Metallurgical reactions in composite 90Pb10Sn/lead-free solder joints and their effect on reliability of LTCC/PWB assembly |
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| Authors: | O Nousiainen J Putaala T Kangasvieri R Rautioaho J Vähäkangas |
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| Affiliation: | (1) Materials Engineering Laboratory and EMPART Research Group of Infotech Oulu, University of Oulu, P.O. Box 4200, 90014 Oulu, Finland;(2) Microelectronics and Materials Physics Laboratories and EMPART Research Group of Infotech Oulu, University of Oulu, P.O. Box 4500, 90014 Oulu, Finland |
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| 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. |
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| Keywords: | Lead-free solder 90Pb10Sn sphere reliability thermal cycling |
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