Undercut structures fabricated by microtransfer printing combined with UV exposure and their applications

In this paper. the undercut structures were fabricated by microtransfer printing of metal films on the surface of photoresist combined with UV exposure and photoresist film developing. The patterned metal films were used as mask to realize the selective UV exposure of photoresist Firstly. The undercut structures. which consist of the top metal films and the patterned bottom photoresist, formed in the subsequent developing process because of the lateral dissolving of photoresist at the edge of the unexposed regions. The method proposed in this paper has wider tolerance to the changing of the patterning parameters. but, without effect on patterning resolution since the metal film was used as the top layer. The undercut Structures were Used as separators to pattern passive-matrix display of organic light-emitting diodes (OLEDs). No visible difference of the device performance was observed Compared with the OLEDs patterned by the shadow mask.

Patterned self-adaptive polymer brushes by "grafting to" approach and microcontact printing

Patterned self-adaptive PS/P2VP mixed polymer brushes were prepared by "grafting to" approach combining with microcontact printing (muCP). The properties of the patterned surface were investigated by lateral force microscopy (LFM), XPS and water condensation figures. In the domains with grafted P2VP, the PS/P2VP mixed brushes demonstrated reversible switching behavior upon exposure to selective solvents for different components. The chemical composition of the top layer as well as the surface wettability can be well tuned due to the perpendicular phase segregation in the mixed brushes. While in the domains without grafted P2VP, the grafted PS did not have the capability of switching. The development and erasing of the pattern is reversible under different solvent treatment.

Metal printing with modified polymer bonding lithography

SOFT CONTACT LAMINATION; LIGHT-EMITTING DEVICES; LIFT-OFF; FABRICATION; TRANSISTORS; DIODES; FILMS; STAMP

Fabrication of arrays of silver nanoparticle aggregates by microcontact printing and block copolymer nanoreactors

A combination of microcontact printing and block copolymer nanoreactors succeeded in fabricating arrays of silver nanoparticle aggregates. A complex solution of polystyrene-block-poly(4-vinylpyridine) micelles and silver salt was used as an ink to form thin films or droplets on polydimethylsiloxane stamp protrusions. After these complex aggregates were printed onto silicon substrates under controlled conditions, highly ordered arrays of disklike, dishlike, and dotlike complex aggregates were obtained. A Subsequent oxygen reactive ion etching treatment yielded arrays of silver nanoparticle aggregates.

Metal transfer printing and its application in organic field-effect transisitor fabrication

The fabrication of multilayer microstructures, for example for organic field-effect transistors, using metal transfer printing (MTP) is demonstrated. The Figure shows a two-layer gold structure produced by MTP. Since MTP is a purely additive technique, in which mechanical adhesion acts as the patterning driving force, it is considered an attractive approach to reel-to-reel processing.

XP. A Common Lisp Pretty Printing System

XP provides efficient and flexible support for pretty printing in Common Lisp. Its single greatest advantage is that it allows the full benefits of pretty printing to be obtained when printing data structures, as well as when printing program code. XP is efficient, because it is based on a linear time algorithm that uses only a small fixed amount of storage. XP is flexible, because users can control the exact form of the output via a set of special format directives. XP can operate on arbitrary data structures, because facilities are provided for specifying pretty printing methods for any type of object. XP also modifies the way abbreviation based on length, nesting depth, and circularity is supported so that they automatically apply to user-defined functions that perform output ??g., print functions for structures. In addition, a new abbreviation mechanism is introduced that can be used to limit the total numbers of lines printed.

XP. A Common Lisp Pretty Printing System

XP provides efficient and flexible support for pretty printing in Common Lisp. Its single greatest advantage is that it allows the full benefits of pretty printing to be obtained when printing data structures, as well as when printing program code. XP is efficient, because it is based on a linear time algorithm that uses a small fixed amount of storage. XP is flexible, because users can control the exact form of the output via a set of special format directives. XP can operate on arbitrary data structures, because facilities are provided for specifying pretty printing methods for any type of object.

Automated Camera Layout to Satisfy Task-Specific and Floorplan-Specific Coverage Requirements

In many multi-camera vision systems the effect of camera locations on the task-specific quality of service is ignored. Researchers in Computational Geometry have proposed elegant solutions for some sensor location problem classes. Unfortunately, these solutions utilize unrealistic assumptions about the cameras' capabilities that make these algorithms unsuitable for many real-world computer vision applications: unlimited field of view, infinite depth of field, and/or infinite servo precision and speed. In this paper, the general camera placement problem is first defined with assumptions that are more consistent with the capabilities of real-world cameras. The region to be observed by cameras may be volumetric, static or dynamic, and may include holes that are caused, for instance, by columns or furniture in a room that can occlude potential camera views. A subclass of this general problem can be formulated in terms of planar regions that are typical of building floorplans. Given a floorplan to be observed, the problem is then to efficiently compute a camera layout such that certain task-specific constraints are met. A solution to this problem is obtained via binary optimization over a discrete problem space. In experiments the performance of the resulting system is demonstrated with different real floorplans.

Inkless microcontact printing on SAMs of Boc- and TBS-protected thiols.

We report a new inkless catalytic muCP technique that achieves accurate, fast, and complete pattern reproduction on SAMs of Boc- and TBS-protected thiols immobilized on gold using a polyurethane-acrylate stamp functionalized with covalently bound sulfonic acids. Pattern transfer is complete at room temperature just after one minute of contact and renders sub-200 nm size structures of chemically differentiated SAMs.

A non-Newtonian computational fluid dynamics study of the stencil printing process

This paper describes the application of computational fluid dynamics (CFD) to simulate the macroscopic bulk motion of solder paste ahead of a moving squeegee blade in the stencil printing process during the manufacture of electronic components. The successful outcome of the stencil printing process is dependent on the interaction of numerous process parameters. A better understanding of these parameters is required to determine their relation to print quality and improve guidelines for process optimization. Various modelling techniques have arisen to analyse the flow behaviour of solder paste, including macroscopic studies of the whole mass of paste as well as microstructural analyses of the motion of individual solder particles suspended in the carrier fluid. This work builds on the knowledge gained to date from earlier analytical models and CFD investigations by considering the important non-Newtonian rheological properties of solder pastes which have been neglected in previous macroscopic studies. Pressure and velocity distributions are obtained from both Newtonian and non-Newtonian CFD simulations and evaluated against each other as well as existing established analytical models. Significant differences between the results are observed, which demonstrate the importance of modelling non-Newtonian properties for realistic representation of the flow behaviour of solder paste.

Correlation of solder paste rheology with computational simulations of the stencil printing process

Soldering technologies continue to evolve to meet the demands of the continuous miniaturisation of electronic products, particularly in the area of solder paste formulations used in the reflow soldering of surface mount devices. Stencil printing continues to be a leading process used for the deposition of solder paste onto printed circuit boards (PCBs) in the volume production of electronic assemblies, despite problems in achieving a consistent print quality at an ultra-fine pitch. In order to eliminate these defects a good understanding of the processes involved in printing is important. Computational simulations may complement experimental print trials and paste characterisation studies, and provide an extra dimension to the understanding of the process. The characteristics and flow properties of solder pastes depend primarily on their chemical and physical composition and good material property data is essential for meaningful results to be obtained by computational simulation.This paper describes paste characterisation and computational simulation studies that have been undertaken through the collaboration of the School of Aeronautical, Mechanical and Manufacturing Engineering at Salford University and the Centre for Numerical Modelling and Process Analysis at the University of Greenwich. The rheological profile of two different paste formulations (lead and lead-free) for sub 100 micron flip-chip devices are tested and applied to computational simulations of their flow behaviour during the printing process.

Stencil printing at sub-100 microns pitch

This article presents the latest print results at less than 100 microns pitch obtained in stencil printing type 6 and 7 lead-free solder pastes and conductive adhesives. The advantages of the microengineered stencil arc presented and compared with other bonding technologies. Characterisation of the print deposits is presented and future applications of stencil printing are described.

Stencil printing at sub-100 microns pitch

This article presents the latest print results at less than 100 microns pitch obtained in stencil printing type 6 and 7 leadfree solder pastes and conductive adhesives. The advantages of the microengineered stencil are presented and compared with other bonding technologies. Characterisation of the print deposits is presented and future applications of stencil printing are described.

Ultra-fine pitch stencil printing for a low cost and low temperature flip-chip assembly process

This paper presents the results of a packaging process based on the stencil printing of isotropic conductive adhesives (ICAs) that form the interconnections of flip-chip bonded electronic packages. Ultra-fine pitch (sub-100-mum), low temperature (100degC), and low cost flip-chip assembly is demonstrated. The article details recent advances in electroformed stencil manufacturing that use microengineering techniques to enable stencil fabrication at apertures sizes down to 20mum and pitches as small as 30mum. The current state of the art for stencil printing of ICAs and solder paste is limited between 150-mum and 200-mum pitch. The ICAs-based interconnects considered in this article have been stencil printed successfully down to 50-mum pitch with consistent printing demonstrated at 90-mum pitch size. The structural integrity or the stencil after framing and printing is also investigated through experimentation and computational modeling. The assembly of a flip-chip package based on copper column bumped die and ICA deposits stencil printed at sub-100-mum pitch is described. Computational fluid dynamics modeling of the print performance provides an indicator on the optimum print parameters. Finally, an organic light emitting diode display chip is packaged using this assembly process

Rheological characterisation and printing performance of Sn/Ag/Cu solder pastes

Lead-free solder paste printing process accounts for majority of the assembly defects in the electronic manufacturing industry. The study investigates rheological behaviour and stencil printing performance of the lead-free solder pastes (Sn/Ag/Cu). Oscillatory stress sweep test was carried out to study the visco-elastic behaviour of the lead-free solder pastes. The visco-elastic behaviour of the paste encompasses solid and liquid characteristic of the paste, which could be used to study the flow behaviour experienced by the pastes during the stencil printing process. From this study, it was found that the solid characteristics (G0) is higher than the liquid characteristic (G0 0) for the pastes material. In addition, the results from the study showed that the solder paste with a large G0 = G0 0 has a higher cohesiveness resulting in poor withdrawal of the paste during the stencil printing process. The phase angles (d) was used to correlate the quality of the dense suspensions to the formulation of solder paste materials. This study has revealed the value of having a rheological measurement for explaining and characterising solder pastes for stencil printing. As the demand for lead free pastes increases rheological measurements can assist with the formulation or development of new pastes.