Roll-to-roll (R2R) processing on film substrates has been demonstrated to have the potential for achieving high throughput manufacturing of organic electronic systems at low cost. However, the ever-growing mobile devices market accompanied by the developments in information and communication technologies require high performance systems at very low power operation, sometimes on larger substrates having sizes in the range of a few metres. Organic electronics often fall short of fulfilling the required computing performance and power requirements of most of the common use cases. Hybrid integration of inorganic monocrystalline silicon chips on polymer films is a means to fulfil the aforementioned requirements. In this context, it is opportune to report our recent activities on R2R processing of plastic films for hybrid integration of flexible electronics. Hybrid integration can be performed with conventional, rigid surface mount devices as well as flexible, ultrathin bare silicon chips. The first section of the paper is dedicated to a brief overview of R2R manufacturing of electronic devices with an example of production of radio frequency identification tags as well as to a discussion emphasising the targets for hybrid integration. Then, detailed descriptions about our processes for R2R manufacturing of metal wiring lines on films and hybrid integration are included. Three-dimensional integration of films and a temperature sensor label manufactured using hybrid integration process are also elaborated on. Furthermore, key results from fatigue reliability assessment of R2R metallised wiring lines are reported. Finally, some of the challenges in transferring the R2R processes for hybrid integration on film substrates from research labs to industrial manufacturing are highlighted.

Mechanical stress induced by mechanical and thermal loading on thin silicon devices breaks the devices at a certain load called the fracture or breaking strength of the device. The displacement experienced by the dies, due to bending, at fracture strength is called the fracture displacement. The strength properties of thin, bare silicon dies have already been reported. This work extends the study further to demonstrate the improvement in the fracture strength of thin silicon dies, of three different thicknesses (30, 65 and 130 mu m), when integrated in flexible foil substrates. The fracture strength of the dies was measured using uniaxial (3-point-bending test) and biaxial (Ring-ball test) bending tests. Experimental results of the fracture strength of thin, bare silicon dies were in good agreement with simulation results obtained from Finite Element Analysis (FEA). Experimental results showed that there was an increase of the fracture strength up to about 190% and an increase in the curvature of bending up to about 85% when silicon dies were integrated in flexible foil substrates. This increase in the fracture strength and curvature of bending can be useful in designing and manufacturing more mechanically robust flexible electronic devices

We report a Finite Element Model to calculate the bending stress of thin and ultra-thin silicon dies embedded in flexible foil substrates (chip-in-foil package) at lower bending radii. The values of fracture strength computed using Finite Element Analysis showed very good agreement with the experimental results. Furthermore, an increase in the fracture or critical stress (bending stress at fracture) of the dies due to embedding in flexible foil substrates was observed. Besides, the impact of foil material and thickness on the bending stress of ultra-thin silicon die is discussed by comparing two foil materials: Stainless Steel and Polyimide

We present technological results on the embedding of ultra-thin microcontroller ICs in flexible film substrates. The novel concept is based on the following technologies: face-up chip mounting in cavities on film laminates, photo-lithographic patterning of vias and interconnects embedding in polymer layer and compatibility with both sheet and roll-to-roll processing. The paper briefly reviews the benefit of embedding for ultra-thin dies in terms of mechanical robustness. For the technological demonstration, we used 25μm thin microcontroller IC and 50μm polyimide film substrates. Electrical interconnections were realized by sputtering of metal layers. Photolithography was performed on “wafer level” using aligner photomasks and a photo-sensitive polymer of 10μm thickness for embedding. The embedding process resulted in a mechanically flexible fan-out chip package of a thickness below 100μm. Perspectives and technological requirements for roll-to-roll manufacture as well as cost estimation for this kind of Thin Chip Foil Package are explained and discussed. Furthermore, we report our recent work on the development of an in-situ bending and electrical test equipment for flexible film modules. The new set-up was evaluated using ultra-thin test chips with daisy chain patterns that were ACA flip-chip bonded onto Polyimide films. It was found that reducing the chip thickness from 28μm to 12μm lead to a strong increase in mechanical strength of the chip-on-film (COF) assemblies tested under recurrent bending