Effects of different printed-circuit-board surface finishes on the formation and growth of intermetallics at thermomechanically fatigued, small outline J leads/Sn-Ag-Cu interfaces

Abstract

The effects of printed-circuit-board (PCB) surface finish and thermomechanical fatigue (TMF) on the formation and growth of intermetallic compounds (IMCs) between small outline J (SOJ) leads and Sn-3.0Ag-0.5Cu solder were investigated. The thickness of the IMC layer formed initially at the as-soldered SOJ/Sn-Ag-Cu interface over a Ni/Au PCB surface finish was about 1.7 times of that over the organic solderability preservative (OSP) PCB surface finish. The parabolic TMF-cycle dependence clearly suggests that the growth processes are controlled primarily by solid-state diffusion. The diffusion coefficient for the growth of the total IMC layer at the SOJ/Sn-Ag-Cu interface over the Ni/Au PCB surface finish is the same as that over the OSP PCB surface finish, and thus, the total IMC layer at the SOJ/Sn-Ag-Cu interface over the Ni/Au PCB surface finish is thicker than that over the OSP PCB surface finish. Using the Cu-Ni-Sn ternary isotherm, the anomalous phenomenon that the presence of Ni retards the growth of the Cu 3 Sn layer while increasing the initial growth of the Cu 6 Sn 5 layer can be addressed.

Coupling effects at Cu(Ni)–SnAgCu–Cu(Ni) sandwich solder joint during isothermal aging

“…2 and 3). In type III solder joint, the presence of Ni element in ternary CuNiSn IMCs suppressed the formation of Cu3Sn phase, which is agreeable with previous investigations [23][24][25]. The discrepancy in IMCs evolution during aging also indicates that the opposite NiAu finish has an influence on the reaction at HASL/solder interface.…”

Effect of multiple reflow processes on the reliability of ball grid array (BGA) solder joints

“…8(b), the IMC layer is much thicker and denser. And, the upper part of the IMC shows a loose flake-layer shape, which is the evidence of the IMC dissolution and spalling during the multiple reflow process [24]. The SAC solder joints also show this kind of phenomena, when comparing Fig.…”

Combined Thermodynamic-Kinetic Analysis of the Interfacial Reactions between Ni Metallization and Various Lead-Free Solders

“…When using Sn-Pb solder or pure Sn the Ni 3 Sn 4 phase is typically the first phase to form in the reaction between Ni and Sn. However, when using Pb-free solders that include even small amounts of Cu the situation changes so that the first phase to form is (Cu,Ni) 6 Sn 5 [ 1 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 ]. This Ni containing Cu 6 Sn 5 intermetallic compound (IMC) is very brittle and has been observed to cause severe reliability problems, especially under mechanical shock loading [ 19 ].…”