Assembly adhesives play a critical role in microelectronic packaging and contribute significant value for circuit assembly interconnection, protection, and thermal management. Of particular interest with today’s more powerful systems is thermal management of high-power density electronic systems, including power modules, power amplifiers, communication systems, and directed energy systems. As requirements for performance and functionality increase, heat generated from these devices increases exponentially. For example, local heat flux can easily exceed 50 W/cm2 for IGBT power modules while it may reach several hundred Watts/cm2 at active areas for Gallium Nitride (GaN) power amplifiers. Simultaneously, many of these systems demand a higher level of electrical insulation to eliminate or minimize current leakage to ensure high reliability over a long service life. Effectively and safely dissipating the high heat and ensuring excellent electrical insulation has become an increasingly critical and challenging task in the microelectronics packaging technology for aerospace and defense systems. This paper presents integration of thermally conductive adhesives with an electrically insulative polyimide film into a carefully engineered laminate, which enables high thermal transfer and robust electrical insulation. This new film adhesive provides outstanding compliance and augmented tolerance to large topographical features and warpage (5-7 mils). This film adhesive is one of the potential solutions to addresses the evolving needs of the electronics assembly industry in the areas of management of high-power systems

The continued integration of smaller, higher-functioning devices in the Aerospace, Defense & Space sectors is making it more challenging than ever to minimize assembly failure, especially where reliability is top priority and fail-safe processes, and materials are the standard. Assembly failures due to poor adhesive bonding tend to linger causing excessive manufacturing downtime, scrap, costly rework, and delays. This paper introduces the science behind adhesion. Regardless of the application, the market or the adhesive technology being used, such as epoxy, silicone, urethane, paste or film, achieving a proper assembly bond is critical for application success. Adhesion is achieved via two mechanisms, mechanical and chemical bonding. To optimize this the adhesive must flow (or wet) across the substrate. This maximizes the interaction between the adhesive and substrate allowing flow into microscopic substrate pores for enhanced mechanical bonding as well as interaction between adhesive and substrate for chemical bonding. The molecular force of attraction between an adhesive and the substrate is determined by the surface energy of the substrates. The substrate surface energy influences the ability of the adhesive to flow and wet the substrate impacting adhesion. Measuring substrate water contact angle is an easy method to determine the relative surface energy thereby gaining information about the pending adhesive bond. This paper reviews these key factors for adhesion and presents results of an application study aimed at understanding the sensitivity and relationship of substrate water contact angle versus substrate cleanliness. The goal is to be able to use substrate water contact angle measurements as a predictive tool for adhesion.

Integration of smaller, higher-functioning devices and use of advanced high thermal chip structures present thermal management challenges in the aerospace sector where reliability is the top priority and fail-safe processes/materials are the standard. As power density increases rapidly, traditional die attaching technology is becoming an increasingly limiting factor in microelectronics packaging for the next generation aerospace and defense systems. This paper introduces an advanced hybrid silver sintering technology, which incorporates ultra-high thermal and electrical performance of silver sintering with high reliability and process friendly of epoxy-based die attach technology. Unlike traditional silver sintering that requires high temperature and pressure, this hybrid sintering paste can be processed without applying any pressures in temperature ranges that are normal in microelectronics packaging processes. This paper presents results of an application study aimed at developing this unique technology in the field of high-power density devices for aerospace applications.