Fatigue Life Evaluation of Lead-free Solder under Thermal and Mechanical Loads

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.

[1]  Jaakko Lenkkeri,et al.  Rapid power cycling of flip-chip and CSP components on ceramic substrates , 2001, Microelectron. Reliab..

[2]  P. Vianco,et al.  Acceleration models, constitutive equations, and reliability of lead-free solders and joints , 2003, 53rd Electronic Components and Technology Conference, 2003. Proceedings..

[3]  Soon-Bok Lee,et al.  Reliability and Failure Analysis of Lead-Free Solder Joints for PBGA Package Under a Cyclic Bending Load , 2008, IEEE Transactions on Components and Packaging Technologies.

[4]  B. Z. Hong.  Thermal fatigue analysis of a CBGA package with lead-free solder fillets , 1998, ITherm'98. Sixth Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (Cat. No.98CH36208).

[5]  H. Reichl,et al.  Reliability assessment of flip-chip assemblies with lead-free solder joints , 2002, 52nd Electronic Components and Technology Conference 2002. (Cat. No.02CH37345).

[6]  A. Syed.  Reliability and Au embrittlement of lead free solders for BGA applications , 2001, Proceedings International Symposium on Advanced Packaging Materials Processes, Properties and Interfaces (IEEE Cat. No.01TH8562).

[7]  Ganesh Subbarayan,et al.  A hybrid model for computationally efficient fatigue fracture simulations at microelectronic assembly interfaces , 2005 .

[8]  Santosh Shetty,et al.  Three- and Four-Point Bend Testing for Electronic Packages , 2003 .

[9]  Guna S Selvaduray,et al.  Solder joint fatigue models: review and applicability to chip scale packages , 2000 .

[10]  Doug Abbott,et al.  Materials characterization of the effect of mechanical bending on area array package interconnects , 2003 .

[11]  S. Sahasrabudhe,et al.  Use-condition-based cyclic bend test development for handheld components , 2004, 2004 Proceedings. 54th Electronic Components and Technology Conference (IEEE Cat. No.04CH37546).