Title :
Fatigue Life Evaluation of Lead-free Solder under Thermal and Mechanical Loads
Author :
Kim, Ilho ; Lee, Soon-Bok
Author_Institution :
Korea Adv. Inst. of Sci. & Technol., Daejeon
fDate :
May 29 2007-June 1 2007
Abstract :
In this study, two types of fatigue tests were conducted. First, cyclic bending tests were performed using the micro-bending tester. A four-point bending test method was adopted, because it induces uniform stress fields within a loading span. Second, thermal fatigue tests were conducted using a pseudo power cycling machine which was newly developed for a realistic testing condition. The pseudo-power cycling method makes up for the weak points in a power cycling and a chamber cycling method. Two compositions of solder are tested in all test condition, one is lead-free solder (95.5Sn4.0Ag0.5Cu) and the other is eutectic lead-contained solder (63Sn37Pb). In the cyclic bending test, the solder that exhibits a good reliability can be reversed depending on the load conditions. The lead-contained solders have a longer fatigue life in the region where the applied load is high. On the contrary, the lead-free solder sustained more cyclic loads in the small load region. A similar trend was detected at the thermal cycling test. Furthermore, to certify the crack behavior, the failed specimen was sectioned. In thermal cycling case, crack initiated inner solder joints. But outmost solder failed first in the cyclic bending test. A three-dimensional finite element analysis model was constructed. A finite element analysis using ABAQUS was performed to extract the applied stress and strain in the solder joints. A constitutive model which includes both creep and plasticity was employed. Thermal fatigue was occurred due to the creep. And plastic deformation is main damage for bending failure. From the inelastic energy dissipation per cycle versus fatigue life curve, it can be found that the bending fatigue life is longer than the thermal fatigue life.
Keywords :
bending; copper alloys; fatigue testing; finite element analysis; plastic deformation; silver alloys; solders; tin alloys; 3D finite element analysis; ABAQUS; SnAgCu; SnPb; creep; cyclic bending tests; eutectic lead-contained solder; fatigue life evaluation; lead-free solder; mechanical loads; microbending tester; plastic deformation; pseudopower cycling machine; solder joints; thermal cycling test; thermal fatigue tests; thermal loads; Creep; Environmentally friendly manufacturing techniques; Fatigue; Finite element methods; Lead; Performance evaluation; Soldering; Testing; Thermal loading; Thermal stresses;
Conference_Titel :
Electronic Components and Technology Conference, 2007. ECTC '07. Proceedings. 57th
Conference_Location :
Reno, NV
Print_ISBN :
1-4244-0985-3
Electronic_ISBN :
0569-5503
DOI :
10.1109/ECTC.2007.373782