Paper SS-TuP9
Effect of Isothermal Aging on the Interfacial Reactions between Sn-58Bi Solder and ENEPIG

Tuesday, October 29, 2013, 6:00 pm, Room Hall B

The interfacial reaction between the Sn-58wt.% Bi solder and a surface finish of ENEPIG (Electroless Nickel Electroless Palladium Immersion Gold) were studied during isothermal aging at 125 ℃ . The thin uppermost layer of immersion gold was resolved into solders bulk and the intermetallic compound (IMC) as known as PdSn₄ was created between tin of solder and Pd-P layer, while the solder was reflowing. As aging time increased, the new IMC creation of Ni₃Sn₄ between Ni-P layer and tin of solder below PdSn₄ became dominent. As aging time increased more, the IMC of PdSn₄ was resolved out into solder bulk and the IMC of Ni₃Sn₄ remained. As aging time went further, Ni-P layer was consumed and pits happened on Ni-P layer made paths Ni₃Sn₄ through Cu layer, and the IMC of Ni₃Sn₄ was discontinuously growing. As result of Cu penetration through Ni-P layer, the IMC became into (Ni,Cu)₃Sn_4, and the new IMC of (Ni,Cu)₆Sn₅ under (Ni,Cu)₃Sn₄ was created and growing. As aging time increased over 500 hour, the main IMC is (Ni,Cu)₆Sn₅ and (Ni,Cu)₃Sn4 between ENEPIG and 58wt.% Bi solder. In addition to Ni-P layer, presence of phosphorous made such as Ni₃P layer and NiSnP layer. Result of this study showed that the surface finish of ENEPIG layer acts as a diffusion barrier and be able to expect the IMC behavior for long term as low temperature solder.