Assessment of microelectronics packaging for high temperature, high reliability applications

This report details characterization and development activities in electronic packaging for high temperature applications. This project was conducted through a Department of Energy sponsored Cooperative Research and Development Agreement between Sandia National Laboratories and General Motors. Even though the target application of this collaborative effort is an automotive electronic throttle control system which would be located in the engine compartment, results of this work are directly applicable to Sandia`s national security mission. The component count associated with the throttle control dictates the use of high density packaging not offered by conventional surface mount. An enabling packaging technology was selected and thermal models defined which characterized the thermal and mechanical response of the throttle control module. These models were used to optimize thick film multichip module design, characterize the thermal signatures of the electronic components inside the module, and to determine the temperature field and resulting thermal stresses under conditions that may be encountered during the operational life of the throttle control module. Because the need to use unpackaged devices limits the level of testing that can be performed either at the wafer level or as individual dice, an approach to assure a high level of reliability of the unpackaged components was formulated. Component assembly and interconnect technologies were also evaluated and characterized for high temperature applications. Electrical, mechanical and chemical characterizations of enabling die and component attach technologies were performed. Additionally, studies were conducted to assess the performance and reliability of gold and aluminum wire bonding to thick film conductor inks. Kinetic models were developed and validated to estimate wire bond reliability

Encapsulation hermétique pour systèmes hydro- et thermo-sensibles

The quantity of MEMS manufacturers has considerably been increasing these last years. This doesn't mean that the introduction of such products on the market has become easier. A packaging operation is needed to obtain a usable product out of a microsystem. The packaging ensures protection but also interconnection with the outside. Too foten, during the conception of a microsystem, the engineer usually does not think about packaging method, which increases costs and time to obtain a product. This thesis is a conception tool to help those who need to realise a microsystem requiring protection against gas and vapours. Some microsystems are sensitive to humidity and temperature. Up to now, to obtain an hermetic package, the easiest solution was soft soldering of a cap on a base. This operation was often done in an oven, which may heat the microsystem to temperatures it can not withstand. In this thesis we describe methods which allow the design and manufacturing of hermetic packages together with a low sealing temperature. In a first phase, material permeability is defined, as well as the notion of package hermeticity and leak measurement methods. The conclusion is that the only materials which allow long-term hermeticity (up to 10 years) are ceramics, glasses and metals. Usual methods for hermetic sealing of packages are then described. Soft soldering by the mean of a laser diode, which is used in this thesis, allows to obtain an hermetic package, together with a low thermal budget. The advantage of the laser diode over another type of laser is its low power density, as well as the possibility to continuously control its power during operation. The power can be controlled during soldering depending on the measured temperature, for example by the mean of a pyrometer. In order to design a package, it is necessary to formalize the requirements in terms of functions that need to be fulfilled by the package. Functional analysis is used to formalize these requirements. This iterative method needs to be done during the conception of the microsystem, but can also be done when the design of the microsystem is already done. In order to reduce reconception phases, most of the functions need to be found at an early stage of the package design. Some methods which allow to find these functions are described. A thermal modelling method is also proposed. This method allows to find an appropriate model to each situation. The first step consists in finding orders of magnitude. The model is then refined by the mean of an electrical analogy or by the mean of numerical simulations when necessary. Several demonstrators have been realized during this thesis. The feasibility of an LTCC (Low Temperature Cofired Ceramic) package for a micromirrors array is demonstrated. The manufacturing of this package is based on screen-printing technology. LTCC packages are suitable for small to medium series of complex microsystems. For complex devices, standard ceramic packages are more expensive than LTCC-based ones, and may not provide the required flexibility. The proposed method is adapted to manufacturing of hermetic cells containing rubidium, for miniature atomic clocks. Sealing time and temperature are drastically reduced compared to anodic bonding, which reduces evaporation of the rubidium during the sealing operation. Some improvements are needed, mainly adhesion of the metallization and atmosphere control during the sealing. The thermal modelling method is illustrated in an example of laser curing of epoxy glue. In order to determine the behaviour of the system, dimensional analysis is used together with experimentation. Versatility of the laser diode is also shown in this project. Finally, some technical points related to the use of a laser diode for soft soldering are also described. Recommendations are given regarding wettability of the solder and reduction of the heating time. Notably, pre-tinning the surfaces with solder is found to be preferable to the use of preforms

Technology 2001: The Second National Technology Transfer Conference and Exposition, volume 1

Papers from the technical sessions of the Technology 2001 Conference and Exposition are presented. The technical sessions featured discussions of advanced manufacturing, artificial intelligence, biotechnology, computer graphics and simulation, communications, data and information management, electronics, electro-optics, environmental technology, life sciences, materials science, medical advances, robotics, software engineering, and test and measurement

1-D broadside-radiating leaky-wave antenna based on a numerically synthesized impedance surface

A newly-developed deterministic numerical technique for the automated design of metasurface antennas is applied here for the first time to the design of a 1-D printed Leaky-Wave Antenna (LWA) for broadside radiation. The surface impedance synthesis process does not require any a priori knowledge on the impedance pattern, and starts from a mask constraint on the desired far-field and practical bounds on the unit cell impedance values. The designed reactance surface for broadside radiation exhibits a non conventional patterning; this highlights the merit of using an automated design process for a design well known to be challenging for analytical methods. The antenna is physically implemented with an array of metal strips with varying gap widths and simulation results show very good agreement with the predicted performance

Beam scanning by liquid-crystal biasing in a modified SIW structure

A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium