Heat transfer and thermal stress analyses were both used to determine the temperature distribution and the stress fields in the solder joint of a surface mounted electronic assembly by a nonlinear finite element method. A second-order three-dimensional element was used. A total of four solder joint shapes, namely flat, concave, triangular and convex shapes were considered. When considering the heat sink effect of the PCB, an empirical equation for small electronic devices was found to be applicable to the structure for calculating the heat transfer coefficients and subsequently for determining the temperature distribution. The stress fields were found using the Ramberg-Osgood equation curve fitted to the experimental data to take into account of the elastoplastic behaviour of the eutectic solder. The concave solder joint shape was found to bear the least Von Mises stresses. Three stress planes were selected to examine the nature of stress variation in the joint within ten seconds of power ramp-up. The results showed that severe stresses developed in the ceramic-solder interface and plastic deformation took place in the solder near the ceramic corner around the sixth second of the power-on operation.

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