Solder Joints In Electronic Packaging Research Articles

Strain Energy Density Criterion for Reliability Life Prediction of Solder Joints in Electronic Packaging

This study concerns the prediction of crack growth rate for solder joints in electronic packages under thermal cycling. The crack growth rate, which is dependent on the intrinsic solder property and the current stress state, is calculated based on the strain energy density criterion. The critical value of the strain energy density represents the intrinsic property of the solder. The comparison of the crack growth predictions with the experimental measurements demonstrates the applicability of the strain energy density criterion for the reliability life prediction of solder joints.

An experimental technique for the strain measurement of small structures using pattern recognition

For an accurate measurement of the material behavior of small structures, an optical experimental technique is proposed. The test method uses a dual field of view microscope and the pattern matching algorithm. The dual field of view microscope can separately magnify the images of two adjacent regions to enhance the measurement resolution. The magnified views of the dual field of view microscope are captured by CCD cameras and the relative deformation is measured by tracing patterns in the images. A pattern matching and tracing algorithm was adapted to measure the movement of region of interests (ROI) in real time. Using the movement information of the patterns, the strain of a specimen can be obtained. This technique is non-contact as well as easy to apply to a specimen. It can be also applied in various types of specimens without any specimen preparation. Using this experimental technique, the deformation of solder joints in electronic packaging and the strain of the nickel thin film are successfully measured.

Experimental damage mechanics of microelectronic solder joints under fatigue loading

Fatigue damage is a progressive process of material degradation. The objective of this study is to experimentally qualify the damage mechanism in solder joints in electronic packaging under thermal fatigue loading. Another objective of this paper is to show that damage mechanism under thermal cycling and mechanical cycling are very different. Elastic modulus degradation under thermal cycling, which is considered as a physically detectable quantity of material degradation, was measured by Nano-indenter. It was compared with tendency of inelastic strain accumulation of solder joints in Ball Grid Array package under thermal cycling, which was measured by Moiré interferometry. Fatigue damage evolution in solder joints with traditional load-drop criterion was also investigated by shear strain hysteresis loops from strain-controlled cyclic shear testing of thin layer solder joints. Load-drop behavior was compared with elastic modulus degradation of solder joints under thermal cycling. Following conventional Coffin–Manson approach, S– N curve was obtained from isothermal fatigue testing with load-drop criterion. Coffin–Manson curves obtained from strain-controlled mechanical tests were used to predict fatigue life of solder joints. In this paper it is shown that this approach underestimates the fatigue life by an order of magnitude. Results obtained in this project indicate that thermal fatigue and isothermal mechanical fatigue are completely different damage mechanism for microstructurally evolving materials.

Coarsening in BGA Solder Balls: Modeling and Experimental Evaluation

The reliability of solder joints in electronic packaging is becoming more important as the ball grid array (BGA) develops rapidly into the most popular packaging technology. Thermal fatigue of solder joints has been a reliability concern in the electronic packaging industry since the introduction of surface mount technology (SMT). Microstructural coarsening (phase growth) is considered to be closely related to thermomechanical fatigue failure. Many researchers proposed coarsening models for bulk scale metals. But these models have never been verified for micron-scale actual BGA solder balls. In the present study, three different phase growth models are investigated experimentally on BGA solder balls in a real-life electronic package. Model simulations obtained from three models were compared against test data. The best performing model was chosen for finite element fatigue reliability studies based on continuum damage mechanics.

패턴 인식을 통한 미소 구조물의 변형 측정 기법 개발

For an accurate measurement of the material behavior of small structures, a new optical experimental technique is proposed to measure the deformation. The test method uses the dual microscope that can measure the relative deformation of two adjacent regions. The magnified view is captured by CCD cameras and the relative deformation can be measured by the pattern matching and tracing method. Using this experimental technique, the deformation of solder joints in electronic packaging and the strain of the nickel thin film are measured.

Optimisation modelling for flip‐chip solder joint reliability

This paper details and demonstrates integrated optimisation‐reliability modelling for predicting the performance of solder joints in electronic packaging. This integrated modelling approach is used to identify efficiently and quickly the most suitable design parameters for solder joint performance during thermal cycling and is demonstrated on flip‐chip components using “no‐flow” underfills. To implement “optimisation in reliability” approach, the finite element simulation tool – PHYSICA, is coupled with optimisation and statistical tools. This resulting framework is capable of performing design optimisation procedures in an entirely automated and systematic manner.

Elastic-Plastic-Creep Simulation of Pb/Sn Solder Alloys by Separation of Plastic and Creep.

For the accurate finite element analysis of solder joints in electronic packaging, a constitutive model which can describe the large time dependent deformation has been required. The requirement is not only the proposal of such a constitutive model but also the establishment of the determination method for the material parameters used in the model. In this study, we discussed on the constitutive model for solder alloys and the determination method of the material parameters for the model. First, the constitutive model that can divide the inelastic deformation into the plastic and creep parts is proposed. Next, we show the numerical method for the determination of the material parameter used in the model. In this method, the material parameters for creep part are determined firstly by pure tensile tests under several strain rates, and the creep strain is calculated. Subtracting the calculated creep strain from the pure tensile deformation, the stress-strain relation for the time independent parts is obtained. Then, the material parameters for the time independent parts such as elastic and plastic deformation are easily determined from the obtained stress-strain relations. The simulations of the stress relaxation after several different preloading are carried out to verify the applicability of the proposed model and numerical method.

The necessity of reexamining previous life prediction analyses of solder joints in electronic packages

There are several different constitutive relations for describing the creep behavior of solder to predict the fatigue life of a solder joint. The differences among these constitutive relations for fatigue life prediction of electronic packages are unknown because analysts using finite element programs such as ABAQUS or ANSI'S are generally limited to specific built-in material models. The objective of this study is to implement a procedure that allows the use of various creep models in the analysis of electronic packages using ANSYS. Special user routines are developed so the user can incorporate virtually any creep relation and determine the inelastic strain energy density developed in the three-dimensional solid elements. Comparisons are performed for the modified creep routines and the viscoplastic formulation of Anand's model in ANSYS. It is found that the scheme used by ANSYS to determine plastic work density is incorrect and will be remedied in a future release. The implications of this revision to ANSYS are critical because a change in scheme will make comparisons with past studies and analyses difficult. The value of the empirical parameters based on previous analyses, which are widely used in the prediction of package fatigue life, will have to be reexamined.

Thermal deformation measurement of the solder joints in electronic packages using electron moiré method

AbstractIn this paper, electron moiré method is used to measure the thermal deformation of electronic packages. In order to observe the electron moiré fringe, a holographic grid was replicated on the cross section of the BGA type package at 150°C. This grid was fabricated on a glass plate using a moving point holographic system, and was replicated to measured area at high temperature. Under SEM, the holographic grid(specimen grid) and a programmed electron beam scan(master grid) interfere and form electron moiré patterns. The shear strain measurement technique using electron moiré method is described. Using the electron moiré method, the shear strains in the different solder joints were measured and analysed. Some useful results were obtained.

Dewetting of molten Sn on Au/Cu/Cr thin-film metallization

On Au/Cu/Cr thin film surface, a drop of molten Sn first spreads out to wet the surface, but it then pulls back to dewet. The latter is due to the spalling of Cu–Sn compounds and exposing the Cr surface to the molten Sn when all of the Cu film has been consumed by the wetting reaction. Dewetting is clearly undesirable for solder joints in electronic packaging; the phenomenon is presented here.

Parameters affecting thermal fatigue behavior of 60Sn-40Pb solder joints

Solder joints in electronic packages experience cyclical thermally induced strain when temperature fluctuations are encountered in service. This study investigates three parameters that affect the microstructure and therefore the thermal fatigue behavior of 60Sn-40Pb solder joints. These parameters are: 1) the effect of a tensile component in thermal fatigue, 2) solder joint thickness variations, and 3) hold time variations at the elevated temperature portion of the thermal cycle. Solder joints were thermally fatigued in a tension/compression deformation mode. Cracks developed both in the interfacial intermetallic layer (early in thermal fatigue) and in the coarsened regions of the microstructure of the solder joint (after many more cycles). The effect of joint thickness on solder joints thermally fatigued in shear was also explored. Solder joint thickness was found not to significantly affect fatigue lifetimes. The effect of an increase in the hold time at the elevated temperature portion of the thermal fatigue cycle was also investigated. It was found that time spent at the high temperature end of the fatigue cycle does not determine solder joint lifetime, rather it is the combination of the amount of deformation induced during thermal fatigue in concert with the elevated temperature.