Surface Mount Technology Solder Joints Research Articles

Thermal Induced Interface Mechanical Response Analysis of SMT Lead-Free Solder Joint and Its Adaptive Optimization.

Surface mount technology (SMT) plays an important role in integrated circuits, but due to thermal stress alternation caused by temperature cycling, it tends to have thermo-mechanical reliability problems. At the same time, considering the environmental and health problems of lead (Pb)-based solders, the electronics industry has turned to lead-free solders, such as ternary alloy Sn-3Ag-0.5Cu (SAC305). As lead-free solders exhibit visco-plastic mechanical properties significantly affected by temperature, their thermo-mechanical reliability has received considerable attention. In this study, the interface delamination of an SMT solder joint using a SAC305 alloy under temperature cycling has been analyzed by the nonlinear finite element method. The results indicate that the highest contact pressure at the four corners of the termination/solder horizontal interface means that delamination is most likely to occur, followed by the y-direction side region of the solder/land interface and the top arc region of the termination/solder vertical interface. It should be noted that in order to keep the shape of the solder joint in the finite element model consistent with the actual situation after the reflow process, a minimum energy-based morphology evolution method has been incorporated into the established finite element model. Eventually, an Improved Efficient Global Optimization (IEGO) method was used to optimize the geometry of the SMT solder joint in order to reduce the contact pressure at critical points and critical regions. The optimization result shows that the contact pressure at the critical points and at the critical regions decreases significantly, which also means that the probability of thermal-induced delamination decreases.

Evaluation of the relationship between stress and lifetime of Pb-free solder joints subjected to vibration load using a generalized local stress approach

The article proposes a generalized high cycle fatigue evaluation methodology for solder joints based on a local stress finite element method (FEM) and compares with experimental results. A method to predict the damage initiation of surface mount technology (SMT) solder joints is accomplished in this article by making use of generic coupon level SAC387 solder specimens. High cycle fatigue (HCF) experiments conducted on generic solder specimens are followed by means of FKM guidelines, which are translated to microelectronic elements for the first time. The FEM predicted lifetime values of solder joints agree with the experimental results performed on SMT components. In addition, the overall results show that the predicted values act as a threshold damage line from which the solder joint failure regimes can be differentiated. The results also show the differences in the predicted damage line and failure line for SMT solder joints.

SMT Solder Joint Inspection via a Novel Cascaded Convolutional Neural Network

Due to the excellent self-learning ability of deep learning, we propose a novel deep-learning-based method to inspect surface-mount technology (SMT) solder joints in this paper. In contrast to the state-of-the-art learning-based methods in which low-level features are extracted before learning, our method directly implements the inspection task without low-level feature extraction, which is based on a novel cascaded convolutional neural network (CNN). Three kinds of CNNs with different network parameters compose the proposed cascaded CNN. First, one kind of CNN is employed to adaptively learn the regions of interest (ROIs) of SMT solder joint images. Then, both the learned ROIs and the entire solder joint images are fed into the other two kinds of CNNs, respectively. Finally, inspection results are achieved by the learned cascaded CNN. Comparison experiments indicate that our proposed method can achieve more excellent inspection performance for SMT solder joints than that of the state-of-the-art methods.

A Study on the Effect of Ageing and Intermetallic Compound Growth on the Shear Strength of Surface Mount Technology Solder Joints

The effect of ageing and intermetallic compound formation on the surface mount solder joints and its shear strength behavior under extreme mechanical and thermal conditions have been discussed in this paper. The specimens used are solder paste (Sn3.8Ag0.7Cu), bench marker II printed circuit boards (PCB), resistors 1206 and the fabrication of solder joints makes use of conventional surface mount technology (SMT). Reflow process was carried out at a peak temperature of 250 °C and the test samples were exposed to isothermal ageing at a constant temperature of 150 °C for a period of 600 h. Shear test was conducted on the PCB’s. The shear strength of the solder joints rapidly increased during isothermal ageing to a certain time period and then started decreasing. Field emission scanning electron microscopy (FESEM) micrograph of the solder joint and energy dispersive X-ray (EDX) was performed on the solder sample to verify the formation of intermetallic compounds.

Damage Mechanics of Surface Mount Technology Solder Joints Under Concurrent Thermal and Dynamic Loading

In the electronic industry, the dominant failure mode for solder joints is assumed to be thermal cycling. When semiconductor devices are used in vibrating environment, such as automotive and military applications, dynamic stresses contribute to the failure mechanism of the solder joint, and can become the dominant failure mode. In this paper, a damage mechanics based unified constitutive model for Pb40/Sn60 solder joints has been developed to accurately predict the thermomechanical behavior of solder joints under concurrent thermal and dynamic loading. It is shown that simultaneous application of thermal and dynamic loads significantly shorten the fatigue life. Hence, damage induced in the solder joint by the vibrations have to be included, in fatigue life predictions to correctly predict the reliability of solder joints. The common practice of relating only thermal cycling induced inelastic strain to fatigue life can be inadequate to predict solder joint reliability. A series of parametric studies were conducted to show that contrary to popular opinion all dynamic loading induced strains are not elastic. Hence, vibrations can significantly affect the fatigue life and reliability of solder joints in spite of their small mass.

Thermo-Elasto-Plastic Stress Analysis in Equilibrium Profile of SMT Solder Joints.

Recently, surface mount technology (SMT) in an electronic packaging is playing a leading role compared to the plated-through-hole technology. SMT allows to place more electric components on a printed circuit board. Many investigations on mechanical and thermal properties of solder have been conducted numerically and experimentally, since the electric components are mounted by only soldering on the board. It is hard to examine the failure of electric components in experiment, since the size of solder joint is relatively small. In this case, a simulation technology is very useful for evaluating the reliability of SMT solder joint. In the present paper, before performing the stress analysis of SMT joints, the shape of solder joint was first determined numerically by solving a multiregion problem considering the surface tension of molten solder and the gravity. The joint profile changing from an initial profile to an equilibrium one was simulated by using a finite difference approximation for time and the boundary element method for domain. The scheme for remeshing technique which is combined a cubic spline and a base spline to interpolate nodes on the free surface is presented in this paper. After that, a nonlinear and thermo-elasto-plastic stress analysis using MARC was performed to study the deformation behavior of solder joints subjected to a cyclic thermal loading. Profile data of SMT solder joint employed for finite element analysis were used the equilibrium profile calculated by BEM. It was shown that a thermal stress concentration occurred in joints with a large quantity of solder and with a small gap between the chip and the base plate. Finally, it was shown that the shape of SMT solder for improving the reliability has equally a little quantity of solder at both sides, a little quantity of solder at upper fillets and a small height between the chip and the base plate.

Fatigue life estimation of surface mount solder joints

A novel and direct method to measure the stress-strain properties of surface mount solder joints is proposed in this paper. The specimen used in the experiments is a quad flat pack (QFP)-solder-printed circuit board (PCB) assembly and the fabrication of solder joints makes use of conventional surface mount technology (SMT). Mechanical cycling and thermal shock testing can be conducted directly on the specimen after assembly. In this manner, the specimen represents practical SMT solder joints in electronic products as far as possible. It is shown that the joint strain and stiffness of chip modules are good evaluation indices to reveal the fatigue status of solder joints. It is further proposed that the criterion of 50% load drop should be used for defining the fatigue life of solder joints. Finally, it is recommended that the total displacement /spl Delta//spl delta//sub 2p/ be used to measure the strain-fatigue life relation for both leaded and leadless joints.

A study of failure of SMT solder joints under thermal cycles by statistics

In this paper, a simulated ceramic chip carrier has been designed to study the reliability of SMT (surface mount technology) solder joints under thermal cycles. Using this simulated ceramic chip carrier, the influence of the solder joint position, the temperature range of thermal cycle and the dwell time on the reliability of SMT solder joints under thermal cycles has been studied using statistics. The results show that the reliability of middle solder joints (MSJ) is statistically higher than that of side solder joints (SSJ). With a rise in the maximum temperature of the thermal cycle and the increase of dwell time, the reliability of SMT solder joints reduces notably. The solder joint reliability of the gold-plated carrier has a greater sensitivity to the dwell time and maximum temperature of the thermal cycle than that of the nickel-plated carrier, which may be related to the intermetallics between the solder and the metal plating of carrier.

A dislocation model of shear fatigue damage and life prediction of SMT solder joints under thermal cycling

A damage model of low cycle shear fatigue has been developed in dislocation theory. On the basis of this model, a formula including the factors of thermal cycle temperature, dwell time, and atmospheric oxidation has been established to predict the life of surface mount technology (SMT) solder joints under thermal cycling. This formula has been verified by experiments on the specimens of actual SMT assemblies. The results show that the life formula established coincides with the experimental results.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Automated Finite-Element Mesh Generation for Surface Mount Technology Solder Joints

The ultimate goal of this work is an improved method to assess the significance of anomalies in surface mount technology (SMT) solder joints, by relating them to field performance and reliability. The fitness-for-purpose approach can be applied to SMT solder joints by relating specific characteristics or flaw indications in individual solder joints to their likelihood of failure, through finite element analysis. An effort is underway to automate the finite element modeling of actual solder joints by generating meshes from optical and X-ray inspection data in the form of thousands of surface points. Computer programs have been written to convert these surface points to finite element meshes. Two trial data sets have been meshed, one from an X-ray laminography system and one from a machine vision system.