Markus Turunen

Mechanical Analysis of Ultrasound-Activated Pins and Resorbable Screws: Two Different Techniques to Fixate Osteosynthesis in Craniosynostosis Surgery

Purpose:Ultrasound activation of resorbable pins directly into drilled holes of the calvarium was introduced to overcome the time-consuming installation in the resorbable osteosynthesis fixation in craniosynostosis surgery. There is paucity in the data comparing the mechanical properties of resorbable screws and ultrasound-activated pins produced by different manufacturers. The aim of this experimental study was to compare the mechanical properties of ultrasound-activated pins and resorbable screws. Methods:A mechanical testing machine was used to characterize the mechanical performance of screws and ultrasound pins. The screws and pins were tested individually in 2 directions with respect to the longitudinal axis: vertical, that is, axial pull-out strength and horizontal, that is, shear strength. The mean maximum strength of fixation was determined. Broken screws and pinheads were analyzed by a scanning electron microscope to determine the site of fracture. Results:All of the resorbable screws and pins broke at the point where the device enters bone. In pull-out testing, the mean maximum strength of the ultrasound-activated pins was 30.5u200a±u200a5.4u200aN and that of the resorbable screws was 54.0u200a±u200a0.3u200aN. In shear testing, the mean maximum strength of ultrasound-activated pins was 57.1u200a±u200a20.1u200aN and that of the resorbable screws was 53.9u200a±u200a0.4u200aN. Conclusions:In their intended configuration, there is no clinically significant difference in fixation strength between ultrasound-activated pins and resorbable screws.

A reliability study of adhesion mechanism between liquid crystal polymer and silicone adhesive

Abstract Liquid crystal polymer (LCP) and silicone adhesives are widely used in electronics manufacturing. The integrity of the adhesion between the two materials is crucial to the reliability of electronic products, however, the adhesion mechanism and associated reliability has not been thoroughly understood. In this paper, the adhesion mechanism between a commonly used LCP and a silicone adhesive is evaluated by employing the 85xa0°C/85% RH temperature humidity test, autoclave test, boiling water test (BWT), and dry air reflow aging test. The effects of different plasma treatments of the LCP surface are evaluated by the surface analysis methods, namely XPS and FTIR–ATR spectroscopy, as well as the surface roughness and energy measurements. Moreover, the adhesion strength between the LCP and silicone adhesive is measured by a shear strength tester. The shear strength testing process is simulated by the finite element method for a better understanding of the failure mechanism. The experimental results indicate that the adhesion between the LCP and silicone adhesive is based solely on the hydrogen bonds. It is found that the humidity significantly weakens the adhesion strength between the LCP and silicone adhesive. This is related to the breakdown of hydrogen bonds when water molecules are introduced to the system. Furthermore, the reflow test shows that the weakened adhesion strength can be recovered by removing the moisture from the interface.

Introduction to Thermodynamic-Kinetic Method

The basic concepts of the thermodynamic-kinetic method and the science of microstructures are introduced. This chapter begins with a brief introduction to thermodynamics. It is assumed that the reader is somewhat familiar with the basic definitions and laws of classical thermodynamics. Different types of equilibriums are considered and calculation and utilization of binary and ternary phase diagrams are discussed. The uses of molar Gibbs free energy diagrams are then considered. Basic diffusion theory and related equations are discussed next along with some phenomenological concepts such as the diffusion path. The rest of the chapter is dedicated to the theories of microstructures. By going through this chapter the reader will obtain all the necessary information to apply the thermodynamic-kinetic method and the microstructural considerations to one’s own problems.

Hyperelastic Property Measurements of Heat-Cured Silicone Adhesives by Cyclic Uniaxial Tensile Test

Most of the commonly used linear elastic properties of silicone adhesives cannot precisely represent their material behavior, knowledge of which is crucial to the reliability study of electronic devices. For this reason, in this paper a widely used silicone adhesive, namely Loctite 5404, is chosen for measuring hyperelastic properties via cyclic uniaxial tensile tests. A special sample preparation procedure is developed to avoid the formation of detrimental air bubbles in the samples. Two maximum strain levels, 20% and 40%, are used in the tests. Each test includes five cyclic loadings to produce a stable stress–strain loop. Three orders of magnitude of strain rate changes are studied, and the stress–strain response of the material is found to be strain rate dependent. The measured stress–strain data are imported into Abaqus finite-element software to calibrate the material coefficients of hyperelastic material models (Mooney–Rivlin, Yeoh, Ogden, and van der Waals models). This is the first time that the hyperelastic properties of the studied silicone adhesive are presented. The determined material coefficients can be used directly in finite-element analyses and thus in reliability studies of electronic devices.

Materials and Interfaces in Microsystems

The most common stress factors and related failure mechanisms in electronic devices at different interconnection levels are presented. The emphasis is placed on the miniaturised heterogeneous structures of microsystems, which are composed of different types of materials in contact with each other. The interfacial reactions between the materials and their environment are examined from manufacturability, functionality and reliability points of view.

Evolution of Different Types of Interfacial Structures

In this chapter, the feasibility of the thermodynamic-kinetic method and the associated science of microstructures are demonstrated by going through a large amount of examples concerning interfacial compatibility problems from the various fields of microtechnologies. The chapter is divided to sections based on the types of material interfaces considered. Thus, first metal–metal, then metal–ceramic and finally metal–polymer examples are discussed. It will become evident that only by using all the theoretical tools introduced earlier in this book (i.e.): (i) thermodynamics of materials (ii) reaction kinetics (iii) theory of microstructures and (iv) stress and strain analysis, it is possible to obtain fundamental understanding of the interfacial problems at hand.

Introduction: Away from Trial and Error Methods

In this chapter, the challenges of electronics hardware development and the limitations of the commonly used “trial and error” methods are discussed. An introduction is given to an alternative development methodology to understand and control the performance of multimaterial systems.

Interfacial Adhesion in Polymer Systems

In this chapter, interfacial adhesion between dissimilar materials is discussed. Several aspects of surface and interfacial phenomena are presented covering such topics as adsorption, surface free energy models, and the kinetics of wetting. These concepts are then related to typical adhesion mechanisms acting across various interfaces found in microsystems. Attention is also given to processing, testing of adhesion, inspection of interfaces and effect of typical environmental stressing on the durability of adhesion. This is done to address the complexity of relating the science of adhesion with the practical adhesion. Finally, some theoretical means to better understand, test and design reliable interfaces using dissimilar materials are given.

Introduction to Mechanics of Materials

An overview of the mechanical properties of different classes of materials typically encountered in microsystems is presented. The response of materials to mechanical loading is discussed from the perspective of the deformation mechanisms of the materials. After that the formation of stresses and strains under commonly encountered loading conditions is discussed. Emphasis is placed on thermomechanical, mechanical shock and vibrational loadings. Finally, formation of typical failures in electronic devices is briefly discussed.