Development of a stretchable and removable electrical interconnection solution for ultra-thin electronic components

International audienceCurrently, the solutions for interconnecting electronic components with their active face facing on substrates are based on metallic soldering. The mechanical contacts are therefore rigid. In order to enhance the reliability of the bonding, underfill is usually used to redistribute the thermo-mechanical stress created by the Coefficient of Thermal Expansion (CTE) mismatch between the silicon chip and substrate. Underfill is done with epoxy resins containing silica fillers (SiO2). As a result, the removal of components is no longer possible. Moreover, this solution is not suitable for devices integrating ultra-thin silicon components (<100 µm) hybridized on flexible substrates that may be subject to deformation. This is the case, for example, of medical "patches" worn on the person and continuously solicited. Indeed, the rigid contact points are likely to break. To address this issue, we are developing a thin anisotropic conductive and stretchable adhesive film inspired by the adhesion of the gecko.. Thanks to the microstructuration of its toes involving about 1 million setae, the gecko can develop a large contact surface and thus a large force of attraction by the multiplication of van der Waals interactions (1). In this work, this "dry adhesion" based on the principle of "contact splitting", was implemented in order to improve the adhesion of a flexible interconnection. For this purpose, the surface of a polydimethylsiloxane (PDMS) film was structured with micrometric mushroom-shaped patterns known to be the most efficient form of contact (2,3). To this end, silicon molds with varying mushroom geometries were used to shape the PDMS (with different cap and pillar diameters) and the adhesion force microstructured films were assessed (shear and pull-off experiments). To make these films locally conductive through the thickness, a conductive composite was prepared and locally deposited in the mold. One approach we investigated, was using a screen-printing mask. This approach has been implemented and characterized using electrical tests (I-V measurements) in order to select the most suitable films to realize a flexible interconnection

Development of a stretchable and removable electrical interconnection solution for ultra-thin electronic components

International audienceCurrently, the solutions for interconnecting electronic components with their active face facing on substrates are based on metallic soldering. The mechanical contacts are therefore rigid. In order to enhance the reliability of the bonding, underfill is usually used to redistribute the thermo-mechanical stress created by the Coefficient of Thermal Expansion (CTE) mismatch between the silicon chip and substrate. Underfill is done with epoxy resins containing silica fillers (SiO2). As a result, the removal of components is no longer possible. Moreover, this solution is not suitable for devices integrating ultra-thin silicon components (<100 µm) hybridized on flexible substrates that may be subject to deformation. This is the case, for example, of medical "patches" worn on the person and continuously solicited. Indeed, the rigid contact points are likely to break. To address this issue, we are developing a thin anisotropic conductive and stretchable adhesive film inspired by the adhesion of the gecko.. Thanks to the microstructuration of its toes involving about 1 million setae, the gecko can develop a large contact surface and thus a large force of attraction by the multiplication of van der Waals interactions (1). In this work, this "dry adhesion" based on the principle of "contact splitting", was implemented in order to improve the adhesion of a flexible interconnection. For this purpose, the surface of a polydimethylsiloxane (PDMS) film was structured with micrometric mushroom-shaped patterns known to be the most efficient form of contact (2,3). To this end, silicon molds with varying mushroom geometries were used to shape the PDMS (with different cap and pillar diameters) and the adhesion force microstructured films were assessed (shear and pull-off experiments). To make these films locally conductive through the thickness, a conductive composite was prepared and locally deposited in the mold. One approach we investigated, was using a screen-printing mask. This approach has been implemented and characterized using electrical tests (I-V measurements) in order to select the most suitable films to realize a flexible interconnection

A multi-scale mechanical behavior study of an electrical interconnection solution stretchable and removable for flexible electronic components for biomedical applications

International audienceCurrently, the solutions for interconnecting electronic components with their active face facing on substrates are based on metallic soldering. The mechanical contacts are therefore rigid. In order to enhance the reliability of the bonding, underfill is usually used to redistribute the thermo-mechanical stress created by the Coefficient of Thermal Expansion (CTE) mismatch between the silicon chip and substrate. Underfill is done with epoxy resins containing silica fillers (SiO2). As a result, the removal of components is no longer possible. Moreover, this solution is not suitable for devices integrating ultra-thin silicon components (<100 μm) hybridized on flexible substrates that may be subject to deformation. This is the case, for example, of medical "patches" worn on the person and continuously solicited. Indeed, the rigid contact points are likely to break. To address this issue, we are developing an ultra-thin anisotropic conductive adhesive film integrated in a stretchable flex inspired by the adhesion of the gecko. This film can be placed between the electronic component and the substrate. Thanks to the microstructuration of its legs involving about 1 million setae, the gecko can develop a large contact surface and thus a large force of attraction by the multiplication of van der Waals interactions (1).In this work, this "dry adhesion" based on the principle of "contact splitting", was implemented in order to improve the adhesion of a flexible interconnection. For this purpose, the surface of a polydimethylsiloxan (PDMS) film was structured with micrometric mushroom-shaped patterns known as the most efficient form of contact (2,3). To this end, silicon molds with varying mushroom geometries were etched to shape the PDMS (with different flange and pillar diameters). This approach makes it possible to do reproducible achievement of micro structured films with few defects. Studies at the macro and micro-scale were conducted in order to better understand the PDMS-mushrooms mechanical behavior. Mechanical results (using shear tests, pull-off experiments and Nano indentation) were modeled by finite element numerical calculations. Modelling and mechanical experiments at imposed displacement make possible to deduce the stiffness for one PDMS-mushroom in order to predict the number of mushroom contributing to maintain the adhesion. In the other hand, macro-scale experiments have an interest in the mechanical understanding on the total PDMS-film micro patterned. Finally, the impact of adding localized electrical connections through the structured film on the adhesion properties was also evaluated in order to select the most suitable films to obtain a flexible interconnection for biomedical applications

A multi-scale mechanical behavior study of an electrical interconnection solution stretchable and removable for flexible electronic components for biomedical applications

International audienceCurrently, the solutions for interconnecting electronic components with their active face facing on substrates are based on metallic soldering. The mechanical contacts are therefore rigid. In order to enhance the reliability of the bonding, underfill is usually used to redistribute the thermo-mechanical stress created by the Coefficient of Thermal Expansion (CTE) mismatch between the silicon chip and substrate. Underfill is done with epoxy resins containing silica fillers (SiO2). As a result, the removal of components is no longer possible. Moreover, this solution is not suitable for devices integrating ultra-thin silicon components (<100 μm) hybridized on flexible substrates that may be subject to deformation. This is the case, for example, of medical "patches" worn on the person and continuously solicited. Indeed, the rigid contact points are likely to break. To address this issue, we are developing an ultra-thin anisotropic conductive adhesive film integrated in a stretchable flex inspired by the adhesion of the gecko. This film can be placed between the electronic component and the substrate. Thanks to the microstructuration of its legs involving about 1 million setae, the gecko can develop a large contact surface and thus a large force of attraction by the multiplication of van der Waals interactions (1).In this work, this "dry adhesion" based on the principle of "contact splitting", was implemented in order to improve the adhesion of a flexible interconnection. For this purpose, the surface of a polydimethylsiloxan (PDMS) film was structured with micrometric mushroom-shaped patterns known as the most efficient form of contact (2,3). To this end, silicon molds with varying mushroom geometries were etched to shape the PDMS (with different flange and pillar diameters). This approach makes it possible to do reproducible achievement of micro structured films with few defects. Studies at the macro and micro-scale were conducted in order to better understand the PDMS-mushrooms mechanical behavior. Mechanical results (using shear tests, pull-off experiments and Nano indentation) were modeled by finite element numerical calculations. Modelling and mechanical experiments at imposed displacement make possible to deduce the stiffness for one PDMS-mushroom in order to predict the number of mushroom contributing to maintain the adhesion. In the other hand, macro-scale experiments have an interest in the mechanical understanding on the total PDMS-film micro patterned. Finally, the impact of adding localized electrical connections through the structured film on the adhesion properties was also evaluated in order to select the most suitable films to obtain a flexible interconnection for biomedical applications

Flexible Hybrid Electronics Including Ultrathin Strain Sensors or Radio Frequency Identification Dies Manufactured on Wafer Silicon Carrier

International audienceFlexible hybrid electronics (FHE) is becoming a disruptive technology in the packaging of electronic components. Indeed, thanks to the thinness and flexibility of devices, it is conceivable to add a function to any object without changing its aspect. However, this approach faces critical issues such as the management of ultrathin components from different sources and the cost of individual operations. In this paper, a wafer-level packaging (WLP) process for integrated silicon dies coming from various foundries in a flexible label is presented. The process is performed in a microelectronic component manufacturing line on a 200 mm temporary wafer carrier, thus achieving a high level of integration. The purpose of this article is to present results for different hybridization methods of ultrathin silicon dies inside a flexible label. In addition, the process was applied to two demonstrators. The first comprises an ultrathin silicon strain sensor based on a doped crystalline (100) silicon piezoresistive effect that is embedded in a flexible label and bonded to a printed circuit board. When the printed circuit board is mechanically stressed, the die resistances are changed as a result of the piezoresistive effect, and a Wheatstone bridge circuit is used to measure the change in resistance. The second demonstrator is a heterogeneous flexible system including an ultrathin radio frequency identification die integrated within a small flexible label and bonded to a flexible antenna. The functionality of the two demonstrators has been successfully demonstrated

Development and characterizations of fine pitch flip-chip interconnection using silver sintering

Flip-chip interconnects made of silver are promising candidates to overcome the intrinsic limits of solderbased interconnects and match the demand for increased current densities of high-performance microprocessors. Dipbased interconnects have been demonstrated to be a promising approach to form electrical interconnects by sintering paste between copper pillars and pads. However, the quality of the process is limited by residual porosity and poor performances of the sintered joint formed between the pillar and the pad during sintering if a pressure > 50 MPa is not applied in order to decrease the final porosity. In this study, development has been focused on varying key dipping process parameters allowing a pressureless sintering process. Dip-transfer process was optimized on test vehicle and has shown electrical continuity over 700 interconnections with diameter down to 50 µm. We demonstrate high reliability of the process with microstructural observations, tomography X and thermal cycle up to 200 cycles without breakdown

Development and characterizations of fine pitch flip-chip interconnection using silver sintering

International audienceFlip-chip interconnects made of silver are promising candidates to overcome the intrinsic limits of solderbased interconnects and match the demand for increased current densities of high-performance microprocessors. Dipbased interconnects have been demonstrated to be a promising approach to form electrical interconnects by sintering paste between copper pillars and pads. However, the quality of the process is limited by residual porosity and poor performances of the sintered joint formed between the pillar and the pad during sintering if a pressure > 50 MPa is not applied in order to decrease the final porosity. In this study, development has been focused on varying key dipping process parameters allowing a pressureless sintering process. Dip-transfer process was optimized on test vehicle and has shown electrical continuity over 700 interconnections with diameter down to 50 µm. We demonstrate high reliability of the process with microstructural observations, tomography X and thermal cycle up to 200 cycles without breakdown

Low-temperature silver sintering by colloidal approach

ISBN 978-1-7281-6293-5International audienceThe interest of silver nanostructures has surged in recent years as they are becoming promising materials in a growing number of applications. In particular, they have received intense attention for their use as lead-free die attach materials, photoactive devices engineering or more broadly electronic packaging. One of the challenges is the elaboration of conductive and printable patterns by Low-Temperature and Pressureless Sintering Techniques (LTPST) to achieve electric circuits on heat-sensitive substrates such as paper, plastic, polymeric substrates. Here, we present a facile method for synthesizing conductive patterns at low temperature based on the formation of self-assembled Ag nanocubes on Active Metal Brazing (AMB) substrates. The elaboration of 3-D arrays with nanogap of 2-3 nm between the cubic building units allows to get dense and compact packed nanoparticle solids which sinter at lower temperature than conventional commercial silver pastes. The impact of the capping agent and the size of the building units on the sintering properties were investigated and discussed

Haptic interface based on an innovative piezo-in-flex piezoelectric patch technology

International audienceThe tremendous development of tactile interface in many customers applications, such as smartphone, leads industrials to study haptic interfaces which allow the user to interact with its environment by the sense of touch. Piezoelectric actuators are commonly used to actuate such interfaces. In this paper, we present a new and innovative technology to integrate collectively commercial piezoceramics into flexible piezoelectric patches able to be integrated on any surface. We glue the flexible patch on a 4×3cm² glass plate to obtain a plug and play interface. A displacement amplitude of 1µm was measured on a Lamb mode at 58.49kHz, using only 20V. A haptic effect was felt by the finger when we modulate at 60Hz the actuation signal, proving the potential of our piezo-in-flex haptic interface