Surface finish is coated layer plated on a bare copper board of printed circuit board
(PCB). Among PCB surface finishes, Electroless Nickel/Immersion Gold (ENIG)
finish is a top choice among electronic packaging manufacturer due to its excellent
properties for PCB. However, the use of gold element in ENIG is very high cost and
the black pad issue has not been resolved. Thus, by introducing an Electroless
Nickel/Immersion Silver (ENIMAG) as alternative surface finish hopefully can
reduce the cost and offer better properties. The aim of this study is to investigate the
effect of alloying element in lead-free solders on interfacial reaction during reflow
soldering between Sn-2.5Ag (SA25), Sn-2.5Ag-0.5Cu-1.0Bi (SACB25051), Sn�2.0Ag-0.7Cu-3.0Bi (SACB20073) and Sn-3.4Ag-4.8Bi (SAB3448) with an
ENIMAG surface finish. Solder balls with sizes of 500μm diameters were used. All
samples were subjected to an isothermal aging process with four different aging
times which are 250 hours, 500 hours, 1000 hours and 2000 hours at 150°C. The
characteristics of intermetallic compound (IMC) were analyzed by using scanning
electron microscopy (SEM), optical microscope (OM) and energy dispersive x-ray
(EDX). The results revealed that there is one layer of (Cu,Ni)6Sn5 IMC was formed
at the interface after reflow soldering and a new layer of (Cu,Ni)3Sn4 IMC has been
found after isothermal aging take place. Subsequently, the grain size and thickness of
IMC for SACB20073 is smaller and thinner compared to the SACB25051 followed
by SAB3448 and SA25. This is due to the existence of Bi element which can reduce
the grain size and the growth rate of IMC. The IMC thickness is proportional to the
aging duration and IMC morphology for all solders are became thicker, larger and
coarser after exposed to isothermal aging. Furthermore, the nanoindentation test had
been conducted and ENIMAG was found reliable and suitable as protective layer for
PCB. In addition, it is proved that there was electrical connection between solder ball
and ENIMAG through conductivity test and the value of conductivity of SA25 is
higher than SAB3448, SACB2551 and SACB20073
