Challenges and Directions in Mobile Device Packaging
Authors: Bezuk Steve 
Published: October 2015

Mobile devices such as phones, tablets and subnotebooks are driving innovation in device packaging. These devices currently are jammed full of advanced capabilities, such as HD video, GPS, WLAN, cellular, touchscreens, Bluetooth, and dual cameras - with significantly more functionality than “sophisticated” notebooks. These features drive demand for mobile devices and provide significant challenges to the packaging community for solutions such as thinner packages while still controlling warpage, new materials, both polymers and solders, as well as innovative structures moving into 2.5 and 3D. Solving these challenges allows innovation to drive demand for mobile devices, providing a providing a platform for many innovative uses that are still being tapped, such as entertainment, video recording, web access, computer vision, augmented reality, all readable, recognizable, locatable, addressable, and controllable through the internet, the Internet of Things (IOT) concept. This talk will discuss current and future innovations to address these formidable issues in the mobile environment.
Many extreme temperature applications such as power converters and motor drivers operate from power rails that are floating, noisy and have extremely high voltages. Typically the logic signal is only a few volts but is must be transmitted in an environment with hundreds or thousands of volts of common mode voltage. In some cases isolation is required for safety reasons to prevent leakage currents that could present an electrical shock hazard. For example the ground reference for a high side driver of an all N channel half bridge is referenced to the switch pin and switches between ground and the power rail within a few nanoseconds. At normal operating temperatures there are many specialized components such as opto-isolators, capacitive coupled devices and devices with integrated high frequency transformers that transmit logic signals across the isolation barrier. These specialized integrated circuits that provide isolation may not function reliably at elevated temperatures; those that do tend to be expensive. With special consideration of the system partitioning, it may be possible to avoid the need for galvanic isolation at extreme temperatures. It may be possible to provide the isolation in a remote more benign environment and send the isolated signal down a cable with appropriate impedance matching. When galvanic isolation at extreme temperatures is necessary, there must be temperature considerations for the components used. For example, when designing pulse transformers, the temperature effects on the magnetic core material properties such as permeability and frequency response must be considered as well as the Curie temperature. Modulation of the logic signals can help to reduce transformer size. Since the isolated driver functions typically require power, a novel method of winding the transformer is discussed; this method allows the drive signal to be transferred across the isolation barrier in the same transformer core that is used to provide isolated power to the driver. This paper addresses these topics and provides several alternative solutions to the problem of galvanic signal isolation at extreme temperatures.