal structure of the cross section of the lead-free solder The deterioration parameter set based on the determined deterioration index is compared with the deterioration parameter set based on the predetermined deterioration index. As a result of the comparison, the deterioration parameter obtained from the metal structure and the predetermined deterioration parameter are compared. Is a deterioration diagnosis method for lead-free solder, including a deterioration diagnosis step for determining whether lead-free solder has deteriorated depending on whether or not.
[0008]
The “degradation index” described in the present specification means a change in the metal structure exposed in the cross section of the lead-free solder before and after the 1000 cycles of the thermal cycle test, for example, change in crystal grains of tin or zinc, or 1000 cycles of the thermal cycle. It means the change in characteristic X-ray energy detected by X-ray analysis before and after the test.
[0009]
Further, the “degradation parameter” described in the present specification means numerical data symbolizing a degradation index, such as the grain size of tin crystals, the spheroidization rate of tin or zinc, and the energy value of characteristic X-rays. To do.
[0010]
In addition, the spheroidization rate described in this specification is also called roundness and is defined by the following formula (1).
Spheroidization rate = (peripheral length of area equivalent circle) / (actual perimeter) ... Formula (1)
FIG. 24 is a diagram for explaining the spheroidization rate. In the figure, a substantially cross-shaped figure is an object to be measured for the spheroidizing rate, and a thick line represents the perimeter of the figure to be measured for the spheroidizing rate.
[0011]
The area of the substantially cross-shaped figure that is the measurement target of the spheroidization rate is 12 pixels.
The circumference of a circle having the same area as this area, in other words, the perimeter of the area equivalent circle is (12 / π) ^1/2 × 2 × π.
[0012]
On the other hand, the actual perimeter of the measurement target of the spheroidization rate is 16 pixels.
[0013]
Therefore, the spheroidization rate of the substantially cross-shaped figure shown in FIG. 24 is as follows:
Spheroidization rate = (perimeter of area equivalent circle) / (actual perimeter)
= {(12 / π) ^1/2 × 2 × π} /16=76.7 (percent).
[0014]
One pixel is a value obtained by configuring the dimensions. For example, when the magnification is 1000 times, 1 μm is about 0.2 pixels.
[0015]
As described above, the surface of the lead-free solder is polished by the surface polishing process, so that the metal structure of the cross-section of the lead-free solder is exposed, and the metal structure of the polished lead-free solder is observed by the observation process. As a result, the deterioration parameter set based on the deterioration index obtained from the metal structure of the cross section of the lead-free solder and the deterioration parameter set based on the predetermined deterioration index are compared by the deterioration diagnosis step, and the comparison As a result, whether or not lead-free solder has deteriorated is determined based on whether or not the deterioration parameter obtained from the metal structure matches the predetermined deterioration parameter. Therefore, the deterioration diagnosis of lead-free solder can be performed simply by comparing the deterioration parameters. Can be easily performed.
[0016]
The second invention is the lead-free solder deterioration diagnosis method according to the first invention, wherein the lead-free solder contains zinc, and the deterioration parameter is information for detecting a change in the crystal of zinc in the lead-free solder. The diagnosis step is a lead-free solder deterioration diagnosis method for determining whether or not lead-free solder has deteriorated depending on whether or not zinc changes to a substantially circular shape or a substantially elliptical shape.
[0017]
Thereby, in addition to having the same effect as the first invention, it is determined whether or not lead-free solder has deteriorated depending on whether or not zinc changes to a substantially circular or substantially elliptical shape. By observing the metal structure, it can be easily understood that the lead-free solder has deteriorated.
[0018]
The third invention is the lead-free solder deterioration diagnosis method of the first invention, wherein the lead-free solder contains zinc, and the observation step is an analysis result of characteristic X-rays from the lead-free solder at the time of deterioration diagnosis for the cross-section of the lead-free solder In the deterioration diagnosis step, the deterioration parameter indicating that the lead-free solder has deteriorated is compared with the deterioration parameter obtained from the analysis result of the characteristic X-ray, and as a result of the comparison, the characteristic X from the lead-free solder is obtained. This is a lead-free solder deterioration diagnosis method for determining whether or not lead-free solder has deteriorated depending on whether or not a predetermined characteristic X-ray is detected as a result of wire analysis.
[0019]
As a technique for analyzing the lead-free solder described in this specification by characteristic X-rays, for example, a technique using a well-known X-ray spectroscopy, specifically, a well-known EPMA (Electron Probe Micro Analysis) is used. And a method using an analysis result of AES (Auger Electron Spectroscopy).
[0020]
Regarding the details of EPMA and AES, publicly known documents at the time of filing, such as “Electron / Ion Beam Handbook (3rd edition); issued on October 28, 1998; published by Nikkan Kogyo Shimbun; Japan Society for the Promotion of Science It is described in detail in “132nd Committee”.
[0021]
Thereby, in addition to having the same effect as the first invention, it is possible to determine whether or not the lead-free solder has deteriorated from the analysis result of the characteristic X-rays. Deterioration diagnosis can be performed.
[0022]
4th invention is a lead-free solder alloy, Comprising: It is a lead-free solder alloy containing a tin, zinc, and an acicular crystal | crystallization.
[0023]
In addition, the lead-free solder alloy described in this specification means a solder alloy that does not contain lead.
[0024]
Thereby, since the needle-like crystal is contained in the lead-free solder alloy, the needle-like crystal prevents the progress of cracks accompanying the deterioration of the lead-free solder alloy, so that the life of the lead-free solder alloy can be extended.
[0025]
A fifth invention is the lead-free solder alloy of the fourth invention, wherein the needle-like crystal is a lead-free solder alloy made of a single metal element.
[0026]
Thereby, the same operation as that of the fourth invention can be surely achieved.
[0027]
A sixth invention is a lead-free solder alloy according to the fourth invention, wherein the needle-like crystal is made of zinc.
[0028]
Thereby, the same operation as that of the fourth invention can be surely achieved.
[0029]
A seventh aspect of the invention is a lead-free solder deterioration diagnosis device for diagnosing lead-free solder deterioration from a change in the cross-section of the lead-free solder, the observation means for observing the cross-section of the lead-free solder, and the lead-free solder Deterioration parameter setting means for setting deterioration parameters indicating that the solder has deteriorated, deterioration parameter storage means for storing deterioration parameters set by the deterioration parameter setting means, and observation of a cross section of lead-free solder subject to deterioration diagnosis The deterioration diagnosis means for determining whether or not the lead-free solder has deteriorated by comparing the obtained deterioration parameter with the deterioration parameter stored in the deterioration parameter storage means, and the determination by the deterioration diagnosis means This is a lead-free solder deterioration diagnosis device comprising output means for outputting a result.
[0030]
Thereby, the cross section of the lead-free solder is observed by the observation means, and the deterioration parameter indicating that the lead-free solder has deteriorated is set by the deterioration parameter setting means from the result of the observation, and the lead-free solder subject to the deterioration diagnosis is set by the deterioration diagnosis means. Based on the result of observation of the cross section of the solder, it is determined whether or not the lead-free solder has deteriorated by comparing the obtained deterioration parameter with the deterioration parameter stored in the deterioration parameter storage means. Since the determination result is output, deterioration diagnosis of lead-free solder can be easily performed.
[0031]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0032]
FIG. 1 is a flowchart showing an example of a lead-free solder deterioration diagnosis method according to this embodiment, and FIG. 2 is a lead-free solder to which the lead-free solder deterioration diagnosis method according to the first embodiment of the present invention is applied. It is a schematic diagram which shows the structural example of 1 A of deterioration diagnostic apparatuses.
[0033]
In the following embodiment, an example in which a deterioration parameter is set using a chip capacitor as shown in FIGS. 3 and 4 will be described. 3 is a plan view of the printed circuit board 12 on which the chip capacitor 11 is mounted, and FIG. 4 is a cross-sectional view of the printed circuit board 12 on which the chip capacitor 11 is mounted. The chip capacitor 11 and the printed circuit board 12 are solder-bonded by lead-free solder 14 between the chip capacitor 11 and the land 13 on the printed circuit board 12.
[0034]
The lead-free solder to which the lead-free solder deterioration diagnosis of the present embodiment is applied includes tin 90 Wt% (weight percent), zinc 9 Wt% (weight percent), and zinc needle crystals 1 Wt% (weight percent). Contains tin-zinc based lead-free solder.
[0035]
According to the results of experiments conducted by the present inventors, no distribution of zinc oxide was found at the site where cracks in the tin-zinc based lead-free solder occurred.
[0036]
According to the inventor's consideration, during the thermal cycle test, the tin-zinc-based lead-free solder mainly composed of tin and zinc does not have the zinc metal crystal after segregation of the zinc metal crystal first. Deterioration of lead-free solder from the portion, in other words, cracks generated in the metal structure of lead-free solder develop.
[0037]
FIG. 5 is a schematic diagram showing an example of the progress of cracks when a needle-like metal crystal is added to the metal structure of a tin-zinc based lead-free solder, and FIG. It is a schematic diagram which shows an example of the mode of a crack progress in the case where the acicular metal crystal is not added to the metal structure.
[0038]
According to the inventor's consideration, as shown in FIG. 5, when a needle-like metal crystal 23 is added to the metal structure of a tin-tin zinc-based lead-free solder composed of tin 21 and substantially circular zinc 22. In the thermal cycle test, the crack 24 generated in the metal structure of the lead-free solder propagates while avoiding the added needle crystal of zinc.
[0039]
On the other hand, when the needle-like metal crystal 23 is not added to the lead-free solder, there is no needle-like metal crystal 23 that prevents the growth of the crack 24 as shown in FIG. As a result, the crack 24 progresses rapidly.
[0040]
Therefore, the present inventor considers that it is more preferable to add needle-like metal crystals to the tin-zinc based lead-free solder from the viewpoint of extending the life of the tin-zinc based lead-free solder.
From the above considerations, the present inventors have devised adding needle-like metal crystals to a tin-zinc-based lead-free solder in order to prevent the progress of cracks.
[0041]
In addition, since it is desirable that the needle-like metal crystal does not contain other metal elements, it is more preferable that the needle-like metal crystal is composed only of zinc.
[0042]
The lead-free solder deterioration diagnosis apparatus 1A according to the present embodiment includes an imaging unit 2 (observation means), a deterioration parameter setting unit 3A, a deterioration parameter database 4A, a deterioration diagnosis unit 5A, and an output unit 6A. The
[0043]
In addition, each part which comprises 1 A of lead-free solder deterioration diagnostic apparatuses which concern on this Embodiment may be comprised from either the combination of software or hardware, or software and hardware.
[0044]
The lead-free solder deterioration diagnosis apparatus 1A according to the present embodiment has each function realized by, for example, a computer whose operation is controlled by a program installed in advance from a recording medium or a communication network.
[0045]
In addition, the said communication network should just be what can communicate bidirectionally, and it does not ask | require whether it is wired or wireless.
[0046]
The imaging unit 2 (observation means) observes the metal structure exposed on the surface of the lead-free solder, images image data of the metal structure, and uses the captured image data as the deterioration parameter setting unit 3A or the deterioration Output to the diagnosis unit 5A.
[0047]
The degradation parameter setting unit 3A performs image analysis on the image data output from the imaging unit 2, extracts a degradation index for diagnosing lead-free solder degradation from the result of the image analysis, and the extracted degradation index. It has a function of setting numerical data indicating that it has appeared in the metal structure as a deterioration parameter based on a parameter setting command inputted from the outside, and a function of storing the set deterioration parameter in the deterioration parameter database 4A.
[0048]
The deterioration parameter database 4A stores deterioration parameters set by the deterioration parameter setting unit 3A.
[0049]
When the degradation diagnosis unit 5A receives the image data of the cross-section of the lead-free solder imaged, the degradation diagnosis unit 5A searches the image parameter analysis function and the degradation parameter database 4A, and reads a degradation parameter set in advance as a retrieval result. A function for determining whether the lead-free solder has deteriorated by comparing the read deterioration parameter with the analysis result described above, and a function for outputting the determination result to the output unit 6A.
[0050]
The output unit 6A outputs the determination result output from the deterioration diagnosis unit 5A to the outside.
[0051]
Hereinafter, the outline of the tin-zinc-based lead-free solder deterioration diagnosis method according to the present embodiment will be described.
[0052]
The deterioration diagnosis method according to the present embodiment includes a process A1 to a process A5 until the deterioration parameter is set by observing a cross section of the lead-free solder, and a process A6 to a process A9 that performs the deterioration diagnosis using the deterioration parameter. It consists of.
[0053]
First, a thermal cycle test that simulates thermal stress is performed using a tin-zinc-based lead-free solder (A1).
[0054]
Next, the cross section of the tin-zinc based lead-free solder subjected to the thermal cycle test is mirror-polished (A2).
[0055]
Next, the metal structure of the cross-section of the tin-zinc-based lead-free solder that has been mirror-polished is observed (A3).
[0056]
Next, a deterioration index indicating a sign of deterioration of the cross section of the lead-free solder is investigated from the relationship between the deterioration progress state and the observed deterioration state of the metal structure (A4).
[0057]
Next, the deterioration parameter setting unit 3A receives a deterioration parameter setting for detecting a deterioration index of the cross section of the lead-free solder from the diagnostician, and stores the deterioration parameter in the deterioration parameter database 4A (A5).
[0058]
Next, the cross section of the tin-zinc-based lead-free solder subject to deterioration diagnosis is mirror-polished (A6).
[0059]
Next, the imaging unit 2 observes the metal structure of the cross-section of the lead-free solder that is mirror-polished and subject to deterioration diagnosis (A7).
[0060]
Next, the deterioration diagnosis unit 5A performs image analysis on the image data of the cross section of the lead-free solder that is a deterioration diagnosis target imaged by the image pickup unit 2, and obtains the result of the image analysis and the deterioration parameter stored in the deterioration parameter database 4A. In comparison, a deterioration diagnosis process for detecting the presence or absence of deterioration is executed as the comparison result (A8).
[0061]
Next, the output unit 6A outputs the result of deterioration diagnosis by the deterioration diagnosis unit 5A (A9).
[0062]
Hereinafter, the lead-free solder deterioration diagnosis method realized by the lead-free solder deterioration diagnosis apparatus 1A will be described in more detail with specific examples.
[0063]
First, a thermal cycle test that simulates thermal stress is performed using a tin-zinc-based lead-free solder (A1).
[0064]
Here, as a method for performing the thermal cycle test, for example, a thermal cycle test in which the temperature is changed between −40 ° C. and + 125 ° C. in 30 minutes is one cycle, and thermal stress is continuously applied to lead-free solder up to 1000 cycles. There is a technique to load.
[0065]
In step A2, the surface of the lead-free solder after any cycle of the thermal cycle test is polished until it becomes a mirror surface. Thereby, the metal structure of the lead-free solder which is a degradation diagnosis target is exposed.
[0066]
Here, as a method for mirror-polishing the surface of the lead-free solder, for example, after polishing with five types of water-resistant abrasive papers with SiC grain sizes of # 120, # 320, # 500, # 1000, and # 2400, There is a method of mirror polishing using a paste in which 1 μm diamond particles are dispersed.
[0067]
In this polishing method, the metal structure of the lead-free solder cross-section is not exposed only by using five types of water-resistant abrasive papers having different SiC particle sizes. Therefore, mirror polishing is performed using a paste in which 1 μm diamond particles are dispersed. This is an important process for exposing the metal structure of the cross section of the lead-free solder.
[0068]
In step A3, the imaging unit 2 observes the metal structure of the cross section of the tin-zinc-based lead-free solder exposed by mirror polishing.
[0069]
In step A4, the deterioration index is investigated from the result of observation of the metal structure exposed on the surface of the lead-free solder.
[0070]
Here, as a technique for observing the metal structure of lead-free solder, a technique for analyzing the image data captured as image data by imaging the metal structure, an X-ray analyzer using a well-known X-ray spectroscopy, For example, there are a method of receiving characteristic X-rays radiated from the surface of a lead-free solder metal structure by an X-ray microanalyzer (EPMA), analyzing the energy of the characteristic X-ray, and a method of visually observing the metal structure.
[0071]
FIG. 7 is a diagram showing an example of a cross-sectional metal structure of the lead-free solder in the initial state before the thermal cycle test, and FIG. 8 is a schematic diagram showing an example of a cross-sectional metal structure of the lead-free solder in the initial state. FIG. 9 is an enlarged view of an example of the metal structure of the cross section of the lead-free solder in the initial state, and FIG. 10 is a schematic diagram of an example of the metal structure of the cross section of the lead-free solder in the initial state. Further, FIG. 11 is a histogram showing an example of the area ratio of crystal grains in the cross section of the lead-free solder in the initial state.
[0072]
In FIG. 11, crystal grains of less than 2500 [square micrometers] are purple, and crystal grains of 2500 [square micrometers] or more and less than 4000 [square micrometers] are blue, and 4000 [square micrometers] or more. The crystal grains of less than 5000 [square micrometer] are dark green, and the crystal grains of 5000 [square micrometer] to 7500 [square micrometer] are green, and 10500 [square micrometer] to 11500 [square micrometer] The crystal grains are yellowish green, the crystal grains of 15500 [square micrometer] or more and less than 16500 [square micrometer] are displayed in dark blue, and the crystal grains of 24500 [square micrometer] or more are displayed in red.
[0073]
In the cross section of the lead-free solder in the initial state, as shown in FIGS. 8 and 10, tin crystal grains 31 having an irregular shape and a metal structure 32 in which tin and zinc are mixed exist. The metal structure 32 includes tin 21 and zinc crystal grains 23 having a needle-like shape. Since it is impossible to orient the crystal grains of zinc in a uniform direction, the needle-like zinc crystal grains 23 present along the direction substantially perpendicular to the cross section are substantially circular or elliptical. It looks like a shape.
[0074]
On the other hand, FIG. 12 is a diagram showing an example of the metal structure of the cross section of the lead-free solder exposed after the 1000 cycles of the thermal cycle test, and FIG. 13 is a cross section of the lead free solder after the 1000 cycles of the thermal cycle test. It is a schematic diagram which shows an example of this metal structure. FIG. 14 is an enlarged view showing an example of a metal structure after execution of a 1000 cycle cooling cycle test, and FIG. 15 is a schematic view of an example of a metal structure after execution of a 1000 cycle cooling cycle test. . Further, FIG. 16 is a histogram showing an example of the crystal grain area ratio in the cross section of the lead-free solder after the 1000 cycles of the thermal cycle test.
[0075]
In FIG. 16, crystal grains of less than 1100 [square micrometer] are purple, and crystal grains of 1100 [square micrometer] or more and less than 1750 [square micrometer] are blue, and 1750 [square micrometer] or more and 2250 [square]. Crystal grains of less than 2 micrometres] are dark green and crystals of 2250 square meters to less than 2750 [square micrometres] are green, and crystals having 2750 [square micrometres] to 3500 [square micrometres] The grains are yellow-green, the crystal grains of 5750 [square micrometer] or more and less than 6250 [square micrometer] are displayed in yellow, and the crystal grains of 10750 [square micrometer] or more are displayed in red.
[0076]
According to the observation of the present inventor, zinc crystal grains 23 having a needle-like cross-sectional shape in the metal structure 32 in the initial state are shown in FIG. 15 in the metal structure 33 after the thermal cycle test. As shown briefly, the amorphous crystal 31 of tin changes to a fine crystal having a substantially polygonal shape, and the zinc, which is a needle-like crystal, has an approximately circular shape or a substantially elliptical cross-sectional shape. Zinc 34 is changed.
[0077]
In addition, after the cooling test, tin crystal grain boundaries that were not clear in the initial state are clear.
[0078]
Thus, cracks are observed when the zinc needle-like crystals contained in the lead-free solder are changed to substantially circular or substantially elliptical zinc oxide.
[0079]
Therefore, the present inventor considers that the presence of substantially circular zinc crystal grains in the metal structure of the cross-section of the lead-free solder can be used for the determination of the deterioration parameter using the deterioration index.
[0080]
FIG. 17 is a diagram showing the relationship between the spheroidization rate of tin in the metal structure of the lead-free solder in the initial state and the number of tin crystals having the corresponding spheroidization rate, and FIG. 18 is a 1000 cycle thermal cycle test. FIG. 19 is a diagram showing the relationship between the spheroidization ratio of tin in the metal structure of the lead-free solder after the execution of the above and the number of tin crystals having the corresponding spheroidization ratio. It is the figure which plotted the spheroidization rate of the crystal | crystallization of the tin of a metal structure.
[0081]
In FIG. 19, the spheroidization rate of the metal structure of the lead-free solder in the initial state before the cooling cycle test shown in FIG. 17 is plotted on the left side, and the lead-free solder in the initial state after the cooling cycle test shown in FIG. The spheroidization rate of the metal structure is plotted on the right side.
[0082]
In addition, the present inventor considers that it is possible to diagnose deterioration of tin-zinc-based lead-free solder by paying attention to the change in the grain size of tin crystals.
[0083]
That is, according to the experimental results obtained by the present inventor, as shown in FIG. 17, in the initial state, the average value of the spheroidization rate of the tin crystals is about 43.3 percent, and the standard deviation is about Whereas the average value of the spheroidization rate of the tin crystal after the execution of the 1000 cycles of the thermal cycle test is 10.0, the average value of the spheroidization rate of the tin crystal is approximately 67.9, and the standard deviation is , Approximately 7.26.
[0084]
In other words, in the metal structure after the execution of the thermal cycle test, the spheroidization rate of tin crystals is higher than that in the initial state as shown in FIG.
[0085]
Thus, when the spheroidization rate of the tin crystal becomes high, the occurrence of cracks is observed.
[0086]
Accordingly, the fact that the spheroidization rate of tin crystals in the metal structure of lead-free solder is high can be used for setting deterioration parameters as a deterioration index of lead-free solder.
[0087]
Further, according to the experimental results obtained by the present inventor, as shown in FIG. 11 described above, the exposed crystal grains in the cross section of the lead-free solder in the initial state are 7500 [μm. ² The following areas account for about 60% of the total, but 24500 [μm ² ] 25500 [μm] ² ] The following area is 25% of the total, 15500 [μm ² ] 16500 [μm] ² ] The following area is about 15% of the total, and 10500 [μm ² ] 11500 [μm] ² The following areas are present at a ratio of approximately 10 percent of the total, and it can be said that there are various sizes of crystal grains.
[0088]
On the other hand, the exposed crystal grains in the cross section of the lead-free solder after the 1000 cycles of the thermal cycle test are approximately 3500 [μm as shown in FIG. ² The following areas account for about 85% of the total.
[0089]
In other words, it can be said that after execution of the 1000 cycles of the thermal cycle test, the grain size of the tin crystals is smaller than that in the initial state.
[0090]
In this way, cracks are observed when the grain size of the tin crystals is reduced.
[0091]
Therefore, the present inventor believes that detection of a change in the grain size of tin grains in the metal structure of the cross section can be used to determine the deterioration parameter as a deterioration index.
[0092]
In step A5, the deterioration parameter setting unit 3A sets information for detecting substantially circular zinc crystal grains from the image data of the exposed metal structure of lead-free solder obtained as a result of observation, as the deterioration parameter. The set deterioration parameter is stored in the deterioration parameter database 4A.
[0093]
Here, as the deterioration parameter to be set, for example, numerical data regarding the shape of the substantially circular or substantially elliptical zinc crystal, the ratio of the crystal grain size, the average value of the crystal grain size, the tin crystal Examples thereof include a spheroidization rate.
[0094]
In step A6, the cross section of the tin-zinc-based lead-free solder to be subjected to deterioration diagnosis is mirror-polished by the same method as in step A2.
[0095]
In step A <b> 7, the imaging unit 2 observes the state of the exposed metal structure of the cross section of the lead-free solder to be subjected to deterioration diagnosis.
[0096]
In step A8, the deterioration diagnosis unit 5A reads a deterioration parameter that is information for detecting zinc having a substantially circular shape or a substantially elliptic shape stored in advance in the deterioration parameter database 4A, and is observed as the read deterioration parameter. By checking the cross-sectional image of the lead-free solder subject to deterioration diagnosis, the lead-free solder is subject to lead-free solder depending on whether the cross-section of the lead-free solder subject to deterioration diagnosis has substantially circular or substantially elliptical crystal grains. It is determined whether the solder has deteriorated.
[0097]
In Step A8 of the present embodiment, whether or not lead-free solder has deteriorated is determined depending on whether or not zinc crystal grains having a substantially circular shape or a substantially elliptic shape are generated in the cross section of the lead-free solder. Not limited to this, whether or not the lead-free solder has deteriorated may be determined according to whether or not the grain size of the tin crystal grains has become smaller than a predetermined value as a deterioration parameter, and a predetermined area Whether or not the lead-free solder has deteriorated may be determined based on whether or not the proportion of particles having the following particle diameters in the entire cross section is equal to or greater than a predetermined value as a deterioration parameter.
[0098]
In step A9, the output unit 6A outputs the diagnosis result output from the deterioration diagnosis unit 5A to the outside.
[0099]
As the output unit 6A, for example, a device that visually outputs a diagnosis result, such as a printer or a CRT, or a device that outputs a diagnosis result by sound such as a speaker may be used.
[0100]
As described above, in the present embodiment, by setting the deterioration parameter, the deterioration index can be clearly defined from the state of the metal structure of the lead-free solder, and at the time of determining whether the lead-free solder has deteriorated or not. Degradation parameters can be set.
[0101]
Further, according to the present embodiment, the deterioration diagnosis of lead-free solder can be easily performed by comparing the set deterioration parameter with the observation result of the cross section of the lead-free solder.
[0102]
Furthermore, according to the present embodiment, by adding a zinc needle crystal to a tin-zinc-based lead-free solder, since the crack propagates while avoiding the needle crystal, the needle crystal is not added Compared to lead-free solder, the life can be extended.
[0103]
According to the present embodiment, a device product trouble can be detected in advance, and a maintenance cycle can be determined.
[0104]
According to the present embodiment, by adding zinc needle-like crystals to lead-free solder, crack growth is prevented, so the crack growth rate is slow, and long-term reliability is maintained in a thermal fatigue environment. I can do it.
[0105]
<Second Embodiment>
FIG. 20 is a flowchart for explaining an example of the lead-free solder deterioration diagnosis method according to the second embodiment of the present invention.
[0106]
FIG. 21 is a schematic diagram showing an example of a lead-free solder deterioration diagnosis apparatus 1B according to the present embodiment. The same parts as those in the above-described drawings are denoted by the same reference numerals, and detailed description thereof is omitted. Here, different parts will be mainly described.
[0107]
The application target of the lead-free solder deterioration diagnosis method according to the present embodiment is the same tin-zinc-based lead-free solder as the application target in the lead-free solder deterioration diagnosis method according to the first embodiment.
[0108]
The lead-free solder deterioration diagnosis method according to the present embodiment is a measurement in which the intensity of characteristic X-rays detected by an X-ray analyzer using a well-known X-ray spectroscopy, for example, an electron beam microanalyzer (EPMA) is measured. It is a method of performing deterioration diagnosis of lead-free solder by setting deterioration parameters using the results.
[0109]
Lead-free solder deterioration diagnosis apparatus 1B according to the present embodiment includes an electron beam irradiation unit 41, a characteristic X-ray intensity measurement unit 42, a deterioration parameter setting unit 3B, a deterioration parameter database 4B, and a deterioration diagnosis unit 5B. And an output unit 6B.
[0110]
In addition, each part which comprises the deterioration diagnostic apparatus 1B of the lead-free solder which concerns on this Embodiment may be comprised from any combination of software, hardware, or software and hardware.
[0111]
In addition, the lead-free solder deterioration diagnosis apparatus 1B according to the present embodiment has each function realized by a computer whose operation is controlled by a program installed in advance from a recording medium or a communication network, for example.
[0112]
In addition, the said communication network should just be what can communicate bidirectionally, and it does not ask | require whether it is wired or wireless.
[0113]
The electron beam irradiation unit 41 has a function of irradiating the cross section of the lead-free solder 14 with an electron beam.
[0114]
The characteristic X-ray intensity measuring unit 42 has a function of measuring characteristic X-rays emitted from the cross section of the lead-free solder 14 and a function of outputting the measurement result to the deterioration parameter setting unit 3B.
[0115]
Note that the characteristic X-ray intensity measurement unit 42 of the present embodiment corresponds to the observation means.
[0116]
The deterioration parameter setting unit 3B has a function of setting the energy level of oxygen output from the characteristic X-ray intensity measurement unit 42 as a deterioration parameter based on a parameter setting command input from the outside, and the set deterioration A function of storing parameters in the deterioration parameter database 4B.
[0117]
In the deterioration parameter database 4B, data relating to the energy level of oxygen is stored as a deterioration parameter.
[0118]
The deterioration diagnosis unit 5B receives the measurement result output from the characteristic X-ray intensity measurement unit 42, reads the deterioration parameter from the deterioration parameter database 4B, and receives the oxygen energy level preset as the read deterioration parameter. A function for determining whether or not lead-free solder has deteriorated by determining whether or not characteristic X-rays corresponding to the energy level of oxygen are detected as a result of the comparison. Have.
[0119]
The output unit 6B has a function of outputting the result of the lead-free solder deterioration diagnosis output from the deterioration diagnosis unit 5B to the outside.
[0120]
Next, a lead-free solder deterioration diagnosis method according to the present embodiment will be described with reference to the drawings.
[0121]
The process B1 and the process B2 are the same as the process A1 and the process A2 described above.
[0122]
In step B3, the characteristic X-ray intensity measurement unit 42 measures the intensity of characteristic X-rays radiated from the cross section of the lead-free solder by a well-known X-ray spectroscopy, and outputs the measurement result to the deterioration parameter setting unit 3B.
[0123]
In step B4, a deterioration index indicating a sign of deterioration of the lead-free solder is investigated from the relationship between the progress of deterioration of the lead-free solder and the analysis result of the measured characteristic X-ray.
[0124]
FIG. 22 is a diagram showing measurement results of characteristic X-rays by a well-known X-ray spectroscopy performed by the present inventor before the thermal cycle test, and FIG. It is a figure which shows the measurement result of the characteristic X ray by X-ray spectroscopy. 22 and 23, the vertical axis represents the number of X-ray detections per second, in other words, the X-ray intensity (unit: [cps: counts per second]), and the horizontal axis represents the energy level ( The unit is [keV]).
[0125]
As shown in FIG. 22, before the thermal cycle test, characteristic X-rays of energy corresponding to the energy levels of carbon, zinc, and tin are detected. Note that this carbon is deposited on the surface of zinc for electrical conduction.
[0126]
On the other hand, after 1000 cycles of the thermal cycle test, as shown in FIG. 23, characteristic X-rays of energy corresponding to the energy levels of carbon, oxygen, and zinc are detected. Here, the characteristic X-ray of the energy corresponding to the energy level of oxygen in the vicinity of 0.5 (kev) was detected because zinc was changed to zinc oxide by an oxidation reaction during the thermal cycle test. .
[0127]
Thus, when the characteristic X-ray corresponding to the energy level of oxygen is detected, the crack of the lead-free solder has occurred.
[0128]
Therefore, the present inventor believes that it can be determined whether or not lead-free solder has deteriorated by detecting characteristic X-rays of energy corresponding to the energy level of oxygen by X-ray spectroscopy.
[0129]
In step B5, the deterioration parameter setting unit 3B receives a deterioration parameter setting for detecting a deterioration index of lead-free solder from a diagnostician, and stores the deterioration parameter in the deterioration parameter database 4B.
[0130]
Here, as the deterioration parameter to be set, for example, the energy level of characteristic X-rays detected by a well-known X-ray spectroscopy method can be cited.
[0131]
In step B6, the surface of the lead-free solder is mirror-polished as in step A6 described above.
[0132]
In step B7, the characteristic X-ray intensity measuring unit 42 measures the intensity of the characteristic X-rays emitted from the cross section of the lead-free solder as in the above-described step B3.
[0133]
In step B8, the deterioration diagnosis unit 5B reads the deterioration parameter from the deterioration parameter database 4B, compares the read deterioration parameter with the measurement result of the characteristic X-ray emitted from the cross section of the lead-free solder, and as a result of the comparison, Whether or not the lead-free solder has deteriorated is determined depending on whether or not characteristic X-rays matching the energy level of the lead-free solder are detected.
[0134]
In step B9, the output unit 6B outputs the result of the deterioration diagnosis by the deterioration diagnosis unit 5B.
[0135]
As described above, according to the present embodiment, in addition to the effects of the first embodiment, by setting the energy value of the characteristic X-ray as a deterioration parameter, there is no sign of deterioration of lead-free solder without using image data. It is possible to clearly define a degradation index indicating
[0136]
The method described in each of the above embodiments is a program that can be executed by a computer as a magnetic disk (flexible disk, hard disk, etc.), optical disk (CD-ROM, DVD, etc.), magneto-optical disk (MO). It can be stored in a storage medium such as a semiconductor memory and distributed.
[0137]
In addition, as long as the storage medium can store a program and can be read by a computer, the storage format may be any form.
[0138]
Further, an OS (operating system) operating on the computer based on an instruction of a program installed in the computer from the storage medium, MW (middleware) such as database management software, network software, or the like is an embodiment of the present invention. You may perform a part of each process for implement | achieving.
[0139]
Furthermore, the storage medium in the embodiment of the present invention is not limited to a medium independent of a computer, but also includes a storage medium in which a program transmitted via a LAN, the Internet, or the like is downloaded and stored or temporarily stored.
[0140]
In addition, the number of storage media is not limited to one, and a case where the processing in the embodiment of the present invention is executed from a plurality of media is also included in the storage medium in the embodiment of the present invention. It's okay.
[0141]
The computer according to the present invention executes each process in the present embodiment based on a program stored in a storage medium, and a single device such as a personal computer or a plurality of devices are connected to a network. Any configuration such as a system may be used.
[0142]
In addition, the computer in the present invention is not limited to a personal computer, but includes an arithmetic processing device, a microcomputer, and the like included in an information processing device, and is a generic term for devices and devices that can realize the functions of the present invention by a program. .
[0143]
The program that realizes the method described in each of the above embodiments can be provided by transmitting via a communication network such as the Internet or an intranet.
[0144]
As a program providing method via this communication network, for example, an ASP (Application Service Provider) method is included.
[0145]
Further, the program is written in any programming language such as C (registered trademark), C ++ (registered trademark), JAVA (registered trademark), etc., as long as it realizes the above functions. It may be.
[0146]
The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention at the stage of implementation.
[0147]
Each of the above embodiments includes inventions at various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements. For example, when an invention is extracted by omitting some constituent elements from all the constituent elements shown in the embodiment, the omitted part is well known when the extracted invention is implemented. It is supplemented appropriately by conventional techniques.
[0148]
In addition, the present invention can be variously modified and implemented without departing from the scope of the invention.
[0149]
【The invention's effect】
As described in detail above, according to the present invention, it is possible to provide a lead-free solder deterioration diagnosis method and apparatus that can easily perform lead-free solder deterioration diagnosis. Furthermore, according to the present invention, it is possible to provide a lead-free solder alloy capable of extending the life.
[Brief description of the drawings]
FIG. 1 is a flowchart for explaining a lead-free solder deterioration diagnosis method according to a first embodiment of the present invention.
FIG. 2 is a schematic diagram showing a configuration example of a lead-free solder deterioration diagnosis apparatus 1A according to the present embodiment.
FIG. 3 is a plan view of a printed circuit board 12 on which a chip capacitor 11 is mounted.
FIG. 4 is a cross-sectional view of a printed circuit board 12 on which a chip capacitor 11 is mounted.
FIG. 5 is a schematic view showing an example of a state of crack growth when a needle-like metal crystal is added to the metal structure of a tin-zinc-based lead-free solder.
FIG. 6 is a schematic diagram showing an example of a state of crack growth when no needle-like metal crystal is added to the metal structure of a tin-zinc based lead-free solder.
FIG. 7 is a view showing an example of a metal structure of a cross section of a lead-free solder in an initial state before a thermal cycle test.
FIG. 8 is a schematic view showing an example of a metal structure of a cross section of lead-free solder in an initial state.
FIG. 9 is an enlarged view of an example of a metal structure of a cross section of a lead-free solder in an initial state.
FIG. 10 is a schematic diagram of an example of a metal structure of a cross section of lead-free solder in an initial state.
FIG. 11 is a histogram showing an example of an area ratio of crystal grains in a cross section of lead-free solder in an initial state.
FIG. 12 is a diagram showing an example of a metal structure of a cross section of an exposed lead-free solder after a 1000-cycle thermal cycle test.
FIG. 13 is a schematic diagram showing an example of a metal structure of a cross-section of a lead-free solder after a 1000-cycle thermal cycle test is performed.
FIG. 14 is an enlarged view showing an example of a metal structure after execution of a 1000-cycle thermal cycle test.
FIG. 15 is a schematic diagram of an example of a metal structure after execution of a 1000-cycle thermal cycle test.
FIG. 16 is a histogram showing an example of an area ratio of crystal grains in a cross section of lead-free solder after a 1000-cycle thermal cycle test.
FIG. 17 is a graph showing the relationship between the spheroidization rate of tin in the metal structure of lead-free solder in the initial state and the number of tin crystals with the corresponding spheroidization rate. .
FIG. 18 is a diagram showing the relationship between the spheroidization ratio of tin in the metal structure of the lead-free solder after the 1000-cycle thermal cycle test and the number of tin crystals having the corresponding spheroidization ratio.
FIG. 19 is a graph plotting the spheroidization rate of tin crystals of the lead-free solder metal structure before and after the thermal cycle test.
FIG. 20 is a flowchart for explaining an example of a lead-free solder deterioration diagnosis method according to the second embodiment of the present invention.
FIG. 21 is a schematic diagram showing an example of a lead-free solder deterioration diagnosis apparatus 1B according to the present embodiment.
FIG. 22 is a diagram showing the result of measurement of characteristic X-rays by a well-known X-ray spectroscopy performed by the present inventor before the thermal cycle test.
FIG. 23 is a diagram showing a characteristic X-ray measurement result by a well-known X-ray spectroscopy performed by the present inventor before a thermal cycle test.
FIG. 24 is a diagram for explaining a spheroidization rate.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1A ... Lead-free solder deterioration diagnostic device, 1B ... Lead-free solder deterioration diagnostic device, 2 ... Imaging unit, 3A ... Degradation parameter setting unit, 3B ... Degradation parameter setting unit, 4A ... Degradation parameter database, 4B ... Degradation parameter database, 5A Deterioration diagnosis unit, 5B ... Degradation diagnosis unit, 6A ... Output unit, 6B ... Output unit, 11 ... Chip capacitor, 12 ... Printed circuit board, 13 ... Land, 14 ... Lead-free solder, 21 ... Tin, 22 ... Zinc oxide, 23 ... acicular crystals, 24 ... cracks, 31 ... amorphous crystal grains of tin, 32 ... metal structure containing tin and zinc, 33 ... metal structure after execution of the thermal cycle test, 34 ... zinc oxide, 41 ... Electron beam irradiation unit, 42 ... Characteristic X-ray intensity measurement unit

Claims (1)

A lead-free solder deterioration diagnosis method for diagnosing deterioration of the lead-free solder from a change in cross-sectional shape of the lead-free solder,
A surface polishing step for exposing the cross-sectional metal structure of the lead-free solder by polishing the surface of the lead-free solder;
An observation step of observing a metal structure of a cross section of the lead-free solder polished by the surface polishing step;
As a result of the observation by the observation step, the deterioration parameter set based on the deterioration index obtained from the metal structure of the cross section of the lead-free solder is compared with the deterioration parameter set based on the predetermined deterioration index. As a result, a deterioration diagnosis step for determining whether or not the lead-free solder has deteriorated depending on whether or not the deterioration parameter obtained from the metal structure and the predetermined deterioration parameter match ,
The lead-free solder includes zinc;
The deterioration parameter is information for detecting a change in the crystal of zinc in the lead-free solder,
Deterioration diagnosis of lead-free solder, wherein the deterioration diagnosis step determines whether or not the lead-free solder has deteriorated depending on whether or not the zinc changes to a substantially circular shape or a substantially elliptical shape. Method.

Images