JP2007255925A - Joint evaluation method and joint evaluation device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To precisely perform the reliable judgment of accelerated life with respect to a solder joint part by a simple method. <P>SOLUTION: The joint evaluation device is equipped with a cooling part 12 and a heating part 13 both of which repeatedly perform heating and cooling with respect to a solder joint part 8, a measuring circuit part 11 and a measuring part 22 both of which measure the resistance value of the solder joint part 8 at a predetermined cycle during hot supply, an arithmetic part 23 for calculating a resistance change ratio and the change speed of the resistance change ratio from the resistance value at each time when the resistance value is measured, a judge part 24 for judging whether the resistance value reaches an inflection point, where the lowering of the change speed of the resistance change ratio is started, from the calculated change speed of the resistance change ratio, an evaluation part 25 for starting the evaluation related to the reliability of the solder joint part 8 by comparing the resistance change ratio with a preset reference threshold value and an information part 3 for reporting that the resistance change ratio exceeds the preset reference threshold value. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a bonding evaluation method and apparatus related to reliability due to thermal fatigue or the like of a solder joint soldered to a solder ball or solder bump for mounting an electric element or the like on a printed circuit board or the like.

  Conventionally, various methods have been proposed as methods for evaluating the lifetime of a bonding material such as solder used for a bonding portion for mounting a circuit element such as a semiconductor IC chip on a wiring board. In general, an accelerated life evaluation test using a temperature cycle test in which heating and cooling are alternately applied to a solder joint is employed, and an electrical resistance method is known as a method for determining when a solder crack occurs and breaks. . However, this method has a problem that the product development period becomes long because the test period takes several months. Patent Document 1 discloses a bonding material in which a resistance value between a pair of solder joints is repeatedly measured by a four-terminal method during the temperature cycle test, and a thermal fatigue degree can be continuously observed from a change in the resistance value. A method for measuring thermal fatigue is described.

Further, as another method for predicting the life of the solder joint, thermal stress obtained from two-dimensional elasto-plastic analysis of the finite element method as described in the following Patent Documents 2 to 6 and Non-Patent Documents 1 and 2. Using the crack growth rate equation obtained from the plastic strain caused by the crack and the crack growth rate obtained from observation of the solder joint, using the relational equation between the life cycle number and strain amplitude and thermal stress simulation Have been proposed that utilize changes in the surface roughness of solder joints.
JP 61-138153 A JP 2005-148016 A JP 2000-46905 A JP 2004-45343 A Japanese Patent Laid-Open No. 3-128431 JP 2002-310888 A "Evaluation of crack propagation behavior of solder bump connection", Japan Society of Mechanical Engineers, Proceedings A, published in March 2001 "Evaluation of thermal fatigue crack initiation by phase growth in Sn-3.0Ag-0.5Cu solder joints" published by Japan Institute of Electronics Packaging, September 2004

  However, in the methods described in the above-mentioned documents, it is difficult to accurately predict the bonding life, and verification is required for practical use. Further, it is necessary to construct a necessary database by conducting a test in advance, and further, complicated calculation by computer simulation is required. Moreover, since there are many analysis steps, there exists a problem that it can utilize only for the use limited for the labor.

  The present invention solves the above-mentioned conventional problems, and by evaluating the reliability after exceeding the inflection point, it becomes possible to evaluate the reliability more efficiently and with high accuracy. It is an object of the present invention to provide a bonding evaluation method and apparatus capable of accurately performing reliability evaluation of accelerated life for a soldered portion by a simple method.

  The joint evaluation apparatus of the present invention includes a heat supply unit that repeatedly heats and cools a solder joint, and a resistance value measurement unit that measures an electrical resistance value of the solder joint during heat supply in a predetermined cycle. And a calculating means for calculating a resistance change rate and a change rate of the resistance change rate from the resistance value obtained each time the resistance value is measured, and a change in the resistance change rate from the calculated change rate of the resistance change rate. Judgment means for judging whether or not the inflection point at which the speed starts to decrease has been reached, and after reaching the inflection point, the resistance change rate is compared with a preset reference threshold value to compare the solder. It is characterized by comprising evaluation means for starting an evaluation relating to the reliability of the joint portion, and a notifying portion for notifying that when the resistance change rate exceeds a preset reference threshold value.

  Further, in the bonding evaluation method of the present invention, heating and cooling are repeatedly performed on the solder joint by the heat supply unit, and the electrical resistance value of the solder joint during heat supply is determined by the resistance value measurement unit at a predetermined cycle. The resistance change rate and the change rate of the resistance change rate are calculated from the resistance value obtained each time the resistance value is measured, and the change rate of the resistance change rate is calculated from the calculated change rate of the resistance change rate. Whether or not an inflection point at which a decrease starts has been reached, and after reaching the inflection point, the resistance change rate is compared with a preset reference threshold value to determine the reliability of the solder joint. The evaluation regarding the property is started, and when the resistance change rate exceeds a preset reference threshold value, a notification to that effect is given.

  According to these configurations, the solder joint is repeatedly exposed to the heating atmosphere and the cooling atmosphere, and during this time, the electrical resistance value of the solder joint is measured at a predetermined period. The resistance change rate and the rate of change of the resistance change rate are calculated from the resistance value measured periodically, and whether or not the inflection point at which the rate of change of the resistance change rate starts decreasing after the start of the test is determined. Judgment is made. If the inflection point has been reached, the resistance change rate is compared with a preset reference threshold value to start evaluation regarding the reliability of the solder joint. Therefore, the evaluation process is not performed until the inflection point is exceeded, and erroneous determination is eliminated. Then, after the inflection point is exceeded, by evaluating the reliability, it is possible to evaluate more efficiently and with high accuracy. That is, in order to obtain the reliability evaluation result earlier, it is preferable that the reference threshold value is lower. However, when the reference threshold is low, there is a possibility that the resistance change rate exceeds the reference threshold and an erroneous evaluation result is obtained before the inflection point appears from the start of the test. Therefore, the evaluation judgment is made after the inflection point is exceeded in consideration of the thermal fatigue characteristics of the solder joint that is repeatedly exposed to the heating atmosphere and the cooling atmosphere. Thereby, although it is a simple method, the reliability evaluation of the accelerated life with respect to a solder joint part is performed accurately.

  The resistance value measurement unit preferably shortens the measurement cycle after reaching an inflection point at which the rate of change in the resistance change rate starts to decrease. According to this configuration, since the measurement cycle is shortened after the inflection point is generated in the resistance change rate and the measurement frequency is increased, the evaluation can be performed earlier.

  Further, the present invention is characterized in that an oscillating portion for applying vibration to the solder joint portion is provided after the inflection point at which the rate of change of the resistance change rate starts to decrease. According to this configuration, after the inflection point is exceeded, there is a high possibility that cracks are present in the solder joints. Therefore, by applying an operation to promote the cracks by applying vibration. Reliability evaluation can be accelerated.

  In addition, the notification unit performs a notification regarding the life when the resistance change rate exceeds a preset reference threshold value. According to this configuration, in consideration of the fact that the rate of change in resistance and the residual strength are correlated, the evaluation of the reliability of the solder joint is determined to be a life based on whether the rate of change in resistance exceeds a reference threshold. The

  The reference threshold value is preferably a value corresponding to 10% or a residual intensity of 50%. According to this configuration, the reference threshold value is set with 10% or the remaining strength of 50% as a guideline, so that a test in accordance with the actual situation is possible.

  Moreover, the counter which counts the repetition frequency of the said heating and cooling is provided, and the said alerting | reporting part alert | reports the said count value at the time of alerting | reporting of the said evaluation result. According to this configuration, information on the time from the start of the test to the lifetime can be obtained.

  According to the first and seventh aspects of the invention, it is possible to evaluate the reliability more efficiently and with high accuracy by evaluating the reliability after exceeding the inflection point. And although it is a simple method, the reliability evaluation of the accelerated lifetime with respect to a solder joint part can be performed accurately.

  According to the second and eighth aspects of the present invention, it is possible to perform the evaluation earlier because the measurement cycle is shortened and the measurement frequency is increased after the inflection point is generated in the resistance change rate.

  According to the third and ninth aspects of the present invention, after the inflection point is exceeded, there is a high possibility that cracks are present in the solder joints, so vibration is applied to promote the cracks. The reliability evaluation can be further accelerated by performing the operation.

  According to the fourth and tenth aspects of the present invention, in consideration of the fact that the rate of change in resistance and the residual strength are correlated, the evaluation regarding the reliability of the solder joint portion is performed, whether the rate of change in resistance exceeds a reference threshold value. Therefore, it is possible to determine the life and accurate life evaluation is possible.

  According to the fifth and eleventh aspects of the present invention, the reference threshold value is set based on 10% or the remaining strength of 50%, so that a test in accordance with the actual situation is possible.

  According to invention of Claim 6, 12, the information regarding the time from the test start to the lifetime can be obtained.

  FIG. 1 is a block diagram showing an embodiment of a bonding evaluation apparatus according to the present invention. The apparatus includes a test tank 1, a control unit 2, a notification unit 3, an input operation unit 4, and a memory unit 5. The test tank 1 can employ a known environmental tester. The test tank 1 includes a measurement circuit unit 11 for measuring an electrical voltage value (substantially resistance value) with respect to the test object shown in FIG. Is cooled to -40 ° C., for example, using the Peltier effect, the cooling unit 12 for supplying cold heat, and the test object is heated to a predetermined high temperature, here 125 ° C. A heating unit 13 that uses a heater to supply high heat and a vibration unit 14 that applies predetermined vibrations, here, periodic minute vibrations, to the test object are provided.

  FIG. 2 is a side sectional view showing an example of a test object. FIG. 2 (a) shows a state at the start of the test, and FIG. 2 (b) shows that a crack 81 has developed in the solder joint 8 during the test. It shows the state. In FIG. 2A, the test object is placed on a test table (not shown). The test object includes a printed circuit board 6, an electric element 7 such as a semiconductor IC chip, and a solder joint 8. A metal land 61 having a required thickness is formed on the upper surface of the printed circuit board 6, and an electrode 71 formed on the electric element 7 is mounted thereon via a solder joint 8.

  The measurement circuit unit 11 employs a known four-terminal method in order to increase measurement accuracy. Although not shown in the figure, a contact terminal that supplies a predetermined level of current to the land 61 and the electrode 71 and a contact terminal that measures the voltage between the land 61 and the electrode 71 are in contact with or connected to each other. ing. Each contact terminal is led out of the test chamber 1 through an electrical lead wire.

  The heating unit 13 has a configuration in which, for example, a heater is brought into direct contact with the electric element 7 or the electrode 71, and the electric element 7 or the electrode 71 is heated by supplying electric power to the heater. Thermal stress is generated in the solder joint portion 8 in the same manner as in reality due to the difference in coefficient of thermal expansion between the electrode 71 and the land 61 or the printed circuit board 6 and the temperature difference in the time direction between the electrode 71 and the land 61 during heating. To be able to.

  The control unit 2 adjusts the test environment such as cooling, heating, and vibration operation, passes the current between the contact terminals for supplying current at a predetermined cycle, and sets the voltage between the contact terminals for voltage measurement. The resistance value between the land 61 and the electrode 71 is calculated from the voltage value detected every time the voltage value is detected by the measurement unit 22 to be detected, and the resistance value change rate (%) and the resistance change rate. A calculation unit 23 for calculating the change rate of the resistance, and a determination unit 24 for determining whether or not the calculated rate of change in the resistance change rate has reached an inflection point at which the rate of change in the resistance change rate starts decreasing after the test starts. And an evaluation unit 25 that evaluates reliability (for example, life) of the solder joint 8 due to thermal fatigue of the solder joint 8 and a counter 26 that counts the number of temperature cycles from the start of the test.

  The notification unit 3 is a speaker, a buzzer, a monitor, or a lighting lamp that outputs an evaluation result or the like by the evaluation unit 25 in a voice or visually recognizable manner. It is notified by voice on the speaker and by character information or graphs on the monitor. The input operation unit 4 includes, for example, a numeric keypad, and is used to input various test conditions such as a resistance change rate (R) as a reference threshold described later and a heating cycle. The memory unit 5 includes a ROM for storing test operation programs and necessary arithmetic expressions, and a RAM for temporarily storing measurement results and calculation results.

  The computing unit 23 calculates the rate of change of the resistance change rate from the detection period and the detected resistance value or the calculated resistance change rate, in addition to calculating the above-described change rate (%) of the resistance value.

  The environment control unit 21 is a command for alternately switching the operation of heating the electric element 7 to 125 ° C. by the heating unit 13 in the test chamber 1 in a cooling environment of −40 ° C. at a predetermined cycle, here 15-minute cycle. Is output to the cooling unit 12 and the heating unit 13.

Further, when the determination unit 24 determines that the inflection point has been reached, the environment control unit 21 can output a vibration command to the vibration unit 14 thereafter. When the determination unit 24 determines that the inflection point has been reached, the measurement unit 22 shortens the voltage detection cycle compared to the previous cycle, for example, a cycle of 1 second or less, preferably μ (micro). It can be changed to the order of seconds.
Here, the evaluation principle of the present invention will be described. FIG. 3 is a characteristic diagram showing the relationship between the number of cycles and the resistance change rate in the temperature cycle test of the solder joint 8. The test is started, that is, the temperature cycle test is started, and the resistance change rate is calculated at a predetermined period, for example, every 30 minutes (or every 15 minutes) which is the same as the temperature cycle, and the result is plotted.

  The test period is divided into regions A, B, and C depending on the change in resistance value. Under this test condition, the region A is up to about 900 times in the temperature cycle, the region B is around 900 to 2400 times in the temperature cycle, and the region C is thereafter. Each region depends on the shape, material, and test conditions of the solder joint 8 (particularly, the cooling temperature, the heating temperature, its cycle, etc.).

  In the region A, it is considered that the initial stage of crack generation, and it can be seen that the resistance value rapidly increases. The change in the resistance value indicates that the solder joint portion 8 is subjected to thermal fatigue and cracks, thereby increasing the resistance value and reducing the strength (residual strength) of the joint portion itself. I can say that. In the subsequent region B, it can be seen that the increase in resistance value is stable. Finally, it can be seen that in region C, the resistance value suddenly increases and the solder joint 8 is broken. In the vicinity of the boundary between the region A and the region B, the inflection point appears. As shown in FIG. 3, the inflection point is a state in which the rate of change in the resistance change rate (corresponding to the slope of the characteristic line indicating the resistance change rate in FIG. 3) is stable from a certain level (small) after the start of the test. This is the point in time when switching to (status).

  And the quality evaluation with respect to the solder joint part 8 is performed by whether the change rate of resistance change rate exceeds a predetermined magnitude | size. In the example of FIG. 3, the rate of change of the resistance change rate in the region B exceeds a predetermined magnitude. As a result, the rate of change in resistance suddenly increases in the middle of the region C, that is, a crack is generated. Has broken (life reached). Here, by setting 7.5% as the reference threshold (R), reliability (life) evaluation can be performed in a short period, that is, in the region B. That is, in order to obtain the reliability evaluation result earlier, it is preferable that the reference threshold value (R) is low. However, when the reference threshold value (R) is low, there is a possibility that the rate of change in resistance exceeds the reference threshold value before the inflection point appears from the start of the test, that is, in the region A, and an erroneous evaluation result is output. It is done. Therefore, considering the thermal fatigue characteristics of the solder joint 8 that is repeatedly exposed to the heating atmosphere and the cooling atmosphere, the life evaluation is judged after exceeding the inflection point.

  In this way, by evaluating the reliability after exceeding the inflection point, it is possible to evaluate more efficiently and with high accuracy. Thereby, although it is a simple method, it becomes possible to accurately evaluate the reliability of the accelerated life for the solder joint.

  4A and 4B are diagrams showing experimental results of eutectic solder, and FIG. 4B is a diagram showing experimental results of lead-free solder, for solder joints 8 having the same size chip resistance. This is for comparing the characteristics of the two. The horizontal axis is the number of temperature cycles, and the vertical axis is the resistance change rate and the residual strength. The residual strength is obtained by performing a strength test on the solder joint 8. Furthermore, the degree of progress of cracks by cross-sectional observation (see, for example, FIG. 2B) may be included in consideration.

  In FIG. 4, in the case of eutectic solder and lead-free solder, when the temperature cycle test is started, the same tendency as the basic characteristics seen in the regions A and B shown in FIG. 3 appears. 4 (a) and 4 (b), characteristic lines A1 and B1 are examples with the highest resistance change rate, characteristic lines A2 and B2 are examples with the lowest resistance change rate, and lines A0 and B0 show their averages. . Looking at the characteristic lines A1, A2, B1, and B2, in any case, an inflection point occurs around 1000 temperature cycles.

  In the characteristic line A1 in FIG. 4 (a), the rate of change in resistance is large at the initial stage of crack generation, and the rate of change in the high rate of resistance change is slightly lower than the region A after the inflection point. It can be seen that the resistance value increases. And the fracture | rupture has arisen about 1600 times of temperature cycles. In the characteristic line A2 of FIG. 4A, the increase in the resistance change rate is small at the initial stage of crack generation, and the resistance value increases at a slightly lower rate of change in the resistance change rate than the region A after the inflection point. I understand. And the rate of change of a higher resistance change rate is shown around 2500 temperature cycles. In line A0, an inflection point appears after the resistance change rate continues to increase at the initial stage of crack generation, and thereafter the resistance value increases at a slightly lower rate of change in resistance change rate than region A. . And the fracture | rupture has arisen about 1600 times of temperature cycles. It can be seen that the residual strength of the solder joint 8 is 50% or less when the rate of change in resistance is 10% (up).

  In the characteristic line B1 in FIG. 4B, the resistance change rate increases greatly at the initial stage of crack generation, and after the inflection point, although slightly lower than the region A, the resistance change rate is relatively high. It can be seen that the resistance value increases at the rate of change. And the rate of change of a higher resistance change rate is shown around 2500 temperature cycles. In the characteristic line B2 of FIG. 4B, the increase in the resistance change rate is slightly smaller than that in the characteristic line B1 at the initial stage of crack generation, and the resistance value at a lower rate of change in the resistance change rate than the region A after the inflection point. It can be seen that there is a slight increase. The resistance change rate does not exceed 10% within the test temperature cycle. In line B0, an inflection point appears after the resistance change rate continues to increase in the initial stage of crack generation, and thereafter the resistance value increases at a lower rate of change in resistance change rate than that of region A. The resistance change rate exceeds 10% per 2000 temperature cycles. It can be seen that the residual strength of the solder joint 8 is 50% or less when the rate of change in resistance is 10% (up).

  Here, when the resistance change rate of 5% is set as a criterion for determining reliability (life), the difference is 1.09 times as seen from the lines A0 and B0, and no significant difference is observed. . On the other hand, when a resistance change rate of 10% is set as a criterion for determining reliability (life), as described above, the residual strength is 50% or less, and as can be seen from the lines A0 and B0, The difference is 1.24 (2025/1636) times, and a significant difference is seen.

  4 (a) and 4 (b), the point of entry into the region C correlates with the rate of change in the resistance change rate in the region B, and this phenomenon is confirmed in other types of test objects. is made of. From this, by observing the speed change of the resistance value change rate in the region B, it is relatively faster to predict the lifetime, that is, without waiting for the steep rise in the resistance value change rate occurring in the region C. Can be done.

  FIG. 5 is a flowchart for executing the joint evaluation method according to the present invention. First, prior to the test, the resistance change rate (R) that is to be used as a reliability criterion is taken into the memory unit 5 as a reference threshold value through the operation of the input operation unit 4 (step S1). Then, the test is started (step S3). That is, by controlling the driving of the cooling unit 12 and the heating unit 13, the temperature change between −40 ° C. and 125 ° C. is repeated at a cycle of 15 minutes. This period is counted by the counter 26. Further, the operation of detecting the voltage value between the land 61 and the electrode 71 by the four-terminal method is also started by the measuring unit 22. In particular, by using the four-terminal method, even a minute voltage can be measured with high accuracy.

  Next, the voltage value detected by the measurement unit 22 is converted into a resistance change rate (r) (%) from the resistance value obtained by using the supply current value and the first resistance value obtained by the calculation unit 23. Then, the rate of change in resistance change rate (dr / dt) is calculated and stored in the memory unit 5 (step S7). The rate of change in resistance change rate (dr / dt) indicates the slope of the characteristic line in FIGS.

  Subsequently, the change in the change rate of the resistance change rate in the temporal direction is monitored to determine whether or not the inflection point has been exceeded (step S9). Whether the change rate of the rate of change of resistance in the direction of time is monitored is whether the difference between the rate of change of the previous rate of change of resistance and the rate of change of the rate of change of resistance obtained this time has decreased, or has been reduced by a predetermined value. Judgment is based on no. Instead of the change rate of the previous resistance change rate, an average value for the previous two times or a predetermined number of times may be adopted, and unnecessary fluctuation elements may be removed. In addition, the determination of whether or not the threshold value has become smaller is not limited to a single determination. When it is determined that the predetermined threshold value is continuously small, it is determined that the inflection point has been reached, and thus an erroneous determination is made. May be prevented. If the inflection point is not exceeded, the process returns to step S3, and the latest rate of change in resistance change is calculated (step S7).

  When the inflection point is exceeded, a command is issued from the environment control unit 21 to activate the vibration unit 14 (step S11), and at the same time, the detection cycle of the voltage value between the land 61 and the electrode 71 is shortened. The instruction | indication to perform is output to the measurement part 22 (step S13). Then, it is determined whether or not the resistance change rate exceeds the reference resistance change rate (R) within a predetermined number of temperature cycles from the newly obtained change rate of the resistance change rate (step S15). If not exceeded, the process returns to step S3, and if exceeded, a message to the effect that the life has been reached is output from the notification unit 3 (step S17). At this time, as a form of the notification content, in addition to the notification that the life has been reached, the number of temperature cycles counted by the counter 26 may be combined, that is, the life content may be notified. Since the number of temperature cycles for the life is determined in relation to the life of the electronic device or the like to which the electric element 7 mounted on the printed circuit board 6 is applied, it is regarded as the life when making an affirmative determination in step S15. You may make it alert | report the number of temperature cycles to be performed.

In addition, the present invention may adopt the following aspects.
(1) In the present embodiment, the process of step ST11 is adopted. However, it is not always necessary, and in this case, the vibration unit 14 is not necessary, and the configuration is simplified.
(2) In the present embodiment, the process of step ST13 is adopted, but it is not always necessary, and in that case, the burden of software for the measurement operation of the control unit 2 is reduced.
(3) In this embodiment, the four-terminal method is adopted for measuring the voltage between the land 61 and the electrode 71. However, a general two-terminal method may be used, and in this case, the configuration of the measurement circuit unit 11 is simple. It becomes.
(4) The method of giving the temperature cycle is not limited to this embodiment, and various forms can be adopted. As for the heating method, instead of the direct heating method for the sample, a heating method in which the temperature in the tank itself is heated is also conceivable. Similarly, for cooling, either direct or indirect methods are possible.

It is a block diagram which shows one Embodiment in the joining evaluation apparatus which concerns on this invention. FIG. 2A is a side sectional view showing an example of a test object, and FIG. 2A shows a state at the start of the test, and FIG. 2B shows a state in which a crack is developed in the solder joint part during the test. . It is a characteristic view which shows the relationship between the cycle number and resistance change rate in the temperature cycle test of a solder joint part. FIG. 4A is a diagram showing experimental results of eutectic solder, and FIG. 4B is a diagram showing experimental results of lead-free solder for solder joints having the same size chip resistance. Is to do. It is a flowchart which performs the joining evaluation method in this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Test tank 2 Control part 3 Notification part 4 Input operation part 5 Memory part 11 Measurement circuit part (resistance value measurement part)
12 Cooling unit (heat supply unit)
13 Heating unit (heat supply unit)
14 Excitation Unit 21 Environmental Control Unit 22 Measurement Unit (Resistance Measurement Unit)
23 arithmetic unit 24 determination unit (determination means)
25 Evaluation Department (Evaluation Means)
26 Counter 61 Land 71 Electrode 8 Solder joint 81 Crack

Claims (12)

  A heat supply unit that repeatedly heats and cools the solder joint, a resistance value measurement unit that measures an electrical resistance value of the solder joint during heat supply in a predetermined cycle, and a resistance value are measured A calculation means for calculating a resistance change rate and a change rate of the resistance change rate from the resistance value obtained every time, and an inflection in which the change rate of the resistance change rate starts to decrease from the calculated change rate of the resistance change rate A judgment means for judging whether or not a point has been reached, and after reaching the inflection point, the resistance change rate is compared with a preset reference threshold to evaluate the reliability of the solder joint. A joining evaluation apparatus comprising: an evaluation unit that starts; and a notification unit that notifies that when the rate of change in resistance exceeds a preset reference threshold value.   The joint evaluation apparatus according to claim 1, wherein the resistance value measurement unit shortens a measurement cycle after reaching an inflection point at which a change rate of the resistance change rate starts to decrease.   3. The joint evaluation according to claim 1, further comprising a vibration unit that applies vibration to the solder joint after the rate of change of the resistance change rate reaches an inflection point at which a decrease starts. apparatus.   The joint evaluation apparatus according to any one of claims 1 to 3, wherein the notification unit performs a notification regarding a life when the resistance change rate exceeds a preset reference threshold value.   The joint evaluation apparatus according to claim 1, wherein the reference threshold value is a value corresponding to 10% or a residual strength of 50%.   The bonding evaluation apparatus according to claim 1, further comprising a counter that counts the number of repetitions of heating and cooling, wherein the notification unit notifies the count value when the evaluation result is notified.   Heating and cooling are repeatedly performed on the solder joint by the heat supply unit, and the electrical resistance value of the solder joint during heat supply is measured at a predetermined cycle by the resistance value measurement unit, and the resistance value is measured. The resistance change rate and the change rate of the resistance change rate are calculated from the resistance value obtained every time, and the inflection point where the change rate of the resistance change rate starts to decrease from the calculated change rate of the resistance change rate is reached. After reaching the inflection point, the resistance change rate is compared with a preset reference threshold to start evaluation on the reliability of the solder joint, and the resistance change When the rate exceeds a preset reference threshold, a notification to that effect is provided from the notification unit.   The joint evaluation method according to claim 7, wherein the resistance measurement unit shortens the measurement cycle after reaching an inflection point at which the rate of change of the resistance change rate starts to decrease.   The joint evaluation method according to claim 7 or 8, wherein after the inflection point at which the rate of change of the resistance change rate starts to decrease, vibration is applied to the solder joint by a vibration unit.   The joint evaluation method according to any one of claims 7 to 9, wherein when the rate of change of resistance exceeds a preset reference threshold, the notification unit performs notification regarding a life.   The joint evaluation method according to claim 7, wherein the reference threshold value is a value corresponding to 10% or a residual strength of 50%.   The joint evaluation method according to claim 7, wherein the number of repetitions of heating and cooling is counted by a counter, and the notification unit notifies the count value when the evaluation result is notified. .

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