JP3993442B2 - Metal structure observation method and degradation diagnosis method and apparatus for lead-free solder - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a metallographic observation method, a deterioration diagnosis method, and an apparatus for lead-free solder for diagnosing lead-free solder deterioration.
[0002]
[Prior art]
A general electronic circuit is equipped with an electronic component with printed wiring. Electronic components are soldered to the substrate to form an electronic circuit.
[0003]
Solder joints deteriorate over time, and cracks and peeling occur due to the deterioration. Cracks and delamination occur mainly due to thermal stress, mechanical stress, and the like. The greater the stress load, the shorter the period until cracking or peeling occurs, resulting in a difference from the original product life.
[0004]
By adjusting the solder component by attaching Ag or the like to the conventional eutectic solder, the solder has a long life.
[0005]
In addition, since lead contained in eutectic solder is harmful to the environment, lead-free solder (lead-free solder) not containing lead is being used, and the life of this lead-free solder is being extended.
[0006]
However, there is a limit to extending the life of the solder. Therefore, it is important to detect the deterioration of the solder joint, grasp the maintenance timing, and prevent troubles due to cracks and peeling.
[0007]
Conventionally, in order to diagnose the deterioration and life of solder joints, life tests and stress analysis such as heat cycle tests and vibration tests assuming local environments have been performed.
[0008]
[Problems to be solved by the invention]
In life tests such as heat cycle tests and vibration tests that assume the local environment as described above, and stress analysis, actual assumptions were made based on changes in usage conditions, environmental changes, and the state of soldering of electronic components (solder amount, etc.) Cracks and delamination may occur for a shorter time than the lifetime.
[0009]
Further, in the above life test and stress analysis, since the entire real environment cannot be reflected, the actual life of the product may be shorter than the estimated life.
[0010]
On the other hand, in eutectic solder, the lead particles in the eutectic become coarse and deteriorate in strength as deterioration due to thermal stress or the like proceeds. For this reason, as a method for diagnosing deterioration of eutectic solder, there is a method in which a cross section of a solder joint is mirror-polished with a polishing machine or the like and lead particles in the eutectic are observed with a metal optical microscope.
[0011]
However, in lead-free solder, the metal structure does not appear clearly only by mirror-polishing the cross section of the solder joint. Therefore, unlike eutectic solder, deterioration is diagnosed even when the polished cross section is observed with a metal optical microscope. Difficult to do.
[0012]
Furthermore, in lead-free solders, it is not clear what kind of indicators indicate signs of deterioration, so the criteria for determining deterioration are not established, and deterioration diagnosis is difficult.
[0013]
The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a lead-free solder metal structure observation method, deterioration diagnosis method, and apparatus suitable for easily diagnosing lead-free solder deterioration.
[0014]
[Means for Solving the Problems]
Specific means taken for realizing the present invention will be described below.
[0015]
The lead-free solder metal structure observation method according to the first invention includes a polishing step for polishing a cross-section of the lead-free solder, an etching step for performing etching for exposing the metal structure to the cross-section polished by the polishing step, And a metal structure observation step of observing the metal structure of the cross section after etching by the etching step.
[0016]
In this way, by etching the cross-section of the lead-free solder after polishing, the grain boundaries of the cross-section can be clarified, and the state of the metal structure of the cross-section of the lead-free solder that has been difficult to observe only by polishing can be easily observed.
[0017]
The deterioration diagnosis method for lead-free solder according to the second invention includes a polishing step for polishing a cross section of the lead-free solder, an etching step for performing etching for exposing the metal structure to the cross section polished by the polishing step, and an etching step. The observation result of the metallographic structure of the cross section deteriorates based on the metallographic observation process for observing the metallographic structure of the cross-section after etching by the etching and the deterioration parameter set in advance according to the index for detecting the deterioration of the cross section of the lead-free solder A diagnostic step of determining whether or not
[0018]
Thus, the metal structure of lead-free solder that does not appear only by mirror polishing can be exposed by polishing and etching the cross section of the lead-free solder. The deterioration of the lead-free solder can be diagnosed based on the observation result of the exposed cross section of the metal structure and the deterioration parameter.
[0019]
In the etching step, the cross section may be etched with a corrosive solution containing at least one of ferric chloride and hydrochloric acid and alcohol.
[0020]
By using this corrosive solution, the metal structure of the cross section can be accurately exposed.
[0021]
The deterioration parameter is information for detecting a polygonal pattern, and the diagnosis process detects deterioration when a polygonal pattern is detected from the observation result of the metal structure of the cross section based on the deterioration parameter. It is good.
[0022]
An island-like (elliptical) structure appears in the cross section of the lead-free solder after polishing and etching. The case where the island-like structure is changed to a polygonal shape can be used as a deterioration index of lead-free solder.
[0023]
For example, when the lead-free solder contains tin, the tin structure of the cross section changes from an island shape to a polygonal shape, so that deterioration can be diagnosed based on this tin structure.
[0024]
In addition, the initial X-ray diffraction result for the cross-section after etching and the X-ray diffraction result at the time of deterioration diagnosis for the cross-section are acquired, and the diagnosis process shows the change in the X-ray diffraction result for determining that the lead-free solder has deteriorated. The deterioration diagnosis may be performed by comparing the parameter and the change from the initial X-ray diffraction result to the X-ray diffraction result at the time of the deterioration diagnosis.
[0025]
As lead-free solder deteriorates, the X-ray diffraction result of the cross section after polishing and etching changes. For this reason, the change of a X-ray-diffraction result can be utilized as a deterioration parameter | index of lead-free solder.
[0026]
The deterioration diagnosis method of the third invention includes an observation step of observing the pattern of the lead-free solder surface, Crystal From the observed surface based on pre-set degradation parameters to detect glandular patterns Crystal And a diagnostic step of detecting degradation when a glandular pattern is detected.
[0027]
Lead-free solder has a dendritic pattern on the surface as it progresses. Crystal It changes to a glandular pattern. Therefore, Crystal The occurrence of glandular patterns is used as a degradation indicator for lead-free solder for diagnosis of degradation. Thereby, deterioration of lead-free solder can be appropriately diagnosed nondestructively.
[0028]
According to a fourth aspect of the present invention, a deterioration diagnosis method includes an observation step of observing initial waviness of the surface of the lead-free solder and waviness during the deterioration diagnosis on the surface, a deterioration parameter indicating a change in waviness that determines that the lead-free solder has deteriorated, A diagnosis process may be included in which a deterioration diagnosis is performed by comparing a change from an initial waviness observation result to a waviness observation result at the time of deterioration diagnosis.
[0029]
As lead-free solder deteriorates, surface waviness decreases. Therefore, the level at which the surface waviness is reduced is used for diagnosis of deterioration as a deterioration index of lead-free solder. Thereby, deterioration of lead-free solder can be appropriately diagnosed nondestructively.
[0030]
Note that the lead-free solder deterioration diagnosis apparatus may be provided with an observation means for realizing the observation process of the above inventions and a diagnosis means for realizing the diagnosis process.
[0031]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. In the following description, the same parts are denoted by the same reference numerals.
[0032]
<First Embodiment>
In the present embodiment, a method for diagnosing the deterioration of the lead-free solder based on the cross-section of the lead-free solder will be described.
[0033]
FIG. 1 is a flowchart showing an example of a lead-free solder deterioration diagnosis method according to the first embodiment of the present invention.
[0034]
FIG. 2 is a diagram illustrating an example of a configuration of a deterioration diagnosis apparatus that performs the lead-free solder deterioration diagnosis method according to the present embodiment. The deterioration diagnosis apparatus 1 includes a setting unit 2, a database 4 that stores deterioration parameters 3, an observation unit 5, a diagnosis unit 6, and an output unit 7.
[0035]
The deterioration diagnosis method mainly includes steps S1 to S6 until the deterioration parameter is set and S7 to S11 for performing the deterioration diagnosis using the set deterioration parameter.
[0036]
In step S1, a thermal cycle test that simulates thermal stress is performed using various lead-free solders such as tin-based lead-free solder, silver-based lead-free solder, and copper-based lead-free solder.
[0037]
In step S2, the cross section of the lead-free solder subjected to the thermal cycle test is mirror-polished.
[0038]
In step S3, the cross section of the lead-free solder polished to a mirror surface is etched.
[0039]
In step S4, the metal structure of the cross section of the lead-free solder etched after polishing is observed. By performing etching after mirror polishing in this way, the characteristics of the metal structure in the cross section become remarkable and observation becomes easy.
[0040]
In step S5, a deterioration index indicating a sign of deterioration of the cross section of the lead-free solder is investigated from the relationship between the progress state of deterioration and the observed change state of the metal structure.
[0041]
In step S <b> 6, the setting unit 2 receives the setting of the deterioration parameter 3 for detecting the deterioration index of the cross section of the lead-free solder from the diagnostician and registers the content in the database 4.
[0042]
For example, the degradation parameter 3 uses information for detecting a case where the metal structure after the cross section of the lead-free solder is mirror-polished and etched is changed from an island shape to a polygonal shape. When the lead-free solder contains tin, information for detecting when the tin structure after the cross-section of the lead-free solder is mirror-polished and etched is changed from an island shape to a polygonal shape as the deterioration parameter 3 Also good.
[0043]
In step S7, the cross section of the lead-free solder 8 subject to deterioration diagnosis is mirror-polished.
[0044]
In step S8, the cross-section after mirror polishing of the lead-free solder 8 subject to deterioration diagnosis is etched. Also in this case, as described above, the feature of the metal structure in the cross section of the deterioration diagnosis target becomes remarkable.
[0045]
In step S <b> 9, the observation unit 6 observes the metal structure of the cross section of the lead-free solder 8 subject to deterioration diagnosis that has been etched after mirror polishing. In the present embodiment, a metal optical microscope is used as the observation unit 5, but a gold phase microscope or a stereomicroscope may be used.
[0046]
In step S10, the diagnosis unit 6 performs image analysis on the image information of the cross section of the lead-free solder 8 to be deteriorated, which is observed by the observation unit 5, and compares the analysis result with the deterioration parameter 5 of the database 4 to determine deterioration. A deterioration diagnosis process for detecting presence / absence is executed. That is, the diagnosis unit 6 is equipped with an image processing function for recognizing a pattern. The diagnosis unit 6 compares the characteristics and values indicated by the deterioration parameter 3 read from the database 4 with the characteristics and values of the data observed by the observation unit 5 and performs deterioration diagnosis.
[0047]
In step S <b> 11, the output unit 7 outputs a deterioration diagnosis result by the diagnosis unit 6. For the output unit 7, 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 can be used.
[0048]
Here, steps S1 to S6 until the deterioration parameter 3 is set will be described in detail with a specific example.
[0049]
Here, the deterioration parameter is set using a chip capacitor as shown in FIG. 4 mounted on a printed board as shown in FIG. 3 is a plan view of the printed circuit board 10 on which the chip capacitor 9 is mounted, and FIG. 4 is a cross-sectional view of the printed circuit board 10 on which the chip capacitor 9 is mounted. Cu pattern 11 provided on printed circuit board 10 and chip capacitor 9 are joined by lead-free solder 12.
[0050]
In the cooling / heating cycle test performed on the printed circuit board 10 in step S1, for example, a test in which the temperature is changed from −55 ° C. to + 125 ° C. in 30 minutes is defined as one cycle. It is assumed that this test is performed from 1 cycle to 1000 cycles. By this thermal cycle test, thermal stress is applied to the lead-free solder 12 to be tested.
[0051]
In step S2, the cross-section of the lead-free solder 12 after any cycle in the above-described thermal cycle test is polished until it becomes a mirror surface. In this example, water-resistant abrasive papers of 5 types of SiC with particle sizes of # 200, # 320, # 500, # 1000, and # 2400 are used for cross sections of 250 cycles, 500 cycles, 750 cycles, and 1000 cycles, respectively. After polishing, mirror polishing is performed using a paste in which 1 μm diamond particles are dispersed.
[0052]
When such a polishing process is not performed, the metal structure of the cross section of the lead-free solder 12 is not exposed, and therefore, the importance of performing the mirror polishing process using the fine diamond particles is great.
[0053]
As the corrosive liquid (reagent) used in the etching in step S3, for example, a corrosive liquid in which alcohol is used as a basic solution and ferric chloride and hydrochloric acid are added to the basic solution is used. As the corrosive liquid, for example, a liquid in which a ratio of alcohol and hydrochloric acid is mixed at a volume ratio of about 10 to 1 and ferric chloride is further mixed is used. More specifically, a corrosive solution in which about 10 to 15 ml of hydrochloric acid and 5 g of ferric chloride are mixed with 100 ml of alcohol is used for etching. Etching using this corrosive solution can further expose the metal structure of the cross section of the lead-free solder 12 that is not exposed only by polishing.
[0054]
FIG. 5 is a perspective view showing a state in which the metal structure is exposed by etching.
[0055]
Grain boundaries 13a existing in the mirror-like cross section before etching are emphasized by etching and become grain boundaries 13b. In the mirror-like cross section before etching, the grain boundary 13a cannot be confirmed by visual observation or the like, but the part where the grain boundary 13a actually exists is indicated by a dotted line.
[0056]
In the investigation of the degradation index in step S4, the cross section after etching is observed with a metal optical microscope or a stereomicroscope.
[0057]
FIG. 6 is a diagram illustrating an example of a metal structure of a cross section of the lead-free solder 12 in an initial state before the thermal cycle test.
[0058]
FIG. 7 is a schematic view showing an example of a metal structure of a cross section of the lead-free solder 12 in an initial state.
[0059]
The cross section of the lead-free solder 12 in the initial state is in a state where crystal grains of amorphous island-shaped tin 14 are dispersed. Moreover, in the cross section of the lead-free solder 12 in the initial state, the intermetallic compound 15 of tin and silver is present in a linear shape (needle shape) or granular shape. Moreover, the intermetallic compound 16 of copper and tin exists in a granular form.
[0060]
FIG. 8 is a diagram showing an example of a metal structure of a cross section of the lead-free solder 12 at a stage where a considerable thermal stress is applied in the cooling cycle test.
[0061]
FIG. 9 is a schematic view showing an example of a metal structure of a cross section of the lead-free solder 12 at a stage where a considerable thermal stress is applied.
[0062]
In the cross section of the lead-free solder 12 after the cooling cycle test has been performed for a corresponding cycle, tin 14 exists as polygonal crystal grain boundaries. Further, the intermetallic compound 15 of tin and silver is not linear but granular. Further, the tin and copper metal compound 16 is present in an enlarged state than in the initial state.
[0063]
In the thermal cycle test, the polygonal crystal grain boundaries of tin are generated from around 750 cycles, and there are cracks in the cross section.
[0064]
FIG. 10 is a diagram showing a relationship between the number of cycles of the thermal cycle and the measurement result of the bonding strength (kg) of the lead-free solder 12.
[0065]
From FIG. 10, the bonding strength of the lead-free solder 12 from the initial state to 500 cycles is not substantially lowered. However, a decrease in strength occurs at 750 cycles. That is, it is understood that the strength of the lead-free solder 12 is reduced between 500 cycles and 750 cycles.
[0066]
FIG. 11 shows a cross-sectional state of the lead-free solder 12 in the initial state, FIG. 12 shows a cross-sectional state of the lead-free solder 12 at the 500th cycle, and FIG. 13 shows a cross-sectional state of the lead-free solder 12 at the 750th cycle.
[0067]
As described above, it can be seen that the strength does not substantially decrease from the initial state to the 500th cycle, but the state of the metal structure of the cross section from the initial state to the 500th cycle is substantially unchanged.
[0068]
On the other hand, at 750 cycles, the bonding strength of the lead-free solder 12 is reduced, but it can be seen that the metal structure of the cross section has changed to a polygonal shape.
[0069]
From the above results, as a result of the thermal cycle test, it is confirmed that the lead-free solder 12 is cracked in the cross-section and the joint strength of the lead-free solder is reduced and the polygonal pattern is generated in the metal structure of the cross-section. .
[0070]
Therefore, the occurrence of a polygonal pattern in the metal structure of the cross section is used to determine the deterioration parameter 3 as a deterioration index.
[0071]
As the deterioration parameter 3 set in step S6, information for detecting a polygonal pattern from the cross-sectional metal structure is used as a result of the above.
[0072]
Note that the shape of the intermetallic compound 15 of silver and tin, which was linear before deterioration, changes to particles after the deterioration. Therefore, the deterioration parameter 3 may be set by using the intermetallic compound 15 of silver and tin as particles as a deterioration index.
[0073]
When the deterioration diagnosis is performed on the lead-free solder 8 subject to deterioration diagnosis based on the deterioration parameter 3 set as described above, the polishing in the step S7 is performed in the same manner as the above step S2, and the etching in the step S8 is performed in the above step S3. The corrosive liquid used in can be used.
[0074]
If the state of the metal structure of the cross section of the lead-free solder 8 subject to deterioration diagnosis that has been etched after mirror polishing in step S9 is observed, a polygonal pattern is formed on the cross-section of the lead-free solder 8 that is subject to deterioration diagnosis in step S10. It is determined whether or not there is a deterioration parameter 3. In step S10, the determination result is provided to the diagnostician.
[0075]
As described above, in the present embodiment, the cross-section of the lead-free solders 8 and 12 is mirror-polished and etched so that the grain boundaries of the cross-sections of the lead-free solders 8 and 12 become clear and the metal structure is exposed. Easy to observe.
[0076]
Further, in the present embodiment, it is possible to grasp what kind of factor the degradation index correlates with, the degradation index can be clearly defined from the state of the metal structure of the cross section of the lead-free solder 12, and degradation that becomes a criterion for degradation diagnosis Parameter 3 can be set.
[0077]
In the present embodiment, the cross-section of the lead-free solder 8 subject to deterioration diagnosis is mirror-polished and then etched to observe the metal structure and compared with the deterioration parameter 3 to easily diagnose deterioration of the lead-free solder 8. Can do.
[0078]
As a result, troubles in devices and products can be prevented in advance, and the maintenance cycle can be determined appropriately.
[0079]
In addition, by using the deterioration diagnosis device 1 according to the present embodiment, accurate deterioration diagnosis can be performed in a short time even without being an expert.
[0080]
Note that the corrosive liquid in the present embodiment may be a mixed liquid containing, for example, alcohol, hydrochloric acid, and picric acid.
[0081]
In this case, for example, the ratio of alcohol and hydrochloric acid is mixed at a volume ratio of about 10 to 1, and picric acid is mixed. More specifically, a corrosive solution obtained by mixing 1 g of picric acid in a solution obtained by adding about 10 to 15 ml of hydrochloric acid to 100 ml of alcohol is used for etching.
[0082]
<Second Embodiment>
In the present embodiment, a modification of the deterioration diagnosis method according to the first embodiment will be described.
[0083]
In this embodiment, instead of observing the metal structure of the cross-section of the lead-free solder etched after polishing, an X-ray diffraction test is performed on the cross-section of the lead-free solder etched after polishing, and the deterioration is caused by the change in the result. Diagnose.
[0084]
FIG. 14 is a flowchart showing an example of a lead-free solder deterioration diagnosis method according to the second embodiment of the present invention.
[0085]
The configuration of the deterioration diagnosis apparatus that performs the deterioration diagnosis method according to the present embodiment is the same as that shown in FIG. 2, and will be described with reference to FIG.
[0086]
The observation unit 5 of the degradation diagnosis apparatus 1 according to the present embodiment is an X-ray generation unit and an X-ray intensity measurement unit.
[0087]
Steps T1 to T3 are the same as steps S1 to S3 in FIG.
[0088]
In step T4, an X-ray diffraction test is performed on the cross section of the lead-free solder 12 etched after polishing, and an X-ray diffraction result is obtained.
[0089]
In step T5, the deterioration index of the cross section of the lead-free solder 12 is investigated from the change state of the acquired X-ray diffraction result.
[0090]
FIG. 15 is an X-ray diffraction chart showing an example of the X-ray diffraction result for the cross section of the lead-free solder 12 in the initial state before the thermal cycle test.
[0091]
The main crystal structure orientations in the cross section of the lead-free solder 12 in the initial state are the (101) plane, the (200) plane, and the (301) plane. That is, the X-ray intensity peaks at the plane indices (101), (200), and (301).
[0092]
FIG. 16 is an X-ray diffraction chart showing an example of an X-ray diffraction result of a cross section of the lead-free solder 12 when a thermal stress of 750 cycles is applied in a cooling cycle test.
[0093]
Compared with the diffraction chart after execution of 750 cycles and the diffraction chart in the initial state of FIG. 15, the states of the (200) plane and the (112) plane are greatly changed.
[0094]
The X-ray intensity of the (200) plane of tin after 750 cycles is significantly smaller than that of the tin (200) plane in the initial state.
[0095]
On the other hand, the X-ray intensity of the (112) plane of tin after 750 cycles is significantly higher than that of the initial (112) plane of tin.
[0096]
Changes in the X-ray diffraction results before and after the occurrence of cracks and a decrease in bonding strength due to such deterioration are detected and used as a deterioration index.
[0097]
In step T <b> 6, the setting unit 2 receives the setting of the deterioration parameter 3 that is information for detecting a deterioration index from the X-ray diffraction result from the diagnostician, and registers the content in the database 4.
[0098]
Steps T7 and T8 are the same as steps S7 and S8 in FIG.
[0099]
In step T9, the observation unit 5 acquires the X-ray diffraction result in the cross section of the lead-free solder 8 subject to deterioration diagnosis that has been etched after mirror polishing.
[0100]
In step T10, the diagnosis unit 6 compares the X-ray diffraction result with the deterioration parameter 3 read from the database 4, and diagnoses the presence or absence of deterioration.
[0101]
Step T11 is the same as step S11.
[0102]
In the present embodiment described above, the cross section of the lead-free solder 8 is polished and etched, and a change in crystal structure due to X-rays can be detected to easily diagnose deterioration. According to the present embodiment, the same effect as that of the first embodiment can be obtained.
[0103]
In this embodiment, the deterioration diagnosis is performed using the X-ray diffraction method. Instead, the XPS (X-ray photoelectron spectroscopy) method or the X-ray emission spectroscopic analysis is used. (X-ray emission spectrometry) may be used.
[0104]
<Third Embodiment>
In the present embodiment, a method for diagnosing the deterioration of the lead-free solder based on the state of the pattern on the surface of the lead-free solder will be described.
[0105]
FIG. 17 is a flowchart showing an example of a lead-free solder deterioration diagnosis method according to the third embodiment of the present invention.
[0106]
The configuration of the deterioration diagnosis apparatus that performs the deterioration diagnosis method according to the present embodiment is the same as that shown in FIG. 2, and will be described with reference to FIG.
[0107]
The observation unit 5 of the degradation diagnosis apparatus 1 according to the present embodiment is a metal optical microscope for observing the pattern of the surface of the lead-free solder joint.
[0108]
In step U1, the same thermal cycle test as in step S1 in the first embodiment is performed.
[0109]
In the process U2, the pattern of the surface of the lead-free solder 12 after any cycle execution in the thermal cycle test is observed.
[0110]
In step U3, a deterioration index is investigated from the observed surface pattern of the lead-free solder 12.
[0111]
FIG. 18 is a diagram illustrating an example of a surface pattern of the lead-free solder 12 in an initial state before the thermal cycle test.
[0112]
FIG. 19 is a schematic view showing an example of a pattern on the surface of the lead-free solder 12 in the initial state.
[0113]
The surface of the lead-free solder 12 in the initial state has a feature that a dendritic pattern 17 exists.
[0114]
FIG. 20 is a diagram illustrating an example of a pattern on the surface of the lead-free solder 12 at a stage where a considerable thermal stress is applied in the cooling cycle test. FIG. 20 shows a state in which a thermal stress of 750 cycles is applied in the cold cycle test.
[0115]
FIG. 21 is a schematic view showing an example of a metal structure of a cross section of the lead-free solder 12 at a stage where a considerable thermal stress is applied.
[0116]
The surface of the lead-free solder 12 after 750 cycles of the thermal cycle test has a feature that a crystal-like pattern 18 composed of a plurality of polygonal grains exists. The surface on which the crystal-like pattern 18 is generated shows a state in which an infinite number of small crystals are grown and clustered.
[0117]
From the above results, it is determined that when the lead-free solder 12 is deteriorated, the dendritic pattern 17 on the surface of the lead-free solder changes to a crystal-shaped pattern 18. Therefore, this pattern change is used as a degradation index and is used to determine the degradation parameter 3. The pattern of the dendritic pattern 17 on the surface of the lead-free solder 12 is changed to the crystal-shaped pattern 18 because the island-shaped pattern of the cross section is changed to a polygonal pattern in the first embodiment. It corresponds to.
[0118]
In step U4, the setting unit 2 receives the setting of the deterioration parameter 3 which is information for detecting that the surface of the lead-free solder has changed from the dendritic pattern 17 to the crystal-gland-shaped pattern 18 from the diagnostician, The contents are registered in the database 4.
[0119]
In step U5, the observation unit 5 observes the pattern of the surface of the lead-free solder 8 to be subjected to deterioration diagnosis.
[0120]
In step U6, the diagnosis unit 6 compares the observation result of the surface of the lead-free solder 8 with the deterioration parameter 3 read from the database 4, and diagnoses that the observation result includes deterioration when the observation result includes a crystal-gland-like pattern 18. .
[0121]
In step U7, the output unit 7 outputs a diagnosis result of deterioration by the diagnosis unit 6.
[0122]
In the present embodiment described above, the pattern of the surface of the lead-free solder 8 can be detected and deterioration can be easily diagnosed.
[0123]
Accordingly, in addition to the same effects as those of the first embodiment, it is possible to perform non-destructive deterioration diagnosis on a sample, a component to be subjected to deterioration diagnosis, and the like. In addition, the process of deterioration diagnosis can be simplified by omitting steps such as polishing and etching, and the diagnosis time can be shortened.
[0124]
<Fourth embodiment>
In the present embodiment, a modification of the deterioration diagnosis method according to the third embodiment will be described.
[0125]
In the present embodiment, instead of observing the surface pattern of the lead-free solder, the shape of the surface of the lead-free solder is observed, and deterioration is diagnosed from the change in the result.
[0126]
FIG. 22 is a flowchart showing an example of a lead-free solder deterioration diagnosis method according to the fourth embodiment of the present invention.
[0127]
The configuration of the deterioration diagnosis apparatus that performs the deterioration diagnosis method according to the present embodiment is the same as that shown in FIG. 2, and will be described with reference to FIG.
[0128]
The observation unit 5 of the degradation diagnosis apparatus 1 according to the present embodiment is a surface shape measuring instrument. For example, a light wave interference type surface roughness measuring instrument or the like can be used for the observation unit 5.
[0129]
Step V1 is the same as step U1 in FIG.
[0130]
In step V2, the shape of the surface of the lead-free solder 12 after any cycle execution in the thermal cycle test is observed.
[0131]
In step V3, a deterioration index is investigated from the observed shape of the surface of the lead-free solder 12.
[0132]
FIG. 23 is a diagram illustrating an example of a measurement result of the surface waviness of the lead-free solder 12 in an initial state before the thermal cycle test.
[0133]
The waviness curve of FIG. 23 measured by the light wave interference type surface roughness measuring instrument has a maximum wave waviness (WCM) of 63.11 [μm] and a wave wander centerline waviness (WCA) of 10.36 [μm].
[0134]
FIG. 24 is a diagram showing an example of the measurement result of the surface waviness of the lead-free solder 12 at a stage where a considerable thermal stress is applied in the cooling cycle test. FIG. 24 shows the measurement results for the lead-free solder 12 loaded with 750 cycles of thermal stress in the thermal cycle test.
[0135]
The waviness curve in FIG. 24 has a maximum wave waviness of 39.05 [μm] and a wavelet centerline waviness of 4.90 [μm].
[0136]
From the above results, when lead-free solder deteriorates, it is determined that the undulation of the surface of lead-free solder is reduced.
[0137]
Therefore, a case where the measured swell is smaller than the initial state by a certain level is used as a deterioration index and is used for determining the deterioration parameter 3.
[0138]
In step V4, the setting unit 2 receives the setting of the deterioration parameter 3 which is information for detecting a case where the waviness of the surface of the lead-free solder is smaller than the initial state by a certain level, and receives the contents thereof. Register in database 4.
[0139]
In step V5, the observation unit 5 observes the shape (swells here) of the surface of the lead-free solder 8 to be subjected to deterioration diagnosis.
[0140]
In step V6, the diagnosis unit 6 compares the observation result of the surface of the lead-free solder 8 subject to deterioration diagnosis with the deterioration parameter 3 read from the database 4, and determines whether or not deterioration is indicated.
[0141]
In step V <b> 7, the output unit 7 outputs a deterioration diagnosis result by the diagnosis unit 6.
[0142]
In the present embodiment described above, it is possible to detect deterioration of the surface of the lead-free solder 8 and diagnose deterioration.
[0143]
Therefore, similarly to the effect similar to that of the third embodiment, it is possible to nondestructively diagnose deterioration of a sample or a component to be subjected to deterioration diagnosis. In addition, the deterioration diagnosis procedure can be simplified and the diagnosis time can be shortened.
[0144]
In addition, as a method for obtaining the size of the swell, for example, a method for obtaining the maximum height, a method for obtaining the centerline average value by applying a low-frequency cutoff, or the like may be used. Waviness measures at least one of four types of wave maximum waviness, wave centerline waviness, rolling circle maximum waviness (WEM), and rolling circle centerline waviness (WEA).
[0145]
Another setting example of the deterioration parameter 3 will be described.
[0146]
For example, it is assumed that the waviness (maximum wave height) of the lead-free solder 12 in the initial state is 62 [μm] on average in the waviness measurement inspection. On the other hand, the swell (maximum wave height) after execution of 750 cycles is assumed to be 30 [μm] on average. In such a case, for example, a threshold value for detecting a case where the surface waviness of the lead-free solder 8 subject to deterioration diagnosis is ½ or less from the initial waviness may be used as the deterioration parameter 3.
[0147]
【The invention's effect】
As described above in detail, according to the present invention, it is possible to easily observe the state of the metal structure of the cross section of the lead-free solder, and use the deterioration parameter that is an index for the deterioration diagnosis of the lead-free solder set based on the observation result. The deterioration of lead-free solder can be easily diagnosed.
[Brief description of the drawings]
FIG. 1 is a flowchart showing an example of a lead-free solder deterioration diagnosis method according to a first embodiment of the present invention.
FIG. 2 is a diagram illustrating an example of the configuration of a deterioration diagnosis apparatus that performs the lead-free solder deterioration diagnosis method according to the present embodiment.
FIG. 3 is a plan view of a printed circuit board on which a chip capacitor is mounted.
FIG. 4 is a cross-sectional view of a printed circuit board on which a chip capacitor is mounted.
FIG. 5 is a perspective view showing a state in which a metal structure is exposed by etching.
FIG. 6 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. 7 is a schematic view showing an example of a metal structure of a cross section of lead-free solder in an initial state.
FIG. 8 is a diagram showing an example of a metal structure of a cross section of a lead-free solder at a stage where a considerable thermal stress is applied in a thermal cycle test.
FIG. 9 is a schematic view showing an example of a metal structure of a cross section of a lead-free solder at a stage where a considerable thermal stress is applied.
FIG. 10 is a diagram showing the relationship between the number of cycles of the thermal cycle and the measurement result of the bonding strength (kg) of lead-free solder.
FIG. 11 is a diagram showing a cross-sectional state of lead-free solder in an initial state.
FIG. 12 is a diagram showing a cross-sectional state of a lead-free solder at 500 cycles.
FIG. 13 is a diagram showing a cross-sectional state of a lead-free solder at the time of 750 cycles.
FIG. 14 is a flowchart showing an example of a lead-free solder deterioration diagnosis method according to the second embodiment of the present invention.
FIG. 15 is an X-ray diffraction chart showing an example of an X-ray diffraction result of a cross section of an lead-free solder in an initial state before a thermal cycle test.
FIG. 16 is an X-ray diffraction chart showing an example of an X-ray diffraction result of a cross section of a lead-free solder when a thermal stress of 750 cycles is applied in a cold cycle test.
FIG. 17 is a flowchart showing an example of a lead-free solder deterioration diagnosis method according to the third embodiment of the present invention.
FIG. 18 is a diagram showing an example of a surface pattern of a lead-free solder in an initial state before a thermal cycle test.
FIG. 19 is a schematic view showing an example of a pattern of a surface of lead-free solder in an initial state.
FIG. 20 is a diagram showing an example of a pattern on the surface of the lead-free solder 12 at a stage where a considerable thermal stress is applied in a cooling cycle test.
FIG. 21 is a schematic view showing an example of a metal structure of a cross section of a lead-free solder at a stage where a considerable thermal stress is applied.
FIG. 22 is a flowchart showing an example of a lead-free solder deterioration diagnosis method according to the fourth embodiment of the present invention.
FIG. 23 is a diagram showing an example of the measurement result of the surface waviness of the lead-free solder in the initial state before the thermal cycle test.
FIG. 24 is a diagram showing an example of the measurement result of the undulation of the surface of the lead-free solder at a stage where a considerable thermal stress is applied in the thermal cycle test.
[Explanation of symbols]
1 ... Deterioration diagnosis device
2 ... Setting section
3. Degradation parameters
4 ... Database
5 ... Observation Department
6 ... Diagnosis Department
7 ... Output section
8 ... Lead-free solder
9 ... Chip capacitor
10 ... Printed circuit board
11 ... Cu pattern
12 ... Lead-free solder
13a ... Grain boundary
13b ... Grain boundary
14 ... Tin
15 ... Intermetallic compound of tin and silver
16: Intermetallic compound of copper and tin
17 ... Dendritic pattern
18 ... Crystalline pattern

Claims (10)

A metal structure observation method for observing the metal structure of lead-free solder,
A polishing step of polishing a cross section of the lead-free solder;
An etching step for performing etching for exposing the metal structure to the cross section polished by the polishing step;
And a metal structure observation step of observing the metal structure of the cross-section after etching by the etching step. A lead-free solder deterioration diagnosis method for diagnosing lead-free solder deterioration,
A polishing step of polishing a cross section of the lead-free solder;
An etching step for performing etching for exposing the metal structure to the cross section polished by the polishing step;
A metal structure observation step of observing the metal structure of the cross section after etching by the etching step;
And a diagnostic step of determining whether the observation result of the metal structure of the cross section indicates deterioration based on a deterioration parameter set in advance according to an index for detecting the deterioration of the cross section of the lead-free solder. Degradation diagnosis method for lead-free solder. In the lead-free solder deterioration diagnosis method according to claim 2,
The etching process is a lead-free solder deterioration diagnosis method in which the cross section is etched with a corrosive solution containing at least one of ferric chloride and hydrochloric acid and alcohol. In the lead-free solder deterioration diagnosis method according to claim 2 or claim 3,
The deterioration parameter is information for detecting a polygonal pattern,
Deterioration detection method for lead-free solder, wherein the diagnosis step detects deterioration when a polygonal pattern is detected from the observation result of the metal structure of the cross section based on the deterioration parameter. In the lead-free solder deterioration diagnosis method according to any one of claims 2 to 4,
The lead-free solder includes tin;
The deterioration parameter is information for detecting a polygonal tin structure in the cross section,
Deterioration detection method for lead-free solder, wherein the diagnosis step detects deterioration when the tin structure indicated by the observation result of the cross section is determined to be polygonal based on the deterioration parameter. In the lead-free solder deterioration diagnosis method according to claim 2,
The metal structure observation step acquires an initial X-ray diffraction result for the cross section after etching and an X-ray diffraction result at the time of deterioration diagnosis for the cross section,
The diagnosis step is performed by comparing a deterioration parameter indicating a change in an X-ray diffraction result for determining that lead-free solder has deteriorated and a change from the initial X-ray diffraction result to an X-ray diffraction result at the time of the deterioration diagnosis. Deterioration diagnosis method for lead-free solder, characterized by performing diagnosis. A lead-free solder deterioration diagnosis method for diagnosing lead-free solder deterioration,
An observation process to observe the surface pattern of lead-free solder;
Based on a preset deterioration parameter in order to detect the crystal glands like pattern, when the crystals gland-like pattern is detected from the observed said surface, characterized in that it comprises a diagnostic step for detecting deterioration Degradation diagnosis method for lead-free solder. A lead-free solder deterioration diagnosis method for diagnosing lead-free solder deterioration,
An observation process for observing the initial undulation of the surface of the lead-free solder and the undulation at the time of deterioration diagnosis for the surface;
A deterioration parameter indicating a change in undulation for determining that lead-free solder has deteriorated, and a diagnosis process for performing a deterioration diagnosis by comparing the change from the initial undulation observation result to the undulation observation result at the time of the deterioration diagnosis. Characterized lead-free solder deterioration diagnosis method. A lead-free solder deterioration diagnosis device for diagnosing lead-free solder deterioration,
Observation means for observing the surface pattern of lead-free solder ;
Storage means for storing deterioration parameters set for detecting a crystal-like pattern ;
Deterioration of lead-free solder, comprising diagnostic means for detecting deterioration when a glandular pattern is detected from the observed surface based on the deterioration parameter stored in the storage means Diagnostic device. A lead-free solder deterioration diagnosis device for diagnosing lead-free solder deterioration,
An observation means for observing the undulation of the surface of the lead-free solder;
Storage means for storing a deterioration parameter indicating a change in swell to determine that the lead-free solder has deteriorated ;
Based on the deterioration parameter stored in the storage means, a diagnosis means for performing deterioration diagnosis by comparing the initial waviness observation result of the surface observed by the observation means and the change to the waviness observation result at the time of deterioration diagnosis And a lead-free solder deterioration diagnosis device.

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