A new investigation of the system Ni–P

Abstract

a b s t r a c tThe binary system Ni-P is one of the constituents of the ternary system Ni-P-Sn which provides the basic knowledge for understanding the interactions between Sn-based solders and common Ni(P) metallization. In this study a new version of the Ni-P phase diagram was established based on XRD, EPMA and DTA measurements. The present diagram differs in some important details from the literature version. For the phases Ni 5 P 2 high temperature (HT) and Ni 12 P 5 HT the existence of a considerable homogeneity range is proposed. In Ni 5 P 2 the transformation between HT and low temperature (LT) modification comprises a peritectic and a eutectoid reaction, whereas for the transition in Ni 12 P 5 two eutectoids are proposed. Unfortunately, the high temperature phases cannot be stabilized by quenching, so that all data have to rely on the results of thermal analyses. Furthermore, Ni 5 P 4 was found to be formed by a peritectic reaction, and a eutectic was observed between Ni 5 P 4 and NiP. The phase NiP 1.22 that had been reported in the literature could not be found at all. Although the experimental work was complicated by the high vapor pressure of phosphorus at P concentrations higher than 40 at.% (which caused the explosion of quartz tubes and prevented the preparation of equilibrium samples at higher temperatures), it could still be shown that the phase NiP 3 is probably stable down to room temperature in contrast to the literature reports.

Redetermination of the Eutectic Composition of the Ni-P Binary Alloy

“…It is seen that all the samples begin to melt (onset temperature, T onset ) at 1163 K during heating, meaning that the eutectic temperature is 1163 K, a value in excellent agreement with the recent experimental result. [2] The curves have different peak temperatures (T p ), which corresponds to the highest melting rates upon Fig. 1 The published Ni-P binary alloy phase diagram [1] Basic and Applied Research: Section I heating.…”

“…1 was presented by Lee and Nash based on various experimental studies. [1] It indicates a eutectic reaction at the composition of 19.0 at.%P around 1143 K: L fi a-Ni + Ni 3 P. Nevertheless, recent thermal analyses suggested that the eutectic temperature should be 1164 K, [2] which leads to a natural suspicion over the exactness of the eutectic composition of 19.0 at.%P.…”

The Ni-rich Part of the Ni-P-Sn System: Isothermal Sections

“…General difficulties in the sample preparation due to the high vapor pressure of P were described in Ref. 8. Although in the Ni-rich corner of the ternary Ni-P-Sn system, i.e., at P contents below 40 at.%, these problems were less severe, similar difficulties were encountered at higher P concentrations.…”

“…Although in the Ni-rich corner of the ternary Ni-P-Sn system, i.e., at P contents below 40 at.%, these problems were less severe, similar difficulties were encountered at higher P concentrations. 6 Generally, quartz tubes having a wall thickness of 2 mm instead of the usual 1 mm were used.…”

“…During the soldering process, this Ni(P) metallization reacts with the solder (usually a Sn-based alloy), forming an interfacial layer of intermetallic phases, comprising, e.g., Ni 3 Sn 4 1,2 if no Cu is involved, (Cu,Ni) 6 Sn 5 (for Cu contents of 0.7 wt.% or more in the solder 3,4 ), and (Cu,Ni) 3 Sn 4 (for 0.5 3 or 0.2 4 wt.% Cu in the solder), or even both (for 0.5 wt.% Cu 4 ). The original Ni(P) layer will also start to crystallize due to Ni depletion and formation of Ni 3 P. 1,3 Thus, depending on the concentration of P in the layer and the composition of the solder, different IMC layers can be formed during soldering.…”