Fauzi, Muhamad Razizy (2023) Interfacial reaction and corrosion behaviour between SAC305 and SAC307 solder on electroless nickel/immersion silver (ENImAg) and electroless nickel/immersion gold (ENIG) surface finish. Masters thesis, Universiti Tun Hussein Onn Malaysia.

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Abstract

Tin-Silver-Copper (SAC) solder was recognized as the preferable for lead-free solder composition, while electroless nickel/immersion gold (ENIG) was recognized as the most popular surface finish for printed circuit board (PCB). However, ENIG has disadvantages, including the high cost of gold (Au) material and the black pad issue on the surface coating. Therefore, this study aims to investigate the interfacial reaction and corrosion behaviour between Sn-3.0Ag-0.5Cu (SAC305) and Sn-3.0Ag-0.7Cu (SAC307) solder on electroless nickel/immersion silver (ENImAg) and ENIG surface finish through laser soldering process. Laser soldering was chosen because of its good performance. ENImAg was chosen as an alternative for ENIG due to its low cost and no black pad issue reported on surface coating. The samples were subjected to isothermal ageing at 150°C for different ageing duration 250, 500, 750 and 1000 hours. Then polarization test was conducted, and potassium hydroxide (KOH) was used as an alkaline solution that acted as melting battery. The result revealed that SAC/ENImAg and SAC/ENIG showed the intermetallic compound (IMC) grain microstructure was constantly increased when the percentage of Cu in solder paste increases. The different Cu composition is chosen to know the effect of Cu composition on IMC. The IMC formation after laser soldering and the ageing process was detected as (Cu, Ni)6Sn5, (Ni, Cu)3Sn4, and Ag3Sn. The observation showed that ENIG’s IMC thickness and microstructure is thinner and smaller than ENImAg. During the ageing process, the IMC thickness for both surfaces gradually increases with the ageing time. Regarding corrosion rate analysis, SAC305/ENIG is much better than SAC305/ENImAg. However, both surface finish still in acceptable range for corrosion rate where the reading is not more than 0.1 mm/year. This research discovered that ENImAg can be an alternative surface finish to ENIG

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