Mervi Paulasto-Kröckel

Shock impact reliability characterization of a handheld product in accelerated tests and use environment

Abstract The effect of mechanical shock impacts is a key factor in the reliability of modern handheld products. Due to differences in product enclosures, impact orientations, strike surfaces and mountings of component boards, the loading conditions induced in a true product drop differ from those encountered in standardized board-level tests. In order to better understand the correlation between board-level drop testing and actual drops of a complete device, series of board and product-level drop tests were conducted using specialized test boards. The mechanical shock impact response of the commercial handheld device component board was characterized with the help of acoustic excitation laser vibrometry and finite element analysis. The results were used to design the mechanically compatible specialized test board for both 4-point supported board-level and unsupported product-level drop tests. Special care was taken to ensure that the vibration behavior of the test board accurately represented the vibration behavior of the commercial component board. Additional board-level drop tests were conducted using a JEDEC JESD22-B111 compliant component board for comparison. The drop test results showed that, even though the test board design and supporting method have a marked influence on the strain conditions and lifetime of solder interconnections, the primary failure mode and mechanism under the product-level drop tests is comparable to that typically encountered in the standard JEDEC JESD22-B111 board-level drop tests. More detailed analyses suggest that the comparability of the shock impact loading conditions affecting solder interconnections can be characterized using three metrics: (1) the maximum component board strain rate, (2) the maximum board strain amplitude and (3) the damping of the component board.

Effects of thermal cycling parameters on lifetimes and failure mechanism of solder interconnections

The work presented in this paper focuses on a) clarifying the underlying physical failure mechanism of Sn-rich solder interconnections under thermomechanical loading and b) identifying the means to accelerate the failure mechanism by optimizing the dwell-times and ramp-rates of thermal cycling test. The statistical results showed that as the dwell-times were decreased the number of cycles to failure increased but the shortest testing time was achieved with 10-minute dwell-times. Increase of ramp-rate did not affect the number of cycles to failure but the time to failure was significantly reduced. Investigations of the nucleation of cracks in solder interconnections revealed that nucleation is much more dependent on the number of thermal cycles than on the studied test parameters and that the nucleation took place within about the first quarter of the average lifetimes. Furthermore, cracking of the SnAgCu interconnections under all thermal cycling conditions studied took place through the bulk of the solder interconnections along the continuous network of grain boundaries produced by recrystallization. An approach to further accelerate thermal cycling tests is proposed based on the formed understanding of the failure mechanism.

Migration From PLC to IEC 61499 Using Semantic Web Technologies

This paper proposes a new methodology of migration from IEC 61131-3 PLCs to IEC 61499 function blocks. The aim of this migration process is to recreate IEC 61131-3 applications in IEC 61499 implementations with equivalent execution behavior. The formal model of the IEC 61131-3 standard for migration and cyclical execution model is defined. This method also creates a foundation for correct-by-design development tools and automatic migration between the IEC 61131-3 and IEC 61499 standard. Formal migration rules based on ontology mappings, restoring execution model including tasks and programs scheduling and variables mapping with different access levels, are provided. A transformation engine for importing PLC code, mapping from PLC ontology model to function block model and code generation is implemented based on the ontological knowledge base and semantic query-enhanced web rule language. The migration approach is demonstrated on a simple airport baggage handling system.This paper proposes a new methodology of migration from IEC 61131-3 PLCs to IEC 61499 function blocks. The aim of this migration process is to recreate IEC 61131-3 applications in IEC 61499 implementations with equivalent execution behavior. The formal model of the IEC 61131-3 standard for migration and cyclical execution model is defined. This method also creates a foundation for correct-by-design development tools and automatic migration between the IEC 61131-3 and IEC 61499 standard. Formal migration rules based on ontology mappings, restoring execution model including tasks and programs scheduling and variables mapping with different access levels, are provided. A transformation engine for importing PLC code, mapping from PLC ontology model to function block model and code generation is implemented based on the ontological knowledge base and semantic query-enhanced web rule language. The migration approach is demonstrated on a simple airport baggage handling system.

Toward comprehensive reliability assessment of electronics by a combined loading approach

Many electronic applications, such as portable handheld devices or automotive electronics, experience various loadings during their common operation. Recent investigations have shown, however, that the interactions of the different load components can be highly significant. The commonly employed standardized single load tests neglect these interactions and, therefore, do not represent well enough the use environment loading conditions of many electronic devices. Thus, it has become clear that modifications to the reliability evaluation procedures are necessary. But before loading conditions can be combined in a meaningful manner, the failure mechanisms under single load environments and their possible interactions must be clarified. This paper makes a brief review to the reliability of electronic assemblies under different loading conditions from the perspective of failure modes and mechanisms. The failure modes and mechanisms under pure thermal cycling, power cycling, mechanical shock impact, or vibration conditions are discussed first. Thereafter, the interactions of the loading conditions, when they are combined consecutively or concurrently, are discussed.

Structural and chemical analysis of annealed plasma-enhanced atomic layer deposition aluminum nitride films

Plasma-enhanced atomic layer deposition was utilized to grow aluminum nitride (AlN) films on Si from trimethylaluminum and N2:H2 plasma at 200 °C. Thermal treatments were then applied on the films which caused changes in their chemical composition and nanostructure. These changes were observed to manifest in the refractive indices and densities of the films. The AlN films were identified to contain light element impurities, namely, H, C, and excess N due to nonideal precursor reactions. Oxygen contamination was also identified in the films. Many of the embedded impurities became volatile in the elevated annealing temperatures. Most notably, high amounts of H were observed to desorb from the AlN films. Furthermore, dinitrogen triple bonds were identified with infrared spectroscopy in the films. The triple bonds broke after annealing at 1000 °C for 1 h which likely caused enhanced hydrolysis of the films. The nanostructure of the films was identified to be amorphous in the as-deposited state and to become n...

Failure mechanism of solder interconnections under thermal cycling conditions

Increasing miniaturization, power densities and internal heat dissipation of novel electronic packages have made their solder interconnections more vulnerable to failures. To improve the reliability of electronic devices the underlying physical failure mechanisms of solder interconnections must be clarified in detail in order to find means to control, or even prevent, the development of failures. Therefore, the evolution of microstructures and the development of failures in Snrich lead-free solder interconnections were investigated by employing methods of orientation imaging microscopy: cross-polarized light imaging and electron backscatter diffraction. The as-solidified microstructures of the SnAgCu solder interconnections (composed of a few large Sn colonies) were observed to undergo a notable change of microstructures at the strain/stress concentration regions before cracking. The investigations of microstructures indicate that the change of microstructures take place at two different stages in the course of thermal cycling: 1.) a gradual formation of low angle tilt grain boundaries caused by a rotations of small volumes of the as-solidified microstructures around the [100] and [110] axes. It is suggested that these boundaries are formed by recovery, i.e. the boundaries are a consequence of the rearrangement of dislocations by polygonization. 2.) In subsequent stages the microstructures in the strain concentration regions transformed into a more or less equiaxed grain structure by recrystallization. It is evident that cracking of solder interconnections under thermomechanical loadings is enhanced by the recrystallization, because the network of high-angle grain boundaries extending through the interconnections provide favorable paths for cracks to propagate intergranularly.

Microstructural Evolution and Mechanical Properties of Au-20wt.%Sn|Ni Interconnection

In this paper, the microstructural evolution and properties of Au-20wt.%Sn|Ni reaction couples were investigated from two perspectives: (1) by analyzing the microstructure of the as-soldered and aged samples, as well as (2) by measuring the mechanical properties of the intermetallic compounds formed within the reaction zone. The evolution of interfacial reaction products for both the as-soldered and aged interconnections was rationalized by using the experimental results in combination with assessed thermodynamic data from the Au-Ni-Sn system. Moreover, nanoindentation tests were implemented to measure the indentation modulus and hardness of the compounds formed at the interface. It was found that aging had a negligible influence on the elastic modulus and hardness of AuSn and Au5Sn, while the solubility of the third element significantly changed the indentation modulus and hardness of the intermetallic compounds.

Improving the function of dopamine electrodes with novel carbon materials

For therapeutic purposes, an accurate measurement of dopamine level in situ would be highly desirable. A novel strategy for the selective determination of dopamine concentration based on the diamond-like carbon (DLC) electrode is presented in this abstract. The developed DLC electrode is able to detect 10 μM dopamine and has improved sensitivity compared to platinum. Compared to carbon fiber electrodes, the DLC electrode is more stable because the background current is much lower.

Reliability assessment of a MEMS microphone under mixed flowing gas environment and shock impact loading

In this work the reliability of a Micro-Electro-Mechanical Systems (MEMS) microphone is studied through two accelerated life tests, mixed flowing gas (MFG) testing and shock impact testing. The objective is to identify the associated failure mechanisms and improve the reliability of MEMS devices. Failure analyses are carried out by using various tools, such as optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS). Finite element analysis is also conducted to study the complex contact behaviors among the MEMS elements during shock impact testing. The predicted failure sites are in agreement with the experimental findings.

Thermal impact of randomly distributed solder voids on Rth-JC of MOSFETs

The work presented applies a statistical approach to study randomly distributed solder voids in MOSFET products. The grid size was varied as independent of the mesh element to account for typical void sizes observed in X-ray images. Thereafter the impact of random voids for different chip sizes was quantified. Results show that higher maximum chip temperatures can occur with voids located in the corner of the die. A simple analytical expression thereafter was developed to understand and explain this. Rth-JC (thermal resistance junction-to-case) and IR (infrared) measurements of selected test devices with known void distribution were performed as well. Measurement and simulated results were compared. In this work we attempt to establish a model for the evaluation of the process impact on Rth-JC. It also leads to some guidelines of solder joint inspection criteria for power devices.