Lower Temperature Soldering of Capacitor Using Sn-Bi Coated Sn-3.5%Ag Solder

Kim, Mi-Jin; Cho, Sun-Yun; Kim, Sook-Hwan; Jung, Jae-Pil

JWJ > Volume 23(3); 2005 > Article

Journal of KWJS 2005 June;23(3) :61-67.
Published online July 15, 2005.

Lower Temperature Soldering of Capacitor Using Sn-Bi Coated Sn-3.5%Ag Solder

Mi-Jin Kim, Sun-Yun Cho, Sook-Hwan Kim, Jae-Pil Jung

Correspondence: Published online July 15, 2005

ABSTRACT

Since lead (Pb)-free solders for electronics have higher melting points than that of eutectic Sn-Pb solder, they need higher soldering temperatures. In order to decrease the soldering temperature we tried to coat Sn-Bi layer on Sn-3.5%Ag solder by electroplating, with applies the mechanism of transient liquid phase bonding to soldering. During heating Bi will diffuse into the Sn-3.5Ag solder and this results in decreasing soldering temperature. As bonding samples, the 1608 capacitor electroplated with Sn, and PCB, its surface was finished with electroless-plated Ni/Au, were selected. The Sn-95.7%Bi coated Sn-3.5Ag was supplied as a solder between the capacitor and PCB land. The samples were reflowed at 220℃, which was lower than that of normal reflow temperature, 240~250℃, for the Pb-free. As experimental result, the joint of Sn-95.7%Bi coated Sn-3.5Ag showed high shear strength. In the as-reflowed state, the shear strength of the coated solder showed 58.8N, whereas those of commercial ones were 37.2N (Sn-37Pb), 31.4N (Sn-3Ag-0.5Cu), and 40.2N (Sn-8Zn-3Bi). After thermal shock of 1000 cycles between -40℃ and +125℃N and 45.1N. As the microstructures, in the solder Ag₃Sn intermetallic compound (IMC), and along the bonded interface Ni₃Sn₄ IMC were observed.