A simple and physically meaningful analytical model is developed for the evaluation of the interfacial stresses in a simple lap shear joint (LSJ). The emphasis is on the “peeling” stress, i.e., the stress acting in the through-thickness direction of the joint. The model is a modification and an extension of the model developed earlier for the shearing stress. Based on the developed model, we were able to explain a paradoxical situation due to the “transverse groove effect” (TGE). This effect has been detected by one of the authors of this paper (Reinikainen) from the finite-element-analysis (FEA) computations: deep enough transverse grooves deliberately introduced in the LSJ adherends (“pins”) resulted in an appreciable reduction in the magnitude, and in a significant improvement in the uniformity, of the distribution of the interfacial shearing stress. It was determined that the stress relief due to the grooves was caused by the favorable effect of the increased interfacial compliance, while the adverse effect of the increased axial compliance of the pins (also due the grooves) was relatively small in a particular LSJ design and was suppressed by the favorable impact of the TGE. We show that the peeling stress in the LSJ is considerably lower than the interfacial shearing stress and that the TGE is even stronger for the peeling stress than for the shearing stress. This is because the grooves affect the peeling stress not only directly, through the increased interfacial compliance, but also indirectly, through the lower gradient of the interfacial shearing stress in the longitudinal direction. We show that this gradient can be reduced considerably if the interfacial compliance is increased, especially in a small size joint. We would like to point out that, although reasonably satisfactory agreement between the analytical and the finite-element analysis (FEA) predictions was obtained, the objective of our analysis was not so much to develop a more or less accurate analytical or a FEA model, but rather to demonstrate that the peeling stress, whatever technique is employed to evaluate it, can be reduced considerably by introducing the transverse grooves. The results of this article can be used in the analyses and design of LSJs, both in electronic packaging and beyond.

It is important for learning that students receive enough of educational feedback of their work. To get the students to be seriously disposed to the feedback it has to be personal, objective and consistent. In large classes ensuring such feedback can be difficult. Grading rubrics are a solution to the objectivity and consistency. ALOHA is an online grading tool based on rubrics which all the graders have to use. Particularly, ALOHA provides features that make the grading process more convenient for the graders and the teacher. By facilitating the graders work ALOHA allows them to focus more on feedback writing. To test the effectiveness of ALOHA in objectivity and consistency we did a comparative statistical analysis on the distribution of grades. The results supported the assumptions showing improvement resulting in similar distribution of grades amongst different graders who used the tool.

A solder is considered lead free if lead (Pb) content in it is less than 0.2 wt % (USA) and 0.1 wt % (EU). Sn-Ag-Cu (Tin, Silver, and Copper) solder is among the selected alloys as one of the options to replace tin-lead solders in electronic assemblies. In this paper is reported the mechanical and thermo-mechanical aspect of Sn-Ag-Cu solder alloys that have been tested for their deformation behavior. Commercially available Sn3.8Ag0.7Cu was considered as base alloy in this study. Constant stress and strain-rate tests were performed in tensile and shear configuration. Deformations were measured using bulk solder tensile specimens and grooved lap shear specimens which enabled a stress-state of nearly pure shear in the solder joint. The strain rate range was between 0.1/sec and 10 −6 /sec, and test temperatures were 25°C, 75°C and 125°C. Both freshly prepared and thermally aged samples were tested. The influence of Au addition in SAC solder alloy on it effect on the strength in tensile loading is also studied. The measured tensile stress-strain data were utilized to derive the constants for the visco-plastic Anand's constitutive model. Coefficient of thermal expansion (CTE) for those Sn-Ag-Cu lead (Pb) – free alloys were measured in the temperature range of −40 to 160°C using a thermo-mechanical analyzer (TMA). The tensile and shear properties of 95.5Sn3.8Ag0.7Cu solder and solder joint specimens were found to be dependent on test temperature and strain rate. The mechanical strength of SAC bulk solder and solder joint decreases with increase in temperature and increases with increase in strain rate. CTE for the SAC lead-free alloys were found to be relatively lower compared with tin-lead solder. The steady-state creep test data for 95.53.8Ag0.7Cu solder was curve-fitted to a hyperbolic-sine creep model. Despite change in solder specimen methodology and a change in lead free failure model methodology the material constitutive parameters developed are in line with similar studies.

A concern-based approach to support software comprehension and analysis is proposed. Concerns represent various aspects of a system that are interesting for some stakeholders, like features, architectural solutions, units of work, etc. Using concern-based queries on the software artefacts, new derived information on the system can be exposed. The results of the queries are also represented as concerns and added to the concern repository. The approach thus supports the analyzer in gradually building up an understanding on the subject system to be analyzed. The proposed approach and tool support is applied in the analysis of an industrial large-scale product platform and products built on top of this platform.

A concern-based approach to support software comprehension and analysis is proposed. Concerns represent various aspects of a system, like features, architectural solutions, units of work, etc., which are interesting for some stakeholders. Using concern-based queries on the software artefacts, new derived information on the system can be exposed. The results of the queries are also represented as concerns and added to the concern repository. The approach thus supports the analyzer in gradually building up an understanding on the subject system to be analyzed.

In this paper is reported the mechanical and thermomechanical aspect of SnAgCu solder alloys that have been tested for their deformation behavior. Commercially available Sn3.8Ag0.7Cu was considered as base alloy. The constant stress and strain-rate tests were performed in tensile and shear configuration. Mechanical deformations were measured using bulk solder tensile specimens and grooved lap shear specimens which enabled a stress-state of nearly pure shear in the solder joint. The strain rate range was between 0.1/sec and 10-6/sec, and test temperatures were 25°C, 75°C and 125°C. Both as-prepared and thermally aged samples were tested. The aging condition was 24hrs at 125°C. The measured tensile stress-strain data were utilized to determine the constants for the visco-plastic Anand's constitutive model. Thermo-mechanical properties like coefficient of thermal expansion (CTE) for those SnAgCu lead free alloys were measured in the temperature range of - 40 to 160°C using thermo-mechanical analyzer (TMA). The tensile and shear properties of 95.5Sn3.8Ag0.7Cu solder and solder joint specimens are highly dependent on test temperature and strain rate. The mechanical strength of SAC bulk solder and solder joint decreases with increase in temperature and increases with increase in strain rate. CTE for the SAC lead-free alloys were relatively lower compared with tin-lead solder. The steady-state creep test data for 95.53.8Ag0.7Cu solder was curve-fitted to a hyperbolic-sine creep model. The material constitutive parameters developed are in line with similar studies.

Many mass programming courses face the problems related to using multiple graders for student assignments: achieving objectivity and consistency in grading. Grading rubrics are a possible solution to this problem. ALOHA is an online grading tool that provides rubrics that all the graders have to use. ALOHA also provides features that make the grading process, including the writing of a feedback text, more convenient for the graders and the teacher.

Optimal parameter selection is a crucial step in improving the quality of electronic packaging processes. Traditional approaches usually start with a set of physical experiments and then employ Design of Experiment (DOE) based response surface methodology (RSM) to find the parameter settings that will optimize a desired system response. Nowadays deterministic computer simulations such as Finite Element Analysis (FEA) are often used to replace physical experiments when evaluating a system response, e.g., the stress level in an electronic packaging. However, FEA simulations are usually computationally expensive due to their inherent complexity. In order to find the optimal parameters, it is not practical to use FEA simulations to calculate system responses over a large number of parameter combinations. Nor will it be effective to blindly use DOE-based response surface methodology to analyze the deterministic FEA outputs. In this paper, we will utilize a spatial statistical method (i.e., the Kriging model) for analyzing deterministic FEA outputs from an electronic packaging process. We suggest a sequential method when using the Kriging model to search for the optimal parameter values that minimize the stress level in the electronic packaging. Compared with the traditional RSM, our sequential parameter selection method entertains several advantages: it can remarkably reduce the total number of FEA simulations required for optimization, it makes the optimal solution insensitive to the choice of the initial simulation setting, and it can also depict the response surface and the associated uncertainty over the entire parameter space.

System-in-Package (SiP) such as multi-chip or stacked die BGA modules with wirebond, flip-chip or hybrid interconnect are getting popular for advanced packaging applications. The design of SiP is more dependent on modeling as the package structure and failure mechanism are too complicated to be studied. It is known that drop impact reliability of lead-free BGA solder joints is a critical challenge. Drop impact life of IC packages mounted on board becomes a hot topic, especially for design and qualification of handheld electronic products. Actual drop test and sample preparation are very expensive and time-consuming, requiring much manpower in measurement and failure analysis, and therefore, there are limited drop test results reported to advise on the package design enhancement, especially for lead-free packages. In this paper, various design parameters are studied experimentally and numerically, to understand the effects of ball height, ball size, and ball layout. A thorough understanding of design variables on impact life of IC packages are obtained based on such well-designed and controlled experiments. On the other hand, more that 10 BGA packages with different package size, ball layout, package layout, and die thickness are tested with well-controlled drop tester. For the first time, an accurate drop impact life prediction model is established for lead-free (SnAgCu) BGA packages and modules, having good correlation with 16 cases of actual board level drop testing results. This quantitative approach is different from traditional qualitative modeling, as it provides both accurate relative and absolute impact life prediction. The validated model is applied to provide design guidelines for lead-free BGA and modules to improve their drop impact reliability. One point to be noted is that the relative performance of package may be different under board level drop test and thermal cycling test. Therefore, different design guidelines should be considered, depending on application and area of concern.

With the increased requirements for smaller size and more functions, hand held devices will use more and more small components to reduce the PWB areas. One of the solutions is stacked package. There are two kinds of stacked packages: one is die stacking and the other is package stacking. The package stacking is a more flexible solution for device manufacturers because the packages to be stacked could come from different vendors. All the packages can be tested separately before stacking so that there is no need for device manufacturers to acquire good dies or intellectual properties for die testing. In this study, the focus will be on the package stacking. The package stacking can be ASIC and memory stacking or memory and memory stacking. Three different stacked packages are selected for this study. Here the focus is on FEA modeling and simulation method for package stacking. Finally, the simulation results are compared with the results of thermal cycling test. A reasonable correlation is achieved based on current simulation method.

Three SnAgCu solder alloys (Sn2AgO.5Cu, Sn3.4AgO.8Cu, Sn4AgO.5Cu) have been tested to determine their deformation behavior in the temperature range 23-110/spl deg/C, strain-rates varying 10/sup -7/-10/sup -1/ 1/s. It is shown by optical micro-graphs of CSP solder joints that microstructure of SnAgCu may undergo through significant changes due to various loading conditions, which can occur during usage of microelectronic devices, such as thermal cycling, mechanical bending, and drop impact. The solidification microstructure consists typically of very large Sn-matrix colonies, with eutectic structure and intermetallic particles distributed within the colonies in cellular form. Typical observed temperature- and deformation-induced microstructural evolution includes recrystallization and twinning. The deformation mechanisms of the alloys have been predicted based on the values of measured activation energies and stress exponents. The constant stress and constant strain-rate tests have been performed in the shear configuration, which enables a stress-state of nearly pure shear in the solder joint. In the intermediate stress regime, the deformation appears to occur by the slip mechanism, and the rate is likely to be controlled by the dislocation climb process. The measured shear stress-strain data are utilized to determine the constants for the visco-plastic Anand's constitutive model.

The semiconductor industry is driving toward lead-free solder due to environmental concern and legislation requirement. The industry has also concluded that SnAgCu solder alloy so far is the best lead-free alternative to SnPb solder. Therefore, most existing and new packages have to be tested and qualified using lead-free solder. One of the critical concerns is board level solder joint reliability during thermal cycling test. In this paper, the methodology for an absolute life prediction is described for virtual qualification of packages. A good absolute fatigue life prediction requires an appropriate solder creep model and actual test data on packages. Two new sets of lead-free Anand's constants for SnAgCu solder are introduced for creep models. These Anand's creep models are compared with other lead-free and eutectic solder model and the relative design trend is similar. A fatigue corrective factor is introduced to integrate the different solder models together for convenient relative design enhancement with acceptable range of absolute life prediction. These fatigue corrective factors can also be used to compare different finite element modeling assumptions such as element size and solution time step. Subsequently, design analysis is performed to study the effects of 11 key package dimensions and material properties. It is found that the relative design trend for packages with lead-free and eutectic solder is similar. Therefore, the design guidelines established for the previous eutectic solder is still valid for lead-free solder.

This paper presents two design optimization approaches, the deterministic approach and the reliability-based approach, for the solder joint reliability of a 2/sup nd/-level land ball array (LGA) package under temperature cycling. The printed wiring board (PWB) thickness, Young's modulus, and coefficient of thermal expansion are considered as controllable design parameters. With the conventional deterministic design optimization, the solder joint plastic work per temperature cycle is taken as the design objective to be minimized. In the reliability-based design optimization, both the mean value of the plastic work and its variation are considered as the design objectives. Finite element simulations and response surface approximation are utilized to evaluate the thermo-mechanical performance in the design optimization procedure. A differential evolution algorithm serves as the optimum search engine. A quasi-Monte Carlo method is adopted to perform the probability analysis in the reliability-based design optimization. Finally, the optimal solutions from the two approaches are discussed and compared.

Land grid array IC-packages are gaining popularity among portable electronics, for low cost, mechanical reliability, direct Pb-free assembly process compatibility, and their low profile on the PWB. LGA technology is an excellent choice to fulfil future environmental requirements in thin and compact products. The reliability performance of 0.5 mm pitch LGA structure is compared to ball grid array (BGA). Reliability performance is evaluated through comparative tests designed for a portable environment. These tests consist of temperature cycling test for operation performance evaluation and board level drop test for mechanical shock durability performance evaluation. The stress distributions in LGA and BGA are analysed by the finite-element method (FEM). Furthermore, reliability investigation is done for LGA components using both standard SnPb- and Pb-free assembly processes. The differences in the reliability performance between the SnPb- and Pb-free assemblies are explained through microstructural analysis. Reliability issues relating to the transition from conventional assembly process to Pb-free process are discussed, based on the test and simulation results.

Many mass courses face the problems related to using mul- tiple graders for student assignments: achieving objectivity and consistency in grading. Grading rubrics are one possible solution to this problem. ALOHA is an online grading tool providing rubrics which all the graders have to use. ALOHA also provides features that make the grading process, includ- ing the writing of a feedback text, more convenient for the graders and the teacher. To test the effectiveness of ALOHA in objectivity and consistency we did a comparative sta- tistical analysis on the distribution of grades. The results supported the assumptions showing great improvement re- sulting in similar distribution of grades amongst different graders who used the tool.