Characterizing Metallurgical Reaction of Sn3.0Ag0.5Cu Composite Solder by Mechanical Alloying with Electroless Ni-P/Cu Under-Bump Metallization after Various Reflow Cycles

Authors: Hsiao, Li-Yin; Kao, Szu-Tsung; Duh, Jenq-Gong

Source: Journal of Electronic Materials, Volume 35, Number 1, January 2006 , pp. 81-88(8)

Publisher: Springer

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Abstract:

Electroless Ni-P/Cu under-bump metallization (UBM) is widely used in electronics packaging. The Sn3.0Ag0.5Cu lead-free composite solder pastes were produced by a mechanical alloying (MA) process doped with Cu₆Sn₅ nanoparticles. In this study, the detailed interfacial reaction of Sn3.0Ag0.5Cu composite solders with EN(P)/Cu UBM was investigated after reflow. A field-emission scanning electron microscope (FESEM) was employed to analyze the interfacial morphology and microstructure evolution. The intermetallic compounds (IMCs) formed at the interface between the Sn3.0Ag0.5Cu composite solders and EN(P)/Cu UBM after one and three reflows were mainly (Ni_1−x,Cu_x)₃Sn₄ and (Cu_1–y,Ni_y)₆Sn₅. However, only (Ni_1–x,Cu_x)₃Sn₄ IMC was observed after five reflows. The elemental distribution near the interfacial region was evaluated by an electron probe microanalyzer (EPMA) as well as field-emission electron probe microanalyzer (FE-EPMA). Based on the observation and characterization by FESEM, a EPMA, and an FE-EPMA, the reaction mechanism of interfacial phase transformation between Sn3.0Ag0.5Cu composite solders and EN(P)/Cu UBM after various reflow cycles was discussed and proposed.

Keywords: ELECTROLESS NI-P; UNDER-BUMP METALLIZATION (UBM); SN3.0AG0.5CU COMPOSITE SOLDER; INTERMETALLIC COMPOUND; PHASE TRANSFORMATION

Document Type: Research article

Publication date: 2006-01-01