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Electronics production technology


Professor Mervi Paulasto-Kröckel
Tel +358 9 451 2715
Gsm +358 50 5113197

General

The research and development activities focus on the manufacturing and reliability of miniaturized, high performance and multifunctional electronic products. The reliability is to a large extent determined by the ability of electrical interconnections to withstand various loadings during products´ operational lifetime. Among these the combined effects of power cycling and mechanical shocks (due to accidental droppings) are the most influential, because they alter most strongly the microstructures of solder interconnections and hence the reliability of electronic products. Similarly, the solder volumes are continuously decreasing and therefore electromigration in solder joints is becoming a more serious concern along with higher stresses experienced by the solder interconnection owing to their decreased height.

In addition, electronic equipment are also operating in hot and humid environments during their daily use, thus posing problems related to excessive chemical reactions and corrosion. All the above challenges require deep enough understanding of stability, properties and reactivity of these thin material layers with their surroundings during processing as well as use of the devices. This knowledge can be achieved by combining careful experimental work with modelling and simulation of the evolution of interconnection microstructures by utilizing for example combined thermodynamic-kinetic analyses and thermomechanical simulations. Hence, by understanding the fundamental relations between real service loading conditions of electronic equipment and the mechanisms behind the observed failure modes - both in accelerated reliability tests and in use of the products - the potential reliability risks in present and future designs can be identified and solved.

The main ongoing research projects are:

I Development of A Novel Reliability Testing Method of Consumer Electronics

The first objective of this research project is to establish a new cost-efficient testing method based on the concept of concurrent reliability testing that simulates the operational loadings of electronic products as realistically as possible. Only by having a thorough understanding of the failure modes and mechanisms taking place independently under the stated loading conditions, the concurrent loadings can be combined in a meaningful way. The second objective is to design and manufacture a test system that is capable of producing discrete shock impacts with higher accuracy and better repeatability than the currently commercially available methods. Besides, in addition to mechanical shocks the test system must enable the simultaneous power cycling and environmental control. The third objective is to construct a new kind of lifetime prediction model that would take into account, for the first time, the microstructural evolution of components´ solder interconnections that occurs during the operation of products.

II A Novel Reliability Evaluation Method for Portable Electronics

The first objective of the research proposal is to identify the key loading parameters that affect the onset of recrystallization in lead-free Sn-based solder interconnections, primarily based on near eutectic SnAgCu and most recently developed Sn0.5Ag0.5Cu0.1Ni solder alloys. By having means to control the recrystallization/recovery behaviour of solder interconnections we can also improve the reliability of present as well as future high performance portable electronics. The second objective is to clarify in detail the effect of recrystallization on the mechanical behaviour of the solder interconnections. The fact that the interconnections start to recrystallize gradually makes the recrystallized and nonrecrystallized parts mechanically different. The third objective is to construct a new type of lifetime prediction model, which would take into account, for the first time, the microstructural evolution of solder interconnections.

III Advanced Solder Materials for High Temperature Application (HISOLD), COST MP0602

COST is supported by the EU Framework Programme.

Co-operation

The research and development projects bring together both Finnish and international research organizations for developing new cost-efficient testing methods and reliability prediction models for electric designers and R&D engineers as well as to analyse compatibility of dissimilar materials used in electronic devices. These multidisciplinary objectives are achieved by executing co-operation with such academic partners as University of California (UCLA), the Osaka University, the Technical University of Eindhoven and companies such as Efore, Nokia, Bluelec, Nokia Siemens Networks (NSN), National Semiconductor (NSC), NXP Semiconductors, etc.