Taik-Min Lee

Improvement of Inverted Hybrid Organic Light-emitting Diodes Properties with Bar-coating Process

Solution processed conjugated molecules enable to manufacture various electronic devices by unconventional and cost effective patterning methods as screen or gravure printing. Spin-coating is the most popularly used method to form conjugated polymeric film for various electronic devices. The coating method has certain disadvantages such as a large amount of unwanted wastes, difficulty forming a film with a large area, and impossible to apply roll-to-roll manufacturing. We present here a promising alternative coating method, bar-coating for conjugated polymer film and OLED with the bar coated light emitting layer. In this papers, we show atomic force microscope images of spin- and bar-coated Poly[(9,9-di-n-octylfluorenyl-2,7- diyl)-alt-(benzo[2,1,3]thiadiazol-4,8-diyl)] (F8BT) films on substrate. The bar-coated film showed a slight lower RMS roughness (1.058 [nm]) than spin-coated film (1.767 [nm]). It means the barcoating is suitable method to form light emitting layers in OLEDs. By using bar-coating process, an OLED obtained with 4.7 [cd/A] in maximum current efficiency.

Effect of particle size distribution on the mechanical and electrical properties of reverse-offset printed Sn–Ag–Cu solder bumps

A reduction of the particle size used in solder pastes was shown to affect the electrical and mechanical properties of finely printed solder bumps. Sn–3.0Ag–0.5Cu solder nanoparticles were synthesized using a radio frequency thermal plasma system, and solder pastes were formulated for reverse-offset printing of solder bump arrays with a size of 30xa0µm. As the nanoparticle ratio in the paste increased, the degree of supercooling, ΔT, increased with a separation of the exothermic peaks for the solidification of β-Sn and the precipitation of intermetallic compounds (IMCs). The networks of finely precipitated IMCs formed at the boundaries of large β-Sn increased the shear strength to 73xa0MPa. However, insufficient flux deteriorated the electrical and mechanical properties because it delayed the solidification of primary β-Sn as well as the melting of the solder. As a result, the Sn–3.0Ag–0.5Cu solder paste containing a nanoparticle ratio of 25% exhibited an optimum printability for reverse-offset printing of solder bumps, and the resulting bumps had an electrical conductance of 0.4xa0mΩ and a shear strength of 73xa0MPa.

Precision Measurement and Control of Synchronization Errors in a Contact-Type Printing Machine for Fine Pattern Printing and Overlay Improvement

Next-generation patterning processes have been extensively studied recently, with a view to replacing the photo-lithographic process and to reducing production costs. For micron scale patterning, the printing process is one of major candidates. In particular, contact printing is more promising in view of the possibilities for mass production. In this process, the motion of the two printing contact surfaces should be synchronized perfectly to prevent slip and unwanted distortion in the surfaces and to make precise ink transfer between the surfaces. In this article, a force-based direct measurement method of the synchronization error is proposed, and the effect of synchronization error on the printing process is analyzed.Copyright