Fiber alignment shift formation mechanisms of fiber-solder-ferrule joints in laser module packaging

The fiber alignment shifts of fiber-solder-ferrule (FSF) joints in laser mo dule packaging under temperature cycle testing using PbSn and AuSn solders are studied experimentally and numerically. The measured results showed tha t the fiber shifts of FSF joints with the hard AuSn solder exhibited shifts two times less than that with the soft PbSn solder. This suggests that the hard solder may be more suitable for FSF assembly than the soft solder. Th e results also showed that fiber shifts increased as the temperature cycle number and the initial fiber eccentric offset increased. The experimental m easurements of fiber shifts were in good agreement with the numerical calcu lations of the finite-element method analysis. The major fiber shift format ion mechanisms of FSF joints in temperature cycling may come from the local ized plastic solder yielding introduced by the local thermal stress variati on, the redistribution of the residual stresses, and the stress relaxation of the creep deformation within the solder. Furthermore, the stress relaxat ion of creep deformation in solder with either 21% (PbSn solder) or 5% (AuS n solder) may have significant influence on the fiber shifts. This study ha s provided an optimum approach for reduction of the fiber alignment shift o f FSF joints in laser module packaging under temperature cycle testing, whi ch is to solder the fiber near to the center of the ferrule and to select t he AuSn hard solder.