FLEXIBLE AND STRETCHABLE CIRCUIT TECHNOLOGIES FOR SPACE APPLICATIONS EMPPS WORKSHOP, NOORDWIJK, THE NETHERLANDS 20-22 MAY 2014 Maarten Cauwe, Frederick Bossuyt, Johan De Baets, Jan Vanfleteren Centre for Microsystems Technology, imec and Ghent University, Technology Park 914, B-9052 Ghent, Belgium, Email: Maarten.Cauwe@imec.be ABSTRACT Flexible and stretchable circuit technologies offer reduced volume and weight, increased electrical performance, larger design freedom and improved interconnect reliability. All of these advantages are appealing for space applications. In this paper, two example technologies, the ultra-thin chip package (UTCP) and stretchable moulded interconnect (SMI), are described. The UTCP technology results in a 60 μm thick chip package, including the embedding of a 20 μm thick chip, laser or protolithic via definition to the chip contacts and application of fan out metallization. Imec’s stretchable interconnect technology is inspired by conventional rigid and flexible printed circuit board (PCB) technology. Stretchable interconnects are realized by copper meanders supported by a flexible material e.g. polyimide. Elastic materials, predominantly silicone rubbers, are used to embed the conductors and the components, thus serving as circuit carrier. The possible advantages of these technologies with respect to space applications are discussed. 1. INTRODUCTION The driving application for flexible and stretchable circuit technologies is consumer electronics, especially handheld and mobile devices, which benefit the most from the reduction in form factor, the increased functional density and enlarged user comfort that is made possible with these technologies. Reduced volume and weight, increased electrical performance, larger design freedom and improved interconnect reliability are benefits that are also appealing for space applications. Traditionally, electronics and sensor circuits are fabricated on flat rigid substrates, like FR4 Printed Circuit Boards (PCBs). In this conventional technology, packaged integrated circuits (ICs) and passive components are assembled onto the rigid PCB by soldering. For many applications, especially for mobile, portable, wearable and implantable electronics, the circuit should preferably be seamlessly integrated into the object which is used for transportation, is carried along, or worn on or inside the body. The electronics should be comfortable and unnoticeable to the user. In general, standard circuits do not fulfil these requirements. The user comfort can be increased in two ways. Extreme miniaturisation of the circuit reduces the presence of the system. A second approach is to transform the flat rigid circuit into a three-dimensional, conformable variant, following the random shape of the object or body part onto which it is integrated. In this contribution, two original technologies developed at imec-CMST are presented. The ultra-thin chip package (UTCP) technology embeds 20 μm to 30 μm thick chips in a stack of spin-on polyimide (PI) layers. Adding thin-film, fan-out metallization results in an extremely miniaturized, lightweight and flexible chip package with a total thickness below 100 μm. Next to flexible electronics, a number of technologies for dynamically or one-time deformable stretchable circuits are under development. The stretchable concept is based on the interconnection of individual components or component islands with meander shaped metal wirings and embedding in elastic polymers like silicone rubbers (PDMS), polyurethanes (PU) or other plastics. Although these technologies were not explicitly developed for space applications, their unique features create the potential for use in this new application domain. Miniaturization through UTCP use and 3D integration through circuit random deformability significantly reduces system size and weight, which is an important advantage for space applications. An interesting point of view, further discussed in this paper, is the possible improvement in interconnect reliability that these new technologies offer. Thanks to the embedding in elastic materials, stretchable circuits could show a decreased sensitivity to vibration. UTCPs can be embedded in flexible or rigid PCBs using lamination, through-hole drilling, and via metallization. UTCP production and PCB embedding is completely solderless, thus avoiding associated reliability problems, usually encountered in harsh environments. The following two sections describe the process flow and application examples for flexible chip packaging and stretchable electronics. Section 4 discusses the advantages these technologies can offer for space applications. 2. FLEXIBLE CHIP PACKAGING One of the main drivers in packaging research is to integrate as much functionality into a single package as possible, without increasing the overall size of that