Interfacial reactions between Sn-0.4Cu solder and Cu substrate with or without ENIG plating layer during reflow reaction

摘要

The interfacial reaction and morphology change of intermetallic compound (IMC) between the Sn-0.4 wt.percent Cu solder and two different kinds of substrates (Cu and electroless nickel-immersion gold (ENIG)) during reflow at 255 deg C for up to 60 min were studied. Until the reaction time of 1 min, only Cu_6Sn_5 IMC was formed on the Cu substrate. After reflow for 5 min, the solder/Cu interface exhibited a duplex structure of Cu_6Sn_5 and Cu_3 Sn. According to the top view observation, the Cu_6Sn_5 IMC formed on the Cu substrate had a well-known morphology of a round or scallop shape. In the case of the ENIG substrate, the reaction between molten Sn-0.4Cu solder and electroless Ni-P layer resulted in the formation of a (Ni,Cu)_3Sn_4 layer at the interface. Until the reaction time of 10 min (Ni,Cu):,Sn4 IMC layer was formed and attached well on the electroless Ni substrate. And, the Cu content in the (Ni,Cu)_3Sn_4 IMC layer increased with increasing reaction time. From the top view micrograph of the interface, it was known that three types (needle-type, boomerang-type and chunk-type) of (Ni,Cu)_3Sn_4 IMC were formed. Also, P-rich Ni (Ni_3P) and Ni-Sn-P layers were observed between IMC layer and electroless Ni-P layer. On the other hand, the reaction for 60 min resulted in the formation of two IMCs, a relatively thin and continuous (Ni,Cu)_3Sn_4 and a relatively big discontinuous (Cu,Ni)_6Sn_5, at the interface. After reflow for 60 min, the electroless Ni-P layer in some parts of the sample was completely consumed by reaction between molten solder and substrate.