Progress in Organic Coatings 99 (2016) 308–313 Contents lists available at ScienceDirect Progress in Organic Coatings j o ur nal ho me pag e: www.elsevier.com/locate/porgcoat Natural rubber based thin coating for MEMS encapsulation K. Ayche a , A. Ventura a , J.-F. Bardeau a , B. Minisini b , J.F. Pilard a,∗ , N. Delorme a,∗ a Institut des Molécules et Matériaux du Mans, UMR-CNRS 6283, Université du Maine, 72085 Le Mans, France b Institut Supérieur des Matériaux et Mécaniques Avancés du Mans, UNAM, Le Mans, France a r t i c l e i n f o Article history: Received 14 March 2016 Received in revised form 14 June 2016 Accepted 15 June 2016 Available online 30 June 2016 Keywords: Thin coating Polymer Thermal reticulation Rubber Crosslinking Spectroscopy a b s t r a c t A new telechelic liquid natural rubber is used to elaborate thin coating (<1 m). The nature of the crosslinking reaction was elucidated via a combined FTIR spectroscopy/ab initio simulation study. This study allows the optimization of the crosslinking reaction (curing temperature and time) through kinetic studies. The modification of the physical properties (i.e. morphology and mechanical properties) dur- ing the crosslinking were followed by atomic force microscopy (AFM). We believe that because of its physical properties as well as its processing conditions, the proposed material is a good candidate for encapsulation MEMS encapsulation. © 2016 Elsevier B.V. All rights reserved. 1. Introduction Microelectronic systems (MEMS) play a major role in many fields such as communication, biomedical, automotive, and aerospace with major classes of devices being: inertial sensors, microfluidics, pressure sensors and inkjet heads. In order to protect sensitive components from exposure to moisture, heat or mechan- ical stress, a protective coating that is both hard and flexible, with high requirements for outdoor durability such as corrosion pro- tection, adhesion, and resistance to chemicals is required [1]. In addition, the race for faster, smaller and cheaper systems leads to develop new fabrication strategies. Polymer encapsulation has the advantage compared to other strategy to provide a low cost, easy implementation, low weight and smaller dimension solution. Usually the polymer coating is deposited over the component in solution or in a viscous form. Then a curing procedure (i.e. thermal or irradiation) is applied in order to give to the coating a bet- ter mechanical strength, thermal stability, and chemical resistance [2,3]. Usually thermoset resins such as epoxy resins are used to coat MEMS [4]. However cured epoxy systems are characterized by a rel- atively high Young modulus and low toughness which means poor ∗ Corresponding authors at: Institut des Molécules et Matériaux du Mans, UMR- CNRS 6283, Université du Maine, 72085 Le Mans, France. E-mail addresses: jean-francois.pilard@univ-lemans.fr (J.F. Pilard), Nicolas.delorme@univ-lemans.fr (N. Delorme). resistance to crack propagation [5]. In addition to the environmen- tal argument, natural rubber based resin offers the advantage of a better flexibility [5] and for electronic applications, NR has already been used as an effective electrical insulator [6] or dopped as a conductive polymer [7]. To our knowledge very few works have been reported regard- ing the application of NR based polymer as thin coatings (< m) [8,9]. One of the reason is probably due to the low thermal sta- bility of NR which is known to degrade at a high temperature or when exposed to oxygen, ozone or ultraviolet [10]. To improve its intrinsic properties, we choose to work with a telechelic liquid nat- ural rubber (TLNR) obtained by fragmentation of the natural rubber (cis-1,4-polyisoprene). In our laboratory a methodology has been optimized to cut the polyisoprene chains of natural rubber into telechelic oligomers that bear functional groups at the chain ends, which allows performing further chemical reactions [11,12]. TLNR has various specificities: high elasticity, low molecular weight and can be crosslinked via the presence of C C double bonds [13–15]. In this study, thin coating of a di-acrylate functionalized TLNR will be prepared and thermally crosslinked via a sulfonyl azide compounds (1,3-BDSA). Sulfonyl azide compounds are known to crosslink different kinds of polymers such vinyl ether polymers, alpha-alkyl polymers and ethylene polymers [16–18]. However, the study of thin films based on unsaturated polymers and sul- fonyl azides has not earlier been addressed in literature. The main objective of the present work is to investigate the crosslinking reaction and the induced thermal treatment of natural rubber based thin coatings. To this end, important factors like the nature http://dx.doi.org/10.1016/j.porgcoat.2016.06.010 0300-9440/© 2016 Elsevier B.V. All rights reserved.