Current trends in military microelectronic component packaging

The U.S. Department of Defense (DoD) has historically relied on the use of hermetically-sealed ceramic and metal component packages for the reliability and integrity of military hardware. During the last twenty years, military electronics have become a very small segment of the total electronic market. Within this time frame, military research, development and standards have fallen behind private industry innovation and practices. Due to the low volume, “high reliability” materials and processes, many in line process controls cannot be utilized as with the higher volume commercial parts. As a result, the cost of MilSpec components is typically twice to ten times those of commercial parts. The DoD is currently seeking to use commercial parts and practices, yet still maintain superior reliability in military electronic systems. This is being accomplished through two major thrust technologies; the first, the use of plastic encapsulated microcircuits (PEM´s) and the second, the use of environmentally protected chip-on-board (COB) processing. The traditional use of hermeticity and requirements of military electronic components are reviewed. Preliminary commercial task force testing, which investigated the use of silicone gels and other organic materials, as a method to seal plastic packages, is addressed. A recent U.S. Air Force (reliability without hermeticity [RWOH]) study and follow on work, conducted by the joint military/industry plastic package availability (PPA) program, investigated the use of two ceramic layers (SiO₂ and SiC) over silicon die, designed to increase the reliability of commercial plastic packages. These studies utilized highly accelerated stress testing (HAST) as an indicator of reliability. The use of ceramic and organic coatings to encapsulate COB hardware has also been undertaken. These studies have not only targeted single chip applications, but also multichip applications, such as, MCM-L packages. An overview of these investigations is presented, along with a discussion of and directions in DoD microelectronic packaging research