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Modelling and testing the impact of hot solder dip process on leaded components

The use of microelectronics components with lead-free solder finishes on their terminations in high reliability and safety critical defence and aerospace equipment is associated with major long-term reliability issues due to tin-whisker growth phenomena. A potential solution to this problem is to “re-finish” the package terminations by removing the tin coating from the leads and replace with conventional tin-lead solder in a post-manufacturing process known as hot solder dip (HSD). This paper details a modelling approach to the thermo-mechanical characterisation of leaded components subjected to a double-dip HSD process. Transient thermal finite element analysis (FEA) is used to evaluate the temperature distribution and gradients in a QFP-type component and then used as thermal loads to predict the stress evolution in the package. The risk of thermally induced damage in the part at package level is assessed using the model predictions and compared with findings from electrical and CSAM tests undertaken on a pre- and post- refinished samples. It is concluded that in the instance of the studied part no thermo-mechanical damage is induced as a result of the HSD.