Metallurgical Reactions in Composite 90Pb10Sn/Lead-Free Solder Joints and Their Effect on Reliability of LTCC/PWB Assembly

摘要

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 deg C to 125 deg 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.