Morphology and growth kinetics of intermetallic compounds in solid-state interfacial reaction of electroless Ni-P with Sn-based lead-free solders

Abstract

A comparative study of solid/solid interfacial reactions of electroless Ni-P (15at.%P) with lead-free solders, Sn-0.7Cu, Sn-3.5Ag, Sn-3.8Ag-0.7Cu and pure Sn,, was carried out by performing thermal aging at 150oC up to 1000 h. For pure Sn and Sn-3.5Ag solder, three distinctive layers, Ni3Sn4, SnNiP and Ni3P, were observed in between the solder and electroless Ni-P; while for Sn-0.7Cu and Sn-3.8Ag-0.7Cu solders, two distinctive layers, (CuNi)6Sn5 and Ni3P, were observed. The differences in morphology and growth kinetics of the intermetallic compounds (IMCs) at the interfaces between electroless Ni-P and lead-free solders were investigated, as well as the growth kinetics of the P-enriched layers underneath the interfacial IMC layers. With increasing aging time, the coarsening of interfacial Ni3Sn4 IMC grains for pure Sn and Sn-3.5Ag solder was significantly greater than that of the interfacial (CuNi)6Sn5 IMC grains for Sn-0.7Cu and Sn-3.8Ag-0.7Cu solders. Furthermore, the Ni content in interfacial (CuNi)6Sn5 phase slightly increased during aging. A small addition of Cu (0.7 wt.%) resulted in differences in the type, morphology and growth kinetics of interfacial IMCs. By comparing the metallurgical aspects and growth kinetics of the interfacial IMCs and the underneath P-enriched layers, the role of initial Cu and Ag in lead-free solders is better understood

Growth Mechanism of a Ternary (Cu,Ni)6Sn5 Compound at the Sn(Cu)/Ni(P) Interface

“…With increasing annealing time, the morphology of the interfacial compound layer gradually transformed to the more layered type of the (Cu,Ni) 6 Sn 5 compound. This morphological evolution of the interfacial (Cu,Ni) 6 Sn 5 compound layer found in our present Sn-0.7Cu study is similar to the findings of Huang et al 8 We examined the activation energy for the interfacial (Cu,Ni) 6 Sn 5 layer compound layer while performing two more solid-state aging reactions at 150°C and 200°C for the Sn-0.7Cu, Sn-1.8Cu, and Sn-3.0Cu cases. The thickness of the ternary (Cu,Ni) 6 Sn 5 formation at the Sn-0.7Cu/Ni(P), Sn-1.8Cu/Ni(P), and Sn-3.0Cu/ Ni(P) interfaces can be estimated from SEM crosssectional images.…”

First-principle study on substitution of Cu or P into Ni–Sn intermetallic compounds

“…2, the important physical properties such as the bulk modulus and the melting point are reflected by the ped hybridization between d state of transition metal (Ni and Cu) and p state of metal (Sn) or metalloid (P). Thus, we compared the orbital Table 2 Equilibrium lattice parameters ( A), volume ( A 3 /cell), total energy E T (eV), heat of formation DH(meV/atom) and cohesive energy E c (eV/atom) for given Ni 3 Sn 2 , (Ni,Cu) 3 [27], and its third-order expansion is expressed as follows…”

“…However, the investigation on lead-free assemblies has been recently intensified due to the anticipated legislation to ban the use of lead in electrical and electronic products. Therefore, many researchers have developed and studied on the alternative solder materials instead of lead [1,2] and the alloys produced during soldering [3]. Another important issue in the semiconductor package is the compatibility of the surface finishes with solder materials.…”

Effect of Ni addition on the Sn-0.3Ag-0.7Cu solder joints

“…The ratio value is about from 0.59 to 0.44, composition varies from (Cu 0.62 Ni 0.38 ) 6 Sn 5 to (Cu 0.69 Ni 0.31 ) 6 Sn 5 and the average Ni concentration in (Ni x Cu 1-x ) 6 Sn 5 is about 19-21at% after aging for 384h. It was reported that 0-25at%Ni in (Ni x Cu 1-x ) 6 Sn 5 phase formed at 240°C [6][7][8]. In contrast to the initial composition of (Ni x Cu 1-x ) 6 Sn 5 , the result is 21-23 at% Ni 34-36 at% Cu 45-47at% Sn.…”