Kwon-Yong Shin

Silver inkjet printing with control of surface energy and substrate temperature

The characteristics of silver inkjet printing were intensively investigated with control of surface energy and substrate temperature. A fluorocarbon (FC) film was spincoated on a silicon (Si) substrate to obtain a hydrophobic surface, and an ultraviolet (UV)/ozone (O3) treatment was performed to control the surface wettability of the FC film surface. To characterize the surface changes, we performed measurements of the static and dynamic contact angles and calculated the surface energy by Wus harmonic mean model. The surface energy of the FC film increased with the UV/O3 treatment time, while the contact angles decreased. In silver inkjet printing, the hydrophobic FC film could reduce the diameter of the printed droplets. Merging of deposited droplets was observed when the substrate was kept at room temperature. Substrate heating was effective in preventing the merging phenomenon among the deposited droplets, and in reducing the width of printed lines. The merging phenomenon of deposited droplets was also prevented by increasing the UV/O3 treatment time. Continuous silver lines in the width range of 48.04–139.21 µm were successfully achieved by inkjet printing on the UV/O3-treated hydrophobic FC films at substrate temperatures below 90 °C.

Periodic fuel supply to a micro-DMFC using a piezoelectric linear actuator

A reciprocating pump using a piezoelectric linear actuator is introduced as a fuel supply module for a direct methanol fuel cell (DMFC) stack. The results show that the key advantage of the pump with the linear actuator is its ability to operate at a low frequency, which enables high flow rectification performance. At the end of this study, the pump is applied to a DMFC system to demonstrate that the output voltage of a DMFC stack remains stable with time even when the pumping pressure oscillates periodically at frequencies of a few Hz. It is also demonstrated that the maximum output power of the stack exceeds 6 W with power consuming 3.5% of the stack power for the fuel pump.

Characterization of Inkjet-Printed Silver Patterns for Application to Printed Circuit Board (PCB)

In this paper, we describe the analysis of inkjet-printed silver (Ag) patterns on epoxycoated substrates according to several reliability evaluation test method guidelines for conventional printed circuit boards (PCB). To prepare patterns for the reliability analysis, various regular test patterns were created by Ag inkjet printing on flame retardant 4 (FR4) and polyimide (PI) substrates coated with epoxy for each test method. We coated the substrates with an epoxy primer layer to control the surface energy during printing of the patterns. The contact angle of the ink to the coated epoxy primer was 69˚, and its surface energy was 18.6 mJ/m². Also, the substrate temperature was set at 70℃. We were able to obtain continuous line patterns by inkjet printing with a droplet spacing of 60 ㎛. The reliability evaluation tests included the dielectric withstanding voltage, adhesive strength, thermal shock, pressure cooker, bending, uniformity of line-width and spacing, and high-frequency transmission loss tests.

Modification of Surface Properties for Industrial Ink-jet Printing

characteristics of silver inkjet printing were intensively investigated under control of surface energy and substrate temperature. A fluorocarbon (FC) film was spincoated on a polyimide (PI) substrate to obtain a hydrophobic surface, and an ultraviolet (UV)/ozone (O3) treatment was performed to control surface wettability of the FC film surface. To characterize the surface changes, we performed measurements of the static and dynamic contact angles and calculated surface energy by Wus harmonic mean model. In silver inkjet printing, the hydrophobic FC film could reduce the diameter of the printed droplets. Merging of deposited droplets was observed when the substrate was kept at room temperature. Substrate heating was effective in preventing the merging phenomenon among the deposited droplets, and in reducing the width of printed lines. The merging phenomenon of deposited droplets was prevented also by increasing the UV/O3 treatment time.

A Bonding Method For Electrical Connection Between Chip And Substrate Using Inkjet Printing Technology

Inkjet printing technology has merits such as simple manufacturing process, low cost, small pollution source and high productivity. It is utilized in the production of printed electronics, Radio Frequency (RF) devices and flexible displays [1-2]. A new application includes bump fabrication to electrically connect chip and substrate on semiconductor packages. In practice, wire bonding technology has been mainly used for these electrical connections, which can be bonded at a low price. At higher frequencies, however, the wire bonding technique reaches the limit for RF applications, because the bonding wire generates a parasitic inductance that degrades the transmission characteristics. On the other hand, flip chip bonding technology has been developed to overcome the disadvantages of wire bonding [3]. Although flip chip bonding technology can be performed minimizing the distance between chip and substrate, the bump fabrication process is very complex. To solve the disadvantage of flip-chip bonding, we propose a new technique, using inkjet-printed bump technology. The key of this technology is to make bumps using inkjet printing technology, which is cheaper and simpler when compared to the flip chip bonding method. This paper presents a transmission line for direct current (DC T-line) bonded using inkjet-printed bumps. The bonded DC T-lines were fabricated and tested to verify electrical connection stability, before applying the inkjet-printed bump technique in packages with variable area. Finally, the characteristics of the DC T-lines were compared with straight lines.

Fuel Supply to Micro DMFC using Reciprocating Pump with Ultrasonic Linear Actuator

A reciprocating pump operated by a piezoelectric linear actuator is introduced as a fuel supplying module for a DMFC. A series of experiments are conducted to characterize the performance of the present pump and effects of low reciprocating frequency pumping of fuel on output power of DMFC. The performance of the pump is studied with respect to reciprocating frequency and operating duty. The results show that the key advantage of the current pump is an ability of low frequency operation which enables high flow rectification performance and that power consumption of the pump is almost linearly proportional to the flow rate. It is also shown that the output voltage of the DMFC is stable with time even though the pumping pressure oscillates periodically

Effects of substrate treatments on silver ink-jet printing

In this study, characteristics of silver ink-jet printing were investigated under various substrate treatments such as substrate heating, hydrophobic coating, and ultraviolet (UV)/ozone soaking. Fluorocarbon (FC) film was spin-coated on the polyimide (PI) film substrate to obtain a hydrophobic surface. The coated FC film surface was estimated to have a fairly hydrophobic nature in that it exhibited a large water contact angle of 110‐113°. Although hydrophobicity of the FC film could reduce the diameter of the printed droplets, the singlet images printed on the FC film surface showed irregularities in the pattern size and the position of the printed droplet along with droplet merging phenomenon. The proposed UV/ozone soaking of the FC film improved the uniformity of the pattern size and the droplet position after printing and substrate heating was very effective way in preventing droplet merging. By heating of the substrate after UV/ozone soaking of the coated FC film, silver conductive lines of 78‐116 μm line were successfully printed at relatively low substrate temperatures of 40 °C and 70 °C.