A versatile system for the fabrication of surface microstructures is demonstrated by combining the photomechanical response of supramolecular azopolymers with structured polarized illumination from a high resolution spatial light modulator. Surface relief structures with periods 900 nm - 16.5 µm and amplitudes up to 1.0 µm can be fabricated with a single 5 sec exposure at 488 nm. Sinusoidal, circular, and chirped surface profiles can be fabricated via direct programming of the spatial light modulator, with no optomechanical realignment required. Surface microstructures can be combined into macroscopic areas by mechanical translation followed by exposure. The surface structures grow immediately in response to illumination, can be visually observed in real time, and require no post-exposure processing.

Thin film supramolecular azopolymers support the all‐optical generation of dynamic surface microstructures. Using a spatial light modulator (SLM) illuminated at 488 nm, structured polarized light drives surface waves of sinusoidal profile with periods 700 nm–5 µm at speeds up to 1 µm s−1. Multiple regions on the film surface within the SLM focal plane can be independently set into motion, each with unique period, speed, amplitude, and propagation direction. The underlying mechanism is the photomechanical response of the azopolymer, which is more commonly exploited for the fabrication of static surface microstructures. Hydrogen‐bonded systems such as the supramolecular system described here are particularly advantageous due to their facile fabrication from commercially available components. In addition to applications in dynamic diffractive optics, this programmable system for optical surface waves is well‐suited for studies in nanoparticle manipulation, as well as in bioengineering as a reconfigurable surface template for directed cell growth.

Surface micrograting arrays have applications ranging from diffractive optics to bioengineered surfaces. We report a versatile fabrication platform for the maskless photofabrication of these arrays based on structured polarized light and photoresponsive azopolymer films. The films are patterned using a spatial light modulator (SLM) configured as a polarization modulator. The light source is a 488 nm laser with exposure times of order 5 sec or less. Structured polarized light from the SLM is imaged onto the film, writing a 120 µm x 80 µm surface relief pattern with amplitudes and periods controllable from 25 nm to 1 µm and 700 nm-10 µm respectively. These are stitched into larger area patterns via XY translation. The versatility is demonstrated through a variety of micrograting patterns, including diffractive optical elements, multiplexed surface grating arrays, and diffractive optically variable image devices for optical security applications. In a different application, the biocompatibility of the polymeric film can be leveraged since cellular interaction with synthetic microscale structures influences a wide array of cell responses. We demonstrate this by showing directed cell growth mediated by the micrograting array. In all examples, the surface gratings required no post-exposure processing, are stable in ambient conditions, and can be replicated using nanoimprint lithography.

In microelectronic packaging, encapsulation by compression and transfer molding is a crucial process block to ensure device reliability. Material properties of encapsulants, highly filled systems of reactive epoxy molding compounds (EMC), strongly depend on process conditions in a complex manner and vary over time. Shear-thinning behavior, as well as time- and temperature-dependent conversion strongly impact the viscosity of the polymer melt. In all fields of application, such as automotive or IoT, demands towards miniaturization, lifetime and environmental conditions increase. Thus, detailed understanding of the complex material behavior is of vital importance. Typically, shear-thinning behavior of polymer melts is characterized using a conventional rheometer in oscillation mode under varying shear-rates and temperatures. Limitations of this approach are, that measurements at process temperature typically cannot be performed due to the high reactivity of the encapsulant at these temperatures (e.g. 175 °C for transfer molding). Therefore extrapolation to the correct temperature range is required. Furthermore, measurements in oscillation mode cannot necessarily be transferred to real process conditions, where a continuous flow is present. To overcome these limitations the inline viscometer can be used, a specially designed measurement tool for a transfer molding machine developed by Fico/Besi. The polymer melt is pressed through a narrow slit under known volumetric flow at process temperature. By measuring the pressure difference before and after the slit, the viscosity can be calculated. In order to better understand and also predict material behavior, inline viscosimetry is combined with rheometer measurements. This allows to maintain the advantages of conventional rheometry regarding material consumption and large shear-rate measuring range. At the same time, the inline approach provides relevant data under process conditions. The synthesis of both approaches yields a correction of the rheometer measurements, ultimately improving viscosity modeling and being an improved basis for process simulation.

No abstract