Comparative Study on the Effects of Fe and Ni Additions on the Electromigration Properties of Sn58Bi Solder Joints

Abstract

Sn <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> 8Bi eutectic solder is the preferred material for low temperature solder in multistage packaging. However, the brittleness and reliability problems of Sn <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> 8Bi eutectic solder, especially the phase separation of electromigration, bring great challenges to its application for multi-stage package interconnection. The modification of Sn <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> 8Bi eutectic solder by alloying has many significant technical advantages, such as effective control of interfacial wetting, intermetallic compounds phase transformation, growth kinetics, and improvement of resistance to electromigration. In this paper, Sn <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> 8Bi, Sn <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> 8Bi-lFe/lNi solder were prepared by melting method and fabricated to the solder joint for electromigration test. The electromigration test of solder joint were carried out with 0.5×104A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> current density at 50°C, and the influence of Fe, Ni alloy elements addition on interfacial IMC growth and microstructure evolution of solder joint interface were studied. The results show that Fe and Ni alloy elements react with Sn to form FeSn2 and Ni <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> IMC, respectively. FeSn2 are triangle or square, and distributed near the interface and embedded in bismuth rich phase and tin rich phase after electromigration test. Compared these two kinds solder joints, it can be seen that the Fe alloy elements can promote the growth of interface IMC and the aggregation of bismuth rich phase, while the Ni alloy elements can greatly inhibit the growth of interface IMC and the aggregation of bismuth rich phase. It may be due to the existence of FeSn2 near the interface, which changes the growth behavior of bismuth rich phase and bin rich phase near the interface of Sn <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> 8Bi-1Fe/Cu solder joints and promotes their growth. As for the inhibition of Ni alloy elements on the growth of interfacial IMC and bismuth rich phase in the anode under the condition of EM, the reason is that Ni <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> forms a barrier in the solder matrix, which hinders the diffusion of atoms.