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Thermally induced stresses created during package manufacturing and their roles in mechanical failure are important issues for the microelectronic industry. In the present paper, a numerical analysis of the die embedding process into a printed circuit board by means of the package assembling and lamination is presented. The complex package consisting of a silicon die, an adhesive, a copper foil, an epoxy resin and prepregs (an E-glass woven structure pre-impregnated with an epoxy resin) is investigated in terms of warpage and stress development. Both are mainly introduced due to a mismatch of coefficients of thermal expansion and particularly to shrinkage of the polymer parts (adhesive, epoxy resin). Their impact on possible package failures is discussed. A two-dimensional axisymmetric numerical model is employed for investigation of the embedding process flow. Temperature dependent material properties for all materials are used in the analysis. A special focus is set on the orthotropic properties of the prepreg materials. Those are analytically homogenized based on the lamination theory of plain woven fabric composites and implemented into the numerical model. The numerical results of embedding process steps are validated experimentally by an X-ray diffraction method (Rocking-Curve-Technique) showing a good agreement of the calculated and measured curvature radius values.

International audience; In recent years, in order to increase density and performance of electronic boards, components are embedded in internal layers of printed circuit boards (PCBs). The reliability of this new technology has to be investigated to ensure the working of the electronic boards submitted to harsh environment and long mission profiles. To study the thermo-mechanical behavior of these boards, finite element simulations have been performed. It is observed that embedded passive chips are subjected to complex loading during the lamination process, due mostly to shrinkage of the resin, differences in material properties and also because of temperature excursion. The effects of material parameters and of the geometrical configuration are investigated in details. It will be shown that the generated stresses are not critical for the passive chip size considered in the present work.

This paper deals with the design of Q-band filters using a low-cost multilayered Printed Circuit Board (PCB) substrate. In order to meet strong electrical specifications, the Substrate Integrated Waveguide (SIW) technique has been used to take profit of the complete build-up of the multilayered PCB. Advanced fabrication techniques of vias and micro-vias have also been developed in this project to implement 4th and 6th-order filters in this technology. The challenge here is to use a standard PCB process to design complex microwave devices that usually require accurate fabrication process and very low tolerances, especially in such frequency ranges. Based on that, two 2.8x8mm² prototypes have been designed, simulated and fabricated on a 1mm-thick PCB made of copper and blend of high performance resin material. Regarding the results of these filters, measured insertion & return losses are in a very good agreement with the simulation while exhibiting high rejections and low footprint.

The knowledge of thermally induced strains created during the assembly in Printed Circuit Boards (PCB) is an important issue for electronic packages. In the assembly process, a thin silicon-chip is attached onto a copper foil. The curing of the adhesive is followed by the cooling down of the assembled structure to room temperature. The different properties of the involved materials and the geometry of the structure induce stresses and deflection in the substrate, which can become critical for the further lamination process. In this work, the chip assembly process is investigated by means of a parametric FE analysis. The aim is to estimate the stress distribution in the silicon die and the deflection (warpage) of the entire architecture based on the assembly conditions. The key material properties (i.e. thermal expansion coefficient (CTE) and elastic constants) of all involved materials were determined as a function of the temperature (process relevant temperature up to 200°C) and used as input for the FE model. Special attention has been given to the determination of the volumetric shrinkage of the adhesive during the curing. The results predicted by the FE model are validated with experimental measurements using an X-ray diffraction method (Rocking-Curve-Technique), which enables the deflection of the attached silicon die to be determined. Good agreement between simulation and experiments is achieved.

With the trend towards increasing complexity of Printed Circuit Boards (PCB), there has been considerable interest of investigation of the embedding process. The main focus has been set on the first step, the chip attachment by using an adhesive. Investigation of the adhesive thickness underneath the component by a numerical and an analytical model has been provided. The numerical model was produced with commercial program Ansys FLUENT. The results of both models are compared with experimental data to validate the models.

The aerospace and defense electronics industry leans henceforth on the technologies developed for consumer applications, particularly for digital boards. However, the requirements of aerospace and defense products in terms of reliability and mission profile are tougher than those for consumer ones. In addition, with the increase of circuit density in electronics and the arrival of new technologies of printed circuit boards (e.g. stacked microvia, embedded active components), the PCB build-up construction is more and more complex and becomes a critical element for the reliability of the solder joints of the electronic components assembled on PCB, also called second-level interconnects. The material characterization results showed that the physical data supplied by the manufacturers of base materials are not sufficient to represent the mechanical behavior of the PCB. The mechanical behavior of a whole PCB build-up is very dependent on its total resin and glass-fibers contents. The conclusions of this comprehensive design-of-experiments study demonstrate the impact of the PCB build-up construction on second-level reliability. In particular, test results point out the strong influence of the total resin-content, on the solder joints reliability of fine-pitch lead-less packages.

The Flexible Printed Circuits (FPC) used in high-end applications have some specific characteristics. It has a more complex build-up and must be compatible with repair processes. Moreover, they are used in harsh environment and long mission profile. Current FPC design are based on industrial standards, which propose design rules, such as minimum bending radius calculated from the maximum accepted copper elongation. This work is part of a large study focused on the development of a new generation of digital board solutions for electronic interconnection. In this paper, a finite element simulation study will be applied to FPC bending analysis beyond industrial standard limits. As a conclusion, we propose to consider the maximum copper strain and the bending shape for the minimum bending radius definition.

Embedded electronics merge always more and more enhanced functionalities, which implies that the printed circuit boards (PCB) need to achieve higher integration levels. Furthermore, signal integrity must be ensured, and the increasing use of multi-gigabits serial links requires a detailed analysis of the electrical behavior of tracks and vias for frequencies up beyond 10MHz. Thus, the different stack-up are enhanced in order to satisfy data rate beyond 10 Gbps. This paper relies on stacked microvias, which are a very innovative technology permitting a better level of integration compared to usual microvias or through hole vias. Indeed, they have a very good electrical behavior on a large frequency range (DC to 18 GHz) contrary to classical through hole via where possible stub effects deteriorate signal integrity. Moreover, it is easier to optimize the stacked microvia structure compared to standard microvias. Electrical characterization of these vias structures are evaluated through measurement on test vehicles and 3D modelling using CST Microwave Suite.

Latest electronic component package types are pushing the need to more efficiently remove the dissipated heat using optimized thermal paths going through the printed circuit board (PCB) to reach PCB inner thermal planes. So, to optimize board cooling, the designer has more and more to deal with PCB architecture including high density interconnect (HDI) technology, which relies on small diameter laser drilled micro-vias. Compared with conventional PCB technologies, HDI creates denser interconnect substrates, containing multilevel micro-via structures that play a decisive role in the miniaturization of circuit boards but will exacerbate the component cooling design complexity. To improve the understanding of conventional and future configurations of via structure and their influence on the component thermal performances, a study was leaded on an micro lead frame package, which is now mainstream for both analog and digital functions. For still air conditions, the thermal simulation results show that via and micro-via structures allow to drain more than 90% of the component power through the PCB metallic planes and are mandatory to limit the temperature excess. Thus, the thermal modeling of the latest 3D Integrated Circuit is reinforcing the need to simulate in more thin details its board surrounding architecture as well as its packaging. However, a fine detailed modeling of board layers layout always exceeds the simulation tool capabilities and requires new modeling methodologies able to define the most significant thermal model. Based on DEvelopment of Libraries of PHysIcal models (DELPHI) methodology, the creation of a compact thermal model, compliant to a set of boundary conditions was investigated for a local board area. The thermal behavior prediction, found to be within ± 5% of error, demonstrates the feasibility of extending the boundary condition independence principle to board modeling in order to achieve a more efficient and accurate board cooling optimization.

International audience; For SnAgCu alloys, the results of previous studies suggest that high-temperature thermal ageing causes quick and significant deterioration of their mechanical properties. However, the acceleration law of thermal ageing and the relationship between thermal ageing and the cyclic mechanical behaviour remain unknown. The aim of this study was to investigate the influence of isothermal ageing on the cyclic mechanical behaviour of Sn3.0Ag0.5Cu. First, ageing conditions were defined by taking into account the in-field operational conditions. Then, for all ageing conditions (75 °C, 125 °C and 150 °C up to 6500 h), the Vickers hardness was measured and the changes in this value were analysed during thermal ageing. At the same time, cross-polarised light microscopy observations on the same samples demonstrated the relation between the decrease in hardness and the changes in the microstructure for various samples. Finally, reversed mechanical cyclic tests were carried out at room temperature on specimens before and after ageing (125 °C, 500 h) in various conditions (strain rate / strain amplitude / dwell time).

The content of this paper is based on the study published at ESREF 91 in Bordeaux under the title ‘Plastic Encapsulated IC's in military equipments: reliability prediction modelling’. The first paper introduced the theoretical aspects of plastic encapsulated IC reliability prediction modelling. This paper presents the results of statistical studies done to complete the model with numerical data. Dependence of failure rates on year of manufacturing, dependence of thermo-mechanical failure rate on die diagonal, distribution of the quality of ICs in the market, and environment factor defect values are the principal topics addressed in this paper.

International audience; For the SnAgCu alloys, previous hardness test results suggested that high temperature thermal ageing causes a quick and significant drop in the mechanical properties. However, to date, the acceleration law of thermal ageing and the relationship between thermal ageing and fatigue mechanical behavior of SnAgCu alloys are still unknown. The aim of this paper is to understand the mechanical changes during thermal ageing of Sn3.0Ag0.5Cu alloy and their impact on solder joint reliability under mechanical stresses. In a first part, influence of thermal ageing on mechanical behavior is analyzed by means of hardness tests, reversed tensile tests on dog-bone specimens and compression test on solder balls used for electronic components. In the second part, the impact of thermal ageing on the solder joint reliability is analyzed thanks to torsion tests on assembled boards. The results show systematically a decrease of 20–60% of the mechanical properties or of the number of cycles to failure (in the case of torsion test). These results lead to enlarge tests conditions in order to define the fields where the influence of thermal ageing cannot be neglected.

The objective of this work is to analyze the link between the room temperature cyclic mechanical behavior and the evolution of the microstructure of Sn3.0Ag0.5Cu alloy before and after thermal ageing. Because the microstructure of solder joints may be very different from the one in bulk specimens, the study was divided into two parts: the first one studies the bulk alloy and the second one the same alloy at the solder joint scale. In the first part, cyclic tensile tests were carried out on specimens before and after ageing in various conditions. Regarding the experimental mechanical responses, two viscoplastic constitutive models were chosen and characterized from these cyclic results for each ageing condition. In the second part, compressive tests on solder balls were achieved. Five diameters between 250 μm and 760 μm were analyzed, representing many kinds of BGA packages. The experimental results have been compared with finite elements simulations using the constitutive models and associated parameters coming from the first part. A good agreement is obtained.

The manufacturing process of Printed Circuit Boards (PCB) with embedded active components requires several modifications on the build-up layer configuration, including the use of thinner layers and heterogeneous composite materials. From the point of view of second level interconnects the increase in density and complexity of the build-up of electronic board leads to an increase of the total resin-content. As demonstrated in a previous work, this increase of the ratio between resin and glass has a major consequence on the mechanical behavior of the assemblies, particularly on the fatigue resistance of component solder joints.

This paper introduces a reliability prediction model for plastic encapsulated integrated circuits to be used in professional or defence electronics applications. The first part is a comparison between different reliability prediction models: their hypotheses, assumptions and validity domains are examined; constructive criticism is made and model amendments proposed for plastic encapsulated ICs reliability prediction. The second part presents the model itself. It addresses also thermal and environmental aspects. The third part explains how numerical values are found to fill the model and how it reflects the reliability of today's state-of-the-art of plastic encapsulation. In conclusion, we present the improvements that this model can bring to reliability prediction, in the particular case of plastic packages.

Reliability of SnAgCu solder joints under mechanical stress is not proven, in particular for Aeronautic and High Performance (AHP) products. They are subjected to high temperatures, severe mechanical stresses and long-term mission profiles. This work is comprehended within a larger study, which has as objective the characterization of the SnAgCu alloys mechanical behaviour at the solder joint scale and the influence of thermal ageing on it. The aim of this first work is to improve the understanding of the relationship between the microstructural and mechanical behaviour evolution of SnAgCu alloys under thermal ageing.

The Aerospace and High Performance (AHP) electronics industry leans henceforth on the technologies developed for consumer applications. However, the requirements of AHP products in terms of reliability are stronger than for consumer ones.

Electronic second level interconnect reliability characterization by accelerated thermal-cycling (ATC) test for long-term mission profile is costly and high time consuming. In order to reduce test duration, the torsion test was applied using some specific test parameters to reproduce the same failure modes found in ATC tests and in the field. To define the torsion test parameters, we carried out a complete design of experiments varying the values of temperature, torsion angle and dwell time. The test results indicate a strong dependence of the number of cycles to failure and the three torsion parameters. In this paper, we present the finite element analysis techniques applied to predict lifetime of ball grid array (BGA) assemblies under torsion test. The main objective is to interpret the torsion test program results and to develop a damage law for electronic interconnects under torsion test. The results suggest that solder joint damage under torsion test is induced by two different failure mechanisms: the damage generated by instantaneous plastic strain and the damage generated by creep plastic strain.

Accelerated reliability tests are used to evaluate product life and to ensure a good fit with mission profile. Adequate detecting failure methods and criteria are fundamental to ensure the validity of the test results. In electronic interconnect reliability tests, several types of in-situ electrical continuity methods or manual resistance measurements with crack length analyses are used as failure indicator. Continuous monitoring at high sampling rate shows intermittent signals before permanent failure. In this paper we present a new test approach to improving physical understanding of these intermittent failures. Two different test benches are used to monitor BGA component solder joints under stress. Cross-section analysis, electrical circuit models and signal analysis are used to highlight the relationship between crack propagation and electrical continuity. Finally, basic electric contact theory is applied to explain resistance value fluctuations before permanent failure. The results suggest that high sampling rate in-situ monitoring methods have to be used in order to have an appropriate failure criterion and consequently be more representative of reliability results for electronic interconnects in the field.

This paper deals with electronic board assembly reliability studies, where most of the failures in the field are known to be caused by electrical discontinuities, and often intermittent ones. To choose the test method and to define the testing conditions, the mission profile has to be evaluated. It is necessary to verify and consider all the possible failure mechanisms in order to avoid any violation of acceleration factor hypothesis for the reliability prediction. The test vehicle has to be representative of the real products and to take into account all the relevant parameters which can change the test results, like raw materials, subparts dimensions, etc. The last point, and one of the most important, is the failure detection. This paper illustrates a methodology applicable to the second level interconnect reliability evaluation, and proves that the early detection of intermittent failures is necessary.

More than 10 years ago a so-called mechanical deflection system (MDS) for highly accelerated tests has been developed in order to evaluate the solder joints reliability. The objective was to replace long accelerated thermal cycling (ATC) tests by shorter mechanical ones. This promising concept has not been recognized as an industrial standard test method because of the misunderstanding of solder joint loading conditions. In the field, fatigue failures of solder joints are principally induced by shear stress as a consequence of relative displacement between package and board solder pads. Indeed, any accelerated test should take it into account. Based on this fact, this work is focused on the understanding of stress distribution and on the definition of torsion test conditions to ensure the fact that the solder joints are stressed in shear mode. Three main actions, finite element analysis, dedicated test program and strain gage measurements, have been conducted in parallel to guaranty consistency of data results and model calibration. Firstly, on the board we observed shear strains as the main behaviour and important edge effects for low and high torsion angles values. An area of homogeneous strain was identified: finite element analysis (FEA) and strain measurements were in good agreement. Secondly, on the boards equipped with BGA (ball grid array) package, we analyzed the stress distribution in solder joints. Experimental torsion tests and cross section analyses were made to identify the failure mode. Components placed in the homogeneous strain area showed equivalent failure mode and the observed cracks confirmed the shear stress as fatigue mechanism

This paper presents TH-CSF3, a reliability prediction model for plastic encapsulated integrated circuits used in rugged environment or military electronics applications. First part is an analysis of diffierent reliability prediction models: their hypotheses, assumptions. validity domains are examined; constructive criticism is made and model amendments are proposed for plastic encapsulated ICs reliability prediction. Second part presents the model itself and the methodology used to built it. It addresses how physical parameters which have in influence on the predicted reliability are inuoduced. Third part is a presentation of first calculations made with do model. In conclusion, we present the improvments that this model can bring to reliability calculation methods, in particular for plastic packages.

This paper proposes a new approach of electronic components reliability using Bayesian statistics. The purpose is to estimate the failure rate in use conditions through data from accelerated tests. Priors densities used in the model has been built with physics considerations and simulations. Furthermore, this work provided new forms of accelerated factors. >

The authors describe the strategy and the main results of the first phase of a program whose goal is to introduce PICs (plastic integrated circuits) in certain types of military equipment. The first phase of the French Ministry of Defense's Plastic Component Plan (PCP) has demonstrated the realistic applicability of PICs in military equipment. During the test program, PICs have been able to survive in very severe environmental conditions (such as HAST, or highly accelerated stress test). Failure mechanisms are not related to corrosion alone, and it is obvious that package integrity is a key factor for achieving good component reliability. In addition, a close relationship between package and soldering process for SMDs (surface mounting devices) dictates the need to define a new military standard which takes into account the specificity of plastic SMDs and user constraints. >

Important topics for electronic packages are thermally induced stresses created during package manufacturing and their role in mechanical failure. In the present paper, an analytical and a numerical analysis of the assembly process (component attached with an adhesive to a copper foil) is investigated. This process is prior to the lamination of the printed circuit board. Stresses develop due to a mismatch of coefficients of thermal expansion and particularly to shrinkage associated with adhesive polymerization. The analytical investigation is based on the classical laminate theory and an interfacial model. The three-dimensional numerical finite element model is capable to use geometric and material properties which are not possible to investigate analytically. In particular, the influence of the adhesive meniscus and plastic material models for copper and adhesive are investigated. The models are validated experimentally by an X-ray diffraction method (Rocking-Curve-Technique) showing a good agreement of the calculated and measured curvature radius values.