Solder metallization interdiffusion in microelectronic interconnects

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.

“…In addition, the electronics manufacturing industry is not ready to convert over to Pb-free circuitboard finishes 4,15,17 and component-lead finishes.…”

Section: Introductionmentioning

confidence: 97%

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

Huang

Lee

et al. 2004

“…In fact, it is well established that Ni can replace up to 50% of the Au sites in AuSn 4 forming (Au 0.5 Ni 0.5 )Sn 4 . [19][20][21] Accordingly, we represent the Au-Sn-Ti layer as (Au,Ti,Ni,Cu)Sn 4 .…”

Section: Discussionmentioning

confidence: 99%

Reactive interdiffusion between a lead-free solder and Ti/Ni/Ag thin-film metallizations

Ghosh

2004

The reactive interdiffusion between a Sn-3.0wt.%Ag-0.7wt.%Cu solder and thin-film Ti/Ni/Ag metallizations on two semiconductor devices, a diode and a metal-oxide-semiconductor field-effect transistor (MOSFET), and a Au-layer on the substrates are studied. Comprehensive microanalytical techniques, scanning electron microscopy, transmission electron microscopy (TEM), and analytical electron microscopy (AEM) are employed to identify the interdiffusion processes during fabrication and service of the devices. During the reflow process of both diode and MOSFET devices, (1) the Ag layer dissolves in the liquid solder; (2) two intermetallics, (Ni,Cu) 3 Sn 4 and (Cu,Ni) 6 Sn 5 , form near the back metal/solder interface; and (3) the Au metallization in the substrate side dissolves in the liquid solder, resulting in precipitation of the (Au,Ni,Cu)Sn 4 intermetallic during solidification. During solid-state aging of both diode and MOSFET solder joints at 125°C and 200°C, the following atomic transport processes occur: (1) interdiffusion of Cu, Ni, and Sn, leading to the growth of a (Ni,Cu) 3 Sn 4 layer until the Ni layer is completely consumed;(2) interdiffusion of Au, Cu, Ni, and Sn through the (Ni,Cu) 3 Sn 4 layer and unconsumed Ni layer to the Ti layer to form a solid solution; and (3) further interdiffusion of Au, Cu, Ni, and Sn through the (Ni,Cu) 3 Sn 4 layer to from an (Au,Ti,Ni,Cu)Sn 4 layer. The growth of the latter layer continues until the entire Ti layer is consumed.

“…5) shows that it is an Au-Ni-Sn ternary-phase compound. Some research 8,17 has found that this compound is Au 0.5 Ni 0.5 Sn 4 . In this study, EDX analysis inside this phase (Fig.…”

Section: Microstructure Evolution During Agingmentioning

confidence: 98%

“…This mechanism suggests that the formation of the Au 0.5 Ni 0.5 Sn 4 layer is attributed to the dissolution and redeposition of the AuSn 4 in the solder. 8,17 The Au from the solder diffused toward the solder/Ni interface and then reacted with the Sn and Ni atoms to form Au 0.5 Ni 0.5 Sn 4 with greater thermodynamic stability. 5,8 Interestingly, a continuous layer of the Pb-rich phase of the solder formed above the Au 0.5 Ni 0.5 Sn 4 layer during aging ( Fig.…”

Section: Microstructure Evolution During Agingmentioning

confidence: 99%

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Aging study on interfacial microstructure and solder-ball shear strength of a wafer-level chip-size package with Au/Ni metallization on a Cu pad

Chang

Chiang

2004

Eutectic solder balls (63Sn-37Pb) joined to Cu pads with an Au/Ni metallization have been widely used in wafer-level chip-size package (WLCSP) technology for providing electrical and mechanical interconnections between components. However, some reliability issues must be addressed regarding the intermetallic compounds (IMCs). The formation of a brittle IMC layer between the solder/Cu pad interface impacts considerably upon the solder-ball shear strength. In addition, it will degrade the long-term operating reliability of the WLCSP. This study investigates, by means of experiments, the growth of the IMC layer under isothermal aging for the eutectic Sn-Pb solder reflowed on a Cu pad with an Au/Ni metallization. Forming the Cu pad with an Au/Ni metallization was achieved by a simple semiconductor-manufacturing process. The effects of the intermetallic layer on solder-ball shear strength were examined for various parameters, including the thickness of the Au layer, solder-ball size, and the diameter of the Cu pad. Experimental results indicate that two IMC layers, Au 0.5 Ni 0.5 Sn 4 and Ni 3 Sn 4 , form at the solder/Cu pad interface after aging. The Au 0.5 Ni 0.5 Sn 4 intermetallic layer dominates the total thickness of the IMC layer and grows with aging time while the solder-ball shear strength decreases after aging. The degradation of the solder-ball shear strength was found to be caused mainly by the formation of the Au 0.5 Ni 0.5 Sn 4 layer. The experimental results established that a thinner Au layer on Cu pad can effectively control the degradation of solder-ball shear strength, and this is especially true for smaller ball sizes.