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New High Entropy Alloy (HEA) Reinforced SAC 305 Solder
Sri Harini Rajendran(라젠드란 스리 하리니),Hye Jun Kang(강혜준),Jae Pil Jung(정재필) 대한용접·접합학회 2021 대한용접학회 특별강연 및 학술발표대회 개요집 Vol.2021 No.5
In order to meet the demands for the developing packaging technologies and to be in pace with the WEEE (2012-19-EU) and RoHS (2002-95-EU) implementations, series of lead-free solders has been developed. Sn-3.0Ag-0.5Cu and Sn-58Bi are the interesting solders fulfilling the demands and environmental standards of consumer electronic industries. However, the brittle phases remain a serious threat in terms of mechanical reliability. Many methods have been adopted by the researches to enhance the reliability of existing solders such as micro-alloying and the addition of second phase particles. However, the quest for new solders remains among the researchers. In the present work, new high entropy alloys have been incorporated in the soldering field. Varying compositions of high entropy solder reinforced SAC alloys were prepared by mechanical mixing. The solder paste was printed and reflowed with 1608 chip capacitor. The microstructure and intermetallic phase evolution along the solder/capacitor for the high entropy solder addition has been characterized by scanning electron microscope. The optimum composition with good solderability were analyzed using wetting and spreading test (JIS-Z-319). The shear tests were analyzed for the mechanical reliability and the data is interpreted using Weibull statistical distribution. High entropy solders added have optimistic microstructure and solderability. Besides, high entropy solders are found to be beneficial in their mechanical properties.
Sri Harini Rajendran,Cho Do Hoon,Seong Min Seo,Jae Pil Jung 대한용접·접합학회 2021 대한용접학회 특별강연 및 학술발표대회 개요집 Vol.2021 No.11
Mini LED is one of the key technologies for 2019 and now making its way into display of consumer electronics. Sn-Ag-Cu solders received noticeable attention for flexible electronics due to their excellent creep resistance and thermal fatigue properties. However, the growth of Cu-Sn intermetallic compounds (IMC) at the interface during aging seriously impacts the solder joint’s mechanical properties. With the continuous miniaturization in the size of the solder joints, the impact of IMC growth is getting highly influential on the reliability of the solder joints. Recently, nanoparticles are added to the solder alloy to refine the microstructure and retard the growth of IMC at the interface and improve the solder joints’ reliability. The main limitation being the dispersion of nanoparticles in the solder alloy. Presently, nanoparticle dispersion by powder mixing is a widely used method. The main drawback in the powder mixing technique is that approximately only 20-30% of the added NPs are retained in the solder joint after reflow, and the rest are segregated along the edges. These segregated nanoparticles remain a threat as they can initiate the bridging of the solder in fine-pitch interconnections such as mini LED bonding. Therefore, it is necessary to move on to techniques wherein nanoparticles are in-situ dispersed during atomization of the solder balls. One such method is the ultrasonic dispersion of nanoparticles in the solder alloy. The present work attempts to make a comparative study between the conventional dispersion (CD) and ultrasonic dispersion (UD) of ZnO nanoparticles in Sn3.0Ag0.5Cu (SAC 305) solder alloy. The results show that UD has improved the wetting property of the solder alloy compared to CD. Also, the microstructure of UD exhibits higher refinement as compared to CD. More importantly, UD-SAC 305 solder displayed slower grain growth during high-temperature aging, thereby retaining higher tensile strength. The findings can be potential use for solder paste industries to develop in-situ nanoparticle reinforced type 6 and type 7 solder balls used in futuer for micro LED soldering.
전욱상,Sri Harini Rajendran,정재필 한국마이크로전자및패키징학회 2019 마이크로전자 및 패키징학회지 Vol.26 No.3
Wettability is an important factor to decide solderability of solder, flux, other soldering-related materials and soldering conditions. The wettability also affects the reliability of solder joint. Wetting balance test is a good method for quantitatively measuring wettability between solder and substrate. The wetting balance test is easy to reproduce the wetting experiment and to measure the wetting time and force. And this test provides wetting curve to calculate the surface tension of the molten solder. Development of new solder has been continued in accordance with various and harsh environment in the electronics industry. In this paper, the principle of wetting balance test and recent research issues including nanocomposite solder are explained. Keywords: wetting balance test,