Soeren Majcherek

Application of a method for characterization of thermo mechanical stress caused by packaging processes

This paper reports on a method for the investigation of mechanical stress on MEMS sensor and actuator structures due to packaging processes. A silicon test chip is developed and manufactured to validate the simulation results. Finite element analysis (FEA) is used to optimize the geometric parameters and to find a stress sensitive sensor geometry. A diaphragm structure is used as mechanical amplifier for bulk induced stresses during the packaging process. Piezo resistive solid state resistors are doped into the surface of the chip to measure the stress in the diaphragms and at the contact pads being most significant locations for analysis. A high precision ohmmeter was used to measure the resistance prior and past the packaging process. The captured data allows for computation of the resulting stress loads in magnitude. Therefore, a stress evaluation of different packaging technologies is conducted and the impact of the packaging process on reliability can be estimated immediately.

Microwave based method of monitoring crack formation

The formation of cracks in glass particles was monitored by application of linearly polarized microwaves. The breakage behavior of glass spheres coated with a thin gold layer of about 50?nm, i.e. a thickness that is lower than the microwave penetration depth, was tested. In this way the investigation of fracture behavior of electronic circuits was simulated. A shielding current was induced in the gold layer by the application of microwaves. During the crack formation the distribution of this current changed abruptly and a scattered microwave signal appeared at the frequency of the incident microwaves. The time behavior of the scattered signal reflects the microscopic processes occurring during the fracture of the specimen. The duration of the increasing signal corresponds to the crack formation time in the tested specimen. This time was estimated as particle size divided by crack development speed in glass. An intense emission of electrons occurs during the formation of cracks. Due to this, coherent Thomson scattering of microwaves by emitted electrons becomes significant with a delay of a few microseconds after the initial phase of crack formation. In this time the intensity of the microwave signal increases.

Peculiarities of structure formation of layered metal-oxide system Ti-Ta-(Ti,Ta)xOy during electro-spark alloying and thermally stimulated modification

The study focuses on high-performance combined electro-spark alloying of titanium and titanium alloy (VT1-0, VT16) surface and porous matrix structure oxidation. The metal-oxide coatings morphology is the result of melt drop transfer, heat treatment, and oxidation. The study establishes the influence of technological regimes of alloying and oxidation on morphological heterogeneity of biocompatible layered metal-oxide system Ti-Ta-(Ti,Ta)xOy. It was found that during electro-spark alloying the concentration of tantalum on the titanium surface ranges from 0.1 to 3.2 at.%. Morphology of the deposited splats is represented by uniformly grown crystals of titanium and tantalum oxides, which increase from nano- to submicron size.

S 3 MD, Stress Sensitive Surface Mounted Devices for in-situ monitoring of mechanical processes in PCB manufacturing

In the past, silicon based measurement system were used to characterize packaging induced stresses of electronic devices. In this paper a new approach for qualifying mechanical PCB manufacturing processes is presented. Silicon based package equivalents (S3MD; Stress Sensitive Surface Mounted Devices) are used instead of real devices at locations of expected dangerous mechanical impact. The silicon based package equivalents have strain sensitive structures implemented. These structures are formed by thin film processes and are designed as strain sensitive metal resistors. Therefore, the mechanical impact of the following steps in the PCB process chain can be monitored. The sensor devices are qualified in the AEC Q200 “board flex” test to get the limiting strain values. In the result, we show a new method to get in situ measured data of the mechanical impact of PCB manufacturing processes.

A MEMS based measurement system for structure health monitoring applications

The structure health monitoring becomes more and more important to increase the reliability of important assemblies and structures. Therefore, a silicon test chip was developed to analyse acting mechanical loads at critical structure locations. Standard MEMS technologies are used for manufacturing an array structure of stress sensitive elements. Up to 16 sections with each 6 stress sensitive resistors can be measured continuously by one measurement hardware unit. Interpretation and correction of the measured raw data is performed in proper computer software. The whole system can be utilized as a self-sufficient measurement chain for structure health monitoring.