Innovative thermo-mechanical prediction and optimisation methods for virtual prototyping of miniaturised electronic packages and assemblies

As a complement in Kitrons very strong service portfolio of quality analysis and reliability verification, in troubleshooting cases as for yield problems in running production and field return issues as an external service for customers or as an internal support for Kitron production sites. Based on technical or legal aspects a product re-design might be necessary. In redesign and cost reduction projects saving material cost and/or enhancing yield. This can be offered as an external service for customers or as an internal support for Kitron production sites. The service including use of methods and tools from the Mevipro project will be used in real customer cases. No other Scandinavian company competing with Kitron can today offer the added value of virtual prototyping. The business potential is especially obvious in the automotive industry with more and more electronics in cars and vehicles and the accelerating requirements of high reliability. The Swedish automotive industry is very strong and Kitron have several coustomers among manufacturers of cars and vehicles as well as among the automotive components suppliers. There is also potential in other high reliability application areas like defence electronics and medical electronics. The end-users of this service can be found among Scandinavian product-owners and components suppliers as existing Kitron customers today using manufacturing and/or engineering services. There is a clear possibility for Kitron to expand business with existing customer and also attract new customers with the new service and added value.

Combined experimental-numerical methodologies for failure analysis applicable in the field of microsystems and new electronic packaging solutions have been developed. The results are related to the in-situ determination of critical thermo-mechanical failure processes for electronic materials under thermal fatigue loadings. Additionally, a methodology related to materials interface fracture has been developed. Strength criterions based on elastic materials descriptions are commonly used in industry. In contrast, descriptions of materials non-linearity and related failure criteria as well as failure criteria based on fracture mechanics, required for a new quality of predictive capabilities, are proposed. The phenomenon of material fatigue was shown to be particularly important for several dominant failure modes induced by cyclic temperature changes. However, no standard testing methodology is available for thermal fatigue investigations. To fill the gap a combined experimental-theoretical procedure is proposed by the IZM, called the "Thermal Lap Shear Test". In collaboration with a subcontractor a laboratory prototype of a loading stage was developed for deformation of material compounds subjected to cyclic thermally induced shear loading. The test specimen is a single- or double lap shear specimen made from one material containing an arbitrary shaped joint. The joint can be made forming a layer, a cluster of bumps, or a similar array, and can contain cracks or interface cracks. It allows also investigations of fatigue crack initiation and propagation. The temperature loading can be applied in a thermal cycle equipment, i.e. an air-to-air thermal shock oven. Microscopic in-situ observation of the damage progress is one part of the methodology. The damage progress can also be monitored by electrical resistance measurement performed in parallel. The localized loadings in the joint have to be calculated by the finite element method. The experiment can be accompanied by quantitative deformation analysis by the microDAC Method®. This deformation measurement allows for checking of the constitutive material assumptions used in the FE-analyses. Both improved constitutive descriptions and damage properties of the joint material can result from the procedure. A second failure mode addressed was the interface delamination of electronic polymers on ceramic substrate. An interface fracture mechanics approach was developed to determine advanced failure measures. The theoretical framework was accompanied with an interface adhesion testing methodology. The test setup requires in-situ deformation measurement facilities and is combined with the microDAC Method®.

The goal of the project was to improve the currently available design for optimization algorithms, procedures and tools with a special focus on: - Reduce the number of required experiments by 40% compared with the presently available DOE methods, such as full-factorial design. - Develop methods that can result in more accurate models of the responses with less than 5% derivations with the computed results. - Develop an easy-to-use-and-modify application based on "MATLAB" that will be used for testing and verification of the elaborated prototyping algorithms. - Inclusion of the DOE/RSM algorithm in the existing software package OPTIMUS for testing purpose. All the above objectives were succeeded and finally contributed to a more efficient way of optimization, using numerical modelling. This is applicable to research institutes, universities and software houses.

Philips Applied Technologies is a general Philips department that sells engineering services to different Philips and non-Philips customers. The services include product design, production system design and process development. Philips Applied Technologies will sell the virtual prototyping service to different customers. It can be of interest for a wide spectrum of customers, e.g. semiconductor industry, medical systems, lighting. This will safeguard a part of the turnover of Philips Applied Technologies. However the real big advantages can be found at the customers. In the Mevipro project the Virtual Prototyping method was already applied to a Philips Semiconductor business carrier with convincing results. Significant reduction of cost and process time.

Research and education by the Mechanics of Materials group of the department Precision and Microsystems engineering is focused on Material Modelling and Characterization and application of the attained materials models on engineering problems. Within the present project the group has developed an adequate description of material behaviour of curing moulding compounds. The model is applied to the problem of QFN package warpage. The developed capabilities of the group in modelling as well as in thermal mechanical material characterization are well applicable to various research institutes and industries dealing with fabrication induced reliability problems. The group has presented the research results on many international conferences and symposia. Also the work has been implemented in the regular master courses. Various industrial courses have also been given. The research has already resulted in a number of further research contracts with new industrial partners.

Scope: Thermo-mechanical reliability is becoming an increasing challenge in electronics and microsystems due to ongoing miniaturisation, higher power densities and stricter demands due to operation in harsh environments. The common approach for assessing the reliability of new microelectronics and microsystems entails destructive and non-destructive testing of physical prototypes. If necessary, changes are made to the design and new tests are carried out on adjusted prototypes. This process is repeated until a design is obtained that meets the criteria, which is time consuming and expensive. Description: Within the mevipro project, numerical and experimental tools are being developed to shorten the time required to design a component or product. In particular, the following results are to be exploited by TNO: - Numerical models for determining the critical thermo-mechanical loads on microelectronics and microsystems (failure criteria for bulk materials and interfaces). - Numerical models for predicting thermo-mechanical stresses in polymers during and after cure (adhesives, moulding compounds, underfill encapsulants). - A method for determining the fatigue behaviour of thin wires or strips (e.g. electrical leads of electronics components, wire-bonds). - A method for investigating the thermo-mechanical fatigue behaviour of solder or adhesive joints (thermal lap shear test). Status: Simulation techniques (models for thermo-mechanical behaviour of polymers, failure criteria) have been developed and assessed. Methods for assessment of the fatigue behaviour of thin wires and the fatigue behaviour of solders and adhesives have been developed and assessed. The thermal lap shear test has been demonstrated for the investigation of solder materials. In a recently started national project, the ideas behind the wire fatigue test and the thermal lap shear test are being developed for investigating the thermo-mechanical behaviour of electrically conductive adhesives. The results that are sufficiently mature (numerical models and characterisation experiments, wire fatigue experiments) are included in the portfolio of services that TNO offers to its customers in the electronics and microsystems field for reliability and lifetime assessment. These results are expected to be applicable in other fields as well possibly after some modifications. Expected benefit: In 2004, the MES department of TNO Industrial Technology derived about 2.5 MEuro turnover in the field related to product design, reliability and lifetime assessment for microelectronics and microsystems. Numerical simulation in combination with characterisation capabilities is considered as an important instrument by which TNO can distinguish itself from its competitors. By strengthening this field by means of the project results, the department expects to increase this turnover by 5 - 10 % leading to an additional 125 - 250 kEuro income annually. In addition to the expected benefit for TNO itself, there is the benefit for TNO's customers having access to the results via TNO's services. The results enable them to react more rapidly to market demands and to deliver more reliable products giving them the possibility to increase their market shares.

One of the major aims of the MEVIPRO Project is to significantly impact the Product Development Process with the introduction of Virtual Prototyping methodologies that go beyond the product simulation stage but also include optimization techniques in order to produce products of better quality in faster development times. In fulfilling this we aimed at reducing the computational expense required to reach that. WP4 deals with the reduction on the number of Virtual Prototyping experiments required to reach an optimized product, while WP5 deals with the technologies that utilizing the results of the Virtual Experiments result in the best representation of the design space. LMS International in co-ordination with the Technical University of Worclaw have developed methodologies to make the optimization on the virtual prototype level a reality. The Efficient Global Optimization (EGO) algorithm provides for a significant reduction in the time required to reach an optimized product, while maintaining the highest accuracy of the predicted optimum. Beyond, LMS International has over the past eight years developed and promoted a commercial software package for applying optimization techniques on virtual prototypes. The software package OPTIMUS provides the user of simulation software with a number of methodologies to achieve optimized designs. The new EGO methods researched and prototyped as part of the MEVIPRO project will after further productization become a module of OPTIMUS and become commercially available. The product is marketed in the area of Mechanical CAE worldwide via our extensive Marketing and Sales organization.

The use of simulation, optimization and analysis of thermo mechanical issues in the design and verification phase, will save a great deal of development time and lower the amount of physical prototypes needed. Also the future design will experience higher yield in manufacturing and lower field-return and recall issues. This can be done as a part of a Kitron development project or as a separate service or as a part of a customer's design or verification project. The service including use of methods and tools from the Mevipro project will be used in real customer cases. No other Scandinavian company competing with Kitron can today offer the added value of virtual prototyping as a part of the product design & development service. The business potential is especially obvious in the automotive industry with more and more electronics in cars and vehicles and the accelerating requirements of high reliability. The Swedish automotive industry is very strong and Kitron have several customers among manufacturers of cars and vehicles as well as among the automotive components suppliers. There is also potential in other high reliability application areas like defence electronics and medical electronics. The end-users of this service can be found among Scandinavian product-owners and components suppliers as existing Kitron customers today using manufacturing and/or engineering services. There is a clear possibility for Kitron to expand business with existing customer and also attract new customers with the new service and added value.

Thermo-mechanical optimisation of Multi Chip Modules. The MEVIPRO virtual prototyping methodology was applied on a Ceramic based Multi Chip Module having a large area dam & fill epoxy encapsulant. Thermo-mechanical FEM simulation provides a satisfactory prediction of geometric parameters such as module warpage. The MEVIPRO approach leads to the main following potential benefits: design optimisation by selecting better material (thanks to better knowledge of the effect of material parameters), better specification of dimensional features (e.g.: warpage), process optimisation thanks to better knowledge of critical process parameters (e.g.: curing profile) as well as reliability improvement thanks to better material selection, optimised process and design. In addition this approach should bring development lead-time reduction (development of new products based on similar packaging configurations). The Virtual Prototyping methodology could be improved by taking into account the adhesion mechanisms and propagation of delamination (IZM results) to provide a better prediction of the thermo-mechanical reliability trends.

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