Fabrication of Multi-Dimensional Metallic Micro-Interconnections with Molten Lead-Free Solder by Piezoelectric Ink-jet Printing Method

• Main Authors: Chien-HsunWang, 王建勛
• Other Authors: Weng-Sing Hwang
• Format: Others
• Language: zh-TW
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/53m3r3

博士 === 國立成功大學 === 材料科學及工程學系 === 105 === Inkjet printing technology has made great improvements in print quality and reproduction speed, and is now widely used in the modern electronics packaging industry. The merits of this approach include variable drop size, high precision in positioning, rapid prototyping, and low production cost. However, parameter adjustment is necessary when operating a piezoelectric device at high temperature in order to pile up the molten metallic droplets in stable formations. The Sn-3Ag-0.5Cu lead-free solder material was employed in this study for observing droplets pile up and micro line structures during inkjet printing, and bonding silicon thin-film solar cell modules of the ink-jet printing method. First, the effects of the jet height and variations in impact velocity of successive droplets piled up shapes were observed. The other objective is to obtain the widths and shapes of the molten micro droplets. The effects of the dot spacing, sample temperature and variations in motion velocity of consistent droplets on the shapes of the conducting lines were recorded. Finally, the purpose of this study is to investigate the wetting behavior of the Sn-3Ag-0.5Cu solder alloy and inkjet printing for bonding on the aluminum electrode of a silicon thin-film solar cell substrate. Molten lead-free solder was deposited by utilizing inkjet printing to replace silver paste, thus improving the bonding strength of the connections between the back electrode of the aluminum and copper ribbon in the fabrication of thin-film solar cell modules. A high-speed digital camera was used to record the solder impact and examine the accuracy of the pile up. These impact conditions correspond to We =2.1-15.1 and Oh =5.4×10-3-3.8×10-3. The diameter, volume and velocity of the inkjet solder droplet are around 37-65 μm, 25-144 picoliters, and 2.0-3.7 m∙s-1, respectively. The vertical and inclined column structures of molten lead-free solder can be fabricated using piezoelectric ink-jet printing systems. The line width of each sample was then calculated using a formula over a temperature range of 30 to 70 °C. The results showed that a metallic line with a width of 55 μm can be successfully printed with dot spacing (50 μm) and the stage velocity (50 mm∙s-1) at the substrate temperature of 30 °C. The experimental results revealed that the height (from 0.63 to 0.58) and solidification contact angle (from 72° to 56°) of the metallic micro droplets decreased as the temperature of the sample increased from 30 to 70 °C. The peel strength of the Sn-3.0Ag-0.5Cu solder alloy is better than that of silver paste when the dot spacing of solder droplets is lower than 200 μm (a density of over 50 μg∙mm-2). The findings also show that the contact resistance of the solder alloy is better than that of silver paste when the dot spacing of solder droplets is lower than 100 μm. This results in a low power loss of solar cells of 1.1%, and a good photovoltaic conversion efficiency of over 8.3%. This study thus demonstrates the feasibility of decreasing the efficiency loss of solar cells by employing the proper spacing of lead-free solder droplets by inkjet printing.