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|Pb-Free Solder for Portable and High Temperature Electronic Devices|
|Keywords: Solder , High Temperature , Electronic Devices|
|As the European Union’s (EU’s) RoHS directives came into force on July 2006, the transition to lead-free solder has occurred at a rapid pace. Many manufacturers have adopted Sn/Ag/Cu (SAC)-type solder alloys as a representative Pb-free solder to substitute the conventional Tin-Lead (Sn-Pb) system with many reliability anomalies unanswered. This paper is an effort to compare solder reliability between the two most popular Pb-free solders SAC305 and SAC 105 for temperature cycling and drop test. This paper is an effort to collect the data and compare the results for SAC105 and SAC305 with respect to the following approach for both temperature cycling and drop test:- 1) Temperature cycling and drop test failure characteristics for an on-board package were determined experimentally. Data from these experiments were analyzed using 2-parameter Weibull statistics and the characteristic lives from each set of experiments were determined. The result of 1st failure and 50% failure for SAC 105 and SAC 305 is discussed. Site of failure and intermetallic thickness on the package side were investigated using the cross-sectioned samples. 2) Dynamic simulation of the temperature cycling and drop test were conducted to investigate the stress/strain induced in interconnects using ANSYS. Simulation was done using finite element model to illustrate the temperature flow and stress distribution throughout the joint. The effect of accumulated stress per drop cycle and the hot spot is reported in the paper. The effect of the package integrity and weak joints with respect to drop reliability is also discussed. The results were interpreted and the recommendations for the right Pb-free solder were made for practical applications.|
|Ganesh Iyer, Co-Design Engineer