(Copper, nickel) tin intermetallic formation kinetics on electroless nickel when varying copper concentration and reflow process.

摘要

In electronics the initial intermetallic formed on electroless Ni substrates during component ball attach can be exposed to high concentrations of Cu when components are assembled to Cu based circuit boards such as Immersion Ag, Immersion Sn, Cu OSP, or HASL. Ni solubility limits in SnPb37, SnAg3.5, and SAC304 are compared and determined to affect the kinetic intermetallic formation at the electroless Ni boundary.;Short and long reflow profiles are used to empirically control the Ni concentration within the alloys. All combinations were then subjected to limitless Cu in a second reflow. SEM/EDS, XPS, and EPMA were used to assess the initial intermetallic of the ball attach as compared to the intermetallic formed following the addition of limitless Cu. Addition of limitless Cu was introduced to the solder joint by either adding Cu powder or by using Cu pins in Hot Bump Pull (HBP) testing. Cold Bump Pull (CBP) and HBP testing was performed in order to characterize the mechanical behavior of the resulting intermetallic morphologies. Morphologies were then correlated to the mechanical failure mode and peak load to failure.;Ni solubility limits affect the chemical potential difference between initial ball attach and after the ball is allowed to become saturated with Ni in a long ball attach profile. In cases of higher Ni solubility (lead free) a dual phase intermetallic was observed, however in cases of low Ni solubility (SnPb37) a dual phase Ni-Sn intermetallic condition was not observed. It was observed that in SnPb little to no intermetallic morphology variations were produced with long and short ball attach profiles. In lead free however the higher solubility seemed to result in dramatic morphological differences during short and long reflow ball attach. The differences in morphology observed during ball attach continued following the addition of limitless Cu in a second reflow. These morphologies also resulted in marked differences in mechanical behavior ball pull testing. The results of this study present a favored material and reflow process for improved mechanical behavior.