Investigation of NiSn₄ Formation in the Reaction between SnBi Solder and ENEPIG Substrate

Reflow is a very critical process for interconnection. The reflow temperature directly influences intermetallic compounds. Investigation of Cu<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</inf>Sn<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf>, Cu<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf>Sn or 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> is widely studied for decades. Nevertheless, NiSn<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> becomes more important with the decrease in reflow temperature. The relevant study of NiSn<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> is limited. The trend of low-temperature solder development drives the low-temperature reflow. Sn58Bi is a common low-temperature solder. It is considered as a potential low-temperature solder. On the other hand, surface finish protects substrate from oxidation and enhances wettability. ENEPIG (electroless nickel/electroless palladium/ immersion gold) is a high-quality surface finish. Ni serves as a diffusion barrier to inhibit the diffusion between Sn and Cu. 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> is a common intermetallic compound that form at the joint. The reflow temperature influences the type of intermetallic compound significantly. The aim of this study is to observe the growth of Ni-Sn compounds and estimate the application of Sn58Bi and ENEPIG at low-temperature reflow. The results show that NiSn<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> is dominated phase after 160°C reflow. The related studies of NiSn<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> are few. It is worth observing the growth of NiSn<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> for low-temperature reflow. NiSn<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> 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> are stable phases after 100–130 °C aging. Microstructure evolution of NiSn<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> 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> was investigated completely in this study.