Enhancement of Thermal cycle and Drop Shock Reliability at Board Level with Developed Solder Composition by Optimized Bi, Cu, Ni Contents in Lead Free Solder Composition

• Main Authors: Son, J.Y., Lee, S.G., Park, J.W., Lee, Y.W., Jung, S.B.
• Format: Conference Proceeding
• Language: English
• Subjects: Electric shock; Environmentally friendly manufacturing techniques; Lead; Nickel; Precipitation; Thermal shock; Young's modulus
• ISSN: 2150-5942
• DOI: 10.1109/IMPACT59481.2023.10348757

We did study for development of new solder composition to cover the positive reliability of SAC305 as high thermal shock and SAC1205N as high drop shock reliability. However, general Sn-Ag-Cu solder composition have limitation of stable material property in thermal affecting condition because solder hardness is easily changed by microstructure due to merging of Ag3Sn particles which makes decreasing of precipitation hardening mechanism [1]. So, Sn-Ag-Cu-Ni-Bi solder has broadly studying at IDMs, OSATs and universities for application of FOWLP, FCBGA, SiP and DSP [2]-[7]. However, it must show lower drop shock reliability than SAC1205N solder composition due to high brittle property. The material hardness of new solder composition is controlled by substitutional hardening mechanism by Bi element instead of precipitation hardening in Sn based solder composition. The high contents of Bi in SNC (Sn-0.065Ni-0.75Cu) makes the high brittle property compare to non-Bi solder composition. However, we find that optimum Bi contents in SNC composition as below 2wt%. The 3wt% Bi solder also has reasonable ductile property at fractured area after tensile test. However, brittle fracture was seriously increased over Bi 5 wt% in SNC solder composition due to Bi segregation by excessive Bi element which is high brittle property as rhombohedral structure [8]. So, we find that when Bi contents is the 1.5 to 2.0 wt% in SNC solder (JY T2), that compositions can overcome the higher thermal shock reliability than SAC305 and higher drop reliability than SAC1205N solder composition. Even 3wt% Bi in SNC solder (JY T4) had lower elongation property than SAC305, it shown higher drop shock reliability because Ni additive makes more stable interfacial IMC layer than that of SAC305 after drop shock test. Our developed solder composition called JY T2(1.5Bi) and JYT4(3.0Bi) The optimized Bi content in JY solder composition shown higher drop than SAC1205N about 2 times on Cu OSP pad finish. And also, Thermal shock reliability of optimized Bi contents solder shown higher than SAC305 solder composition around 2 times on Cu-OSP pad finish. Therefore, the optimized Bi in JY composition can be replace of all lead-free solder composition because it shown satisfaction of drop and thermal shock reliability.