Failure Mechanisms of Thermomechanically Loaded SnAgCu/Plastic Core Solder Ball Composite Joints in Low-Temperature Co-Fired Ceramic/Printed Wiring Board Assemblies |
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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, 90014 Oulu, Finland;(2) Microelectronics and Materials Physics Laboratories and EMPART Research Group of Infotech Oulu, University of Oulu, Oulu, Finland |
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Abstract: | The thermal fatigue endurance of completely lead-free 95.5Sn4Ag0.7Cu/plastic core solder ball (PCSB) composite joint structures
in low-temperature Co-fired ceramic/printed wiring board (LTCC/PWB) assemblies was investigated using thermal cycling tests
over the temperature ranges of −40°C–125°C and 0°C–100°C. Two separate creep/fatigue failures initiated and propagated in
the joints during the tests: (1) a crack along the intermetallic compound (IMC)/solder interface on the LTCC side of the joint,
which formed at the high-temperature extremes; and (2) a crack in the solder near the LTCC solder land, which formed at the
low-temperature extremes. Moreover, localized recrystallization was detected at the outer edge of the joints that were tested
in the harsh (−40°C–125°C) test conditions. The failure mechanism was creep/fatigue-induced mixed intergranular and transgranular
cracking in the recrystallized zone, but it was dominated by transgranular thermal fatigue failure beyond the recrystallized
zone. The change in the failure mechanism increased the rate of crack growth. When the lower temperature extreme was raised
from −40°C to 0°C, no recrystallized zone was detected and the failure was due to intergranular cracks.
(Received ...; accepted ...) |
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Keywords: | Low-temperature co-fired ceramic (LTCC) lead-free plastic core solder ball (PCSB) fatigue creep thermal cycling |
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