Metallurgical Reactions in Composite 90Pb10Sn/Lead-Free Solder Joints and Their Effect on Reliability of LTCC/PWB Assembly
Authors: Nousiainen, O.; Putaala, J.; Kangasvieri, T.; Rautioaho, R.; Vähäkangas, J.
Source: Journal of Electronic Materials, Volume 35, Number 10, October 2006 , pp. 1857-1865(9)
Abstract:Use of 90Pb10Sn solder as a noncollapsible sphere material with 95.5Sn 4Ag0.5Cu and SnInAgCu lead-free solders is investigated. Practical reflow conditions led to strong Pb dissolution into liquid solder, resulting in >20 at.% Pb content in the original lead-free solders. The failure mechanism of the test joints is solder cracking due to thermal fatigue, but the characteristic lifetime of 90Pb10Sn/SnInAgCu joints is almost double that of 90Pb10Sn/95.5Sn4Ag0.5Cu in a thermal cycling test (TCT) over the temperature range from −40°C to 125°C. It is predicted that this is mainly a consequence of the better fatigue resistance of the SnPbInAgCu alloy compared with the SnPbAgCu alloy. Indium accelerates the growth of the intermetallic compound (IMC) layer at the low temperature co-fired ceramic (LTCC) metallization/solder interface and causes coarsening of IMC particles during the TCT, but these phenomena do not have a major effect on the creep/fatigue endurance of the test joints.
Document Type: Regular Paper
Publication date: October 1, 2006