Life predicting method for solder joint, life predicting apparatus for solder joint and electronic device

A life predicting method for a solder joint includes a step of referring to a temperature history of a measurement object having a solder joint, a step of examining at least one physical quantity selected from the group consisting of amplitude, a cycle number, a mean temperature, and a periodic length of a temperature variation with a cycle count method from the temperature history, a step of calculating a strain range by utilizing a previously prepared response surface from the physical quantity examined with the cycle count method, and a step of calculating a strain range increasing rate from a strain range with reference to a previously obtained damage index and a strain variation history of the strain range.

CROSS REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2010-208553, filed on Sep. 16, 2010, the entire contents of which are incorporated herein by reference.

FIELD

Embodiments relate basically to a life predicting method for a solder joint, a life predicting apparatus for a solder joint and an electronic device.

BACKGROUND

There exist various kinds of malfunctions of electronic devices under usage conditions thereof. Above all, a malfunction of a joint portion such as a solder joint is particularly one of troublesome defect phenomena which occur frequently. Once such a malfunction occurs, the malfunction causes a serious influence to device operation. Even a small strain fracturing nothing at one time could accumulate at a solder joint as a result of repetition of various loads, e.g., thermal loads due to power ON/OFF or external mechanical loads, thereby causing metallic fatigue at the solder joint. There is known a structural health monitoring technology of an electronic device to predict a life of the electronic device until the electronic device breaks down because of solder joint trouble due to such a fatigue phenomenon.

In order to accurately predict a metallic fatigue life for solder joints or other parts metals, it is important to accurately estimate an amount of strain occurring at a point to be estimated. However, in most cases, variations in the strain involved in a damage progression such as a crack progression at a solder joint are not estimated in the life prediction of a BGA (Ball Grid Array) solder joint. The variations in the strain amount involved in the crack progression at the solder joint are not taken into consideration for the life prediction of the BGA solder joint. That is, in most cases, a strain estimation is carried out as is for an initial damage progression at a solder joint even for the damage progression subsequent to the initial one, i.e., even after the strain amount becomes large as a result of a decrease in stiffness at the solder joint. Here is a time-consuming job to prepare a damage model (i.e., a model to estimate damage indexes of a solder joint on the basis of a temperature change) and simpler algorithm for implementation. When such a time-consuming job is taken into consideration, a method without involving the time-consuming job may provide a practical prediction even though the life prediction accuracy thereof lowers. However, under normal conditions, strain amplitude accumulated at the solder joint promotes cracks in the solder to decrease stiffness of the solder joint. Therefore, a rate of stress to be received by each solder joint varies in accordance with temperature change. Accordingly, a life of a signal bump at an inner location which is predicted from a dummy bump at an outer location is to cause an error against an actual life unless progression of damage is considered. Here, the error of life is mainly caused by a difference between estimated strain and actual strain of each bump due to stiffness variations.

DESCRIPTION

As will be described below, according to an embodiment, a life predicting method for a solder joint includes a step of referring to a temperature history of a measurement object having a solder joint, a step of examining at least one physical quantity selected from the group consisting of amplitude, a cycle number, a mean temperature, and a periodic length of a temperature variation with a cycle count method from the temperature history, a step of calculating a strain range by utilizing a previously prepared response surface from the physical quantity examined with the cycle count method, and a step of calculating a strain range increasing rate from the strain range with reference to a previously obtained damage index and a strain variation history of the strain range.

According to another embodiment, a life predicting apparatus for a solder joint includes a first memory, a second memory unit, a third memory, a fourth memory, a first control unit, a second control unit, a third control unit, and a fourth control unit. The first memory stores a temperature history of a measurement object having a solder joint. The second memory stores a response surface for obtaining a strain range from at least one physical quantity of amplitude, a cycle number, a mean temperature, and a periodic length of temperature variations. The third memory stores a history of a damage index. The fourth memory stores strain variations for obtaining a strain range increasing rate from a damage index. The first control unit obtains the temperature history with reference to the first memory unit. The second control unit examines at least one physical quantity selected from the group consisting of amplitude, a cycle number, a mean temperature, and a periodic length of temperature variations with a cycle count method from the history information of temperature. The third control unit calculates a strain range from the physical quantity examined with a cycle count with reference to the second memory unit. The fourth control unit calculates the strain range increasing rate from the strain range calculated by the third control unit with reference to the third memory unit and the fourth memory unit.

According to another embodiment, an electronic device includes an electronic component, a mounting board, a first joint, a second joint, and a third joint. The first joint mechanically connects the electronic component and the mounting board and mediates an exchange of an electric signal between the electronic component and the mounting board. The second joint mechanically connects the electronic component and the mounting board and not to mediate the exchange of the electric signal between the electronic component and the mounting board. The third joint formed between the first joint and the second joint mechanically connects the electronic component and the mounting board and monitors a connection state between the electronic component and the mounting board.

First Embodiment

As a first embodiment, a predicting method of a solder life will be explained with reference toFIGS. 1 and 2.

A first control unit (i.e., an update event detection unit)11detects an event of life updating to refer to a second memory unit (i.e., a temperature history database)22for temperature information stored by the time of the updating.

An instruction program to trigger the event of life updating at regular time intervals is stored in firmware stored in a first memory unit (i.e., an update event storage unit)21, and the update event detection unit11executes the program to enable the event of life updating.

A history of previous temperatures is stored in the temperature history database22. The temperature of a board1is measured by a detection unit7and is stored in the temperature history database22.

A second control unit (i.e. a cycle count examination unit)12examines information such as temperature amplitude, a cycle number, a mean temperature and a periodic length with a cycle count method to be mentioned below, with reference to the temperature history database22.

The temperature history database22stores a temperature measured by the detection unit7and time at which the temperature is measured as time-series data.

A third control unit (i.e., a temperature-amplitude/strain-range conversion unit)13converts temperature amplitude ΔT into a strain range Δε on the basis of the information including temperature amplitude, a cycle number, a mean temperature and a periodic length obtained by the cycle count examination unit12with reference to a response surface stored in a third memory unit (i.e., a response surface database)23.

The response surface database23stores the response surface which is a function of amplitude, a cycle number, mean temperature and periodic length of temperature variation and a strain range. The strain range can be obtained from the amplitude, the cycle number, the mean temperature and the periodic length of the temperature variation by utilizing the response surface. The response surface is previously stored in the third memory unit (i.e., the response surface database)23.

A fourth control unit (i.e., a strain-range increasing rate calculation unit)14calculates an increasing rate of a strain range (referred to as strain-range increasing rate below) occurring as a result of a progression of damage accumulated at a solder joint71at the time when an event is currently updated by utilizing the converted strain range Δε with reference to a fourth memory unit (i.e., a damage index database)24and a fifth memory unit (i.e., a strain variation history database)25.

The damage index database24stores a damage index and time at which the damage index is obtained as time-series data. The strain variation history database25stores a function of the damage index and a strain-range increasing rate.

For example, after a damage index D1is obtained at certain time t1from the damage index database24, a strain-range increasing rate α can be obtained from the damage index D1. Then, for example, a new strain range Δε2=α·Δε1can be obtained from the strain range Δε1by utilizing the strain-range increasing rate α.

A fifth control unit (i.e., a strain-range recount unit)15recounts a damage index with considering the strain range increasing rate calculated at S005. Then, the newly obtained damage index is stored in the fourth memory unit (the damage index database)24with the time at which the current event is updated.

In the above example, a damage index D2can be newly obtained from the newly obtained strain range Δε2by utilizing the equation 1 and the equation 2 both to be mentioned later. The newly obtained damage index D2is stored in the damage index database24along with the time t2thereof.

A sixth control unit (i.e., a damage index determination unit)16determines whether or not the new damage index is equal to a specific threshold value or larger with reference to a seventh memory unit (i.e., a threshold value database)27. When the new damage index is equal to the specific threshold value or larger, the damage index determination unit16is allowed to transmit an instruction signal to take a predetermined action.

Examples of the predetermined action include automatically taking backups of data on the assumption that a malfunction is coming, informing a user of a possibility of a malfunction, informing a server managing devices that the devices have little time left to perform, or the like.

The specific threshold value can be appropriately set in accordance with a product type, a product usage or the like. For example, the threshold value may be strictly set for an electric power plant or medical equipment which require high reliability. In contrast, the threshold value may be loosely set for a server of a network system having a backup mechanism in case of failure.

(Operation, Function and Technical Significance)

Here, a mounting board having solder joints is assumed as a product to be a measurement object. The technical significance of the first embodiment will be further explained with reference to a method of predicting a fatigue life of a ball grid array (BGA), the method aiming at thermally-varied loads under actual usage conditions after the product is shipped.

The first embodiment is characterized by predicting the lives of solder joints on the basis of decreases in stiffness due to damage of the respective solder joints.

FIG. 6is a schematic graph showing a damage progression of a solder joint.FIG. 6schematically shows variation of strain ranges caused by the damage progression when a BGA receives a temperature cyclic load for a dummy bump1(A-1), a dummy bump2(B-2) and a signal bump3(C-3) of solder joints shown inFIG. 5. Here, the dummy bump1, the dummy bump2and the signal bump3are included in an area A2surrounded by a dashed-dotted line at the upper right corner of a component4-7shown inFIG. 4. The area A2shown inFIG. 4is a detailed view showing a part of an area A1surrounded by a dashed-dotted line of the component4-7of an electronic device shown inFIG. 3. In this specification, a position of a solder joint is denoted on the basis of A, B, C, . . . from the right to the left and 1, 2, 3, . . . from the top to the bottom with the upper-right dummy bump as an original point inFIG. 5.

In accordance with a progression of temperature cycles ΔT, the strain range of the dummy bump1locating at the outermost expands firstly. Then, the strain range of the dummy bump2expands secondly and the strain range of the signal bump3expands lastly. This phenomenon is caused by decreases in stiffness of solder joints as cracks progress at the solder joints as a result of strain accumulation. Accordingly, the strain variation histories of the dummy bumps are preliminarily examined for calculating strain on the basis of information on temperature variations, thereby allowing it to calculate strain with considering the decreases in stiffness and to accurately predict a life of an electronic device.

FIG. 7is a graph showing an example of strain variation histories of dummy bumps (A-2to E-2) and the signal bump shown inFIG. 4through a finite element method (FEM), i.e., a numerical analysis. InFIG. 4, it is observed that the strain variation becomes larger starting from the outer dummy bump. Accordingly, the result shows a tendency similar toFIG. 6.

On the other hand,FIG. 8is a view showing strain amplitude estimated with a traditional estimation method. The strain amplitude is determined regardless of a fracture and a progression of damage such as cracks at solder joints.

The first embodiment can be embodied on the basis of the above consideration as follows.

First, a database indicating a strain variation history is previously prepared to estimate each solder joint, of which life is to be predicted, for stiffness deceases with a progression of temperature cycle.

Here, a method considering stiffness decreases of solder joints due to damage thereof is applied to a numerical analysis such as FEM, provided that a temperature cycle is repeated as shown inFIG. 9. The method provides a relation as shown inFIG. 6between the temperature cycle number and the strain range Δε. The relation as shown inFIG. 6varies depending on temperature amplitude (i.e., ΔT inFIG. 9), holding time (i.e., ΔT2and ΔT4inFIG. 9) and rise time and fall time (i.e., ΔT1and ΔT3inFIG. 9). Products on the market do not receive the cycle shown inFIG. 9having constant temperature amplitude and constant time but receive a more complicated temperature cycle as shown inFIG. 10. Such a complicated temperature cycle requires a database to allow it to predict a correct strain range with considering the damage at the solder joints.

Then, a relation between the damage index and an increased amount of the strain range at each solder joint to require life prediction is utilized as information to be stored in the database. The damage index D is an index indicating a fatigue degree when applying different amplitude loads. The solder joint reaches the end of its life at the time when D equals to 1, thereby leading to a fracture.FIG. 11is a graph to be utilized for a life predicting method when repeating amplitude in the constant strain range Δε0. Repeating the amplitude in the constant strain range Δε0yields the repetition number N0from starting to the fracture. The number N0is derived from an exponential law (i.e., an exponential law called the Coffin-Manson's law or the Basquin's law particularly for a case of solder). Here, the denotation is as follows.α, β: Constant determined for each materialNf: Crack occurrence cycleN0: Crack occurrence cycle number on the assumption of repletion of strain Δε0N: Cycle number of actually loaded Δε0Δε: Strain rangeD: Damage index after N cycle load

Meanwhile, a life predicting method for two or more kinds of amplitude in different strain ranges (i.e., temperature ranges) is shown inFIG. 1andFIGS. 12 to 14.

The temperature history data (seeFIG. 10) is converted into the temperature amplitude data (i.e., Step S003inFIG. 1) with a method so called “cycle count (also referred to as a cycle count method).” Further, the cycle number and cycle length of a temperature history are simultaneously examined.FIG. 12is a graph showing an example of the temperature amplitude data. There is known a specific method of the CYCLE COUNT, for example, ASTM E 1049-85 “Standard practices for cycle counting in fatigue analysis”, ASTM Standards, Vol. 03.01 (Reapproved 1997), Philadelphia, 1999.

Further, the temperature amplitude data are converted into the strain range to occur at the solder joint with reference to the previously prepared response surface (i.e., Step S004inFIG. 1).FIG. 13shows an example of the data converted into the strain range. Here, the response surface is an expression prepared through a numerical analysis assuming various temperature ranges and being capable of accurately predicting strain to occur at a solder joint. At preparing the response surface, each solder joint is assumed to have constant stiffness regardless of the cycle progression in order to eliminate complications without considering stiffness decreases due to damage progression at the solder joint. A life is derived from a summation D of the reciprocal of each fracture life Nkto be derived from each strain range (see equation 1 and equation 2) in accordance with a linear cumulative damage law (also called a Miner's law) when applying amplitude in different strain ranges Δεk.

FIG. 14is a graph showing relations between the damage index D denoted by the horizontal axis and an increasing rate of the strain range Δε denoted by the vertical axis at the three solder joints (i.e., A-1, A-2and B-1inFIG. 5). Here, the increasing rate of the strain range Δε is an increasing rate of a strain range to occur owing to the application of the temperature amplitude same as that at a damage index of D with respect to an initial strain range Δε0, provided that the initial strain range Δε0is defined as a strain range to occur at a solder joint owing to the application of temperature amplitude in an initial state before a damage progresses at the solder joint. Numerical analyses including FEM can provide the increasing rate of the strain range Δε. A specific analysis is recited in “Damage Path Simulation at Solder Bump Joints,” Japan Society of Mechanical Engineers, Collection of Papers (Volume A), 73-736 (2007-12).

The above relations are previously stored in the strain variation history database25through a numerical analysis and the like, and then, the increasing rate of the strain range Δε due to a damage progression can be obtained by checking the damage index D obtained from the temperature history under the usage conditions for products.FIGS. 15 and 16are block diagrams showing a preparation process of the strain variation history database and an apparatus to prepare the strain variation history database, respectively.

(Preparation Process of Strain Variation History Database)

An eleventh control unit (i.e., a cycle determination unit)31determines a temperature range, temperature holding time, temperature rise time, temperature fall time and the number of temperature cycle repetition.

A twelfth control unit (i.e. a numerical analysis unit)32conducts a numerical analysis with considering a damage progression. Specifically, temperature conditions specified by FEM are set up, and then, a life-ended portion is deleted or stiffness thereof is extremely decreased at the time when the strain range occurring inside solder reaches the cycle number of fatigue life determined by the Coffin-Manson's law or the Basquin's law, thereby simulating cracks and estimating a damage progression. The details are recited in Vol. 73 (736) (2007-12), Collection of Papers (A), Japan Society of Mechanical Engineers.

A thirteenth control unit (i.e. a strain variation history calculation unit)33calculates a strain variation history for each temperature cycle. Further, the strain variation history calculation unit33stores the strain variation history obtained for each temperature cycle in the fifth memory unit (i.e., the strain variation history database)25.

A fourteenth control unit (i.e., a damage index calculation unit)34calculates (i.e., estimates) the damage index D for each temperature cycle with reference to an eleventh memory unit (i.e., a solder fatigue database)26. Further, the damage index calculation unit34stores the increasing rate of the strain range Δε for each temperature cycle and the obtained damage index D corresponding thereto in the fifth memory unit (i.e., the strain variation history database)25.

Alternatively, Step S015may be executed taking an arbitrary opportunity, in real time, at given timing or the like. For example, Step S015may be executed periodically or at the timing of ON or/and OFF of power as the given timing.

Here, the first benefit of using the damage index D in order to obtain an increased amount of the strain range Δε is to obtain the strain range increasing rate Δε with reference only to the damage index without considering a range, holding time and rise and fall time of an applied temperature. That is, the preparation process of strain variation history database is easy to apply to complicated temperature variation under real usage conditions which is not the same as a simple temperature variation like constant temperature amplitude. As the second benefit, there are no large variations in the relation between the damage index D and the increasing rate of the strain range Δε to be caused by the range and holding time etc. of the applied temperature as a result of robustness of the relation.

According to the above benefits, the relation between the damage index and the strain range due to the typical temperature history are previously examined through a numerical analysis, thereby allowing it to obtain the strain-range increasing rate due to a variety of temperature history with ease and relatively high accuracy.

In order to predict the strain-range increasing rate more accurately, it is also possible to utilize a method to store two or more relations ofFIG. 14in the database through a numerical analysis having the temperature range, holding time, rise time and fall time as parameters and to apply a relational expression appropriate for the applied temperature range.

Here, in the first embodiment, a method to calculate a strain range has been described. The method examines the amplitude, cycle number, mean temperature and periodic length of temperature variations from temperature history information by means of the CYCLE COUNT to calculate the strain range on the basis of a response surface previously prepared. However, the first embodiment is not limited to the method. The strain range could be predicted even without all the physical quantities such as the temperature amplitude, the cycle number and the periodic length, depending on usage environment of an object to be checked. Specifically, only the amplitude and the cycle number allow it to predict the strain range in some cases.

Accordingly, it is possible to predict a life of a solder joint on the basis of the following two conditions:(1) At least one of physical quantities such as the amplitude, cycle number, mean temperature and periodic length of temperature variations can be examined by means of cycle number from temperature history information; and(2) The strain range can be calculated on the basis of a response surface previously prepared for at least one of the physical quantities examined in (1).

(Modification of First Embodiment)

A modification of the first embodiment will be explained. The process of life prediction of the present modification is different from that of the first embodiment in a point that the modification is provided with a routine. The routine calculates an error between an estimated life and an actual life of a dummy bump to correct the error when a fracture of the dummy bump is detected.FIG. 17shows a life predicting method having the routine of the error correction mounted. Further,FIG. 18shows a structure added to the first embodiment of structures necessary for performing the life predicting method.

A dummy bump fracture detection event is arranged before the life predicting method of the first embodiment (i.e. Step S025).

A twenty-first control unit51(i.e., a fracture event detection unit) determines whether or not the dummy bump fractures (Step S022). When the control unit51determines that the dummy bump does not fracture, the control unit51performes the method of the first embodiment (i.e., Step S001to Step S009) is performed (seeFIG. 1).

When it is determined that the dummy bump fractures, a twenty-second control unit (i.e., a damage index correction unit)52reads the previously obtained damage index with reference to the damage index database24. Then, the damage index correction unit52performs a comparison between the previously given damage index and the newly obtained damage index. Further, when a certain difference is definite between the damage indexes in the comparison result, the damage index correction unit52corrects a predicted life of a solder joint which has not fractured yet (Step S023).

A correction method of the predicted life will be explained with reference to an example shown inFIG. 19. A fracture is supposed to occur when the damage index D reaches 1. Here, the fracture is assumed to be detected at the solder joint when D=0.75 as shown inFIG. 19. In this case, it is determined that the damage corresponding to ΔD=0.25 (=1−0.75) has been applied for some unexpected reason. Accordingly, the damage index of a solder joint which has not yet fractured is divided by D=0.75. That is, a new damage index is to be 0.533 which is obtained by dividing a damage index of 0.4 by 0.75.

Further, the damage index correction unit52stores the corrected damage index 0.533 through the above calculation in a memory unit (i.e., a dummy bump situation database)61. The fracture information and damage index of the solder joint stored in the memory unit (i.e., the dummy bump situation database)61are provided to a host side by utilizing media such as a self-monitoring, analysis and reporting technology (SMART) as needed. Subsequently, the process of the first embodiment (i.e., Step S001to Step S009) is executed (seeFIG. 1).

Second Embodiment

A second embodiment will be described with reference toFIGS. 2 and 3. The second embodiment relates to a life predicting apparatus for a solder joint.

FIG. 3is a schematic view showing an example of the second embodiment having semiconductor memories4-1to4-8, a capacitor6, a detection unit7and a control unit10mounted on the mounting board1. The semiconductor memories4-1to4-8are connected to the mounting board1via solder joints and the like. The detection unit7measures electric characteristics of the respective joints of the semiconductor memories4-1to4-8and observes connection states thereof. Further, the detection unit7measures a temperature of the mounting board1. A part of the semiconductor memory can be used as the memory unit20.

FIG. 2is a block diagram according to the second embodiment. The second embodiment includes the detection unit7, the control unit10and the memory unit20as components. These are mutually connected via a signal line L through which information and signals are exchanged. The signal line may adopt a wired form, a wireless form or a mixed form thereof.

Corresponding to the first embodiment, the control unit10is provided with the update event detection unit11, the cycle number examination unit12, the temperature-amplitude/strain-range conversion unit13, the strain-range increasing rate calculation unit14, the strain-range recount unit15and the damage index determination unit16. The memory unit20is provided with the update event storage unit21, the temperature history database22, the response surface database23, the damage index database24, the strain variation history database25, the solder fatigue database26, and the threshold value database27.

Corresponding to the modification of the first embodiment, the control unit10may be further provided with the fracture event detection unit31and the damage index correction unit32and the memory unit20may be further provided with a dummy-bump state database61.

A CPU is utilized as the control unit10, for example. Further, a semiconductor memory may be utilized for the memory unit20. However, not being limited to the above, the memory unit is only required to be a recording medium capable of storing information and programs. Accordingly, an LSI such as a NAND type semiconductor memory, an HDD or a ROM may be utilized therefor.

The detection unit7(i.e., the fracture event detection unit51) may be provided with a circuit to measure a resistance value of the solder joint71, a circuit to measure impedance or/and the like, for example. The detection unit7can detect a fracture by measuring electric characteristics of a solder joint. For example, it is possible to detect subsidiary fracture by detecting rapid increase of electric resistance caused by the fracture of the joint. Further, the detection unit7may be provided with a thermocouple for measuring temperatures. When the circuit to measure impedance is an analog circuit and the output of the thermocouple is an analog signal, the detection unit7may include an A/D converter. Conversion from analog signals to digital signals enables the control unit10and the memory unit20to easily deal with these signals.

Operation, function and effects of the second embodiment will not be repeated as described in the first embodiment and the modification thereof.

Third Embodiment

Next, a third embodiment will be explained below with reference toFIG. 20. The third embodiment includes characteristics to form a signal line for detecting a fracture.

As shown inFIG. 20, two or more solder joints71are arranged in a rectangular semiconductor memory4. A silicone chip73included in the semiconductor memory4is slightly smaller than the outermost circumference of the semiconductor memory4and is formed inside the semiconductor memory4.

The solder joints71are arranged in a dummy bump area (i.e., a second joint B-1), a fracture detection area (i.e., a third joint B-2), a signal line area (i.e., a first joint B-3), a fracture detection area (i.e., a third joint B-4) and a dummy bump area (i.e., a second joint B-5) which are formed in this order in the direction of a line-symmetric axis of the rectangular semiconductor memory4. That is, the fracture detection area is formed between the signal line area and the dummy bump area.

The respective dummy bump areas (B-1, B-5) are surrounded by a double-dotted line inFIG. 20. The dummy bumps in the areas mechanically connect the semiconductor memory and the mounting board1to each other, but do not relay the semiconductor memory and the mounting board1electrically.

The signal line area (B-3) is surrounded by a dash-dotted line inFIG. 20. The solder joints in this area provide not only a mechanical connection between the semiconductor memory4as an electric device and the mounting board1, but also an electrical connection therebetween.

The respective fracture detection areas (B-2, B-4) are surrounded by a dashed line inFIG. 20. The solder joints in the areas provide the mechanical connection between the semiconductor memory4as an electric device and the mounting board1but do not provide the electrical connection therebetween. Here, a signal line72for detecting a fracture is formed by utilizing a part of the solder joints in the areas. The signal line72is connected to the detection unit7to be capable of monitoring the connection state between the semiconductor memory4and the mounting board1. In the example shown inFIG. 20, when pairing two solder joints adjacent to each other at the outermost of the fracture detection area, four pairs of joints to mutually face are connected serially with one line. In some cases, only one pair of joints or only two pairs thereof occupying contrapositive locations on the rectangular semiconductor memory4may be connected. At this time, choosing the pairs of the joints having the most drastic change in the temperature enables it to detect the fracture of solder joints at an early stage.

Arranging the fracture detection area between the dummy bump area and the signal line area as described above enables it to use the fracture detection area having less influence of its variations on the life prediction than the dummy bump area and to accurately predict the life. The dummy bump area in the vicinity of the outer circumference is to fracture earlier than the fracture detection area or the signal line area. This can be physically understood in terms of the fact that solder joints receive more mechanical load toward the outer side of a package and all the inner joints averagely receive any loads other than the load received by the outer joints. Strain ranges of the respective inner solder joints are more averaged than those of the outer solder joints. The respective inner solder joints receive an equivalent load averaged over the inner solder joints. As a result, variations in the life are reduced. The tendency of the variations is proved with a load test such as a temperature cycle test.

Fewer variations in the characteristics of the fracture detection area are beneficial to the damage index correction of the signal bump performed at Step023of the first embodiment. The solder joints for the fracture detection having fewer variations allow the other solder joints for the damage index correction to have fewer variations, thereby enabling it to accurately predict the life. The fracture detection is performed preferably at the dummy bump area in the outer side of the package to value an early detection while the fracture detection is performed preferably at the solder joints in the inner side of the dummy bump area to enable an accurate prediction. Appropriately selecting a solder connection portion for fracture detection enables it to keep balance between early detection and an accurate life prediction.

(Modification of Third Embodiment)

A modification of the third embodiment combines the first and second embodiments with a chain for fracture detection to enable it to appropriately predict a life.FIG. 21shows the modification of the third embodiment.

Each semiconductor memory (4-1,4-2, . . . ,4-N) inFIG. 21is connected to the detection unit7in a traversable manner with the fracture detection signal line72. Accordingly, solder joints of two or more semiconductor memories4can be monitored with the detection unit7locating at one point.

At least any one of the above-described embodiments can prepare a test schedule to enable it to efficiently execute test items considering loads to be applied by diagnostic itself to devices.

While a certain embodiment of the invention has been described, the embodiment has been presented by way of examples only, and is not intended to limit the scope of the inventions. Indeed, the novel elements and apparatuses described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods described herein may be made without departing from the spirit of the invention. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the invention.