Composition influence on Cu/Sn-xBi bonds by means of TLPB for Pb-free technology applications

M. O. PONTET; S. SOMMADOSSI

Wels

Workshop; 2nd IIW European-South American school of Weldig and Correlated Process; 2012

TU-Graz, IWW

The aim of this work is to understand the influence of composition and temperature in the isothermal phase transformations in Cu/Sn-xBi (20, 40, 57, 80% Bi) couples between 300 and 500ºC in the frame of the Transient Liquid Phase Bonding (TLPB). The identification and characterization is carried out by optical and electron microscopy. At 400°C only the ε-Cu3Sn phase is observed, while at 500°C, δ-Cu41Sn11 and ε-Cu3Sn are present for all alloys. The solid-liquid interfaces are faceted for both temperatures. In addition, at 300°C both η-Cu6Sn5 and  ε-Cu3Sn are develop, and the solid-liquid interface presents a mixed morphology: 20 and 40% Bi  alloys show lobular shape, while 57 (eutectic) and 80% Bi have a single ε-Cu3Sn faceted layer. Parabolic growth is predominant for the layer development. At 300°C ε-Cu3Sn phase shows a substantially higher growth rate for the eutectic alloy. The hardness testing indicated values between 400-500 HV/0,01 for the phases of interest.