Vesa Vuorinen - Academia.edu (original) (raw)
Papers by Vesa Vuorinen
Journal of Electronic Materials
Wafer-level solid liquid interdiffusion (SLID) bonding, also known as transient liquid-phase bond... more Wafer-level solid liquid interdiffusion (SLID) bonding, also known as transient liquid-phase bonding, is becoming an increasingly attractive method for industrial usage since it can provide simultaneous formation of electrical interconnections and hermetic encapsulation for microelectromechanical systems. Additionally, SLID is utilized in die-attach bonding for electronic power components. In order to ensure the functionality and reliability of the devices, a fundamental understanding of the formation and evolution of interconnection microstructures, as well as global and local stresses, is of utmost importance. In this work a low-temperature Cu-In-Sn based SLID bonding process is presented. It was discovered that by introducing In to the traditional Cu-Sn metallurgy as an additional alloying element, it is possible to significantly decrease the bonding temperature. Decreasing the bonding temperature results in lower CTE induced global residual stresses. However, there are still sev...
IEEE Transactions on Components, Packaging and Manufacturing Technology
The wafer-level Solid Liquid Interdiffusion (SLID) bonds carried out for this work take advantage... more The wafer-level Solid Liquid Interdiffusion (SLID) bonds carried out for this work take advantage of the Cu-In-Sn ternary system to achieve low temperature interconnections. The 100mm Si wafers had µ-bumps from 250µm down to 10µm fabricated by consecutive electrochemical deposition of Cu, Sn and In layers. The optimized wafer-level bonding processes were carried out by EV Group and Aalto University across a range of temperatures from 250C down to 170C. Even though some process quality related challenges were observed, it could be verified that high strength bonds with low defect content can be achieved even at a low bonding temperature of 170C with an acceptable 1-hour wafer-level bonding duration. The microstructural analysis revealed that the bonding temperature significantly impacts the obtained phase structure as well as the number of defects. A higher (250C) bonding temperature led to the formation of Cu3Sn phase in addition to Cu6(Sn,In)5 and resulted in several voids at Cu3Sn|Cu interface. On the other hand, with lower (200C and 170C) bonding temperatures the interconnection microstructure was composed purely of void free Cu6(Sn,In)5. The mechanical testing results revealed the clear impact of bonding quality on the interconnection strength.
Applied Physics Letters
Blistering of protective, structural, and functional coatings is a reliability risk pestering fil... more Blistering of protective, structural, and functional coatings is a reliability risk pestering films ranging from elemental to ceramic ones. The driving force behind blistering comes from either excess hydrogen at the film-substrate interface or stress-driven buckling. Contrary to the stressdriven mechanism, the hydrogen-initiated one is poorly understood. Recently, it was shown that in the bulk Al-Al 2 O 3 system, the blistering is preceded by the formation of nano-sized cavities on the substrate. The stress-and hydrogen-driven mechanisms in atomic-layer-deposited (ALD) films are explored here. We clarify issues in the hydrogen-related mechanism via high-resolution microscopy and show that at least two distinct mechanisms can cause blistering in ALD films.
Annals of Diagnostic Pathology
Idiopathic pulmonary fibrosis (IPF) is a chronic lung disease with a dismal prognosis and an unkn... more Idiopathic pulmonary fibrosis (IPF) is a chronic lung disease with a dismal prognosis and an unknown etiology. Inorganic dust is a known risk factor, and air pollution seems to affect disease progression. We aimed to investigate inorganic particulate matter in IPF lung tissue samples. Using polarizing light microscopy, we examined coal dust pigment and inorganic particulate matter in 73 lung tissue samples from the FinnishIPF registry. We scored the amount of coal dust pigment and particulate matter from 0 to 5. Using energy dispersive spectrometry with a scanning electron microscope, we conducted an elemental analysis of six IPF lung tissue samples. We compared the results to the registry data, and to the population density and air quality data. To compare categorical data, we used Fisher's exact test; we estimated the survival of the patients with Kaplan-Meier curves. We found inorganic particulate matter in all samples in varying amounts. Samples from the southern regions of Finland, where population density and fine particle levels are high, more often had particulate matter scores from 3 to 5 than samples from the northern regions (31/50, 62.0% vs. 7/23, 30.4%, p = 0.02). The highest particulate matter scores of 4 and 5 (n = 15) associated with a known exposure to inorganic dust (p = 0.004). An association between particulate matter in the lung tissue of IPF patients and exposure to air pollution may exist.
Handbook of Solid State Diffusion, Volume 2, 2017
Journal of Electronic Materials, 2016
Journal of Electronic Materials, 2005
Interfacial reactions between SnPbAg, SnAg, and SnAgCu solders and Ni/Au surface finish on printe... more Interfacial reactions between SnPbAg, SnAg, and SnAgCu solders and Ni/Au surface finish on printed wiring board and especially the redeposition of AuSn 4 intermetallic compound have been investigated. The following major results were obtained. The first phase to form during soldering in the (SnPbAg)/Ni/Au and the (SnAg)/Ni/Au systems was Ni 3 Sn 4. During the subsequent solid-state annealing, the redeposition of AuSn 4 as (Au,Ni)Sn 4 occurred in both systems. This was explained with the help of the concept of local equilibrium and the corresponding ternary phase diagrams. It was concluded that the stabilizing effect of Ni on the (Au,Ni)Sn 4 provided the driving force for the redeposition. Contrarily, when the solder alloy contained some Cu, the first intermetallic to form was (Cu,Ni,Au) 6 Sn 5 and no redeposition of AuSn 4 was observed. Thus, a very small addition of Cu to the Sn-rich solder alloys changed the behavior of the interconnection system completely. This behavior was explained thermodynamically by using Cu-Ni-Sn and Au-Cu-Sn ternary phase diagrams. The growth kinetics of the interfacial reaction products in the three systems was observed to be somewhat different. The reasons for the observed differences are also discussed.
Journal of Electronic Materials, 2007
Solid-state interfacial reactions between Sn and Cu(Ni) alloys have been investigated at the temp... more Solid-state interfacial reactions between Sn and Cu(Ni) alloys have been investigated at the temperature of 125°C. The following results were obtained. Firstly, the addition of 0.1 at.% Ni to Cu decreased the total thickness of the intermetallic compound (IMC) layer to about half of that observed in the binary Cu/Sn diffusion couple; the Ni addition decreased especially the thickness of Cu 3 Sn. Secondly, the addition of 1 to 2.5 at.% Ni to Cu further decreased the thickness of Cu 3 Sn, increased that of Cu 6 Sn 5 (compared to that in the binary Cu/Sn couple) and produced significant amount of voids at the Cu/Cu 3 Sn interface. Thirdly, the addition of 5 at.% Ni to Cu increased the total thickness of the IMC layer to about two times that observed in the binary Cu/Sn diffusion couple and made the Cu 3 Sn disappear. Fourthly, in contrast to the previous case, the addition of 10 at.% Ni to Cu decreased the total IMC (Cu 6 Sn 5 ) thickness again close to that of the Cu/Sn couple. With this Ni content no voids were detected. The results are rationalized with the help of the thermodynamics of the Sn-Cu-Ni system as well as with kinetic considerations.
Thermodynamics, Diffusion and the Kirkendall Effect in Solids, 2014
ABSTRACT This chapter deals with diffusion in the phases with wide homogeneity range. Different a... more ABSTRACT This chapter deals with diffusion in the phases with wide homogeneity range. Different approaches, which could be used to estimate the variation of interdiffusion coefficients with composition, are described. Following the Kirkendall effect is introduced along with the estimation of the intrinsic diffusion coefficients. The estimation of the tracer diffusion coefficients from a diffusion couple is also explained.
Thermodynamics, Diffusion and the Kirkendall Effect in Solids, 2014
Thermodynamics, Diffusion and the Kirkendall Effect in Solids, 2014
ABSTRACT In this chapter, we will discuss some aspects related to reactive phase formation in thi... more ABSTRACT In this chapter, we will discuss some aspects related to reactive phase formation in thin films. We try to utilize as much as possible the information accumulated during the earlier chapters and built on that. We will first have a brief look on nucleation issues, especially in solid state, before moving into effect of microstructure and impurities on the reactive phase formation. Finally, we will introduce some of the models for phase growth that have been introduced in the past and then discuss in detail about their pros and cons.
Materials Science and Engineering: R: Reports, 2010
Thermodynamics, Diffusion and the Kirkendall Effect in Solids, 2014
ABSTRACT In this chapter, we analyze the diffusion mechanisms in metals from an atomistic point o... more ABSTRACT In this chapter, we analyze the diffusion mechanisms in metals from an atomistic point of view. It is shown that the defects of crystalline structure, mainly vacancies and interstitial atoms, mediate diffusion. The fundamental difference between self-diffusion and tracer (self- or impurity) diffusion is introduced, and the basic concept of correlation factors is discussed. Further, the temperature and orientation dependence of diffusion according to both substitutional and interstitial mechanisms are examined. The complications related to specific structure of compounds, including the effect of ordering, are introduced.
Metallurgical and Materials Transactions A, 2011
Incremental diffusion couple experiments are conducted to determine the average interdiffusion co... more Incremental diffusion couple experiments are conducted to determine the average interdiffusion coefficient and the intrinsic diffusion coefficients of the species in the Ni 6 Nb 7 (l phase) in the Ni-Nb system. Further, the tracer diffusion coefficients are calculated from the knowledge of thermodynamic parameters. The diffusion rate of Ni is found to be higher than that of Nb, which indicates higher defect concentration in the Ni sublattice.
Journal of Electronic Materials, 2005
Interfacial reactions between SnPbAg, SnAg, and SnAgCu solders and Ni/Au surface finish on printe... more Interfacial reactions between SnPbAg, SnAg, and SnAgCu solders and Ni/Au surface finish on printed wiring board and especially the redeposition of AuSn 4 intermetallic compound have been investigated. The following major results were obtained. The first phase to form during soldering in the (SnPbAg)/Ni/Au and the (SnAg)/Ni/Au systems was Ni 3 Sn 4 . During the subsequent solid-state annealing, the redeposition of AuSn 4 as (Au,Ni)Sn 4 occurred in both systems. This was explained with the help of the concept of local equilibrium and the corresponding ternary phase diagrams. It was concluded that the stabilizing effect of Ni on the (Au,Ni)Sn 4 provided the driving force for the redeposition. Contrarily, when the solder alloy contained some Cu, the first intermetallic to form was (Cu,Ni,Au) 6 Sn 5 and no redeposition of AuSn 4 was observed. Thus, a very small addition of Cu to the Sn-rich solder alloys changed the behavior of the interconnection system completely. This behavior was explained thermodynamically by using Cu-Ni-Sn and Au-Cu-Sn ternary phase diagrams. The growth kinetics of the interfacial reaction products in the three systems was observed to be somewhat different. The reasons for the observed differences are also discussed.
Microelectronics Reliability, 2009
The effect of Ag, Fe, Au and Ni on the interfacial reactions between Sn-based solder and Cu subst... more The effect of Ag, Fe, Au and Ni on the interfacial reactions between Sn-based solder and Cu substrate has been investigated in this paper. Based on the solubility of the alloying elements in the Sn-Cu intermetallic compound (IMC) layers these elements can be divided into two categories: (i) alloying elements that do not dissolve significantly in either Cu 6 Sn 5 or Cu 3 Sn and (ii) elements that exhibit significant solubility in Cu 6 Sn 5 and also to Cu 3 Sn. It is shown that the latter group of elements have stronger effect on the growth behaviour of IMC's in the Sn-Cu system than those belonging to the first group. Of the investigated elements Ni had the most prominent effect on the growth kinetics. It reduced greatly the thickness of Cu 3 Sn and consequently also the total IMC layer thickness. Au had similar but markedly weaker effect. On the contrary, Fe and Ag only slightly decreased the total IMC layer thickness, and more importantly did not change the thickness ratio of Cu 6 Sn 5 to Cu 3 Sn in comparison to the pure Sn-Cu system.
Microelectronics Reliability, 2007
Failure mechanisms of lead-free solder interconnections in power cycling and thermal shock tests ... more Failure mechanisms of lead-free solder interconnections in power cycling and thermal shock tests have been investigated in this work. Even though there are some characteristic differences between the two tests, the failures in both cases were induced by recrystallizationassisted crack nucleation and propagation. The three major differences between the tests were: (i) minimum temperature during power cycling was considerably higher in comparison to thermal shock, (ii) the current flow in the power cycling test resulted in electromigration, and (iii) in the power cycling test heat originates locally from components themselves. These differences were also reflected in the test results in the following way: firstly, in the power cycling test the recrystallization occurred earlier than in the thermal shock test, mainly owing to the higher average temperature and secondly, the enhanced growth of intermetallic compound layer at the anode side due to the electromigration was observed during power cycling.
Journal of Electronic Materials
Wafer-level solid liquid interdiffusion (SLID) bonding, also known as transient liquid-phase bond... more Wafer-level solid liquid interdiffusion (SLID) bonding, also known as transient liquid-phase bonding, is becoming an increasingly attractive method for industrial usage since it can provide simultaneous formation of electrical interconnections and hermetic encapsulation for microelectromechanical systems. Additionally, SLID is utilized in die-attach bonding for electronic power components. In order to ensure the functionality and reliability of the devices, a fundamental understanding of the formation and evolution of interconnection microstructures, as well as global and local stresses, is of utmost importance. In this work a low-temperature Cu-In-Sn based SLID bonding process is presented. It was discovered that by introducing In to the traditional Cu-Sn metallurgy as an additional alloying element, it is possible to significantly decrease the bonding temperature. Decreasing the bonding temperature results in lower CTE induced global residual stresses. However, there are still sev...
IEEE Transactions on Components, Packaging and Manufacturing Technology
The wafer-level Solid Liquid Interdiffusion (SLID) bonds carried out for this work take advantage... more The wafer-level Solid Liquid Interdiffusion (SLID) bonds carried out for this work take advantage of the Cu-In-Sn ternary system to achieve low temperature interconnections. The 100mm Si wafers had µ-bumps from 250µm down to 10µm fabricated by consecutive electrochemical deposition of Cu, Sn and In layers. The optimized wafer-level bonding processes were carried out by EV Group and Aalto University across a range of temperatures from 250C down to 170C. Even though some process quality related challenges were observed, it could be verified that high strength bonds with low defect content can be achieved even at a low bonding temperature of 170C with an acceptable 1-hour wafer-level bonding duration. The microstructural analysis revealed that the bonding temperature significantly impacts the obtained phase structure as well as the number of defects. A higher (250C) bonding temperature led to the formation of Cu3Sn phase in addition to Cu6(Sn,In)5 and resulted in several voids at Cu3Sn|Cu interface. On the other hand, with lower (200C and 170C) bonding temperatures the interconnection microstructure was composed purely of void free Cu6(Sn,In)5. The mechanical testing results revealed the clear impact of bonding quality on the interconnection strength.
Applied Physics Letters
Blistering of protective, structural, and functional coatings is a reliability risk pestering fil... more Blistering of protective, structural, and functional coatings is a reliability risk pestering films ranging from elemental to ceramic ones. The driving force behind blistering comes from either excess hydrogen at the film-substrate interface or stress-driven buckling. Contrary to the stressdriven mechanism, the hydrogen-initiated one is poorly understood. Recently, it was shown that in the bulk Al-Al 2 O 3 system, the blistering is preceded by the formation of nano-sized cavities on the substrate. The stress-and hydrogen-driven mechanisms in atomic-layer-deposited (ALD) films are explored here. We clarify issues in the hydrogen-related mechanism via high-resolution microscopy and show that at least two distinct mechanisms can cause blistering in ALD films.
Annals of Diagnostic Pathology
Idiopathic pulmonary fibrosis (IPF) is a chronic lung disease with a dismal prognosis and an unkn... more Idiopathic pulmonary fibrosis (IPF) is a chronic lung disease with a dismal prognosis and an unknown etiology. Inorganic dust is a known risk factor, and air pollution seems to affect disease progression. We aimed to investigate inorganic particulate matter in IPF lung tissue samples. Using polarizing light microscopy, we examined coal dust pigment and inorganic particulate matter in 73 lung tissue samples from the FinnishIPF registry. We scored the amount of coal dust pigment and particulate matter from 0 to 5. Using energy dispersive spectrometry with a scanning electron microscope, we conducted an elemental analysis of six IPF lung tissue samples. We compared the results to the registry data, and to the population density and air quality data. To compare categorical data, we used Fisher's exact test; we estimated the survival of the patients with Kaplan-Meier curves. We found inorganic particulate matter in all samples in varying amounts. Samples from the southern regions of Finland, where population density and fine particle levels are high, more often had particulate matter scores from 3 to 5 than samples from the northern regions (31/50, 62.0% vs. 7/23, 30.4%, p = 0.02). The highest particulate matter scores of 4 and 5 (n = 15) associated with a known exposure to inorganic dust (p = 0.004). An association between particulate matter in the lung tissue of IPF patients and exposure to air pollution may exist.
Handbook of Solid State Diffusion, Volume 2, 2017
Journal of Electronic Materials, 2016
Journal of Electronic Materials, 2005
Interfacial reactions between SnPbAg, SnAg, and SnAgCu solders and Ni/Au surface finish on printe... more Interfacial reactions between SnPbAg, SnAg, and SnAgCu solders and Ni/Au surface finish on printed wiring board and especially the redeposition of AuSn 4 intermetallic compound have been investigated. The following major results were obtained. The first phase to form during soldering in the (SnPbAg)/Ni/Au and the (SnAg)/Ni/Au systems was Ni 3 Sn 4. During the subsequent solid-state annealing, the redeposition of AuSn 4 as (Au,Ni)Sn 4 occurred in both systems. This was explained with the help of the concept of local equilibrium and the corresponding ternary phase diagrams. It was concluded that the stabilizing effect of Ni on the (Au,Ni)Sn 4 provided the driving force for the redeposition. Contrarily, when the solder alloy contained some Cu, the first intermetallic to form was (Cu,Ni,Au) 6 Sn 5 and no redeposition of AuSn 4 was observed. Thus, a very small addition of Cu to the Sn-rich solder alloys changed the behavior of the interconnection system completely. This behavior was explained thermodynamically by using Cu-Ni-Sn and Au-Cu-Sn ternary phase diagrams. The growth kinetics of the interfacial reaction products in the three systems was observed to be somewhat different. The reasons for the observed differences are also discussed.
Journal of Electronic Materials, 2007
Solid-state interfacial reactions between Sn and Cu(Ni) alloys have been investigated at the temp... more Solid-state interfacial reactions between Sn and Cu(Ni) alloys have been investigated at the temperature of 125°C. The following results were obtained. Firstly, the addition of 0.1 at.% Ni to Cu decreased the total thickness of the intermetallic compound (IMC) layer to about half of that observed in the binary Cu/Sn diffusion couple; the Ni addition decreased especially the thickness of Cu 3 Sn. Secondly, the addition of 1 to 2.5 at.% Ni to Cu further decreased the thickness of Cu 3 Sn, increased that of Cu 6 Sn 5 (compared to that in the binary Cu/Sn couple) and produced significant amount of voids at the Cu/Cu 3 Sn interface. Thirdly, the addition of 5 at.% Ni to Cu increased the total thickness of the IMC layer to about two times that observed in the binary Cu/Sn diffusion couple and made the Cu 3 Sn disappear. Fourthly, in contrast to the previous case, the addition of 10 at.% Ni to Cu decreased the total IMC (Cu 6 Sn 5 ) thickness again close to that of the Cu/Sn couple. With this Ni content no voids were detected. The results are rationalized with the help of the thermodynamics of the Sn-Cu-Ni system as well as with kinetic considerations.
Thermodynamics, Diffusion and the Kirkendall Effect in Solids, 2014
ABSTRACT This chapter deals with diffusion in the phases with wide homogeneity range. Different a... more ABSTRACT This chapter deals with diffusion in the phases with wide homogeneity range. Different approaches, which could be used to estimate the variation of interdiffusion coefficients with composition, are described. Following the Kirkendall effect is introduced along with the estimation of the intrinsic diffusion coefficients. The estimation of the tracer diffusion coefficients from a diffusion couple is also explained.
Thermodynamics, Diffusion and the Kirkendall Effect in Solids, 2014
Thermodynamics, Diffusion and the Kirkendall Effect in Solids, 2014
ABSTRACT In this chapter, we will discuss some aspects related to reactive phase formation in thi... more ABSTRACT In this chapter, we will discuss some aspects related to reactive phase formation in thin films. We try to utilize as much as possible the information accumulated during the earlier chapters and built on that. We will first have a brief look on nucleation issues, especially in solid state, before moving into effect of microstructure and impurities on the reactive phase formation. Finally, we will introduce some of the models for phase growth that have been introduced in the past and then discuss in detail about their pros and cons.
Materials Science and Engineering: R: Reports, 2010
Thermodynamics, Diffusion and the Kirkendall Effect in Solids, 2014
ABSTRACT In this chapter, we analyze the diffusion mechanisms in metals from an atomistic point o... more ABSTRACT In this chapter, we analyze the diffusion mechanisms in metals from an atomistic point of view. It is shown that the defects of crystalline structure, mainly vacancies and interstitial atoms, mediate diffusion. The fundamental difference between self-diffusion and tracer (self- or impurity) diffusion is introduced, and the basic concept of correlation factors is discussed. Further, the temperature and orientation dependence of diffusion according to both substitutional and interstitial mechanisms are examined. The complications related to specific structure of compounds, including the effect of ordering, are introduced.
Metallurgical and Materials Transactions A, 2011
Incremental diffusion couple experiments are conducted to determine the average interdiffusion co... more Incremental diffusion couple experiments are conducted to determine the average interdiffusion coefficient and the intrinsic diffusion coefficients of the species in the Ni 6 Nb 7 (l phase) in the Ni-Nb system. Further, the tracer diffusion coefficients are calculated from the knowledge of thermodynamic parameters. The diffusion rate of Ni is found to be higher than that of Nb, which indicates higher defect concentration in the Ni sublattice.
Journal of Electronic Materials, 2005
Interfacial reactions between SnPbAg, SnAg, and SnAgCu solders and Ni/Au surface finish on printe... more Interfacial reactions between SnPbAg, SnAg, and SnAgCu solders and Ni/Au surface finish on printed wiring board and especially the redeposition of AuSn 4 intermetallic compound have been investigated. The following major results were obtained. The first phase to form during soldering in the (SnPbAg)/Ni/Au and the (SnAg)/Ni/Au systems was Ni 3 Sn 4 . During the subsequent solid-state annealing, the redeposition of AuSn 4 as (Au,Ni)Sn 4 occurred in both systems. This was explained with the help of the concept of local equilibrium and the corresponding ternary phase diagrams. It was concluded that the stabilizing effect of Ni on the (Au,Ni)Sn 4 provided the driving force for the redeposition. Contrarily, when the solder alloy contained some Cu, the first intermetallic to form was (Cu,Ni,Au) 6 Sn 5 and no redeposition of AuSn 4 was observed. Thus, a very small addition of Cu to the Sn-rich solder alloys changed the behavior of the interconnection system completely. This behavior was explained thermodynamically by using Cu-Ni-Sn and Au-Cu-Sn ternary phase diagrams. The growth kinetics of the interfacial reaction products in the three systems was observed to be somewhat different. The reasons for the observed differences are also discussed.
Microelectronics Reliability, 2009
The effect of Ag, Fe, Au and Ni on the interfacial reactions between Sn-based solder and Cu subst... more The effect of Ag, Fe, Au and Ni on the interfacial reactions between Sn-based solder and Cu substrate has been investigated in this paper. Based on the solubility of the alloying elements in the Sn-Cu intermetallic compound (IMC) layers these elements can be divided into two categories: (i) alloying elements that do not dissolve significantly in either Cu 6 Sn 5 or Cu 3 Sn and (ii) elements that exhibit significant solubility in Cu 6 Sn 5 and also to Cu 3 Sn. It is shown that the latter group of elements have stronger effect on the growth behaviour of IMC's in the Sn-Cu system than those belonging to the first group. Of the investigated elements Ni had the most prominent effect on the growth kinetics. It reduced greatly the thickness of Cu 3 Sn and consequently also the total IMC layer thickness. Au had similar but markedly weaker effect. On the contrary, Fe and Ag only slightly decreased the total IMC layer thickness, and more importantly did not change the thickness ratio of Cu 6 Sn 5 to Cu 3 Sn in comparison to the pure Sn-Cu system.
Microelectronics Reliability, 2007
Failure mechanisms of lead-free solder interconnections in power cycling and thermal shock tests ... more Failure mechanisms of lead-free solder interconnections in power cycling and thermal shock tests have been investigated in this work. Even though there are some characteristic differences between the two tests, the failures in both cases were induced by recrystallizationassisted crack nucleation and propagation. The three major differences between the tests were: (i) minimum temperature during power cycling was considerably higher in comparison to thermal shock, (ii) the current flow in the power cycling test resulted in electromigration, and (iii) in the power cycling test heat originates locally from components themselves. These differences were also reflected in the test results in the following way: firstly, in the power cycling test the recrystallization occurred earlier than in the thermal shock test, mainly owing to the higher average temperature and secondly, the enhanced growth of intermetallic compound layer at the anode side due to the electromigration was observed during power cycling.