| Summary: | The electronic packaging industry is now being driven towards smaller, lighter, and
thinner electronic products but with higher performance and more functions. Thus, smaller solder
ball sizes are needed for fine solder joint interconnections to fulfill these requirements. This study
investigates the interfacial reactions during reflow soldering and isothermal aging between Sn4.0Ag-0.5Cu
(SAC405) and electroless nickel (boron)/ immersion palladium/immersion gold
(EN(B)EPIG). Reliability of solder joint has also been investigated by performing solid state
isothermal aging at 125˚C for up to 2000 hours. The results revealed that after reflow soldering, (Cu,
Ni)6Sn5 IMC is formed between solder and substrate while after aging treatment another IMC was
found between (Cu, Ni)6Sn5 and substrate known as (Ni, Cu)3Sn4. Aging time of solder joints
resulted in an increase in IMC thickness and a change in morphology into more spherical, dense and
with larger grain size. By using optical microscope, the average thickness of the intermetallics was
measured and it found that the larger solder balls produced thicker IMC than the smaller solder balls
during reflow soldering. However, after aging the smaller solders produced thicker IMC than the
larger solders.
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