JP4095511B2 - Lead-free solder joint strength determination method and apparatus - Google Patents

Description

  The present invention relates to a method and apparatus for determining the bonding strength of lead-free solder that determines the bonding strength of lead-free solder.

Conventionally, with regard to the metal structure including lead-free solder, as a method related to the method of determining the joint strength of the lead-free solder, crack propagation is based on the equivalent strain amplitude obtained from the finite element method three-dimensional thermoelastic analysis and the observed shear strain. A method for obtaining a connection life by obtaining a life evaluation reference equation after obtaining a speed equation is disclosed (see Patent Document 1).
Japanese Patent Laid-Open No. 3-128431

  However, this method requires advanced expertise such as the finite element method three-dimensional thermoelastic analysis, crack growth rate equation, and life evaluation criterion equation, so it is easy to lead-free without using these advanced expertise. It is not possible to determine the joint strength related to the metal structure of the solder.

  Moreover, when determining the joint strength of lead-free solder by this method, the shear strain and the like must be calculated with high accuracy, but this requires extremely skilled techniques.

  There is currently no known method for determining the bonding strength of lead-free solder, which can easily determine the bonding strength of lead-free solder without using advanced expertise and skilled techniques.

  In general, when a circuit is to be changed by modifying a product or the like, the component is re-mounted on the printed circuit board, so that the lead-free solder that fixes the component on the printed circuit board may be reheated.

  In such a case, whether or not the reheating of the lead-free solder has caused a problem in the solder joint between the component mounted on the printed circuit board and the lead-free solder, in other words, the solder joint strength has a problem. If it can be easily known whether or not it has occurred, parts can be reused smoothly, but such a method is not known.

  According to the inventor's consideration regarding lead-free solder, it is easy to determine whether reheating of lead-free solder has caused a problem in the bonding strength between the lead-free solder and the component from the viewpoint of smoothly reusing the component. There is an increasing demand for a method and apparatus for determining the bonding strength of lead-free solder that can be obtained in a simple manner.

  The present invention has been made in consideration of the above circumstances, and it is possible to easily determine the bonding strength of lead-free solder without the need for advanced specialized knowledge and skill. It is an object to provide a method and apparatus.

  The essence of the present invention is to compare the strength of the lead-free solder without the need for advanced specialized knowledge and skill by comparing the structure parameters determined in advance with the observation results of the surface of the lead-free solder. It is to achieve the effect of making it easy to know.

  The “structure parameter” described in the present specification refers to an index value indicating that the joint strength of the lead-free solder has not decreased more than a certain level.

  The gist of the present invention as described above is specifically achieved by taking the following means.

  The lead-free solder joint strength determining method according to one aspect of the present invention is a lead-free solder joint strength determining method for determining the lead-free solder joint strength based on a change in the metal structure of the lead-free solder. A metal structure observation step for observing the metal structure of the metal, and a structure parameter comparison step for comparing the observation result obtained by the metal structure observation step with a structure parameter indicating that the bonding strength of the lead-free solder is not reduced. This is a method for determining the bonding strength of lead-free solder.

  As a result, it is possible to determine whether the bonding strength of lead-free solder is reduced simply by comparing the observation result of the metal structure on the surface of lead-free solder with the structural parameters indicating that the bonding strength of lead-free solder is not reduced. Therefore, it is possible to easily know the joint strength of lead-free solder without the need for advanced specialized knowledge and skill.

  The lead-free solder preferably contains at least tin and silver.

  The weaving parameter may be numerical data calculated from image data of the surface of the lead-free solder stored correspondingly at least for each heating time.

  The parameter may be numerical data calculated from image data of the surface of the lead-free solder stored correspondingly at least every number of times of heating.

  Furthermore, the structure parameter may be numerical data calculated from image data of the surface of the lead-free solder stored correspondingly at least for each mounting on the board.

  In the method for determining the bonding strength of lead-free solder according to one aspect of the present invention, the structural parameters are the length in the major axis direction and the length in the minor axis direction of tin crystal grains contained in the lead-free solder when the number of heating times is one. This ratio is a lead-free solder joint strength determination method that determines that the joint strength of lead-free solder is not lowered when the ratio is twice or more.

  Thereby, when the number of times of heating is one and the ratio between the length in the major axis direction and the length in the minor axis direction of the tin crystal grains contained in the lead-free solder is twice or more, the joint strength of the lead-free solder Therefore, it is possible to easily know the bonding strength of the lead-free solder without requiring a high level of expertise and skill.

  In the method for determining the strength of lead-free solder according to one aspect of the present invention, the structural parameters are the length in the major axis direction and the length in the minor axis direction of tin crystal grains contained in the lead-free solder when the number of heating times is two. This ratio is a lead-free solder joint strength determination method in which it is determined that the joint strength of lead-free solder is not lowered when this ratio is twice or less.

  Thereby, when the number of times of heating is 2 and the ratio of the length in the major axis direction to the length in the minor axis direction of the tin crystal grains is twice or less, it is determined that the bonding strength of the lead-free solder is not lowered. Therefore, it becomes possible to easily know the bonding strength of the lead-free solder without requiring high specialized knowledge and skill.

  In the lead-free solder joint strength determination method according to one embodiment of the present invention, the structure parameter is the thickness of the intermetallic compound when the lead-free solder is mounted once, and the thickness of the intermetallic compound is 0.5 μm. When it is below, it is the joint strength determination method of the lead-free solder which determines that the joint strength of the lead-free solder is not lowered.

  As a result, when the lead-free solder is mounted once and the thickness of the intermetallic compound is 0.5 μm or less, it is determined that the joint strength of the lead-free solder is not lowered. This makes it possible to easily know the bonding strength of lead-free solder without the need for such techniques.

  In the method for determining the bonding strength of lead-free solder according to one aspect of the present invention, the structure parameter is the thickness of the intermetallic compound when the number of times the lead-free solder is mounted is 2, and the thickness of the intermetallic compound is 0.5 μm. When the thickness is 1.0 μm or less, the lead-free solder joint strength determination method determines that the joint strength of the lead-free solder is not lowered.

  As a result, when the lead-free solder is mounted twice and the thickness of the intermetallic compound is 0.5 μm or more and 1.0 μm or less, it is determined that the bonding strength of the lead-free solder is not lowered. Therefore, it is possible to easily know the joint strength of lead-free solder without the need for advanced specialized knowledge and skill.

  In the lead-free solder joint strength determination method according to one aspect of the present invention, the structure parameter is the thickness of the intermetallic compound when the lead-free solder is mounted three times, and the thickness of the intermetallic compound is 3.0 μm. When it is the above thickness, it is the joint strength determination method of the lead-free solder which determines with the joint strength of lead-free solder not reducing.

  Accordingly, when the lead-free solder is mounted three times and the thickness of the intermetallic compound is 3.0 μm or more, it is determined that the bonding strength of the lead-free solder is not lowered. It becomes possible to easily know the joint strength of lead-free solder without requiring specialized knowledge and skill.

  A lead-free solder joint strength determining device according to one aspect of the present invention is a lead-free solder joint strength determining device that determines the lead-free solder joint strength based on a change in the metal structure of the lead-free solder surface. An observation means for observing the surface of the structure, a structure parameter setting means for setting a structure parameter indicating that the bonding strength of the lead-free solder is not reduced from the result of observation by the observation means, and a structure parameter set by the structure parameter setting means Is compared with the structure parameter stored in the structure parameter storage means based on the observation result of the metal structure of the lead-free solder whose bonding strength is to be determined. The joint strength judging means for judging whether or not the joint strength of the lead-free solder has decreased, and the judgment by the joint strength judging means. A configuration in which an output means for outputting a result.

  According to such a configuration, as a result of observation of the metal structure of the lead-free solder whose bonding strength is to be determined, by comparing the obtained structure parameter with the structure parameter stored in the structure parameter storage means, Since it is determined whether or not the bonding strength is reduced, it is possible to easily know the bonding strength of the lead-free solder without requiring a high level of expertise and skill.

  According to the present invention, it is possible to provide a lead-free solder joint strength determination method and apparatus that makes it possible to easily know the joint strength of lead-free solder without requiring high-level specialized knowledge and skill.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a functional block diagram illustrating a configuration example of a lead-free solder joint strength determination apparatus 1 to which a lead-free solder joint strength determination method according to an embodiment of the present invention is applied.

  FIG. 2 is a view of joining a chip resistor 11 and a land 13 provided on a printed circuit board 12, which is one of objects to which a lead-free solder joining strength determination method according to an embodiment of the present invention is applied. 3 is a plan view of lead-free solder 14. FIG.

  FIG. 3 shows a lead-free solder 14 that joins a chip resistor 11 and a land 13 provided on a printed circuit board 12, which is one of objects to which the lead-free solder joining strength determination method according to the embodiment is applied. FIG.

  In addition, the application object of the joining strength determination method of the lead-free solder according to the present embodiment is a tin-silver-based lead-free solder containing at least tin and silver.

  In particular, the lead-free solder used in this embodiment is a lead-free solder containing 3 Wt percent silver and 0.5 Wt percent copper and tin, or 3.5 Wt percent silver and 0.7 Wt percent copper and tin. It is more preferable to use lead-free solder contained.

  The lead-free solder joint strength determining apparatus 1 according to the present embodiment includes an imaging unit 2, a command input unit 3, an image input switching unit 4, a tissue parameter setting unit 5, a tissue parameter database 6, and a joint strength determination. The unit 7 and the output unit 8 are configured.

  In the lead-free solder joint strength determination device 1 according to the present embodiment, each function is realized by a computer whose operation is controlled by a program installed via a recording medium or a communication network, for example.

  The imaging unit 2 observes the metal structure on the surface of the lead-free solder, images image data of the metal structure, and outputs the captured image data to the image input switching unit 4.

  The command input unit 3 has a normal data input function, and parameter setting commands and observation conditions for setting tissue parameters mainly by the operation of the operator, for example, the number of heating times, the number of times of mounting on the substrate, and A set of heating time per one time and a joining strength determination command for determining the joining strength are input.

  The image input switching unit 4 has a function of determining whether or not a parameter setting command has been input from the command input unit 3, and is output from the imaging unit 2 when it is determined that a parameter setting command has been input as a result of the determination. When it is determined that the bonding strength determination command is input as a result of the above-described determination and the function of outputting the image data to the tissue parameter setting unit 5 and the determination described above, the image data output from the imaging unit is output to the bonding strength determination unit 7 With functions.

  The tissue parameter setting unit 5 performs well-known image processing on the image data output from the image input switching unit 4, and extracts a strength index for determining a decrease in the bonding strength of lead-free solder from the result of the image processing. Function, a function for setting numerical data indicating that a strength index for determining whether or not the extracted bonding strength has decreased appears in the metal structure as a structure parameter, the set structure parameter, and observation It has a function of storing in the tissue parameter database 6 a set of conditions, for example, the number of times of heating, the number of times of mounting on the substrate, and the heating time per time.

  The tissue parameter database 6 stores the tissue parameters set by the tissue parameter setting unit 5 and the observation conditions, for example, the number of heating times, the number of times of mounting on the substrate, and the heating time per time.

  When receiving the image data output from the image input switching unit 4, the bonding strength determination unit 7 performs a function of executing image processing on the image data, a function of extracting a tissue parameter from the result of the image processing, Lead-free solder bonding by searching the parameter database 6 and comparing the read-out tissue parameter with the function of reading out the tissue parameter set in advance as a search result and the tissue parameter extracted from the result of the image processing described above A function of determining whether the strength has decreased, and a function of outputting the determination result to the output unit 8;

  The output unit 8 outputs the determination result output from the bonding strength determination unit 7 to the outside.

  Hereinafter, an outline of the lead-free solder joint strength determination method according to the present embodiment will be described with reference to the drawings.

  FIG. 4 is a flowchart for explaining an example of a method for determining the bonding strength of lead-free solder according to the present embodiment.

In the lead-free solder joint strength determination method according to the present embodiment, the number of heating times, the heating time, and the number of mounting times on the printed circuit board are known in order to set the structure parameters of the lead-free solder. By observing the metal structure, the steps ST1 to ST3 until the structure parameter is set, and the joining of lead-free solder whose heating number, heating time, and mounting number on the printed circuit board are not known using this structure parameter It consists of process ST4-process ST6 which performs intensity | strength determination.

  First, a metal structure of lead-free solder whose structure parameters are to be extracted and whose number of heating times, heating time, and number of mountings on the substrate are known is imaged (ST1).

  Next, a strength index indicating an indication of a decrease in the bonding strength of the lead-free solder is investigated from the relationship between the degree of decrease in the bonding strength and the observed decrease in the bonding strength of the metal structure (ST2).

  Next, the structure parameter setting unit 5 accepts a structure parameter setting command for detecting the strength index of lead-free solder from the determiner, and corresponds the set of the structure parameter and the observation condition, for example, the number of times of mounting and the number of times of heating. And stored in the organization parameter database 6 (ST3).

  Next, the imaging unit 2 images the metal structure of lead-free solder, whose number of heating times, heating time, and number of mountings on the substrate, which are the determination targets of the bonding strength (ST4).

  Next, the bonding strength determination unit 7 performs image processing on the image data of the surface of the lead-free solder to which the bonding strength is applied, which is imaged by the imaging unit 2, and the image processing result and the tissue stored in the tissue parameter database 6. The parameters are compared with each other, and as a result of the comparison, a bonding strength determination process for detecting whether or not the bonding strength is reduced is executed (ST5).

  Next, the output unit 8 outputs the result of determination of the bonding strength by the bonding strength determination unit 7 (ST6).

  The joint strength of lead-free solder is determined by a series of procedures as described above.

  Hereinafter, the lead-free solder joint strength determination method realized by the lead-free solder joint strength determination device 1 will be described in more detail with specific examples.

  In the process ST1, the metal structure of the tin-silver-based lead-free solder is observed by the imaging unit 2.

  Here, as a technique for observing the metal structure of the lead-free solder, a technique for performing known image processing on the captured image data by imaging the metal structure, and an X using a known X-ray spectroscopy. A characteristic X-ray emitted from the surface of a lead-free solder metal structure is received by an X-ray microanalyzer (EPMA), for example, and the energy of the received characteristic X-ray is analyzed, and the metal structure is visually observed. There is a technique to do.

  In step ST2, the strength index is investigated from the result of observation of the metal structure exposed on the surface of the lead-free solder.

  In step ST3, the structure parameter setting unit 5 sets numerical data for detecting substantially elliptical tin crystal grains from the image data of the metal structure of the lead-free solder obtained as a result of observation, as a structure parameter. A set of the set tissue parameter and the observation condition input from the command input unit 3 is stored in the tissue parameter database 6.

  Here, as the texture parameter to be set, for example, numerical data related to the shape of the substantially elliptical tin crystal, for example, the ratio of the length in the major axis direction to the length in the uniaxial direction of the tin crystal grains can be given. It is done.

  FIG. 5 is a diagram illustrating an example of image data obtained as an imaging result of the metal structure of the lead-free solder 14 at the first mounting on the printed circuit board according to the present embodiment.

  FIG. 6 is a schematic diagram of image data obtained as an imaging result of the metal structure of the lead-free solder 14 shown in FIG.

  In this example, the tin crystal grains 15 contained in the metal structure of the lead-free solder 14 have a substantially elliptical shape arranged along a substantially constant direction such as a substantially horizontal direction or a substantially vertical direction.

  Thus, the reason why the crystal grains of the lead-free solder are arranged in a substantially constant direction is due to cooling during solidification.

  According to the measurement by the present inventor, the length in the major axis direction of the tin crystal grains 15 having the substantially elliptical shape has a value more than twice the length in the minor axis direction.

  Moreover, according to the observation of the present inventor, when the length in the major axis direction of the tin crystal grains 15 is not less than twice the length in the minor axis direction, lead-free There was no particular problem with the solder joint strength.

  Here, as a technique for determining the length in the major axis direction and the length in the minor axis direction, for example, the technique may be determined by a technique including a series of procedures (1) to (9) as follows. Good.

(1) An arbitrary number of crystal grains are extracted as sample from the image data.

(2) Extract a high density portion from the extracted crystal grain image.

(3) Draw a boundary line that forms the outer frame of the crystal grain.

(4) Count the number of pixels contained in the area inside the outer frame.

(5) The area of each crystal grain is calculated by multiplying the number of pixels by the area per pixel.

(6) Draw two straight lines that bisect the area of the crystal grains.

(7) The center of rotation for rotating the outer frame is obtained as the intersection of these two straight lines.

(8) When a straight line passing through the rotation center is rotated around the rotation center, and the distance between the intersections of the straight line and the outer frame is maximum, the maximum value is determined as the long axis.

(9) On the other hand, when the distance between the straight line and the outer frame is minimum, the minimum value is set as the minor axis.

  Accordingly, the present inventor assumes that the number of times lead-free solder is mounted and that the heating temperature and heating time of the lead-free solder are substantially the same, the tin crystal grains are in a substantially constant direction. And the strength of the lead-free solder is constant when it is detected that the ratio of the length of the major axis of the tin crystal grains to the length of the minor axis is twice or more. It is considered that the tissue parameter can be set as an intensity index indicating that it has not decreased below.

  FIG. 7 is a diagram illustrating an example of image data obtained as a result of imaging the lead-free solder 14 at the time of the second mounting on the printed circuit board according to the present embodiment.

  FIG. 8 is a schematic diagram of image data obtained as a result of imaging the metal structure of the lead-free solder 14 shown in FIG.

  In this example, the arrangement of lead-free solder crystal grains along a certain direction as seen in the first image data disappears.

  According to the measurement by the present inventor, the length in the major axis direction of the tin crystal grains 16 having a substantially elliptical shape has a value not more than twice the length in the minor axis direction.

  Moreover, according to the observation of the present inventors, when the length in the major axis direction of the tin crystal grains 16 is not more than twice the length in the minor axis direction, lead-free There was no particular problem with the solder joint strength.

  Therefore, the present inventor further assumes that the lead-free solder is mounted twice and the lead-free solder and the heating time are substantially the same. As a strength indicator to indicate that the joint strength of the lead-free solder metal structure is not reduced when it is detected that the ratio of the length of the major axis to the length in the minor axis direction is twice or less. I think that it can be set to the structure parameter of lead-free solder.

  Next, the present inventor observed the same metal structure with respect to the metal structure of lead-free solder in which the number of mountings on the substrate was limited to one and the heating time was changed. The observation results will be specifically described below.

  FIG. 9 shows an example of image data obtained as a result of imaging the joint boundary surface of lead-free solder when soldered in a time of 3 seconds or less during the first mounting on the printed circuit board according to the present embodiment. FIG.

  In this example, an intermetallic compound layer 17 having a thickness of 0.5 μm or less was found at the boundary between the lead-free solder 14 and the land 13 on the printed circuit board.

  The intermetallic compound 17 observed here is a compound of Cu and Sn. As shown in FIG. 9, the shape of the intermetallic compound 17 has an uneven shape, and the thickness is measured by measuring the maximum value of the convex portion and the maximum value of the concave portion at ten locations, and evaluating the average value thereof. Yes.

  According to the observation of the present inventor, in this state, no particular problem was found in the bonding strength of the lead-free solder.

  Therefore, the present inventor has found that when the intermetallic compound layer 17 having a thickness of 0.5 μm or less is seen at the interface between the lead-free solder and the land, the bonding strength of the lead-free solder metal structure is reduced. I think that it can be set to the structure parameter of lead-free solder as a strength index showing that there is no.

  FIG. 10 shows an image obtained as a result of imaging the joint interface of lead-free solder when soldering is performed for 3 to 10 seconds during the first mounting on the printed circuit board according to the present embodiment. It is a figure which shows an example of data.

  In this example, an intermetallic compound layer 18 having a thickness of 0.5 μm or more and 1.0 μm or less was found at the boundary surface between the lead-free solder 14 and the land 13 on the printed circuit board.

  The intermetallic compound 18 observed here is a compound of Cu and Sn. As shown in FIG. 10, the shape of the intermetallic compound 18 has a concavo-convex shape, and the thickness is measured by measuring the maximum value of the convex portion and the maximum value of the concave portion at ten locations, and evaluating the average value thereof. Yes.

  According to the observation of the present inventor, in this state, no particular problem was found in the bonding strength of the lead-free solder.

  Accordingly, the present inventor has found that when the intermetallic compound layer 18 having a thickness of 0.5 μm to 1.0 μm is seen at the interface between the lead-free solder and the land, the bonding strength of the metal structure of the lead-free solder It is considered that the structure parameter of lead-free solder can be set as a strength index indicating that the resistance is not lowered.

  FIG. 11 is obtained as a result of imaging the joint boundary surface of the lead-free solder 14 in the case where solder joining is performed for 10 seconds to 60 seconds during the first mounting on the printed circuit board according to the present embodiment. It is a figure which shows an example of image data.

  In this example, an intermetallic compound layer 19 having a thickness of 3.0 μm or more was found at the boundary surface between the lead-free solder 14 and the land 13 on the printed circuit board.

  The intermetallic compound 19 observed here is a compound of Cu and Sn. As shown in FIG. 11, the shape of the intermetallic compound 19 has a concavo-convex shape, and the thickness is measured by measuring the maximum value of the convex portion and the maximum value of the concave portion at ten locations, and evaluating the average value thereof. Yes.

  According to the inventor's observation, in this state, the environment used as a product is very severe, and when used for a product that requires long-term reliability, the bonding strength becomes a problem, In other cases, a bonding strength that is not particularly problematic was obtained.

  From the above, when it is assumed that the heating temperature is substantially the same temperature, the thickness of the intermetallic compound layer of tin and silver is increased at the bonding interface of the lead-free solder as the heating time of the lead-free solder increases. It has been found. The solder joining described above was performed using a soldering iron heated to a temperature of 280 ° C to 350 ° C.

  Therefore, the present inventor believes that the thickness of the intermetallic compound can be used as the structure parameter of the lead-free solder indicating that the bonding strength of the lead-free solder is not lowered.

  FIG. 12 is a diagram illustrating an example of a relationship between bonding strength and the number of temperature cycles to be loaded.

  In FIG. 12, the number of temperature cycles when the heating time per load is divided into three heating times of 3 seconds, 10 seconds, and 60 seconds for the same lead-free solder, and the temperature The relationship between the lead-free solder joint strength after loading for the number of cycles is shown.

  In addition, the square mark in FIG. 12 means data when the heating time per time is 3 seconds. The substantially round mark in FIG. 12 means data when the heating time per time is 10 seconds. The substantially triangular mark in FIG. 12 means data when the heating time per time is 60 seconds.

  As shown in FIG. 12, when the heating time per time for lead-free solder in the same state is 60 seconds, the bonding strength is compared with the case where the heating time per time is 3 seconds and 10 seconds, It is extremely small.

  In addition, as the number of temperature cycles loaded on the lead-free solder increases, the bonding strength of the lead-free solder significantly decreases when the heating time is 60 seconds.

  Therefore, the inventor of the present invention has a feature of the metal structure of lead-free solder when the heating time per one time is 60 seconds, for example, the spheroidization rate of tin crystals contained in the lead-free solder, or the crystal grains per one It is considered that the average area and the like can be set as the organization parameter. In addition, when the heating time is 60 seconds, the Cu land and the substrate inside the substrate are damaged, and this damage also causes a decrease in the bonding of lead-free solder.

  In this case, as a method for the structure parameter setting unit and the bonding strength determining unit 7 to calculate the average area of the crystal grains, for example, the method may be calculated according to the following procedures (1) to (6).

(1) An arbitrary number of crystal grains are extracted as sample from the image data.

(2) Extract a high density portion from the extracted crystal grain image.

(3) Draw a boundary line that forms the outer frame of the crystal grain.

(4) Count the number of pixels contained in the area inside the outer frame.

(5) The area of each crystal grain is calculated by multiplying the number of pixels by the area per pixel. (6) The average area is calculated by calculating the arithmetic average of the calculated area of each crystal grain.

  In the above method, an arbitrary crystal grain is extracted as a sample. However, the present invention is not limited to this, and an arithmetic average, a geometric average, or a harmonic average of the areas of all crystal grains may be calculated.

  FIG. 13 is a diagram illustrating an example of the relationship between the heating time and the average value of bonding strength.

  In addition, the numerical value of the vertical axis | shaft in FIG. 13 shows what expressed the arithmetic mean value of the joint strength of the lead-free solder 14 and the land 13 in Newton unit, and the numerical value of a horizontal axis | shaft shows the value of heating time in second unit The one represented by

  In addition, as shown in FIG. 13, by calculating the relationship of the linear expression that is approximately established between the average value of the bonding strength and the heating time, the life equation that is established between the bonding strength and the heating time is obtained. You may ask for it.

  As a result of calculation based on the data obtained by the inventor's verification experiment, when the heating time is X and the average value of the bonding strength is Y, an approximate expression of Y = −0.3689X + 59.977 was gotten.

  In this case, as numerical data to be stored in the tissue parameter database 6, a set of an average value of bonding strength and a heating time is used.

  In step ST4, the imaging unit 2 observes the metal structure of the surface of the lead-free solder whose bonding strength is to be determined.

  In step ST5, the bonding strength determination unit 7 reads out the tissue parameter that is numerical data for detecting substantially elliptical tin stored in advance in the tissue parameter database 6 using the observation condition as a key, A determination process for determining whether or not the bonding strength of the lead-free solder has decreased is performed by comparing the structural parameters calculated from the image of the surface of the lead-free solder whose bonding strength is to be determined.

  In step ST6, the output unit 8 outputs the determination result output from the bonding strength determination unit 7 to the outside.

  As the output unit 8, for example, a device that visually outputs a determination result, such as a printer or a CRT, or a device that outputs a determination result by sound such as a speaker may be used.

<Verification experiment of tissue parameters>
Next, the present inventor, in order to verify the relationship between the set structure parameters and the lead-free solder metal structure in the lead-free solder joint strength determination method as described above, for the lead-free solder metal structure, The following verification experiment was conducted.

  The verification experiment performed by the present inventor is to load a lead-free solder metal structure up to 1000 cycles with a temperature cycle in which the temperature is changed from -40 degrees to 125 degrees per cycle for 30 minutes.

  In this verification test, whether or not the metal structure was changed was determined based on the change in the grain boundary of tin contained in the lead-free solder.

  That is, in this demonstration experiment, tin crystal grains 20 whose crystal grain boundaries were not clear in the initial state as shown in FIG. 14 were changed to crystal grains 21 with clear crystal grain boundaries as shown in FIG. It is determined that the metal structure has changed.

  In the metal structure shown in FIG. 14, there is no particular problem with the bonding strength of the lead-free solder, but when the metal structure changes to that shown in FIG. 15, the bonding strength of the lead-free solder is lowered.

  FIG. 16 is a diagram showing an example of the relationship between the number of solder joints and the number of temperature cycle loads until the metal structure changes in a verification experiment conducted by the present inventor.

  In FIG. 16, the data shown on the leftmost side shows the number of solder cycles, in other words, the number of temperature cycles required for the metal structure to change to lead-free solder with one solder joint, The data shows the number of solder cycles, in other words, the number of temperature cycles required for the metal structure to change to lead-free solder with two solder joints. In other words, it shows the number of temperature cycles required until the metal structure is changed to lead-free solder having three solder joints.

  According to the experiment of the present inventor, when the above-described temperature cycle was loaded on the lead-free solder having the first solder joint number, as shown in FIG. 16, the change in the metal structure was performed at a load number of 600 cycles or more and 900 cycles or less. As a result, the joint strength between the lead-free solder and the land on the printed circuit board was significantly reduced.

  Further, when the above-described temperature cycle was loaded on the lead-free solder at the second solder joint, as shown in FIG. 16, the metal structure was changed at a load number of 450 cycles or more and 600 cycles or less. The joint strength with the upper land was significantly reduced.

  Furthermore, when the above-mentioned temperature cycle was loaded on the lead-free solder at the third solder joint, as shown in FIG. 16, the metal structure was changed with the load number of 200 cycles or more and 300 cycles or less. There was a significant decrease in the strength of the bond with the upper land.

  From the results of the above verification experiment, the present inventor has come to believe that the strength index set as the structure parameter can be used as an index value that appropriately indicates that the joint strength of the lead-free solder is not reduced.

  In addition, since the joint strength of lead-free solder with only one solder joint was higher than the joint strength of lead-free solder with the second solder joint, the structural parameter should be considered to indicate the life of the lead-free solder. Is also possible.

  As described above, according to the present embodiment, as a result of observation of the metal structure of the lead-free solder whose bonding strength is to be determined, the obtained structure parameter is compared with the structure parameter stored in the structure parameter database 6. Whether or not the bonding strength of the lead-free solder has been reduced is determined by the bonding strength determination unit 7 and the result of the determination is output by the output unit 8, without the need for advanced specialized knowledge and skill, You can easily know the bonding strength of lead-free solder.

  According to the present embodiment, the structure parameter can be set as an index value for determining the bonding strength of lead-free solder.

  According to the present embodiment, as lead-free solder, lead-free solder containing 3 Wt percent silver and 0.5 Wt percent copper and tin, or 3.5 Wt percent silver, 0.7 Wt percent copper and tin When the lead-free solder is used, the bonding strength of the lead-free solder can be determined based on the structure parameter, so that a product having a lead-free solder with high reliability can be provided to the manufacturing department and the market.

  According to the present embodiment, it is possible to select an appropriate soldering condition without requiring highly specialized knowledge and skill.

  Note that the methods described in the above embodiments are magnetic disks (flexible disks, hard disks, etc.), optical disks (CD-ROM, DVD, etc.), magneto-optical disks (MO), semiconductors as programs that can be executed by a computer. It can be stored in a storage medium such as a memory and distributed.

  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.

  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.

  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 or the Internet is downloaded and stored or temporarily stored.

  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.

  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.

  In addition, the computer in the present invention is not limited to a personal computer, but includes a processing unit, 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. .

  It should be noted that a program that realizes the technique described in each of the above embodiments can be provided by transmitting via a communication network, for example, the Internet, an intranet, or an Ethernet.

  As a program providing method via this communication network, for example, an ASP (Application Service Provider) method is included.

  The program is written in any programming language such as C (registered trademark), C ++ (registered trademark), or JAVA (registered trademark) as long as it realizes the above functions. It may be.

  The present invention also includes a data structure, a machining program, and various hardware on which the machining program functions, which are indispensable for configuring a program that implements the functions described above.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying constituent elements without departing from the scope of the invention in the implementation stage. Various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the above embodiments. For example, some components may be deleted from all the components shown in the embodiment.

The functional block diagram which shows the structural example of the lead-free solder joint strength determination apparatus 1 to which the joint strength determination method of the lead-free solder which concerns on one embodiment of this invention is applied. A lead-free solder 14 that joins a chip resistor 11 and a land 13 provided on a printed circuit board 12, which is one of objects to which a lead-free solder joining strength determination method according to an embodiment of the present invention is applied. Plan view. A lead-free solder 14 that joins a chip resistor 11 and a land 13 provided on a printed circuit board 12, which is one of objects to which a lead-free solder joining strength determination method according to an embodiment of the present invention is applied. Side view. The flowchart for demonstrating an example of the joining strength determination method of the lead-free solder which concerns on this Embodiment. An example of image data obtained as an imaging result of the metal structure of the lead-free solder at the first mounting on the printed circuit board according to the present embodiment is shown. The schematic diagram of the image data obtained as an imaging result of the metal structure of the lead-free solder shown in FIG. An example of image data obtained as a result of imaging of lead-free solder at the second mounting on the printed circuit board according to the present embodiment is shown. The schematic diagram of the image data obtained as an imaging result of the metal structure of the lead-free solder shown in FIG. An example of image data obtained as a result of imaging of a joint boundary surface of lead-free solder in the case of solder joining in a time of 3 seconds or less at the first mounting on the printed circuit board according to the present embodiment is shown. An example of image data obtained as a result of imaging the joint boundary surface of lead-free solder when soldered for 3 to 10 seconds at the first mounting on the printed circuit board according to the present embodiment Show. An example of image data obtained as a result of imaging of the joint boundary surface of lead-free solder when soldered for 10 seconds to 60 seconds at the first mounting on the printed circuit board according to the present embodiment Show. The figure which shows an example of the relationship between joining strength and the number of temperature cycles to load. The figure which shows an example of the relationship between heating time and the average value of joining strength. The image which shows an example of the initial state of the crystal grain of the tin contained in the metal structure in the demonstration experiment which this inventor conducted. The image which shows an example of the state after the change of the crystal grain of the tin contained in the metal structure in the demonstration experiment which this inventor conducted. The figure which shows an example of the relationship between the frequency | count of the load of the temperature cycle until the number of times of joining of solder in the verification experiment which this inventor implemented, and metal structure changes.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Lead-free solder joint strength determination apparatus, 2 ... Imaging unit, 3 ... Command input unit, 4 ... Image input switching unit, 5 ... Tissue parameter setting unit, 6 ... Tissue parameter database, 7 ... Bond strength determination unit, 8 ... Output section

Claims (5)

Based on the change in the metal structure of the lead-free solder, the lead-free solder joint strength determination method for determining the lead-free solder joint strength,
A metal structure observation step of observing the metal structure of the surface of the lead-free solder;
A structure parameter comparison step for comparing the observation result obtained by the metal structure observation step and a structure parameter indicating that the bonding strength of the lead-free solder is not reduced,
The texture parameter is a ratio of the length in the major axis direction to the length in the minor axis direction of the crystal grains of tin contained in the lead-free solder when the number of heating times is one time.
The structure parameter indicating that the joint strength of the lead-free solder is not reduced refers to the structure parameter when the ratio is twice,
The structure parameter comparison step is a method for determining the bonding strength of lead-free solder that determines whether the structure parameter of the observation result is twice or more. Based on the change in the metal structure of the lead-free solder, the lead-free solder joint strength determination method for determining the lead-free solder joint strength,
A metal structure observation step of observing the metal structure of the surface of the lead-free solder;
A structure parameter comparison step for comparing the observation result obtained by the metal structure observation step and a structure parameter indicating that the bonding strength of the lead-free solder is not reduced,
The texture parameter is a ratio of the length in the major axis direction to the length in the minor axis direction of the crystal grains of tin contained in the lead-free solder when the number of heating times is two times.
The structure parameter indicating that the joint strength of the lead-free solder is not reduced refers to the structure parameter when the ratio is twice,
The structure parameter comparison step is a method for determining the bonding strength of lead-free solder that determines whether the structure parameter of the observation result is twice or less. In the method for determining the bonding strength of lead-free solder according to claim 1 or claim 2,
The lead-free solder is
A method for determining the bonding strength of lead-free solder containing at least tin and silver. Based on the change in the metal structure of the surface of the lead-free solder, the lead-free solder joint strength determination device for determining the joint strength of the lead-free solder,
Observation means for observing the surface of the lead-free solder;
The ratio of the length in the major axis direction and the length in the minor axis direction of the crystal grains of tin contained in the lead-free solder in the case where the number of times of heating is one is used as a structural parameter, and from the result of observation by the observation means, the lead-free solder A tissue parameter setting means for setting the tissue parameter indicating that the bonding strength of the material is not reduced to 2 times,
Organization parameter storage means storing organization parameters set by the organization parameter setting means;
Based on the observation result of the metal structure of the lead-free solder whose bonding strength is to be determined, the obtained structure parameter is compared with the structure parameter stored in the structure parameter storage means, and the obtained structure parameter is doubled. If it is above, the bonding strength determination means for determining that the bonding strength of the lead-free solder is not reduced,
A lead-free solder joint strength judging device comprising: output means for outputting a judgment result by the joint strength judging means. Based on the change in the metal structure of the surface of the lead-free solder, the lead-free solder joint strength determination device for determining the joint strength of the lead-free solder,
Observation means for observing the surface of the lead-free solder;
The ratio of the length in the major axis direction and the length in the minor axis direction of the crystal grains of tin contained in the lead-free solder in the case where the number of times of heating is two is used as a structural parameter, and from the result of observation by the observation means, the lead-free solder A tissue parameter setting means for setting the tissue parameter indicating that the bonding strength of the material is not reduced to 2 times,
Organization parameter storage means storing organization parameters set by the organization parameter setting means;
Based on the observation result of the metal structure of the lead-free solder whose bonding strength is to be determined, the obtained structure parameter is compared with the structure parameter stored in the structure parameter storage means, and the obtained structure parameter is doubled. If it is below, the bonding strength determination means for determining that the bonding strength of the lead-free solder has not decreased,
A lead-free solder joint strength judging device comprising: output means for outputting a judgment result by the joint strength judging means.

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