Dariusz R. Pryputniewicz

Effect of Process Parameters on TED-Based Q-Factor of MEMS

Continued advances in microelectromechanical systems (MEMS) technology have led to development of numerous applications including, but not limited to: automotive, communication, information technology, deep-space, medical, safety, national security, etc. These developments are being made possible because of creative designs and novel packaging based on use of some of the most sophisticated analytical and experimental tools available today. These tools are also employed to overcome limitations due to inherent behavior of materials fabricated into miniature shapes subjected to extremely harsh operating conditions while satisfying very challenging specifications/requirements of their applications. Thermoelastic internal friction is present in all structural materials and has been found experimentally in miniature silicon resonators (e.g., microgyroscopes, accelerometers, as well as biological, chemical, and other sensors/actuators) that rely on vibrations of either sensing elements or application-specific elastic suspensions that resonate. Regardless of their applications, sensors are always designed to provide the most sensitive responses to the signals they are developed to detect and/or monitor. One way to describe this sensitivity is to use the Quality (Q) factor. Most recent experimental evidence indicates that as the physical sizes of sensors decrease (especially because of continued advances in fabrication, e.g., by surface micromachining) the corresponding Q-factors become more and more dependent on thermoelastic damping (TED). This form of damping depends on material properties such as coefficient of thermal expansion, thermal conductivity, specific heat, density, and modulus of elasticity. It is also related to such design/operating parameters as resonator dimensions and temperature. This paper reviews a theoretical analysis of the effects that thermoelastic internal friction has on the Q-factor of microscale resonators and shows that the internal friction relating to TED is a fundamental damping mechanism in determination of quality of high-Q resonators over a range of operating conditions. Furthermore, the analysis also shows that the Q of resonators can be critical to the development of modern sensors. Microscale resonators are often used as basic sensing elements in the modern micromachined sensors. These sensors are frequency-modulated devices and exhibit a change in output frequency that is related to measurements and/or control of a physical variable. Accuracy and precision of these measurements/controls are inherently dependent on the frequency stability of the sensor/device output. This, in turn, greatly depends on damping in the resonating element itself.Copyright

Augmenting Computer-Aided Design Software With Multi-Functional Capabilities to Automate Multi-Process Additive Manufacturing

The ability to access individual layers of a part as they are being printed has allowed additive manufacturing (AM) researchers to experiment with the in situ placement of components, thereby creating multi-process parts with additional functionality, such as customized printed electronics. As AM has evolved to become an established method for creating end-use parts, this interest in multi-process printing has increased. Although progress has been made in developing multi-process hardware, which can combine AM with other technologies, holistic design software, capable of readily integrating these processes, is developing at a slower rate. In this paper, an integrated software solution capable of supporting multi-process 3D printing from design through manufacture is described, featuring the integration of electronic components and circuits interconnected by copper wires. This solution features automated generation of the cavities that accommodate electronic components as well as toolpath generation for a multi-process 3D printer capable of automated wire embedding. As a case study of the developed technology, a hexagonal 3D printed body, which included a microcontroller, four LEDs, a USB connector, two resistors, and a Zener diode, all interconnected by embedded copper wires, was fabricated within a short cycle time: 5.75 h from design to fabricated part. Short cycle times allow multiple design iterations to be realized and printed within the same day.

Dynamic Analysis to Confirm Lead Failure of a 352-Pin CQFP Under Shock

During qualification testing of an electronics module, several leads in one corner of a 352 pin ceramic quad flat pack (CQFP) component failed. The module was exposed to several different environments including sine vibration, thermal cycling, random vibration, and shock. The last test environment applied was seven consecutive shocks normal to the printed wiring board. Given the severity of the shock response spectrum, it was believed that the shocks normal to the board were the culprit. Therefore, a finite element model (FEM) was created of the module to diagnose the cause of the failure. The FEM modeled all 352 CQFP leads using quadratic beam elements. Besides the CQFP, the FEM also included the aluminum frame, the printed wiring board, and several adjacent components. It was validated by comparing the board’s mode frequencies and shapes computed in ANSYS to those imaged by optoelectronic holography on the test hardware. ANSYS was also used to rule out sine vibration, random vibration, and thermal cycling as causes of the failure. To evaluate the stress levels in the leads during the shock pulse, the actual acceleration experienced by the hardware during a shock pulse was recorded and used in an explicit dynamic analysis in LS-DYNA. In addition, a bilinear elastic-plastic material model was used for the kovar leads. The analysis showed that the suspect leads reached their ultimate tensile strength by the fourth consecutive shock. These results confirmed that the leads failed due to the consecutive shock pulses. The FEM was subsequently used to evaluate a redesign of the module to mitigate the risk to mechanical shock.Copyright

Study of Heat Transfer in Microscale Systems

Progress in micromachining technology enabled fabrication of micron-sized mechanical devices, which have had a major impact on many disciplines. These devices have not only led to development of miniature transducers for sensing and actuation, but also a chip-based chemical laboratory (μChemLab) and other microelectromechanical systems (MEMS). Applications of these microscale systems frequently demand heat removal and temperature control. This paper presents preliminary results of a study of heat transfer in microscale systems. Computational modeling is based on Thermal Analysis System (TAS), which facilitates multiscale modeling/simulation, and measurements are made using infrared (IR) microscopy. Representative applications describe multiscale modeling and measurement results obtained for a microhotplate of a μChemLab and a high-power GaAs FET amplifier. Comparison of the preliminary experimental/measurement and computational/modeling results shows good correlation.Copyright

Preparation and Use of Chip Capacitors in Ultra-Dense Multi-Chip Modules

Draper Laboratory designs and produces ultra-dense multi-chip modules that achieve an integration density, which is only exceeded by that of custom ASIC chips. These modules are fabricated by tiling an adhesive coated substrate with bare integrated circuit chips and passive components that are thinned to 150 microns thick. Multiple layers of thin film copper conductors, supported on Kapton film dielectric, are used to route signals between these components. Connections to their I/O pads and between signal layers are made through laser drilled vias, which are copper plated. The various types of capacitors used in modules for RF applications present several fabrication challenges. In comparison to active IC devices, capacitors have wider dimensional tolerances, are more easily damaged by mechanical handling, and are more susceptible to damage during laser drilling of vias. This paper will discuss these issues and the approaches that have been taken to address them.