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Ultrathin bare die chips and small-size surface mount device components were successfully soldered using a novel roll-to-roll compatible soldering technology. A high-power xenon light flash was used to successfully solder the components to copper tracks on polyimide (PI) and polyethylene terephthalate (PET) flex foils by using a lead-free solder paste. Results are compared with oven-reflowed solder joints on PI substrates. The delicate PET foil substrates were not damaged owing to the selectivity of light absorption, leading to a limited temperature increase in the PET foil while the chip and copper tracks were heated to a temperature high enough to initiate soldering. The microstructure of the soldered joints was investigated and found to be dependent on the photonic flash intensity. Reliability of the photonically soldered joints during damp heat testing and dynamic flexing testing was comparable with the reflowed benchmark and showed increased reliability compared with anisotropic conductive adhesives bonded on PET foils.

In this work photonic energy from a high power xenon flash lamp is used for soldering thin chips on polyimide and polyester foil substrates using standard Sn-Ag-Cu lead free alloys. The absorption of the xenon light pulse leads to rapid heating of components and tracks up to temperatures above the solder melting temperature, while the temperature in the organic foil substrates remains low. Due to its high transparency the temperature in the delicate polyester foil remains low enough to avoid damage and allows fast soldering with standard lead-free alloys. The technology is fast and could be applied in-line in roll-to-roll fabrication of flexible electronics. In situ temperature measurements were performed and compared to finite element model predictions of the temperature in the chip during and after application of the photonic pulse. The accuracy of the model is within 10°C for the tested samples, which allows it to be used in developing photonic flash soldering compatible circuit designs.[Figure not available: see fulltext.].

Colloidal suspensions of nanoparticles are increasingly employed in the fabrication process of electronic devices using inkjet-printing technology and a consecutive thermal treatment. The evolution of internal stresses during the conversion of silver nanoparticle-based ink into a metallic thin-film by a thermal sintering process has been investigated by in-situ XRD using the sin2ψ method. Despite the CTE mismatch at the film/substrate interface, the residual stress in silver films (below 70 MPa) remains lower than in conventional PVD thin-films, as a result of the remaining porosity. A Warren-Averbach analysis further showed that the crystallite growth is associated with a minimization of the twin fault density and the elastic microstrain energy above 150°C. A stabilization of the microstructure and internal stress is observed above 300°C. Inkjetprinting technology thus appears as a good alternative to conventional metallization techniques and offers significant opportunities asset for interconnect and electronic packaging. cop. (2014) Trans Tech Publications, Switzerland. 'Conseil General de l'Aube'; Conseil National de la Recherche Scientifique (CNRS); et al; Grand Troyes; Proto Manufacturing; Region Champagne-Ardenne

Le developpement recent d'encres fonctionnalisees constituees de nanoparticules metalliques, associe a la maitrise du procede d'impression par jet de matiere, a rendu possible l'emergence de l'electronique imprimee. Les structures imprimees peuvent etre traitees par des techniques de recuit selectif qui permettent de realiser la coalescence de nanoparticules de 20 nm a une temperature de procede compatible avec les substrats plastiques flexibles. Cet article aborde les differents aspects lies a la realisation de pistes metalliques sur substrat souple, depuis les technologies d'impression directes, jusqu'a l'adequation entre les caracteristiques microstructurales et les proprietes electriques de telles structures pour la fabrication de dispositifs tels que des antennes, des pistes de routage ou des electrodes.

International audience; The effect of thermal profile on microstructure is studied in the frame of thin films deposited by inkjet-printing technology. The role of sintering temperature and thermal ramp is particularly investigated. Fast heating ramps exhibit coarse grains and pores, especially when a hybrid microwave curing is performed. This enhanced growth is attributed to the quick activation of densifying sintering regimes without undergoing thermal energy loss at low temperature. Microstructural evolution of various sintered inkjet-printed films is correlated with electrical resistivity and with the Young's modulus determined by nanoindentation. A strong link between those three parameters is highlighted during experiments giving credit to either a surface or a fully volumetric sintering, according to the process. Sintering is then mainly triggered by surface mass transfer or by grain boundary diffusion respectively. Silver thin-films with an electrical resistivity 4 to 5 times higher than the bulk has been reached in a few minutes and with a Young's modulus of 38 GPa.

This paper describes an in-line process for the realization of 3D electronic components on A4 format substrate by piezo inkjet printing. This process is developed within a semi-industrial prototype system named “JETPAC”. JETPAC includes an oxygen plasma torch for surface preparation and post-process modules as a variable frequency microwave oven and an UV lamp for metal selective sintering and dielectric ink curing, respectively. JETPAC is used to achieve passive components by chaining conductor and dielectric layers on kapton® substrate: silver nanoparticles based ink is used to print conductors. For multilayer component elaboration, the metal ink is deposited both on kapton® and on printed dielectric materials. Due to a low surface energy (S.E) of the printed dielectric, the realization of efficient silver tracks is compromised. A special process combines O2 plasma treatment and UV exposure before printing, allowing the reaching of S.E. value on dielectric near the optimum one (55mN/m). This pre-process allows printing of well-defined conductive structures on top of the dielectric. In-line sintering of printed structures is then performed using variable frequency microwave source. The process allows the elaboration of multilayer structures including stacked resistors and capacitors. These results make the developed process very promising for the realization by inkjet printing of passive devices for smart tag applications.

In this paper, silver nanoparticles with a mean diameter of 40 nm are studied for future applications in microelectronic devices. The enhanced diffusivity of nanoparticles is exploited to fabricate electrical interconnects at low temperature. Sintering condition has been tuned to tailor the grain size so that electrical resistivity can be lowered down to 3.4 μOhm∙cm. In this study, a {111}-textured gold thin film has been used to increase diffusion routes. The combined effects of the substrate crystalline orientation and the sintering condition have been demonstrated to have a significant impact on microstructures. In particular, a {111} fiber texture is developed above 300°C in printed silver only if the underlying film exhibits a preferential orientation. This condition appeared as essential for the efficiency of the gold wire-bonding process step. Thus, inkjet-printed interconnects show a prospective potential compared to conventional subtractive technique and offers new opportunities for low cost metallization in electronics packaging.

An efficient strategy for the up-scaling of processing technology for inkjet printing of silver nanoparticle inks towards industrially relevant manufacturing volumes is described. This has been demonstrated by the roll-to-roll production of fine conductive patterns on polymer foils. Starting with small-scale benchmarking to identify the most suitable ink–substrate combination from a range of commercial products, the processing conditions for inkjet printing and sintering were continuously optimized during three consecutive stages. During each iteration, the scale of the experiments in terms of complexity, time requirement and materials usage was increased, thereby more closely resembling the final industrial-scale production conditions. This increased effort was, however, counterbalanced by limiting the number of necessary experiments by purposeful selection based on the results obtained at the lower levels. In addition, the outcome of each previous iteration round served as a starting point for the optimization during the next higher stage. In this way, it was possible to strongly restrict the number of experiments to obtain valuable information about the most ideal conditions at the final stage, which was a roll-to-roll pilot production line. Following this approach, large-area functional conductive structures on plastic foils could be prepared in a continuous manner at process speeds of up to 10 m min–1. These samples showed promising properties for application in printed electronic devices.