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서성민,황승준,라젠드란 스리 하리니,정재필 대한용접·접합학회 2021 대한용접학회 특별강연 및 학술발표대회 개요집 Vol.2021 No.11
Recently, the development of augmented reality(AR)/virtual reality(VR) and inorganic-based LEDs such as GaN have been in the spotlight as technologies to replace liquid crystal displays (LCDs) and organic light-emitting diode displays (OLEDs). A basic study was conducted on type 6 (5-15 μm) Sn-3.0 wt%Ag-0.5 wt%Cu (SAC305) solder paste used to solder the gradually decreasing mini LEDs and micro LEDs to the substrate. SAC305 solder is mainly used in the industry due to its characteristics such as melting temperature of 217°C to 219°C, excellent soldering and electrical performance, high-temperature resistance, strength, and ductility. However, SAC305 has a disadvantage in that the Cu substrate reacts with Sn, and the Cu-Sn-based intermetallic compound (IMC) excessively grows at the Solder/Cu interface, which is the junction, thereby degrading mechanical properties. As a method for inhibiting the growth of Ag3Sn particles and Cu6Sn5 IMC, there is a method of adding nanopowder into a solder matrix. In this research, five types of nanocomposite solder paste consisting 0.05 wt%, 0.10 wt%, 0.15 wt%, 0.30 wt%, and 0.60 wt% of Tb4O7 nanopowder were added to Type 6 SAC305. Density differences of SAC305 and Tb4O7 are 7.38 g/㎤and 7.3 g/㎤, respectively, thereby reducing nanoparticle separation due to buoyancy effects. The mechanical characteristics and high temperature and humidity reliability of the nano-reinforced SAC305/Cu junction are studied. The microstructure of the nanocomposite solder confirmed that β-Sn area decreased from an average of 2256.38 μ㎡ to 722.26 μ㎡ as the amount of Tb4O7 added increased from 0 wt% to 0.30 wt%. However, when an excess of 0.60 wt% was added, the β-Sn region increased to 1,398.28 μ㎡. Similarly, 0 wt% to 0.30 wt% Tb4O7 added solder exhibited improved mechanical characteristics such as tensile strength, microhardness, and shear strength. However, property degradation is observed for higher addition as the excessive amount of nanoparticles is added, uneven dispersion and voids caused by the nanoparticles’ aggregation to lower the solder matrix’s interface energy make it easy to propagate cracks.