Reactive Interdiffusion between a Lead-Free Solder and Ti/Ni/Ag Thin-Film Metallizations

G. Ghosh*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

15 Scopus citations

Abstract

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)3Sn4 and (Cu,Ni) 6Sn5, 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)Sn4 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) 3Sn4 layer until the Ni layer is completely consumed; (2) interdiffusion of Au, Cu, Ni, and Sn through the (Ni,Cu)3Sn 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)3Sn4 layer to from an (Au,Ti,Ni,Cu)Sn4 layer. The growth of the latter layer continues until the entire Ti layer is consumed.

Original languageEnglish (US)
Pages (from-to)229-240
Number of pages12
JournalJournal of Electronic Materials
Volume33
Issue number3
DOIs
StatePublished - Mar 2004

Keywords

  • Analytical electron microscopy (AEM)
  • Interdiffusion
  • Interfacial reaction
  • Intermetallic compounds
  • Lead-free solder
  • Transmission electron microscopy (TEM)

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Electrical and Electronic Engineering
  • Materials Chemistry

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