Chad B. O'Neal

Challenges in the packaging of MEMS

Unlike IC packaging, MEMS dice must interface with the environment for sensing, interconnection, and/or actuation. MEMS packaging is application specific and the package provides the physical interface of the MEMS device to the environment. In the case of a fluid mass flow control sensor, the medium flows into and out of the package. This type of packaging is referred to as media compatible packaging. Harsh environments may create different challenges for the packaging of MEMS. In addition to challenges related to the MEMS chip environment and interfacing with that environment, challenges also exist inside the MEMS package, such as die handling, die attach, interfacial stress, and outgassing. These new challenges in MEMS packaging need immediate research and development efforts. To date, most of what is known about MEMS packaging remain proprietary secrets and published literature is scarce. The challenges of MEMS packaging have been known for some time, but little open research has been done to collect data and work toward meeting these challenges. A disproportionality exists between money spent on MEMS packaging and time spent researching MEMS packaging. Currently, the cost of MEMS packaging typically accounts for 75% or more of the device sale price. MEMS packaging is already far behind the capabilities of MEMS designers, and it is the purpose of this paper to share the challenges of MEMS packaging and create an awareness and an interest in MEMS packaging within the packaging community.

Temperature dependence of high dielectric strength potting materials for medium voltage power modules

Voltage insulation inside power modules is paramount for functional and reliable operation. Dielectric potting materials are stressed as the overall size of these modules is reduced due to size, weight, and cost considerations while the operating voltage of these modules continue to increase. In particular, voltage ratings of silicon carbide (SiC) device technologies will continue to increase above 6.5 kV into the tens of kilovolts in the future. SiC devices are also often operated at higher junction temperatures to take advantage of the high-temperature capabilities of the material. As the module temperature increases, the dielectric strength of insulating materials in the module tends to decrease, which is a serious concern for a compact power module operating at many kilovolts. A plurality of high-temperature-rated, high dielectric strength potting materials was tested for voltage breakdown and leakage current up to 30 kV and 250°C. A range of different materials, both conventional and novel, were test...

Compact, high-temperature, single-level power modules for 10 to 25 kV DC link voltages using silicon carbide power electronics

Power modules designed explicitly for silicon carbide (SiC), single level power converters between 10 and 24 kV are presented. Using silicon power electronics, multi-level converters are required to reach multiple kV DC link voltages. Multi-level converters require more complex topologies and a larger number of switches, diodes, and/or capacitors. Due to the very high blocking voltages of SiC, it is now possible to build single level converters up to 24 kV. Single level SiC converters have the potential of dramatic cost savings over multi-level silicon-based converters as the device costs of SiC are reduced. Two modules are presented here designed for 15 kV/ 120 A and 24 kV / 30 A. These modules are designed to be compact, while meeting all creepage and clearance standards for their voltage ratings, operate at 200 °C, have a very low inductance, and fast switching speed.

Effects of Die Attachment Induced Stress on the Reliability of a Packaged MEMS Device

A microelectromechanical systems (MEMS) actuator was selected to study the effects of packaging induced stress on device reliability. In this work, MEMS devices were obtained and packaged using cyanate ester, 96.5/3.5 Sn/Ag, and 92.5/5/2.5 Pb/Sn/Ag die attachment materials. The die attachment materials were then cured or reflowed appropriately and cooled to room temperature which induced stress through the coefficient of thermal expansion mismatches between the silicon die and alumina package. In this work, a MEMS microengine developed at Sandia National Laboratories, which is a device that has been well studied, was selected as a test vehicle to understand the effects of various die attachment solders and related processes parameters on the ultimate functionality of the packaged MEMS microengine. Particularly, the operational lifetime of these devices was measured by testing these devices to failure. These lifetimes were then compared with baseline values to determine the effect of stress on these device...

Effect of storage life and drive signals on the reliability of the Sandia Microengine

In this study, the parameters affecting operational and nonoperational reliability of the Sandia Microengine were investigated. It was found that using a non-outgassing die attach material greatly improves storage life. The minimum force required to drive the microengines initially decreased from a much higher voltage to settle in at around 1250 V2 for all devices tested. Drive signal parameters were optimzed for individual engines and the resulting device lifetimes were found to be marginally better that when average values were used (1.2x106 cycles compared to 1.0x106 cycles). There was no correlation between the value of the lumped parameter kr/a and lifetime found, however the longest living engines used a kr/a of around 1000 V2. ues. Optimized drive signal lifetimes were found to be a factor of two higher than when sinewave drive signals were used (5x105 compared to 1.2x106),indicating the advantage of using optimizzed drive signals, but not the two order of magnitude in lifetime that was desired.