High-Reliability Applications Need High-Reliability Conformal Coatings For RF Circuits

Radio frequency (RF) micro-electronics are used everywhere in today’s technology, from the Internet of Things (IoT) to military radar systems. Many of these systems, such as military active electronically scanned array (AESA) radar, read and analyze a high volume of RF signals and data using sophisticated analog-to-digital conversation and high-power processors. However, it is challenging for these advanced RF systems to meet size, weight, power and cost requirements set by consumer market or defense agency demand, or what the military calls “SWaP-C.” 

Some of these challenges are centered around the need for packaging of the RF components and integrated circuits (ICs) to ensure long term reliability. Reliability concerns traditionally necessitate the environmental protection of these high-frequency RF devices at either the component or the assembly level by hermetically sealing the device in a bulky, heavy, expensive metal enclosure to prevent degradation caused by hazards in device operating environments. Industry standard conformal coatings are unusable due to the significant signal degradation which occurs if applied directly over an RF circuit. There is a critical need for a coating alternative which is compatible with high-frequency RF devices to provide a lower weight and lower volume environmental protection method with high-reliability and negligible performance impact for RF devices. This approach would allow RF device integration on SWaP-C effective PCBs.

GVD initially developed the SignalSeal coating as a long-term electrical insulator for neurological implants where failure during the life of the implanted device is not an option. The deposition process simultaneously adsorbs molecules of monomer units on the surface of the device and crosslinks those monomer units to grow a cohesive polymer film, resulting in molecular-level conformal coverage of the surface. This molecular-level coverage ensures excellent adhesion to the device, which is critical in providing protection from exposure to harsh operating environments. The dense networked structure renders SignalSeal resistant to dissolution or delamination. Chemical compatibility has been demonstrated through long-term soak testing with a variety of solvents and liquids, specifically in aerospace operating environments, such as acetone, isopropyl alcohol, jet fuel, hydraulic fuel, and de-icing agents.

SignalSeal can be applied to both the bare device and completed assemblies. GVD’s coatings are applied through a dry, room-temperature vapor deposition process that gently encapsulates RF boards and/or components in a micron-thin polymer. The coating’s low dielectric constant and low thickness has been demonstrated to have negligible impact on RF signal integrity when applied directly to the surface of Monolithic Microwave Integrated Circuits (MMICs) operating in Ku, Ka, and W bands, as validated by independent testing. SignalSeal’s high thermal stability makes it compatible with hot-running semiconductor technologies, such as gallium nitride (GaN) components.