Fatigue Lifetime Of Solder Joints Research Articles

Thermal Fatigue Failure of Micro-Solder Joints in Electronic Packaging Devices: A Review

In electronic packaging products in the service process, the solder joints experience thermal fatigue due to temperature cycles, which have a significant influence on the performance of electronic products and the reliability of solder joints. In this paper, the thermal fatigue failure mechanism of solder joints in microelectronic packages, the microstructure changes of the thermal fatigue process, the influence factors on the joint fatigue life, and the simulation analysis and forecasting of thermal fatigue life are reviewed. The results show that the solder joints are heterogeneously coarsened, and this leads to fatigue cracks occurring under the elevated high-temperature phase of alternating temperature cycles. However, the thickness of the solder and the hold time in the high-temperature phase do not significantly influence the thermal fatigue. The coarsened region and the IMC layer thicken with the number of cycles, and the cracks initiate and propagate along the interface between the intermetallic compound (IMC) layer and coarsened region, eventually leading to solder joint failure. For lead-containing and lead-free solders, the lead-containing solder shows a faster fatigue crack growth rate and propagates by transgranular mode. Temperature and frequency affect the thermal fatigue life of solder joints to different degrees, and the fatigue lifetime of solder joints can be predicted through a variety of methods and simulated crack trajectories, but also through the use of a unified constitutive model and finite element analysis for prediction.

Role of aging temperature on thermomechanical fatigue lifetime of solder joints in electronic systems

PurposeThe purpose of this study is to investigate the effect of aging temperature on the barrel-type solder joint lifetime of electronic devices and to include these effects in the modified prediction model.Design/methodology/approachSeveral accelerated shear stress tests under different stress amplitudes and aging temperatures were performed.FindingsIt was found that by aging temperature increasing, the lifetime decreases. Morrow energy model was also found as the best prediction model when the aging temperature is taken into consideration.Originality valueIt is confirmed.

Finite element analysis of the effect of process-induced voids on the fatigue lifetime of a lead-free solder joint under thermal cycling

Process-induced voids remain one of the key concerns in thermo-mechanical reliability of solder alloys. Previous studies reported that the void effect on fatigue failure reliability of solder joints depends on the void configuration and some other specific characteristics of the electronic package. This paper investigates the void effect on the solder material layers used in power modules subjected to thermal passive cycles. The Anand's visco-plastic model of the solder alloy is identified based on experimental data obtained with a micro-tester. The constitutive model is then used in a finite element analysis to study the behaviour of Innolot Pb-free solder joint used in an electronic assembly. An algorithm called Monte Carlo Representative Volume Element Generator is used to generate, based on the statistical probability law for the diameters, the 2D disk distribution of the voids (thereafter extruded in the form of cylinders) within the solder layer. The dissipated plastic energy is considered as a damage variable indicator representing the void effect on the fatigue lifetime of the solder. Results suggest that the fatigue reliability of solder joints depends not only on the size, location and ratio of the voids but also on their statistical distribution. The critical sites for damage are located at the corners of the joint, as well as at the border of voids. Fatigue lifetime of the solder joint decreases as the volume fraction of voids increases. Moreover, voids near the critical sites facilitate initiation of damage significantly. On the contrary, the solder joint behaviour is almost not affected by voids located far from the critical sites.

Micromechanical model for describing intergranular fatigue cracking in a lead-free solder alloy

Solder joints possess a small thickness of the order of a few grains but they remain one of the key concerns in thermo-mechanical reliability of high-power electronic systems. Fatigue lifetime of solder joints subjected to thermal and mechanical loading cycles is generally predicted based on phenomenological and macroscopic fatigue models that use the effective material properties as inputs. Such semi-empirical models will thus only provide a gross estimation of the engineering lifetime for some specific boundary and loading conditions while ignoring the deformation mechanisms at micro-scale. Microscopic analysis of fractured solder joints points rather to crack propagation at grain boundaries. Therefore, a 3D microstructure-informed model is developed in this study for reproducing the intergranular fatigue crack in the solder joint of a power module. The submodeling technique has been applied in order to only investigate the critical zone of the solder joint. A global model of the whole module is first simulated to obtain the inputs for a submodel focused on the zone of interest where failure is expected to develop. The submodel simultaneously makes use of the cohesive zone and the crystal plasticity theories to represent decohesion at grain boundaries and plastic slips in the grains of the solder joint, respectively. The needed crystal plasticity parameters were fitted out with the help of the Berveiller-Zaoui homogenization scheme using experimental data, while the parameters for the cohesive zone model were estimated from some physical quantities. Simulations of repeated thermo-mechanical loading on the power module demonstrate how cracking occurs at grain boundaries in the solder joint of the submodel. In addition, it is shown that the crack propagation rate is almost constant during the whole loading time. This suggests an ability of the present approach to give a fatigue lifetime estimate for the entire solder joint by extrapolating some specific computed quantities from the local model.

Lifetime prediction of a viscoplastic lead-free solder in power electronics modules under passive temperature cycling

It is well-established now that solder joint in power electronics undergoes a thermal-mechanical fatigue in service. In order to provide a predictive tool to assess fatigue lifetime of solder joint subjected to passive temperature cycling, a cohesive zone method (CZM) based fatigue model, accounting for mixed-mode loadings, is presented in this paper. A cohesive zone model with a specific fatigue traction-separation law is used in conjunction with the Anand viscoplastic behavior for the bulk solder for modelling the interfacial fatigue crack growth. Temperature dependence of both stiffness and fracture energy is incorporated in the CZM based fatigue model. The CZM based fatigue model as well as the Anand viscoplastic constitutive law is implemented in the Abaqus finite element code. Numerical simulations are carried out under passive temperature cycling. A particular attention is given to information in the region ahead of the crack tip such as stress concentration, process zone size, damage distribution. The evolution of the crack extension is used to estimate the number of cycles to failure at which the device becomes faulty.

J0610202 高剛性ラップジョイント試験体を用いたはんだ接合部の疲労寿命に及ぼすひずみ速度の影響評価

J0610202 高剛性ラップジョイント試験体を用いたはんだ接合部の疲労寿命に及ぼすひずみ速度の影響評価

Impact of Isothermal Aging on Long-Term Reliability of Fine-Pitch Ball Grid Array Packages with Sn-Ag-Cu Solder Interconnects: Surface Finish Effects

The interaction between isothermal aging and the long-term reliability of fine-pitch ball grid array (BGA) packages with Sn-3.0Ag-0.5Cu (wt.%) solder ball interconnects was investigated. In this study, 0.4-mm fine-pitch packages with 300-μm-diameter Sn-Ag-Cu solder balls were used. Two different package substrate surface finishes were selected to compare their effects on the final solder composition, especially the effect of Ni, during thermal cycling. To study the impact on thermal performance and long-term reliability, samples were isothermally aged and thermally cycled from 0°C to 100°C with 10 min dwell time. Based on Weibull plots for each aging condition, package lifetime was reduced by approximately 44% by aging at 150°C. Aging at 100°C showed a smaller impact but similar trend. The microstructure evolution was observed during thermal aging and thermal cycling with different phase microstructure transformations between electrolytic Ni/Au and organic solderability preservative (OSP) surface finishes, focusing on the microstructure evolution near the package-side interface. Different mechanisms after aging at various conditions were observed, and their impacts on the fatigue lifetime of solder joints are discussed.

Reflow profile optimization of μBGA solder joints considering reflow temperature and time coupling

PurposeThe purpose of this paper is to present a novel reflow profile optimization method using mechanical reliability estimation of micro‐ball grid array (μBGA) solder joints, based on the heating factor, Qη is introduced, where the coupling effect of reflow temperature and time on the mechanical reliability of μBGA joints is considered.Design/methodology/approachThe method presented is actualized through vibration fatigue tests. First, a two‐parameter Weibull distribution is used to model the collected data of vibration fatigue lifetime for different Qη. After that, two explicit functions are deduced in a unified mathematic expression form, which give an intuitionistic description of the mean time to failure and reliability of solder joints against induced variable Qη, thus revealing definitely the effect of Qη on the mechanical fatigue lifetime of solder joints suffering from cyclic vibration loading. Finally, for a specified reliability goal, how to choose proper Qη values, based an improved Golden Section Search arithmetic, is discussed.FindingsNumerical analysis and calculation are performed. The results show that the solder joints made at Qη near 510 have higher mechanical reliability, and those reflowed farther away this optimal value have less reliability.Originality/valueThis paper presents a useful and applicable solution to achieve reflow profile optimization and process control for a quantitative mechanical reliability estimation of μBGA solder joints.

IMC Growth Mechanisms of SAC305 Lead-Free Solder on Different Surface Finishes and Their Effects on Solder Joint Reliability of FCBGA Packages

Intermetallic compound (IMC) growth behavior of lead-free solder plays an important role in ball grid array (BGA) solder joint reliability for flip chip BGA (FCBGA) packaging applications. The growth mechanism of IMC is reported based on a diffusion model. Thermal treatment such as accelerated thermal cycling (ATC) and isothermal aging exposure also contribute to the growth rate and morphology of lead-free solder IMC. Among the lead-free solder alloys, Sn-3.0wt.%Ag-0.5wt.%Cu (SAC305) solder is a promising substitute for Sn-Pb because of its good mechanical properties and wettability with current surface finishes. After thermal exposure, BGA solder joint reliability is degraded due to IMC formation and growth. In this study, two different thermal treatments, ATC and isothermal aging, and two different pad surface finishes, solder on pad (SOP) and electroless Ni immersion gold (ENIG), are considered in terms of IMC growth rate and mechanical solder joint reliability. An SOP finished interface forms a thin ε-phase Cu3Sn layer and a scallop-like η-phase Cu6Sn5 layer. In contrast, the ENIG finished interface forms a thick (Cu,Ni)6Sn5 IMC layer and prevents overall IMC growth. Different surface finished test vehicles are evaluated in an ATC test in a 0°C to 100°C temperature range and the Ni diffusion layer shows a longer solder joint fatigue lifetime than the nondiffusion barrier interface based on the micro cross-section and dye penetration analysis results. In an isothermal aging test at 100°C and 150°C, the aging temperature and time are valid factors to decide mechanical shock reliability. Interfacial fractures are found in the 100°C aged test vehicle due to easier crack propagation at the interface between the thin Cu3Sn layer and the scallop-like Cu6Sn5 layer based on SEM microstructure analysis results. Finally, this investigation proposes how to improve solder joint reliability and prevent interfacial fracture for SAC305 lead-free application.

Fracture mechanics analysis of the effect of substrate flexibility on solder joint reliability

Solder joint fatigue failure is a serious reliability concern in area array technologies, such as flip chip and ball grid array packages of integrated-circuit chips. The selection of different substrate materials could affect solder joint thermal fatigue life significantly. The reliability of solder joints in real flip chip assembly with both rigid and compliant substrates was evaluated by the accelerated temperature cycling test and thermal mechanical analysis. The mechanism of substrate flexibility on improving solder joint thermal fatigue lifetime was investigated by fracture mechanics methods. Two different methods (crack tip opening displacement, CTOD and virtual crack closure technique, VCCT) are used to determine the crack tip parameters which are considered as the indices of reliability of solder joints, including the strain energy release rate and phase angle for the different crack lengths and temperatures. It was found that the thermal fatigue lifetime of solder joints in flip chip on flex assembly (FCOF) was much longer than that of flip chip on rigid board assembly (FCOB). The flex substrates could dissipate energy that otherwise would be absorbed by solder joints, that is, substrate flexibility has a great effect on solder joint reliability and the reliability improvement was attributed to flex buckling or bending during thermal cycling.

Effects of solder joint shape and height on thermal fatigue lifetime

Solder joint thermal fatigue failure is a major concern for area array technologies such as flip chip and ball grid array technologies. Solder joint geometry is an important factor influencing thermal fatigue lifetime. In this paper, the effects of solder joint shape and height on thermal fatigue lifetime are studied. Solder joint fatigue lifetime was evaluated using accelerated temperate cycling and adhesion test. Scanning electron microscopy (SEM), energy dispersive x-ray analysis (EDX), scanning acoustic microscopy (nondestructive evaluation) and optical microscopy were utilized to examine the integrity of the joint and to detect cracks and other defects before and during accelerated fatigue tests. Our accelerated temperature cycling test clearly shows that solder joint fatigue failure process consists of three phases: crack initiation, crack propagation and catastrophic failure. Experimental results indicated that both hourglass shape and great standoff height could improve solder joint fatigue lifetime, with standoff height being the more effective factor. Experimental data suggested that shape is the dominant factor affecting crack initiation time while standoff height is the major factor influencing crack propagation time.

Effect of substrate flexibility on solder joint reliability

Solder joint fatigue failure is a serious reliability concern in area array technologies, such as flip chip and ball grid array packages of integrated-circuit chips. The selection of different substrate materials could affect solder joint thermal fatigue lifetime significantly. The reliability of solder joint in flip chip assembly for both rigid and compliant substrates was evaluated by accelerated temperature cycling test. Experimental results strongly showed that the thermal fatigue lifetime of solder joints in flip chip on flex assembly was much improved over that in flip chip on rigid substrate assembly. Debonding area of solder joints in flip chip on rigid board and flip chip on flex assemblies were investigated, and it was found that flex substrate could slow down solder joint crack propagation rate. The mechanism of substrate flexibility on improving solder joint thermal fatigue was investigated by thermal mechanical analysis (TMA) technique. TMA results showed that flex substrate buckles or bends during temperature cycling and this phenomenon was discussed from the point of view of mechanics of the flip chip assembly during temperature cycling process. It was indicated that the thermal strain and stress in solder joints could be reduced by flex buckling or bending and flex substrates could dissipate energy that otherwise would be absorbed by solder joints. It was concluded that substrate flexibility has a great effect on solder joint reliability and the reliability improvement was attributed to flex buckling or bending during temperature cycling.

Effect of intermetallic compounds on vibration fatigue of μBGA solder joint

This paper studies the vibration fatigue failure of /spl mu/BGA solder-joints reflowed with different temperature profiles, and aging at 120 /spl deg/C for 1, 4, 9, 16, 25, 36 days. The effect of the Ni/sub 3/Sn/sub 4/ and Cu-Sn intermetallic compound (IMC) on the fatigue lifetime is also reported. During the vibration fatigue test, in order to identify the failure of /spl mu/BGA solder joint, electrical interruption was monitored continuously through the daisy-chain network. Our results show that the fatigue lifetime of the solder joint firstly increases and then decreases with increasing heating factor (Q/sub /spl eta//), which is defined as the integral of the measured temperature over the dwell time above liquidus (183/spl deg/C) in the reflow profile. The greatest lifetime occurs when Q/sub /spl eta// is near 500s/spl deg/C. Moreover, the lifetime of the solder joint decreases almost linearly with the increasing fourth root of the aging time. The SEM/EDX inspection shows that Ni/sub 3/Sn/sub 4/ IMC and Cu/sub 6/Sn/sub 5//Cu/sub 3/Sn IMCs are formed at the interface of the solder/nickel-plated PCB pad, and the no-aging solder/component-metallization, respectively. And during long term aging, Ni/sub 3/Sn/sub 2/ and NiSn were found at the Ni/Solder interface with X-ray diffraction, except Ni/sub 3/Sn/sub 4/. For nonaged solder joint, the fatigue crack generally initiates at the interface between the Ni/sub 3/Sn/sub 4/ IMC and the bulk solder. Then it propagates mostly near the Ni/solder, and occasionally in the LMC layer or along the Ni/solder interface. After aging, the fatigue track mostly initiates and propagates in the Cu/sub 6/Sn/sub 5/ -phase/bulk-solder interface or the Cu/sub 3/Sn/Cu/sub 6/Sn/sub 5/ interface on component-metallization. Evidently, the intermetallic compounds contribute mainly to the fatigue failure of /spl mu/BGA solder joints. The thicker the IMC layer, the shorter the fatigue lifetime of solder joint. The initial formation of the IMCs at the interface during soldering ensures a good metallurgical bond between the solder and the substrate. However, a thick IMC layer influences the toughness and strength of the solder joint, which results in mechanical failure.

Effect of cooling rate on the isothermal fatigue behavior of CBGA solder joints in shear

This paper investigates the distribution characteristics of the isothermal fatigue lifetime of ceramic ball grid array (CBGA) solder joints in shear. Placement direction of the board-level assembly on the oven conveyor during reflow critically influences the fatigue lifetime of solder joints in shear: the front or outer solder joints have a longer shear lifetime than the rear or inner ones. The solder joints that moved diagonally during reflow have a longer fatigue lifetime and a tighter distribution. Cracks initiated in the eutectic solder region on the card and package side and tend to propagated in that region, while final failure occurred mainly on the card-said eutectic solder region. This phenomenon can be explained that the front or outer solder bumps have a resistant effect to the gas fluid which passes through the rear or inner solder bumps, and lower these solder joints' cooling rate during solidification. Fast cooling rate can cause a more fine-grained and homogeneous microstructure in eutectic solder alloy, which can delay crack initiation and slow crack growth. When the board-level assembly moves diagonally during reflow, the resistant effect of front solder bumps to the gas fluid reduces markedly. So the fatigue lifetime of solder joints and its distribution characteristic enhance substantially. The theories of fluid dynamics and heat transmission are used to calculate the decrease of gas fluid velocity and the corresponding reduction of mean coefficient of heat transfer (h/sub m/).

Fatigue Lifetimes of PBGA Solder Joints Reflowed at Different Conveyor Speeds

The shear cycle fatigue lifetimes of plastic ball grid array (PBGA) solder joints formed using different reflow profiles are studied in this paper. The profiles were devised to have the same “heating factor” but to have different conveyor speeds. The test results show that, by increasing the conveyor speed during reflow, the shear fatigue lifetime of solder joints can be improved substantially. On the other hand, the fatigue lifetime of the test specimens decreased with increasing the cycle displacement amplitude. Heat transmission analysis shows that increasing conveyor speed increases the cooling rate during solder solidification. SEM micrographs reveal that cracks initiated at the acute point near the PCB solder pad, then propagate along the interface of the bulk solder/IMC layer. The test results are ascribed to roughing interface of the bulk solder/IMC of the solder joints that results on increasing the cooling rate. The frictional sliding mechanism is used to explain the test results.

Response spectrum methods in tank-vehicle design: Olofsson, U., Svensson, T. and Torstensson, H. Exp. Mech. (1995) 35, 345–351

A mechanistic model for fatigue life prediction of solder joints has been developed. The model utilized fracture mechanics theory using J-integrals and assumed the crack propagation determines the fatigue lifetime of solder joints. The model is expressed in terms of crack length ‘α’, platic strain range ΔεP and temperature T. Constitutive relation and crack propagation of 62Sn-36Pb-2Ag solder were tested at various temperatures. Good agreement is found between the model and the experimental results. The model has been applied to leadless surface mount solder joints with FEM analysis, which provided the capability of the fatigue life prediction of solder joints of electronic packages under thermal cyclic loading.

A mechanistic model for fatigue life prediction of solder joints for electronic packages

A mechanistic model for fatigue life prediction of solder joints has been developed. The model utilized fracture mechanics theory using J-integrals and assumed the crack propagation determines the fatigue lifetime of solder joints. The model is expressed in terms of crack length ‘α’, platic strain range Δε P and temperature T. Constitutive relation and crack propagation of 62Sn-36Pb-2Ag solder were tested at various temperatures. Good agreement is found between the model and the experimental results. The model has been applied to leadless surface mount solder joints with FEM analysis, which provided the capability of the fatigue life prediction of solder joints of electronic packages under thermal cyclic loading.

Mechanical behaviour of eutectic SnAg and SnZn solders: Mavoori, H., Vaynman, S., Chin. J., Moran, B., Keer. L.M. and Fine, M.E. Materials Research Society Conference: Flec'tronic Packaging Materials Science VIII, San Francisco, California, USA 17–20 Apr. 1995), pp. 161–175

A mechanistic model for fatigue life prediction of solder joints has been developed. The model utilized fracture mechanics theory using J-integrals and assumed the crack propagation determines the fatigue lifetime of solder joints. The model is expressed in terms of crack length ‘α’, platic strain range ΔεP and temperature T. Constitutive relation and crack propagation of 62Sn-36Pb-2Ag solder were tested at various temperatures. Good agreement is found between the model and the experimental results. The model has been applied to leadless surface mount solder joints with FEM analysis, which provided the capability of the fatigue life prediction of solder joints of electronic packages under thermal cyclic loading.